Question for Great Bustard

Started 3 months ago | Discussions thread
HumanTarget Senior Member • Posts: 1,551
Re: Question for Great Bustard

Michael Fryd wrote:

kiwi2 wrote:

Michael Fryd wrote:

The simple explanation is that if the angle of view, shutter speed, and aperture diameter are the same, you will get the same image noise and depth of field, independent of sensor size.

There is no need to use the word "equivalent".

For instance. Consider a full frame camera with a 75mm lens with a 25mm aperture diameter, compared to a 1.5X crop with a 50mm lens and the same 25mm aperture diameter.

We know from the crop factor and focal lengths that both cameras have the same angle of view. Both cameras are set to the same aperture diameter. Assuming both sensors are of similar technology, we expect to see the same overall image noise from both systems, and the same depth of field.


Another way to look at the example is that a 75mm lens with a 25mm aperture diameter is f/3, and the 50mm lens with the a 25mm aperture is f/2. Therefore some would say that that 50mm on a 1.5X crop body is "equivalent" to 75mm on a full frame, and that f/2 on a crop body is "equivalent" to f/3 on a full frame.

That's fine when you can get lenses for the smaller sensor that are fast enough to compensate. (f/2 vs f/3)

However, quite often in practice, like in my favourite subject of wide field astro, either camera system owner is going to be shooting with the fastest lenses they can get their hands on. I could look at a FF camera with a 24mm f/1.4 lens on. I won't find a 16mm f/0.95 lens to reach equivalence with my APS-C camera.

When I chose the APS-C X-T2 for wide field astro work, I fully realized the disadvantage of over one stop in light gathering ability I would be taking. That was a trade-off I was happy to make for other aspects like quality of lenses and camera interface, and also having a smaller lighter system for casual daytime photography as well.

People can decide they are not concerned with reaching "equivalence" - the same level of image quality. But nonetheless still get on with creating the photos that they had envisioned with their chosen camera system.

Astrophotography is a good example. When you are taking photos of something infinitely far away, your depth of field is infinitely deep. In such a case, you can afford to give up some depth of field by using a smaller aperture.

I assume you meant larger aperture (smaller f-number) here?

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