Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
08-13-2008, 09:08 PM   #1
Inactive Account




Join Date: Jun 2007
Location: Toronto, Ontario
Photos: Gallery
Posts: 429
Focus problems for both manual and auto?!

Man, this one has me stumped.

I recently bought a Katz Eye focus screen to use with a couple of new, fast, manual focus lenses. Even with the Katz Eye screen, I still seemed to mis-focus an awful lot. When taking pictures of some berries yesterday (with a 50mm f/1.2, wide open), I noticed that the leaf in front of them was in nice focus with the berries blurry. I had seen this a few times before, that stuff in front of my focus point was in better focus..

I phoned Katz Eye and talked to Rachael. She explained that some camera's can be misaligned for manual focus. Their remedy is to swap out the shim beside the focus screen mount (hope I got that correct). She emailed me a focus test that she uses to gauge the problem.

So, I tried two manual focus lenses and both of them 'front focus'. Here is where it gets strange...

On a whim, I try my FA 50mm f/1.4. It front focuses too! So I go into the menu (K20D) and give a -10 adjustment for all lenses. Low and behold that almost fixes the FA50mm.

Rachael had mentioned that the AF and manual focus systems are two separate things... Is it really possible that both of out of whack that much?!

My (camera) body is under warranty so I guess I could send it in. I wanted to take a photography course in September, though, and I'm worried the camera won't be back in time. Plus some people have mentioned that Pentax Canada service is not great.

If anyone has any ideas, or can simply offer some guess as to what the problem might be, I'd appreciate hearing from you.

Thanks, Don

08-13-2008, 10:13 PM   #2
Pentaxian
Wheatfield's Avatar

Join Date: Apr 2008
Location: The wheatfields of Canada
Posts: 10,157
It is absolutely possible for both focus mechanisms to be out of alignment, as they are completely independant of each other, and must both be accuratly aligned. It's just blind luck that the AF is off in the same direction as manual focus.
08-13-2008, 11:34 PM   #3
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
An important thing I learned about manual focus with fast lenses is that the focus screen lies. The stock one, anyhow, is not capable of rendering DOF any less than that of f/2.8. Not sure about Katz Eye. But the issue is that things look in focus in the viewfinder but won't be in the picture when shooting wider than f/2.8 or so because the DOF of the picture is narrower.

This fact of focus screens complicates manual focus with fast lenses. Not sure that it by itself completely explains what you are seeing, but it really does take quite a bit of getting used to in order to overcome.
08-13-2008, 11:50 PM   #4
Veteran Member




Join Date: Sep 2006
Photos: Gallery
Posts: 5,713
QuoteOriginally posted by Marc Sabatella Quote
An important thing I learned about manual focus with fast lenses is that the focus screen lies.
I wonder if that's just a Pentax thing.
I shoot my K-Mount 55mm f1.8, along with my screwmount 50mm f1.4 without a problem on my Sigma, but have problems focusing with my K100D.

08-14-2008, 04:12 AM   #5
Inactive Account




Join Date: Jun 2007
Location: Toronto, Ontario
Photos: Gallery
Posts: 429
Original Poster
Wheatfield, thanks.

Marc, I think the Katz Eye will accurately focus for fast lenses. Rachael from Katz Eye suggests doing the focus test with an f/1.4 and remarked that the f/1.2 would be ideal for the test. As well, the long throw of the manual focus lenses has shown that the focus screen has a LOT of granularity - you can make really tiny focus adjustments and see results on the screen (at least when you are close up).

When I tried using my FA50 on the focus test (auto focus), I could actually see when it was out by a small amount (you could see it on the split screen). I just eased up on the shutter release and then depressed again and repeated for several interations until the focus motor stepped into place.

I hope that these manual focus screens are good for fast lenses - that is acutally the reason I bought one :-) It is a remarkable improvement over the stock focus screen.
08-14-2008, 06:01 AM   #6
Pentaxian
Wheatfield's Avatar

Join Date: Apr 2008
Location: The wheatfields of Canada
Posts: 10,157
QuoteOriginally posted by dkittle Quote
Wheatfield, thanks.

Marc, I think the Katz Eye will accurately focus for fast lenses. Rachael from Katz Eye suggests doing the focus test with an f/1.4 and remarked that the f/1.2 would be ideal for the test. As well, the long throw of the manual focus lenses has shown that the focus screen has a LOT of granularity - you can make really tiny focus adjustments and see results on the screen (at least when you are close up).

When I tried using my FA50 on the focus test (auto focus), I could actually see when it was out by a small amount (you could see it on the split screen). I just eased up on the shutter release and then depressed again and repeated for several interations until the focus motor stepped into place.

I hope that these manual focus screens are good for fast lenses - that is acutally the reason I bought one :-) It is a remarkable improvement over the stock focus screen.
My manual focus accuracy improved tremendously when I put a Katz-Eye into my K20. The 50/1.2 is a difficult lens to focus accurately at best. I'm not sure about the screens "lying" with lenses faster than 2.8, I'd like to see some citations (other than Wikipedia, which often can only be trusted to spread internet theories) on this one.
08-14-2008, 06:23 AM   #7
Veteran Member




Join Date: Nov 2006
Location: Hong Kong
Posts: 1,934
True, they *both* can.

Also, as the focusing screen position seems to be fixed (and so does the CCD as well), I am afraid that you *have to* get a replacement unit.

For more about focus alignment and calibration, you can read:

RiceHigh's Pentax Blog: Focus Calibrations for (Pentax) (D)SLR Bodies and Lenses

QuoteOriginally posted by dkittle Quote
Man, this one has me stumped.

I recently bought a Katz Eye focus screen to use with a couple of new, fast, manual focus lenses. Even with the Katz Eye screen, I still seemed to mis-focus an awful lot. When taking pictures of some berries yesterday (with a 50mm f/1.2, wide open), I noticed that the leaf in front of them was in nice focus with the berries blurry. I had seen this a few times before, that stuff in front of my focus point was in better focus..

I phoned Katz Eye and talked to Rachael. She explained that some camera's can be misaligned for manual focus. Their remedy is to swap out the shim beside the focus screen mount (hope I got that correct). She emailed me a focus test that she uses to gauge the problem.

So, I tried two manual focus lenses and both of them 'front focus'. Here is where it gets strange...

On a whim, I try my FA 50mm f/1.4. It front focuses too! So I go into the menu (K20D) and give a -10 adjustment for all lenses. Low and behold that almost fixes the FA50mm.

Rachael had mentioned that the AF and manual focus systems are two separate things... Is it really possible that both of out of whack that much?!

My (camera) body is under warranty so I guess I could send it in. I wanted to take a photography course in September, though, and I'm worried the camera won't be back in time. Plus some people have mentioned that Pentax Canada service is not great.

If anyone has any ideas, or can simply offer some guess as to what the problem might be, I'd appreciate hearing from you.

Thanks, Don
08-14-2008, 06:39 AM   #8
Inactive Account




Join Date: Jun 2007
Location: Toronto, Ontario
Photos: Gallery
Posts: 429
Original Poster
Hey RiceHigh, thanks for the confirmation.

Rachael from Katz Eye indicated that the focus screen housing is shimmed, just FYI. When they adjust manual focus (one of their services), they have a selection of 6 different shims they use to get the focus as accurate as possible. In my case, the focus seems to be out by quite a lot (and for both manual and auto) so a replacement might be warranted, but she seemed confident that she could fix the manual focus issue.


Last edited by dkittle; 08-14-2008 at 06:40 AM. Reason: typos :-)
08-14-2008, 06:49 AM   #9
Veteran Member




Join Date: Nov 2006
Location: Hong Kong
Posts: 1,934
QuoteOriginally posted by dkittle Quote
Hey RiceHigh, thanks for the confirmation.

Rachael from Katz Eye indicated that the focus screen housing is shimmed, just FYI. When they adjust manual focus (one of their services), they have a selection of 6 different shims they use to get the focus as accurate as possible. In my case, the focus seems to be out by quite a lot (and for both manual and auto) so a replacement might be warranted, but she seemed confident that she could fix the manual focus issue.
I would still suggest that you should insist for a replacement from Pentax so that at least the *standard screen* by Pentax should work just fine, before you go further adjustment or customization for the MF and AF.
08-14-2008, 06:53 AM   #10
Inactive Account




Join Date: Jun 2007
Location: Toronto, Ontario
Photos: Gallery
Posts: 429
Original Poster
Agreed, that's my plan today. I'm actually hoping the store will exchange it, even though it's a little more than two months old :-)
08-14-2008, 07:50 AM   #11
Pentaxian
Wheatfield's Avatar

Join Date: Apr 2008
Location: The wheatfields of Canada
Posts: 10,157
QuoteOriginally posted by RiceHigh Quote
I would still suggest that you should insist for a replacement from Pentax so that at least the *standard screen* by Pentax should work just fine, before you go further adjustment or customization for the MF and AF.
Absolutely. If the product is under warranty, then adjustment and calibration is Pentax's problem, not yours, since the problem is caused by poor quality control at the factory.
I'm hearing far too many stories relating back to slack QC by Pentax to cut them any slack any longer. They seem to have given up on even the most minimal attempts to put properly built equipment on the market, and if they don't start being held accountable for it by having to do warranty work, they will only get worse.
08-14-2008, 09:01 AM   #12
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
QuoteOriginally posted by little laker Quote
I wonder if that's just a Pentax thing.
No. I first saw the issue described in detail by either an Olympus user:

Manual Focus with AF DSLRs

But I've also seen it discussed with respect to Nikon and Canon. Baiscally, it's a question of whether the focus screen is optimized for use with "kit" lenses or whether it is optimized for faster lenses. Focus screens on pretty much any entry level camera would be likely to be optimized for entry level lenses. And it totally makes sense that the Katz-Eye would be optimized for faster lens.

Here's a simple test for someone who has a fast lens and the Katz-Eye but is *not* having problems; I'd be curious to hear what folks say. Open the lens up wide, aim at a newspaper at a 45 degree angle, focus anywhere you like, and make a mental note of how many lines of text appear to be in acceptably sharp focus. Actually, best to note both the first and the last such line. Then take the picture and examine it and see if the results match. They definitely don't with the stock screen. With my A50/1.7, there are lines of text at both ends of the focus range that I can read clearly in the viewfinder but are hopelessly out of focus in the actual picture.

An even simpler test would be to simply pont at the target and do a DOF preview to see if anything changes. Wide open, nothing should of course. But each time you stop down, you should see more of the image coming in to focus in the DOF preview. What I see with my A50/1.7 is no discernible difference at all stopping down to f/2.0 or f/2.4 - not even in brightness. Stopping down to f/2.8, I do at least see a very slight dimming, but if there's any change at all in DOF, it's minimal. not until f/3.5 can I say there is a difference I'd have a chance of identifying reliably in a blind test (ie, where I didn't know which was supposed to have the greater DOF).

QuoteOriginally posted by RiceHigh Quote
I would still suggest that you should insist for a replacement from Pentax so that at least the *standard screen* by Pentax should work just fine, before you go further adjustment or customization for the MF and AF.
Have we actually established there is a problem when using the standard screen? If the problem is just in the shimming of the Katz-Eye - as seems perfectly likely - it may well be there that is nothing wrong with the stock screen placement. Unfortunately, for the reasons I am describing, that's harder to test than it seems at first - but not impossible. You just need to really pay attention to the whole zone of acceptable focus in the viewfinder and image to see if they are actually *off* in the sense of something being *in focus* in the picture that wasn't in the viewfinder, or if it's just a matter of not everything that was in focus in the viewfinder being in focus in the picture, which unfortunately is absolutely unavoidable with the stock screen.
08-14-2008, 10:41 AM   #13
Inactive Account




Join Date: Jun 2007
Location: Toronto, Ontario
Photos: Gallery
Posts: 429
Original Poster
Marc, that is an interesting test. I'll give a try with my 50mm f/1.2 when I get the body back from Pentax Canada.

For anyone interested, apparently Pentax Canada will explain what they do to resolve the issue. I'll post what they put on the invoice into this thread.
08-14-2008, 01:49 PM   #14
New Member




Join Date: Aug 2008
Location: Northumberland, England (Gt Britain)
Posts: 17
Be gentle with me - I've had my K100D Super for only two days.
I bought it (new, from ebay - it arrived still sealed) to use with my extensive range of KA manual lenses.
After half a dozen (successful) exposures with the bundled 18-55mm lens I fitted a Sigma 75-300mm APO KA (manual) lens to try out the ShakeReduction system.
Using the body on manual focus I tried some distant views including car registration plates (licence plates).
All are distinctly out of focus, despite appearing to be in focus on the focussing screen.
I've just repeated the exercise using a monopod without SR engaged and, again, the distant objects are way out of focus.
The lens was focussed on infinity.

I haven't tried any other lenses (yet) but I doubt that the Sigma lens is faulty . . .

So, what is wrong (and what can I do?)?

Although I've been using ME Supers and Super As for a couple of decades but I've never had an autofocus camera before.
08-14-2008, 03:10 PM   #15
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
I guess first order of business would be to make sure you aren't simply seeing camera shake or lens softness (neither of the lenses you mention win awards for sharpness). Could you post images with EXIF intact?

Assuming it really does look like focus issues, next step would be for you to download one of the online focus test charts, like the one at focustestchart.com, and then - after carefully reading the instructions - to do controlled tests on a tripod.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
50mm, berries, camera, dslr, eye, focus, front, guess, katz, lenses, photography, screen
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
10 Reasons why manual focus primes are better than those new auto focus zoom lenses JoepLX3 Pentax SLR Lens Discussion 188 07-25-2012 03:28 PM
Can a manual-focus lens have back focus problems? PocketPixels Pentax DSLR Discussion 33 02-13-2011 05:37 AM
k-7 auto focus problems garyk Pentax DSLR Discussion 5 10-21-2010 11:50 PM
Auto focus problems??? Moorby Troubleshooting and Beginner Help 8 12-24-2009 02:24 AM
DS auto focus problems rangitata Pentax DSLR Discussion 3 02-21-2007 12:53 AM



All times are GMT -7. The time now is 06:58 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top