Sigma 10 20 (Canon)

cowboy

cowboy

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I've had this lens for a few weeks now and I am struggling to get decent sharp photos with it.

I've tried it at f8, f11, f13 and all distances from 10 to 20mm and it just seems like pot luck if I'm going to get a decent image.

I've tried auto focus, manual focus and hyperfocal focus but none are consistantly good or bad.

I am using a tripod for most of my shots, when I'm using auto focus I use the AI focus.

To be honest I'm getting no better shots than I was with my 18-55 kit lens only wider.

Any help or advice would be great.

Thanks.
 
I never use AI focus with my 10-20, one shot if the subject is stationary or AI-Servo if moving.

AI Focus just gives the camera room to **** the shot up :D
 
cowboy said:
I've had this lens for a few weeks now and I am struggling to get decent sharp photos with it.

I've tried it at f8, f11, f13 and all distances from 10 to 20mm and it just seems like pot luck if I'm going to get a decent image.

I've tried auto focus, manual focus and hyperfocal focus but none are consistantly good or bad.

I am using a tripod for most of my shots, when I'm using auto focus I use the AI focus.

To be honest I'm getting no better shots than I was with my 18-55 kit lens only wider.

Any help or advice would be great.

Thanks.
Click to expand...

Need to post an example to check there's nothing amiss, but what you say there is exactly what you should get!

Edit: sharpness will deteriorate signifcantly at f/numbers higher than about f/11, due to diffraction - not something the lens can do much about. Peak sharpness in the centre will probably be around f/5.6-8.
 
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These are a few I took yesterday.

They were all taken on a tripod, using 2 second timer to minimise movement and hyperfocally focused on the white snowdrops at approx 15 feet.
The focus was set the same for each picture.


Test 1 by cowboy72, on Flickr


Test 2 by cowboy72, on Flickr


Test 3 by cowboy72, on Flickr

100% crop as shot.
 
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MF on lens
AI focus on camera.

Focused at just before infinity (5') on lens for f8 and 4' for f11.

Thanks
 
cowboy said:
MF on lens
AI focus on camera.

Focused at just before infinity (5') on lens for f8 and 4' for f11.

Thanks
Click to expand...

So the focus was adjusted manually between each shot ? were you going by the scale on the lens or did you look through the viewfinder ?
 
Go back to 1 shot auto focus and start from there.

If you are manually focussing keep in mind that infinity is a variable thing due to temperature/air pressure etc. So one day it may be to the left of the "hockey" stick, another it will be to the right.
 
cowboy said:
These are a few I took yesterday.

They were all taken on a tripod, using 2 second timer to minimise movement and hyperfocally focused on the white snowdrops at approx 15 feet.
The focus was set the same for each picture.

<snip>
Click to expand...

cowboy said:
MF on lens
AI focus on camera.

Focused at just before infinity (5') on lens for f8 and 4' for f11.

Thanks
Click to expand...

So what distance did you use? Those pictures look very near-focused to me. Hyperfocal distance for 16mm lens at f/8 is 6.4ft. Ignore the lens scale markings, they are usually inaccurate, sometimes wildly. Estimate six-ish feet by eye and focus on something at that distance using centre AF point.

Hyperfocal distance is a technique for maximising depth of field, not for testing sharpness. Only the actual subject focused on will be optimally sharp.
 
HoppyUK said:
So what distance did you use? Those pictures look very near-focused to me. Hyperfocal distance for 16mm lens at f/8 is 6.4ft. Ignore the lens scale markings, they are usually inaccurate, sometimes wildly. Estimate six-ish feet by eye and focus on something at that distance using centre AF point.

Hyperfocal distance is a technique for maximising depth of field, not for testing sharpness. Only the actual subject focused on will be optimally sharp.
Click to expand...

I used the SimpleDOF meter app on my phone.
16mm Focal length at f8 for 15 ft came out with 5ft 6 inch hyperfocal distance and I used the scale on the lens.

Looks like the app is a bit out, with my "guessing at five and a half foot on the lens scale probably accounts for the focus problems.

Thanks very much for your help :thumbs::thumbs:
 
cowboy said:
I used the SimpleDOF meter app on my phone.
16mm Focal length at f8 for 15 ft came out with 5ft 6 inch hyperfocal distance and I used the scale on the lens.

Looks like the app is a bit out, with my "guessing at five and a half foot on the lens scale probably accounts for the focus problems.

Thanks very much for your help :thumbs::thumbs:
Click to expand...

Try this DoF calculator - DoFmaster http://www.dofmaster.com/dofjs.html You can donwload it as a phone app.

Your DoF app may be calibrated to a different standard, or be set for the wrong format. Anyway, DoFmaster above uses the international standard.
 
DOF calculators are only good for checking / working out the DOF after you've focused, the scale on the lens is about as much use as a chocolate teaspoon :)


IMO etc ;)
 
cowboy said:
MF on lens
AI focus on camera.

Focused at just before infinity (5') on lens for f8 and 4' for f11.

Thanks
Click to expand...

so that's about 1.5m in proper units? I'd go for 2m for the start, so that's close enough... And the camera didn't override the focus in some strange way, did it?

So that looks pretty awful if your focus was anywhere near infinity. If you didn't tell use I'd say that's more like 30-40cm. That points to something very faulty in the lens assembly (and I am not surprised with that at all).

Get it back to the shop or send away for warranty repair as an alternative.
 
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