Autofocus / Manual Focus / Poor Eyesight

[TechKnowBabble]

I rarely use manual focus because I have a bad astigmatism and am concerned with the photos not being as clear as I'd like. I was wondering if autofocus would always be better to use for me OR would it still be better to try to focus manually? I know it's a somewhat vague question, hope you understand what I meant.

Nikki

[Scottes]

My astigmatisms aren't so bad, but my eyesight is horrible. I use AF a lot for long stuff, but when DoF is an issue I have to do manual. I do a lot of small birds (big glass at close distances), butterflies, and other macro/closeup stuff, so DoF is usually an issue.

I played with my diopter quite a bit before I got it "right" - it can be tricky. With me I find that I can spend some time getting manual focus perfect, and then if I look away and let my eye relax then go back to the viewfinder I'm off and have to refocus. So now I make that a habit. Of course this is only good when the subject isn't moving.


I played with a macro lens and a deck of playing cards to set my diopter. Autofocus, then take a picture. Flip to MF, add a card, click, add another, click, remove them, click, remove another, click, remove another, click. Check the pictures and find the sharpest one - hopefully the original AF one. Then go back and play with the diopter until that card looked the sharpest. Relax the eyes often.

So now the diopter's set, so start looking at other things, non-macro. Set the lens to MF and focus. Click. Flip to AF, click. Check the pictures - does your manual look as sharp as the AF one? Or vice versa?

Take a picture of something flat like a brick wall. The AF won't be fooled by focusing on something other than what you know it's focusing on. Set the AF point on a large flat section of the wall, but have a window nearby. The sill will be a little closer than the wall, but the panes a little further away. If either one of those is sharper than the wall itself then you'll have to adjust.

It certainly took a while but it seems to be worth it. And I'm finding that I get more used to it as time goes on. My photos now are much sharper than they were even a month ago.


If I'm still worried - or shooting an unknown subject - I'll go up an ISO stop and down an aperture stop in an attempt to get more DoF.

[Qurlyjoe]

Nikki,

I also am astigmatic, and have the same problem with focusing. The downside of using autofocus (one of them, at least) is that you have to keep futsing with the composition in the viewfinder to focus on what you want and then maintain that focus while you recompose. I have tons of negatives (from before my 10D arrived) where the image is focused in the middle of the frame just because that was easiest, and I'd recompose in the darkroom by cropping when I printed stuff.

With the 10D's multiple focus spots, this is mitigated somewhat, but it can still be a drag to set the focus point you want, and then get what you want in precisely the right spot in the frame. This is nearly impossible if your subject is moving.

One thing you might try, at least for static shots, is do it both ways. (Isn't it wonderful not having to worry about using up film?) It may turn out that you're better at focusing manually than you think. That wasn't the case for me when I tried it, unfortunately.

Bill

[TechKnowBabble]

Ok. Taking those suggestions in mind, I have (currently) two Sigma lenses that have the AF/M switch on the lens, are all Canon lenses like that as well? If so, is it very stressful on the camera to keep switching back and forth?

Thanks for your help!!

nikki

[Scottes]

Every lens should be able to switch back and forth. No it's not stressful at all.