Viewfinder Diopters: Learning has occurred

As with many people my age, my near vision is getting weaker and I now need some form of reading glasses to read anything at distances closer to arms' length. This has made focusing SLRs difficult, but I have noted I could do so with my 1.5x drugstore readers. I assumed that meant a +1.5 diopter for my cameras would be appropriate.

Then, I found a guy on ebay selling a 3 pack of diopters in +0.5, +1.0, and +1.5 for less than the normal price of just one. I bought that and assumed I would use the +1.5 and toss or give away the others.

I was surprised when I found that it was the +0.5 diopter I needed. The +1.5 was way off and the +1.0 was better than no diopter but still a tad fuzzy.

I'm glad I found the seller with 3 because if I had to buy just the one, I would have assumed +1.5 and that wasn't even close. At least now I have 2 steps stronger as my eyes get older and weaker.

Now I just need a +0.5 for my other SLR...

Chris

I always thought the point of the optics in a typical SLR viewfinder is that you focus your eye on infinity or close to it, so regular degeneration of close focus ability isn't really a problem.

I don't know. All I know is I couldn't tell from the microprism when the shot was in focus unless I had on my reading glasses or now a diopter.

Chris

from Nikon information. The standard correction is 1 meter.

Nikon SLR cameras (without built-in adjustable eyepiece correction) have a base diopter value of minus one. This is why you won’t find an accessory Nikon eyepiece diopter valued at minus one. Minus one is considered the optimum starting point for the majority of SLR users with normal vision. The combination of the camera’s viewfinder components and a clear (standard) eyepiece form a virtual image of a subject on the camera’s focusing screen that is the approximate equivalent of a viewing distance of one meter.

mtnbkr said:

As with many people my age, my near vision is getting weaker and I now need some form of reading glasses to read anything at distances closer to arms' length. This has made focusing SLRs difficult, but I have noted I could do so with my 1.5x drugstore readers. I assumed that meant a +1.5 diopter for my cameras would be appropriate.

Then, I found a guy on ebay selling a 3 pack of diopters in +0.5, +1.0, and +1.5 for less than the normal price of just one. I bought that and assumed I would use the +1.5 and toss or give away the others.

I was surprised when I found that it was the +0.5 diopter I needed. The +1.5 was way off and the +1.0 was better than no diopter but still a tad fuzzy.

I'm glad I found the seller with 3 because if I had to buy just the one, I would have assumed +1.5 and that wasn't even close. At least now I have 2 steps stronger as my eyes get older and weaker.

Now I just need a +0.5 for my other SLR...

Chris

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That is correct at least with Nikon. The 0 diopter is actually +1 piece because the built in eyepiece is considered as -1 diopter. They consider it -1 because it put the apparent distant of the focusing screen at 1 meter away from your eye.

I guess it depends on if the OP is using Nikon SLRs.

I know that I had to source five 'zero' diopters for the mechanical Nikon SLRs I acquired recently.

ic-racer said:

I guess it depends on if the OP is using Nikon SLRs.

I know that I had to source five 'zero' diopters for the mechanical Nikon SLRs I acquired recently.

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That is the way Nikon specifies their diopters but I don't know if other manufacturers do the same. However, I found that most other manufacturers viewfinder the apparent distance of the image in the viewfinder is 1 meter or very close to that.

koraks said:

I always thought the point of the optics in a typical SLR viewfinder is that you focus your eye on infinity or close to it, so regular degeneration of close focus ability isn't really a problem.

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[Note: multple posts in this thread since I started typing; I'm just posting as I originally typed it.]

Yes, seems like that would be a sensible way to do things, but... for some reason the camera makers seem to always make the "viewfinder image" much closer. I have a pet theory as to why this is done, but I guess the reason doesn't really matter.

I've seen people online say that the normal viewfinder image is set to be at about 1 meter, but in my experience this is not the usual situation either. At one time I decided to investigate this thing a bit; looking at a handful of 35mm camera brands the virtual distance seemed to be typically over a meter, maybe up to 5 or 6 meters. (I don't remember clearly... long time since I did this.)

I rigged up a bench test setup for testing this, but also a way for multple slr owners to check on their own. The basic method is to first set the test camera on some sort of stand, focused on a scene. Then, using a second slr camera, look into the viewfinder of the test camera and manually focus the second camera on the test camera's viewfinder image. Then, without changing the focus setting, move the second camera into the real world and find the actual distance at which it is focused. For example, view some object through the second camera viewfinder, moving forward or back until said object comes into focus. Then use a tape measure to find the distance from said object to the front of the second camera lens. (This real-world distance, which can be physically measured, is the same as the "virtual distance" observed through the eyepiece of the test camera.)

I didn't mention the camera because I didn't think it mattered, but I'm using a Canon FT (the one that has the diopter now) and Canon New F-1 (diopter ordered now that I know what I need).

Chris

Chan Tran said:

That is the way Nikon specifies their diopters but I don't know if other manufacturers do the same. However, I found that most other manufacturers viewfinder the apparent distance of the image in the viewfinder is 1 meter or very close to that.

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That sounds about right given how my reading glasses improved the situation.

I'm still unsure why my +1.5 reading glasses worked, but the +1.5 diopter actually made things worse compared to nothing at all.

Chris

mtnbkr said:

That sounds about right given how my reading glasses improved the situation.

I'm still unsure why my +1.5 reading glasses worked, but the +1.5 diopter actually made things worse compared to nothing at all.

Chris

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It is because the +1.5 diopter eyepiece is actually a +2.5 diopter lens so that when you mount it on a -1 viewfinder it's considered +1.5.

Chan Tran said:

It is because the +1.5 diopter eyepiece is actually a +2.5 diopter lens so that when you mount it on a -1 viewfinder it's considered +1.5.

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That would be critical need to know information.

But, finding 3 for the price of one got me there and now I have a couple stronger ones in case my eyes get worse.

Chris

Going down the rabbit hole....I just had cataract surgery and now need readers to see this computer screen (I was always near-sighted, since the age of five). I'm noticing all sorts of changes, most of them good ones, but one negative is that I can no longer pull focus on myself in the bathroom mirror when I want to do close work, like finding an object in my eye that's causing irritation. I need to use the readers to see the eyeball close up, but those same readers get in my way. As I was trying to solve this problem, I noticed that my eye is focusing on the "virtual" distance of an object reflected in the mirror. If I stand with my eyes about a foot from the mirror, my face is in focus, but if I maintain the same distance and shift slightly to one side, the bathroom wall next to the mirror is out of focus. So my eyes are seeing an object in the mirror as if it were more distant than the surface of the mirror itself: the combined distance of my eye to the mirror and the apparent distance of my face in the virtual space behind the mirror. So, just now, I picked up my F2 and pulled focus on the venetian blind on my window (from several feet away) and I was able to do so clearly, with only my "new" eyes and their artificial-implant lenses. Normally, without the readers, I can pull focus about 2 feet away. So my brain looks in the VF of my camera and sees an image that is not a few inches away in the groundglass but rather several feet away and therefore within the 2-feet-to-infinity range of my now-unaided normal vision.

I think this is consistent with Koraks' point: somehow the eye/brain system is able to perceive the distance the light has traveled from the object despite travelling through lenses and being reflected off mirrors. Is that true?

Tel said:

Is that true?

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It's more that the optical system of the viewfinder projects an aerial image at a certain distance that's chosen as a starting point for the viewfinder design. It stands to reason that viewfinders are designed with an eye focus distance that's a reasonable compromise between what different individuals are capable of easily accommodating. Given how many of is need reading glasses, it's obvious that no camera manufacturer would designate viewfinder that would exacerbate this problem specifically.

When you look at objects in a flat mirror, you always focus on the distance that is (eye to mirror) + (mirror to object). Unless the mirror is dirty and you focus on the spots on the mirror. You can also try this by pointing a camera at the mirror and focusing on the back wall of the bathroom - you'll see a distance on the focus scale that is the far distance, not the distance to the mirror. The mirror only changes the direction of light, it doesn't make an image (it's not like a ground glass).

For SLR finders, the physical distance from the eyepiece to the focusing screen is just a few inches (even counting the reflections in the pentaprism), and few people can focus that close. So the SLR eyepiece contains a diverging lens that makes the apparent image somewhat further away, 1 meter or a few meters. Many people can focus on this unaided, even after they need reading glasses for book-distance. This is what Nikon is calling the -1 diopter.

If you get diopter lenses from some other source, it is not guaranteed that the labeling is the same, so the diopter label may not match your reading glasses. Also different cameras have different conventions.

FWIW, I took the now-diopter-equipped camera out for a woodland photo walk. It was so nice being able to clearly see and interpret the microprism.

Chris

mtnbkr said:

I didn't mention the camera because I didn't think it mattered, but I'm using a Canon FT (the one that has the diopter now) and Canon New F-1 (diopter ordered now that I know what I need).

Chris

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I hate to disappoint/concern you, but there is no guarantee that two Canon SLR models designed for two such different markets - amateur vs. professional - will approach the diopter issue the exact same way.
Do you have manuals for both?

MattKing said:

I hate to disappoint/concern you, but there is no guarantee that two Canon SLR models designed for two such different markets - amateur vs. professional - will approach the diopter issue the exact same way.
Do you have manuals for both?

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No, I don't have manuals for either, but I have read the online version of at least the FT and I don't recall reading anything about diopters in it. However, having the same thought as you when I decided to buy one for the F-1, I did hold the ones I got for the FT in place on the F-1 and it worked, so I'm confident it should be about right.

ETA:
I went to the Butkis website and pulled up both manuals. The New F-1 manual says the viewfinder has a -1 diopter setting. The FT manual doesn't state the viewfinder's native adjustment but does reference the availability of diopters for users who are near or far-sighted.

Chris

reddesert said:

When you look at objects in a flat mirror, you always focus on the distance that is (eye to mirror) + (mirror to object). Unless the mirror is dirty and you focus on the spots on the mirror. You can also try this by pointing a camera at the mirror and focusing on the back wall of the bathroom - you'll see a distance on the focus scale that is the far distance, not the distance to the mirror. The mirror only changes the direction of light, it doesn't make an image (it's not like a ground glass).

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Thanks! It's as if there's a real person looking out of the mirror, in that other room that looks just like my bathroom. This puts me in mind of one of Vivian Maier's self-portraits with an infinite repetition in two mirrors arranged on the same axis. The best part is that with my new interocular implants I can pull focus without any glasses or diopters. (I was terrified of somebody cutting an incision in my cornea and put it off for several years, but I can say now that the improvement was spectacular.)

I don't know if my limited experience has anything to do with reality, but more of the newer cameras that I have include a viewfinder adjustment. The first camera of mine that had it was the Yashica Samurai -- a half-frame camera!

Adjustable diopter viewfinders are fabulous. You can even add one to a Leica M.

xkaes said:

I don't know if my limited experience has anything to do with reality, but more of the newer cameras that I have include a viewfinder adjustment. The first camera of mine that had it was the Yashica Samurai -- a half-frame camera!

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My M43 digital has an adjustable diopter. Unfortunately, the two film SLRs (60s and 80s vintages) do not have them.

Chris

The diopter for the F-1 arrived and it's perfect. +0.5 is what I needed there too.

Chris