[Rob Barron]

Some people, me included, have taken pictures that seemed sharp when taking them but when they are processed they look soft and we blame our AF or our manual focusing techniques but that might not be the problem at all. It might be that the viewfinder is not accurately adjusted to your eye. This applies even for people who THINK they don't need glasses as the odd 0.5 dioptre inaccuracy can be compensated for in real life but will cause problems when manually focusing a camera.

I know it is a bit of a fag but it is worth taking time to accurately set the dioptric adjustment on your camera to ensure it is as close to your eye needs as possible. There are various methods for this so if you don't mind I'll give you a couple of them and hope these methods prove effective.

First of all, if you have an eye correction of more than 3.5 - 4 dioptres then you will not get it perfectly just using this adjustment as most cameras I know of have a max of +/- 4 dioptres. However, you can buy more powerful adjustment viewfinder lenses for the major brands like Canon and Nikon so it is worth getting it exactly right for your eye.

You can ignore any astigmatism as this relates to the alignment of both eyes. You don't use both eyes for focusing so that doesn't come into it.

Ok, the simple method of alignment:

1. Using an AF lens on its widest aperture setting, stand about ten feet from something that is flat and has straight edges with the BG a fair distance away. it is best to do this outside and in good light. Now, using the AF, focus on the subject and do not move away. Take a photo.

2. Now, without your glasses, look through the lens and adjust the dioptric adjustment wheel until it looks nice and sharp.

3. Move away so the previous focus is now wrong. Point at the subject from this new distance and using manual focus, focus as sharply as you can on the subject. Take a photo.

If you have done this properly, the second photo should be as clear and sharp as the first photo. I recommend putting both images onto your computer, opening in your favourite processing program and looking at the image at full pixel level. This will show clearly whether you are sharply in focus or not.

If it isn't as sharp, you might need to try the more long-winded but more accurate method.

Slower, more accurate method if needed:

1. Set your camera lens to manual focus. NB, to ensure accurate results, it is best to use RAW mode for this so that the camera does not process the images.

2. Set the dioptric adjustment wheel (usually right next to the viewfinder) as far as it will go one way. Now, slowly turn the wheel counting the clicks to the far end of the range. Do it again to check! - sorry, this only works if your camera has a clicking wheel, Canon does as does Nikon I believe.

3. Put the wheel back to the extreme, either end is fine as long as you know which way you worked.

4. Without your glasses on, focus on a set subject at a set distance so that you take identical pictures. When you have it as clear and sharp as you can get it, take a photo.

5. Move the wheel by one click. Repeat step 4.

6. Continue moving the wheel one click at a time and repeating step four.

7. When you have got to the other extreme, check the numbers of your pictures so you will know which was one click, two clicks etc.

8. Transfer all the photos to your computer and look at them zoomed in to full pixel level. Some will be badly out of focus (OOF) and then they will get better and better to a point where they will start getting worse again. Note which picture is the best, sharpest picture.

9. Now you know which click adjustment gave you the most accurate focusing, turn the wheel to its starting position and then count the clicks to the position you used for the sharpest picture.

10. Now it is fully adjusted AND if it ever gets moved, you will always know how to reset it to your eye. Please note, over long periods, eyes do deteriorate so it is worth checking it whenever you get your eyes tested, especially if your optician has said there is a change since your previous test.

I hope that is of some help in getting the most out of this very important tool.

Cheers,
Rob