A standard zoom for D800?

Started Nov 11, 2012 | Questions thread
le_alain Senior Member • Posts: 1,839
Re: A standard zoom for D800?

olyflyer wrote:

Unfortunately the underlined text is incorrect.

I used DOF master to check it and took the following example:

70/2.8 at 3m subject distance gives 0.31m DOF. With the 120/4 you must back off to 5.1m from your subject to get the same image and in that case the DOF will be 0.41m. It may not be a lot and may not even matter in most cases but never the less, the DOF is more and not smaller for the same image. The 5.1 meter subject distance comes from the fact that 120mm is 70% more than 70mm and 5.1 meter is about 70% more than 3 meter.

Humm ...

perhaps I am wrong, but aperture is

70/2.8=25 and 120/4=30, so a little more for the 120 f4, should have a swallower DOF

I Just did a test with the 70 at 2.8 and 120 at F4, with same framing.

not so easy to compare as perspective is different, but DOF seems to be a little smaller with the 120f4, that was supposed to be with the larger aperture.

Am I wrong or didn't compare correctly ?

 le_alain's gear list:le_alain's gear list
Epson R-D1 Sony Alpha a7S Sony Alpha a7R II Sony FE 55mm F1.8 Sony FE 24-70mm F4 OSS
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