03-03-2012, 05:14 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]
The MFD is a function of the lens design, not whatever size sensor you put behind it. The only thing the sensor size really influences is the field of view, hence we talk about "equivalent focal lengths" to get a similar field of view for different sensor sizes.
If one lens has a closer MFD, it stays that way no matter what sensor size you put behind it.
So if a particular 85mm lens can focus closer than a particular 135mm lens, it remains that way when you put the 85mm on an APS-C camera and the 135mm on a FF camera. Or the other way around. The 85mm lens always will have the closer focus ability, no matter on what camera with whatever sensor size you put it.
85mm on APS-C is equivalent to 135mm on FF, they give a similar field of view. They do not have the same focal length, so what you typed was actually incorrect. You meant, equivalent focal length or roughly the same field of view.
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]
The MFD is a function of the lens design, not whatever size sensor you put behind it. The only thing the sensor size really influences is the field of view, hence we talk about "equivalent focal lengths" to get a similar field of view for different sensor sizes.
If one lens has a closer MFD, it stays that way no matter what sensor size you put behind it.
So if a particular 85mm lens can focus closer than a particular 135mm lens, it remains that way when you put the 85mm on an APS-C camera and the 135mm on a FF camera. Or the other way around. The 85mm lens always will have the closer focus ability, no matter on what camera with whatever sensor size you put it.
85mm on APS-C is equivalent to 135mm on FF, they give a similar field of view. They do not have the same focal length, so what you typed was actually incorrect. You meant, equivalent focal length or roughly the same field of view.