 Pat Harry |
Bi-Focals & manual focus Grr... I'm about to pull my hair out! When you wear bi-focals, should the camera's diopter be adjusted to the top part of the eyeglass lens (distance vision), or the lower part (near vision)? I've tried both, and my images still aren't focused. I assume I need to tweak the diopter, but I'm not sure which vision I need to tweak it for! I use auto focus on everything but macro, but I'm having a heck of a time focusing macro images. Of course, cataracts aren't helping either (but at least one is getting removed next month).
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Glenn E. Urquhart |
Hi Pat - I have... Tri-focals!!! When I shoot, I neve have my glasses on. I have, through trial and error, adjusted my camera's diopter to my eyes, without glasses!!! It takes a little time, but give it a try and I believe you will be happy with the results. Best wishes, Glenn.
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Todd Bennett |
Pat, I remember reading a post, not sure if it was here or somwhere else, but, the poster said his/her eyes had gotten so bad they could only trust the auto focus. I agree with Glenn that you probably should leave the glasses off. I know it's a pain switching back and forth. I am far sighted and I honestly do not trust my eyes when looking through the view finder. I have been very succesful with the auto focus. Even with macro shots. It may just take some experimenting.
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Pat Harry |
Glenn - I tried tri-focals and didn't like them. So now I just have two pare of glasses. My near/far glasses, and my near/intermediate glasses. And whichever ones I have on....I need the other. :) I'll keep tweaking the diopter. I don't think I've tried yet without my glasses. I'll give that a shot and see if I have better luck.
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Pete H |
Pat, I will assume you are nearsighted? I am too, yet I have resisted getting bifocals...nothing to do with photography, more to do with "I'm not getting older am I?" LOL You should be looking thru the top part of your glasses and tweak the diopter adjustment for that. The image in a SLR is TTL (Thru the lens) so you are looking at a distance.
Pete
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Alan N. Marcus |
Hi Pat, The eyepiece lens of a camera viewfinder is designed to present parallel rays of light to the user. In the trade this is called is called collimated rays. When the average person looks at a distance vista his/her eye lens muscles tug on the eye lens and it becomes thinner. In this position we feel relaxed. When looking at close objects the eye lens muscles push the flexible lens, it gets thicker adds power). Older eyes lose flexibility, as the eye ages the lens becomes rigid. Eye glasses generally correct vision for distance. The bifocal segment adds power. The unit of measure is the diopter. 1 diopter is a lens with a focal length of 1000mm. 2 diopter 500mm. 3 diopter 333.3mm. 4 diopter 250mm. The formula is 1/d * 1000 = convert to millimeter unit. The diopter unit is used because it simplifies lens formula math. It’s use allows addition and subtraction to be substituted for multiplying and dividing. The entire eye ware industry uses this unit. If you go to the drugstore and buy off-the-shelf reading glasses the power stated will be in diopters. When an eye doctor writes a proscription, he writes in diopters. You should take your camera to the drugstore and try reading glasses with and without your normal distance glasses. In a matter of minutes you will discover the diopter power you need for both conditions. You can wear only a pair of these cheep glasses during you picture taking session. You can have a pair of specal glasses made with the bifocal add (power) you now know works for you. Some camera makers will adjust the diopter power of the eyepiece lens for a fee. Using your ingenuity you can cut the store-bought plastic and make a mount that overlays you camera eyepiece. You can find a clever optical repair shop and maybe they will make you a lens and a mount it to your eyepiece. The first step is to see what add you need. Your eye doctor has a kit that contains trial lenses of every possible power. This simple solution is have made a special pair with the revised add in only one side. You have a master eye, it’s the one you use when you compose and focus. Good luck, Alan Marcus (marginal technical gobbledygook)
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