Mamiya RB67: how to choose eye correction lenses

I've got a Mamiya RB67 with both "chimney" and pentaprism view finders. Being somewhat presbyoptic, I'm not entirely happy with either the magnifier lens in the "chimney" view finder, or the straight view through the pentaprism. On the auction site, correcting lenses are available for both, in a variety of strenghts. However: it seems there's a basic correction built into the pentaprism, and the standard magnifier lens is not "+0", so I'm rather confused. I know that I need glasses at about +1 diopters to comfortably view far-away objects -- so how do I translate that into Mamiya correction lenses?

there are diopters you can buy for those viewfinders.

the best way to find your diopter is take your camera n viewfinders to the store.

with no lens, camera facing a nicely lit wall. insert the diopter and as you look through the vf.... check to see how sharp the markings on your focusing screen. the sharpest image is the right one for you.

the more technical n easiest but not cheapest is to have a place that makes glasses test your eyes n match you to the diopter you need for your camera.

No store around here that carries those things, I'm afraid, so I'll have to buy them untested, over the net.

Now, I *have* had my eyes tested; I need +0.75 for regular walking around use. What I'm wondering is if that means I need +1 diopter lenses (which would be the closest to +0.75) for the camera viewfinders, too. The confusing factor is that the standard magnifier lens for the chimney viewfinder is specified as -1.5, and the prism viewfinder is said to have -0.8 built in. So, do I really need +2.25 and +1.55, respectively, rounded to +2 for the chimney, and +2 or +1 for the prism?

hahaha yeah that is a problem figuring what you need.

The wlf has a removable diopter, the prism doesnt.

The chimney is adjustable... turn the chimney eye diopter till the screen focuses with no lens on the body.

Maybe do a search, there have been lots of threads on this subject.

A lot of people swear by the tilt-up magnifiers for the prisms - they only give you the center area as I understand it.

The diopter thing confuses me as well, I've never found a guide to how this works. I'd be curious to find something out though - on my Nikon DSLRs, there's a diopter knob by the VF, and you just dial it in til it's right. Always wondered if there's a way to translate that to add-on diopters.

Just looked at my D7100, and the diopter is set 3 clicks to the "plus" side - I think the entire range is 4 or 5 clicks each direction. Wonder if there's a real-world translation of that?

Dead Link Removed is -2 to +1, but doesn't state what each "click" is worth. But seems to me this could be a good way to get an idea for what correction you need.

I'm almost-legally-blind nearsighted, but contacts correct this just fine. Now I wear bifocal contacts, but I still have to wear readers to work on the computer/etc., so my prescription has made me functionally farsighted, and Nikon's page confirms this, that farsighted users need a "plus" setting.

If I understand the OP's question,

• the standard viewfinder eyepiece has a correction (let us assume it is -1 diopter for discussion purposes)
• so assuming that for my vision I need +1 diopter for reading (compared to my standard Rx -3.0 for distant vision)

...Do I (the RB67 user)

1. look for a '0' eyepiece from Mamiya (which is +1 compared to the -1 diopter standard eyepiece +1 + (-1) = 0), or do I
2. look for a '+1' eyepiece from Mamiya (+1 from the standard eyepiece value)

Unfortunately there is not a single common practice followed by all camera manufacturers! Manufacturer A might say "Buy the the '0' eyepiece option", but Manufacturer B says "Buy of '+1' eyepiece option" simply because their labelling adheres to different conventions!

wiltw said:

If I understand the OP's question,

• the standard viewfinder eyepiece has a correction (let us assume it is -1 diopter for discussion purposes)
• so assuming that for my vision I need +1 diopter for reading (compared to my standard Rx -3.0 for distant vision)

...Do I (the RB67 user)

1. look for a '0' eyepiece from Mamiya (which is +1 compared to the -1 diopter standard eyepiece +1 + (-1) = 0), or do I
2. look for a '+1' eyepiece from Mamiya (+1 from the standard eyepiece value)

Unfortunately there is not a single common practice followed by all camera manufacturers! Manufacturer A might say "Buy the the '0' eyepiece option", but Manufacturer B says "Buy of '+1' eyepiece option" simply because their labelling adheres to different conventions!

Click to expand...

From the RB67 owner manual:



So it appears that you seek the 'adjustment lens value (delta to the standard finder lens)'

For the OP, we don't care what you need for walking around, what we need to know is what lens diopter value allows you to READ something at a distance of about 30-36" away (again, there is not a single apparent viewfinder distance standard followed by all manufacturers!). Your normal distance lens is +0.75 diopter, but what adjustment value do your eyes need for reading?!

wiltw said:

For the OP, we don't care what you need for walking around, what we need to know is what lens diopter value allows you to READ something at a distance of about 30-36" away (again, there is not a single apparent viewfinder distance standard followed by all manufacturers!). Your normal distance lens is +0.75 diopter, but what adjustment value do your eyes need for reading?!

Click to expand...

In other words, if your usual distant vision lens prescription is +0.75, is your reading prescription +2.25, which means that your reading adjustment is +1.50?... so that you need to buy +1.50 in the eyepiece correction.

My Mamiya RB67 and Bronica GS1 finders have dioptre correction lenses fitted but I made them myself.

Because my eyes no longer accommodate I have lots of cheap (like about $2) reading glasses of powers from +0.75 up to +3.0 lying about to suit whatever task I'm pursuing. When I look through a camera viewfinder and the view is blurry I try all the various reading glasses to find the one that gives me a sharp image. That's the dioptre strength I need to add. Then I extract the plastic spectacle lens from the frame and cut and shape (hacksaw and file) it to fit the camera viewfinder eyepiece. Because the tiny piece of lens is so light a couple of miniscule dots of Blu-Tac or similar will hold it in place. An hours work and a trip back to the bargain shop for replacement readers is the total cost.

Well, I went ahead and ordered "+1" ocular lenses for the RB67 (chimney and prism), and for my Pentax MX as well. My optician rechecked my eyes the other day, and I need +0.75 on the left eye, +1.25 on the right for my distance prescription. Turns out the new eye pieces work just fine - but marginally better for my left than for my right eye; with the left one, I get a perfect view of the ground glass without effort, while I need to actively focus the right eye a little bit.

So it seems to me, anyway, that it's the distance prescription that should be matched, for Mamiya and Pentax both. This fits my recollection of how I could, when I was much younger, using the MX, keep both eyes open, and see the viewfinder superimposed on what the other eye was seeing, with a sharp image, and sharp viewfinder indicators.