Depth of field for various formats and lenses

Started May 30, 2012 | Discussions thread
stoic little
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Re: Depth of field for various formats and lenses
In reply to Graystar, Jun 1, 2012

Graystar wrote:

amangupta wrote:

... and adjusted the subject distance.

...

I hope I've not made a mistake above. What do you think?

That's your mistake but it wasn't fatal.

An important aspect of comparing images from different sized sensors is perspective, and perspective changes with distance. When this topic is discussed, the presumptions are:
same F-number
same distance
same field of view (meaning focal length must be adjusted by the crop factor.)

When these criteria are followed it's easy to see from the DOF calculator that DOF is more shallow on the larger sensor. It's because the focal length is shorter for the smaller sensor.

When working with a single format, yes, when focal length and distance are increased proportionally, DOF remains about the same as long as the F-number remains the same (within limits...limits that are far from the portraiture range of focal lengths.)

.

Your explanation is very concise and easy to understand so I really don't understand why many are still confused.

Basically DOF is affected by ONLY 2 factors:
A. Actual physical size (diameter/area) of lens aperture chosen

  1. Bigger aperture = less DOF

  2. Smaller = more

B. Subject distance

  1. Nearer = less DOF

  2. Farther = more

Choice of sensor format and lens affects framing and FOV. If you use 50mm F1.4 on 4/3s and FF, A won't be a factor but perspective and FOV will depend on B. If you plan to shot the same FOV then you'll have to put your subject farther (side effect of which is B-2) on the smaller format.

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