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Old Jul 5, 2007, 2:47 PM   #1
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I got my pentax fa-50mm f1.4 last week. Yesterday I got a real chance to test is and it seems to have front focus in dim light and back focus in good light, altough the back focus is less then the front focus.

I can send it back and the shop will test it for me, but before I do, maybe someone can tell me that mabe I'm doing something wrong with my K100D and this lens combo.

Arperture is set to A on the lens and the camera is set to AV priority (as allways), but maybe there is something else I should do with this lens.....

Thanks......



Rudo


Hmm... tested it again tonight in very low light (only the tv turned on) and it seemed fine, at 1,4 through 4.0 I did us the flash though (I didn't last night) and tested it in spot light (f2.0) and it seemed fine again.....

The only thing I can think of is that I used the lens at a indoor swimmingpool, and while using it suddenly the lens was covered with condens on the glass.... maybe there was a bit on the inside as wel and that it's dry now.....

Any suggestions?

Rudo
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Old Jul 6, 2007, 12:10 AM   #2
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Were you using it wide open? the DOF at 1.4 is very thin and it's not hard to get it ever so slightly off. To get a better idea of whether there's something wrong with the lens, you can take a book or a page of typing, underline one line of text, put the camera on a tripod at a 45 degree angle to the page (I did approximately that) then use the center focus spot (usuallythe most accurate)toauto focuson the marked line. See what the picture looks like on the monitor - try it with a couple of apertures and in good light first. That will give you an indication whether it is the lens or not. Then try it in progressively lower light. Remember that an AF system requires contrast to focus - no systemwill focus on a flat object without any features, so that means it will really struggle in very low light (no contrast), unless you use the flash's focus assist.
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Old Jul 6, 2007, 5:55 PM   #3
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I'll try and test it my self, thanks for the advice.

It seems to work for now, but I'll do a test anyway in different light and from f1.4 and up.



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