What is the dioptric adjustment used for?

[Ah Pao]

Some SLRs come with built-in dioptric adjustment in their viewfinders, e.g. -2.5 to +0.5 diopter. I first thought they are used to help people with myopia or astigmatism (I have both) to focus without their eyeglasses, but of course it was not meant to be used like that.

Can anyone kindly explain what is dioptric adjustment and what is it used for? Thanks!

 

[PLRBEAR]

Hello Ah Pao,

As taken from Canon's website glossary:

Diopter
The degree to which the light ray bundles leaving the viewfinder converge or disperse. The standard diopter of all EOS cameras is set at — 1 dpt. This setting is designed to allow the finder image to appear to be seen from a distance of 1m. Thus, if a person cannot see the viewfinder image clearly, the person should attach to the camera's eyepiece a dioptric adjustment lens having a power which, when added to the viewfinder's standard diopter, makes it possible to easily see an object at one meter. The numerical values printed on EOS dioptric adjustment lenses indicate the total diopter obtained when the dioptric adjustment lens is attached to the camera.

 

[chucks]

I reckon u r talking about viewfinder diopter adjustment.

Simply put, it is for u to adjust so that u can see more clearly thru the viewfinder. We are not talking about the image sharpness here or whether the image is in focus or not. Thus some pple prefer to remove the lens b4 doing any diopter adjustment.

All u need to do is to look thru the viewfinder (u can point ur cam towards a evenly-lit object eg sky or a white wall), and then adjust the diopter till the focusing brackets look as sharp as possible to you. Once set, u r done. There is no need to adjust anymore after that. If your eyesight is really very bad that the range on the diopter adjustment is not enuff, u may need to find add-on correction lenses with a bigger range.

 

[Ah Pao]

I see...it's for focusing the viewfinder silkscreen...
Then my eyesight is really bad...