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Viewfinder magnifiers - do they help with focussing?


The Kevster

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Again, rangefinder accuracy has nothing to do with the lens or focal length. It varies with base, distance, vision, and magnification. The accuracy is the difference between the plane of focus, and where you intended it. What you are talking about--just getting the focus somewhere in the depth of field--is another matter.

 

Jaap is trying to tell you that all this is theory.

Magnification will give you better accuracy because in theory you can infinitely coincide the 2 patches more accuratelly. However in practice this is not happening because there are mechanical joints where you have your control elements (the lens focusing ring) and because maybe the slight movement you get because of the magnifier will not yield any usefull output difference in focusing.

I also have the 1.4x and besides the fact that it gives me the oportunity to have a VF of the same FoV as my other eye (which is why I bought it, it does not helping me with focusing).

 

Your best option is to test a large lens 75mm, 90mm with and without the magnifiers. Only then we will be certain of whether theory meets practice.

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Erwin Puts tells it better than I can in his new Compendium - but his conclusion is, for a 50 mm lens, that the RF accuracy throughout the whole system is about equal to the accuracy of the average human eye.

and far more than the average photographer needs
without introducing DOF once btw.

 

Which makes a magnifier superfluous - in theory. As I said repeatedly, for some eye conditions and for some users in general it may be more comfortable to use, but some others, me included, feel it detracts from focussing directly. The only way to find out is empirical. If, for instance you have a habit of using contrast focussing instead of coincidence or broken line focussing, a magnifier is quite counterproductive. But then, if you have reached that level of RF focussing, it is doubtful you would be contemplating a magnifier at all.;)

Edited by jaapv
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Jaap is trying to tell you that all this is theory.

Magnification will give you better accuracy because in theory you can infinitely coincide the 2 patches more accuratelly. However in practice this is not happening because there are mechanical joints where you have your control elements (the lens focusing ring) and because maybe the slight movement you get because of the magnifier will not yield any usefull output difference in focusing.

I also have the 1.4x and besides the fact that it gives me the oportunity to have a VF of the same FoV as my other eye (which is why I bought it, it does not helping me with focusing).

 

Your best option is to test a large lens 75mm, 90mm with and without the magnifiers. Only then we will be certain of whether theory meets practice.

 

The "backlash" in the system you're talking about is a separate matter, like calibration or miscalibration of the equipment. I'm talking about one thing, the inaccuracy of the rangefinder due to limited resolution of the eye. And this doesn't have anything to do with cameras, just rangefinders. In the theory, when you visually determine the range you can be off plus or minus some x centimeters, say. That number will be smaller or larger depending on what magnification you have in front of the eye.

 

Now what do you want to compare that accuracy (x centimeters) to?...If you compare it to the true distance, you do not have any "extra" accuracy. If you are trying to place the artillery shell exactly, or the focus plane, you will do better with more magnification. If you still want to compare it (x centimeters) to something, the logical thing would be the depth of field. Then you could say you had some "extra" accuracy. But how much extra will still depend on the magnification.

 

I did not make any claims about how things work in practice. It's no bother to me if someone wants to use a magnifier or not.

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Erwin Puts tells it better than I can in his new Compendium - but his conclusion is, for a 50 mm lens, that the RF accuracy throughout the whole system is about equal to the accuracy of the average human eye. without introducing DOF once btw.

 

Which makes a magnifier superfluous - in theory. As I said repeatedly, for some eye conditions and for some users in general it may be more comfortable to use, but some others, me included, feel it detracts from focussing directly. The only way to find out is empirical. If, for instance you have a habit of using contrast focussing instead of coincidence or broken line focussing, a magnifier is quite counterproductive. But then, if you have reached that level of RF focussing, it is doubtful you would be contemplating a magnifier at all.;)

 

50's are about all I shoot commercially, including the 50/1. Your friend Osterloh recommends a magnifier for 50mm.

 

But back to the quote, you haven't quoted any theory, just a conclusion as said for the "average photographer." I would love to know what's in the compendium, but it's asking too much to track down the new edition. I heard that compared to the first edition he added some formula to the section on accuracy. On the website (from 1st ed.?) he gives some tables, which involve the depth of field; it fact it takes some time to figure out the constants he used.

 

Again, it does not quite make sense to say the "RF accuracy...is about equal to the accuracy of the average human eye." One is a constant, and the other an expression involving that constant.

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Quite simply, the longer the focal length and/or shallower the DoF - the more a magnifier can potentially help. Why shouldn't it? It enlarges the rangefinder patch and corresponding framelines and increases the effective baselength.

 

Naturally, the quality of the magnifier is important too as not all are created equal.

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50's are about all I shoot commercially, including the 50/1. Your friend Osterloh recommends a magnifier for 50mm.

 

But back to the quote, you haven't quoted any theory, just a conclusion as said for the "average photographer." I would love to know what's in the compendium, but it's asking too much to track down the new edition. I heard that compared to the first edition he added some formula to the section on accuracy. On the website (from 1st ed.?) he gives some tables, which involve the depth of field; it fact it takes some time to figure out the constants he used.

 

Again, it does not quite make sense to say the "RF accuracy...is about equal to the accuracy of the average human eye." One is a constant, and the other an expression involving that constant.

Well, if you feel the need to dismiss a conclusion to four pages you did not read, I suggest you take it up with the author, not with the messenger.
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I must admit that I may be missing something in this discussion.

 

Who cares who wrote what or when?

 

The first question I would ask is why did they make magnifiers at all?

 

The answer is simple (assuming the rest of the system is properly calibrated) ... it makes the rangefinder patch larger and easier to see. If I want to work on something small, I use a magnifier so I can see it better.

 

"See it better", nothing more or less. It's just common sense.

 

Perhaps not for everyone, but it works for me. If it didn't, I probably couldn't shoot anywhere near as accurately with a 50/0.95 like I am able to do now.

 

-Marc

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Well, if you feel the need to dismiss a conclusion to four pages you did not read, I suggest you take it up with the author, not with the messenger.

 

I did not say anything about the book...I have no idea what you're talking about from that description.

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I must admit that I may be missing something in this discussion.

...

 

I'll recap; he says that magnifiers are redundant in theory for 50mm lenses, and the proof is in Osterloh, or the Puts Compendium.

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My vision is only short sighted by less than 1 diopter including the effect of an slight astigmatism.

 

I went for the 1.25 Leica magnifier initially and it didn't help at all. While everything was bigger, it didn't help me to achieve critical focus. :eek: YMMV

 

I put on a -0.5 diopter (by trying 0.5 and 1.0 diopter adjustments) and found the -0.5 to do the job enabling me to focus with a higher degree of accuracy.

 

In terns of -0.5 versus using -1.0, apparently Leica already adjusts for -0.5 shortsightedness in the viewfinder, I was told by the salesman. To me it didn't matter, as I could see with my own eye, that 0.5 suited me better.

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The "backlash" in the system you're talking about is a separate matter, like calibration or miscalibration of the equipment. I'm talking about one thing, the inaccuracy of the rangefinder due to limited resolution of the eye. And this doesn't have anything to do with cameras, just rangefinders. In the theory, when you visually determine the range you can be off plus or minus some x centimeters, say. That number will be smaller or larger depending on what magnification you have in front of the eye.

 

...Unless the system's combined errors are larger than your control elements which is your eye/hand. For practical reasons, you can't have access to magnifiers more than 1.4x, nor is it needed...

 

Anyways, try a mag or don't try. I tried and did not liked. My photos were infocus before and after the xmag

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#12, I'll set it out one last time, and afterwards I'll give up.

 

a. Yes, you can increase optical accuracy in a rangefinder system ad infinitum by adding larger and larger magnifiers. That is undisputed.

b. You need to consider what accuracy is in the context. In the case of a photograph the answer should be "when I get a decent print", but in this discussion it means you put your plane of focus within the zone of equal focus given by the pixel pitch of the sensor.

c. You need to consider the maximum consistency of the accuracy given by the tolerances in the focussing mechanism, the rangefinder coupling, and dexterity of the user. Strangely Puts claims the mechanical tolerance of the rangefinder itself is zero, which I find hard to believe. These inaccuracies are such in the Leica rangefinder that condition b. is met.

 

When b. and c. are met, a. has reached its limit for the application.

 

In the case of the Leica M one can reach this state without magnifier, given a proper technique, a proper dioptre correction and a normal eyesight.

 

 

In other words, you cannot hit a target more accurately than a bullseye, even if you can see it more accurately.

 

 

Now we come to focussing technique.

One can use

1.the broken line method - turn until the line is whole again

2.the coincidence method -turn until the structures in the patch overlap

3. the contrast method - turn to the contrast jump

 

The last needs a bit of explanation.

When two identical images are superimposed, but not quite overlap, one loses contrast. When exact coincidence is reahed, contrast will increase sharply. In the M rangefinder this produces a quite perceptible "jump" in contrast at the moment of exact focus.

 

Obviously the last method gets compromised by adding contrast-reducing appliances to the system, like a magnifier.

I strongly suspect that the disagreement about the practical effectiveness of magnifiers has to do with the method one uses (maybe even subconsciously) for focussing.

 

 

There is no moral superiority in either using or not using a magnifier, nor in which focussing method one uses (often it varies with the subject). Nobody seeing your print is going to ask. It is quite possible that using one will help you get better, easier, or more consistent focus. But then again, it may not,

I simply want to set out - whether one wants to use one is solely determined by personal preference and there are no absolutes as far as the user is concerned.

Edited by jaapv
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...

b. You need to consider what accuracy is in the context. In the case of a photograph the answer should be "when I get a decent print", but in this discussion it means you put your plane of focus within the zone of equal focus given by the pixel pitch of the sensor.

 

 

This is not the "accuracy" or the "rangefinder accuracy," which has one conventional definition in standard sources.

 

c. You need to consider the maximum consistency of the accuracy given by the tolerances in the focussing mechanism, the rangefinder coupling, and dexterity of the user. Strangely Puts claims the mechanical tolerance of the rangefinder itself is zero, which I find hard to believe. These inaccuracies are such in the Leica rangefinder that condition b. is met.

 

 

O.K., your previous argument was about focal length; now you want to add a bunch of things to the mix. Should we consider the accuracy from leaving the lens cap on, or moving subjects, or ground fog?... The accuracy is the accuracy. Someone put some thought into the definition, and there has been no reason to change it.

 

...

 

In the case of the Leica M one can reach this state without magnifier, given a proper technique, a proper dioptre correction and a normal eyesight.

 

 

In other words, you cannot hit a target more accurately than a bullseye, even if you can see it more accurately.

 

The limit is when you can't distinguish the bulls-eye, not when you can.

 

...contrast....

 

 

Well it's a piece of glass, so obviously there is going to be a point of diminishing returns; you can see this by stacking magnifiers. But even this doesn't have to come down to "personal preferences"; it's something you could measure if you really wanted to.

 

I strongly suspect that the disagreement about the practical effectiveness of magnifiers has to do with the method one uses (maybe even subconsciously) for focussing.

 

 

I'll buy that; but it could also be who wears glasses, or hobby vs. vocation, or who knows what.

 

 

 

As for the theory, you either understand the arguments and can reproduce them, or you quote a source who can. Here you have accuracy charts and tables and it's pretty cut-and-dried; you can either draw the chart and fill in the table, or you can't.

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I'm pretty sure even people with 20/20 vision can still capture out OOF photos with am M9. It's just par for the course with a rangefinder it seems. If in doubt, take sone extra photos. Not always easy when you are shooting action/street type subjects. But in that case just stop down and hopefully you'll get decent enough focus. I'm thinking about a magnifier myself for my 90mm which I find unruly to say the least. But I think it's back focussing like a bast anyway. I just nudge it a smidge past focus on the focus area and it seems fine.

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...Unless the system's combined errors are larger than your control elements which is your eye/hand. For practical reasons, you can't have access to magnifiers more than 1.4x, nor is it needed...

 

...

 

Again...you can get a separate (uncoupled) rangefinder, and the accuracy of the rangefinder is determined in the same way--nothing to do with the lens and the camera.

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Again...you can get a separate (uncoupled) rangefinder, and the accuracy of the rangefinder is determined in the same way--nothing to do with the lens and the camera.

 

A separate rangefinder is accurate to find the distance but other than that it won't help you. Please do realize that your goal is NOT how to find the distance. but to shoot a sharp photo.

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