03-03-2012, 10:25 PM
[quote name='nandadevieast' timestamp='1330792906' post='16382']
Tell me something you knowledgeable people <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='
' />
How does the minimum focussing distance come to play when a FF lens is mounted on a crop camera?
Lets say 85 1.4 vs. 135 F2
85 on crop is roughly the same as 135 on FF. In terms of DOF and focal length both.
But 85 has a MFD of .85 meters and 135 has a MFD of 1.1 meters.
Which means with 85 on a crop camera, i have a 135 F2 with better close focussing ability.
Is this right?
[/quote]
85 mm at .85 meters gives a magnification of .0127, 135 mm at 1.1 meters 0.165, IOW the magnification of the 135 m is larger, and hence effectively focuses more closely. Magnfiication doesn't change with sensor used, only the framing changes. On an APS-C camera you will seemingly have a larger magnification, by the crop factor, than with a FF camera, but this is not really the case; it is just a crop.
And in this example, with the 135 mm, which effectively has th esame AoV as a 200 mm + on FF when mounted on a crop camera, you still have a larger magnifcation than with the 85 mm.
[quote name='nandadevieast' timestamp='1330797622' post='16385']
Exactly. I can have a 135 F2 with better close focussing ability.
As a result, slightly different DOF implications as well perhaps...
[/quote]
This is really borderline macro, so likely, yes.
Canon 5D II, 85 mm at 85 cm, F/18 (eq. aperture to F/11 APS-C): DoF from 0.804 m to 0.901 m, for a total of 0.097 m (CoC 0.03 mm)
Canon 5D II, 85 mm at 85 cm, F/11 (eq. aperture to F/7.1 APS-C): DoF from 0.821 m to 0.882 m, for a total of 0.061 m (CoC 0.03 mm)
Canon 7D, 85 mm at 85 cm, F/11, DoF from 0.831 m to 0.869 m for a total DoF of 0.038 m (CoC 0.0186 mm)
Canon 5D II, 135 mm at 110 cm, F/18 (eq. aperture to F/11 APS-C): DoF from 1.069 m to 1.132 m, for a total of 0.063 m (CoC 0.03 mm)
Canon 5D II, 135 mm at 110 cm, F/11 (eq. aperture to F/7.1 APS-C): DoF from 1.081 m to 1.120 m, for a total of 0.040 m (CoC 0.03 mm)
Canon 7D, 135 mm at 110 cm, F/11, DoF from 1.088 m to 1.112 m for a total DoF of 0.025 m (CoC 0.0186 mm)
IOW, less DoF with crop when the same lens is used. It will be approximately the same at the same magnification when an equivalent AoV is used, at the same aperture.
And once one gets to 1:1 and beyond, it doesn't make a difference anymore.
Kind regards, Wim
Tell me something you knowledgeable people <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='
' />How does the minimum focussing distance come to play when a FF lens is mounted on a crop camera?
Lets say 85 1.4 vs. 135 F2
85 on crop is roughly the same as 135 on FF. In terms of DOF and focal length both.
But 85 has a MFD of .85 meters and 135 has a MFD of 1.1 meters.
Which means with 85 on a crop camera, i have a 135 F2 with better close focussing ability.
Is this right?
[/quote]
85 mm at .85 meters gives a magnification of .0127, 135 mm at 1.1 meters 0.165, IOW the magnification of the 135 m is larger, and hence effectively focuses more closely. Magnfiication doesn't change with sensor used, only the framing changes. On an APS-C camera you will seemingly have a larger magnification, by the crop factor, than with a FF camera, but this is not really the case; it is just a crop.
And in this example, with the 135 mm, which effectively has th esame AoV as a 200 mm + on FF when mounted on a crop camera, you still have a larger magnifcation than with the 85 mm.
[quote name='nandadevieast' timestamp='1330797622' post='16385']
Exactly. I can have a 135 F2 with better close focussing ability.
As a result, slightly different DOF implications as well perhaps...
[/quote]
This is really borderline macro, so likely, yes.
Canon 5D II, 85 mm at 85 cm, F/18 (eq. aperture to F/11 APS-C): DoF from 0.804 m to 0.901 m, for a total of 0.097 m (CoC 0.03 mm)
Canon 5D II, 85 mm at 85 cm, F/11 (eq. aperture to F/7.1 APS-C): DoF from 0.821 m to 0.882 m, for a total of 0.061 m (CoC 0.03 mm)
Canon 7D, 85 mm at 85 cm, F/11, DoF from 0.831 m to 0.869 m for a total DoF of 0.038 m (CoC 0.0186 mm)
Canon 5D II, 135 mm at 110 cm, F/18 (eq. aperture to F/11 APS-C): DoF from 1.069 m to 1.132 m, for a total of 0.063 m (CoC 0.03 mm)
Canon 5D II, 135 mm at 110 cm, F/11 (eq. aperture to F/7.1 APS-C): DoF from 1.081 m to 1.120 m, for a total of 0.040 m (CoC 0.03 mm)
Canon 7D, 135 mm at 110 cm, F/11, DoF from 1.088 m to 1.112 m for a total DoF of 0.025 m (CoC 0.0186 mm)
IOW, less DoF with crop when the same lens is used. It will be approximately the same at the same magnification when an equivalent AoV is used, at the same aperture.
And once one gets to 1:1 and beyond, it doesn't make a difference anymore.
Kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....