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02-16-2015, 09:40 AM   #1
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Sigma 100-300 autofocus problem

Gear: Pentax K-5II, Sigma 100-300 f4.
Hi everyone!
I've just got Sigma 100-300 f4 in mint condition a week ago. Indoor testing showed perfect results. The problem I'm experiencing now is a presence of severe back focus at long distances. When focusing at 2-5m it is almost correct, but at infinity or distant objects, everything is out of focus. On the other hand, when using Live View, all the shots are perfectly sharp. AF adjustment +10 (maximum a can make on K-5ii) improves focusing accuracy, but doesn't solve the problem completely. I see several solutions to that, and would be grateful for your suggestions!
- Using service menu and adjust the AF to higher "+" values. But, all other lenses will have focusing problems afterwards (by now, DA 18-270, FA35, FA100 macro and F-50 1.7 I have focus perfectly accurate). Will I lose the guarantee for the body?
- Use MF or Live View. But the lens was thought for definitely the other kind of shooting.
- Is it possible to calibrate the lens some how? Or this is only possible for HSM Sigma lenses?
- Can Pentax do something, or all non-Pentax lens problems are not recognized by Pentax?
Thanx

02-16-2015, 10:17 AM   #2
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QuoteOriginally posted by ars Quote
Gear: Pentax K-5II, Sigma 100-300 f4.
Hi everyone!
I've just got Sigma 100-300 f4 in mint condition a week ago. Indoor testing showed perfect results. The problem I'm experiencing now is a presence of severe back focus at long distances. When focusing at 2-5m it is almost correct, but at infinity or distant objects, everything is out of focus. On the other hand, when using Live View, all the shots are perfectly sharp. AF adjustment +10 (maximum a can make on K-5ii) improves focusing accuracy, but doesn't solve the problem completely. I see several solutions to that, and would be grateful for your suggestions!
- Using service menu and adjust the AF to higher "+" values. But, all other lenses will have focusing problems afterwards (by now, DA 18-270, FA35, FA100 macro and F-50 1.7 I have focus perfectly accurate). Will I lose the guarantee for the body?
- Use MF or Live View. But the lens was thought for definitely the other kind of shooting.
- Is it possible to calibrate the lens some how? Or this is only possible for HSM Sigma lenses?
- Can Pentax do something, or all non-Pentax lens problems are not recognized by Pentax?
Thanx
I have a Sigma 100-300 and had a K5iis. I now own a K3 and here are my findings/experience:

With the K5iis, no matter what I tried, it did not play well with the Sigma, I, too experienced severe back focus on many many shots even after calibration. On occasion I would get a keeper (I'd guess about 50% of the time) but it required a technique of focus, stop, refocus if the subject lacked contrast such as animal fur etc. High contrast/texture objects it generally did very well with, but if that high contrast/texture was behind my subject, the lens would lock onto that object like dog on a scent. I'd have to recompose, focus intentionally on an near object, then refocus and hope that the lens would choose my subject. The problem was that often I could not tell in the viewfinder, only once I could see the image at 50-100% on my computer. I have posted several rants about this very issue over the years, but I won't link them here...lol

On my K3, after all my frustrations with the K5iis, I have been much more thorough in my investigations and slightly happier with the results. My first impression is that the smaller center AF point of the K3 was a BIG help, right off the bat. The 100-300 was more consistent and reliable. So much of your frustration is due to the "poor" AF system of the K5ii(s) bodies.

The next step took about 3 hours and a test target/calibration ruler. Using combinations of LV, MF and AF I discovered some quirks of my 100-300. At 300mm and f4 at less than 10m I needed a +8 adjustment. At 300mm and about f8 at the same distance my adjustment was 0! I tried it at 50m with a 300mm focal length and found that my needed adjustment was also based on aperture, ranging from +7 at f4 to -2 at f11. Essentially, subject distance AND aperture affected front/back focus response. I have no clue why or what causes this so I'm chalking up to the fact it's a legacy lens and there's probably been some movement of elements or what not. I've just resigned myself to "missing" some shots and if I can, trying to tweak focus manually.

Here's the other thing I noticed, at least in my copy, the physical focusing mechanism has some play. If I had to guess it would be the equivalent of about 2 feet (.6m) of depth of field as we get to the mid to long focus distances. Close to minimum focusing distance, it's a little more accurate . This means that the lens will tell my K3 body it is focused at say 25m when it can actually be 24.3 to 25.6m. At 300mm and f4, that's the difference between a nose in focus and the tail being in focus instead. It was even greater if I have the quick shift ring in MF mode and the body in AF. There's probably 3-4ft (1-1.3m) of play, especially close to infinity.

My conclusion is that the Sigma 100-300 is a great lens optically, but it doesn't really play well with the K5 series because of the HUGE auto focus points. It could be sample variation, because others have raved about how well this lens performs on their bodies, but you sound like you have a quirky copy like mine.

The "only" thing you can do is be aware of the issues and develop techniques to try and compensate, but for quick action scenes you may not have that luxury. You may also consider going to a K3. Lately I've been using 9 point AF-C and shooting in 3-4 shot bursts and that seems to have upped my keeper rate. Single shot and AF-S is still inconsistent.

In terms of service, CRIS Camera told me last year that there were NO parts even available for service or maintenance work, so there was nothing they could do to help. They are a Sigma Authorized Repair Center, so they would probably know. I haven't talked to them recently after my marathon testing session in January, but I'm not sure if anything can be done for the focus mechanism play anyway.

Last edited by nomadkng; 02-16-2015 at 10:41 AM.
02-16-2015, 10:23 AM   #3
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Mine works like a charm with my K5II and k3.
02-16-2015, 10:29 AM   #4
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I had problems with my K5. None with my K3

02-16-2015, 11:13 AM - 1 Like   #5
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There are two batches of the 100-300 Sigma. At least some lenses of the older batch are known to have a "focus jump" at f6.3. It means that the lens will show severe backfocus from f4-f5.6. From f6.3 onwards the lens will focus correctly. They fixed that issue in the newer batch of lenses. You can distinguish the two batches by the look of the rubber on the focus- and zoomrings.
Old: http://www.lenstip.com/aparaty_image/2190_sig100-300_1.jpg
new: http://www.dyxum.com/images/Lenses/269/269_1.jpg
02-16-2015, 11:21 AM   #6
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I have what you call "old version". With my K5 it had back focus at all apertures. I used debug mode to correct it in the camera and the lens would focus correctly. With my K-3 this extra adjustment is not necessary
02-16-2015, 11:34 AM   #7
ars
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Original Poster
QuoteOriginally posted by nomadkng Quote
I have a Sigma 100-300 and had a K5iis. I now own a K3 and here are my findings/experience:

With the K5iis, no matter what I tried, it did not play well with the Sigma, I, too experienced severe back focus on many many shots even after calibration. On occasion I would get a keeper (I'd guess about 50% of the time) but it required a technique of focus, stop, refocus if the subject lacked contrast such as animal fur etc. High contrast/texture objects it generally did very well with, but if that high contrast/texture was behind my subject, the lens would lock onto that object like dog on a scent. I'd have to recompose, focus intentionally on an near object, then refocus and hope that the lens would choose my subject. The problem was that often I could not tell in the viewfinder, only once I could see the image at 50-100% on my computer. I have posted several rants about this very issue over the years, but I won't link them here...lol

On my K3, after all my frustrations with the K5iis, I have been much more thorough in my investigations and slightly happier with the results. My first impression is that the smaller center AF point of the K3 was a BIG help, right off the bat. The 100-300 was more consistent and reliable. So much of your frustration is due to the "poor" AF system of the K5ii(s) bodies.

The next step took about 3 hours and a test target/calibration ruler. Using combinations of LV, MF and AF I discovered some quirks of my 100-300. At 300mm and f4 at less than 10m I needed a +8 adjustment. At 300mm and about f8 at the same distance my adjustment was 0! I tried it at 50m with a 300mm focal length and found that my needed adjustment was also based on aperture, ranging from +7 at f4 to -2 at f11. Essentially, subject distance AND aperture affected front/back focus response. I have no clue why or what causes this so I'm chalking up to the fact it's a legacy lens and there's probably been some movement of elements or what not. I've just resigned myself to "missing" some shots and if I can, trying to tweak focus manually.

Here's the other thing I noticed, at least in my copy, the physical focusing mechanism has some play. If I had to guess it would be the equivalent of about 2 feet (.6m) of depth of field as we get to the mid to long focus distances. Close to minimum focusing distance, it's a little more accurate . This means that the lens will tell my K3 body it is focused at say 25m when it can actually be 24.3 to 25.6m. At 300mm and f4, that's the difference between a nose in focus and the tail being in focus instead. It was even greater if I have the quick shift ring in MF mode and the body in AF. There's probably 3-4ft (1-1.3m) of play, especially close to infinity.

My conclusion is that the Sigma 100-300 is a great lens optically, but it doesn't really play well with the K5 series because of the HUGE auto focus points. It could be sample variation, because others have raved about how well this lens performs on their bodies, but you sound like you have a quirky copy like mine.

The "only" thing you can do is be aware of the issues and develop techniques to try and compensate, but for quick action scenes you may not have that luxury. You may also consider going to a K3. Lately I've been using 9 point AF-C and shooting in 3-4 shot bursts and that seems to have upped my keeper rate. Single shot and AF-S is still inconsistent.

In terms of service, CRIS Camera told me last year that there were NO parts even available for service or maintenance work, so there was nothing they could do to help. They are a Sigma Authorized Repair Center, so they would probably know. I haven't talked to them recently after my marathon testing session in January, but I'm not sure if anything can be done for the focus mechanism play anyway.
Thanks for so detailed answer! I'll keep the lens by now to see how it performs. From my visit to the local zoo over the weekend I was very satisfied with the results (mainly Live view or MF...). Probably I'll test if with K-3) W.r.t. to the play in focusing mechanism, I've just checked that and it is negligible. Also, in Live View, there is no focus hunting, so I also think that it just couples bad with K-5 PDAF.

---------- Post added 02-16-15 at 11:38 AM ----------

QuoteOriginally posted by jayman_1975 Quote
Mine works like a charm with my K5II and k3.
Ok, thanks for info!

QuoteOriginally posted by wisent Quote
There are two batches of the 100-300 Sigma. At least some lenses of the older batch are known to have a "focus jump" at f6.3. It means that the lens will show severe backfocus from f4-f5.6. From f6.3 onwards the lens will focus correctly. They fixed that issue in the newer batch of lenses. You can distinguish the two batches by the look of the rubber on the focus- and zoomrings.
Old: http://www.lenstip.com/aparaty_image/2190_sig100-300_1.jpg
new: http://www.dyxum.com/images/Lenses/269/269_1.jpg
Mine is the old version. This explains a lot. If they've released the corrected version - these problems must have been common.

QuoteOriginally posted by sergysergy Quote
I had problems with my K5. None with my K3
If the lens would worth it - I might consider K-3.

02-16-2015, 12:15 PM   #8
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I think it is worth it
If not try the debug mode, it is worth a try.
02-16-2015, 02:00 PM   #9
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QuoteOriginally posted by wisent Quote
There are two batches of the 100-300 Sigma. At least some lenses of the older batch are known to have a "focus jump" at f6.3. It means that the lens will show severe backfocus from f4-f5.6. From f6.3 onwards the lens will focus correctly. They fixed that issue in the newer batch of lenses. You can distinguish the two batches by the look of the rubber on the focus- and zoomrings.
Old: http://www.lenstip.com/aparaty_image/2190_sig100-300_1.jpg
new: http://www.dyxum.com/images/Lenses/269/269_1.jpg
LOL... well I guess I'm not losing my mind. I have the older version and that seems to be it in a nutshell. I've thought about changing the AF correction value if I know ahead of time what I'm going to shoot at. That my be the answer for me. Too bad I can't program the camera to turn on and turn off Auto correction based on aperture...lol
02-17-2015, 03:18 AM   #10
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QuoteOriginally posted by nomadkng Quote
My conclusion is that the Sigma 100-300 is a great lens optically, but it doesn't really play well with the K5 series because of the HUGE auto focus points. It could be sample variation, because others have raved about how well this lens performs on their bodies, but you sound like you have a quirky copy like mine.
Sorry to hear about your issues - there is a rumor floating around on the internet that the Sigma lens dock may be able to tweak focus settings for older lenses. But so far nothing has surfaced to substantiate such a rumor.


Pentax K5IIs - Sigma 100-300mm f/4 APO EX DG

Last edited by Digitalis; 03-03-2015 at 08:09 AM.
03-03-2015, 08:07 AM   #11
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Wow... exact description of what I'm experiencing. Exact hit with the rubber ring pictures. I hoped that there would be a solution for this in a service center, but I guess I'm out of luck :-(
03-03-2015, 09:00 AM   #12
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I had similar problems on my Sigma 100-300 +K5/K5iis. Although I got good results from it, I felt that I couldn't get the setup to such a critical focus as the images I've seen on the forum. I didn't get a chance to use it on the K3, I ended up selling it right before the switch, bying a Sigma 300mm f2.8 Ex instead. I've also read from forum members who got their lenses serviced that Sigma often addresses such issues with chip upgrades and calibrations. I don't know how much that'd cost but it might be worth considering.
04-01-2015, 06:52 AM - 1 Like   #13
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Now here's an interesting turn in this story. I thought I'd give the local service center a try anyway (Ott+Wyss, owy.ch, Switzerland). I sent them a description of the problem together with some information I've found here and in linked sources. They told me that they couldn't do anything about it, but would send it to Japan for a revision. I thought oh well, why not give it a try? Sent it to the distributor, not expecting it back for another 10+ weeks (that's what I've been waiting for the 2.8/50-150mm to return so far...).

But then, two days ago, it was back at my door. It only took about three weeks for the return trip - much too fast for a journey to Japan and back imho. The document said something along the lines "replaced electronics", no invoice added!

I only had some quick testing (we're currently having really poor weather over here - poor pre-conditions to test focussing to the far distance). But early results are _very_ promising. Keep in mind this is a v1 version which is known to be problematic. But I reset the out-of-focus correction in my k3 and shot along. Biggest problem was blurred pictures due to the wind. But the autofocus seems to be spot on!

So... kudos to Sigma & Ott+Wyss and their SSC service (allows for one free maintenance service per year). I had almost given up on that lens, but now can't wait to take it back outdoors for some serious shooting again! If you are in the same situation as I was, it might be worth pestering your local dealer or distributor.
05-25-2015, 11:44 PM - 1 Like   #14
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Ok, I previously mentioned that my lens had been repaired, or the electronics replaced. Here are a few sample shots I took over the weekend in Zürich Zoo's Masoala Rainforest. They show objects at 300mm/1:5, 220mm/1:4, 125mm/1:4.5. Due to the dim light in there I had to shoot at rather high ISO values. I particularly like the third shot, which really shows great performance of the lens, as well as the K3 at higher ISO (2500).

I'm happy again with my Sigma EX 100-300!
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05-28-2015, 03:49 AM   #15
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These are really nice shots.
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