Are any of you using diopters for the Mamiya RB67 waist lever viewfinder? Do you have spare ones?

[mshchem]

I have glasses with progressive lenses. Depending on the camera I'm using I find myself looking through slightly different parts of my eyeglass lens (or at least I think I am?). No diopter will correct for certain things, for me astigmatism.

 

[Mr Bill]

Your description about 0, -1, and -1.5 confused me a little. What does it mean for my eye to be "focused at infinity" when I look into a waist level viewfinder? What does it mean for "the [image to appear] at 75cm distance" when I look into a waist level viewfinder?

For example, let's say I have a subject (a rabbit) 10 feet away from me. I pull out my camera, look through the waist level viewfinder, pull up the diopter, and look through the diopter as I begin moving the bellows so the lens is hunting for focus. At what point would my eye be "focused at infinity?" At what point would the image be "focused at 75cm?

Let me describe a little procedure that may help you get a handle on what these things mean. From looking at your blog I recollect that you also have a Nikon SLR camera. This can be used to find out the actual distance that your eye "must be focused at."

Here's how to do it... first set up your RZ on a stable surface or mount, pointed at some brighter object. Preferably focus the camera on it, but not strictly necessary.

Next step, using the flip-up magnifier/diopter - whatever you wanna call it - and use the Nikon to look into the magnifier. Use a basic lens, like a 50mm or whatever, in preference to a zoom. Get the Nikon lens pretty close to the magnifier then focus the Nikon on the RZ's ground glass (through the magnifier). (Focus on either the image or grid or dust on the ground glass; any of these will be good enough.)

Whatever distance the Nikon SLR is focused at is the same distance (roughly) that your eye must "focus at" to use RZ camera. In essence the Nikon lens has temporarily stood in for your eyeball as a means to "measure" the "virtual distance."

Here's the next part: without changing the focus setting on the Nikon lens, move the camera forward or back in order to focus on some object (a wall perhaps). Measure the distance between that object and the front of the Nikon lens. (Approximate is plenty good enough.) Whatever distance you measure is the same distance your eye must focus at when you use the RZ, when using that specific magnifier. This will be true no matter where the photographic subject is, whether the rabbit 10 ft away or a distant mountain range.

So now that you know what is the "virtual distance" that your eye must focus at (for this specific magnifier/diopter, at the specific height where it is set) you can see, outside of the cameras, how well your eye does at that "real" distance. You could, for example, set a magazine page, or cereal box, or whatever, at that distance, and see how well you can read it. (Especially try this in dimmer light; the pupil of your eye will open up wider and maybe affect the result.)

Now, this is not gonna answer the question of how to select different diopter, etc., but maybe will help you to better understand what several of the more knowledgeable posters are trying to explain.

 

[mshchem]

One other thing to consider is that someone has probably switched over the diopter in your camera. Stop trying to use the diopter and with your contacts in place try a pair of the $5 reader eyeglasses they sell at Walmart. I wouldn't be surprised if you have some way " not normal" diopter in place

 

[gordrob]

If these are of any use to you and you are interested in them send me a PM.
Gord

 

[Hassasin]

I cannot tell from photo anything, but if you feel focus is off, first thing to do is check screen alignment. I bought a screen that was actually in different plane, even if it looked like never messed with and marks on frame. Changed screen and all’s been well since.

 

[L Gebhardt]

Thanks,

I can see dust and hairs that look fairly sharp when I point the lens at a bright light source.

I can also see extremely thin, faint rings extending out from the center micro prism (not split prism).

Focusing becomes a chore as soon as a move away from a brilliant light source like a light bulb. E.g., if I try focussing on the edge of a cardboard box in the corner of an average lit room. At night, it's still too tough to focus on a model lit by fairly bright street lamps.



Try turning off your VPN if you have one and use this link without the quotations: "" . It's safe. I can add an attachment later.

Your description about 0, -1, and -1.5 confused me a little. What does it mean for my eye to be "focused at infinity" when I look into a waist level viewfinder? What does it mean for "the [image to appear] at 75cm distance" when I look into a waist level viewfinder?

For example, let's say I have a subject (a rabbit) 10 feet away from me. I pull out my camera, look through the waist level viewfinder, pull up the diopter, and look through the diopter as I begin moving the bellows so the lens is hunting for focus. At what point would my eye be "focused at infinity?" At what point would the image be "focused at 75cm?"


I will do the focus test. So far it has been easier to type up for a few minutes between working than pull everything out for a serious test!

. . .

Do any of you happen to know what the diopter on a Yashica 124g is? I'm looking around because I always nailed focus when I owned that camera - even in low light. I always used the diopter on it.

It sounds like you should be just fine focusing the camera if you can see the faint rings and the surface dust. That means the installed lens in the viewfinder is letting you focus where you need to. I sense some confusion about how ground glass focusing works. Simply put the ground glass has a rough texture that scatters the incoming light rays instead of letting them continue straight into your eye. This results in a glowing image originating ate the plane of the ground glass. So no matter what distance the lens is focused at your eye will only need to be focused at plane of the ground glass to see the image. To improve brightness, since the light is scattered, most screens also incorporate a flat fresnel lens that bends scattered light towards a point in effect ensuring more reaches your eyes.

If your screen isn’t at the same distance from the lens as the film plane is you will end up focusing at a plane that isn’t what the film records. So do the focus test I mentioned above, focus on an angled plane with enough detail so you can clearly see if the focused plane is in front or behind the film plane.

I would also recommend looking into a prism if the focus test confirms things are setup correctly. Not only will it ensure you always use the camera on a tripod because of the considerable extra weight, but it should make it much easier to see whole focus screen at once. I have an RZ prism that is starting to desilver at the bottom edge, but not enough to block much of the image. If it will fit your RB you can have it for the cost of postage. I’ve seen conflicting accounts of compatibility.

 

[Mr Bill]

It sounds like you should be just fine focusing the camera if you can see the faint rings and the surface dust. That means the installed lens in the viewfinder is letting you focus where you need to.

I would concur, except... note that the OP says this is "when I point the lens at a bright light source." Then, "Focusing becomes a chore as soon as a move away from a brilliant light source like a light bulb."

This suggests to me that perhaps the OP needs the bright light, shrinking the pupil of his eye, to see things clearly. As though the virtual image seen by viewing through the magnifier is barely within the range where he can focus his eye. (Similar to stopping down a camera lens to increase depth-of-field.) The test I described will pretty conclusively establish what is the effective "viewing distance" to the virtual image. Something that the human eye, on its own, has difficulty doing simply because it is so adaptable.

One other thing to consider is that someone has probably switched over the diopter in your camera... I wouldn't be surprised if you have some way " not normal" diopter in place

I agree, this is a definite possibility.

The test I described would most likely reveal if there is a problem here. If the "virtual distance" through the magnifier is within the general range of 3 to 20 feet then the existing "diopter" is most likely fine. But if, for example, the secondary viewing camera - the Nikon SLR - cannot be focused on the virtual image (through the magnifier) then we know that this is a "not normal" diopter installed.

 

[Alan Edward Klein]

The system isn't designed to cause you to focus on the magnifier itself, or on the focusing screen itself.
It is designed so that when you use the magnifier to view the image on the focusing screen, your eye should be focused in the same way that your eye is focused when you look at something a long way away - effectively infinity.
To make that happen, the standard magnifier will have a built in magnification factor - its "diopter".
If your eyesight is such that you normally need correction to see objects in the distance clearly, you need a magnifier with a different diopter than the diopter needed for those with standard distance eyesight.
The additional confusing factor is that the accessory correction lenses may have their power (diopter) shown in two ways - either the actual diopter measurement, or the offset from the standard diopter measurement that the accessory lens incorporates. And sometimes it can be difficult to know which approach was used by the manufacturer.

This reminds me when I took up scuba diving 45 years ago. I decided to put eyeglass lenses in my mask so I can see better. It's not just a matter of gluing your normal lens to the inside of the mask's glass. Due to light refraction (not defraction) through the mask's glass from water to air, the scene is magnified by about a third. So everything appears a third closer. (Same thing happens with an underwater camera. A 33mm lens acts like a 50mm lens). (It's the same reason the fish isn't where you see it when looking from above the water). So I had to have a special optometrist provide the lens with a different prescription than my regular eyeglasses. They also had to factor in the greater distance from my eye to the lens.

 

[L Gebhardt]

It definitely could be just an issue viewing a dim screen. I find prisms help on the RZ I have. And on the Hasselblad the acute-matte screens are very nice and do seem easier to focus with to me. Getting a faster lens like the 110 f/2.8 should also help if the focal length works. But before recommending spending money I'd do the simple focus test first and confirm there's nothing wrong with the camera, which is my assumption.

 

[itsdoable]

Try turning off your VPN if you have one and use this link without the quotations: <snip>. It's safe. I can add an attachment later.

Your description about 0, -1, and -1.5 confused me a little. What does it mean for my eye to be "focused at infinity" when I look into a waist level viewfinder? What does it mean for "the [image to appear] at 75cm distance" when I look into a waist level viewfinder?

For example, let's say I have a subject (a rabbit) 10 feet away from me. I pull out my camera, look through the waist level viewfinder, pull up the diopter, and look through the diopter as I begin moving the bellows so the lens is hunting for focus. At what point would my eye be "focused at infinity?" At what point would the image be "focused at 75cm?"
....

I don't have VPN, and still have issues viewing anything from Imgur, and it's blocked at my work place.

But I did eventually manage to view the image, which looks fine. So the question is, are your miss-focused images consistently front focused, back focused, or random? That will tell you a bit about the problem.


Diopters; In the absence if other optical system, ie: by itself,

+2 diopter lens is a convex lens with a focal length of 0.5m
+1 diopter lens is a convex lens with a focal length of 1m
0 diopter lens is a parallel glass plane (ie: infinity lens)
-1 diopter lens is a concave lens with a focal length of 1m
-2 diopter lens is a concave lens with a focal length of 0.5m

This is how eyeglass lenses are defined.

If you look through your waist level finders magnifier, the lens that would be 0 diopter would make the focus screen appear sharp when your eyes are focused to infinity. A lens with a diopter labelled -1 would make the focus screen sharp if your eyes are focused at 1m. Keep in mind that you are looking at the focus screen, not the object you are photographing.

If your eyes can view something at infinity clearly, then you should be able to clearly view the screen with a magnifier labelled 0 diopter. Similarly if you can clearly see an object 1m away, the you should be able to see the screen clearly with a magnifier labelled with -1 diopter. Obviously the magnifier with a label of 0-diopter is not a lens with infinity focus (parallel glass), it's a lens with a focal length that is the distance from the eyepiece to the focus screen (typically 4~6cm) - hence the term magnifier. When the magnifier is labelled -1 diopter, that means that lens is modified with a correction equivalent with the 1m concave lens. This can be pretty subtle - for instance a magnifier that uses a 5cm lens would become a 5.05cm lens when it has a -1 diopter correction. They are labelled this way so that you can use your eyeglass diopter correction to buy the correct lens. And a -1 diopter magnifier is only so on the part that it was designed for, as other WLF's and prisms have a different distance to the focus screen.

The bottom line is that if you can clearly see the focus screen (ie: it is a sharp as it'll ever get), then you probably have the correct diopter, and you need to look at other things like front focus, back focus, motion blur, brighter screen, etc... - but keep in mind that correcting these issues will not help if you cannot see the screen clearly.

 

[Mr Bill]

It definitely could be just an issue viewing a dim screen.

Hi, no I'm not saying that the issue is JUST a dim screen. I'm saying that perhaps it is a not-quite-right diopter for the OP's vision. One which is good enough in bright light when the eye's pupil is closed down. But if the pupil is wide open it can perhaps no long accommodate the difference.

For a more concrete example say that my current older eyes could only focus accurately down to about 4 feet (just my eyes, no camera involved). And say that I use a viewfinder magnifier which places the "virtual image" at a distance of 3 feet. One might expect that I could not focus accurately with such a setup. But in reality I MIGHT be able to in bright light, with smaller pupils. However, when the light is dim I would probably lose my ability to focus accurately. Whereas with a slightly different diopter I might be fine.

 

[L Gebhardt]

Hi, no I'm not saying that the issue is JUST a dim screen. I'm saying that perhaps it is a not-quite-right diopter for the OP's vision. One which is good enough in bright light when the eye's pupil is closed down. But if the pupil is wide open it can perhaps no long accommodate the difference.

For a more concrete example say that my current older eyes could only focus accurately down to about 4 feet (just my eyes, no camera involved). And say that I use a viewfinder magnifier which places the "virtual image" at a distance of 3 feet. One might expect that I could not focus accurately with such a setup. But in reality I MIGHT be able to in bright light, with smaller pupils. However, when the light is dim I would probably lose my ability to focus accurately. Whereas with a slightly different diopter I might be fine.

Good point. I hadn't considered the pupil closing down with bright light. My eyes have also lost closeup distance so I fully get what you are saying and it makes sense.

 

[wiltw]

From the RB67 owner manual:

So it appears that you may be seeking the 'adjustment lens value (delta to the standard finder lens)'. I suggest you take your camera into the chain drugstore near you, and put on reading glasses of various strengths as trials, until you find the diopter strength that best permits your eye to visualize the texture of the focusing screen (or edges of the focusing aid in the center). Then, the optical strength diopter to buy is [-1.3 diopter + best drugstore strength], for example, if you find +2 diopter drugstore lens works to best see the focus screen texture, a replacement for the standard magnifier of the focus hood is
-1.5 diopter + (+2 diopter) = +0.5 diopter.
What is not clear is how Mamiya defined the strength for its diopter magnifier...they could have called the correction for YOU either by +2 (relative) or by +0.5 (absolute). ..unfortunately the camera manufacturers vary from one another about how they do that! I surmise that if +2 in the drugstore were best for you, you would want +1 to replace the standard -1.5. But you have the additional uncertainty about the diopter value supplied with your used WLF, there is that issue, too! It seems that if you cannot find a store that you can try out different diopter lenses in your finder, that you seek mailorder store willing to sell you several different strengths and that let you return the ones that do not work for you!

[edit]In reviewing a Mamiya RB67 price list, it appears that they sell ABSOLUTE value "Diopter Correction Lens" for the Single-action hood, values ranging from +1 to -3, including the standard -1.3 diopter

 

[reddesert]

Thanks,

I can see dust and hairs that look fairly sharp when I point the lens at a bright light source.

I can also see extremely thin, faint rings extending out from the center micro prism (not split prism).

Focusing becomes a chore as soon as a move away from a brilliant light source like a light bulb. E.g., if I try focussing on the edge of a cardboard box in the corner of an average lit room. At night, it's still too tough to focus on a model lit by fairly bright street lamps.

The faint rings you see are the pattern of the Fresnel lens that is part of the focusing screen. If you can see the texture, you should be able to focus on some reasonably sharply detailed object in an average lit room. If it's so dim that you can't, then some things to check are: focusing screen dirty, reflex mirror dusty/dirty/damaged coating, lens aperture/shutter not open to full for viewing, lens hazy. Of course, an f/5.6 lens will be dimmer than a f/2 lens on a 35mm SLR. At night, it can be difficult to focus a slow lens without a light source, and some people will put a light (like a mini flashlight) in the scene to use as a focus target, then remove it for taking the picture.

Your description about 0, -1, and -1.5 confused me a little. What does it mean for my eye to be "focused at infinity" when I look into a waist level viewfinder? What does it mean for "the [image to appear] at 75cm distance" when I look into a waist level viewfinder?

For example, let's say I have a subject (a rabbit) 10 feet away from me. I pull out my camera, look through the waist level viewfinder, pull up the diopter, and look through the diopter as I begin moving the bellows so the lens is hunting for focus. At what point would my eye be "focused at infinity?" At what point would the image be "focused at 75cm?"


I will do the focus test. So far it has been easier to type up for a few minutes between working than pull everything out for a serious test!

. . .

Do any of you happen to know what the diopter on a Yashica 124g is? I'm looking around because I always nailed focus when I owned that camera - even in low light. I always used the diopter on it.

If you put your eye all the way up to the WLF without the flip-up magnifier, physically your eye is only a few inches away from the focusing screen. Most people even with perfect vision can't focus that close. The magnifier serves the same function as the eyepiece lens in a 35mm SLR. It is a positive lens with a focal length that is similar to the physical distance between eyepiece and focusing screen. This causes it to make an apparent image of the focusing screen that is about 1 meter away from your eye. This apparent image distance does not depend on where the camera lens is focused. The whole point of a focusing screen is that it is a matte surface on which the lens projects an image, and your eye looks at that image, not through the lens directly.

The apparent image formed by the magnifier is a lot easier to illustrate than describe in words, so I drew a diagram. The eyepiece lens of a 35mm SLR does the same thing, creating an apparent image. The chief difference between 35mm eyepiece and WLF magnifier is that you never use a 35mm SLR without some kind of eyepiece lens - the eyepiece may be permanently attached to the back of the prism.

 

[Maris]

Here's a crude but effective fix I did when I couldn't focus my eyes on the grain of my Mamiya RB67 focussing screen:

From my collection of old and varied reading glasses I tried on successive examples to look down through the WL finder and through its installed magnifier lens.
Eventually I found reading spectacles that enabled a grain sharp view of the Mamiya RB focussing screen. These glasses were obviously the optical power I needed to add to the standard magnifier.
Then I cracked the (cheap!) spectacle frame and removed the plastic lens. The lens got edge shaped on a workshop bench grinder until it was round and the same size as the original Mamiya lens.
I attached the "new" lens concentrically on top of the Mamiya lens with some tiny dots of BluTac. It's been there for years and focus is now easy and perfect.

Downside: Focus is good but only for me. The WL finder closes almost perfectly but not quite .... works, doesn't matter.

 

[wiltw]

I have glasses with progressive lenses. Depending on the camera I'm using I find myself looking through slightly different parts of my eyeglass lens (or at least I think I am?). No diopter will correct for certain things, for me astigmatism.

One of the reasons why the same part of your eyeglasses is not the same for use with different cameras is that the apparent distance on different cameras is not unitorm...some might be 30", some might be 1m (39").

 

[Certain Exposures]

Thanks, everyone! Please feel free to continue to share any thoughts and stories you might have. I am reading everything. I will respond to everyone eventually.

Also, I will update you with that test of the focus point in a few days. I will do it on Delta 100 in HC-110 dilution B.

Let me know if you have any comments on my approach before 7 PM EST today if you happen to see this:

Focus Test Setup

- I'll do it door indoors at night in what I consider an "average lit" room.

- Five AA batteries lined in a diagonal row adjacent to the camera.

- I will make the length between each battery equal to one battery's diameter.

- I'll focus on the middle battery with the 90mm, 150 SF, 180, and 250 wide open. I'll shoot each shot at the listed minimum focus distance of the lens.

- I'll use mirror lock-up for each shot. However, part of me wonders if I should compare ML to no ML.

- I'm debating if I should set a time limit to focus for each shot. Models tend to fidget if you're hunting for focus too long, in my experience. The faster you can compose, focus, and shoot, the better the chance of a sharp shot.

- I'll do the same test with a 150mm F5.6 wide open on my Graflex crown graphic for reference.

. . .


By the way, I'd appreciate it if any of you who regularly use the 180mm and 250mm for portraits could comment on what you changed about your shooting technique or communication with the model, if anything, to improve your results and consistency.

Are you often getting sharp eyes in the F8 range?

 

[Mr Bill]

Let me know if you have any comments on my approach before 7 PM EST today if you happen to see this:

Hi, based on your post #21 I don't think you have established whether or not you are able to focus consistently with your RB. One way to establish this would be, using a fixed setup, to simply focus the camera 4 or 5 times and see if you hit the same point every time. If so, you're fine. If not...?

One way to try this test is to put a small piece of masking tape on the rotating part of the lens barrel. Then focus on some object and make a pencil mark on the tape. Repeat this several times. If the pencil marks all overlap, or close to it, great! But if they are spread out a bit... well, some issue exists.

 

[L Gebhardt]

Thanks, everyone! Please feel free to continue to share any thoughts and stories you might have. I am reading everything. I will respond to everyone eventually.

Also, I will update you with that test of the focus point in a few days. I will do it on Delta 100 in HC-110 dilution B.

Let me know if you have any comments on my approach before 7 PM EST today if you happen to see this:

Focus Test Setup

- I'll do it door indoors at night in what I consider an "average lit" room.

- Five AA batteries lined in a diagonal row adjacent to the camera.

- I will make the length between each battery equal to one battery's diameter.

- I'll focus on the middle battery with the 90mm, 150 SF, 180, and 250 wide open. I'll shoot each shot at the listed minimum focus distance of the lens.

- I'll use mirror lock-up for each shot. However, part of me wonders if I should compare ML to no ML.

- I'm debating if I should set a time limit to focus for each shot. Models tend to fidget if you're hunting for focus too long, in my experience. The faster you can compose, focus, and shoot, the better the chance of a sharp shot.

- I'll do the same test with a 150mm F5.6 wide open on my Graflex crown graphic for reference.

. . .


By the way, I'd appreciate it if any of you who regularly use the 180mm and 250mm for portraits could comment on what you changed about your shooting technique or communication with the model, if anything, to improve your results and consistency.

Are you often getting sharp eyes in the F8 range?

I think it's important to know for sure that your camera is setup correctly. So I would do every thing possible to ensure you are sure of the focus. So bright light, take as much time as you need to trust you got it, mirror lockup, and a flat subject like a detailed paper or a ruler with fine markings and no gaps bigger than what you are willing to tolerate missing focus by (in other words not the batteries). A bright monitor might at an angle with a grid/pattern and focal point might be an easy subject. You can probably do the test for just your longer lenses but the shorter ones will allow you to focus closer so it will be good test to do them all.

Once those shots are done I'd also do your more realistic tests. Try one in dim light but still with the camera on tripod with mirror lockup. One in bright light but without mirror lockup. One focused fast on a real subject like a model's eye. Plan it out so you only waste one roll of film. If you need to I'd cut the number of lenses you test down to the fastest and the slowest ones since if it's the camera the issue should be the same across all the lenses but more visible at closer distances.

edit: I don't shoot a lot of people with film anymore, but you should definitely be getting sharp eyes at f/8.

also see https://petapixel.com/2013/03/12/gh...tion-tool-for-micro-adjustment-enabled-dslrs/, https://www.bobatkins.com/photography/technical/focus_testing.html and https://www.pointsinfocus.com/learning/diy/diy-autofocus-calibration-target/ for some ideas on making a focus testing target.

 

[wiltw]

Rather than a series of cylindrical targets placed along an inclined plane, I would suggest FLAT front surface objects with which there is ZERO ambiguity about the plane of focus... like a series of paperback books, or VCR tapes that you may have, arranged like this example...

In this example, the focus plane was located on the center VCR box, and the inclined plane (ruler) should have had best focus at the 14" location on the ruler...if the actual focus plane were located in front or behind the plane of the center VCR box, it would be detected to be in 'best focus' somewhere else along the ruler.
Canon instructions for AutoFocus testing and microfocus adjustment of its AF dSLRs explicitly instructed to target FLAT PLANE focus targets. Canon also recommended that focus distance be 50 * FL for checking focus calibration.

 

[Certain Exposures]

Apologies everyone - I am pressed for time due to a project.

I shot the RB67 Pro-S test you all suggested today. I also shot the test on my Graflex Crown Graphic as a point of reference. I did it in poor light conditions just similar to what I've been struggling with.

I haven't read any of your messages since 2:30 PM EST yet. Unfortunately, I cannot develop the RB67 shots until Sunday. You might not hear back from me until then.

Here's the Graflex Crown Graphic shot. I did this first because I need to use the camera this weekend. Detailed notes are in the Imgur link:



Also, here's the Imgur link .

 

[Certain Exposures]

I had enough time to develop the shots yesterday due to a change of plans.

I’ll try to scan these frames sooner than later.

 

[Certain Exposures]

I had enough time to develop the shots yesterday due to a change of plans.

I’ll try to scan these frames sooner than later.

You know what they said about best-laid plans of mice and men...

Here's a link to scans from the focusing test. I haven't made time to read all your latest replies yet but I will. I will follow up with you all early this week.

Please let me know what you think based on these results:

Mamiya RB67 Pro-S Focusing Test

 

[L Gebhardt]

It's hard to tell using round batteries with a lot of space between them, but your camera seems fine. If it's hard to focus with the installed diopter try removing the finder and use your large format loupe to see how it compares. You might be able to just drop it into the finder if it's a long one.

Or just shoot with the 150 soft focus lens all the time and you'll never worry about getting sharp focus at all

 

[Certain Exposures]

Let me describe a little procedure that may help you get a handle on what these things mean. From looking at your blog I recollect that you also have a Nikon SLR camera. This can be used to find out the actual distance that your eye "must be focused at."

Here's how to do it... first set up your RZ on a stable surface or mount, pointed at some brighter object. Preferably focus the camera on it, but not strictly necessary.

Next step, using the flip-up magnifier/diopter - whatever you wanna call it - and use the Nikon to look into the magnifier. Use a basic lens, like a 50mm or whatever, in preference to a zoom. Get the Nikon lens pretty close to the magnifier then focus the Nikon on the RZ's ground glass (through the magnifier). (Focus on either the image or grid or dust on the ground glass; any of these will be good enough.)

Whatever distance the Nikon SLR is focused at is the same distance (roughly) that your eye must "focus at" to use RZ camera. In essence the Nikon lens has temporarily stood in for your eyeball as a means to "measure" the "virtual distance."

Here's the next part: without changing the focus setting on the Nikon lens, move the camera forward or back in order to focus on some object (a wall perhaps). Measure the distance between that object and the front of the Nikon lens. (Approximate is plenty good enough.) Whatever distance you measure is the same distance your eye must focus at when you use the RZ, when using that specific magnifier. This will be true no matter where the photographic subject is, whether the rabbit 10 ft away or a distant mountain range.

So now that you know what is the "virtual distance" that your eye must focus at (for this specific magnifier/diopter, at the specific height where it is set) you can see, outside of the cameras, how well your eye does at that "real" distance. You could, for example, set a magazine page, or cereal box, or whatever, at that distance, and see how well you can read it. (Especially try this in dimmer light; the pupil of your eye will open up wider and maybe affect the result.)

Now, this is not gonna answer the question of how to select different diopter, etc., but maybe will help you to better understand what several of the more knowledgeable posters are trying to explain.

Thanks, what do you mean in the sentence I bolded? Do you mean that I should measure the gap between the front of the Nikon lens and the top of the diopter I focused through on the RB67? Or do you mean I should measure the distance between the Nikon lens and the object itself in the real world?

I also italicized a couple of your sentences. My vision is best close up. The further away anything is in general, the worse it gets. If I understand your point, I should use a diopter that makes the virtual image as close as possible. I will try your test once you have a second to clarify that point about measuring the distance.