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Forum: Monthly Photo Contests
08-22-2022, 03:13 AM
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Forum: Pentax SLR Lens Discussion
04-24-2022, 05:44 PM
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Hi eles,
I tested my copy of the Samyang 135mm in the same manner you described with a K1ii. ie. Camera in manual, lens in auto-aperture, the cycled up and down through the aperture range and made equivalent shutter speed steps to equalize the exposure.
The histogram always stayed in the correct spot and I didn't notice any significant changes to the exposure simulation brightness levels being displayed in live view. I could not reproduce the effect you are seeing unfortunately.
For what its worth, the aperture mechanism is quite noisy on my copy too, and I have noticed issues when mounting my lens on other older Pentax bodies with the auto aperture coupling arm. Basically I could not select the lens auto-aperture position on some bodies unless I had that position set when I mounted the lens. The auto-aperture mechanism has always worked correctly though once selected.
My take away is that generally, the aperture coupling arm on the Samyang may not be the most highly toleranced component.
Thats where I would be looking on your copy of the lens, as my guess is the aperture is not retracting fully open again in live view from certain selected apertures. Actuate it with your finger and see if it feels different opening from f5 vs opening from f10 (or whatever your problem range is).
For my usage, I don't really use the exposure preview functionality in live view, so if you have a good optical copy of the lens with good centering/collimation (ie you have already won the Samyang QA lottery), I'd personally think twice about moving to a second copy hahaha. Its in the top 3 sharpest lens I've used in K-mount, and thats what I'd try and focus on.
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Forum: Pentax SLR Lens Discussion
04-15-2022, 05:12 PM
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This lens is an excellent combination of cost, size and sharpness.
However, I think any discussion of this lens should note its Achilles heel, its susceptibility to shutter shock on the K1. The worst speed is 1/100, where it has the most shutter shock of any lens I've ever tested. To avoid it completely I skip the range of 1/40 to 1/320.
If you always carry a tripod and can use electronic shutter its a non-issue, but as a day time walk-around lens, I've always found this a frustrating limitation. Its a shame, because its optical performance is genuinely impressive for its size and cost.
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Forum: Pentax SLR Lens Discussion
04-12-2022, 10:43 PM
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I think you are over thinking this! As wadge22 mentions, the time in a given position is irrelevant as long as the microscopic amount of mount flexure is elastic deformation, rather than plastic deformation. Long term material creep is possible, but not is likely to be relevant unless it'll be on the tripod for years at a time.
As for the rings, they only support the lens itself, and camera hangs off the back ([URL="https://m.media-amazon.com/images/I/71jBLXbzBZS._AC_SX679_.jpg?tag=pentaxforums-20&[/URL]). The centre of mass of the camera is very close to the mount, so the torque being applied is much lower than supporting the camera body and having the lens hang off the front.
Once you stop overthinking it, just get out and shoot some images. Mount it however you need to to get it rotating around the no-parallax point. Take as long as you need. The only thing I'd recommend is not leaving it attached in your bag during travel.
Its a great lens, definitely in my top 3 lens available for K-mount all time, just try and enjoy the process of using actually using it!
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Forum: Pentax SLR Lens Discussion
04-12-2022, 06:18 PM
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Forum: Pentax SLR Lens Discussion
09-05-2021, 04:29 PM
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For star performance, I'd recommend the Pentax-M or Pentax-A 50mm f1.4 or f1.7 (or equivalent film era lenses) over the SMC DA.
I posted sample shots of this exact comparison in the thread linked below:
The Great Astro Lens Test - Astrophotography - PentaxForums.com
I really need a better place to post these comparisons, they seem to be genuinely helpful, but nobody every finds them in this thread haha
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Forum: Pentax SLR Lens Discussion
08-18-2021, 04:18 PM
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The DFA 50mm struggles with aberrations off axis wide open (so the starts will not be points of light in the corners). I've included a review of this lens for astro at the end of my post. the long and the short is that once stopped down to f2.8 it should be looking good, but at that aperture, the M 50mm f1.4 that you already own will be looking just as good. That's the lens I'd be focussing on practising with if I was you.
The 70-200mm f2.8 should work well for astro. I've included another link, showing the coma performance of the Tamron version of this lens. I haven't used this lens, but I've used the second generation Tamron 70-200mm on another mount, and its one of the most impressive lens I've ever used around.
I don't have any info on the 77 f1.8 for astro, but my expectation would be thats its not great. This is based on its coma performance reported on Lenstip, also linked at the end of this post.
Regarding the Sigma 35mm f.4 it definitely works as is on the K1. I think it may have scratched the original K1 body very slightly above the lens mount, but I use a K1ii and I've never even seen a mark at all. In very cold conditions, I wrap a USB powered lens warmer around the 35mm to prevent condensation. I do this on every lens, its not specific to the Sigma 35mm, nor is it something that Pentax WR will prevent.
So once you get the K1ii, go out and practice with Pentax-M 50mm you already own, whilst you decide between the Sigma 35mm or the Samyang 135mm as your astro specific lens purchase (why not both hahaha).
Pentax D FA? 50mm f/1.4 Review - MilkyWayPhotographers.com
Tamron SP 70-200 mm f/2.8 Di VC USD review - Coma, astigmatism and bokeh - LensTip.com
Pentax smc FA 77 mm f/1.8 Limited review - Coma and astigmatism - LensTip.com |
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Forum: Pentax SLR Lens Discussion
08-15-2021, 03:52 PM
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Hi Igor,
There is a thread in the groups section where I recently posted documented the astro performance of the Sigma 35mm F1.4:
The Great Astro Lens Test - Astrophotography - PentaxForums.com
In short, I think its the best option for wide field astro on Pentax cameras. I don't think lacking WR is an issue, if its raining, you won't be shooting an astro hahaha
As for the DFA 50mm f1.4, its not particularly good at astro, nor is the recent DFA 85mm unfortunately. Based on my other tests in the thread linked, I'd suggest a film era 50mm f1.4 instead.
Given you mentioned other camera brands, the gold standard for wide field astro on a DSLR is the Sigma 40mm f1.4 ART, however its not available in Pentax mount. If you can go to any camera system, the Sony 24mm GM, 35mm GM and 20mm G are all amazing for wide field astro.
In the 100-150 range on Pentax, the best option is the Samyang 135 f2. Nothing else is even close.
I'll let other people comment on the long lens options, but I assume that the best budget option would be a small telescope (~300mm), and utilise a smaller sensor to get the field of view you need.
Finally, whilst astrotracer is a great function to use when shooting the night sky, I wouldn't be planning on using pixel shift for astro photography. You can achieve an equivalent or better result by just manually stacking multiple normal exposures, with the added benefit of some dithering due to small tracking errors depending on your setup
Either way, good luck, please post your results as you go along for everyone to see!
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Forum: Mini-Challenges, Games, and Photo Stories
08-08-2021, 05:08 AM
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I'd always thought these processing challenges sounded like fun, but this is the first time I actually decided to get involved. This is a photo I would have been happy to take myself, so it was a good image to start with.
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Forum: General Photography
08-03-2021, 11:25 PM
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I'll create some nice panels when I get a chance showing the Sigma 35mm f1.4 corner and centre star rendering at each aperture. being a nerd, that sounds like legit fun to me!
Clear skies are rare where I live currently, but I also plan on comparing the Sigma 35mm f1.4 to the Sigma 18-35mm f1.8 in the same manner when I get a chance. My view is that these lens are so far ahead of the rest of the pack when it comes to wide field astro photos on Pentax DSLRs, but I'm interested in seeing how they perform head to head. Obviously one is FF and one is APS-C, but I think I can still create a fair comparison by shooting both of them on each format.
I don't own the Pentax 85mm f1.4, but its aberration control for star images doesn't look great based on this review:
Pentax D FA? 85mm f/1.4 Review ? For Astro! - MilkyWayPhotographers.com
Its not as bad as the recent 50mm f1.4, but I don't think I could justify purchasing it specifically for astro.
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Forum: General Photography
08-03-2021, 06:19 PM
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My dream lens from Pentax would be a wide angle prime that is fast and well corrected for Astrophotography usage where astigmatism, spherical aberration, curved focal planes and coma are killers. Something like the Sony 35 f1.4 GM, the 24 f1.4 GM, or the Sigma 40mm f1.4 Art.
Reading this thread though, I see I am probably alone on that front, so I don't think it will be coming any time soon haha.
I love all the dedicated astro features Pentax adds to their cameras (I regularly use astrotracer and the night view mode), but its a shame not to have any lenses that can make best use of them.
---------- Post added 2021-08-04 at 11:26 AM ----------
Do you own the Sigma 35mm f1.4? I find it usable wide open for astro, especially in a pano where I can crop out the extreme corners. For excellent performance across the whole image circle, I cannot fault my copy from f2.2.
I read all your lens reviews that feature sample star field image. They are very helpful! I can send you the same star fields shot back-to back from f1.4 to f2.8 for this lens if you are interested.
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Forum: Pentax K-1 & K-1 II
08-03-2021, 12:09 AM
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Its already been explained by mossy rocks and others, but I'll just second that this appears to to be tangential astigmatism of the lens, combined with the effects of using astrotracer on a very wide rectilinear lens. It doesn't appear to be a calibration issue.
I find astrotracer has a sweet spot of focal lengths it is most accurate. Nominally I try to keep the focal lengths from 28mm to 300mm (FF equivalent). If I need a wider field of view, I will stitch together a panorama. I also keep the exposure times to 60 seconds or less. Within this sweet spot I find astrotracer to be super useful. Outside of this range, I use a portable equatorial mount, however they are a million times less convenient to carry to a site, setup, and align, so I'll always prioritize astrotracer if possible.
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Forum: Pentax SLR Lens Discussion
07-24-2021, 03:56 AM
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Thanks for taking the time to shot these and then upload them for us to look at. I love these back to back lens comparison tests.
I enjoyed looking around them at 100% magnification.
To my eye, the M-28 looks a bit better at the wider apertures, but by F8 there is very very little to split them. If anything, at F8 I think the centre of the K-28 is slightly sharper, but at the edges the M-28 is a touch better.
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Forum: Pentax SLR Lens Discussion
07-21-2021, 06:36 PM
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I agree with all your points.
A brick wall is photo is not the ultimate test of image quality. Its just the easiest way to get an indication of a problem with a lens by looking for asymmetries.
For my shooting, the ultimate test of a lens' performance is to shoot it wide open at a clear/dark night sky. This will highlight in painful detail just about every lens aberration there is. Obviously this would not constitute a relevant lens test for everyone!
If Klaus is the author of OpticalLimits, then I'm sure his review of the 18-135 ruffled a lot of Pentax fans feathers when it was released, and he is not very popular on these forums haha
I have a copy of the 18-135mm (it came with a camera used camera body I purchased). Looking at the QC first, unfortunately my copy is soft on the left side from around 60mm and narrower. In its defense, if you have the light to stop it down to F8, it performs very well from around 21-45mm. More than enough performance for my needs.
In this "sweet spot" it performed better than either of the 16-85mm copies I tested (both decentred however), it also matched the first 16-50mm F2.8 I tested (not perfectly centred), and beat the more decentred other copy of the 16-50mm I also tested. For context though, In this limited range (21-45mm stepped down a lot), basically any OEM kit 18-55mm would be more than sufficient for my needs.
I think OpticalLimit's main issue is that after your get past 50mm (even with a well centred lens), the perform drops off so significantly. On one hand, that's the price you would expect to pay for the convenience of the zoom range. On the other hand, the competitors lens, the Nikon DX 18-140mm, and the Canon EFS 18-135mm STM both maintain a significantly better performance at the long end. I have borrowed a friends copy of the Nikon 18-140mm, and its very impressive optically for its range. It edges the Pentax 18-135 even in its sweet spot, and absolutely blitzes in at the long end (even on the Pentax's "good side" haha).
Ultimately, I still get good use out of my Pentax 18-135. I use it as the default lens on my K10D. I find the lower pixel density of this camera a good means of masking the lens' QC issues. The vast majority of the images I have posted on this forum have been taken with that combination if you want to look them up.
Nice duck photo too! Looking at the exif data, is that a native 860mm lens? I'm still learning about Pentax's lens range. Or is that through a teleconverter?
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Forum: Pentax SLR Lens Discussion
07-20-2021, 07:28 PM
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Thank you for the detailed response
I can send you a link to my spreadsheet by PM if you like, I can upload it to Google drive. Let me know if you are interested. I'll add a column to indicate which ones I still have the RAWs available on.
I would genuinely like to see the RAWS of a few of the lens you listed shooting a brick wall at various apertures. I have a few of them, but I'd be particularly keen to see how the 28-105 and 70-210 perform optically, compared to some of the lens I'm familiar with. the quantitative data that's available on the Tamron 70-210 is other mounts on the internet indicates its an excellent lens.
I read all of the Roger Cicala content I can find on LensRentals and/or DPreview (i'm a big fan too), but I must have missed when he addressed Pentax lens QA specifically, sorry. In terms of quantitatively derived lens reviews that do comment on the optical centring of the lens, I find OpticalLimits and LensTip to be the most helpful. They have both reviewed a large catalogue of Pentax lens. I'm sure you are familiar with them.
Regarding your last point, I agree, re-centring a lens is in typically not possible, the adjustments physically do not exist for all the elements, even on high end lens. Even the adjusting of the optical elements that can be moved is still even done manually on the production line, although the internet rumours are that Canon RF lens may be automating this process. The lens QA that you or I are observing is a Gaussian distribution, a function of the costs/quality/consistency of the optical batches being used, and the mechanical tolerancing of the lens construction.
---------- Post added 2021-07-21 at 12:34 PM ----------
The only two film era lens I've tested had excellent optical centring for what its worth! I have usually only purchased digital era lenses.
These are the 8 element Super Takumar 50mm f1.4 and the F series 50mm F1.7 (which has the most plasticky build quality you can get hahaha)
The double Gauss design of these lens is very tried and tested, and I suspect is "quite tolerant" of lens collimation in general. After all, they have been in use for 90-100 years at this point!
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Forum: Pentax SLR Lens Discussion
07-20-2021, 02:53 AM
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It will not be a popular observation, but I've found that Pentax lenses have the worst optical alignment (collimation) of any OEM lens in my experience. At least for the modern digital lens I most typically use. I don't test my lens auto-focus accuracy or assess their long term durability, but I setup test shots of every new lens I get and compare its performance to other lens of a similar FoV. Usually this means a flat, even textured wall (brickwork or similar), shot exactly perpendicular. I shot at every aperture setting, and zoom in to 100%, comparing each side of the frame against itself, and then against the a known "good lens".
I have found ~40% (yes I'm a nerd, and I have a spreadsheet haha) of the Pentax lens I tested to have a noticeable amount of softness mismatched around the frame. Whether the result of some degree of the optical elements being tilted/decentred, or the focal plain being asymmetrically curved due to individual lens profile/power tolerances.
I accept that this level of testing is not necessary, and as a result, it is highlighting issues that most people would never notice. In many cases I continue using the "bad lens", as the issue is not noticeable in everyday use.
For the record, this ratio of bad lenses (~40%) is still much better the Samyang lens I have tested (admittedly, not a high bar). However with the Nikon/Canon lens I have tested, the rate of optical alignment issues is <10%, so its noteworthy to me. I really like Pentax camera bodies, so I just see the lens QC issues as the price I have to pay to use them! I should also acknowledge that I buy all my Pentax lenses used, so what I am observing may be the result of previous damage/wear, not manufacturing issues. That said, I buy all my lens used, so I don't put much weight on that fact.
Getting back to the OPs original point, I have tested two copies of the Pentax 16-85mm, and both had poor optical alignment. So you are not alone on that lens being an issue for you at least haha
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Forum: Pentax DSLR Discussion
06-27-2021, 02:44 AM
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I picked up a K100D recently. The intention is to utilise it primarily for IR photography, making use of the weak factory IR filter. It was the dustiest DSLR I'd ever seen, but the price was right. Most importantly, the sensor has cleaned up alright and it's got me started with a new type of photography. Its been an enjoying challenge so far, I just need more clear sky days to keep practicing with!
K10D, 18-55 DA-L, 850nm lens filter  |
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Forum: Pentax DSLR Discussion
06-19-2021, 11:31 PM
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Forum: Pentax DSLR Discussion
05-11-2021, 04:55 AM
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Another Tree
K10, 18-135  |
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Forum: Pentax DSLR Discussion
04-29-2021, 09:11 PM
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Thankyou. I spotted the tree behind a construction fence just after sunset. By the time I went to my car and came back and found the best angle, it was close to darkness. I've never shot the K10D at high ISO before, and this was the sharpest of about 10 frames to try and handhold the slow shutter speed still required. Overall then, its one of my worst photos technically, but I really, really like is creatively!
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Forum: Pentax DSLR Discussion
04-27-2021, 11:00 PM
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Autumn Perseveres
K10D, 18-135mm  |
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Forum: Mini-Challenges, Games, and Photo Stories
04-15-2021, 11:39 PM
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Don't forget your KP has an electronic shutter mode.
That is what I used for the 1200 frames for the photo I posted. I used it to minimise vibrations, but it also avoids any wear on the shutter.
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Forum: Mini-Challenges, Games, and Photo Stories
04-05-2021, 09:51 PM
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Yes 100%. Any processing that amplifies noise will definitely benefit from a higher SNR image as a starting point. I was just trying to convey that for this particular image, the amount of tone mapping I did was orders of magnitude less aggressive than the sharpening, with no colour adjustments, or drizzling.
Yes, I believe the wavelet editing in the advanced tab could provide an analogous output to wavelet sharpening in Registax. When I was playing with it I got confused though (as is typical when I use a new function in RawTherapee for the first time haha), so I reverted to a saved sharpening profile in Registax.
I haven't used Hugin for image stacking, but I have used PTgui fairly extensively for 360 image stitching. I understand it uses the same stitching/aligning engine as Hugin. It is very very robust at aligning images via uniform geometric transformation. That said, I'm confident the aligning engine in Autostakkert will blow it out of the water when it comes to warping/skewing an image locally for the specific case of correcting atmospheric distortion. I understand my image falls a long way short of demonstrating this, but that is a limitation on the optics rather than the stacking accuracy.
Excluding some percentage of 'bad images" is fundamental to the process of Lucky Imaging. Both PIPP and Autoskattert can quality grade the individual frames, so you can skip the PIPP step altogether if you prefer. I like the visualisation options of PIPP personally.
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Forum: Mini-Challenges, Games, and Photo Stories
04-02-2021, 09:34 PM
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Thank you. The good news is that 95% of the editing can be done in freeware programs that are pretty user friendly. Aside from Photoshop to do some final touches and blend in the moon glow and stars, I used RawTherappe for raw development, then PIPP to centre the moon for stacking, Autostakkert for stacking, and Registax for wavelet sharpening.
The basic premise is to create a single moon photo of very high SNR, so you can aggressively sharpen it without introducing artefacts.
This video is a thorough guide:
You Tube
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src="https://www.youtube.com/embed/FYLz7mxGHTg?controls=1" allowfullscreen>
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If anything is unclear or you get stuck, PM me, and I can help you out.
My photo was only so tricky to edit because the long focal length, combined with the slow shooting speed of the KP. This meant I had to re-centre the moon manually 40 times. In short, this created more rotation from start to finish than Autoskattert could correct for. So I manually de-rotated the moon in the raw development stage for all 1200 photos, taking a long time. If you can take say 200 photos to stack at a shorter focal length without moving the camera once, you could probably skip straight to the Autostakkert stage of the above video.
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Forum: Pentax DSLR Discussion
04-02-2021, 09:22 PM
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Path to the Cathedral
K10D, 18-135  |
