# Why recommend a superzoom for deep dof?

Started May 16, 2012 | Discussions thread
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 Re: Neither lenses, focal lengths, nor apertures have a DOF In reply to jrtrent, May 18, 2012

jrtrent wrote:

Great Bustard wrote:

Neither lenses, focal lengths, nor apertures have a DOF

Who's saying they do?

People who say the DOF depends only on the focal length and use the DOF scales on some lenses as "evidence".

The youtube video simply said that depth of field is determined by aperture, focal length, and distance from subject.

It also depends on display size, viewing distance, and visual acuity.

These are the same parameters that you can input into various online depth of field calculators.

These calculators assume an 8x10 inch photo (or any photo with a 13 inch diagonal), viewing distance of 10 inches, and 20-20 vision.

What's at issue here is Barrie's statement, "Focal length doesn't affect Depth of Field." Well, of course it does, otherwise it wouldn't be part of a formula for calculating depth of field.

I don't know the context of his statement, but let's give it a new one. Consider a person with a 4/3 sensor using a lens at 50mm f/2. The photo will have the same DOF as one taken with a FF sensor at 100mm f/4, if the focal distance is the same, the display diagonal is the same, and the photos are viewed from the same distance and visual acuity.

But let's say we stay within a system. If we keep the framing the same, then the same f-ratio will result in the same DOF for the same framing. For example, 50mm f/2 10 ft from the subject and 100mm f/2 20 ft from the subject on the same format will result in the same DOF.

So, as always, the context for the statement is really essential.

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