Nikon FM eyepiece diopter confusion

[Michel Hardy-Vallée]

I'm not terribly short-sighted, but I thought I might put all chances on my side by ordering a diopter eyepiece for my Nikon FM2n.

My prescription for the right eye is +0.5 sphere. The astigmatism is rather low (-0.5 cylindre), so I don't take it into consideration.

Logically, I told myself, I will use the Nikon +0.5 diopter eyepiece. They say that +0.5 is the combined lens/finder dioptry, so I reason that it means that the entire camera optical system between my subject and my eye is equivalent to +0.5. Lucky me, I need +0.5 in my right eye to see properly. That's what I have in my glasses.

Now here's the catch: I bought the eyepiece, put it on my FM2n, and in fact it makes viewing worse. I checked very carefully again and again, putting the camera on a tripod and not touching the focus, and still, it looks worse with the eyepiece correction.

Did I make the wrong calculations based on my prescription? Or is it just the case that my brain is not used to the corrected view, so he has a hard time processing the new visual data? I fail to see how the fact that the viewfinder is -1.00 by default has anything to do with my problem.

 

[Chan Tran]

My reading glasses are +2.0 and I have a 0 diopter (a 0 diopter is actually a +1 lens, not the one that came with the camera) and it's good. The reason is that I need a +2 to see at 12-15" but I only need a +1 to see at 39" (or 1 meter) that's what I need to add to the viewfinder.

 

[Steve Smith]

If your prescription is positive then you are long sighted, not short.

So if you are actually short sighted rather than long, the -0.5D lens may have worked.


Steve.

 

[Michel Hardy-Vallée]

Oh, sorry about the vocabulary error. I'm long-sighted then! My prescription glasses are working correctly. The confusing thing is that my left eye is short sighted (- 0.5) and my right eye is long sighted (+ 0.5). I have a different degree of astigmatism in either eye, mostly concentrated in the left one.

 

[polaski]

Michel -- I tried to figure this out for myself, but finally just asked my eye doctor. He wrote the diopter correction down on a piece of paper for me, and I've been OK ever since.

 

[PhotoJim]

Ask your optometrist for the diopter you require at a viewing distance of 1 metre. That's the diopter that you will require.

 

[Michel Hardy-Vallée]

Ask your optometrist for the diopter you require at a viewing distance of 1 metre. That's the diopter that you will require.

Ah... That's something I did not think of. As I said, I'm actually long-sighted in my right eye, so I need correction for reading up close. My glasses are doing a good job, so I was thinking that the same correction would suffice.