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04-05-2019, 12:07 PM - 4 Likes   #1
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K10D and the new HD Pentax-FA 35mm f/2

I stopped by Adorama today meaning to pick up a Pentax 20-40 Limited but instead walked out with the new Pentax HD-FA 35mm f/2. I figured I could use the 35mm on both my K10D, my daughter's K-30, and my K1-II, plus I wanted to see what the new HD coatings brought to the table.

Only after slapping the lens on my K10D did I discover that particular body suffers from a backfocus issue; something I didn't really notice when using an older 17-135WR (most likely because I often use it stopped down past f5.6). It seems the K10D suffered terrible backfocus on fast lenses... which was remedied quickly by adding +130um in the AF adjustment screen in the debug menu.

But I digress. That's not why I'm posting this thread. I just wanted to share a few quick photo samples of what the HD 35mm f/2 can do when mated to the K10D. Perhaps tomorrow when the weather is better, I'll slap it onto the K1-II and take a walk. Perhaps then I'll be able to tell if there's any difference the HD coatings does over the standard 35 f/2 that makes it worth almost $100 more.

FWIW, wide open is a tad softer than I'd like, but then again this is a pretty cheap lens all things considered. Stopping down to f2.8 and higher and it becomes pretty decent across the frame. I'm not sure if this particular copy suffers slight decentering around the upper left hand corner, but I'll check that tomorrow.

Full size JPGs here: https://jamespaulsarte.com/temp/K10D_HD_35_F2/

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04-05-2019, 12:30 PM   #2
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QuoteOriginally posted by amstel78 Quote
I stopped by Adorama today meaning to pick up a Pentax 20-40 Limited but instead walked out with the new Pentax HD-FA 35mm f/2. I figured I could use the 35mm on both my K10D, my daughter's K-30, and my K1-II, plus I wanted to see what the new HD coatings brought to the table.
Good choice!

QuoteOriginally posted by amstel78 Quote
Only after slapping the lens on my K10D did I discover that particular body suffers from a backfocus issue; something I didn't really notice when using an older 17-135WR (most likely because I often use it stopped down past f5.6). It seems the K10D suffered terrible backfocus on fast lenses... which was remedied quickly by adding +130um in the AF adjustment screen in the debug menu.
Both of my K10D-based Samsung GX-10s back-focus. One requires +90 to +150 depending on which lens have fitted. The other is somewhat better, but still requires adjustment. It seems to be a very common thing...

QuoteOriginally posted by amstel78 Quote
But I digress. That's not why I'm posting this thread. I just wanted to share a few quick photo samples of what the HD 35mm f/2 can do when mated to the K10D. Perhaps tomorrow when the weather is better, I'll slap it onto the K1-II and take a walk. Perhaps then I'll be able to tell if there's any difference the HD coatings does over the standard 35 f/2 that makes it worth almost $100 more.

FWIW, wide open is a tad softer than I'd like, but then again this is a pretty cheap lens all things considered. Stopping down to f2.8 and higher and it becomes pretty decent across the frame. I'm not sure if this particular copy suffers slight decentering around the upper left hand corner, but I'll check that tomorrow.
Those photos look great! I've looked at the full size versions. Honestly, I think that's pretty sharp at f/2... especially considering the age of the design. I'd be very happy with that, frankly.

Thanks for posting these
04-05-2019, 12:43 PM   #3
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Thanks Mike! For a small lens, the 35mm f/2 does deliver. I've briefly seen what it could do on the K-1, but decided not to post any of those photos since they're just quick snaps of my fridge magnets under poor light. Tomorrow in NYC, it's supposed to be warm and sunny so I'll put it through its paces then.

As for my comment about it being soft; I've been using a 50mm HD FA* on my K1-II which is ridiculously sharp wide open. I've also been blessed with owning a K1 that has perfect AF calibration out of the box, meaning I haven't had to adjust anything. I guess I've been spoiled. To be fair though, the 50mm star lens cost almost 3x the price (as well as size and weight) of this 35mm prime.

Regarding the backfocus issues on the K10D; only after googling today did I also discover that it seems to be a fairly common issue with that particular body. I also started going through some of my older photos in lightroom taken with the K10D and the 17-135WR, and noticed that most photos under F8 were soft or OOF. Some at f4.5 looked sharp enough to pass muster, so not really sure what's going on there. I've had the focus screen out a few times for periodic maintenance but haven't touched the primary or secondary AF mirrors, so I doubt whatever I've done could have caused an AF discrepancy from when I first bought the body to today.
04-05-2019, 12:50 PM   #4
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Back or front focus is the result of combining the tolerances in a camera body and a lens, which is why it changes depending on the body/lens combo. The K10D is not the culprit on its own.

04-05-2019, 01:14 PM - 1 Like   #5
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QuoteOriginally posted by JohnX Quote
Back or front focus is the result of combining the tolerances in a camera body and a lens, which is why it changes depending on the body/lens combo. The K10D is not the culprit on its own.
Yes, that I understand. What threw me for a loop was why some shots at f4.5 on the K10D using a 17-135WR were in focus while some at f5.6 or lower where OOF or slightly soft. I guess I just wasn't paying too much attention with the K10D and 17-135WR combo in the past as it isn't my primary camera. And when I shot with the K10/17-135 combo, most times I was north of f/8 for either landscape or architectural shots. To be honest, I've only used the K10 a handful of times, and that's only when I wanted to replicate a certain look in the finals.

Fast forward to today, the 35mm f/2 (before I adjusted the AF calibration) was horrendously OOF on every test shot I took despite the image in the viewfinder being sharp. Even manually focusing resulted in OOF images. That's when I put the 17-135WR back on to see if it was the lens, and discovered that at 18 to 35mm wide open, 99% of test images were also garbage. Fortunately I was able to correct the backfocus issue and now the K10D works very well on fast apertures with both lenses.

For instance, have a look at the following image (larger JPG here: https://jamespaulsarte.com/temp/K10D_HD_35_F2/oof_sample_k10_17-135.jpg). This was shot with the K10 and the 17-135 at f/4.5. Focus point was on the left eye but my instead, the collar around my youngest daughter's coat, or the last step behind her seems to be sharper indicating a backfocus issue.
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04-05-2019, 01:15 PM - 1 Like   #6
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QuoteOriginally posted by amstel78 Quote
Thanks Mike! For a small lens, the 35mm f/2 does deliver. I've briefly seen what it could do on the K-1, but decided not to post any of those photos since they're just quick snaps of my fridge magnets under poor light. Tomorrow in NYC, it's supposed to be warm and sunny so I'll put it through its paces then.

As for my comment about it being soft; I've been using a 50mm HD FA* on my K1-II which is ridiculously sharp wide open. I've also been blessed with owning a K1 that has perfect AF calibration out of the box, meaning I haven't had to adjust anything. I guess I've been spoiled. To be fair though, the 50mm star lens cost almost 3x the price (as well as size and weight) of this 35mm prime.
Yeah, that D FA*50/1.4 will skew your view of sharpness compared to any other lens, I think

I have a fondness for the rendering of film-era lenses, so maybe I'm pre-disposed to liking the HD FA35/2's output.

Incidentally, my K-3 and K-3II were identical out of the box on AF calibration. Four of my HD DA Limiteds, my D FA100/2.8 Macro WR, HD DA55-300 and DA50/1.8 are spot on with no AF fine adjustment. My other HD DA Limiteds and FA50/1.4 are wihin +/-2, and my DA35/2.4 requires -3. Exactly the same on both bodies. Like you, I consider myself very fortunate on that score.

QuoteOriginally posted by amstel78 Quote
Regarding the backfocus issues on the K10D; only after googling today did I also discover that it seems to be a fairly common issue with that particular body. I also started going through some of my older photos in lightroom taken with the K10D and the 17-135WR, and noticed that most photos under F8 were soft or OOF. Some at f4.5 looked sharp enough to pass muster, so not really sure what's going on there. I've had the focus screen out a few times for periodic maintenance but haven't touched the primary or secondary AF mirrors, so I doubt whatever I've done could have caused an AF discrepancy from when I first bought the body to today.
Using a couple of the HD DA Limited lenses I know are perfect on my K-3 and K-3II with zero AF fine adjustment, through trial and error I was able to find out that my first GX-10 required +110 to get the same accurate focus. I was also able to figure out that a +1 adjustment increment on the K-3 is equal to a -10 increment on the GX-10, while a -1 increment on the K-3 is equivalent to +10 on the GX-10. Based on that, I came up with the following translation table for adjusting the GX-10 for each of my lenses, given a known K-3 adjustment:



It works perfectly, every time. Any time it doesn't, those are outlier shots, IMHO. Obviously, my numbers are specific to my K-3 and GX-10, but it's worth remembering (if you didn't know already) that +1 and -1 increments on the K-3 AF fine adjustment (and, I'd guess, on the K-1?) are equivalent to -10 and +10 respectively on the GX-10 / K10D...
04-05-2019, 01:23 PM - 1 Like   #7
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QuoteOriginally posted by BigMackCam Quote
Using a couple of the HD DA Limited lenses I know are perfect on my K-3 and K-3II with zero AF fine adjustment, through trial and error I was able to find out that my first GX-10 required +110 to get the same accurate focus. I was also able to figure out that a +1 adjustment increment on the K-3 is equal to a -10 increment on the GX-10, while a -1 increment on the K-3 is equivalent to +10 on the GX-10. Based on that, I came up with the following translation table for adjusting the GX-10 for each of my lenses, given a known K-3 adjustment:



It works perfectly, every time. Any time it doesn't, those are outlier shots, IMHO. Obviously, my numbers are specific to my K-3 and GX-10, but it's worth remembering (if you didn't know already) that +1 and -1 increments on the K-3 AF fine adjustment (and, I'd guess, on the K-1?) are equivalent to -10 and +10 respectively on the GX-10 / K10D...
Great info Mike. I was always curious as to how much a +1 or -1 adjustment equaled to on the K-1. Question answered! Much obliged.
04-05-2019, 02:18 PM   #8
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You mean K10D's and K-3's adjustments are opposite? I know on my K10D I had to dial +110 but never thought if I need to have more to the front, I need to reduce the adjustment.

04-05-2019, 02:21 PM   #9
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QuoteOriginally posted by amstel78 Quote
Great info Mike. I was always curious as to how much a +1 or -1 adjustment equaled to on the K-1. Question answered! Much obliged.
You're welcome, James It's a little confusing initially, but you get used to it

Looking forward to seeing your K-1 shots with the new lens...

QuoteOriginally posted by hyyz Quote
@BigMackCam
You mean K10D's and K-3's adjustments are opposite? I know on my K10D I had to dial +110 but never thought if I need to have more to the front, I need to reduce the adjustment.
Yes, that's correct - opposite, and for the K10D, multiplied by 10. Assuming you know your K-3 is accurate with a specific lens at zero AF adjustment, and your K10D requires +110 for that same lens, if you now fit a lens to your K-3 that needs +2 AF fine adjustment, you'd set the K10D at +90 for that lens. If it required +2 on the K-3 instead, you'd set the K10D to +130.

Weird, isn't it?
04-05-2019, 03:21 PM - 1 Like   #10
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QuoteOriginally posted by amstel78 Quote
Regarding the backfocus issues on the K10D; only after googling today did I also discover that it seems to be a fairly common issue with that particular body.
Interesting...I bought K10D new in 2007, shortly before joining Pentax Forums and don't remember any buzz about pervasive backfocus issues nor did I have such a problem in seven years of ownership. That does not mean that your camera does not have such or that there was never a post on this site involving using debug mode on a K10D for global AF fine adjust, only that my camera is fine and that most PDAF problems reported here were related to the usual complaints of poor tracking, slow response, and/or inability to lock focus.


Steve

Last edited by stevebrot; 04-05-2019 at 04:18 PM.
04-05-2019, 04:38 PM   #11
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It's possible Steve; perhaps I just got a bad one out of the box and never realized it until now.

But, Google searches do turn up quite a few results on backfocus issues with the K10D. Then again, those without problems are likely the larger majority of owners who'd never bother to post online about their experiences anyway.

Glad to hear your K10D never had such quibbles!

04-05-2019, 04:56 PM   #12
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QuoteOriginally posted by amstel78 Quote
For instance, have a look at the following image
As an aside, that image is a good example of one of the common AF 'risks' indicated here (courtesy of Nikon):
04-07-2019, 09:48 AM   #13
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Finally got around to testing the HD FA 35mm f2 on the K1-II here: HD Pentax-FA 35mm f/2 on K1-II - PentaxForums.com
04-07-2019, 10:34 AM   #14
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QuoteOriginally posted by stevebrot Quote
Interesting...I bought K10D new in 2007
I too bought my K10D in 2007. I still use it occasionally at ISO 100. I've always hated the idea of having to make adjustments for a lens to be sharp, so I buy premium lenses, and to this day have never had to make an adjustment for a lens. Honestly I'd be disappointed if I paid a premium price for a premium lens and it wasn't ready to go. That's why I bought the higher-end lens. It would be different for a cheap lens.

Several years into owning the K10D I went to a scheduled shoot and all photos I took of the model were out of focus, just slightly. This had never happened to me before, and after additional testing, every photo was showing just a little back-focus. Something had changed. The camera's focus had always been spot-on before this. I thought it may be due to the original sensor-shift mechanism, as the K10D was the first to have this. I never verified this, and don't have a way to do so.

I used debug mode to adjust the overall focus in my K10D. This was the only time I have had to make an adjustment. Focus has been exact since, and the adjustment was made around eight years ago.
04-07-2019, 05:13 PM   #15
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QuoteOriginally posted by builttospill Quote
Several years into owning the K10D I went to a scheduled shoot and all photos I took of the model were out of focus, just slightly. This had never happened to me before, and after additional testing, every photo was showing just a little back-focus. Something had changed. The camera's focus had always been spot-on before this. I thought it may be due to the original sensor-shift mechanism, as the K10D was the first to have this. I never verified this, and don't have a way to do so.
Could it have been possible that most keepers taken with your K10D were shot using a smaller aperture, where you wouldn't have really noticed a backfocus condition?

In my case, I only noticed it after shooting with the 35mm f2 wide open. When I saw that, I put the 18-135WR on (which I normally used at f5.6 or higher) and noticed the same problems at 18mm and f3.5. Adjusting the K10D's AF adjustment to +130um corrected the backfocus problems for both lenses.
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