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Forum: Pentax Medium Format
10-23-2021, 01:56 AM
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Same here for my GFX50R. It requires way much less cleaning than my 645z. Why? I believe it’s not sensor cleaning mechanism, as GFX50R doesn’t have IBIS. It’s the cover glass.
First, one needs to realize that you will never be able to clean the sensor, unless you completely take apart the camera and the sensor compartment. What you actually clean is the cover glass in front of the sensor. This is true for almost all cameras. (I use the word “almost” just to be conservative.)
On GFX cameras, the cover glass is placed well apart from the sensor. What this means is that even if there are many dusts on the cover glass, their shadows on the sensor will be way out of focus. Unless you use a super small aperture to shoot, you will not notice the existence of the dust. This is very different from 645z, which has a cover glass right in front of the sensor.
Those who assume that mirrorless collects more dust are probably right on other FF mirrorless. GFX is different. Until you actually own and use one for a substantial time, you are believing the wrong things about GFX.
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Forum: Pentax Medium Format
06-28-2021, 11:49 PM
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I have been doing astrophotography with GFX for more than a year. Its focus-by-wire mechanism does concern me a bit. However, in practice, I haven't noticed any real damage to my final image. For example, this image:
Orion | Fujifilm GFX-50R Fujifilm GF 110mm/F2.0 @ F3.2 two f? | Flickr
is composed from a few long sessions of continuous 5-minute exposures. I haven't not seen hints of focus shift in these sessions. The conclusion I got from my other GFX lenses is similar. I think I still prefer normal lenses (AF or not, IF or not), rather than focus-by-wire ones, but my experience on GFX isn't really bad.
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Forum: Pentax Medium Format
08-01-2021, 08:47 PM
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It's not photographic film any more. Film has many other applications. For example, from what I heard, Fuji is a dominant supplier for the film covering the flat panel displays. In fact, if you are reading this with a computer, you may be actually seeing through a thin film produced by Fuji right now. Think how many flat panel displays are produced each day in this world. That's highly profitable.
So when Fuji says its film business is profitable, it doesn't imply photographic film is playing a larger role than digital cameras in Fuji's imaging business. It's not the kind of film you had in mind.
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Forum: Pentax Medium Format
07-27-2021, 08:03 PM
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If your company controls both the camera and the lens, then the extra layer of glass may not be a problem. Telephotos with drop-in filters are designed in such a way that the filter glass is part of the optical formula, and using such lenses without a filter can degrade the optical quality. I can suspect that the cover glass in GFX cameras is factored in the lens design, as it sits right behind the rear lens elements.
And even with that cover glass (part of the optical design or not), Fuji lenses perform brilliantly. Fuji wide-angle lenses on GFX is way better than wide-angle lenses on 645z. Now I use my 645z exclusively for long focal lengths. For anything below 110mm, I go to GFX.
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Forum: Pentax Medium Format
07-21-2021, 07:13 PM
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Probably not. I shoot both 645z and GFX. I do astrophotography, which is highly sensitive to dust (after stacking many exposures to boost weak signals in the image). So far my 645z shots almost always shot dust spots no matter how I clean it, while my GFX shots are almost always clean. I suspect the reason is that there is a cover glass right after the lens mount of GFX and quite far away from the sensor. This cover glass keeps the sensor free from dust, and dust on this cover glass would be almost always out of focus since the glass is far away from the sensor.
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Forum: Pentax Medium Format
02-10-2021, 12:29 AM
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The different sizes of stars aren’t a distance effect. All stars are practically at infinity to camera lens. They have different sizes in the image because they have different brightness. The point-spread function of stars is never an infinitely small point. Brighter stars have brighter outer parts of the PSF so they appear bigger. The outer part of the PSF is not necessarily caused by diffraction. It can be caused by the atmosphere (scatter and turbulence, depending of the location and focal length), by the lens, or by scattering in the sensor or film (particularly worse on color reversals).
I don’t have experience on the 4-element 200mm lens. However, I had used the newer 200mm. It’s OK on 645z, provided that its lens elements are well aligned. Overall, all Pentax 67 lenses that I had used on 67 film are excellent, but poor on 645z. At least in astrophotography, film is much more forgiving to imperfect optics. These 67 lenses either were not designed to satisfy modern CMOS sensors, or their manufacturing accuracy does allow them to last long enough. The 200mm lens I tried had misaligned lenses and a tilted focal plane. This is easily visible on images of stars. Indeed, many 67 lenses I tried on 645z or FF DSLRs have such troubles, leading me to believe that they should stay with film. So far, among the about 20 various film lenses that I had tried on 645z, GFX50R, or FF, the only one that’s still acceptable (in terms of resolution only) is the Mamiya 645 300/2.8. Everything else failed.
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Forum: Pentax Medium Format
01-30-2021, 09:07 PM
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As a 645z user myself, I also agree that 645z is still very capable. But this is not the problem here. The problem is that the sensor used in 645z was discontinued by Sony quite a while ago. All Pentax can do now is to sell 645z with the sensors that they have in stock. Once they sell out, they have nothing to provide to the market. So Pentax has to start developing a new camera, even if 645z is still very capable. And if they are going to provide a new camera to the market, it has to be awesome, because of the competition from Fuji. So talking about whether 645z is capable is totally irrelevant for Pentax's survival in the MF market.
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Forum: Pentax Medium Format
01-28-2021, 08:25 PM
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I think the minimum Pentax needs to do is to put the 100MP 44x33 sensor in their 645 body and update the sensor-related performance (AF, video, 16bit etc).
Lens wise, the few Pentax 645 lenses I had tried are all extremely sharp in the frame center. They out-resolve the 50MP 44x33 sensor at the center, and they should have no problems on a 100MP one. The unfortunate part is that they are lousy in the corners. I can't say the GFX lenses are sharper in the center, but the GFX lenses definitely generate more uniform image quality over the 44x33 frame.
BTW, I am an astropgotographer. My targets are points all over the field, which are highly demanding for image resolution. I can't comments on other kinds of lens performance, like rendering, bokeh etc.
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Forum: Pentax Medium Format
09-06-2020, 09:51 PM
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Sorry to hear the couple of stories on NEOWISE image ruined by the satellites. But generally speaking, the starlink satellites are low-orbit satellites. They only reflect sun light during the one hour or two (depending on where you are) of evening/morning twilight time. After we are well into the dark, we won't see them easily, because the satellites above us should be also hidden from the sun by earth.
For professional astronomy, the starlink satellites mainly threaten the observations that search for near-earth objects. Those objects can only be easily seen during twilight time. For typical astronomical observations conducted during dark time, starlink can sometimes be annoying, but won't be the end of the world nor end of astronomy.
I think the above applies to amateur astrophotography too. For the kind of astrophotography conducted during twilight (astro landscape, and comet imaging), starlink will be a problem. For other kinds of astrophotography conducted at night, it shouldn't be a major threat. We see many high-orbit satellites every night anyway, and we have ways to remove them from our images.
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Forum: Pentax Medium Format
08-24-2020, 08:56 PM
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The modification replaced the IR-blocking filter with one that allows more deep-red to go through (but still blocks IR). This makes the camera more than 3x more sensitive to red nebulas. It is a must for serious deep-sky photography, but not quite so for wide-field Milky Way shots and astro-landscapes.
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Forum: Pentax Medium Format
03-11-2020, 05:45 PM
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Right. Not just that image, all side-by-side test images I took with the GFX50R are more noisy than 645 ones. They use the same sensor. So I suspect that the difference comes from the continuous live view, which keeps the sensor constantly working, and therefore generates lot of heat from the sensor and other internal circuits. Unfortunately I haven't had enough tests to verify that heat is indeed the cause of the extra noise in GFX.
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Forum: Pentax Medium Format
03-10-2020, 09:08 AM
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Did not see this thread before. I have an RAF adapter for P645. It fits the camera nicely, without problems, although I have never really needed to use it.
My telescope has a P67 adapter made by the telescope manufacture. Then I use Pentax's own 67-645 adapter to hook up my 645z. Earlier Stevein mentioned about Astrobin search results. The majority of 645z images you can find on Astrobin was taken by me. And this is my Astrobin gallery.
To be able to to use 645z on a telescope, the adapter is just one of the equations. There are two additional requirements, both of which are more difficult to meet than getting an adapter:
1. The telescope needs to be able to project a flat image circle that's large enough for a 44x33mm sensor. Not many telescopes can do this. It typically requires a large focuser, and a large, dedicated corrector lens (focal reducer, field flattener, or coma corrector, depending on the type of telescope). Most telescopes in the market are designed for APS-C or FF, and they don't have a focuser and a corrector lens large enough for P645.
2. The optimal focus point should be far away from the last lens element of the corrector lens, far enough to accommodate the humongous 71 mm flange-back distance of P645 plus whatever length for the adapter. Among all 645 cameras, P645 has the largest flange-back distance, and not just large, unreasonably large. Pretty much only telescopes that are designed for P67 (very few) can offer this kind of back-focal distance for P645. If we are talking about Fuji GFX here, things will look much better. There are some very nice telescopes that can accommodate GFX but cannot accommodate P645, because of the very stringent requirement on back-focal distance.
The OP wanted to hook up his 645D to C4.5. There is just no hope he can do it, and no point for him to do it. C4.5 does not have the kind of large back-focal distance for P645. Even if it somehow magically has, its focuser is way too weak to support 645D's weight. Even if the weight is not an issue and even if it can reach focus, C4.5 cannot illuminate a 44x33mm area with good image quality from center to corners. If it is an 8inch Newtonian instead of 4.5inch, then it starts to look feasible. It is possible to find a strong focuser to be put on an 8+inch Newtonian with a coma corrector that can accommodate P645 (TV BIG Paracorr).
645z is absolutely a powerful camera for astrophotography. Unfortunately only few telescopes can go along with 645z.
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Forum: Pentax Medium Format
05-31-2019, 11:06 PM
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To me, the real problem of 645z is the size of the camera. That size was already the largest among all old 645 film bodies (judged by the flange-back distances), and is inappropriately big for a 44mmx33mm sensor. Because of the unnecessarily large flange-back distance, it's hard to make a good ultra-wide lens or an excellent wide lens, like those on the Fuji. This large camera body only makes (some) sense for a true 645 sensor. I really love my 645z, but I am very disappointed by the choices of wide/ultra-wide lenses on it, especially after comparing pictures taken with Pentax 25mm and Fuji 23mm side-by-side. I hope the next Pentax 645 camera (if there is one) can solve this.
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Forum: Pentax Medium Format
07-02-2018, 10:20 PM
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What I always do is to put a piece of white paper (instead of the camera body) behind the lens and project a bright scene onto the paper. This way, you can immediately see which lens has a larger illumination area.
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Forum: Pentax Medium Format
12-12-2017, 06:04 AM
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645z update? There is not a new 44x33mm sensor from Sony, except for the to-be-very-expansive 100MP one. Without a new affordable sensor, I don't see how 645z in the current form factor can be updated.
Pentax goes mirrorless? That will be very nice. However, given how slow they have been in the past few years in introducing new DSLR cameras or lenses, I can hardly believe they will produce a mirrorless medium format camera all a sudden.
I really want to see new things coming out from Pentax, but I don't have high hope.
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Forum: Pentax Medium Format
11-15-2017, 07:53 PM
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Few weeks ago, DxO people commented on not publishing 645z's test results for years. They said that they did not publish a complete review because they don't have enough resource (or something like that). I was sort of buying it, and looking forward to their finally publishing 645z's result.
Now, I am very disappointed seeing the review. They already had the numbers two years ago. The most difficult part had been done already. And then it took them two years to come up with the simple text in the review? There is nothing new in the text they wrote, and it's not difficult to write at all.
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Forum: Pentax Medium Format
12-04-2016, 11:27 PM
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Hi Obin,
Yes, all the things (or the similar) you mentioned came across my mind at least once in the past.
I have a Apogee F16M, which has the same CCD (KAF16803) as the G4-16000. I am not impressed by this camera (or cooled CCD in general), as its read noise is about 4x as large as modern CMOS. This severely limits its capability when used with RGB or H-alpha filters. The exposure has to be unreasonably long (under my F7 optics) to make the influence of read noise go away. I realized this after I wasted quite a few nights on this camera, and then I never look back. CCD is old technology, and CMOS is superior in many ways. Once there is a mono version of large format CMOS camera (cooled or not, doesn't matter to me, since I almost always image under cold temperature), I will seriously consider to abandon DSLRs.
AG's D-K has my attention for a long while. At this moment, I am more into wide-field mosaicking, so their focal length is kind of too long to me. However, I may want to shoot smaller things in the near future. Then I will give it a very serious thought. Indeed, it is the top one on my list if I do want to switch to longer focal length.
On the VSD, if one takes a somewhat shallow image, say 0.5 hr of total exposure, and compare it with TAK's FSQ, the two are basically on par with each other. They are equally sharp. The FSQ perhaps has a slight edge in the field center, while the VSD has a slight edge in the FF corners. However, if the integration becomes very long, the stars in the VSD image will start to blow up, while the FSQ stars remain tiny. This means that there is a tiny level of uncorrected spherical (or chromatic?) aberration on the VSD. It's also more expansive than the FSQ, which makes no sense.
Cheers,
Wei-Hao
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Forum: Pentax Medium Format
12-04-2016, 07:27 AM
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Hi,
Thanks. I used the VSD a couple of times. I am not impressed by its sharpness, although the image quality is quite uniform (uniformly mediocre) across the FF.
Like what you said, I now believe it is not a good idea to use any lenses on 645z. I primarily use it on my TAK TOA150. I have its 67 flattener and 645 reducer, and both can cover 645z very well.
The cheap 8" Newtonians do not have coma correctors suitable for 645z, I am afraid. I have TAK Epsilon 180ED, and even that doesn't cover the 645z sensor. The very large flange-back distance of Pentax 645 also makes things extremely difficult. Not many correctors/flatteners in the market are design to have this much back focus.
Very unfortunately, I have to conclude that 645z is not a very good camera for astrophotography, despite the very good sensor in it. The new Fuji mirrorless MP has much shorter flange back distance, which will allow it to be put on many more telescopes. It is also possible that its lenses perform better than 645z's lenses. I am looking forward to this new system.
Cheers,
Wei-Hao
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Forum: Pentax Medium Format
03-28-2016, 05:22 AM
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This is mainly for astrophotography. For stars, the lens need to be sharp at wide apertures in both the center and corners, with as little coma and color aberration as possible. This is kind of different from the requirements of portrait or landscape photography. I am still new to the P645 system, and am trying to figure out what lenses may be used for astrophotography. The best way to find out the answers is to actually shoot stars. At this moment, I only have four lenses that can be attached to 645z. Here are what I got, and some comments. In the image, I show the center, and four extreme corners.
645 DFA 55/2.8
F2.8: https://dl.dropboxusercontent.com/u/15886389/645_lens_tests/645_55mm/f2.8_stack_mosaic.jpg
F3.5: https://dl.dropboxusercontent.com/u/15886389/645_lens_tests/645_55mm/f3.5_stack_mosaic.jpg
F4.0: https://dl.dropboxusercontent.com/u/15886389/645_lens_tests/645_55mm/f4.0_stack_mosaic.jpg
F4.5: https://dl.dropboxusercontent.com/u/15886389/645_lens_tests/645_55mm/f4.5_stack_mosaic.jpg
I feel this lens is borderline OK for astrophotography, and definitely not excellent. It only becomes barely acceptable after stopping down to F4.5. I may be forced to use it at F4.0 in some situations, but I won't have a smile face when I do so.
---------- Post added 03-28-16 at 05:26 AM ----------
This is for the FA 35/3.5.
F4.0: https://dl.dropboxusercontent.com/u/15886389/645_lens_tests/645_35mm/F4.0_mosaic.jpg
F5.0: https://dl.dropboxusercontent.com/u/15886389/645_lens_tests/645_35mm/F5.0_mosaic.jpg
This lens is incredibly sharp in the center. I have never seen such pinpoint stars from any other lenses on my D800, including the highly respected Sigma 50/1.4 Art and 35/1.4 Art.
On the other hand, it has strong coma even when stopped down to F5.0. I will never stop it down further for astrophotography, and F5.0 is acceptable to me give that this is a wide-angle lens.
I kind of wonder whether the new DFA 35/3.5 can perform better. If the coma can be reduced, it will be a killer.
---------- Post added 03-28-16 at 05:32 AM ----------
I have three Pentax 67 lenses. One of them is ED300/F4. On D800, the image shows misaligned optical elements. So I do not bother putting it on 645z. Below are the results from the 67 90/2.8.
F2.8: https://dl.dropboxusercontent.com/u/15886389/645_lens_tests/67_90mm/F2.8_stack_mosaic.jpg
F4.0: https://dl.dropboxusercontent.com/u/15886389/645_lens_tests/67_90mm/F4.0_stack_mosaic.jpg
F4.5: https://dl.dropboxusercontent.com/u/15886389/645_lens_tests/67_90mm/F4.5_stack_mosaic.jpg
There is also a sign of misaligned elements, as stars in the lower-right and upper-left corners are softer than the other corners. Fortunately, it's not too bad. It is acceptable at F4.0, and fairly good at F4.5. The center is a little bit softer than the 645 55/2.8, but the corners are much better. I probably will try to get another one from ebay and see if I have better luck on the corner sharpness.
---------- Post added 03-28-16 at 05:36 AM ----------
Finally, 67 165mm/F2.8
F2.8: https://dl.dropboxusercontent.com/u/15886389/645_lens_tests/67_165mm/F2.8_stack_mosaic.jpg
F4.0: https://dl.dropboxusercontent.com/u/15886389/645_lens_tests/67_165mm/F4.0_stack_mosaic.jpg
F4.5: https://dl.dropboxusercontent.com/u/15886389/645_lens_tests/67_165mm/F4.5_stack_mosaic.jpg
It's acceptable at F4, and quite decent at F4.5. I used to use this lens wide open on P67 with film. Obviously digital sensors demand much more. These are all the lenses I have that can be easily attached to 645z. I have many Mamiya 645 lenses. Unfortunately most of them cannot be put on 645z because of the flange-back distances. However, the M645 300/2.8 APO has a detachable rear end. I am working on modifying it so I can put it on 645z. I will let you know once I make some progress on this.
Cheers,
Wei-Hao
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Forum: Pentax Medium Format
09-26-2016, 10:21 PM
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I am surprised that the Rokinon 8mm does not fully fit the 360 deg circle into an FF. The Sigma 8mm does. See this picture of mine:
http://www.astrobin.com/159762/
The flange back distance of 35mm lenses are much shorter than that of 645 lenses. So there is no convenient way (or entirely no way) to fit the lens to 645 and expect it to work. To adopt a 35mm lens to MF, you need to use a camera back rather than the full camera body. This is what I got after I fit a Canon 15mm fisheye to Mamiya 69 film back:
http://www.astrobin.com/77503/
I suppose you can do the same to an MF digital back, but I believe you will go through lots of troubles that are probably not worthwhile. Just getting a Sigma is much easier.
Alternatively, you can take a picture with your Rokinon 8mm, rotate the camera/lens by 90 deg, and take another picture. You should be able to get a full circe after blending them together.
Cheers,
Wei-Hao
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Forum: Pentax Medium Format
08-03-2016, 11:29 PM
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Forum: Pentax Medium Format
06-19-2016, 09:42 AM
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Two-frame panorama made with FA35/3.5 @F5.6 and 645z. Total exposure is 4.35 hr.
The color aberration of this lens is very severe even at F5.6. This is not an ideal lens for astrophotography, and I doubt any of the current 645 lenses are.
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Forum: Pentax Medium Format
06-23-2016, 10:38 AM
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On dpreview I read that it will soon have a third lens and more lenses in the future and there will be a firmware update to enable electric shutter. I also read that the lenses are made by Nittoh. I can't confirm all these, so let's call them rumors rather than news.
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Forum: Pentax Medium Format
04-19-2016, 03:46 PM
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What's worse, way worse, is that the A7X series try to filter out hot pixels during long exposures taken in the Bulb mode. This simultaneously filters out stars, and this cannot be turned off. See an example of mine made with A7R and Sigma 50/1.4, where many stars in the top two frames disappear:
This problem can only be avoided by taking exposures in the M mode, and therefore the exposure time can't be longer than 30 sec. To achieve a deep image, one has to take many many 30 sec exposures, instead of, for example, just tens of 5 minute exposures. This significantly increases the post-processing time, and the size of the memory card. Also, this leads to compromised image quality if one takes pictures under very dark sky, where longer exposures (of single images, not total integrated exposure) are required to completely eliminate the readout noise of the camera.
This is the same mistake Nikon made 10 years ago, and this is one of (if not THE one) the key reasons that lead to Canon's dominance in amateur astrophotography. Now Sony makes the same mistake again. People complain to Sony about this for more than a year, and there is no sign that Sony is going to address this any time soon.
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Forum: Pentax Medium Format
04-05-2016, 10:12 AM
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That wouldn't change the point. The DOF that one can reach at F11 on 645z may be reached at F8 on a 35mm full frame sensor (roughly speaking) for the same FOV. (You can change this to F16 v F11 if you like.) And the larger aperture of F8 here offers the extra photons to compensate the smaller pixels or the smaller sensor area of the 35mm FF. So again the question is which one delivers a shaper image, a good 645z lens at F11 or a good 35mm FF lens at F8?
This is physics. For the same FOV, the key is always the effective aperture diameter of the lens but not the sensor size, no matter in terms of light gathering power, or diffraction, or focus depth. (This assumes that large sensors and small sensors all have similar quantum efficiency and readout noise. This is roughly true for sensors of the same generation.) On the other hand, in terms of full well potential of the pixels, it's true that larger pixels (and therefore larger sensors) have the advantage. From this point of view, if dynamical range is very important to you, then it is a good idea to pick the larger sensor.
Cheers,
Wei-Hao
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