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FORUMS Photography Talk by Genre Critique Corner 
Thread started 17 Feb 2007 (Saturday) 14:45
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Help, what is causing the poor IQ

 
boufa
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Feb 17, 2007 14:45 |  #1

I am looking for help on why the IQ is soooo bad in this image. My guess is lens quality (it is a POS, Promaster 70-300) It was shot at 1/1600 at 6.3, 200 ISO and at full 300mm. I cropped off the edges of the shot, but did not blow it up any. This shot was JPeg (large) mode, but I looked at the Raw file, and it looks the same. The only PP was levels, mild sharpening, and a touch of saturation. None of the PP changed the overall IQ of the image.

I am using a Digital Rebel XT. This is not the only shot like this, most of the small objects at the far end of the lens comes out this way. I would expect better quality from a 8 mp camera.

I have a Sigma 80-400 OS on order, I would imagine that it would produce a clearer image than this? I did not use a tripod, but at 1/1600 would it really matter? Also I don't think that the OS (IS) allone would make any difference, would it?

Thanks
Kevin


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hTr
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Feb 17, 2007 15:46 |  #2

My guess is you are not steady enough and the problem becomes worst the longer the shot. Try a tripod with remote and any fixed object to check lens.


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Robert_Lay
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Feb 17, 2007 18:10 |  #3

It's really difficult to tell whether this is out of focus or motion blur. It looks more like a focus problem than motion blur to me. The only way to be sure is to make the obvious test. Mount the camera on a tripod or use a bean bag as the camera rest. Either way, use the self timer to fire it, and choose a subject that you know is steady - like a brick wall. Shoot the same aperture, focal length and shutter speed, if possible. I don't think the ISO setting could be an issue at all.

If you get a good picture that way, then you know that it's not the camera or the lens - probably a focusing problem.

I assume you are using manual focusing.


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boufa
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Feb 17, 2007 19:36 as a reply to  @ Robert_Lay's post |  #4

The image was autofocus, maybe it locked onto something else, but the wire, the bird and the clear sky were the only things for it to lock on. I am pretty sure that this is not an infinity focus, on the sky.

If it was motion blur, then hopefully the OS/IS lens will help.

Is it even possible that the camera doen't focus right? Is that something that the camera can be serviced for, or is it primarilly the function of the lens?

Nevermind, I will ask these questions in the appropriate forums. Thanks for the feedback.


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cdifoto
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Feb 17, 2007 19:39 |  #5

boufa wrote:
My guess is lens quality (it is a POS, Promaster 70-300)

This would be my guess too. Stop down to like f/8 or f/10 to see if it's sharper. These results are probably just due to being a crap lens.


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Hellashot
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Feb 17, 2007 21:55 |  #6
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Since that bird is small and from the looks of the shot, the lens did not focus on the bird. The bird is really out of the DOF of the shot. Using a smaller appeture would not help this shot and neither would a tripod. I do not see camera shake or subject movement. You just need better focus selecting techniques. Keep trying.


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Robert_Lay
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Feb 18, 2007 09:03 |  #7

Perhaps I will think differently when I get a digital SLR, but I take it for granted that on a shot like this you would be focusing manually.

I also am a great believer in "isolating the problem" when it comes to troubleshooting. I strongly recommend running a test with a stationary target using similar settings while on tripod or beanbag with timer triggering to avoid touching the camera when it goes off.


Bob
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Help, what is causing the poor IQ
FORUMS Photography Talk by Genre Critique Corner 
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