Lens Sharpness - How to test

[Iguanasan]

Does anyone have a process or an idea of a process on how I can test my lens to see if the softness in my shots is due to my inability to focus or the fact that I'm shooting with a kit lens that just isn't up to the task?

I thought I was causing blur by having too short a DOF but in this shot. (http://www.photography.ca/Forums/showthread.php?t=4158) I was shooting F9.0 @ 1/80 which I would have thought would leave a large enough DOF to get both the wings and the body in focus.

This is an auto-focus shot and I put the spot focus on it's back. I shot a couple of manual focus shots where I made sure I could clearly see the wing structure and still the body was not in focus. If it turns out to be the tool then it's very frustrating. If I can prove it's me making the mistake then maybe I can learn how to correct it.

[Marko]

It's tough to say what happened in this particular shot. It could simply be camera shake if the camera was not on a tripod and you weren't absolutely still.

Just to be sure, what was the file size BEFORE you uploaded it? Thx - Marko

[Iguanasan]

I'll post the full size one tonight via Picasa (and Flickr just to be sure) but I'm sure it wasn't the board as the full size one seems kinda soft when I zoom in on it. I think this one was under the 250KB limit before I posted it. I saved it that way from GIMP.

[Marko]

cool that's what I wanted to know.

Ok then - other possibilities
- is it possible the insect moved a tad during the exposure?
- for macro type subjects depth of field is reduced of course but the part you focused on should of course be tack sharp. I'm not convinced at all that it's even possible for f-9 to cover both wings on yr 55mm.

On older lenses it's easier to see what distance a given F-stop will cover as the info is often right there on the barrel. You'll want to check the specs of yr lens for this info as well as the minimum focusing distance.

If I had to bet on this though, I'd bet on camera shake.
Hope that helps

any other opinions on this?

[F8&Bthere]

Sharpness is a tricky bugger. When I've been unhappy with sharpness in my photos in the past, if I was able to eliminate subject movement, camera shake, and DOF issues first, I'd often end up realizing, or being told, I'm expecting too much (ie. pixel peeping). And it was often when I was trying to assess my copy of a recently bought lens. And other times I have found that lighting/ISO made all the difference of a slightly soft shot to a nice crisp one.

I assume you used a tripod. And if that's the case and if we give the lens the benefit of the doubt here, I'd have to agree with Marko's hunches. But as for the lens quality or possible front/back focus issues, of course it's hard to tell from the size posted here.

Does it look to you in viewing and zooming in the full size photo that the surface of the log is sharper than the insect? The answer to that question may say a lot. The shot looks good to me but I kinda see what you mean about the insect could be crisper- but to me it looks close enough that a little post processing could make an improvement.

Edit- oh and to answer the question- how to properly test- I'm betting by the time you read this post you've already googled it and found a pile of resources, like resolution charts you can print off and place flat on a wall, or the ones for front/back focusing (45 deg angle) etc

[Iguanasan]

Thanks for the feedback. No, I hadn't Googled yet as I was at work but I will shortly thanks for the keywords. Here is the original (in Flickr and PicasaWeb) for discussion. Maybe it is camera shake since I was not using a tripod, however, it is 1/80s and I believe I'm fairly steady - not as steady as a tripod obviously. Also, this has the lens stablization built in, this is the Rebel XSi and finally, the fence rail looks fairly sharp to me but maybe that's just my bad vision ;)

Photos below the EXIF

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Flickr (Click to go to the site) (http://www.flickr.com/photos/eulothg/3672828687/)
http://farm4.static.flickr.com/3599/3672828687_e149ae1a2a_b.jpg

Picasa (Click to go to the site) (http://picasaweb.google.com/lh/photo/ZnUeKeQ3ybDHkS02A66taA?feat=directlink)
http://lh3.ggpht.com/_8Q3edxpMqBs/SklMR5oqR3I/AAAAAAAAGrU/UA829fARJdc/s800/IMG_1825.JPG

[Barefoot]

Don't let it drive you crazy, Iggy. Set up a similar shot and use your timer to make a few exposures if you don't have a remote just to make sure you're not causing any movement.

Also, follow this link for a great chart to test for front/back focus issues and a pretty in depth discussion on the subject..

http://regex.info/blog/photo-tech/focus-chart

[jlabel]

The best way to check technical focus is using your camera on a tripod and focusing and shooting a ruler, chose a number and shoot it if the focus is misplaced it may be a lens problem, some newer cameras have the option to configure this kind of problem, also you will be able to see if your lens is sharp enought for you, you should also use f/5.6 or f/8 for this test.

[tirediron]

Basic lens sharpness isn't difficult to test for.

Print out a page consisting of nothing but the letter 'X' in upper-case, ten or twelve-point size (preferably using a good quality laser printer) and printing as close to the edge of the paper as you can.

Tape this flat against a wall and using a level, square and tape-measure set your camera on a tripod in such a way that it is exactly square to the sheet of paper with the centre of the lens axis pointing directly at the centre of the paper, and with the camera 1 - 2" further away than the minimum focusing distance wide open.

Ensure your camera is set to either RAW or the highest quality .jpg posssible and take a series of pictures of the sheet of paper, wide-open, f8 (or mid-range) and stopped down. Now, with the image size set to 100% in your favorite editor, examine the corners and centre of the different apertures. The differences in sharpness should be readily apparent.

[harvey3]

I do shot shot and shot to test it!

this is very good now I have better way of doing it.
thanks for sharing!

[tomorrowstreasures]

Igs. this is the most maddening thing about the auto focus, isn't it??? so nice that several weighed in on it!!!


Don't let it drive you crazy, Iggy. Set up a similar shot and use your timer to make a few exposures if you don't have a remote just to make sure you're not causing any movement.

Also, follow this link for a great chart to test for front/back focus issues and a pretty in depth discussion on the subject..

http://regex.info/blog/photo-tech/focus-chart
BF -thanks so much for that link!

[Barefoot]

Igs. this is the most maddening thing about the auto focus, isn't it??? so nice that several weighed in on it!!!


BF -thanks so much for that link!

My pleasure.