Diopter Strength

dazedgonebye

dazedgonebye

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I'm having difficulty focusing a Pentax 6x7. Things are much better with my reading glasses on, but I find that awkward.
I'm trying to figure out what diopter I need. My reading glasses are a +2. It seems logical that I'd need a +2 diopter.
Is it that simple?

If not, how do I determine the diopter I need?
 
I don't know. I found this, but it's probably not what you want.

http://en.wikipedia.org/wiki/Eyeglass_prescription

I cannot use diopter adjustments on cameras because of my astigmatism - and it has more to do with me being near-sighted than my recent trip into bifocal land.

Anyway, as far as I know, you just move the diopter adjuster until the camera focuses properly for you with your glasses off.
 
Unfortunately, the 6x7 doesn't have an adjustable diopter. I can buy a single strength diopter for it, I just don't know which to get.

It occurs to me that I can look through a slr with and adjustable diopter and use that to determine what I need, if it indicates a number for the setting.
 
an idea

an idea

Go to the drugstore or dollar store and get (or try) some cheap +1.75 or +1.5 and +2.25 and +2.5 reading glasses and see if any work better than your straight +2.0s.

dazedgonebye said:
I'm having difficulty focusing a Pentax 6x7. Things are much better with my reading glasses on, but I find that awkward.
I'm trying to figure out what diopter I need. My reading glasses are a +2. It seems logical that I'd need a +2 diopter.
Is it that simple?

If not, how do I determine the diopter I need?
Click to expand...
 
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Here is a question, does using/not using a diopter (assuming you need one) effect focusing accuracy beyond making the rangefinder patch more visible?
 
depends

depends

for me, with slight myopia, depends on the distance of the subject i'm focusing on.


Athos6 said:
Here is a question, does using/not using a diopter (assuming you need one) effect focusing accuracy beyond making the rangefinder patch more visible?
Click to expand...
 
This may not be the same for all cameras, but the image in the finder tends to be set to a medium distance, of around two meters. Some cameras have a slight negative diopter built into the eyepiece. It might be on the order of -.5 diopter or so. Therefore the best diopter for the camera may differ somewhat from your eyeglass prescription. What this all means practically is that you need to try before you buy, if at all possible.
 
I've just solved my problem....

Looking through the viewfinder with my reading glasses on works great.
Now I just need to get some real glasses.
 
can you determine this by scale focus? say you focus by distance to the subject by 1 meter. you then focus with your eyes and compare the diffrence? that diffrence is the correction?
 
Ask your optometrist or optician. A good optician will enjoy the challenge (and will find it quite easy). My wife even had a pair of prescription motorcycle goggles made: re-glazed 'Spitfire-pilot' Marks (front glasses only).

Cheers,

R.
 
Many people with good distance vision may still have a small refractive error at distance but enough to ignore for most tasks. Check with your last eye doctor to get your latest distance prescription. If it's been over 2 years, get an eye exam for your own good. Ideally to see the viewfinder and focusing screen clearest, the net power through the finder should be 0 diopters (plano) and many, but not all camera finders have a built-in power of -1 diopter so it's best to consult with the camera specs in the instruction manual to find out what Pentax actually uses for the camera. If, for example the finder power is -1 diopter, you would need a +1 diopter to neutralize it, so if you're slightly farsighted, it will be even greater than +1 diopter. Check with Pentax on how they label their diopter eyepieces before buying one. Nikon for example, can be confusing because the label their accessory diopter eyepieces as the net power when combined with the built-in -1 diopter power from the finder. For example a 0 diopter Nikon eyepiece actually measures as +1 diopter.
 
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dazedgonebye said:
.... My reading glasses are a +2. It seems logical that I'd need a +2 diopter.
Is it that simple?

If not, how do I determine the diopter I need?
Click to expand...

For a camera eyesight correction diopter you need whatever value you need to view a distance of about (*see below) 670mm to 1m, best tested in dim light.

* It depends on the camera. Trial and error, in dim light, is the only sure way. Since your reading glasses are for closer than the figures above, +2 would be too strong (unless the Pentax is unusual).

Also, note that some makers, e.g. Nikon, show the value of the diopter as its intrinsic value added to the camera viewfinder diopter (which they say is always -1). So the one I use from Nikon is labelled -2 but it's a -1 piece of glass.

What's your prescription for distance vision?
 
A 1 meter viewing distance requires a +1 diopter power if you are presbyopic (need readers). If the camera finder is -1 diopter, then you would need a +2 diopter eyepiece to give a net power of +1 diopter which is similar to your original post.
 
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awilder said:
A 1 meter viewing distance requires a +1 diopter power if you are presbyopic (need readers). If the camera finder is -1 diopter, then you would need a +2 diopter eyepiece to give a net power of +1 diopter which is similar to your original post.
Click to expand...


I think that +1 to view at 1m is for someone with excellent distance vision. Correct me if I'm wrong.

So we need to know something about the OP's eyeglass prescription for distance vision, I think. If one is young, the eye has a large range and the diopter value doesn't need to be all that accurately chosen, but as you age, it becomes much more critical. For example, I am 61 and my TOTAL range of adjustment is 0.25 diopter. When I was a young photographer it was about 6.00 diopter. There's a graph (really scary, actually) showing this age-related effect at

http://en.wikipedia.org/wiki/Eyeglass_prescription
 
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I'm going to see an eye doctor. I haven't seen one in years. I get by with drug store readers for the most part. My distance vision has been ok.
I'm not sure, but I think the problems I'm having focusing this camera means it's not as good as it used to be.
In the mean time, it looks pretty good using the camera with my glasses on.
 
AT least with an SLR you need to focus only one distance through the viewfinder, because you're looking at ground glass that doesn't move. With a RF camera, you are looking at the subject at various distance through the viewfinder system, and if you are oldish you will notice the difference. I use a Megaperls x1.15 magnifier which has adjustable diopter and I have optimised it for about 2.5m subject distance which is about where it's most critical for the pictures I take.
 
So after my digression (sorry) in answer to Steve's original question, +2 is going to be an improvement. By trialling the other values available a better choice might be found. But most makers have only 1 diopter increments (Leica has half diopter increments, a big improvement for me at -1.5), so the other options are probably +1 and +3. The +3 is unlikely, since the reading glasses are almost certainly for a viewing distance shorter than the optical equivalent distance of the camera's viewfinder, so +1 and +2 are the choices.

Let us know how it goes.
 
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