DOF where is it?

HeHe! I think it is a testiment to the confusion that this thread was moved from the M8 forum to the Optics and Lenses forum! :D
 
rxmd said:
No.

Just to back this up with some numbers, I have here a medium format wideangle, a Zeiss Jena Flektogon MC 50/f4. Quite a decent lens if I may add this. Here's a couple of hyperfocal distances from the DOF scale engraved on the lens:

f/22: ca 1.8m
f/11: ca 3.5m
f/5.6: ca 6.5m

This is from a 50mm lens. Now Ned, take a Leica 50 of your choice, look at its DOF scale and compare. Then tell me if the DOF markings on my Flektogon are going to be of any use if I use it on a 35mm body. We notice that the 35mm body is a crop camera relative to the sensor format that the DOF scale on the Flektogon was designed for. Then tell me if the DOF scale on your Leica lens is any use on a crop camera.

Philipp
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Don't mix apples and oranges.
 
NB23 said:
Don't mix apples and oranges.
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All I've done is put a lens on a camera with a smaller sensor and take a look at whether its DOF scale is still correct. As per your first post in this thread, it should be, but it isn't.

Where did I compare apples and oranges? If you think the situation should be that fundamentally different between a lens with a DOF scale designed for 56x56mm on a 24x36mm sensor, and a lens with a DOF scale designed for 24x36mm on a 18x27mm sensor, it would be interesting why.

Philipp
 
rxmd said:
All I've done is put a lens on a camera with a smaller sensor and take a look at whether its DOF scale is still correct. As per your first post in this thread, it should be, but it isn't.

Where did I compare apples and oranges? If you think the situation should be that fundamentally different between a lens with a DOF scale designed for 56x56mm on a 24x36mm sensor, and a lens with a DOF scale designed for 24x36mm on a 18x27mm sensor, it would be interesting why.

Philipp
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Ok... I'll come up and post my own samples. Either tonight or tomorrow evening.
 
NB23 said:
Ok... I'll come up and post my own samples. Either tonight or tomorrow evening.
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Will your test be with an M8 or RD-1 for the crop?

It should be very interesting to see practical results! While I trust the mathematics involved, I will not be surprised if the difference in the real world is so small as to be inconsequential.
 
Don't bother too much. If we are cropping and looking at enlarging sections and details we are already distorting the parameters of our DOF comparison. It's impossible to make meaningful DOF comparisons on downscaled 720x540 onscreen pictures anyway; this is one of the things were you really do need a print.

It really does make more sense to look at either the math or at real-world lenses. Your statement in your first answer here basically was that the DOF markings on a lens with a given focal length will be accurate, regardless of the film/sensor format upon which you're using the lens (if I understand you correctly, maybe I'm not). Having two 50s with widely different DOF scales should be enough to prove that this isn't the case.

Philipp
 
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This link?

EDIT: Apparently the forum tries to sanitize "spiсk", from the link URL itself. This is really stupid. Who on earth thinks of removing offensive words from URLs??? What's "spiсk" supposed to mean anyway??

You can trick your way around it by escaping one of the offending characters with % and the hexadecimal code for the character, like this: http://home.planet.nl/~spicken/DOF resolution and perspective.pdf. This works, at least in the web browser I'm using (Opera).
 
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Speaking from the top of my head "Sp*ck" is nineteenthirties New York slang for an Italian immigrant and considered offensive. Any native speaker feel free to correct me....
 
It is funny the forum picks this up from the middle of an URL. Let's try "de*****able"

Edit: you see - this is really dumb software...
 
NB23 said:
Don't mix apples and oranges.
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Haha!

One minute you say a 50mm on a 1.3x crop is the same as a 50mm on a 35mm frame, and then you imply a 50mm on MF is different to 50mm on 35mm. You'll have to explain that one.
 
greypilgrim said:
The one thing that is a "truth" is that DOF is an illusion. By definition, there is only a single plane that is in focus. DOF is purely about the appearance of objects being in focus. There are many quotes at the site above that state this (and it is true based on the "laws" of optics, basic physics).
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THAT is the key. The notion that DOF markings on lenses are ever 'correct', for any format, is false. They are guides. Guides made on assumptions. Assumptions that change as the size of the sensor (among many other things) change.
 
Actually biology has as much to do with it as optics. The basic concept only exists by the grace of the limited resolving power of the human eye. DOF for a cat is much less deep than for a human being....
 
Is it because cat has noctilux eyes? I know how cats could move along nicely at nights so this explains shorter dof also :) damn our human elmar eyes ;)
 
tomasis said:
Is it because cat has noctilux eyes? I know how cats could move along nicely at nights so this explains shorter dof also :) damn our human elmar eyes ;)
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No, they have higher resolution. A vulture has even higher, and its eye has a "tele"' part in the centre allowing him to identify small objects on the ground. Just imagine eyes with varialble enlargement and DOF; it would drive optics designers totally over the edge! :D
The higher sensitivity of cats' eyes comes from two sources, they have a larger iris aka aperture and a reflective layer behind their receptors, the Tapetum Lucidum doubling the amount of light received. They share this with a large number of nocturnal and semi-nocturnal mammals.
 
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Small area captured by a smaller than 24x36mm sensor yes, but this sounds like cropping and not turning a 35mm to a 50mm - which would imply a narrower DOF. When Leica says that a x1.3 factor for its lenses is the result of a smaller recording area inside the camera it does not talk about cropping. Or does it? If it does, then obviously both aperture and focal length remain constant and the DOF markings are also true. But I wonder. The position of the sensor in relation to the prime focal point of the lens (often given with a white line on top of the camera) is different than, say on an M6. Am I right or am I wrong, guys?
 
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