seany65
Well-known
I may not word this question quite as well I'd like, but I'll give it a go:
Is there any way of working out how far the camera/lens maker thinks infinity is? If so, would this solution work for accessory rangefinders as well?
I'm aware that this makes no odds with slrs or rangefinder cameras, but it would matter with scale focus cameras, especially ones with fast apertures which we may want to use this would be a bit more important, or if we have to use an accessory rangefinder which may/will probably have a different last marked distance and a different physical difference between the last marked distance and the infinity mark.
It's said/written that half the physical distance between the last marked distance and the infinity mark, is twice that marked distance, eg. the last marked distance is 30ft/10m on a lens, so half-way between it and the infinity mark would be 60ft/20m.
Is this roughly correct?
Would half-way between the new "guessed" mark and the infinity mark now be 120ft/40m on this lens?
Does this go on until we can't see half-way between any new "guessed" mark and the infinity mark?
Thanks for any help anyone can give, and I hope I can understand any help anyone can give.
Is there any way of working out how far the camera/lens maker thinks infinity is? If so, would this solution work for accessory rangefinders as well?
I'm aware that this makes no odds with slrs or rangefinder cameras, but it would matter with scale focus cameras, especially ones with fast apertures which we may want to use this would be a bit more important, or if we have to use an accessory rangefinder which may/will probably have a different last marked distance and a different physical difference between the last marked distance and the infinity mark.
It's said/written that half the physical distance between the last marked distance and the infinity mark, is twice that marked distance, eg. the last marked distance is 30ft/10m on a lens, so half-way between it and the infinity mark would be 60ft/20m.
Is this roughly correct?
Would half-way between the new "guessed" mark and the infinity mark now be 120ft/40m on this lens?
Does this go on until we can't see half-way between any new "guessed" mark and the infinity mark?
Thanks for any help anyone can give, and I hope I can understand any help anyone can give.
The distance scale on lenses and rangefinders is typically not linear. It tends to be a geometric progression, distance being very compressed the closer you get to infinity. Each halving of the scale is probably about a factor of 2, and probably good enough for focusing. If you are trying to accurately measure distance, might not be good enough. I would not use one to accurately measure the distance to a property line.
OlivierAOP
medium format
For focusing distances D>1m, the lens movement from infinity position is approx f*f/(D-2f), or f*f/D for larger D. So halving the movement halves the focusing distance. You could make a custom distance scale if you knew the helicoid pitch.
For closer distances, the formula is more complex and requires knowing the distance between the principal planes, as well as the true focal length for accuracy.
On accessory rangefinders, the distance scale is usually directly proportional to 1/D so it's easier to make a custom scale. You just need to reverse-engineer the constant from the present scale.
For closer distances, the formula is more complex and requires knowing the distance between the principal planes, as well as the true focal length for accuracy.
On accessory rangefinders, the distance scale is usually directly proportional to 1/D so it's easier to make a custom scale. You just need to reverse-engineer the constant from the present scale.
zuiko85
Mentor
Don’t know why, but thought I’d note that the distance scale on at least some lenses are pure fiction. Same for the DoF scale. I have a 7Artisans 25mm f1.8 and the marked distance on the lens barrel bears no relation to actual distance. This means you cannot pre focus by scale and shoot from the hip with this lens.
So be careful with third party lenses.
So be careful with third party lenses.
David Hughes
David Hughes
I don't think it really matters, with a 50mm lens at f/1 on a 35mm camera focussed at something between 265 and 270 feet away the DoF extends to infinity.
If the subject was at infinity I doubt if the camera would have the resolution to even see it and the light from it wouldn't be enough either, perhaps...
This is an area where theory usually has nothing to do with practice.
Regards, David
If the subject was at infinity I doubt if the camera would have the resolution to even see it and the light from it wouldn't be enough either, perhaps...
This is an area where theory usually has nothing to do with practice.
Regards, David
seany65
Well-known
Thanks for the replies. Some bits of which I think I understand, lol.
Anyway:
Sonnar Brian: I've noticed that the marked distances get further away (from the camera) the nearer to infinity they are, and that the markings often get closer to each other on the lens, eg. they may start off at 0.1ft between (1ft, 1.1ft etc) then go to 0.3ft between, then 2 ft between etc. finally to over 10ft between and the markings can get closer to each other.
OlivierAOP: I think I understand that in your explanation, You're coming back from the infinity mark, and I think you're coming back (eventually) to the camera position.
zuiko85: That's just pure laziness and shameful unprofessionalism on the 7Artisans company. I wonder how bad the scales are on lenses and cameras from a couple of decades and more are?
David Hughes: On an SLR (which I think is most likely to have 50mm f1) it probably doesn't matter at all. If a camera can't resolve what is at infinity (unless it's ginormous, like the moon etc.), does the infinity mark mean a distance that is less than infinity for practical purposes? Could one lens or camera have 200ft marked as infinity, but another one (of the same focal length on the same format) have 150ft marked as infinity?
What I'm interested in, is the focusing scales on scale focus cameras, and especially the bit between the last marked distance and the infinity mark. This is mainly because the nearer distances usually have more distance marks that show distances that are closer together so there's more likelihood of getting something in acceptable focus even if the "guess" is slightly out.
From what I understand of OlivierAOP's post, is that what I'd read about half-way between the last marked distance and infinity is twice the marked distance from the camera is correct.
The other problem is using an accessory rangefinder on a scale focus camera, especially if the last marked distance is different to that on the camera's lens eg. 40ft on the accessory and 16ft on the camera lens. Half-way to infinity on the lens would be 32ft, so if the measured distance on the rangefinder was half-way between 40ft and infinity (80ft), would I just put the lens at the invisible 32ft mark and then half-way berween that and infinity to get to 64ft and then add a tiny bit to get to 80ft? I presume so. BUT what iff the infinity marks are at different distances?
Does everyone else get the inmpression that I'm doing my usual "over-thinking" bit?
Thanks for the attempts at help.
Anyway:
Sonnar Brian: I've noticed that the marked distances get further away (from the camera) the nearer to infinity they are, and that the markings often get closer to each other on the lens, eg. they may start off at 0.1ft between (1ft, 1.1ft etc) then go to 0.3ft between, then 2 ft between etc. finally to over 10ft between and the markings can get closer to each other.
OlivierAOP: I think I understand that in your explanation, You're coming back from the infinity mark, and I think you're coming back (eventually) to the camera position.
zuiko85: That's just pure laziness and shameful unprofessionalism on the 7Artisans company. I wonder how bad the scales are on lenses and cameras from a couple of decades and more are?
David Hughes: On an SLR (which I think is most likely to have 50mm f1) it probably doesn't matter at all. If a camera can't resolve what is at infinity (unless it's ginormous, like the moon etc.), does the infinity mark mean a distance that is less than infinity for practical purposes? Could one lens or camera have 200ft marked as infinity, but another one (of the same focal length on the same format) have 150ft marked as infinity?
What I'm interested in, is the focusing scales on scale focus cameras, and especially the bit between the last marked distance and the infinity mark. This is mainly because the nearer distances usually have more distance marks that show distances that are closer together so there's more likelihood of getting something in acceptable focus even if the "guess" is slightly out.
From what I understand of OlivierAOP's post, is that what I'd read about half-way between the last marked distance and infinity is twice the marked distance from the camera is correct.
The other problem is using an accessory rangefinder on a scale focus camera, especially if the last marked distance is different to that on the camera's lens eg. 40ft on the accessory and 16ft on the camera lens. Half-way to infinity on the lens would be 32ft, so if the measured distance on the rangefinder was half-way between 40ft and infinity (80ft), would I just put the lens at the invisible 32ft mark and then half-way berween that and infinity to get to 64ft and then add a tiny bit to get to 80ft? I presume so. BUT what iff the infinity marks are at different distances?
Does everyone else get the inmpression that I'm doing my usual "over-thinking" bit?
Thanks for the attempts at help.
Retro-Grouch
Well-known
I've noticed that on several of my FSU lenses, the DOF scale is far too generous, corresponding to a stop on other (German and Japanese) lenses of the same focal length; i.e., the near-far scale at f/8 corresponds to that of f/11 on the others. The only explanation I can think of is that the Soviet industry was using a different criterion for the acceptable circle of confusion, based on a premise of less enlargement when printing. They seemed to go their own way and ignored industry standards in many cases. Or just made it up as they went along.
OlivierAOP
medium format
I don't think you should worry about far distances where the DOF is greatest. On my scale focus camera I matched the lens distance scale with that of the accessory RF, making it easier to interpolate the in-between values. It matters more for closer distances. I can help if you need to do that.
seany65
Well-known
Thanks for the new replies.
OlivierAOP: Do you mean you managed to find an accessory rangefinder that has the same distances on it as the on the camera lens, but it has other distances on it, or that you've found one with only the same distances on it?
I've managed to do the latter with a lomo blik and a Welta (Rheinmetall) Weltax. Makes things much easier. I've done the former with a Medis and my Welta Perle, but on the Perle there's a fairly big empty gap between 5ft and 8ft, but a small gap between 30ft and infinity, and on the Medis there's 30ft, 40ft and 50ft, but with a bigger gap between 50ft and infinity than there is between the 30ft and infinity on the Perle. This makes things a little more difficult.
I have been searching for several rangefinders that have the same distances as on the cameras, and ideally only the same distances, but they are rather difficult to find.
OlivierAOP: Do you mean you managed to find an accessory rangefinder that has the same distances on it as the on the camera lens, but it has other distances on it, or that you've found one with only the same distances on it?
I've managed to do the latter with a lomo blik and a Welta (Rheinmetall) Weltax. Makes things much easier. I've done the former with a Medis and my Welta Perle, but on the Perle there's a fairly big empty gap between 5ft and 8ft, but a small gap between 30ft and infinity, and on the Medis there's 30ft, 40ft and 50ft, but with a bigger gap between 50ft and infinity than there is between the 30ft and infinity on the Perle. This makes things a little more difficult.
I have been searching for several rangefinders that have the same distances as on the cameras, and ideally only the same distances, but they are rather difficult to find.
David Hughes
David Hughes
They are not the only ones to go their own sweet way. I raised a point about Olympus a while ago as I was baffled by them.
Looking in older books the theory seems to be that you set the CoC to give a point 0.01" on the print. If we say 35mm negs are 1" x 1½" and enlarged only to 4" x 6" then the CoC need only be 0.01" ÷ 4 and so on. (And to confuse the issue they always quote it in mm's.)
The point I raised was that some DoF's quoted don't seem possible...
Regards, David
Rob-F
Likes Leicas
Seany65: I'm not quite sure if your main concern is to know the actual camera-to-subject distance that constitutes "infinity" for all practical purposes; or if your concern is mainly with the placement of the markings on the lens. But as I read your post, I think you mean the former. I believe the right way to name a distance that is great enough to take as practical infinity should be as some multiple of the lens's focal length.
So let's take note of the following:
1. There seems to be common agreement that a distance of 10 focal lengths is the boundary separating the Macro, or near focusing range, from the normal range.
2. I have an old National Bureau of Standards (now called the National Institute of Standards and Technology) lens resolution chart that states the chart is to be photographed from of distance of 25 focal lengths. Clearly, that's too close to be infinity, but the NBS must have felt it was sufficiently out of the near range to be representative of the lens's performance.
So that gives us a precedent for thinking that the most rational way to think about distance is in terms of focal length. With that in mind, I think the idea would then be to decide how many focal lengths away can be considered as infinity for practical purposes. I think that decision is somewhat arbitrary, but it should be a large enough number so that a difference of one focal length in distance can be considered negligible.
What should that distance be, in focal lengths? Is one hundred focal lengths enough that
there's no important difference between 99, 100, or 101 focal lengths? That's a one precent change. I don't think that's small enough, but I could see how a one-tenth of one percent would be acceptable.. I'm looking for a point where the focal length itself could be considered vanishingly small compared to the focal distance. So a ratio of 1/1000 seems fairly safe. Let's see how that looks for a 50mm (2 inch) lens:
2 inches x 1000 = 2000 inches, or 166 feet. Well, that's doesn't sound like infinity to me.
So maybe we need to go to f x 10,000. Now we have, 1660 feet. That still sounds kind of close, but maybe it's getting into the ball park. Going to f x 100,000 would put infinity at about 3.15 miles, which I believe would agree with common practice.
So, I wonder if a practical definition of infinity might be 100,000 focal lengths?
Edit: With a little time to think about it, 100,000 focal lengths seems excessive. I'm thinking about the practical limitations of rangefinders and lenses for practical photography. For a 50mm lens, I think one mile, or even a half mile, to be more than adequate. One mile is 63,360 inches, or 31,680 focal lengths for a 50mm lens. One-half mile is 15,840 focal lengths. Maybe somewhere around 15,000 focal lengths might be in the right ball park.
So let's take note of the following:
1. There seems to be common agreement that a distance of 10 focal lengths is the boundary separating the Macro, or near focusing range, from the normal range.
2. I have an old National Bureau of Standards (now called the National Institute of Standards and Technology) lens resolution chart that states the chart is to be photographed from of distance of 25 focal lengths. Clearly, that's too close to be infinity, but the NBS must have felt it was sufficiently out of the near range to be representative of the lens's performance.
So that gives us a precedent for thinking that the most rational way to think about distance is in terms of focal length. With that in mind, I think the idea would then be to decide how many focal lengths away can be considered as infinity for practical purposes. I think that decision is somewhat arbitrary, but it should be a large enough number so that a difference of one focal length in distance can be considered negligible.
What should that distance be, in focal lengths? Is one hundred focal lengths enough that
there's no important difference between 99, 100, or 101 focal lengths? That's a one precent change. I don't think that's small enough, but I could see how a one-tenth of one percent would be acceptable.. I'm looking for a point where the focal length itself could be considered vanishingly small compared to the focal distance. So a ratio of 1/1000 seems fairly safe. Let's see how that looks for a 50mm (2 inch) lens:
2 inches x 1000 = 2000 inches, or 166 feet. Well, that's doesn't sound like infinity to me.
So maybe we need to go to f x 10,000. Now we have, 1660 feet. That still sounds kind of close, but maybe it's getting into the ball park. Going to f x 100,000 would put infinity at about 3.15 miles, which I believe would agree with common practice.
So, I wonder if a practical definition of infinity might be 100,000 focal lengths?
Edit: With a little time to think about it, 100,000 focal lengths seems excessive. I'm thinking about the practical limitations of rangefinders and lenses for practical photography. For a 50mm lens, I think one mile, or even a half mile, to be more than adequate. One mile is 63,360 inches, or 31,680 focal lengths for a 50mm lens. One-half mile is 15,840 focal lengths. Maybe somewhere around 15,000 focal lengths might be in the right ball park.
OlivierAOP
medium format
@seany65 I printed a scale and taped it on the lens. You need to figure out the lens helicoid pitch and do some math.
David Hughes
David Hughes
Looking at Leica's "table of focal depths" for the Elmar, it seems to me that infinity is a lot closer than we all think.
Wide open at f/3.5 - because this is the 1937 edition of the tables - infinity is more than 50ft away.
The table shows that if you focus on 30ft at f/3.5 then the DoF goes from 21ft to 50ft.
Focus on 50ft and it's from 29ft to infinity...
Using an online calculator* for f/3.6 the distant limit is 142ft away and the near is 30ft.
And as it doesn't cover f/3.5 the figures for f/3.4 are 31 and 98ft.
I guess we can draw any conclusion we like from that...
Regards, David
* I used www.dofmaster.com
Wide open at f/3.5 - because this is the 1937 edition of the tables - infinity is more than 50ft away.
The table shows that if you focus on 30ft at f/3.5 then the DoF goes from 21ft to 50ft.
Focus on 50ft and it's from 29ft to infinity...
Using an online calculator* for f/3.6 the distant limit is 142ft away and the near is 30ft.
And as it doesn't cover f/3.5 the figures for f/3.4 are 31 and 98ft.
I guess we can draw any conclusion we like from that...
Regards, David
* I used www.dofmaster.com
David Hughes
David Hughes
Macro is a fixed point where the image size is the same as the object's size. Or where u = v = 2f or is was when I did physics. Nowadays macro doesn't seem to have any fixed meaning, which is very confusing.
Regards, David
Rob-F
Likes Leicas
David, the macro range lies between 1:1 and 1:10. So 1:10, which occurs at a distance of 10 focal lengths, is the demarcation point that ends the macro range.
Rob-F
Likes Leicas
So then if we take 50 feet to be infinity, that's 600 inches, or 300 focal lengths. Then for other focal lengths, infinity can be 300 times that focal length. So for a 25mm lens, infinity is 25 feet or greater. For the 90mm Elmar, it would be 90 feet (etc).
In my earlier post I was thinking of the distance needed to ensure accurate rangefinder calibration, rather than the distance of the farthest point that makes any practical difference for focusing purposes, which I see is what the OP wanted.
Although, the 50 feet that David quoted was for an f: 3.5 lens. With a faster lens, focus would be more critical. So I would think that infinity must be a greater distance for, say, a Noctilux than for an Elmar. So it seems that you can't define infinity as a given number of focal lengths without taking aperture into account.
Rob-F
Likes Leicas
So "infinity" is only closer than an infinite distance for a lens slower than infinitely fast. For an infinitely fast lens, the infinity point must be infinitely far away. As the f number approaches zero, the farthest point of focus approaches true infinity. That, and DOF matters. That's how it looks to me now.
OlivierAOP
medium format
Another way to understand the "true" infinity position is via the lens movement. For far subjects, lens moves f*f/D from true infinity position. Say you focus on the moon, D~380 000km with 50mm lens. Lens movement from theoretical infinity is 6 nanometers, about 20 water molecules. Say you focus on a distant skyscraper, D=2km, movement is 1 micrometer. With a regular lens that would be impossible to resolve. A 0.05mm movement maybe? This corresponds to D=50m.
Typically lenses are collimated with a 300mm collimator, so they are not on "true" infinity, but pretty close and within the capacity of the helicoid.
Typically lenses are collimated with a 300mm collimator, so they are not on "true" infinity, but pretty close and within the capacity of the helicoid.
David Hughes
David Hughes
My only interest in what is passed off as infinity is that I have this heap of old cameras and their instruction books and many of then make claims about everything from x feet away to infinity will be in focus and I can't match those figures to what I see and can calculate. And the x feet away is usually fairly close...
However, if they are taking infinity to be somewhere from about 90 to 150ft away it all makes sense if the larger CoC is also used for a 4" x 6" print or enlargement only.
Regards, David
However, if they are taking infinity to be somewhere from about 90 to 150ft away it all makes sense if the larger CoC is also used for a 4" x 6" print or enlargement only.
Regards, David
David Hughes
David Hughes
It was 1:1 when I did physics a long, long time ago and I passed the exams OK. So I guess that, like a lot of other things, it has changed. I shall resist the changes and preserve what is left of my sanity...
It's bad enough reading "analogue" when they mean "film" and wondering how to explain it to them.
Regards, David