Focussing with varifocal eye glasses

[popavvakum]

Regrettably, I now need varifocal spectacles. I have noticed that since about that time some photographs from my Olympus OM2N SLR comes focussed at a plane most often behind and seldom in front of the one intended. This seems to be the case with several lenses even though the shift of focus ranges from barely noticeable to awful. I wonder what part of the varifocals should I use to focus: the part for infinity of close distances, i.e. reading, or the one for the distance at which the image is focussed? The latter may be tricky.

I guessed this problem should not arise with a rangefinder; I recently produced a Frankenstein Kiev in which I adjusted the lens and rangefinder. The first two films are inconclusive though and I seem to be getting a slight shift of focus.

Does anyone have any considerations of how to focus with varifocals?

 

[sevo]

Rangefinders are glasses agnostic - or rather, on them, glasses affect everything alike. With SLRs, it will depend on brand, type and past owner - essentially you should focus with the part matching the apparent distance of the finder image (depending on the camera, usually 1m, 2m or infinity by default, but a past owner might have swapped the dioptre lens for something different).

Personally, I have learned (the expensive way) only to use my glasses for focusing through a finder with a plastic or rubber ring on the eyepiece - wherever the eyepiece glass/dioptre has a bare metal ring, I purchase the appropriate dioptre and focus bare eyed rather than scratch my glasses...

 

[popavvakum]

Thanks for your considerations. The correction lens may only be made of fixed focal length, i.e. diopter strength, so it would only correct my view at one fixed distance. So, it is not really an option.

But even without it how can I possibly focus an SLR at any other distance if I do not know in advance what part of the eye glass to look through?! So, do I understand you right that varifocals and accurate focus in an SLR are incompatible?

 

[madNbad]

If you are wearing progressive lens glasses, use the upper (distance) part of the lens. With bifocals it's fairly easy but trifocals take a little more work. A solution is to order an inexpensive single vision lens set for distance and use those when out with the camera. I wear trifocals and use a rangefinder without any problem but it takes a lot of shifting your eye around to see the entire frame.

 

[sevo]

Thanks for your considerations. The correction lens may only be made of fixed focal length, i.e. diopter strength, so it would only correct my view at one fixed distance. So, it is not really an option.

Yes, it is - the ground glass is at one fixed (apparent) distance! Indeed, you do not want to focus to any other distance than that, or you would miss the grain and focus on some aerial image outside the focal plane (so that the on film image would be out of focus) - that is the main risk when using varifocals.