Equipment & Techniques > Cameras, Lenses and Shooting gear
DOF and Micro Four-Thirds Format
Dan Kehlenbach:
Err1ksen,
Your explanation certainly makes sense. I am wondering how much difference the lens-to-sensor distance makes in DOF. In Panasonic's other 4/3 camera (L10, I believe), the distance from the lens to the sensor is 40mm while the G1 is 20mm.
[attachment=12874:MicroFou...Diag_001.jpg]
I am looking forward to getting out and experimenting.
Thanks.
Dan Kehlenbach
BJL:
--- Quote from: Er1kksen ---It's also easy to remember this way: While a 14mm lens has the same apparent field of view on m4/3 as a 28mm lens would on 35mm, it's still a 14mm lens, and will have the same dof as a 14 mm lens on 35mm.
--- End quote ---
That is very misleading, because the image used from the 14mm lens in 4/3 is only half the width and height of that from the 14mm lens in 35mm format, so when printed at the same size, it must be enlarged twice as much. That extra enlargement doubles out of focus effects too, and so gives half as much DOF as 14mm in the larger format, and also a very different FOV, if comparing with equal f-stop.
But on the other hand, doubling focal length from 14mm to 28mm at equal f-stop reduces DOF by a factor of four (it goes with the square of focal length.) And doubling f-stop doubles DOF (with same focal length same degree of enlargement.)
So, doing the comparison sanely, viewing equal sized images of the same subject from the same distance:
- 14mm in 4/3 has half the DOF of 14mm in 35mm at the same f-stop
- 28mm in 35mm format has one quarter the DOF of 14mm in 35mm format at the same f-stop
- 28mm in 35mm format has twice the DOF of 28mm in 35mm format at half the f-stop
and thus
- 14mm in 4/3 has twice the DOF of 28mm in 35mm at the same f-stop
- 14mm in 4/3 has the same DOF of 28mm in 35mm at twice the f-stop. E.g 14mm f/4 in 4/3 vs 28mm f/8 in 35mm.
The last is my rule of thumb, doubling focal length and f-stop for equal FOV and equal DOF (and equal diffraction effects.)
Hopefully we will not now return to debating whether it is more reasonable to compare images with completely different field of view from the different formats, or to compare crops to equally sized portions of the differently sized sensors!
BJL:
--- Quote from: Dan Kehlenbach ---I am wondering how much difference the lens-to-sensor distance makes in DOF. In Panasonic's other 4/3 camera (L10, I believe), the distance from the lens to the sensor is 40mm while the G1 is 20mm.
--- End quote ---
That is only distance from the lens mount to the sensor; it has no effect of optical properties like DOF, which will be the same for equal focal length, equal aperture, equal subject distance in any 4/3" format camera.
aaykay:
--- Quote from: Dan Kehlenbach ---I am wondering how much difference the lens-to-sensor distance makes in DOF.
--- End quote ---
From a DOF perspective, it has absolutely zero effect. But what that will do, would be to alter the design of the lens itself (especially true for the really challenging ultra-wides and wides), since the new design will not have to compensate for that extra distance to accomodate the mirror. Also, the design itself becomes a lot more simpler, with less propensity for coma and other distortions.
Ray:
--- Quote from: BJL ---Here is my rule of thumb (but beware; many forum wars have been fought on this topic!)
So about 2/3 stop between Four Thirds and either EF-S or DX.
--- End quote ---
BJL,
The G1 sensor size is 18mmx13.5mm. The Canon EF-S sensor is 22.3mmx14.9mm. The DoF difference between the 4/3rds format and specifically the EF-S cropped format, which is slightly smaller than the DX format, should therefore range between 22.3/18=1.2x and 14.9/13.5=1.1x, depending on the previsualised aspect ratio of the composition.
Assuming one maximises the sensor area in relation to the composition (using a zoom) and assuming one crops only to change the aspect ratio, then the DoF advantage of the G1 in relation to the Canon EF-S cropped format will be, at most, slightly more than 1/3rd of a stop and, at least, slightly less than 1/3rd of a stop.
The best approximation would therefore be 1/3rd of a stop difference, in relation to the Canon APS-C format. Nothing to shout about really. Agreed?
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