Question for Great Bustard

Started 9 months ago | Discussions thread
PhotoTeach2 Senior Member • Posts: 8,411
Re: Question for Great Bustard

Michael Fryd wrote:

jrtrent wrote:

tbcass wrote:

You obviously don't understand the concept of equivalence which is understandable since it's a bit abstract. I didn't understand it at first because when it was first brought up it wasn't properly explained. Now I believe I do. Equivalence is about the settings necessary to make photos from 2 different sized sensors look the same relative to exposure, FOV, perspective and DOF. In light of that it's very practical and not an attempt to make a larger sensor seem better than a smaller one which many people seem to believe.

I agree with your post, but would add that many people, including DPR reviews, use the equivalent aperture number to try to tell people that their lens is slower than they think it is. For example, using equivalent aperture rather than actual f-stop numbers, they say that the Stylus 1 at f/2.8 is a stop and a half slower than the RX10 which is also at f/2.8, and even half a stop slower than the FZ1000 at f/4. I find this a confusing misuse of the concept of lens speed.

Yes, "equivalence" can be confusing. You need to be "all in" or you get inconsistent results.

That's why I prefer "angle of view" and "aperture diameter". These are the underlying physical constructs.

When you have the same angle of view and aperture diameter you will get the same results. No need to talk about "equivalence", as long as these two actual values are the same, you get the same results.

Where I found equivalent aperture numbers useful was to realize that with my Olympus E-300 I could get the same depth of field at f/5.6 that I would have needed f/11 to achieve with my Contax film cameras--a very useful two-stop advantage under darker conditions. The FZ200 mentioned by the OP would have as much depth of field at f/2.8 as my Contax would have at f/15.5--nearly a five-stop advantage for the smaller format.

You need to be "all in" in order to get correct results from "equivalence".

Consider a full frame vs. a 1.4X crop camera.

1.4X is a one stop difference.

If we are shooting ISO 200, 1/100 second, 140mm and f/5.6 on the full frame, we would need to shoot ISO 100, 1/100 second, 100mm and f/4 on the 1.4X crop in order to get the same results.

By "same results" I mean, same angle of view, same depth of field, same overall image noise same motion blur, same image brightness, same perspective.

Traditional exposure (light per unit area), is an intermediate step in the process. In order to get the same results, you will end up with different exposures with different sensor sizes.


If your goal is to look at the intermediate "exposure" step in the process, then "equivalence" does not apply. If you are shooting film, you absolutely need to be concerned as traditional exposure issues are designed for the needs of film, not digital.

If you are shooting digital, there is no need to have the same exposure with different sensor sizes. In fact doing so will result in different images from the different sized sensors.

If your goal is to look at the resulting image, then "exposure" is an implementation detail. When I change sensor sizes I need to change focal length in order to maintain the same angle of view. I need to change aperture in order to maintain the same depth of field. I also need to change ISO in order to maintain the same image brightness. Of course the exposure changes with sensor size. It has to in order to get the same result.


Keep in mind that various adjectives apply differently depending on sensor size. For instance is 50mm a wide angle, normal, or telephoto focal length? The answer is that it depends on the sensor it is being used with. On a large format sensor it is wide angle, on a full frame it is normal, and on a 2.8X crop it is telephoto.

Similarly, a "fast" lens is one that allows you to use fast shutter speeds without too much image noise. Depending on the sensor size f/5.6 can be fast or slow.


The problem with this thread is that various people are talking about different things. Some are talking about how to keep the same exposure with different sensor sizes. Others are talking about how to get the same results.

As long as people are talking about different things, it's going to be hard to get a meeting of the minds.

With all due respect, I did NOT read all of the above because you are still comparing DIFFERENT sensor sizes, (to get the SAME image).

What does it matter if you only have ONE sensor size.

And if you have TWO different sensor sizes, you should NOT be trying to get the SAME (exact) image.

Different sensor sizes have different advantages and you should exploit each to indeed result in DIFFERENT IMAGES, (each better in its own UNIQUE way).

WHY care about "equivalence" ???

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