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08-03-2009, 05:14 AM   #1
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What to make of this focus test?

I attended a wedding Friday night and noticed that many of my shots were OOF. So I decided to do a focus test.

First image is with the Sigma 17-70 and shows definite back focus.

Second is with the FA50, and what the hell? It's just crazy-soft all over.

So is the back focus with the lens? It's only a month old, can I send it back?

If not, I can adjust the focus on my K10, but will that throw off my FA50? And do we still have to use that Russian tool or whatever?

Thanks guys.

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08-03-2009, 05:51 AM   #2
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a couple of quick questions...did you use a tripod when testing and did you use spot focusing?

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08-03-2009, 07:58 AM   #3
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Yes, tripod pointed 45 down at a table. Shutter was tripped via wireless remote with 3-sec mirror delay, so ZERO camera shake. Focus was set to center, and "Focus here" was directly in the center of the frame.
08-03-2009, 08:32 AM   #4
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QuoteOriginally posted by lavascript Quote
Yes, tripod pointed 45 down at a table. Shutter was tripped via wireless remote with 3-sec mirror delay, so ZERO camera shake. Focus was set to center, and "Focus here" was directly in the center of the frame.
was the SR set to off

Dave

08-03-2009, 09:41 AM   #5
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QuoteOriginally posted by dafiryde Quote
was the SR set to off

Dave
Wouldn't the remote and delay turn off SR automatically?

Paul
08-03-2009, 09:48 AM   #6
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I think it only turns off for the two second timer.
Both shots look like they aren't perfectly focused anywhere. You haven't got sharpness dialled down on the camera or something have you.
08-03-2009, 09:53 AM   #7
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08-03-2009, 09:54 AM   #8
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The FA50 shot looks like it's showing a lot of longitudinal chromatic aberrations (green cast in back, magenta in front). I don't believe it should do that even if it was back/front focused.

I'm certainly no expert, but it looks to me like a bad copy of the lens.

08-03-2009, 12:43 PM   #9
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When testing my A-50/1.7, I got similar result to yours ("misty" look) when shooting wide open. Everything got normal after closing aperture a bit. I believe the reason is that those lenses are not optimized for digital chip (i.e. the light hits the chip under "wrong" angle)
08-03-2009, 01:09 PM   #10
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QuoteOriginally posted by dafiryde Quote
was the SR set to off

Dave
Nope. Maybe I can test again this evening with SR off.
08-03-2009, 01:54 PM   #11
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QuoteOriginally posted by lavascript Quote
Nope. Maybe I can test again this evening with SR off.
turning the SR off does make a big difference, also you should try and do it in as much daylight as possible. and at its widest open aoerature. forget if it looks fuzzy or soft, some lenses are naturall like that at wide open, but you have to set it at wide open to cut down on the depth of field.
another thing though.
i went thru those test, to the point where i nearly pulled my hair out, and mind you , i dont have much
you do get different results depending on target distance, even with the same lens, and worst is a zoom lens, you will get a different readings for every different focal length setting.
the final subnosis,
take a picture of the test chart and if you get the focus line clear,
and 1/3 front focus clear and 2/3 back focus clear, the lens adjustment is ok.
my problem in the begining was that i was trying to achieve 1/2 to 1/2 clarity to the focus line, but was corrected by JimC on steves digicam. God bless him, he has helped me alot

Dave
08-03-2009, 01:55 PM   #12
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Does look like the FA 50 suffers from softness not due to focus problems from that image - I'd suggest to try again, clean the lens and stop down a little just to see if it will improve.
08-03-2009, 02:04 PM   #13
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QuoteOriginally posted by Ash Quote
Does look like the FA 50 suffers from softness not due to focus problems from that image - I'd suggest to try again, clean the lens and stop down a little just to see if it will improve.
you cannot stop down on the lens, cause you need to cut down on as much depth of field as possible.
this test does not show how clear your lens is, it is to check at what point it is focusing, a soft lens wide open will always show soft wide open. so you are not looking for precision sharpness here, but actually what area of the test chart shows the clearest, and a lens showing 1/3 front 2/3 back is considered good
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08-03-2009, 03:50 PM   #14
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Flare?

Here are four more shots. They are, in order:

Sigma 17-70, 70mm, f/4.5, lit with window light.
Sigma 17-70, 70mm, f/16, lit with window light.
FA50, f/1.4, window light
FA50, f/16, window light.

For all of these, shutter was tripped remotely with 3-sec delay, SR off, tripod angled 45 downward, P mode with +1EV if you care. Shadow in the 17-70 pics is from the blinds; I closed them some for the FA50 pics.

To my eye, everything looks fine this time around.Granted, the f/1.4 shot is still pretty soft, but that's to be expected. Or is it too soft?

Last night's shots were lit with ceiling-bounced flash. Did it really cause enough flare to do THAT? I was not using lens hoods at all.
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08-03-2009, 07:32 PM   #15
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QuoteOriginally posted by lavascript Quote
Here are four more shots. They are, in order:

Sigma 17-70, 70mm, f/4.5, lit with window light.
Sigma 17-70, 70mm, f/16, lit with window light.
FA50, f/1.4, window light
FA50, f/16, window light.

For all of these, shutter was tripped remotely with 3-sec delay, SR off, tripod angled 45 downward, P mode with +1EV if you care. Shadow in the 17-70 pics is from the blinds; I closed them some for the FA50 pics.

To my eye, everything looks fine this time around.Granted, the f/1.4 shot is still pretty soft, but that's to be expected. Or is it too soft?

Last night's shots were lit with ceiling-bounced flash. Did it really cause enough flare to do THAT? I was not using lens hoods at all.
well judging from those pics, you do not have a focus problem
like i mentioned you are not suppose to stop down the lens, and if you look closely at pics 1 & 3 you will see the 1/3 - 2/3 focus area = good

Dave
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