+ 3.0 Diopter S wanted

I'd be obliged if someone would tell me where I might find a Canon

Dioptric Adjustment Lens S (rectangular) for use with my FTb and EF. I

need a +3.0.

 

A friend sent me a +1.5, but that is not of any use and I'll gladly

give it to anyone who needs it.

I have a -3 Canon Dioptric lens, but I guess that wouldn't help you.

Tough one, William. D'you think a vertical line drawn through the minus sign might fool the lens into convexity?

IINM, doesn't Canon still make viewfinder diopters for their current EF bodies? The rectangular viewfinder window on the new cameras is the same as on your FTb, so a new diopter should fit.

 

Ten thousand circus clowns are out of work, and you had to ask for help here... :o)

If Canon still make bodies, and if those bodies have eyepieces, then it is reasonable to suppose that they also make correction lenses. It is not reasonable, though, to assume that one use of the letters EF is the same as another, for the reason that it isn't, or that all rectangles are the same. But if the current eyepieces are rectangular, it certainly is possible that they are of the same dimensions and design as the old ones. Where might I find one of those circus clowns of whom you speak?

Stroke of luck. Found it on the Net. Store in Washington State. Rather a bit of money for a little piece of glass in a plastic and metal frame: but in the market it may have a certain antique value, and for me it will probably make the difference between being in focus and out.

I have several of them, almost one for each camera I own, and I bought them all on ebay. A man with the seller ID wps47 has some.

I just (four minutes back) arranged for a friend in the US to get the Washington State one and send it to me here in India. But, since I shall have two bodies and just one diopter between them, it might make sense to chase up the address you've given. Thanks, Brian. On the other hand, I have a vague notion of getting hold of an F1 (circular eye-piece) and ridding myself of the EF, which I haven't really liked in the two years I've had it. I switch lenses between it and the FTb, and quite often I forget about the "A" position of the aperture ring.

What exactly should be the strength of a diopter? I thought I needed a +3.0 because that is the strength of my reading (near vision) glasses. But when I look through the +3.0 diopter I finally procured, the image in the finder is, if anything, worse than it is without the attachment. In a pair of binoculars, one eyepiece can be focussed differently from the other -- but this joker stays what he is. How I wish Canon had built in variable adjustment as some other manufacturers did and still do.

Finally opting for the practical route, I went to my optician's with a body, a lens and the Canon +3.0. The strength of the diopter as measured was +4.0. I asked for test lenses of different strengths to try out, and hit the jackpot with the third: a +1.5 (physics, not Canon). I had taken along a not so old pair of reading glasses, just 0.25 less than my present near vision prescription. I had the lens for my focussing eye replaced with a +1.5 and left the other alone. Now I can read aperture scales and so on with one eye and focus very comfortably with the other.

My fundamental mistake was to think that I needed a +3.0 diopter because +3.0 is my near vision prescription. What Canon calls +3.0 is +4.0 in terms of optics. The apparent distance at which the eye should focus is 1 metre and the inbuilt finder has a strength of -1.0 diopter. The long and the short of it is that I now have two +3.0 S-type diopters for which I have no use. I shall send them anywhere in the world, by registered air mail, for $15 each. That's rather less than I spent on the things, but it's an old rule that one must pay for one's stupidity.

My fundamental mistake was to think that I needed a +3.0 diopter because +3.0 is my near vision prescription. What Canon calls +3.0 is +4.0 in terms of optics. The apparent distance at which the eye should focus is 1 metre and the inbuilt finder has a strength of -1.0 diopter. The long and the short of it is that I now have two +3.0 S-type diopters for which I have no use. I shall send them anywhere in the world, by registered air mail, for $15 each. That's rather less than I spent on the things, but it's an old rule that one must pay for one's stupidity.

 

Just a couple years later I find myself in a very similar position, but even with this very helpful information I cant figure it out completely yet.

 

My subscription is about +3 on both eyes, so pretty farsighted. To get a sharp view I figured I need a +3 diopter as well (which is pretty impossible to find)

 

If the inbuild finder has a strength of -1, wouldn't I technically need a +4 to get to an +3 in total?! How come (-1) + (+3) turns out to be 4 and not 2?

 

What am I missing?

What am I missing?

 

It gets tricky because several camera mfrs used their own diopter specification instead of common eyeglass diopters, so you can't always simply choose a correction eyepiece based on your drugstore reading or prescription eyeglasses. Complicating matters is the typical fixed -1 optics in many camera viewfinders: some brands ignore this factor and number their correction diopters independent of it, others like Nikon are infamous for subtracting the fixed -1 of their cameras from their correction eyepiece numbers. Then, each individual camera model may vary another fraction of a diopter more or less than the assumed -1 the finder is supposed to have.

 

With Nikon, you buy correction lenses marked 1 diopter less than what you think you need, i.e., if you think you want +2.0, the proper Nikon-brand correction eyepiece is marked +1.0 (in Nikon parlance, +2.0 added to the -1.0 of their viewfinder equals +1 correction). I'm not sure if Canon followed the same pattern: if not, you would need to make the same -1.0 compensation for the viewfinder optics yourself. IOW, if Canon marks its correction eyepieces at their actual strengths, you don't necessarily want the marked lens that matches your eyeglasses: you might need one diopter more, because the Canon (Pentax, Minolta, Leica, whatever) markings don't factor in the -1.0 of the viewfinder?

 

Or not. It can be really confusing (and annoying) if you don't know for certain which labeling scheme the mfr was using for that generation of camera eyepieces: I suspect even my wording above may have got the Nikon vs other brand numbering systems reversed. The key takeaway is you'll likely need to try several different strengths before you hit on the one that works perfect for you, esp if you are modifying a correction eyepiece from a different brand to fit your camera (common practice today, since you can't always find vintage camera diopters).

Edited April 3, 2020 by orsetto

Thank you, although the confusion remains ;)

 

I'm looking for a correct diopter for my AE-1P, I'm quite certain that would be a "S" model - I do own one that gives +1, which helps compared to the naked alternative but isn't ideal. Can you hint in a direction of how to do a custom modification?

Can you hint in a direction of how to do a custom modification?

 

People today typically start with a Nikon correction diopter, as these were/are the most widely available (by far) and were made in a variety of sizes/shapes. If you have a rectangular eyepiece, there are two possible Nikon solutions that will either work out-of-the-box (if you're lucky) or can be hacked to fit somehow.

 

The easiest way to go is look for a correction eyepiece specified for the Nikon EM/FG cameras. these are rectangular lenses in a slide-on rectangular plastic frame. Depending on the exact size of your non-Nikon camera eyepiece frame, these EM/FG diopters will fit reasonably well, or be a bit too small/large to slot over it. Being plastic, you can easily trim or file the slip-on groove of the Nikon diopter for a better fit, or cut the slip-groove entirely away to leave a flat rectangular frame that you can modify with velcro, an O ring. rubber cement, etcc for a perfect fit.

 

OTOH, the EM/FG eyepiece diopter availability is more unpredictable than Nikon's round eyepieces for FM/FE/FA cameras: it may be quicker/easier to find a specific diopter strength in that configuration. To use the round diopter on your rectangular eyepiece, Nikon offered a clever DK22 adapter: basically the EM/FG frame with a round hole into which you screw the FM/FE/FA diopter of your choice. Nikon made a range of diopters in increments of 1 from -5 thru +5 (actually +6), along with 0.0 (actually +1) and +0.5 (actually +1.5). Note the FM/FE/FA correction lenses have metal rims that can scratch plastic eyeglasses: if you wear those, it is better to choose from Nikon F/F2/F3 correction lenses. These have the same 19mm thread diameter as the FM/FE/FA diopters, but slightly larger flatter rims that can be fitted with a nice rubber ring that protects eyeglasses.

 

The DK22 adapter frame (shown below) sells for $12 new or $4 used, diopter prices ride a rollercoaster week to week with supply/demand (Japanese eBay sellers have many of them new for about $20, used ones go for $10- $40 depending on strength and whether the seller is an unrealistically greedy nitwit). Patience and diligent searching will usually net one at very reasonable cost. Bottom pic shows a typical Nikon EM/FG diopter: notice how the glass itself is easily removable and can often fit completely inside your camera's own eyepiece frame.

 

 

Edited April 3, 2020 by orsetto

Take a look at the KEH website. Search for Canon Diopter. If you think you can get buy with a +2, they're selling an exc+ 2.0 S for about $12.00.

Take a look at the KEH website. Search for Canon Diopter. If you think you can get buy with a +2, they're selling an exc+ 2.0 S for about $12.00.

 

Good catch! :)

 

fritzunruh, I would start with this option: its the specific model fitted for your camera, and at $12 if it isn't the right match for your vision you aren't out much money. KEH also has a nice return/refund policy, so at the very least this gives you a chance to evaluate one more diopter strength variation. Since the Canon-marked +1 gave you a slight improvement, chances are very good this +2 should get you very close to perfect.

 

I somehow missed that you already had the (insufficient) Canon +1.0 eyepiece: if all else fails and you need/can't find a Canon +3.0, the easiest "hack" might be to replace the glass in your Canon +1.0 eyepiece with the glass from a Nikon EM/FG +2.0 (actually +3.0) or +3.0 (actually +4.0) eyepiece (should be nearly the same size as Canon's glass, or can be filed down and re-glued).

Edited April 3, 2020 by orsetto

Wow, this is extremely helpful, thanks a lot everybody for taking the time, it is much appreciated!