Question on Aperture, DoF, and teleconverters
Discussion
This is one that's been bugging me, so I wonder if any of you knowledgeable people could shed some light (so to speak)...
It's about the effect of a teleconverter on depth of field.
Say one had a 200mm f2.8 lens and a 2x teleconverter.
The combination would be a 400mm with a 2 stop reduction in the light transmitted - so an f5.6 equivalent. Now I know that the light is reduced, but what is the effect on the depth of field?
I know depth of field is a factor which is affected by
a. the physical size of the aperture
b. the distance from the aperture to the film (sensor) plane
Would it give the same depth of field characteristic as a 400mm f5.6 lens, or would the DoF be more shallow as the physical aperture in the 200mm f2.8 may be physically larger?
Reasons for asking relate to some thoughts on lenses I may be considering...
Many thanks for your thoughts,
Conrad.
P.S. I know in terms of quality a 400mm f5.6 prime lens is likely to be significantly better quality than a 200 f2.8 with teleconverter.
It's about the effect of a teleconverter on depth of field.
Say one had a 200mm f2.8 lens and a 2x teleconverter.
The combination would be a 400mm with a 2 stop reduction in the light transmitted - so an f5.6 equivalent. Now I know that the light is reduced, but what is the effect on the depth of field?
I know depth of field is a factor which is affected by
a. the physical size of the aperture
b. the distance from the aperture to the film (sensor) plane
Would it give the same depth of field characteristic as a 400mm f5.6 lens, or would the DoF be more shallow as the physical aperture in the 200mm f2.8 may be physically larger?
Reasons for asking relate to some thoughts on lenses I may be considering...
Many thanks for your thoughts,
Conrad.
P.S. I know in terms of quality a 400mm f5.6 prime lens is likely to be significantly better quality than a 200 f2.8 with teleconverter.
Well it looks like I've found the answer to my own question!
For anyone that's interested, a 200mm f2.8 with 2x teleconverter (effectively a 400mm f5.6) will have exactly the same depth of field characteristics as an actual 400mm f5.6.
"All lenses of the same focal length and aperture have the same depth of field, so as far as DOF goes, a 600/8 lens is identical to a 300/4 + 2x TC"
Taken from:
http://www.bobatkins.com/photography/reviews/tcs.h...
Cheers,
Conrad.
For anyone that's interested, a 200mm f2.8 with 2x teleconverter (effectively a 400mm f5.6) will have exactly the same depth of field characteristics as an actual 400mm f5.6.
"All lenses of the same focal length and aperture have the same depth of field, so as far as DOF goes, a 600/8 lens is identical to a 300/4 + 2x TC"
Taken from:
http://www.bobatkins.com/photography/reviews/tcs.h...
Cheers,
Conrad.
Yup, taking the simple approach, aperture is focal length / diameter of lens. THerefore adding a 2xTC you double the focal length but don't effect the physical diameter of the hole in the lens.
Similar goes for sensor size - a smaller sensor with the same field of view as a larger one (ie same magnification and therefore shorter focal length) will have larger depth of field for a given aperture. This has the downside that if you took the same shot of a 1.5x crop DSLR vs full frame you need a faster lens to through the background out of focus. Hence compacts and 4/3rds don't appeal.
Similar goes for sensor size - a smaller sensor with the same field of view as a larger one (ie same magnification and therefore shorter focal length) will have larger depth of field for a given aperture. This has the downside that if you took the same shot of a 1.5x crop DSLR vs full frame you need a faster lens to through the background out of focus. Hence compacts and 4/3rds don't appeal.
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