Confused about Eyepiece Diopters

[Pieter12]

According to my eyeglass prescription, I need a +1 diopter correction. From what I can tell, most SLR eyepieces have a default -1 correction. So, does the -1 bring the effective correction to 0? Why is a -1 needed in the first place? Not sure how this works. Would removing the existing eyepiece bring the correction to +1? Or would I need to add a +2 to bring the correction to +1?

 

[ic-racer]

No, if you need a +1, then a +1 is needed to bring your vision to zero. A -1 would put you two diopters from your vision's zero.

 

[Pieter12]

No, if you need a +1, then a +1 is needed to bring your vision to zero. A -1 would put you two diopters from your vision's zero.

I guess I'm still unclear if the standard diopter for a particular viewfinder is -1, wouldn't the addition of a +1 just bring it back to 0? It does not seem all viewfinders off the option of replacing the -1, just the addition of a supplemental corrective lens (Leica M comes to mind). And why is the -1 standard?

 

[reddesert]

This is a subject of much confusion. Properly labeled diopter is the inverse of the focal length in meters, so for ex +2 diopter reading glasses should have a focal length of 0.5 meters (so that if you need to read text at 0.5 meter distance, your eye lenses will be focused at infinity, which they can still do).

Typically, camera eyepieces are set up to produce a virtual image of the focusing screen (or RF image/framelines) at a distance of about 1 meter. So although your SLR focusing screen is physically only a few inches from your eye, a lens is used to put the virtual image at about 1 meter distance. Because it is much easier to focus your eye at 1 meter than at a few inches. This is why it is said that the default eyepiece has -1 diopter.

Manufacturers like Nikon will sell you a "+1" eyepiece additional lens that combines with the existing eyepiece lens to make a correction appropriate for a person with a +1 prescription. The additional lens is labeled "+1" because that's who it's for, but it doesn't actually have the same focal length as a pair of "+1" reading glasses, that's the confusing part. This is because it sits right next to and combines with the existing lens. The confusion is increased when people call the corrective lens a "+1 diopter" which is technically incorrect. So, you should just buy the corrective lens labeled for your prescription. (This holds for Nikon, and Bronica, and probably many others.)

My experience is that I now use reading or progressive glasses with about +2 to read close things, like my phone, or type on the computer, but I can still use an SLR without the glasses, because I can still focus at 1 meter. However, I often have to use the glasses to read tiny print like ISO, shutter speed, DOF markings.

 

[mwdake]

The post above by

reddesert​

Is the clearest explanation I think I’ve ever read on this subject.
I’ve always wondered myself about this.
Thanks for the explanation.

 

[BrianShaw]

https://www.nikonusa.com/fileuploads/pdfs/EP_CompChart.pdf?srsltid=AfmBOoqm9befvRpy15KYKBNJXHPdMajCIdRnu3zhzYhX6m20OPC4cg_G

 

[mshchem]

I just wear my progressive glasses. With the newest SLR cameras I own they're all equipped with adjustable diopters, I usually adjust these once and that's it. Whatever is on most rangefinder and older SLRs work fine with my glasses.

 

[Pieter12]

This is a subject of much confusion. Properly labeled diopter is the inverse of the focal length in meters, so for ex +2 diopter reading glasses should have a focal length of 0.5 meters (so that if you need to read text at 0.5 meter distance, your eye lenses will be focused at infinity, which they can still do).

Typically, camera eyepieces are set up to produce a virtual image of the focusing screen (or RF image/framelines) at a distance of about 1 meter. So although your SLR focusing screen is physically only a few inches from your eye, a lens is used to put the virtual image at about 1 meter distance. Because it is much easier to focus your eye at 1 meter than at a few inches. This is why it is said that the default eyepiece has -1 diopter.

Manufacturers like Nikon will sell you a "+1" eyepiece additional lens that combines with the existing eyepiece lens to make a correction appropriate for a person with a +1 prescription. The additional lens is labeled "+1" because that's who it's for, but it doesn't actually have the same focal length as a pair of "+1" reading glasses, that's the confusing part. This is because it sits right next to and combines with the existing lens. The confusion is increased when people call the corrective lens a "+1 diopter" which is technically incorrect. So, you should just buy the corrective lens labeled for your prescription. (This holds for Nikon, and Bronica, and probably many others.)

My experience is that I now use reading or progressive glasses with about +2 to read close things, like my phone, or type on the computer, but I can still use an SLR without the glasses, because I can still focus at 1 meter. However, I often have to use the glasses to read tiny print like ISO, shutter speed, DOF markings.

Thanks.

 

[Nitroplait]

I once made the mistake to order a neutral 0.0 thinking it was a replacement of the clear glass cover on my FE2, only to realise what Nikon writes in bold in the link above:
The eyepiece’s diopter value is, when combined with the viewfinder’s minus one value, the end-result value.

Having near perfect vision back then, I can attest to the claim that -1 is better than 0.0 for people with normal vision.

When @reddesert writes

The confusion is increased when people call the corrective lens a "+1 diopter" which is technically incorrect. So, you should just buy the corrective lens labeled for your prescription. (This holds for Nikon, and Bronica, and probably many others.)

I guess it should read "the corrective lens labeled for your prescription - when viewing an object at a distance of one meter"? That would align with Nikon's recommendations:

To determine which Nikon diopter value is best suited for you, visit your ophthalmologist, optometrist or dispensing optician. Ask them to determine your diopter from (your corrective prescription) when viewing an object at distance of approximately one meter. Base your selection on this diopter value.​

 

[pentaxuser]

The post above by

reddesert​

Is the clearest explanation I think I’ve ever read on this subject.
I’ve always wondered myself about this.
Thanks for the explanation.

You have taken the very words out of my mouth with the first sentence . A very clear explanation

pentaxuser

 

[Pieter12]

Still a little confused. For camera manufacturers that do not market corrective eyepiece diopters according to the effective correction achieved factoring for the built-in -1, does one take the -1 into account, i.e. adding an actual +2 to achieve a +1 correction, or just ignore the -1 and use an actual +1 diopter? Also is the goal to achieve -1 at the eyepiece instead of the eyeglass prescription of +1? So what would one use to bring and an eyeglass prescription of +1 to the ideal -1 diopter, taking into account the already -1 diopter of the viewfinder?

On the other hand, I have seen a chart for Rolleiflex prism diopters that states that the standard (-.5) diopter actually measures +8.5!

 

[BrianShaw]

I’d be looking for documentation from whatever specific system you are interested in. Otherwise, the generic answer or specifications of other systems could be confusing or wrong Which system are you seeking information about ?

 

[Chan Tran]

For Nikon and for camera without the diopter adjustment and you want to use the camera without glasses. You ask the eye doctor to determine your glasses for to see well at 1 meter distance.(not for reading) So if the Dr said it's +1 then you buy the 0 diopter.

 

[Pieter12]

I’d be looking for documentation from whatever specific system you are interested in. Otherwise, the generic answer or specifications of other systems could be confusing or wrong Which system are you seeking information about ?

Pentax 67.

 

[Pieter12]

For Nikon and for camera without the diopter adjustment and you want to use the camera without glasses. You ask the eye doctor to determine your glasses for to see well at 1 meter distance.(not for reading) So if the Dr said it's +1 then you buy the 0 diopter.

My understanding for the Nikon system, the diopter labeled 0 is actually +1. I assume (usually a mistake, I know) that by needing a +1 eyeglass prescription for the 1 meter distance, my uncorrected eyesight is -1. So by adding the +1, it effectively brings my correction at the viewfinder back to -1. All is good, then?

 

[Chan Tran]

My understanding for the Nikon system, the diopter labeled 0 is actually +1. I assume (usually a mistake, I know) that by needing a +1 eyeglass prescription for the 1 meter distance, my uncorrected eyesight is -1. So by adding the +1, it effectively brings my correction at the viewfinder back to -1. All is good, then?

If you wear a +1 diopter glasses you can see well at 1 meter then it's right.