# Soft images from 40d and 24-70 L USM



## thriveCanada (Sep 20, 2009)

I'm having doubts as to the quality of image I'm getting from my new 40d. I just got it to replace a rebel that has back focus issues. You can see the issues in the next two links. The 40d appears to be focusing properly:

http://www.thrive.ca/photos/dof-rebel.jpg
http://www.thrive.ca/photos/dof-40d.jpg

and here's a couple of raw files comparing the two focusing on the label of the bananas:

http://www.thrive.ca/photos/compare.zip

Should I be expecting something sharper out of the 40d? What level of sharpness should reasonably be applied to a raw file?

DATA:
Rebel xti compared to a 40d with a 24-70 L USM.


----------



## Antithesis (Sep 20, 2009)

Looks pretty sharp to me. I had a 24-70 on a 5D and I found the images looked pretty soft and less contrasty than I would have liked. Considering the reputation of this lens, I went ahead and sold it and bought a few primes with the proceeds. Ended up much happier. 

As far as the application of sharpening, I like this article:

Sharpening 101

But there are more than one way to skin a cat. I've always had a bad habit of over-sharpening stuff.


----------



## Garbz (Sep 21, 2009)

Looks like an f/2.8 image to me, can't tell exactly since you stripped the EXIF.

One thing is that it pretty much doesn't matter what lens you have. Within reason every lens is expected to perform worst shot at it's widest aperture. I see a sharp image with a bit of CA which is too be expected. Take the photo again at f/5.6 and report back with the results.

I say within reason since there's a Noct-Nikkor 58mm f/1.2 that performs best wide open but then with second hand copies selling for $5000US my only experience with it was in a dream I had.


----------



## thriveCanada (Sep 21, 2009)

I'll post a set of raw files with different stops. Unfortunately I'm headed to the hospital in 5 hours and in no shape to do this now.

......But thanks for the info.


----------



## Buckster (Sep 21, 2009)

One of the things I do when I get a new lens is try to get to know it on a more personal level.  One of the ways I do that is to set up a test image like that on a tripod (but I use rulers and other assorted stuff to measure and assess the DOF), then shoot a series of shots at each successive aperture setting, using mirror lockup.  Then I have a good information/capability baseline for that particular lens to work with, independent of what it "should" be doing per others' testing of that type of lens.

From that, I get my "sweet spot" established for that lens, as well as learn what apertures to avoid.


----------



## Big Mike (Sep 21, 2009)

Every camera and lens has an acceptable tolerance for focus accuracy.  As an example, let's say it's plus or minus 5.  So if your camera is -3 and your lens is +4, you are pretty well off because your net is +1, pretty close to perfect.  Now if you grab a different camera, it might be +3.  So when  you use it with that same lens, you now have a net of +7, which can give you real problems.

You can send in cameras and lenses for calibration, but they usually want you to sent in both the camera and the lens.  

This is one big reason why cameras like the 50D are great.  They have a micro focus adjust option, which allows you to adjust the camera's focus on a lens by lens basis.  So you can adjust it for your 24-70mm lens, and it will remember that adjustment for that lens, so you can have different adjustments for different lenses.  

Also of note...as much as the 24-70mm F2.8 L is known as a pro's workhorse, it's also got a reputation for having focus issues.  I know a photographer who has owned 6 different 24-70mm lenses before finding one that was up to his, rather picky, standards.


----------

