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11-01-2012, 05:27 PM   #1
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More FF problems...now with F 50mm 1.7

Hi!

I'm the guy from the Sigma 70-200 2.8 frontfocus, and here i am, with more problems...

My kit lens will not focus correctly, and i have to apply some adjustment (-8), but at least it gets good with that...but i bought a F 50mm 1.7, and using no adjustment leads to great sharp images at closer focus distances (even 3m or so, i guess), but at infinity its a blur!

Really, the frontfocus is bad!

Doing some tests, i've seen that -7 adjustment or so leads to a great image at infinity, but then i get really inconsistent focus at closer distances. Sometimes it focus correctly, sometimes it won't.

I've tried -5 and -4, and everything seemed fine, but then i started noticing that the autofocus then was inconsistent at both infinity and closer distances, and also i can't get pin sharp images like i would get using 0 for closer distances and -7 for infinity.

Can you guys help me out? Have you ever faced a problem like this?
Thank you!

11-01-2012, 05:40 PM   #2
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What are you using as a target to test your adjustments?
11-01-2012, 05:52 PM   #3
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I'm using random boxes, trying to focus on their texts, and well as real world tests (like photographing my family, etc), but the main target to test the AF at close distances has been this :


Moire-pattern images to test the AF.
All tripod-mounted
11-01-2012, 06:35 PM   #4
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I find problems like those you continue to report with every lens you buy and use totally unfathomable. Are you sure that your testing process is not simply flawed, big time?

11-01-2012, 08:13 PM   #5
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Using a focus chart, or at the very least a ruler, is absolutely necessary for this procedure and it must be properly setup. Your chart needs to be at a 45 degree angle to your focal plane. Your auto focus needs to be set on center point and you must be focused on the center of the chart. Of course a tripod is necessary too, but you've already done that.

This is a good chart to use and there are very clear instructions on how exactly to use it: Nikon D70 Focus Chart

Last edited by elliott; 11-01-2012 at 08:22 PM.
11-02-2012, 09:39 AM   #6
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When I had inconsistent focusing problem with my K-r it turned out to be a dirty focus sensor. After cleaning it in a rather unorthodox way it worked fine again and has ever since.

It does need a permanent -10 fine adjustment but that was there from the day iot came out of the box.

On another note I don't think those charts are good for adjusting autofocus. PDAF systems struggle with regular patterns such as those because they generate many 'solution' to the focus point. In other words there are many different offsets that will give an exact same pattern match on the paired sensors. I'm not saying the charts are the problem but they are not helping you to diagnose the problem.
11-02-2012, 02:17 PM   #7
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QuoteOriginally posted by lister6520 Quote
When I had inconsistent focusing problem with my K-r it turned out to be a dirty focus sensor. After cleaning it in a rather unorthodox way it worked fine again and has ever since.

It does need a permanent -10 fine adjustment but that was there from the day iot came out of the box.

On another note I don't think those charts are good for adjusting autofocus. PDAF systems struggle with regular patterns such as those because they generate many 'solution' to the focus point. In other words there are many different offsets that will give an exact same pattern match on the paired sensors. I'm not saying the charts are the problem but they are not helping you to diagnose the problem.
Hey Lister.
Can you tell me how you cleaned the focus sensor?
I was thinking about blowing some air into the PDAF area...is that what you did?
11-03-2012, 02:54 AM   #8
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QuoteOriginally posted by GabrielFFontes Quote
Hey Lister.
Can you tell me how you cleaned the focus sensor?
I was thinking about blowing some air into the PDAF area...is that what you did?
I can tell you what I did but I would not recommend that you do the same. I was not thinking straight at the time, even if in the end it worked out ok. I had spent hours trying with gentler means and then just lost my patience.

I did blow air into all the nooks and crannies of the mirror box. I had no idea here the PDAF sensor was so I just blasted air everywhere.
I used a large air compressor, the type used for pneumatic power tools, and cranked the pressure all the way up to 7 bar and used a 1.5mm cleaning nozzle. With hindsight I don't know how the camera survived that but it did and since then worked as good as new. The biggest challenge was holding the mirror so it wouldn't flap in the hurricane. I held it both in the closed and the opened position. I'm sure there are other things that can get broken with too much pressure and I think it was only through sheer luck that I didn't break anything.

Perhaps a more gentle treatment with an air blower and a sensor cleaning brush but it looks to me quite difficult if at all possible to reach the sensor with a brush.

11-03-2012, 05:41 AM   #9
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QuoteOriginally posted by lister6520 Quote
I used a large air compressor, the type used for pneumatic power tools, and cranked the pressure all the way up to 7 bar...
!!!!!!!!!!!!!!!!!!!!!!!!!!

Certainly a case of 'don't try this at home'.
At least you didn't use a sand-blaster, I guess.
11-03-2012, 07:42 AM   #10
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That's certainly a bit crazy hahah
I'm still getting bad results. Can't seem to find a number that is good for infinity focus and close focus
I will test with -6 today.
Oh, i will print the focus chart as well.
11-24-2012, 11:56 AM   #11
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Hey guys!
Sorry to bother you all again, but i've been adjusting my 50mm to see if i can get it to a sweet spot of sharpness.
The lens suddenly stopped focusing at infinity at all, and i've adjusted it by removing the filter ring and untightening the screw, to disconnect the focus ring and adjust infinity focus.
Now the lens does achieve infinity, but i don't remember how sharp sharp was, to see if there is still anything wrong with my focusing.
I took these shots with the F 50mm 1.7 at f2 without shake reduction.
Those are 100% crops from raw shots, with absolutely no processing (0 sharpening in camera raw and 0 in photoshop), just crop and post.



What do you guys think? Is it how sharp the lens normally is at f2?
11-24-2012, 02:35 PM   #12
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Those images look about right for no RAW sharpening and f2. You ought to compare them with sharpening applied though to RAWs from Pentax K-30 Camera Gallery - Review as no one looks at unsharpened RAWs . Focus Magic detects them as 2 pixels of blur which is a good average, 1 pixel is excellent. My 50A1.7 really sharpens up at f2.8 to something exceptional, i.e. so sharp you could cut yourself
11-24-2012, 04:35 PM   #13
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Those three shots look adequately sharp.

Aside from USM sharpening them up a bit in post, another thing that may make those images look even sharper would be to clean up the purple fringing evident in them.
11-24-2012, 05:20 PM   #14
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QuoteOriginally posted by SteveB Quote
Those images look about right for no RAW sharpening and f2. You ought to compare them with sharpening applied though to RAWs from Pentax K-30 Camera Gallery - Review as no one looks at unsharpened RAWs . Focus Magic detects them as 2 pixels of blur which is a good average, 1 pixel is excellent. My 50A1.7 really sharpens up at f2.8 to something exceptional, i.e. so sharp you could cut yourself
Ahh, i miss Focus Magic...but i'm too lazy to unninstall my Photoshop and install it in 32bit, and i don't like to use the standalone program...
I've been trying to replace it for a while, but its tough!
Thank you

QuoteOriginally posted by rawr Quote
Those three shots look adequately sharp.

Aside from USM sharpening them up a bit in post, another thing that may make those images look even sharper would be to clean up the purple fringing evident in them.
Yes yes, i usually remove the purple fringing in ACR, but i wanted to post the shots completety raw, so i didn't
Thank you!
11-24-2012, 10:25 PM   #15
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Just got an F 50 1.7 myself last week, and I've been putting it through a bit of an amateur gauntlet to let the camera and the lens spread their wings a bit.

Those shots look about right at F2. At least, if I took a picture with your settings and cropped in and saw that, I wouldn't think anything was wrong.

I'm not sure what you're doing to your camera, with all of this tightening and unscrewing business, but it seems excessive.

Last edited by EarlVonTapia; 11-24-2012 at 10:27 PM. Reason: gramer!
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