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01-28-2014, 02:52 PM   #1
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Manual zoom lens focus issue

I recently acquired a Tamron SP 60-300 F/3.8-5.4 lens. I have taken some very nice shots with the lens, but i have noticed when shooting distant objects at 300mm that focus is terrible. To show what i'm running into i set the camera up on a desk, used focus peaking with 6x zoom to get focus as close as i could, and took shots from f32 up to wide open. For each of the shots the camera also confirmed focus. The camera is a pentax k-30 and was set to 2 sec timer so pressing the shutter shouldnt affect the image. To keep the results as close as i could, i simply changed the aperature and pressed the green button to meter, and took each shot. Here is an album of the shots with no PP or cropping. Each image was exported from LR at jpeg 100% quality. In shots 1131 and 1130 i cannot even see the focal plane. Shot 1125 i believe is the one most in focus which would be between f8 and f11 on the lens.

Is there something going on here or am i just being unreasonable? I have taken plenty of shots within say, 25 feet and they all come out great. It just seems when i try to reach out and take a distant shot they all look terrible.

01-28-2014, 03:10 PM   #2
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Based on what I'm seeing in the corners I'd say that there's probably something wrong with the lens. User reviews suggest that this lens is actually pretty sharp. I wouldn't expect it to be stellar but something is definitely up in those test shots I'd say.

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01-28-2014, 03:40 PM   #3
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Thanks for taking a look adam. I updated the album to include building shots that i performed the same test on a few weeks ago. It's easiest to see in the gargoyle in the middle of the building. From what i understand there are set screws under the rubber grip on the lens, but i am hesitant to mess with them without knowing what I'm doing.
01-28-2014, 06:47 PM   #4
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The centre looks ok to me, it's fairly sharp for what looks to be a pretty overcast day.

Roughly how far away is the tree? I know that general weather conditions can reduce sharpness for longer distances (light fog, heat haze, etc) it doesn't look like the case here though.

I'm with Adam though, the outer edges seem oddly blurred... almost like you're using a special effect filter (which you aren't)

I presume you've looked inside to check for fungus, mould, dirt, scratches, haze and the like?

01-29-2014, 08:04 AM   #5
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The tree is just at the end of the building. It's not even to infinity, but past 30ft on the lens scale. I noticed the same problem at 60mm which i hadn't checked for some reason. It seems like once i get to a certain distance away, focus gets messed up. I found a link for adjusting the infinity focus and may give that a shot to see what happens. What gets me is that it seems like its getting to focus and beyond. The lens allows you to focus past infinity and i can watch the image come into focus and then go back out as i move through the focus range. This did give me an idea and i may record a video to see how it looks as i move through focus.

Last edited by rage03usa; 01-29-2014 at 11:36 AM.
01-30-2014, 03:56 PM   #6
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Being able to focus beyond infinity, while annoying, isn't that uncommon on old manual lenses.
I'm not sure if it's an intentional design feature, or a product of slight wear allowing excess movement.

I don't think that's the issue though, that should only account for bad focus all over at infinity.
The fact that the edges are very bad, while the centre is ok, seems to indicate something more to me.

Have you had a look inside the lens yet? (just looking inside with the aperture open, not actual disassembly)
I'm still thinking fungus, since the issues with focus are at the edge, and fungus seems to grow from the edges inwards.

Either that or maybe oil on an element (perhaps it's been left in a hot car and the oils have thinned and leaked onto the glass inside?)

Basically, I think it's something to do with the glass rather than any mechanical parts.
01-30-2014, 09:46 PM   #7
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If you take a look at the first tree picture (imgp1131), there is nothing in focus. the focus was not touched between any of the pictures so I'm not sure what the deal is. Its the same with picture imgp1130. Once i get to around f8 i finally get focus in the center of the image. It seems like it gets close but wont get to 100%. for example I am using the digital zoom and focus peaking to try to get it where it needs to be. I can see the focus getting closer but it never seems to get there.its like focus goes 75% - 85% - 90% - 85% - 75%. This seems to only happen when focusing at distant objects ( i would say 30+ feet). Anything under that is behaves normally. You can also compare the gargoyle in pictures imgp1027 and imgp 1019. Here is a crop comparing them.

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