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Forum: Pentax SLR Lens Discussion
09-28-2023, 07:30 PM
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That's really interesting how the Sony works and how they evolved to solve PDAF focus issues that are aperture variant. They seem to have a well developed autofocus system. I wonder how they solve the other PDAF variations.
Yes, Panasonic is new to PDAF and it shows. The S5II with a 70-200mm F2.8 lens gave me less than a 10% in-focus hit rate in sports including static subjects. I found in testing that the focus shifts to the "natural" backfocus of the lens with each consecutive frame in continuous drive. It also pulses in and out of focus which is strange. So to calibrate I have to take about 10 consecutive shots in C-AF to get where it settles. It also does not work with smaller focus areas. The tighter you go the more the focus will drift around. It needs large areas to determine what is in focus which is a problem for sports when you are trying to isolate your subject. It's really a mess.
After all of the fine tuning I now get the same in-focus hit rate (about 40-50% on action) with the Lumix S5II mirrorless as I do with the Pentax K3III. Before calibration, it's useless for anything. Those that are thinking of jumping ship from Pentax should know that the mirrorless world is not perfect and every time I use the Lumix I miss the way the Pentax works. It's all of the every day simple things that seem to be missing. I basically only use the Lumix in certain (fast focus) situations, otherwise the Pentax is my go to camera.
I wonder how the op is doing with his focus tuning?
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Forum: Pentax SLR Lens Discussion
09-28-2023, 12:44 PM
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I have a brand new Lumix 70-200mm F2.8 that needs -3 tele and -10 wide AF adjustment or every shot is out of focus. Every L-mount lens I have needs at least a nudge of 1 or 2 points. If the camera uses PDAF it doesn't matter if it's a DSLR or mirrorless, the lenses can still vary from copy to copy with backfocus. Since early mirrorless cameras were mostly CDAF it was advertised as a "feature" to not have to calibrate. That all went out the window when the limitations of CDAF were realized and they started using a separate PDAF autofocus sensor. This shouldn't be confused with having to adjust for body variation because the sensor is separated which is less common and only then with DSLR's. The biggest issues is the lens variation so if you care about maximizing your focus hits I'd at least confirm your lens with a target.
I'm pretty happy with the focus methodology that Pentax uses. Human detect features are nice but I'd rather have more accurate focus and at least manual adjustments for more than one focal length.
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Forum: Pentax SLR Lens Discussion
09-27-2023, 12:50 PM
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I've found this to be the case also even to a small degree with CDAF which seems to go against logic.
To compensate they would need to implement an aperture map into the fine adjust menu much like how some cameras have a "wide" and "tele" setting in fine adjust menu. By the time you take target photos at different apertures at each focal length that's an enormous amount of testing especially considering that distance also affects the backfocus adjustment as well as the natural amount of drifting and AF inaccuracy of the camera. We'd end up taking more test photos with a poorly made lens then actual subject photos.
People think that mirrorless cameras are immune to all of these adjustments but that's not true. Those that use a combination of PDAF and CDAF on a stacked sensor can still require adjusting due the variation from lens to lens. Especially since lens mfgs have loosened their backfocus tolerances thinking CDAF doesn't care and then the next model camera (like Lumix S5II) comes out with PDAF (because CDAF hunts too much) and it now won't focus accurately without calibration. It all comes around full circle as they try to make things work without a mirror.
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Forum: Product Suggestions and Feedback
09-27-2023, 12:28 PM
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I second this wholeheartedly! Nearly all of my zooms differ in backfocus from the wide end to the tele end. Many other cameras have a Wide and Tele fine adjustment. Pentax should adopt this to keep PDAF/DSLR alive and compete better with mirrorless.
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Forum: Pentax SLR Lens Discussion
09-26-2023, 09:30 PM
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That's a good point using Live View (CDAF) to test the lens. Unfortunately these older Sigma HSM lenses don't work well with "Live View" on newer cameras. I have an 85mm F1.4 HSM and it can't even be used in live view as it hunts and then settles out of focus most of the time. This is not a failing of the Pentax system but rather the autofocus protocols that Sigma used that is not in compliance with Pentax. Not sure if the 70-200mm will behave better in this regard but it's certainly worth a shot. I would still have an accurate way of confirming focus though.
---------- Post added 09-26-2023 at 11:32 PM ----------
I have a Tamron zoom that does this. I thought I was loosing my mind but it changes focus with aperture and therefore you have to calibrate at an average of many sampled apertures. What a mess.
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Forum: Pentax SLR Lens Discussion
09-21-2023, 08:20 PM
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First these terms are just common usage and not scientific but in general you are correct. We are talking about the point that the camera focused on compared to where focus actually is (the real point of focus). So back focusing is that the shot was actually in focus behind where it should have been. The actual term backfocus refers to the lens/camera relationship behind the lens to the sensor and how it compares to other lenses or other focal lengths. This is a much more common reference. I wouldn't put to much weight behind the terms. You really only need to know which direction to adjust your AF fine adjust. If the actual focus is behind the target then you need to adjust AF in the "+" direction (move it forward). If focus is in front then move in the "-" direction to push it back.
You'll find that the camera itself varies considerably from shot to shot so you need to be looking at averages of several shots and throw away the outliers. I take about 5 at each setting so I can settle on the ones that are consistent. The "Fine adjust" is just that and it's a good idea to move in large increments first and then smaller as you take more and more shots. It is time consuming and is an art in itself because there are so many things that throw you off course. My first go around I had no idea that distance and different zoom settings affected it. I had to discover this the hard way. You can imagine the frustration when someone adjusts a zoom at only one focal length on a tiny up close target and then ends up taking nothing but out of focus shots because the process made it worse.
Hehe, I guess your brother in law shouldn't get a job at grub hub or door dash. :)
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Forum: Pentax SLR Lens Discussion
09-21-2023, 05:37 PM
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Oh gotcha. So then the data should be valid.
The target you have there is too small for the camera to reliably grab it. You need a large flat contrast subject like you had before. You can also add a + with electrical tape on a white background with maybe text around it. Give it something generous to focus on. This also wouldn't make your readers hungry. You can then lay the yard stick next to the target on an angle like the yellow one to aid in visually seeing the DOF. This will be more useful for the shorter focal lengths up close as the yard stick is small. I painted a 2x4 white and painted lines and large numbers on it. Yes, this can get carried away. It is important though and the reason we back up to 50ft or so and use larger targets is because the backfocus (what we are adjusting behind the lens) will change with distance so it is best to calibrate at the distance you plan on shooting at within reason but don't go too far back or you won't see the DOF. There is not much backfocus change between 50ft and 100ft but 50ft and 10ft is a world of difference. Therefore, calibrating telephotos up close will often be wrong at a distance unless you have a high quality lens.
I think these latest results may be off because of the small target. Your original test had the shorter focal lengths focusing behind the subject (requiring a + AF adjust value) where this one is different.
To answer your other question... the term backfocus is used to describe two completely different things. Isn't photography wonderful. Some will say the a lens is back focusing meaning the focus point is behind the intended target. Front focusing would be in front of the target. However the term backfocus usually describes the spacing or distance from the rear glass element or arbitrary point to the focal plane or sensor. It is important because the lenses are interchangeable or can change focal length and therefore this distance must be consistent in order for an autofocus system to operate. This is what we are calibrating with the AF fine adjust in the cameras menu. It will compensate for unwanted backfocus changes from lens to lens by moving the sensor front/back when you change lenses. This then allows the cameras PDAF sensor to predict actual focus based on a consistent value. With CDAF (contrast detect) backfocus is not in the equation because it is focusing off the sensor instead and therefore sees reality. This is why regular autofocus and live view autofocus often don't agree.
What I'd do at this point is go back to your old setup with the above modifications. You can maybe add some text sheets to your other chair backs to help out as well and adjust the distance between them if they get too fuzzy. You can confirm the results of the first test this way and make the AF fine adjust by repeating the test several times and changing the values each time until the DOF is centered in your target. Since your lens has different backfocus calibration at long focal lengths you have a choice as to where you want the lens to be accurate. It will never be accurate at all focal lengths. If it were me I'd adjust the bulk of the range with a + value in AF fine adjust and find out at exactly what focal length it starts to go south. I'd dial in a compromise setting between short and long so that the required AF adjust value does not vary by more than 4 points. Then I'd forget about using the lens at it's longest point unless you are stopping down considerably. If you were to dial it in at 200mm you'd basically be making a fixed focal length lens in terms of accuracy because most of the range would be in error. If you can get reliability from 80-180mm then you have a mostly usable lens.
Fixing this issue in the lens takes some doing. First off there are very few sigma service shops that will even touch these lenses any more. I know of only one. Secondly the cost is close to what the lens is worth so unless you are really in love with the lens it's probably not worth it. Lastly, the fix is to move lens elements. This could potentially give it consistent backfocus throughout the zoom range but potentially at the expense of sharpness where the error is the worst. This is what Sigma did in the later versions and it did make the lens more usable but you are already having softness issues so it would be a gamble. Not sure why yours is behaving this badly.
The reality is that it is a flawed optical design where compromises are struck - this is the nature of lens design. If it makes you feel better the Tamron 70-200mm and many others have the same issue, just at different places in the zoom range. We are basically trying to get the most from a cheap light weight lens. This is an effort that can be well worth it if you have the patience, as a lens that stays home doesn't get good shots either, but if you really want focus to be accurate through the whole range then you will need to comb through many copies of the Sigmas (I did and then sold my best one to Allan), or just buy the Pentax and tell your arms it's worth it.
I'd take you up on the drumsticks but I'm likely very far away. It is on our shopping list though so thanks for that. :)
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Forum: Pentax SLR Lens Discussion
09-21-2023, 08:57 AM
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I must have missed this but I just noticed you said that you didn't refocus for each shot? If so, then any determination of focus in these photos may be in error and the example values I gave for your fine adjust above are likely wrong. These lenses are not parfocal so the focal plane will change when zooming. The point is to find out what the camera/lens is focusing at with each different focal length. This must be confirmed with several individually focused shots that agree on focus. Then and only then can you know if focus is off and make AF adjustments. Once the lens is calibrated to the camera (using AF fine adjust) and the subject is then focused in the center of the DOF you can confirm sharpness. Your first shot is close and hints at the lens being soft but not much else can be determined if focus was not reset each time.
I don't want to be preaching on about something you may already know but I also want to avoid confusion. When we are talking about focus there are two different concepts we are discussing. The focus point (focal plane) of the subject in front of the lens, and the backfocus calibration behind the lens. The backfocus is affected by the distance between lens elements and the sensor. It is a "calibration" that is not supposed to vary much from lens to lens nor is it supposed to vary with focal length while zooming but unfortunately it does. This is a big problem with third party lenses. Their manufacturing standards are not consistent and you get a lot of lens variation and focus issues. Often people may think their lenses are not sharp but it really could just be focus errors. To know what is going on you must test the lens. There is simply no other way to know.
Focus breathing on the other hand is the opposite affect. It is when focal length changes with the focus setting. It can happen on any lens, zoom or prime, and to varying degrees. Some lenses have none; it is really a matter of its design and design goals. This is a big difference between basic photo lenses and cine lenses. A cine lens must both be parfocal (focus does not change with focal length) and have no focus breathing (focal length does not change with focus). That way the affect is not visually seen while shooting video. With our cheap non discriminate photo lenses that are designed for still shots, breathing doesn't matter as much, except getting cheated out of a bit of focal length as you move in. On the other hand if backfocus changes (between the lens and camera), then it can render the lens useless. This is why there is an "AF fine adjust" in the camera menu and why we must "calibrate" our lenses using it. This especially holds true for telephoto lenses where narrow DOF and focus are a delicate balancing act.
By the way, your focus target gave me a craving for drumsticks. :)
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Forum: Pentax SLR Lens Discussion
09-20-2023, 07:00 PM
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Great job on the setup. Your test target is very good. As long as the chair backs are at an even distance (front to back) then this works perfectly. You can also move forward when you zoom out so that the apparent size is about the same making your DOF consistent. Longer focal lengths require more distance.
It appears that the focus is definitely behind the subject at 155mm and 88mm. At 200mm it may be slightly in front as it looks like the front of the target chair is a bit sharper than its back. This is what I mean about inconsistent back focus and how it will vary with focal length. I'm surprised it is this bad on the HSM version since this issue was supposed to be fixed by then. It does this much worse on the original EX version. This is assuming that you took several of each shot and that you threw out the shots that did not consistently agree on focus. These cameras are notorious at not focusing exactly the same every time. Also be sure you are getting the focus confirm at least two times in a row without it driving the lens for each shot as I stated before. If it has to drive the lens a second time after it has already focused once, then it is not a good hit and you need to focus again until it stops driving the lens. After a good shot move the focus ring and start the AF cycle for the next shot.
The AF fine adjustment is a menu in the camera that allows you to change the backfocus for each individual lens. It does this by moving the sensor forward or back when the lens is mounted or camera is powered on. It is really the whole point of this exercise. If you wanted to calibrate this lens to be accurate in the middle focal lengths then based on your above data you'd add numbers on the + side of the slider in that menu (say +5 or so). To adjust for the long end (your first shot) you may do a -1 and then retest but this would make the middle even worse because you only have one setting for each lens you mount. It would be nice if Pentax had multiple settings for different focal lengths on zoom lenses. Assuming these shots are consistent in focus I'd say you have a compromise backfocus adjustment for your zoom range if you were to use the whole range.
When using this lens you may have to do what I did with mine and back off just a bit when you hit the zoom stop at 200mm and pretend it is a 70-180mm lens. You could then add a little in the + direction in your fine adjust making it more accurate avoiding 200mm completely. This would also put you in the sharper region of its focal length. Without having more data I'd say you definitely are a bit soft at 200mm. The F4 shot cleaned it up quite a bit so you may have to stay away from F2.8 all the way in.
The Pentax lens would do a better job and also have consistent backfocus through the zoom range. This is another big difference from Pentax and third party. It really depends on if you can manage the weight.
I'd like to see what your old EX does on the same test. It will likely need more correction.
---------- Post added 09-20-2023 at 09:02 PM ----------
Great shot Allan! I'm glad its working out well. That one served me well and is of the better behaved ones I've owned. The handling of those lenses just can't be beat.
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Forum: Pentax SLR Lens Discussion
09-20-2023, 10:01 AM
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If you want to upload photos cropped is fine. The only thing that matters is the target and chairs. Were you able to center the focus on the target with the AF fine adjust?
Strange about the EX APO lens. Mine is lightning fast and never pauses. Something is not right there.
Also, you want to take your photos with the widest aperture, in this case 2.8. Stopping down will only cause the calibration to be less accurate. Also use spot focus mode for higher accuracy. Once you get the focus centered with equal amount of off focus front and back then the sharpness on the target becomes valid.
Since you have both Sigma lenses it will be interesting to see how the older EX compares to the HSM II once you get AF adjusted. That is, if it will focus for you.
Good luck.
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Forum: Pentax SLR Lens Discussion
09-19-2023, 05:24 PM
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Just to eliminate any possibility of confusion, there are four versions of the Sigma 70-200mm F2.8. There's the EX APO, EX DG APO, EX DG APO HSM II and the EX DG OS HSM. The first EX version has the old style rubber grips and is the version with inconsistent backfocus. I've been through many of these and I'd give real money to get one that doesn't have this problem. The EX DG looks just like the HSM version with the straight line rubber grips. Somewhere between the EX and DG versions the backfocus issue was corrected but with a compromise in sharpness on the long end. The HSM II added closer "macro" focus and made performance softer at 200mm but acceptable in the eyes of many. These issues have been documented in professional reviews and here in the database. I've owned all of these versions and multiple copies of some and my experience agrees with what has been reported. I'm not knocking them... if you need a lightweight 2.8 tele for sports these are the best option. Sigma made these lenses in droves and people loved them, including me, but they aren't perfect and there is a lot of variation among them. Some are good but many are not. I ended up selling the best one I had recently.
I guess the point is that it's certainly possible that some of the softness described in the ops photos are due to these issues/compromises with this lens. The only way to be sure is to rule out what can cause softness by refining the process. i.e. solid tripod, 2s timer, ISO 100, confirming that the test target is perfectly centered in the DOF. I never condemn a lens unless I can see exactly where the focus point is and the bases have been covered. With that being done, you can say, the issue is the lens.
In my opinion, for sports shooting where fast focusing is crucial, the Pentax D FA is the best option if you can manage the weight. If you want to go easy on your arms then the pre OS Sigmas are about the only other option. The OS version is longer/heavier so you might as well go Pentax at that point not to mention that the zoom direction is backwards so it was never a contender for me.
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Forum: Pentax SLR Lens Discussion
09-19-2023, 11:09 AM
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It's hard to differentiate between focus issues and lack of sharpness. Both are a problem when sorting through your sports shots. I've never seen a telephoto lens that didn't require some amount of backfocus correction. The problem with zooms is that the backfocus can change with the zoom focal length. It can also vary with distance. This makes calibrating your lens with "AF fine adjustment" a set of compromises. This still however must be done if you are to get the highest keeper rate.
To start, you must adjust your telephoto lenses at a distance. Up close on batteries will be useless for real application. I made a rig with a long 2x4 painted white with markings, but without going to a lot of effort the easiest way is to setup three chairs front to back on a slight diagonal about 4 feet apart. Setup a flat high contrast target such as poster/sign etc on the middle chair. Take your test shots at a distance of 50ft or more. The point is to mimic the real world situation this lens will be used in. Make sure the target is well lit so that focus will be more consistent and use a tripod and low ISO. We are testing the lens, not the camera. When taking your shots on the test target make sure you get two or three focus confirms without the lens being driven. The camera must agree each time on focus or it is not a good hit. Take at least 5 shots and throw away any that appear to be focus misses. Yes, there will be some even on a static subject and again, we are testing the lens, not the camera. Then look at the furthest and closest chair to determine which one is more in/out of focus. Change your AF fine adjust and repeat. Do this for a range of focal lengths as well 135MM, 160mm, and 200mm. You'll find that your averages may differ at different focal lengths. You will adjust for an average of the three longest focal lengths as these are used most in sports and are also the most critical in terms of DOF.
Once you have done all of this, then you can test sharpness on your target making sure that your front and back objects are an equal amount out of focus. It takes a lot of shots to get this right as you'll find that there will be subtle amounts of misfocus that affect your judgment of sharpness at full open apertures.
My experience with Sigma 70-200mm lenses is that the EX APO series were very sharp and very fast but had backfocus issues on the long end. All zooms will change their backfocus throughout the zoom range but it should be by only 1 or 2 ticks of your fine adjust. The early Sigmas that I tested varied by as much as 8-10 points toward the long end. This was consistent with several copies that I owned and later confirmed in an online article reviewing the "new" HSM version. At some point Sigma realized this and "fixed" the issue but at the expense of sharpness on the long end. In other words, they didn't change the optical formula but rather compromised by adjusting it out. I believe this was done on the final version of the EX DG version (the one that looks like the HSM but isn't) but it could have been before that. This was a trade off that in many cases was an improvement because after all, an out of focus shot is a throw away but sometimes a soft shot can be somewhat salvaged with sharpening in post. When I used my EX APO I adjusted my AF fine adjust at a compromise between 135-160mm and then stayed away from 200mm by backing off whenever I hit the stop zooming. This dramatically improved my keeper rate and made some fantastically sharp shots. When I upgraded to HSM I didn't have to worry about this but I stopped down to F3.5-4 to combat the softness on the long end. It is also hard to find HSM copies that have firmware compatibility with the K3 III so those are worth a premium. What I liked most about the Sigmas (non OS versions) was that they were compact and light weight.
To compare the Sigmas to Pentax DFA is a mixed bag. The Pentax is sharper and has much more contrast (which adds to its perceived sharpness) with much better color rendering. The issues are focus breathing and weight. The focus breathing is more of a problem as you get closer to your subject. At a distance of about 100ft the Pentax at 200mm is about the same as the Sigma at 180-190mm so this isn't huge but is something to consider. Many, not all, lenses (fixed and zoom) have some amount of focus breathing but the Pentax DFA 70-200mm can be a disappointment if you're expecting a full 200mm. I'd take its other quality attributes any day over loosing a bit of focal length. For me the real issue with the DFA is the weight. It has to be the heaviest 70-200 known to man. This is why I only used it on a monopod and also why it stayed home often. It is also why I just listed it on ebay today. For quality photos and highest keeper rate it can't be beet but you pay the price in lugging it around.
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Forum: Pentax SLR Lens Discussion
07-22-2023, 04:08 PM
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I have extensive experience with most of the 70-200mm F2.8 lenses for sports photography on the K1 II and K3 III. I currently have both the Pentax D FA* 70-200mm F2.8 and the Sigma EX DG HSM II 70-200mm F2.8 (updated firmware). They are about the same in terms of auto focus speed however I think the Pentax might be slightly more accurate. The biggest difference between the Pentax and about every other 70-200mm F2.8 out there is the Pentax has more contrast and better color rendition. This is typical of Pentax lenses compared to others. This is easily corrected in post however. Just about every 70-200mm I've used is not as sharp on the long end including the Pentax with the exception of the Tamron (which I used to own) however it is the slowest of all for sports and has a dismal keeper rate.
None of the 70-200mm's out there are as fast as the PLM but with a high frame rate and lots of photos the extra aperture can greatly compensate and get photos that can't be had with the slower lenses. Also the extra aperture in lower light can help focus and compensate for the slower response. My in focus shots for indoor action is about 30-50% for both the Sigma and Pentax. Tamron is not in the game.
The HSM II lenses have the firmware compatibility issue that effect all 2016 and after model cameras and therefore are not usable. Some updated models can be found but are rare. Mine has been updated with firmware and flange.
Here are some pros/cons.
Pentax D FA* 70-200mm F2.8:
Pros: High contrast, accurate color, good auto focus but not PLM fast. Extremely sharp up to about 160mm.
Cons: Horrible focus breathing (not 200mm except at infinity). Heavy as a brick.
Sigma EX DG 70-200mm F2.8 HSM II
Pros: Most compact of all 70-200mm, lighter weight. Average auto focus speed (not PLM fast). Sharp to about 160mm. Accurate back focus through zoom range (Sigma traded sharpness on the long end for consistent back focus when updating the EX to HSM.
Cons: Soft and low contrast past 160mm but usable. Most versions not compatible with K1, K3 III (2016 and later model Pentax cameras) due to firmware.
Pre HSM 70-200mm F2.8 EX Sigmas:
Pros: Same as HSM versions plus sharper to 200mm. Fast focus speed especially on K3 III but check cons.
Cons: Back focus problems past 160mm (example: 135mm -1 correction and 200mm -10 correction) therefore sharpness and focus speed not as usable (unless you stay between 70-160mm) due to focus errors.
Tamron SP 70-200mm F2.8
Pros: Extremely sharp at all focal lengths.
Cons: Slightly darker than others. Horribly slow auto focus - worst of all for sports. Back focus issues throughout zoom range.
The above is my personal experience with those lenses using the copies I have or had. Others may vary as build consistency varies greatly with third party lenses.
I dislike the current Sigma OS version because the zoom direction is backwards to cater to Canon and it slows me down by going the wrong way first. It is also longer and heavier than previous version.
I currently have my updated Sigma HSM II for sale on ebay because I have recently been using a monopod on my Pentax at closer ranges. I'd be willing to discount it here directly. I also have the rare 50-150mm F2.8 HSM which is also firmware updated that I may sell at some point. I've found that nearly all HSM lenses I've used have about the same average focus performance which is similar to Pentax SDM but not as prone to failure.
Hope this helps.
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Forum: Pentax SLR Lens Discussion
05-03-2020, 05:20 PM
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That adapter is made or at least it was. I have one but I got it about 20 years ago and can't even tell you where I found it. It has a small negative FL lens element in it like a TC to extend the focus distance that the adapter adds. If your camera has a shorter focal distance than a regular K camera then you can simple take the lens element out.
I also made one from a cheap TC so that I can use eyepieces on larger Pentax lenses. This again requires the use of a negative element like a barlow lens to extend the focal length through a diagonal to the eyepiece. This is much easier to accomplish on 67 lenses and works extremely well to make outstanding telescopes out of a 400mm F4 or 800mm F6.7.
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Forum: Monthly Photo Contests
10-04-2013, 09:24 AM
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This is a composite of over 100 stacked 15-30 second exposures tracked on a Losmandy mount manually guided. The stacking/registration was done in registax and all processing in Photoshop. No filters were used and the location was just West of St. Louis so there was considerable light pollution. This was my first test of the KX for astrophotography and I was very pleased with the results.
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Forum: Pentax DSLR Discussion
11-25-2009, 11:17 PM
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The button might be a carbon contact type. Those are really common with remotes and it should not be a problem to use a standard open/close switch or opto isolator.
Do you have a link to one of the $80 IR shutter devices? The remotes I'm familar with for Canon and Nikon are made by other companies and they might make a Pentax compatable version.
What an impressive setup! I haven't done any programming since the 8-bit CPU days but still do electronic design. It's great to see such dedication to a hobby. Since your a software engineer, any chance of helping hack the K-x to disable the long exposure DFS? Can't wait to see some of your shots.
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Forum: Pentax DSLR Discussion
11-23-2009, 06:28 PM
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Thanks. Actually the processing on them was quite hurried so they are a bit over processed and saturated with false color. Since then I have redone the processing and they look more realistic now with more detail. Once I get a clearer night I'll spend more time and they should be even better.
Thanks for the galaxy info. The ISS shot is amazing! How were you able to track it with so much focal length? I've watch it go across the sky and it is really moving.
I've never seen the K-x without Kit lens unless someone on ebay was parting it out.
I'd also like to get the DC-84 but I can't find anyone who sells it. I'll continue my search and you let me know if you see one somewhere.
I've only had batteries out of my K-x for five minutes so I know it will go that long but havn't tried any longer.
The K-x uses the same usb style connector so the video cable should be the same for all Pentax cameras.
Live View only works on bright stars but that is enough for live focusing. It tends to flicker a bit but it sure beats the "click and tweak" method.
Remote Assistant is not supported on the K-x and it does not have a remote shutter jack so this could be a deal buster for you since there is no way to start the exposure without the IR remote. I was thinking of making a remote shutter by taking apart a remote F and connecting a jack to the trip button. Then mount the remote on the tripod and now you can control it with all the fancy timers and gear that's out there. Either that or wait until Pentax makes a K200D replacement with this sensor.
The vield of view is the same in movie mode as normal mode so I would assume it would be using all of the sensors area or else it would be cropping the frame.
There are many limitations of the K-x in terms of controlling it and I've been able to get around most of them but the worst is the mandatory DFS for longer than 30s. There is just no reason for this. Even so with all of the limitations the sensor just can't be beat and is worth it even with 30s exposures.
-Andy
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Forum: Pentax DSLR Discussion
11-22-2009, 07:57 PM
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Not much more to add to Leo's comprehensive explanation. You pretty much got it down already. To sum it up, the longer the folcal length, the more the need for a tracking mount, or the more critical the guiding becomes when using a tracking mount. I'd like to reiterate a point that Leo touched on and that is if your equipment get's large enough you will start to get flexure between the guide scope and the lens your photographing through. This will introduce errors as the mount rotates and the equipment weight shifts since the guider won't see the other scope shifting. This will ruin even perfectly guided shots which is why it is so important to have a good mounting system.
Wow, Jack, writing your own guiding software is impressive. Do you have plans to sell it or put it out in shareware? Do you have any samples of your work?
I'd check out Losmandy Astronomical Products for a mount. For the money they can't be beat and you can get a really good start for the budget your talking about. I have a GM8 right now which works great for light to medium weight equipment but will probably upgrade to a G11 for prime focus shots through a telescope. The GM8 just can't handle the weight well and limits me to large telephoto lens work by the time I add up the weight of the lens and guidescope.
I really got a chuckle out of the flower pot as I was reading your site. I thought it was a very engenius and humerous way to solve that problem.
I like your Galaxy shots. Since you also shoot from a rural site and are limited like I am, what would you consider to be the top 10 brightest or easiest Galaxies and nebula for our areas?
You should really try a K-x. I use to shoot with a K100DS, then a K200D and both of them had really bad amp glow and chroma noise. I am finally now not limited by the camera and am going to upgrade to some more serious guiding gear.
-Andy
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Forum: Pentax DSLR Discussion
11-22-2009, 06:43 PM
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Actually stacking is a great alternative to a single long exposure. About the only thing that it wouldn't work for is fast moving subjects such as traffic and fireworks.
For a 2 minute exposure just take 4 - 30s shots and stack them in photoshop. No need for special registration software if you use a tripod and the scene is not moving (like astro shots).
You can use stacking in different ways. The frames can be averaged, summed, or logical add (brightest pixel wins) which is useful for star trails. Below is a shot made up of well over a hundred 30s frames and stacked. Notice how much brighter the stars are compared to a single long exposure. I actually looks much better before it was jpeged to death through the upload process here.
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Forum: Pentax DSLR Discussion
11-20-2009, 06:19 PM
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I don't think LeoTaylor has been on lately but I think I can help.
When we refer to "unguided" that doesn't necessarily mean it is not tracking with a motor drive. Many high quality Eq mounts can track accurately enough to not require quide corrections either manually or with an autoguider up to around 200-500mm depending on the exposure length. If you are using a tripod then you will be limited to wide-angle shots only.
Leo: Did you hit your head on the flower pot hanger again? We need you back.
-Andy
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Forum: Pentax DSLR Discussion
11-20-2009, 06:03 PM
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The K-x works quite well in "bulb" with the IR remote now that it is a toggle on/off so there is not as much of a need for remote computer control. Mirror Lockup is also supported with the timer+3s mode. It basically will throw up the mirror and then wait 3 secs before opening the shutter.
The only real issue that remains is the DFS. I've been quite successful using multiple 30s exposures with the K-x due to the fact that it has a two stop improvement in noise over the CCD Pentax DSLR's.
I think somewhere between 30s to 5 minute exposures are possible however, most DSLR's don't like much longer than this because the sensors are not cooled. If you really don't want to stack multiple photos and need 30 mins of exposure time then no DSLR is for you and you should only be looking at dedicated astro cameras. You will pay much more money for these or the sensor sizes will be smaller. I have an Orion Starshoot pro I'd be happy to sell you simply because I get better results with the K-x and stacking.
I truely wish Pentax would allow DFS to remain off, as the menu setting implies, for any duration exposure. It should be up to us to decide this, after all, that is why the menu option is there and is defaulted to "on".
This is a very hot topic for both the K-x and K-7 and I read on one of the other threads that Pentax responded to a user and said they would recommend this change for the K-7 in the next firmware release. Not sure if that would really happen but if they can do it for the K-7 then they can do it for the K-x as well which is actually more capable for low light anyway.
Maybe we should all send an email to Pentax requesting this and if they get enough response they might do something about it.
-Andy
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Forum: Pentax DSLR Discussion
11-17-2009, 11:52 AM
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Thanks for the notification. From what I can see in the comparometer it looks like the K-x is possibly even sharper than the K-7. It for sure has less noise.
I wish they kept the K10D and K200D samples up.
I think it would be a wise move for Pentax to use this sensor in their future cameras. I'd really like to see a K200D replacement with the features and quality of the K-x.
-Andy
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Forum: Pentax DSLR Discussion
11-17-2009, 09:49 AM
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Do I have to explain everything? The topic of this thread is comparing the K-x to the K200D. This test shows the noise (and only the noise) produced by these two cameras. Noise is a big part of the perceived picture quality especially in low light.
If you don't understand the relavence of this to good photography then perhaps you should just move on and not criticize.
-Andy
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Forum: Pentax DSLR Discussion
11-16-2009, 09:45 AM
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Here is a comparison of hi ISO noise betwen the K-x and K200D with 30sec exposure dark frames.
https://www.pentaxforums.com/forums/811084-post43.html
The results are nearly the same with K-m and K10D. As we all know the hi-ISO performance is great with the K-x and is two stops better than previous generation CCD Pentax DSLRs, but also worth noting is that long exposure noise performance is also fantastic. Exposures of several minutes are possible without appreciable increases in noise, hot pixels, or amplifier glow.
I have also not had any sharpness issues compared to previous CCD Pentax cameras. Images look great, but that is just my opinion so far. I may do some test crops to compare daylight performance.
-Andy
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Forum: Pentax DSLR Discussion
11-15-2009, 12:06 PM
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Yes, I'm sure I could do some 5 and 10 minutes exposures if it wern't for waiting for the DFS! This camera is so darn impressive it just kills me that something this simple is diminishing it's use.
I'd love to use the Orion Starshoot as a guider but my G8 mount has loose bearings that causes it to shift a bit during guide corrections and it really messes with an autoguider. Through manual guiding I can anticipate it's behavior so I think it will be sore eyeballs for a while unless I can raise enough money from my 67 gear to buy a G11.
-Andy
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