Dioptre setting - foolproof method?

[V8S]

I'm pretty short sighted and so wear glasses but they don't offer perfect vision, so I rely on setting the dioptre adjustment wheel to compensate.

The method I've used before (and I think it was recommended in some magazine years back) was take the lens off, turn the dioptre wheel to completely out of focus then adjust it so that the viewfinder setting readouts just become sharp. Of course, what is difficult with this is that after a short while your eyes themselves adjust to make things sharper, so it's very difficult being confident it is set accurately.

I thought about taking manually focussed pictures of a static subject, but that brings in two variables - the dioptre adjustment and the focus adjustment.

Is there a way I can be sure I have set it correctly for my eyesight?

I have a nagging feeling I'm being stupid in some way.

[Simpo Two]

You do seem to have over-complicated the matter!

I'm short-sighted too, so without contact lenses everything in the VF is fuzzy (the AF will still do its job of course so I could still use the camera in a hurry and it would still take sharp images).

In your position I'd start with the dioptre setting at 0, and turn it a little in the appropriare direction (minus for short sight, plus for long sight) until, with your eye muscles relaxed, distant subjects are sharp. That's all.

Remember that the dioptre setting has no effect on the recorded image, it's purely for your viewing pleasure.

Edited by Simpo Two on Tuesday 28th July 19:36

[LongQ]

Manual focus mainly means you need to to set up so that the viewfinder information appears in focus. You then have to assume that your focusing screen (absent a split prism I assume), is focused to the same point. It should be. I am mildly short sighted but find no problems quickly identifying which dioptre click stop, of three or four possibles at first pass, best suits the eye I am adjusting for.

I think most of the viewfinders work on a fairly coarse dioptre difference between settings since an SLR is rarely intended to be used for focusing as one would with a MF/LF ground glass screen, thus absolute accuracy is not the objective of the dioptre adjustment provided.

Edited by LongQ on Tuesday 28th July 22:22

[V8S]

I have the dioptre setting reasonably correct, but I don't think it is spot on and wondered if there is a foolproof method to setting it up. As I wish to get back into some close up and macro photography, being able to choose a focus point with such small depth of fields, without relying on autofocus, is somewhat important.

Cheers.

[Simpo Two]

If as you say 'your eyes adjust themselves' how do you plan to put a marker in this shifting sand?

Sorry I didn't spot your desire to use manual - but what is wrong with AF? DSLR viewfinders are generally that small and dim as to make manual focusing no better than auto, just slower. With no fresnel screen or split prism, they're simply not designed for it IMHO.

[LongQ]

V8S said:

I have the dioptre setting reasonably correct, but I don't think it is spot on and wondered if there is a foolproof method to setting it up. As I wish to get back into some close up and macro photography, being able to choose a focus point with such small depth of fields, without relying on autofocus, is somewhat important.

Cheers.

I checked 2 manuals for different cameras and both mention the adjustment wheel and leave it at that. Other than one that suggests buying additional lenses to provide further adjustment.

If you viewfinder provides something like a box graphic to indicate where it is focusing/taking an exposure reading or whatever, making that sharp (plus the other viewfinder inforomation) is what seems the most logical form of adjustment assessment.

For real subject focussing as you describe I'm with Simpo's comments. Recent cameras with zoomable live view a good screen may help, or attach a computer and use the computer screen. But you may want to consider focus bracketing. Not many DSLRs have interchangable screens and I susect the manufacturers may feel slightly insulted if you beleive you can be more accurate then their expensively developed AF systems. I'm not saying you can't be more accurate for what you need, just that they may not feel much pressure to offer options to make manual focusing easier!

IIRC Michael Reichmann at The Luminous Landscape published an item discussing focussing recently, albeit for large format and landscapes. But some of the issues related to accuracy are not so different.

[Famous Graham]

This has always confused me.

If the viewfinder icons and whatnot are sharp, then that's it.

Your eyes are not going to magically sharpen up something that's not sharp to begin with, with or without glasses.

If, on the other hand, you can NEVER see them as sharp, then it's not adjustable enough to cope with your particular eye/glasses combination and something's awry with your prescription.

[GetCarter]

I have this problem with my music and deaf commissioning editors.

[Simpo Two]

Or to put it another way - the lens focuses the image onto the ground glass screen. That determines whether the recorded image is sharp or not.

In a completely independent stage (from the other side as it were), your eyes then have to focus on that sharp image. Even if they if they don't, the image is still sharp.