Prescription glasses, rangefinder, magnifier and focus-precision (APO-Summicron-M 90 ASPH.)

[DadDadDaddyo]

Advertisement (gone after registration)

I'm coming late to this topic, but hopefully with a useful contribution. I apologize for the length, but there are several separate-but-not-unrelated issues under discussion here. Several points already made deserve emphasis. 

Above all, the effective optical distance from your eye to the projected focus patch does not vary with camera-to-subject distance, and it does not change as you change the focus (setting-for-distance) of the lens.

The effective optical distance from your eye to the projected frame lines is the same as it is to the focus patch, and, again, does not change with camera to subject distance, and it also does not change as you focus the lens.

The focus patch and frame lines are generated by a subsystem of their own, integral to the viewfinder system, and projected onto a screen within the finder.

The viewfinder itself is a comparatively simple fixed-focus telescope. Its focus setting does not change as you change the focus setting of the lens. That said, looking through the viewfinder at a subject element that's close to the camera versus looking at the horizon at distance does require your eye to shift its focus, at least a little. It's not like looking at an lcd screen. 

So, it's a question of looking at (the projected focus patch) versus looking through (the finder view around the projected focus patch) for composition.

Suggestions above about practicing the focus movement are spot-on. It may be helpful to mentally separate focusing from composition.

Try this: take a quick look overall for composition, then select the subject point you'll use as the focus point, then turn your attention to the focus patch itself and bring that subject point into focus (with practice, a one-way move, not back and forth and back and forth). To finish, return your attention to the overall view once again for final composition. At this point you can ignore the focus patch; you've focused already, unless in the throes of composition your camera-to-subject distance has changed. With practice this all becomes so automatic that you'll do it without conscious effort. It's at that point that the rangefinder magic takes place and the camera simply disappears in your hands and becomes an extention of seeing. 

But your view of the focus patch, when you look at it, needs to be clear and in focus. It's that view (of the focus patch) that we adjust, either with glasses, or with different diopter auxiliary lenses added to the viewfinder. 

I'm a big fan of progressive eyeglass lenses, as long as they're true progressives, rather than simply no-line bifocals with only two effective ranges. You can quickly learn which part of the progressive eyeglass lens to look through for the effective distance to the focus patch - if they're true continuous progressives. If they're no-line bifocals and if neither distance zone is correct for the optical distance to the focus patch, you may run into problems, even playing with diopter add-on lenses.

All of these complexities joined forces when, with the M series, Leica moved the focus patch into the same optical system as the viewfinder. In the older I, II, and III series camera bodies, the viewfinder and rangefinder windows were separate.

Finally, cataracts, and surgery. There are some excellent threads here in the forum covering this. I've had lens replacement surgery on both eyes to correct cataracts, and it was both hugely important and utterly beneficial. Check out those other threads. I would urge anyone facing it to embrace the possibility for surgery for cataracts. It can be simply life-changing.

 

[Advertisement]

The Leica Q3 is available for pre-order at B&H Photo Video and Adorama

[Jeff S]

6 hours ago, DadDadDaddyo said:

I'm coming late to this topic, but hopefully with a useful contribution. I apologize for the length, but there are several separate-but-not-unrelated issues under discussion here. Several points already made deserve emphasis. 

Above all, the effective optical distance from your eye to the projected focus patch does not vary with camera-to-subject distance, and it does not change as you change the focus (setting-for-distance) of the lens.

The effective optical distance from your eye to the projected frame lines is the same as it is to the focus patch, and, again, does not change with camera to subject distance, and it also does not change as you focus the lens.

The focus patch and frame lines are generated by a subsystem of their own, integral to the viewfinder system, and projected onto a screen within the finder.

The viewfinder itself is a comparatively simple fixed-focus telescope. Its focus setting does not change as you change the focus setting of the lens. That said, looking through the viewfinder at a subject element that's close to the camera versus looking at the horizon at distance does require your eye to shift its focus, at least a little. It's not like looking at an lcd screen. 

So, it's a question of looking at (the projected focus patch) versus looking through (the finder view around the projected focus patch) for composition.

Suggestions above about practicing the focus movement are spot-on. It may be helpful to mentally separate focusing from composition.

Try this: take a quick look overall for composition, then select the subject point you'll use as the focus point, then turn your attention to the focus patch itself and bring that subject point into focus (with practice, a one-way move, not back and forth and back and forth). To finish, return your attention to the overall view once again for final composition. At this point you can ignore the focus patch; you've focused already, unless in the throes of composition your camera-to-subject distance has changed. With practice this all becomes so automatic that you'll do it without conscious effort. It's at that point that the rangefinder magic takes place and the camera simply disappears in your hands and becomes an extention of seeing. 

But your view of the focus patch, when you look at it, needs to be clear and in focus. It's that view (of the focus patch) that we adjust, either with glasses, or with different diopter auxiliary lenses added to the viewfinder. 

I'm a big fan of progressive eyeglass lenses, as long as they're true progressives, rather than simply no-line bifocals with only two effective ranges. You can quickly learn which part of the progressive eyeglass lens to look through for the effective distance to the focus patch - if they're true continuous progressives. If they're no-line bifocals and if neither distance zone is correct for the optical distance to the focus patch, you may run into problems, even playing with diopter add-on lenses.

All of these complexities joined forces when, with the M series, Leica moved the focus patch into the same optical system as the viewfinder. In the older I, II, and III series camera bodies, the viewfinder and rangefinder windows were separate.

Finally, cataracts, and surgery. There are some excellent threads here in the forum covering this. I've had lens replacement surgery on both eyes to correct cataracts, and it was both hugely important and utterly beneficial. Check out those other threads. I would urge anyone facing it to embrace the possibility for surgery for cataracts. It can be simply life-changing.

 

You might want to read this entire thread, from start to finish, including later contributions from jdlaing, 01af, Rick and Jaap. No unanimity of thought regarding the topic.

Jeff

Edited August 5, 2024 by Jeff S

[Strmbrg]

My "sight-defect" is not at all extreme. But when I use the Bresson, the clearest view is when I have it max screwed out. Strange...
The scale on it is marked "-150 to +350". I don't understand what that mean. Diopter-values are normally expressed in figures like -2,0 or +1,5.

 

[jaapv]

On 8/5/2024 at 6:23 PM, Jeff S said:

You might want to read this entire thread, from start to finish, including later contributions from jdlaing, 01af, Rick and Jaap. No unanimity of thought regarding the topic.

Jeff

But we all agree: trial and error gives th best result. Leica dealers used to have a diopter wheel for the purpose. 

[Jeff S]

15 minutes ago, jaapv said:

But we all agree: trial and error gives th best result. Leica dealers used to have a diopter wheel for the purpose. 

We agree trial and error gives a good result.  I would think Rick, as an eye doc, would argue for some data as well, for best result. I use trial diopters at my local optician.

Jeff

[spydrxx]

I picked up a used diopter wheel (not Leica) a few years ago and routinely use it when I acquire another camera if it doesn't have a built in diopter adjustment or isn't perfectly in focus while wearing my progressive lens eyeglasses. The only caution I would offer is that some diopter lenses (cheap ones) may not be as accurate as those sold by the top providers. I've picked up a couple of Asian ones which seemed to be off by a quarter diopter or so. Best option is to try the one you purchase before committing your cash, if possible.

[spydrxx]

Advertisement (gone after registration)

Over the years and many posts there have been a variety of suggestions on how to adjust rangefinders to infinity focus...most centering around focusing on the moon, stars, towers 1000 meters away, etc. Years ago I found that none of those things were available to me and my new eyeglasses, and my camera definitely needed a touch-up infinity focus adjustment. With a little research I found a method which works in inclement weather, no distant vertical lines, etc. While some will claim it isn't perfect, it has worked as a standby for me for many years. Although the photos show the concept on a Barnack, I can testify that it works on all manual focus rangefinders I've owned over the years.

1. You begin by measuring the distance between the centers of the two windows the rangefinder uses. Here I did it with a simple drafting compass.

2. You transfer that distance to a white card, on one side of the card you draw a cross with normal orientation, and on the other point you measured, you draw a cross rotated 45 degrees.

3. Tape the card to a wall or cabinet making sure when you place a ruler across the two center points it is level. Place your camera about 7-8 feet away on a tripod, level horizontally and directly in line with the cross, not above nor below it. Turn your lens to infinity.

4. If the rf is properly adjusted, when looking thru the rangefinder, you will see three images, the left one you drew on the left, the right one you drew on the right, and a virtual image in the center superimposing the two images forming an 8 sided cross. If the superimposed images don't perfectly align at the center of the cross it will show you whether to adjust the horizontal or vertical adjusting screws on your camera. While it may not be perfect, it works great in a pinch, or on a dark starless night. The pictures below demonstrate what I've described above. It is simple and only takes moments to check and if necessary, adjust your infinity focus.

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!