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05-14-2009, 10:52 PM   #1
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Focus issues with manual?

I just rceived a K85 1.8 and I have a KatzEye. The camera shows in focus and so does the katzeye....but the it's not quite there after I download the pic. Lighting is right and it should be fine being handheld (when I use DA* glass it's usually fine). I am hoping I can tweek the system to get it right or figure out what I am doing wrong....I have had quite a few great shot with my Taks and Ks..but it seems to be a constant fight.

05-14-2009, 11:06 PM   #2
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The rings on the paper should be sharp...but they are not....camera is a k20d
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05-15-2009, 05:12 AM   #3
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I assume you shot wide open?

it may be the lens is a little soft wide open, many fast lenses are.

I bought a vivitar 85mm F1.4 (I gave up waiting for the pentax F1.8) and it is a little soft wide open, but stop down to F2 or f2.8 and it is tack sharp.
05-15-2009, 05:31 AM   #4
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The end ring is just a tad out of focus. Looks like you were pretty close on that shot. Your DOF would be very small at f/1.8. Easy to miss focus at times like that.

05-15-2009, 07:31 AM   #5
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I'll play with it some more. Thanks!
05-15-2009, 07:33 AM   #6
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QuoteOriginally posted by smc Quote
I just rceived a K85 1.8 and I have a KatzEye. The camera shows in focus and so does the katzeye....but the it's not quite there after I download the pic. Lighting is right and it should be fine being handheld (when I use DA* glass it's usually fine). I am hoping I can tweek the system to get it right or figure out what I am doing wrong....I have had quite a few great shot with my Taks and Ks..but it seems to be a constant fight.
1. Try controlled tests with a tripod first. Hand held cannot make any useful conclusion. At minimum focus distance of your lens, at f/1.8 the DOF is ~6mm. If you inadvertently rock forwards or backwards 6mm (1/4") then your focus point will be off. If you are pixel peeping, you would probably notice focus problem even if you moved less than 6mm.

2. f/1.8 is significantly more shallow than f/2.8. From you profile, it looks like all of your other lenses are f/2.8 or dimmer, so they are more tolerant of focus error. If you stop your 85mm down to f/2.8 then the DOF increases to ~10mm, which is significantly (70%) more DOF.

3. All lenses are slightly different, even when the split-screen is set up perfectly. I tested a number of my lenses when I installed a split-image screen. Some were more prone to back-focus, while others were more prone to front-focus. There was no one shim-thickness that was perfect with all my lenses, I had to use one that gave the best compromise between my most BF'ing and FF'ing lenses. So far, it's been acceptable. However, if I had tested only with one lens then it would have skewed my focusing.

4. Repeat, repeat, repeat. Even with a tripod, repeat each test a few times to get an average. At least 3 times, 6 is better. Out of 3 tests, I could sometimes see one image perfect, another FF'ing and a third BF'ing.

5. Focus direction/practice. I find when I focus from close-distance my images tend to FF. When I focus from far-distance, my images tend to BF.

Last edited by dave9t5; 05-15-2009 at 07:34 AM. Reason: sentence fragment fixed
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