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09-13-2016, 03:48 PM   #1
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35mm F3.5 AL [IF] HD FA 645 Chromatic Aberrations

Has anyone any experience with this HD version of the lens. I just received it, in general it looks really sharp with good contrast. Slight distortion easily corrected in Lightroom but CA on small branches and phone lines against the sky seems very bad, by which I mean the worst I have ever seen. I've attached some jpegs zoomed in on the worse areas, whic are out of focus high contrst parts. I'm going to shoot some more controlled test shots tommorrow, but in the meantime would welcome any comments/experience about this lens before deciding if I'm going to send it back.

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09-13-2016, 04:30 PM - 1 Like   #2
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You are correct in that the CA is really bad. Speaking only for myself I have this experience only with both of my long telephoto lenses when shooting against a contrasty sky. With this much CA I am not sure it can be corrected in PPE. If this effect is consistent with this lens, it would have to go back. Hope this helps.

Rgds,

Tony
09-13-2016, 04:35 PM   #3
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This is a film-era lens with new coatings and nothing more, so this doesn't surprise me. That said, the camera and Pentax software should have correction profiles to take care of the CA

Adam
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09-13-2016, 07:38 PM   #4
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QuoteOriginally posted by Adam Quote
This is a film-era lens with new coatings and nothing more, so this doesn't surprise me. That said, the camera and Pentax software should have correction profiles to take care of the CA
Really? Let me make sure. We are talking about the latest 35mm for 645, right?

09-13-2016, 11:20 PM   #5
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QuoteOriginally posted by whwang Quote
Really? Let me make sure. We are talking about the latest 35mm for 645, right?
Correct, it's basically a respin of the FA lens.

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09-14-2016, 04:03 AM   #6
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To quote the pentax description
"Combining a newly designed, high-grade glass-molded aspherical element with a high refractive index low dispersion glass element and a hybrid aspherical element in its optics, this lens effectively compensates for chromatic and spherical aberrations and assures a sufficient peripheral brightness level..."

---------- Post added 09-14-16 at 04:12 AM ----------

I'll try and get across to the Humber Bridge later this evening and repeat a shot I took a few years ago with a Canon 24-105. Strong contrasty lines from the suspension cables (but in focus) should make a solid real world test. I hope that this is just my copy. Lightroom certainly cannot remove these, in fact in many ways it made it worse during the attempt! I think the only question for me is if I will try another coppy of the same, or try and exchange for a completly different lens (but not much wide angle to choose from)
09-14-2016, 05:54 AM   #7
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QuoteOriginally posted by pshersby Quote

I'll try and get across to the Humber Bridge later this evening and repeat a shot I took a few years ago with a Canon 24-105. Strong contrasty lines from the suspension cables (but in focus) should make a solid real world test.
I remember thinking that the 55mm also had an unusual amount of CA when I first started taking a few test images with the 645Z, so I decided to pit it against my Canon 24-70/2.8 II, which has arguably the least CA of any zoom that doesn't feature a white barrel, and I never really thought that it had any, until of course I knew what to look for.

So I set the two cameras up and took some shots of some plants on my window, and it turned out that both lenses actually had about the same amount of CA, it's just that the Z features some 50% higher pixel density, and was showing me stuff at 100% I simply wouldn't have seen on the Canon, but blowing up the Canon shot to-size also made it apparent; it's simply something I never did.

I'm guessing that if you had put your 24-105L on a 5DSR, you'd also have been disappointed by the increase in visible CA... you really do need primo glass to render a flawless image on a sensor this intolerant of artifacts. I didn't even pay as much attention to this on the 645D, even though the resolution difference seems insignificant on paper.

Actually, what we're looking at isn't really CA at all, but a subset of it called purple fringing, which has a tendency to occur even on lenses with perfect CA control. So when I said the 24-70L 2.8 II doesn't have CA I really did mean it, even in the extreme corners at 24mm, but it will have fringing on high-contrast edges, as most lenses tend to show on high-resolution sensors. Similarly, a lot of people mistakenly label the 85L II as having a ton of CA, but having it glued to my camera for the better part of 6 years, I can say it really does not, but it does have a boat-load of fringing.

Last edited by Kolor-Pikker; 09-14-2016 at 06:03 AM.
09-14-2016, 11:28 AM   #8
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This lens is going back, hopefully another copy will be better. I'll post a review when I have it (of course it is out of stock at my dealer now).

While I agree that all lenses exhibit some degree of fringing, the 50% extra pixel density should not really make that much difference, particularly in a lens specifically updated for this body! Examining at 600% so I can clearly see the separate pixels: The 24-105L on a 5DMk2 show approx 1-2 pixel fringe at 35mm at the corners, and I can easily get rid of that in post-process. The pentax lens is giving about 10 pixels lateral on an in-focus edge at f8 and is heavily dependent on the angle of the edge; this is not a cheap lens and it is designed for a significantly larger area than the 645Z sensor, so we are not really even into the corners. Some of the cables and smaller branches are completely mis-coloured and many have lost detail.

Now I do usually get rid of power cables etc, but there is no way I can sort out all the problems in trees and architecture by hand; the worse parts are actually visible on A4 prints. If other users of this lens are experiencing similar problems then let me know and I'll think again about getting another copy of the same, although wide angle alternatives are a little limited. And I purchased the prime lend for the better quality; very depressing

09-14-2016, 12:04 PM   #9
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QuoteOriginally posted by pshersby Quote
Combining a newly designed, high-grade glass-molded aspherical element with a high refractive index low dispersion glass element and a hybrid aspherical element in its optics,
A high refractive index, low dispersion element will by no means correct color as well as a traditional low index, low dispersion (ED) element. Pentax is being overly optimistic here. If your fringing is not reduced by stopping down, it could be lateral chromatic causing the problem. The reason why lateral CA is not reduced by the diaphragm is because image size varies by color in lateral CA, which means that it is distortion by color. Distortion is not affected by the diaphragm. If the diaphragm reduces the fringing, it is probably longitudinal CA. However, digital sensors are much more sensitive to violet/purple than film, so any fringing in those colors will be amplified.
09-14-2016, 02:13 PM   #10
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QuoteOriginally posted by desertscape Quote
A high refractive index, low dispersion element will by no means correct color as well as a traditional low index, low dispersion (ED) element. Pentax is being overly optimistic here. If your fringing is not reduced by stopping down, it could be lateral chromatic causing the problem. The reason why lateral CA is not reduced by the diaphragm is because image size varies by color in lateral CA, which means that it is distortion by color. Distortion is not affected by the diaphragm. If the diaphragm reduces the fringing, it is probably longitudinal CA. However, digital sensors are much more sensitive to violet/purple than film, so any fringing in those colors will be amplified.
I was expecting a little lateral CA but not this much. I was hoping to get some comparative comments from others with the specific lens to know if it is a common problem or I'm just unlucky. To be honest it is just not acceptable so I'm not going to worry about the cause any more. I will try a fresh copy and hope it improves things. Must remember to rent before buying in future!
09-14-2016, 06:03 PM   #11
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I have this lens and it is impressive.
In challenging high contrast I definitely see some CA but not really any different than what I get with some other lenses and it is completely correctable with one box check in ACR, so I do not worry about it.

I did find an example of some challenging light. This is straight out of camera (SOOC) with no corrections of any kind. full image plus 100% crop of the tree/leaves area. It is not bad for this type of situation, IMO.



100% crop


---------- Post added 09-14-2016 at 06:15 PM ----------

in case you just cannot figure out why i took such a lame picture in the first place, i was just noting the shooting location of this tele extraction for future reference:


don't want anybody calling the composition police on me... ;p

Last edited by mikeSF; 09-14-2016 at 06:18 PM.
09-14-2016, 09:10 PM   #12
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my old 35 had obscene levels of CA

The new one, the DFA one - has near zero as far as i have seen.
09-15-2016, 07:23 AM   #13
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QuoteOriginally posted by pshersby Quote
. The pentax lens is giving about 10 pixels lateral on an in-focus edge at f8 and is heavily dependent on the angle of the edge; this is not a cheap lens and it is designed for a significantly larger area than the 645Z sensor, so we are not really even into the corners.
Definitely sounds like a bad sample then, sample variance can occur on lenses of any price.
09-15-2016, 09:01 AM   #14
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QuoteOriginally posted by mikeSF Quote
In challenging high contrast I definitely see some CA but not really any different than what I get with some other lenses and it is completely correctable with one box check in ACR, so I do not worry about it. I did find an example of some challenging light. This is straight out of camera (SOOC) with no corrections of any kind. full image plus 100% crop of the tree/leaves area. It is not bad for this type of situation, IMO.
Thank for that Mike, exactly what I was looking for. The CA is fairly hard to pick out on your 100%, but very obvious on mine.
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