rebel xt focus issues.please see( pics)

[felix21685]

hey guys
reading around i found the focus test which you are probably aware of..
now please take a look at my following 2 pictures.

the first was taken with my 28-80 sigma lens granted its not high end but i think it should still do better than what it did , no ?

the second one was taken with my sigma 70-300 DL macro II
this is also not a high end lens and look at the results..
is this all i can expect from my 2 sigma lenses ? will it be better with a new midrange-high end canon lens?

thanks for your help..

[DReb-MO]

I think it would be helpful to know whether you used AF or MF, the shutter speeed and AV. I am assuming this was from a steady tripod, or did you hand hold? All are relevant .

[tim]

I'd like the answers to those questions too, and also can you put the full sized files on a server somewhere so we can see them?

[felix21685]

alright guys heres the full size files.

http://dana.ucc.nau.edu/~fdt2/rc/xt/IMG_0509.JPG
exif:

1/50 f5.6 80mm tripod.


http://dana.ucc.nau.edu/~fdt2/rc/xt/IMG_0518.JPG

1/50 f5.6 214mm tripod (different lens)

[Steven M. Anthony]

Okay: The test board is not straight (perpendicular to the lens axis). It looks like the focus is fine onthe right side of the images--but because the left side of the test board is shifted a bit towards the camera, the focus seems off.

[kawter2]

What are your issues? overall sharpness or location of the focus..

BTW i don't really see an issue with either, given the lenses you have.... remember, ther is a reason that good lenses are so expensive

[felix21685]

do you think that if i spend more on a quality lens everything will be considerably sharper?

some macro shots which i did arent sharp like i want them to be..
is this only because of the lenses i own or is it partially the camera as well?

[Jon]

Try the same test outside in sunlight so you can use a higher shutter speed. Unless you used a remote release, you probably introduced a bit of vibration when you pressed the shutter. This may also have been a factor in your macro shots.

[robertwgross]

I agree with Jon.

Getting a good amount of light on the scale is important. Also, if possible, place some sort of high contrast target at the zero focus point (the word "perfectly"). I used a tiny red arrow that is about one centimeter long. If the autofocus system struggles with that, then there may be a real problem.

---Bob Gross---

[Phil V]

Okay: The test board is not straight (perpendicular to the lens axis). It looks like the focus is fine onthe right side of the images--but because the left side of the test board is shifted a bit towards the camera, the focus seems off.

Yep:rolleyes:

[Michael_Lambert]

Increase your Feild of Depth.. You are shooting at F/5.6 Increase it to f/11 or higher..

[tim]

Increase your Feild of Depth.. You are shooting at F/5.6 Increase it to f/11 or higher..

Nope, don't do that, that masks the issue. Shoot wide open, the camera should focus perfectly wide open. The image could be a little soft wide open, but that's different to focus.

Felix, do you have a URL to download that focus test?

[fetching]

can someone please point me in the direction of one of these focus tests?

[glangston]

You can pretty much lay a nice metal or wood ruler out on a flat surface and then shoot down on it's length at a 45 angle, focusing on a given mark and them comparing the depth of field in front of the mark and behind it. Should be roughly equal. I'd use a tripod, cable release and mirror lockup to get the best info. Plenty of light so focus issues are not prevalent and shutter speed can be adequate. All this was advice I got back a few weeks or months ago.

[Michael_Lambert]

Nope, don't do that, that masks the issue. Shoot wide open, the camera should focus perfectly wide open. The image could be a little soft wide open, but that's different to focus.

Felix, do you have a URL to download that focus test?

But you are not going to get the whole image Sharp and clear shooting at a F/5.6 on an angle???

[tim]

But you are not going to get the whole image Sharp and clear shooting at a F/5.6 on an angle???

That's the point of a focus test - you want to see if it focuses where you tell it, the way you do that is by focusing on the centre of the image and using a narrow depth of field. If you use a small aperture for a large DOF you're defeating the purpose of doing a focus test.

[felix21685]

i am not at home right now when i get home ill look and see where i got it from

[Michael_Lambert]

I found this?

http://www.photo.net/learn/focustest/

[felix21685]

i saw that one too



the one i used is here

http://md.co.za/d70/chart.html

[tim]

http://md.co.za/d70/chart.html

That's a great resource, especially for people who don't already understand how camera focusing systems work. I have to assume that the D70 descriptions he gave apply to the Canon range too.

[Johnny V]

Here's a really good chart too:

http://www.canon-dslr.com/Canon_Jan05/Canon_SLR_Focus_Test.htm