Newbie - Wearing Glasses and MF

[acroutzet]

Hi Everyone -

First, this forum is super cool. I have read it for several weeks and I find it full of very interesting information.

I have a question regarding the use of glasses and MF.

I have a Canon 300D and when I am trying to focus in MF with my 70-200 at 200mm, although it seems to me that the image is sharp, the focus ends up being either before or behind where I wanted it to be.

I thought this may be due to the magnification effect of my glasses. Could that be?

I understand that there is a possibility to adjust the diopter on the 300D but I do not know whether I am supposed to adjust it with or without my glasses. Could someone help on this?

Thank you.

[Jon]

You'd adjust the diopter setting so the viewfinder display (focussing points, etc.) is sharp the way you use the camera. If you always use it while wearing glasses, that's how you'd adjust it. If you don't wear glasses when photographing, don't wear them when you adjust the viewfinder diopter.

Your focussing problem may well just be that the DR viewfinder rates, at best, mediocre for manual focussing. If there were a lens/camera focussing problem, it'd show up in AF as well. Is there any consistency in how the 70-200 seems to be out of focus (always in front at 70, in back at 200 for example)? If it's all over the place, it's probably something other than the lens' and camera's focussing arrangements. Either just that it's too difficult for you to manually focus on the DR screen, or maybe camera motion or such.

[KevC]

I'm a little confused. If you adjust the diopter to what *you* see correctly, how do you know if the lens is in focus?

Say the lens is out of focus. You don't know this. You assume it is. So you adjust the diopter till your eyes see perfect focus.

Do you see where I'm sensing a flaw?

[BigDan]

Here's one way of doing it. Why not focus using AF then adjust the diopter setting so that you see it clearly. That way when you use MF, the pic should be clear.

Well, it works in my head, might be worth a try

[Jon]

OK When you use the focussing screen to focus, you focus the lens until it gives a sharp image on the matte surface of that screen. You use the diopter adjustment so that when you look at the focussing screen, your eye is focussed on the screen not somewhere in front or in back of it. That's why you use the "permanent" indicators to help you adjust the diopter - they're on the screen where you should be focussing your eye so if they're sharp, you are looking at the screen and should see it clearly. If they're blurry when you look through the finder, you're not focussed on the screen and it doesn't matter where you focus the lens - you'll never see a sharp image. But once you get a sharp image from the lens focussed on the screen and you see the screen claerly yourself, by adjusting the diopter, you should be in focus. It's not like binoculars, where the image that goes through the lens gets formed right on your retina; the lens forms an image on the focussing screen and you need to focus on the screen as well.

If you rely on AF to give you a sharp image to focus on, it assumes that the AF is working correctly, and further assumes that you have a large enough part of the on-screen image in sharp focus. The AF sensor marks and Partial Metering circle are positively on the screen. If you adjust them so they're sharp and forget about what else is showing, your eye will be in focus on the screen.

[acroutzet]

Thanks all for your replies and advices. I believe I was often too close from the subject (less than 15 feet) and probably do not master DOF yet. Will continue to work on it.