Nikon FM Corrective Vison Diopter Eye Piece

[68degrees]

If I know my eyeglass prescription, how can I know which eyepiece diopter piece I need for my nikon FM?

 

[funkydog]

If you're nearsighted and your prescription is -200 then the diopter is -2.

 

[john_s]

According to this Nikon pdf:

http://www.nikonusa.com/en_INC/IMG/...PDF/Eyepiece_Compatibility_Chart_07012008.pdf

Nikon label their eyesight correction diopters with their optical value minus 1 diopter which is built into the camera viewfinder optics. So what funkydog says is generally correct but it might not result in the optimum choice. We are talking about spherical correction. If your prescription includes significant cylindrical correction you won't get a corrective lens to work perfectly.

Also, as we age, the eye's ability to adjust (focus) for small discrepancies diminishes markedly. At my age, 65, a diopter needs to be spot on for me to be happy, but 20 years ago near enough was good enough even though my distance prescription has not changed.

If you're short sighted (negative spherical prescription) and if you have minimal cylindrical, I would try the Nikon corrector equal to your correction. If the value is in-between (nikon's units are at 1 diopter increments) I would go for the weaker rather than the stronger.

I can't advise if you have long sight as I've no experience.

 

[68degrees]

According to this Nikon pdf:

http://www.nikonusa.com/en_INC/IMG/...PDF/Eyepiece_Compatibility_Chart_07012008.pdf

Nikon label their eyesight correction diopters with their optical value minus 1 diopter which is built into the camera viewfinder optics. So what funkydog says is generally correct but it might not result in the optimum choice. We are talking about spherical correction. If your prescription includes significant cylindrical correction you won't get a corrective lens to work perfectly.

Also, as we age, the eye's ability to adjust (focus) for small discrepancies diminishes markedly. At my age, 65, a diopter needs to be spot on for me to be happy, but 20 years ago near enough was good enough even though my distance prescription has not changed.

If you're short sighted (negative spherical prescription) and if you have minimal cylindrical, I would try the Nikon corrector equal to your correction. If the value is in-between (nikon's units are at 1 diopter increments) I would go for the weaker rather than the stronger.

I can't advise if you have long sight as I've no experience.

alright thanks, Ill look up my prescription and see what it is.

 

[Rob-F]

It's interesting (read, confusing) that there's no minus 1 diopter. OK, that must be because the finder's native diopter is already minus one. This would imply that the glass used for minus one is the clear window glass one, for dust protection, that they mention. OK so far; but then, there is another one, above it, labeled as a "replacement."

So here's the confusing part. The "replacement" one is presumably to replace the one that came with the camera--the one that has no diopter power. So that must be the clear window glass one, resulting in an overall power of minus 1. But that would suggest that the one marked 0 isn't the one that is clear glass. After all, the two eyepieces have different model numbers, so there must be some difference.

Does anyone understand what I'm trying to say?

 

[t.s.k.]

Hmmm...interesting and in direct contrast to how Leica handles VF correction.

If I'm reading this correctly, the diopter label represents the final correction for use on Nikon slrs, not the actual correction of the glass.
Ergo, a -2 diopter equals a -1 correction for the diopter alone, right?

 

[farlymac]

I had a diopter on my first FM, and after a while I came to dislike it. Sure, I could read the settings on the camera easier with my glasses off, but then I couldn't focus on a scene until I put the camera up to my eye. So I went back to wearing my glasses while using the camera. And it was the only camera I ever bothered to get diopters for. Maybe if they had come out with those flip-up eyeglasses back then...

PF

 

[craygc]

Work in absolute diopter values, not relative ones when working with Nikon. The standard is -1. As a data point on the long-sighted side, I have had lens transplants on both eyes set to infinity (perfect vision) and I use 175 for reading glasses. I did a trial and error on my FM3A starting at +1 and coming back to 0, with zero being perfect and +1 was worse than the standard -1.

 

[Lflex]

If I'm reading this correctly, the diopter label represents the final correction for use on Nikon slrs, not the actual correction of the glass.

Correct.
As long as you know that the default value of the finder is -1, then it is straightforward.

 

[Robert Lai]

To answer an earlier question, the one labelled "0" is actually a +1 diopter lens. With the -1 in the camera, the two cancel out to 0.
The regular eyepiece glass is planar, and thus you get the standard -1 built into the viewing optics.

 

[rbsinto]

Or, you can remove the glass from a screw-in eyepiece, and then have an Optician grind a custom glass insert to your prescription.
I did this years ago for an FE or FE-2 back in the early 1970s.

 

[Spavinaw]

Much like craygc, my eyes are corrected to infinity (with contact lenses). On my FM2n a 0 lens is perfect.

 

[68degrees]

Or, you can remove the glass from a screw-in eyepiece, and then have an Optician grind a custom glass insert to your prescription.

so does the optician need to know the finder is -1 or does that matter with a custom grind? What would that cost do you think?

This is my prescription
OD -125 -75 x 127
OS -175 -100 x 58

 

[john_s]

Assuming that you are viewing with your right eye (OD) you have some cylindrical but not a huge amount so I think it would be worth trying a Nikon -1 which is labelled -2. The next value stronger is -2 (labelled -3) which might be worth a try if you can do so in a shop, but could be too strong. Test in dim light when your eye has less depth of field since it is operating at max aperture (i.e. the iris).

Bear in mind that if you were to have a custom lens made with cylindrical correction then when you turn the camera 90 degrees to take a portrait then the correction would be worse than no cylindrical correction at all. For Leica cameras there is an eyepiece that turns as the camera turns for people with such a problem. See
http://walterrxeyepiece.com/

Also, some good background at
http://en.wikipedia.org/wiki/Eyeglass_prescription

which illustrates why we old guys need to be careful about getting the right value which didn't matter so much when we were young.

 

[alistair.o]

so does the optician need to know the finder is -1 or does that matter with a custom grind? What would that cost do you think?

This is my prescription
OD -125 -75 x 127
OS -175 -100 x 58

The first thing I would do is let the optician have a copy of the Nikon PDF and remind them that the focal point is 1 metre (IIRC) in front of the camera.

As another person has said a 0 diotre will set the vision to perfect neutral balance i.e. it will cancel out the -1 standard set be Nikon.

Hope this helps.

PS: I wear glasses (varifocals) but with a 0 dioptre on my Nikon, I can photograph without glasses, perfectly.

 

[Ronald M]

First decide if if you wish to use camera with or without glasses. With glasses, -1 is sufficient as it get my old eyes to focus on the screen.

The built in -1 works for no glasses solution.

The drug store readers generally have trial lenses to see what works. Use whatever the sample lens is marked at in your tests.