Finder diopter lens as magnifier?

[Deleted member 88956]

While I am specifically looking to change magnification ratio on some MF finders, I am not sure whether my understanding of this is correct.

Finder diopter lenses are generally referred as eye correcting lenses, and at the same time they do affect how image viewed is magnified. Not sure though if both work in tandem and for a good sight still essentially allow for increase in magnification without affecting the actual use of the finder.

Bronica, Mamiya and possibly some others supply most finders with -1.5 diopter as standard. Other correcting lenses are available. Is it really all there is to it, switch diopter and focusing will get a boost?

 

[Bikerider]

Possibly they will work but not very well. They are designed for use by folk with defective eyesight. I have to wear glasses normally for reading and following your description what you want, using them in conjunction with my Minolta Autocord I could not see when it was in focus or not. Remove the glasses it was much easier.

 

[AgX]

Eyepiece-correcting lenses (diopter lenses as you call them) are single elements. They can be either a converging- or a dispersing lens.

What they are intended for is getting the ground-screen in focus again for ones non-standard (non-focusing) eyes. With those eyes one cannot exchange them without losing focus.

 

[Deleted member 88956]

Eypiece-correcting lenses (diopter lenses as you call them) are single elements. They can be either a converging- or a dispersing lens.

What they are intended for is getting the ground-screen in focus again for ones non-standard (non-focusing) eyes. With those eyes one cannot exchange them without losing focus.

I call them what camera makers call them. Reading through Bronica sales materials they seem to be suggesting what I was hoping for, but what you say is what I was actually expecting yet not hoping for.

 

[AgX]

Well, I was speaking of photographers who no longer can focus (sufficiently) any more.

Anyway, all manufacturers of system-SLRs at least offered as attachment to their eyepieces at least a magnifying loupe (with adjustable focusing). Moreover, some of the right-angle attachments offered an added loupe feature too. These are also offered by 3rd party manufacturers.
However such loupes only show a central fraction of the ground-screen image. Maybe you want full coverage.

 

[Deleted member 88956]

Well, I was speaking of photographers who no longer can focus (sufficiently) any more.

Anyway, all manufacturers of system-SLRs at least offered as attachment to their eyepieces at least a magnifying loupe (with adjustable focusing). Moreover, some of the right-angle attachments offered an added loupe feature too. These are also offered by 3rd party manufacturers.
However such loupes only show a central fraction of the ground-screen image. Maybe you want full coverage.

What got me started this thread were reported by some users concerns about viability of Bronica's Rotary Finder in general use being darker and someone even stating it had zero magnification (in fact it is 0.82 X) and thus was no help in achieving quick and good focus. The finder itself is surely not for every occasion as it quite large and rather heavy to begin with. But it does provide some viewing access with large eye cup. Given that Bronica produced diopters for this finder from +1.5 to - 4.5 I figure I ask if this might be a way to enlarge image without resorting to any other solution.

As I started this thread that finder came along at relatively decent price, so I got one coming and will probably give some deeper feedback in a dedicated thread. Not sure why, but it appears to be not so much talked about, perhaps it was too unique and instead of taking hold, slipped into oblivion much too soon.

 

[ic-racer]

Diopter "correction" accessory lenses for pentaprisms will be either weakly positive or negative. Neither will make a good magnifying lens because there is another lens, inside the pentaprism that is usually stronger positive (magnifying). In terms of flip-up finders, those 'diopter lenses' will be stronger and almost always positive. They might make better magnifiers.

 

[abruzzi]

I don't think they'll work for what you want. The just adjust the focus point for your eyes. Default is 1 meter, but the diopter brings it closer for further away optically. I don't think it has any impact on magnification (I say that because on my F4 which has adjustable diopter, when I adjust, it changes focus, but not size at all.) I don't think Bronica made a viewfinder magnifier attachment, but you might look to see if some other brand's magnifier fits. This is the one I'd want, if it fits:

https://www.ebay.com/itm/MINT-Asahi...r-for-6x7-67-67II-From-Japan-108/143399168183

 

[Deleted member 88956]

I don't think they'll work for what you want. The just adjust the focus point for your eyes. Default is 1 meter, but the diopter brings it closer for further away optically. I don't think it has any impact on magnification (I say that because on my F4 which has adjustable diopter, when I adjust, it changes focus, but not size at all.) I don't think Bronica made a viewfinder magnifier attachment, but you might look to see if some other brand's magnifier fits. This is the one I'd want, if it fits:

https://www.ebay.com/itm/MINT-Asahi...r-for-6x7-67-67II-From-Japan-108/143399168183

What led me to strat this was Bronica's own brochure where they state finder's magnification while also specifically stating with what mounted diopter that ratio applies to, implying there is a connection. Bronica does not make to my knowledge any specific magnifying device for ETRS at least (like Mamiya's chimney adjustable magnifier for RB I have, which is great) for critical focusing. There is a chimney for EC and S line but I don't remember if that has magnification built in.

 

[AgX]

What led me to strat this was Bronica's own brochure where they state finder's magnification while also specifically stating with what mounted diopter that ratio applies to, implying there is a connection.

There is a connection, but the effect is less than you think.
From your ignorance I assume that you are lucky still not to need glasses... If with your glasses set up you would realize that there there is not only a change of sharpness (with young eyes you might counter this), but also a change in image scale. Try it yourself.
However the change of scale is much less than a eypiece loupe would offer, but large enough to be stated in a manual, if one wanted to do so.

 

[John Koehrer]

You could ask a local optometrist to let you try different diopters with your finder & see if anything would be what you have in mind.

 

[reddesert]

Diopters = 1 meter / focal length, so a +1 diopter lens is a convex lens with a focal length of 1 meter, a +2 has a focal length of 0.5 meters = 50 cm, and so on.

By convention, the power of a magnifying lens is defined as magnification = 25 cm / focal length. (The idea, I think, is that a person whose close vision is still good can usually focus as close as 25 cm un-aided, so that's a reasonable definition of 1x.) So a 4x loupe has a focal length of 6.25 cm. This would be +16 diopters.

From this, you can see that typical magnifying lenses, like the flip-up magnifier on a TLR, are much stronger than typical diopters. Additionally, one also has to be concerned about where the lens is in the system (distance from lens to focusing screen), but that's probably not so much of an issue.

I have a camera with adjustable diopters and IIRC, if I tune it to something other than ideal, I don't get any useful magnification. The image just looks out of focus.

 

[Deleted member 88956]

Interesting stuff guys, thanks.

 

[moto-uno]

^^ Thanks for the description , Peter

 

[Deleted member 88956]

Just so don't sleep on this for too long, I am still puzzled by all above and finders we're discussing being supplied standard with a -1.5 diopter designation. Wouldn't that be a Zero? In Bronica's case, what I see in their descriptions all but AE III finders are supplied with -1.5, AE III has a neutral eye piece. Isn't this confusing the issue?.

Just to be clear, I was after replacing eye piece lens with a different rating as available by original manufacturer, no home made workarounds. While all I have seen is actually EYE CORRECTING lens, I don;t really get the -1.5 being supplied as standard.

 

[AgX]

I am still puzzled by all above and finders we're discussing being supplied standard with a -1.5 diopter designation. Wouldn't that be a Zero? .

One may argue what is the best diopter value for a camera eyepiece. To take into account may be the relief (most comfortable) human-eye lens adjusting for the standard eye. Or may be better for the average user etc.
The eyepieces that come to my mind all have negative diopter values (eg. -1).


(As a side note: correcting lenses for eypieces as offered by the camera manufacturer may be designated either for their own diopter value, or for the effective value for the combo of the correcting lens with the eyepiece.)

 

[MattKing]

(As a side note: correcting lenses for eypieces as offered by the camera manufacturer may be designated either for their own diopter value, or for the effective value for the combo of the correcting lens with the eyepiece.)

What he said.
The diopter number is just a reference to how the lens compares to one that focuses normally at a standardized distance - normally one meter. A zero (0.0) diopter system focuses normally at that distance.
A -1.5 diopter system focuses naturally to a different distance. That most likely gives better results for most users' eyesight.