Astigmatism and rangefinders

[pklein]

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This is really interesting. I am using a magnifier with an adjustable diopter correction, and since I started using it, focusing is much easier. It also helps conpensate for the changes that happen between eye appointments when your over 40 (OK, OK, over 50!).

 

The adjustable diopter works at different settings for my glasses and my contact lenses, but I think the "seeing" is better and focusing is easier with my glasses. Maybe that's because glasses correct for astigmatism better. Of course, I can see the edges of the 28mm frame better with contacts.

 

--Peter

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[Bob Ross]

That is really interesting Luigi. In looking at your example, I began wondering how subject distance figures into the astigmatism thing. Do distant subjects have any different affect on this phenominum, from near subjects? As subjects get more distant the DOF might begin to mask the affect, if it stays the same, but if it gets worse at farther distances, it could also aggravate what we've seen as aperture focus shift.

Bob

[Shootist]

That is really interesting Luigi. In looking at your example, I began wondering how subject distance figures into the astigmatism thing. Do distant subjects have any different affect on this phenominum, from near subjects? As subjects get more distant the DOF might begin to mask the affect, if it stays the same, but if it gets worse at farther distances, it could also aggravate what we've seen as aperture focus shift.

Bob

The Leica viewfinder is not straight through, IE you do not look through it from front to back. What comes in the front goes through a prism and is projected through the back, eye piece, with the rangefinder patch added. That is how they can have a X.68 magnification and everything in the viewfinder is displayed at a fixed distance of about 7 feet, even if what you are looking at is 10-30-100-1000 feet away (it just smaller). The only difference is for subjects/objects that are closer then 7 feet.

My +1 diopter is fine for focusing on objects at 7 feet + but to get a good clear image in both the viewfinder and rangefinder patch for subject that are closer then 7 feet I need to use a +1.5 diopter.

[jaapv]

That is really interesting Luigi. In looking at your example, I began wondering how subject distance figures into the astigmatism thing. Do distant subjects have any different affect on this phenominum, from near subjects? As subjects get more distant the DOF might begin to mask the affect, if it stays the same, but if it gets worse at farther distances, it could also aggravate what we've seen as aperture focus shift.

Bob

 

Basically a rangefinder measures the difference in angles. As astigmatism is an aberration that increases with the angle, it is logical that it should affect rangefinder focussing. With close subjects the angles are steeper, so the influence of astigmatism should be larger.

 

Focus shift is something different. that is caused by spherical aberration on the lens. The lightrays that pass through the outer zones of the lens will focus closer than the ones in the centre. The plane of focus is the area of "best focus"of a mix of these rays. So if you close the diaphragm, the closefocussing part of the compromise is cut off, causing the plane of focus to shift away. The focus fault that was made in the first place, be it through mechanical fault of the rangefinder/ focussing mechanism or the eye of the user will stay the same. The only thing that could happen is that the plane of focus, by chance, shifts into the (incorreectly) focussed plane.

[Phillip_Meyer]

The solution, Philip, is to visit an optician and try focussing the camera with the correct trial glass between your eye and the VF. The way you can rule out your eyes as the cause. It seems unlogical, but rangefinders require near-perfect eyesight correction.(or enough experience to compensate)

 

Actually, I am an Optician

 

Someone also mentioned trouble focusing after LASIK, my understanding is (and I am by no means an expert) that the scar tissue on the cornea after this surgery reduces visual acuity significantly, for example, you would not be able to resolve less than half a degree at about normal reading distance.

 

Also, I agree it would be beyond most optical practices to produce a lens of any power to fit the eye piece. These are probably created using a high precision mould, I can't see any way you could grip a lens that small to polish it otherwise.

[Daniel Ortego]

To add another dimension, it is now possible to have eye implants that hold true for corrections without any degradation over time. This is very different from standard laser corrective surgery. The down size is 8k per eye.

Regards,

[dpattinson]

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To add another dimension, it is now possible to have eye implants that hold true for corrections without any degradation over time. This is very different from standard laser corrective surgery. The down size is 8k per eye.

Regards,

 

Sounds like the perfect M accessory - we can only imagine how much the leica branded ones would cost. Of course, you'd then have to fork out for some UV blocking contact lenses as there wouldn't be enough room for a proper UV filter in the implants

[luigi bertolotti]

Sounds like the perfect M accessory - we can only imagine how much the leica branded ones would cost. Of course, you'd then have to fork out for some UV blocking contact lenses as there wouldn't be enough room for a proper UV filter in the implants

 

LOL, I'd suggest Mr. Kaufmann to establish a "Leica optical surgery clinic", a fine building not far from Solms...pleasant country location... people that go there to take a surgical operation, that, of course, besides the std. medical cures, guarantees a SPECIFIC result to fit the Leica RF... cost in the range of 10Keuros per eye... but with a personal GIFT to any patient (RF magnifier, for instance...) :D

[Ronazle]

Luigi, I use the same target, which is excellent for showing how far one's focus is off, but it is terribly hard to focus on the very small line. I get a little better results by putting my camera vertical, which splits the image more clearly, for me anyway. I think I need to place some 45 degree lines across the "focus here line". Of course, distance matters (a lot). I do use a 1.25 magnifier when focusing on this target, it helps a little. Ron

[gyoung]

It should not be forgotten that a dioptre correction lens will not correct for an astigmatism. Consequently, anyone with an astigmatism would need to have correction for that "off-camera"

 

I am a left-eye shooter, with a mild astigmatism and always wear my glasses when shooting. I tried a dioptre corection lens, but had no joy with it at all.

 

I steared clear of the M2/4/6 viewfinder for a long time because I could not see the 35 frame with my glasses on, I tried an off the shelf corection lens but my eyesight has so much astigmatism that it was hopeless. The optician is a real photo enthusiast and we always have a good chat about optics, he said he would have a go at making a correction lens with the astigmatism corrected but it would, of course, have to be rotated 90 degrees for vertical shots (unscrew the lens?). In those days large lenses were fashionable/all you could get, we found a frame with small enough lenses so that I can push the lens back a little into the eyesocket under my eyebrows and then I can see the 35 frame. Would be less of a problem now with the very small lenses which are 'in vogue'.

 

Gerry

[piblondin]

Can someone explain how the rangefinder patch would look different to someone with a slight astigmatism? I'm able to focus correctly, but not as easily as I would like to. Thanks!

[Guest Chris M]

All I can do is speak for myself, I now have wet machular degeneration, so rangefinder (anything)//(manual focusing) is out of the question for me (period). However, during I'd say from about 18 months ago and back I will tell you that having the correct eye glasses or contacts along with (regular) eye exams is the best way to decide if you want to continue using a rangefinder camera, if you are a patient person and are not in a rush to fire off a whole sequence of shots ? then I think a rangefinder system should be quite rewarding for you. I lasted this past 18 months not knowing exactly what was wrong with my eyes until I finally went for an early eye appointment which wasn't covered by my insurance, I'm only able to see an eye Dr. once every two years with out having to pay full boat out of my pocket, call me cheap in that way, but that (was) me then, but not anymore though since my diagnoses. So talk to your eye Dr. about you and your Leica rangefinder and have him recommend or refer you in the rite direction, after al that, you should then decide if you will want to continue squinting, tearing up and straining to focus correctly through that teeny tiny little viewfinder hole.

 

chris m.

[jaapv]

Can someone explain how the rangefinder patch would look different to someone with a slight astigmatism? I'm able to focus correctly, but not as easily as I would like to. Thanks!

Post 24

[ndjambrose]

I also have astigmatism in my dominant eye. It's fairly mild but enough to make RF focusing highly inaccurate without my glasses. Astigmatism is an interesting condition in that it can't be easily corrected in a diopter because it's not a magnification problem. It's also critical with RF focusing as it affects the ability (or inability) of the eye to judge contrast in edge detail. The astigmatic effect is the same regardless of whether you shoot with one or both eyes open. While it may look as though there is an improvement when opening the non-shooting eye, the only thing that changes is your depth perception -- but not the ability to judge focus. One eyeball doesn't become magically spherical just because you opened the other.

 

It might be useful for anyone with persistent rangefinder focus problems to see an optician, if only just to rule it out. It can sometimes avoid an incredible amount of unnecessary frustration with calibrating the RF or lens.

[ho_co]

fwiw

direct link to the Ctein article Bob mentioned at top is:

The Online Photographer: Rangefinder Follies

[Jeff S]

Ok, now that this 2 year old thread has come back to life, I have a perhaps dumb question.

 

With astigmatism (and other vision imperfections), I've been effectively (I think) using Ms for decades with my prescription glasses (corrected for all issues). However, recognizing that M viewfinders have a minus .5 diopter correction built in, does this suggest that using a plus .5 diopter lens over the VF...while still using my glasses...would yield even more effective focusing?

 

Of course I can go to the optician and experiment, but can anyone address the fundamental principle(s) at work here? I read somewhere that the VF negative diopter is there to accommodate 'normal' eye requirements, but of course I can't believe all I read.

 

Jeff

[01af]

... recognizing that M viewfinders have a -0.5 diopter correction built in, does this suggest that using a +0.5 diopter lens over the VF—while still using my glasses—would yield even more effective focusing?

No.

 

The -0.5 dpt preset of the eyepiece just means the viewfinder controls—i. e. frame lines, rangefinder patch, and LEDS—will appear at a virtual distance of 2 m/6 ft to the normal-sighted (or properly corrected) eye. So anybody who can see sharp with the naked eye at a distance of two meters will be able to use the camera without glasses.

[rolu]

No.

 

The -0.5 dpt preset of the eyepiece just means the viewfinder controls—i. e. frame lines, rangefinder patch, and LEDS—will appear at a virtual distance of 2 m/6 ft to the normal-sighted (or properly corrected) eye. So anybody who can see sharp with the naked eye at a distance of two meters will be able to use the camera without glasses.

 

Interesting, do you happen to know or can you estimate, what the virtual distance would be with a +-0 dpt.?

And more importantly: doesn't a -0.5 dpt. preset negatively impact the perception of the RF patch?

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Hallo,

Look here: Leica M

[01af]

Interesting, do you happen to know or can you estimate, what the virtual distance would be with a +-0 dpt?

Infinity.

 

 

And more importantly: doesn't a -0.5 dpt preset negatively impact the perception of the RF patch?

No.

[Jeff S]

No.

 

The -0.5 dpt preset of the eyepiece just means the viewfinder controls—i. e. frame lines, rangefinder patch, and LEDS—will appear at a virtual distance of 2 m/6 ft to the normal-sighted (or properly corrected) eye. So anybody who can see sharp with the naked eye at a distance of two meters will be able to use the camera without glasses.

 

Thanks. I figured something like this had to occur, or else people with normal vision would need diopter correction.

 

Jeff