Need some ideas on focus problem.

D

Doog

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Dougie
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I have a RAW image which I feel is not as sharp at 100% as I'd hoped for. The lens used was a Sigma 10-20 which I know have mixed reviews and I'm trying to establish whether I have a poor copy or whether it's my technique. Basically the focus point is not sharp. I shot at F16, 50th sec at 20mm hand held on AF-A. I'm wondering if I was too close to the subject so that when I pressed the shutter I maybe moved the camera slightly taking it out of focus. Should I have used AF-A, or should I have dropped the aperture to F8 which would have been around the sweet spot for the lens. I used F16 because I was shooting very close and wanted as much depth of field as possible. Maybe I was pushing the lens's capability too much? Right now I'm just not sure where I've went wrong or if I need to look to the lens choice?:shrug:

Any thoughts would be appreciated.
 
1/50 could be the problem, any chance of posting the shot.
 
Need to see the image really. Problem could be one of several issues.
 
Dougie - I think your problem is technique.
On a crop sensor f16 is limited by diffraction and is only capable of producing a sharp 8"x10" print; it will look soft viewed at 100%
Your shutter speed is borderline for hand held to be sharp viewed at 100%; matter of luck. The 1/focal length rule is only good enough for a medium size print and will not look sharp at 100% (and needs the 1.5 crop factor multiplying in).

There's a very similar thread about Canon lenses over here.
Read it and report back :)
 
foggy4ever said:
1/50 could be the problem, any chance of posting the shot.
Click to expand...

Well I don't have anything sorted by way of an image at present, I'll try sorting something later.:thumbs:

PsiFox said:
Need to see the image really. Problem could be one of several issues.
Click to expand...

Thanks

DuncanDisorderly said:
Dougie - I think your problem is technique.
On a crop sensor f16 is limited by diffraction and is only capable of producing a sharp 8"x10" print; it will look soft viewed at 100%
Your shutter speed is borderline for hand held to be sharp viewed at 100%; matter of luck. The 1/focal length rule is only good enough for a medium size print and will not look sharp at 100% (and needs the 1.5 crop factor multiplying in).

There's a very similar thread about Canon lenses over here.
Read it and report back :)
Click to expand...

Thanks for the link. I'll go have a read. I kind of suspected technique, I don't know if I'd be happier finding that out, or finding I've a duff Sigma;)
 
Use a tripod then that will rule out operator error to a greater degree :)

I wouldn't shoot above f11 anyway as apart from anything else it just shows up every spec of dust going.
 
As we don't even know the focal length it's difficult to say for sure, but at 15mm on a crop f11 focussed at 5feet will give you a sharp image from about 2feet to infinity.
f8 is plenty for most situations on a crop, diffraction takes away as much as DoF gives, and to be honest - if I wanted everything in focus I'd use a compact.:thumbs:
 
Are you looking at a RAW unsharpened image? Raws will look soft until sharpened or converted to jpgs with some sharpening added.
 
Main problem is almost certainly diffraction at f/16 - it won't be sharp on close inspection no matter what, and regardless of the lens.

Further, depending on which part of the image you're looking at specifically, there's a fair chance that it will be some way from the point of optimum focus and you're relying on depth of field to make it appear sharp.

Then, shutter speed is possibly marginal and of course you have to sharpen Raws, but whatever you do you'll be stuffed at f/16.
 
Thanks guys. I'm finding it hard not to use small apertures as my mind still drifts back to my 35mm film days when f16 wasn't a big deal. Isn't it strange that manufacturers are making lenses with f16 capability when the fact is pictures are going to suffer from using it:shrug: I'd rather have a lens which had less stops but everyone of them was sharp as a tack. Living in cloud cuckoo land I suppose :)
 
Doog said:
Thanks guys. I'm finding it hard not to use small apertures as my mind still drifts back to my 35mm film days when f16 wasn't a big deal. Isn't it strange that manufacturers are making lenses with f16 capability when the fact is pictures are going to suffer from using it:shrug: I'd rather have a lens which had less stops but everyone of them was sharp as a tack. Living in cloud cuckoo land I suppose :)
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the difraction is the same, it's the ability to pixel peep that has changed. What happens when you print the image?
 
Richard King said:
the difraction is the same, it's the ability to pixel peep that has changed. What happens when you print the image?
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I didn't explain that well. What I meant was I didn't have a problem in those days printing 8x10 B&W. Now that I'm pixel peeping for Alamy it's a different ball game. I'd still like a lens that was usable at all apertures though;) Photos for pleasure are still fine in that they won't find their way off the desk top but shooting for stock has definitely up'd the anti and is putting the squeeze on my abilities and demands. I'm hoping it will make me a better 'tog' though.:geek:
 
Doog said:
I didn't explain that well. What I meant was I didn't have a problem in those days printing 8x10 B&W. Now that I'm pixel peeping for Alamy it's a different ball game. I'd still like a lens that was usable at all apertures though;) Photos for pleasure are still fine in that they won't find their way off the desk top but shooting for stock has definitely up'd the anti and is putting the squeeze on my abilities and demands. I'm hoping it will make me a better 'tog' though.:geek:
Click to expand...

Things have changed Doog ;) Modern standards are so much higher, and I got at least as good quality with my crop format Canons (even my old 350D) than I ever got from the best 35mm Kodachromes. 10x8 black & whites on Tri-X or something were really not very testing.

But you really don't need to use f/16 except for extreme depth of field. On that score, f/16 on 35mm film delivers the same DoF as f/10.7 on your crop format Nikon. The formula is f/number x crop factor (ie x1.5). Diffraction follows the same rule, so that's where you're seeing more of a problem with your D90 - difraction at f/16 is at the same level at it would be with f/24 on film.

Check your DoF here - see how much you really need http://www.dofmaster.com/dofjs.html
 
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