350D w/ any lens focus help PLZ

[Jwreich]

Hello all,

I need a little wisdom from you all. I don't think this is a camera thing or a lens thing.

My problem is I work from a tripod and like to frame my shot. I swich my lens (usually a Tamron 28-75 2.8) to manual focus and focus my subject with the correct composition. When I look at the image on my computer, it is NOT in focus.

If I have a subject anywhere other then dead center, I don't have good tack focus. I have tried all of my lens and have similar issues.

Now if I go hand held and compose with the subject more center and then place the background off to the side all looks fine.

I'm starting to more portraits and the issue of focus is a huge concern of mine. I don't trust my camera system.

I like to open up to f/4 or larger, but with the decreased dof and my focus issues, I never know what I'm going to get.


Can anyone tell me if it is normal to have softness at the edges of the lens after manually focusing and seeing tack focus in the viewfinder?

My lens list is in my signature so you can see what I shot with.

Many thanks!

[robertwgross]

First of all, why don't you isolate the problem to one lens, the other lens, or the camera body? If it refuses to sort out, then maybe it is something that you are doing wrong. It is possible that the diopter setting is screwy. Also, you might test autofocus on the center point and see how that works.

---Bob Gross---

[dgcorner]

I agree with Bob. Check your diopter setting... then have a look at your lenses and narrow it down

[Mike Smith]

I had a similar problem once on an old Canon FT. The mirror became misaligned, and so what appeared to be in focus in the viewfinder was actually way out of focus. But I had no way of knowing until I got the film back (several rolls of vacation film ruined). If your mirror has been bumped or damaged, that could be your problem.

[Ronald S. Jr.]

I don't have my xt with me at the moment, but I think your problem might be that you may have center-weighted your focus. With the AF, you can pick which point you want to use as your "main" area of focus. I believe it's the * button, and then use the wheel ahead of that to choose your point. As far as manual focus...well...ya got me.


Of course you all knew that.

[Jwreich]

Originally Posted by robertwgross

First of all, why don't you isolate the problem to one lens, the other lens, or the camera body? If it refuses to sort out, then maybe it is something that you are doing wrong. It is possible that the diopter setting is screwy. Also, you might test autofocus on the center point and see how that works.

---Bob Gross---

If I were to isolate it down, then it would be the Tamron 28-75 which I use most often. Now if I use auto focus this lens is SHARP. The problem is when I compose a shot using a tripod and manual focus. The viewfinder "looks" good, however the resulting print is out of focus.

I always keep the AF locked to the center focus point, however I have recently been changing this focus point based on the the compositon of my shot so I can use the AF since it can do something my eye seems unable to complete.

I do not know what the diopter setting is or how it can be altered. I'm really at a loss and very worried/upset as I need to be able to rely on Manual Focus.

Any suggestions?

Thanks,

[jimsolt]

Originally Posted by Jwreich

. . . I do not know what the diopter setting is or how it can be altered. I'm really at a loss and very worried/upset as I need to be able to rely on Manual Focus.

Any suggestions?

Thanks,

I don't know if this is your problem, but the diopter is the method used to focus your viewfinder -- most useful for folks like me who use reading glasses.
It is a small wheel near the eyepiece. See page 42 of your XT manual.

Jim

[robertwgross]

It certainly sounds like something wrong between the diopter adjustment and the focus screen. That means the diopter adjustment, itself, the actual alignment of the prism, and the focus screen. There might be little shims holding the focus screen that have gotten lost.

However, you didn't mention whether you tried the other lens, as I had suggested. If both lenses are roughly the same, then this takes us back to the above premise.

---Bob Gross---

[Johnny Thunder]

I've found that manual focus is more then a little difficult to nail down perfect with the standard screen. you may want to purchase a split prism screen to help when you manual focus.

Why dont you use AF in the studio?

-Johnny

[Jwreich]

Johnny,

I'm not in a studio environment very often. When in a controled environment, I use AF or when I'm not on a tripod. I've just been doing family portraits and want everything to be tack sharp. I'm sorry to say, they have not been. I found the diopter and did play with it a little. I'm working on some shots with the camera hooked to my computer.

Thanks for the help.

[Jwreich]

Originally Posted by robertwgross

There might be little shims holding the focus screen that have gotten lost.

Bob same issue with a 700-200 f/4 L. You mention the possible shims. Does anyone know if there are shims holding the focus screen?

I'm fairly sure the issue is with the viewfinder/diopter. Now I just need to see what it takes to figure all this out. I'm just thankful AF on these lens and camera are so good or I would be up a creek...

[Andy_T]

JWreich,

let's apply a bit more reasoning here...

- When focusing manually, You see a sharp image in the viewfinder
- Regarded on the computer, it's not that sharp at all
- When using AF, you get images that are sharp on the computer.

One more question ... when you use AF, does the image look sharp through the viewfinder as well?

Assuming there is something WRONG with your camera (focus screen misalignment, missing/wrong shim etc.), AND that you are able to correctly judge focus from the viewfinder, then the image should NOT be sharp in the viewfinder when using AF.

If - on the other hand - you use AF and
- the image is sharp in the viewfinder AND on the PC, and
- with manual focus it is ONLY sharp in the viewfinder, but not on the PC,
then I assume you have the same problem as I do ... it's pretty hard to focus 100% accurate using MF with the 20D/Drebel XT.

In that case, consider getting a split prism screen, if you want to use MF.

Best regards,
Andy

[Jwreich]

Andy,

I think your right. I have a hard time with the small viewfinder of the XT. I may have to look at a split screen prism. Isn't there a guy in the BST forum listing them. How much do these cost and where is the best place to get one?

--

[zacker]

if you use auto focus and the pics come out sharp, what does it look like in the diopter?? also why not just use the auto focus for the time being till its figured out?
-zacker-

[smasraum]

Yes, my guess is that you just aren't getting it into focus manually. It's very difficult to manually focus these things. A split circle screen would make it much easier, but even then that only works when the center circle is over the subject to be focused on.
Do you wear glasses or need glasses?

My vote is that you need to focus and then recompose.