Re: What is Equivalence

If one asks, "Why are they different?" that's the first step in a journey to a destination of understanding that exposure is not the same as the total light used to make a photo.

Different format camera can work with the same f-stop and same exposure (the same scene brightness per unit area of the sensor) but that does not guarantee those cameras will make the same photo. In fact, it pretty much guarantees the opposite. The photos will be different...potentially significantly so to the eye. At the same exposure, a smaller format camera captures less total light and makes a photo having more prominent shot noise. At the same f-stop but with different focal lengths, a smaller format camera at a shorter focal length will be working with a smaller diameter lens aperture. Depth of field in the resulting photo will probably be greater.

Equivalence helps a photographer understand those differences and how to use a camera of any format to make the photo they're envisioning.

And I allow myself (amateur) to explain to a person unfamiliar with sizes and wondering about my m43/mFT equipment that it is a bit like the old analog Olympus 1/2 frame cameras. Like a Pen F from yesteryear, it will not deliver as e.g. yesteryear's Nikon FM2 did. However, what is expected? A 4x5, an 8x10? 1/2 frame long ago would not disappoint, and mFT nowadays does neither.
Main advantage of the smaller equipment is lesser weight and for lenses mostly lesser costs (and then some). But then also a caveat, in low light my mFT won't be able to shoot as fast as a full frame which will matter when the object is in motion.
...hm, yeah, well, I get to hear, a smartphone is probably all that one needs. I nod except when the interlocutor shows a certain interest in photography beyond smartphonix. Then I point her or him to discussions as all the above and links inclusive.
So, thanks for this thread!

You can if you need depth of field :-) FF must then stop down aperture, and get same noise as you, with same shutter speed.
and finally: use the new Adobe Ai Denoise :-) mFT get much better these days

My goto man for such stuff is Falk Lumo.

This article covers the subject - assuming that the thread discussion is still about equivalence ... LOL.

www.falklumo.com/lumolabs/articles/equivalence/index.html

Thank you for sharing the link.

There's been no train wreck nor will there be 😀

This is one of the more reasonable discussion. The classification of equivalent cameras and looking at the various requirements that class membership places on a member of the class as a function of sensor size is quite instructive and yes size does matter - after a certain point. 🙀 So for an idealized camera, lens, sensor with all things being equal - every camera is the equivalence class is indistinguishable. However, we live the the real world not an idealized world and a f-number of .5 is not physically realizable using refractive optics. en.wikipedia.org/wiki/Numerical_aperture#Numerical_aperture_versus_f-number Maybe when lenses made of meta-materials are common but we aren't there yet.

This is the reason that it is common in many Photography 101 classes in many universities and art institutes - a camera is handed out to the students to use in the class so that they can learn the basics without having to worry about these issues. We were all given 120 TLR cameras with an 80 mm lens and a hand held light meter to use. What are the basics? How the lens projects the image, parallax from twin lenses or rangefinders, proper exposure, the difference between light flux (candles per unit area) and exposure (total light energy per unit area), the difference between incident and reflective light readings and now to calculate exposure from the light reading. Circle of Confusion and all related to CoC like DOF, hyper focal distance, enlargement ratio and the impacts of enlargement, etc. It is much easier to develop a basic understanding of photography using a single format and a single focal length.

While classification cameras by equivalence might be an interesting academic exercise, I'm not sure how useful it is for beginning photographers. Basic photography is somewhat like basic physics - the most important part is the subject is mastered in the labs.

Truman

I think it is strange to involve ISO, noise, and dynamic range in the equivalence discussion. I find Joseph's article much clearer: www.josephjamesphotography.com/equivalence/

I was a physics major at Stanford for more than two years before I came to my senses and switching to EE. About all I remember learning in the labs was to have great respect for the original experimenters. The Millikan oil drop experiment to measure the charge on an electron is a case in point. Hard to see what's going on, lots of noise in the results.

The physics that I still use today has very little to do with what I learned in the labs I did in high school or college.

You confirm my opinion, concerning "equivalence". Simply put, it is totally correct in theory with theoretical sensors and lenses, but fall down in practice with all the variables that you list in your post.

I quess we can say it is useful as a very rough guide for format comparisons.

I never fully got that part either. Thanks for the link, I've read it before.

ISO and noise are factors because, by definition, equivalent photos are made with different format cameras, working with different exposures and ISOs to produce photos having the same lightness, total light, and shot noise visibility.

Equivalence is a method for determining which settings can be used by different format cameras to make equivalent photos. The factors affecting equivalence and practical applications of making equivalent photos are clearly laid out in the top post.

Another possibly interesting question is what falls outside the equivalence, say, when smaller sensors have an advantage (other than weight and size of a camera).

A common mistake when comparing cameras with different or the same sensor sizes is to use "equivalent" ISOs instead of exposures. ISOs are not calibrated across various manufacturers.

Mostly but not always. Let analyse this simple shot below, and see if I could have made an "equivalent" with M43

Shot a 30seconds F11 on a FF sensor with a 24mm shift lens at base ISO64.

Let us imagine I wanted to shoot this on an M43 camera. First off, the easy one. Wide angle shift lenses do not exist for the M43 format.

We know that there is a theoretical two stop difference to consider when comparing formats. Shutter speed makes no difference to the look of this image. None of the smaller formats can match the ISO 64 noise levels by going lower, in the case of M43, it would need to go down to, the only ISO15. M43 sensors arrive at ISO 200. I can close down to F22 to get the same DoF. So I could make an equivalent image regarding DoF, but the M43 image will have more noise and less DR.

On the other hand I could make a theoretically equivalente image by using an MF format camera.

It is not always possible to make an equivalent image, with the gear that is commercially available.