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.
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.
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: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.)
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.
Pentax 67.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 ?
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?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?
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