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Forum: Pentax Lens Articles
07-30-2016, 09:52 AM
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I now have a de-baffled (is that a word?) DA* 60-250mm f/4 lens. I've started to do some systematic testing on the K-1 at FF. I'm posting to this thread at DPReview:
Tests of de-baffled 60-250mm on K-1 at FF
My summary so far, based on the tests and conclusions in the 2nd post in that thread, is:
I now view this as a good 135-250mm f/4 FF lens:
At 135mm, it is good at FF at f/8.
At 200mm, it is good at FF at f/5.6.
At 250mm, it is good at FF at f/4.
It improves on stopping down.
I have better and lighter lenses covering the range wider than 135mm:
At 60mm, it is best seen as an APS-C lens, and never becomes a plausible FF lens.
At 85mm, it is just about OK as an FF lens at f/11.
Other people, with different standards for different purposes, will probably disagree!
I expect to continue with tests and field experience, and then will add to that thread.
For interest, I used a "non-destructive" form of debaffling. I could restore it to its original state in perhaps less than an hour.
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Forum: Pentax Lens Articles
05-03-2016, 02:45 AM
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Right!
I forgot that with SR operating, at any point on the sensor there is now a contribution from positions of the image circle which would normally be further away from that point, and potentially lower in quality.
This would typically be a tiny effect with a proper FF lens, but the DA* 60-250mm is known to be marginal at the corners on FF. (I posted to this thread in 2013 with a link to my own tests).
When I test the 60-250mm on the K-1, (I intend to publish my results), I'll try it with SR on and off.
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Forum: Pentax Lens Articles
05-03-2016, 02:12 AM
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That statement surprised me! I wasn't aware of any such effect.
What is the background to that statement?
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Forum: Pentax Lens Articles
04-25-2016, 11:40 PM
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I ran tests on my own lenses, and I posted a link to my results to this thread in 2013.
Since then, on that page of mine I've maintained links to some other such tests that I became aware of. This thread has become so big and cluttered that I don't know if those particular tests are covered in this thread. I think all the lenses they cover are listed, but perhaps a second opinion may be useful.
So here are copies of the links that I have been maintaining, together with the Pentax DA(*) lenses they examine. Given that the K-1 will soon be in many hands, (including mine!), just about everything in this thread will soon be superseded, but here goes. The tests don't all strictly conform to the thread rules; they are not my own tests.
Karl Knipser - Flickr Set
Many test photos of Pentax lenses on both film and a Canon EOS 5D Mark III
DA* 60-250mm f/4
DA* 300mm f/4
DA 12-24mm f/4
DA 15mm f/4
DA 18-135mm f/3.5-f/5.6
DA 18-250mm f/3.5-f/6.3
DA 21mm f/3.2 Limited
DA 35mm f/2.8 Macro
DA 40mm f/2.8
DA 70mm f/2.4 Limited
DA* 16-50mm f/2.8
DA* 50-135 f/2.8
DA* 55mm f/1.4
DA 50-200mm WR
DA 18-55mm
DA 560mm f/5.6
AMMouse aka Pentax_Prime - photobucket:
Some Pentax lenses on a Pentax Z-1p film camera
Pentax DA 55 (?)
Pentax DA 70 (?)
Wallace Koopmans Artlog:
Pentax Full Frame and APS-c Lenses on film
Pentax SMC-DA* 50-135mm f/2.8 ED [IF] SDM
Pentax SMC DA 50mm f/1.8
Pentax SMC DA 35mm f/2.8 Limited macro
Pentax smc PENTAX-DA 40mm F2.8 XS Lens
Eric Tastad at ERPhotoReview:
K Mount Primes
SMC Pentax DFA 100mm f/2.8 Macro WR on Sony A7R
SMC Pentax DA* 55mm f/1.4 on Sony A7R
K Mount Zooms
HD Pentax DA 20-40mm F2.8-4 Limited WR on Sony A7R
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Forum: Pentax Lens Articles
02-08-2015, 09:19 AM
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In 2013 I tested my DA* 60-250mm on a Pentax film camera, had the film scanned, then uploaded it. (I did the same with several other Pentax lenses, accessible from the link below). See:
DA* 60-250mm f/4 on Z-1p
Conclusion for the 60-250mm:
"This isn't an unqualified FF lens. But neither is it unusable on a 35mm camera. At 60mm on 35mm the corners are soft. At 250mm the corners are darker, but still usable. These improve on stopping down. In other words, similar to (although perhaps worse than) a typical kit lens used on an APS-C sensor. Perhaps that is a way to think about it - an expensive kit lens (unless you already own it, as I do) for an FF camera!
"It appears that this is likely to be a useful lens on an FF camera when used with a 1.4 teleconverter. I am already looking forward to using it on an APS-C sensor as an 84-350mm f/5.6 lens if/when Pentax supply a 1.4x teleconverter. And I think it might be good as an FF lens in that combination."
---------- Post added 8th Feb 2015 at 04:21 PM ----------
Here are some tests of DA and DA* lenses on film that I did in 2013. Their time has come! Spread the word.
Pentax Full Frame tests |
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Forum: Pentax Lens Articles
08-02-2013, 11:19 PM
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Half of what I published duplicated what others had done. (I wanted to check for myself!)
However, I think my tests using a 1.4x Teleconverter may be an important extension to this topic. I couldn't find such tests elsewhere. (Perhaps they exist but I missed them?) I wanted to know what would happen, because I'm sure that if Pentax supply such a Teleconverter I will buy it, and if Pentax supply an FF camera I will often use that Teleconverter with that camera, especially for the longer lenses. That means especially with my DA* 60-250mm f/4 and my DA* 300mm f/4.
If Pentax launched a 420mm f/5.6 lens, we would want to know if it was an FF lens. But that is what we get with a 1.4x Teleconverter plus a 300mm f/4 lens. And the 60-250mm becomes an 84-350mm f/5.6 lens, which sounds like a very useful lens on an FF camera.
A 1.4x Teleconverter works by expanding the image circle. If it expands the whole image circle, rather than just the centre of it, it "uncrops" the lens by the corresponding amount. A lens that was originally a 1.5-crop lens should become about a 1.1-crop lens. A lens that was nearly an FF lens should become a full FF lens. I think the above 85-350mm f/5.6 (60-250mm plus Teleconverter) will be a useful FF lens. Perhaps still a bit soft in the corners at 60mm (now 85mm), but good at longer lengths.
I suspect that if Pentax supply an FF camera, their 1.4x Teleconverter (if any) will play a role in many people's decisions. Perhaps Pentax themselves will promote it. (And I would like to know how the DA* 50-135mm f/2.8, which I don't have, behaves with a 1.4x Teleconverter. Will it be anything like an FF lens?) Unfortunately, Teleconverters tend not to work so well at wider focal lengths, so this will not be a general solution across all lenses.
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Forum: Pentax Lens Articles
08-01-2013, 07:40 AM
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Aaaaaarrrggh!
Thank you for that (very fast) response. I've updated my page for the DA 10-17mm fisheye lens to link to your reply and to that description.
I wouldn't try that myself. But I might pay an expert to do it for me.
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Forum: Pentax Lens Articles
08-01-2013, 06:33 AM
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I hope this thread is still active. This post is the reason I joined Pentax Forums!
I put my DA and DA* lenses on a Pentax Z-1p 35mm camera, and shot 3 films in all. I've uploaded 99 scans to my website for all to see. They are 4976px by 3300px JPEGs, and so are of the order of 4 MB each.
I photographed a brick wall in about one third of the photos, and a simple test target for the other two-thirds. Nearly half of the photos used a 1.4x teleconverter. I've superimposed an APS-C-sized rectangle onto each photo to make comparisons of edge and corner quality easier.
Here is the link to the set of pages describing the tests and providing the photos. There are 3 descriptive pages plus one page per lens. The 6 (Pentax) lenses are: DA 10-17mm fisheye; DA 12-24mm; DA 17-70mm; DA* 55mm; DA* 60-250mm; DA* 300mm. Their pages give a very brief summary of my thoughts on how useful they would be on such a camera.
This is still work-in-progress. I may add more analysis to those pages, and perhaps process some of the scans to see if their failings (if any) can be overcome with post-processing. But in the meantime I feel that others may want to examine the scans and draw their own conclusions and post them here. Or ask me to expand on my own views on those pages.
I made some (fairly obvious) errors in a few of the tests, such as camera shake, bad focusing, etc. It is unlikely that I will re-do any tests. This was a one-off exercise mainly for my own purposes.
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