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02/08/2006 12:30:28 PM · #51 |
Circle of Confusion (sur'kel uv, ov kon-fyu'zhon) n.
1. Group of photographers trying to explain impact of crop factor on DoF
Message edited by author 2006-02-08 12:31:41. |
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02/08/2006 12:39:38 PM · #52 |
Originally posted by Gordon:
Circle of Confusion (sur'kel uv, ov kon-fyu'zhon) n.
1. Group of photographers trying to explain impact of crop factor on DoF |
Finally, a logical explanation! Thank you ... it reminds me a bit of the definition of a "liberal" firing squad. |
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02/08/2006 12:52:21 PM · #53 |
How about corner distortions on wide angle lens? Are distortions the same on 15mm lens with FF vs. 10mm lens with 1.5 crop?
Just to clarify: the distortions I'm talking about make people look like they made of cardboard. This only happens in the corner on wide angle lenses.
Any ideas?
Nick
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02/08/2006 01:12:58 PM · #54 |
Not a prob: the answer is basically yes -
Remember the lens is a round projection at the plane of the film. We only use the center square or rectangular area. Since we are using that square shape the dist from the corners of the film to the center of the lens is shorter than the center of the film to the center of the lens. That is basically the purpose of Aspherical glass, its just not possible too be perfect across a flat plane refracted though a shperical lens. Whereas light is (for this discussion) perfect, they just do the best they can.
Originally posted by Nikolai1024:
How about corner distortions on wide angle lens? Are distortions the same on 15mm lens with FF vs. 10mm lens with 1.5 crop?
Just to clarify: the distortions I'm talking about make people look like they made of cardboard. This only happens in the corner on wide angle lenses.
Any ideas?
Nick |
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02/08/2006 01:28:43 PM · #55 |
Originally posted by Bear_Music:
Originally posted by kyebosh:
Well no not quite the same, the dof will be different (more DOF for the 1.6x crop).
That is
if you shoot with the same settings and distance with a 100 on 1.6x vs a 160 on FF. |
This is not true. For the same reproduction ratio, at a given physical aperture, DOF is identical regardless of the focal length of the lens. At a 1:1 reproduction ratio, my 60mm macro has exactly the same DOF as a 105mm macro lens. I used to believe what you are saying here (essentially, that a 60mm macro lens would have more DOF than a 105mm macro lens), but it turns out not to be true.
R. |
Wouldn't the physical aperture be different? If both shots were to be taken at f/4, the shot using a 100mm lens would have a physical aperture of 25mm, while the shot taken using the 160mm lens would be using a physical aperture of 40mm. Surely, then, the fact that the physical aperture size is reduced when using shorter focal lengths gives rise to the situation where P&S users get loads of DOF.
Anyway, I propose that everyone use the terminology of '35mm equivalent' for comparing lenses used on different sizes of sensor, not because it's correct, but because it's convenient shorthand and really doesn't need to be debated every other day :)
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02/08/2006 02:34:25 PM · #56 |
Originally posted by AJAger:
Originally posted by Bear_Music:
Originally posted by kyebosh:
Well no not quite the same, the dof will be different (more DOF for the 1.6x crop).
That is
if you shoot with the same settings and distance with a 100 on 1.6x vs a 160 on FF. |
This is not true. For the same reproduction ratio, at a given physical aperture, DOF is identical regardless of the focal length of the lens. At a 1:1 reproduction ratio, my 60mm macro has exactly the same DOF as a 105mm macro lens. I used to believe what you are saying here (essentially, that a 60mm macro lens would have more DOF than a 105mm macro lens), but it turns out not to be true.
R. |
Wouldn't the physical aperture be different? If both shots were to be taken at f/4, the shot using a 100mm lens would have a physical aperture of 25mm, while the shot taken using the 160mm lens would be using a physical aperture of 40mm. Surely, then, the fact that the physical aperture size is reduced when using shorter focal lengths gives rise to the situation where P&S users get loads of DOF.
Anyway, I propose that everyone use the terminology of '35mm equivalent' for comparing lenses used on different sizes of sensor, not because it's correct, but because it's convenient shorthand and really doesn't need to be debated every other day :) |
That's why I said "at a given PHYSICAL aperture", not "at a given f/stop".
R.
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02/08/2006 02:39:49 PM · #57 |
Originally posted by Bear_Music:
Originally posted by AJAger:
Originally posted by Bear_Music:
Originally posted by kyebosh:
Well no not quite the same, the dof will be different (more DOF for the 1.6x crop).
That is
if you shoot with the same settings and distance with a 100 on 1.6x vs a 160 on FF. |
This is not true. For the same reproduction ratio, at a given physical aperture, DOF is identical regardless of the focal length of the lens. At a 1:1 reproduction ratio, my 60mm macro has exactly the same DOF as a 105mm macro lens. I used to believe what you are saying here (essentially, that a 60mm macro lens would have more DOF than a 105mm macro lens), but it turns out not to be true.
R. |
Wouldn't the physical aperture be different? If both shots were to be taken at f/4, the shot using a 100mm lens would have a physical aperture of 25mm, while the shot taken using the 160mm lens would be using a physical aperture of 40mm. Surely, then, the fact that the physical aperture size is reduced when using shorter focal lengths gives rise to the situation where P&S users get loads of DOF.
Anyway, I propose that everyone use the terminology of '35mm equivalent' for comparing lenses used on different sizes of sensor, not because it's correct, but because it's convenient shorthand and really doesn't need to be debated every other day :) |
That's why I said "at a given PHYSICAL aperture", not "at a given f/stop".
R. |
I'm sorry, I don't understand. I thought the debate was about the apparent differences that exist when using different sensor sizes. I would take "the same settings" to mean the same f-stop, not the same physical aperture, which I agree is a totally different thing.
I'm not sure that we're actually disagreeing here, rather talking at cross-purposes, maybe?
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02/08/2006 02:42:37 PM · #58 |
Originally posted by AJAger:
I'm not sure that we're actually disagreeing here, rather talking at cross-purposes, maybe? |
You're right, we're not really disagreeing; I was just pointing out that I had ALREADY agreed with you in my original post, effectively. I didn't want anyone else to misconstrue what I had said :-)
R.
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02/08/2006 03:05:37 PM · #59 |
Bear Music: if you are talking about the same 100mm lens on the FF body vs the cropped, then the F4 is 100% identical on both shots.
While the thread has much detail prior - the DOF is a function of the lens "only", its' Ap and FL and dist to subject... regardless what camera its on.
It's very important not too confuse the well mis-understood mag/crop factor - the 100mm on a 1.6x crop body does not convert that lens optically too a 160mm lens, any way, any how.
Its merely a term (and a baed one as it turns out), that the mfg attempted to explain away the lacking image size at the time of the small sensor relative to 35mm. Why, because their 100mm lens did not yield a 100mm relative to a 35mm film, just as my Mamayia RZ medium format 100mm lens is more like a 50mm in 35mm format. Same exact thing.
Importantly, the actual image projected from the 100mm lens on to both 35 and med formats, is, precisely the same physical dim on the film/plane - in the med format however, you just get the more surrounding area; just like the cropped 1.6x 20D vs the FF 1Ds-II. not an ounce of difference.
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02/08/2006 03:14:15 PM · #60 |
Originally posted by jefalk:
Bear Music: if you are talking about the same 100mm lens on the FF body vs the cropped, then the F4 is 100% identical on both shots. |
I'm well aware of this; note that I said "for the same reproduction ratio". There was a digression in this thread that moved into DOF and reproduction ratios. There's no need to go over it all again, it's all there in the previous posts.
R.
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