Information about Dioptric Lenses

Hey,

Just bought the Rebel XT, I am far sighted and wear bifocals. Do I need a dioptric lense if I am shooting on land and is it important to have for a housing? I do wear a single contact (+2.25) in my right eye which I use for reading my gauges, camera settings, anything having to do with reading. Somewhere I have read posts about dioptrics but have no idea about using them.

Thanks.

Wendy

(hopefully the camera will be housed in a year. Until then I plod along with my oly 4040)

Many modern SLRs have a degree of dioptric adjustment built in (though I'm not familiar enough with the camera that you have to know whether it does). The viewfinder image is actually a virtual image (that is, it doesn't exist where it appears to be) and your eye needs to focus on this virtual image without struggling, or so that it is reasonably relaxed. The effective location (where it appears to be to your eye) of the virtual image is probably about 2~3 feet from your eye. If you can focus comfotably at this distance with your contact lens then you probably don't need additional dioptric correction. If you cannot, then you either need to adjust the dioptric correction if it can be varied, or use a dioptric correction lens (which are usually available in 1/2 dioptre increments. To check how your eye feels when focused on the virtual image of the viewfinder, concentrate on focusing on either lines or markings within the viewfinder area or displayed information to the side, not the viewed image as this can mislead. Many optician will help if you show them the camera and ask their advice on what correction to use.

I use a simple correction lens in my mask which works very well underwater and has made a big difference since I cannot get on with contacts. I used to fit a dioptric corrector (prescription lens) inside my film camera housing which was great but meant that only I could use it!