All this talk about "equivalence" is silly

Started Jun 10, 2011 | Discussions
Howard
Howard Senior Member • Posts: 1,857
All this talk about "equivalence" is silly

Someone wrote a web page about "equivalence" some time ago. Let me first say that I perfectly understand the concept (it is really about perspective, DOF, framing, etc.), but I think all this talk about "equivalence" is silly, confusing and mostly bogus.

For example, the "equivalence" adherent will say that a 300 f/4 lens is "equivalent" to a 480 f/5.6 lens on a crop camera, or some such. But this has severely limited applicability -- that is, only if you are narrowly concerned about perspective, DOF and want to duplicate exactly the same image as on a FF camera. But this is not the only, or most important concern for most people. Actually, I want to argue that for most people, this is not a concern at all.

Some cases in point:

Case 1: if you want to stop action, in the same lighting condition, with the same ISO, a f/2.8 lens gives you the same shutter speed on a crop sensor or a FF sensor, so to same something like a 300 f/4 lens is "equivalent" to a 420 f/5.6 lens is completely misleading.

Case 2: if your primary concern is reach, then a 300 f/4 lens is decidedly similar to a 480 f/4 lens on a 1.6 crop camera, not 480 f/5.6.

Anyway, I can go on. But I think this "equivalence" talk is very confusing to beginners and causes more harm (confusion) than good (clarification).

Howard

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tkbslc Forum Pro • Posts: 12,683
Re: All this talk about "equivalence" is silly

I think you should understand what you are talking about before you post a rant.

A FF sensor has better noise characteristics than a crop camera (comparing similar generation sensors) and so you can use 1-1.5 stops higher ISO and get the same image quality. Also, the DOF is at least one stop deeper on APS-C at the same effective focal length and distance to subject. So if you were shooting at 300mm f4 and 1/1000 at ISO 400, a FF shooter would be using a 480mm f5.6 lens at ISO 800 and 1/1000 and getting roughly the same FOV, DOF, and noise at the same shutter speeds. ("roughly" because it is actually just more than 1 stop difference, but figuring with one stop is easier)

The only reasons to use a larger aperture are for more DOF or faster shutter speeds and the FF camera provides that with the larger sensor and better noise control.

Howard
OP Howard Senior Member • Posts: 1,857
I understand it, do you?

That is exactly what I am talking about -- that you are using the term "equivalence" from a very narrow perspective (no pun intended).

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tkbslc Forum Pro • Posts: 12,683
Re: I understand it, do you?

Howard wrote:

That is exactly what I am talking about -- that you are using the term "equivalence" from a very narrow perspective (no pun intended).

It is equivalent! If you have the same DOF, FOV, shutter speed and noise, what is not equivalent?

Howard
OP Howard Senior Member • Posts: 1,857
Reach, shutter speed, see my original post (EOM)
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tkbslc Forum Pro • Posts: 12,683
Re: Reach, shutter speed, see my original post (EOM)

Reach? You are using a longer (and slower) lens on FF to make up for that.

Shutter speed? You can use higher ISO at same noise performance.

It seems like you aren't even reading what I wrote.

AOKH
AOKH Senior Member • Posts: 2,675
Re: All this talk about "equivalence" is silly

Very well said; don't think it can be summarized much better than this. Beginners may not need to worry much about differences between crop and FF, but when they eventually decide to look into it, they may as well get it right IMHO

tkbslc wrote:

I think you should understand what you are talking about before you post a rant.

A FF sensor has better noise characteristics than a crop camera (comparing similar generation sensors) and so you can use 1-1.5 stops higher ISO and get the same image quality. Also, the DOF is at least one stop deeper on APS-C at the same effective focal length and distance to subject. So if you were shooting at 300mm f4 and 1/1000 at ISO 400, a FF shooter would be using a 480mm f5.6 lens at ISO 800 and 1/1000 and getting roughly the same FOV, DOF, and noise at the same shutter speeds. ("roughly" because it is actually just more than 1 stop difference, but figuring with one stop is easier)

The only reasons to use a larger aperture are for more DOF or faster shutter speeds and the FF camera provides that with the larger sensor and better noise control.

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Regards. Anders

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Pultzar Senior Member • Posts: 1,512
Re: All this talk about "equivalence" is silly

I think that you are forgetting that the larger sensor allows you to bump the ISO up a stop and retain relatively the same noise characteristics and image quality.

200mm F2.8, ISO 100 on crop = 320mm F4.5, ISO 200 on FF

Marc de Vries Contributing Member • Posts: 856
Re: All this talk about "equivalence" is silly

Howard wrote:

Someone wrote a web page about "equivalence" some time ago. Let me first say that I perfectly understand the concept (it is really about perspective, DOF, framing, etc.), but I think all this talk about "equivalence" is silly, confusing and mostly bogus.

For example, the "equivalence" adherent will say that a 300 f/4 lens is "equivalent" to a 480 f/5.6 lens on a crop camera, or some such. But this has severely limited applicability -- that is, only if you are narrowly concerned about perspective, DOF and want to duplicate exactly the same image as on a FF camera. But this is not the only, or most important concern for most people. Actually, I want to argue that for most people, this is not a concern at all.

Most people make snapshots, and don't think about most aspects of their photos.
So yes, for most people this is not a concern at all.

The web page about equivalence was meant for people who put thought in their shots.

People who have envisioned a certain shot and have specifcally choosen a certain perspective for their shot, have choosen a certain DoF for their shot, have choosen a certain shutter speed for their shot.

If those factors matters for your shot, than equivalance is extremely important and will explain the implications if you want to make that shot with a different camera.

Some cases in point:

Case 1: if you want to stop action, in the same lighting condition, with the same ISO, a f/2.8 lens gives you the same shutter speed on a crop sensor or a FF sensor, so to same something like a 300 f/4 lens is "equivalent" to a 420 f/5.6 lens is completely misleading.

The mistake you make here is that ISO values on different cameras are NOT the same, even though they are called the same. ISO 1600 on a crop camera doesn't give the same noise level as ISO 1600 on a FF camera or ISO 1600 on a compact camera.
When you say "the same iso" you really mean: "different noise levels".

And yes, in the same lighting conditions with different noise levels a f/2.8 lens gives you the same shutter speed on a FF sensor as on a compact sensor.
But it's a completely useless comparison.

Case 2: if your primary concern is reach, then a 300 f/4 lens is decidedly similar to a 480 f/4 lens on a 1.6 crop camera, not 480 f/5.6.

No it's not the similar, because the 480/f4 lens gives a different DoF compared to the 480 f5.6

If your only concern is resolution and everything else in the shot is not important to you, then indeed equivalence is not a concept that you will use.

And if you really understand equivalence you will also understand the advantages of each camera format and will then be able to make a decision which is best for your situation.

You can then decide that a crop camera gives you more advantages than disadvantages when you are limited in reach.
It is equivalence that lets you understand why!

Anyway, I can go on. But I think this "equivalence" talk is very confusing to beginners and causes more harm (confusion) than good (clarification).

For beginners, the best thing is not to tell them about crop factors and other sensors at all. Just let them learn how to get the best results with their cameras.

The problem is that people always tell them about crop factor, but not about the rest. And then people get confused and want to know how it really works. Either tell them the whole story (equivalence) or not at all. But don't tell them only about crop factor. Because that is far more confusing them equivalence.

Dave_K Regular Member • Posts: 425
Not really.

For those of us who "cut our teeth" on film it's quite important. When I am asked to do a shoot, I need to kind of "pre-shoot" the event in my head. I need to plan ahead so I take the correct lenses to get the effect and shots the customer wants. Failing to take "equivalence" into account can result in having too long a lens to get the job done right. And yes, there ARE times when you simply cannot back-up with your feet any farther.

Cheers.

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tko Forum Pro • Posts: 12,618
you read, but did you understand?

Case 1: if you want to stop action, in the same lighting condition, with the same ISO, a f/2.8 lens gives you the same shutter speed on a crop sensor or a FF sensor, so to same something like a 300 f/4 lens is "equivalent" to a 420 f/5.6 lens is completely misleading.

No. You forgot ISO. Since you can go with a higher ISO for the same noise, you can use a F5.6 on your large sensor instead of a F2.8 and get a similar looking photo.

Using a F2.8 lens on a crop sensor and a FF sensor will give you (1) a different DOF and a (2) a different amount of noise. They are NOT equivalent.

Case 2: if your primary concern is reach, then a 300 f/4 lens is decidedly similar to a 480 f/4 lens on a 1.6 crop camera, not 480 f/5.6.

Nope. . You start to talk about reach, then use aperture as an example. What does aperture have to do with reach? Nothing. DOF is controlled by aperture, not reach. F4 and F5.6 will give you the same DOF, 300MM and 480MM will give you the same reach.

Anyway, I can go on. But I think this "equivalence" talk is very confusing to beginners and causes more harm (confusion) than good (clarification).

Well, obviously it is confusing to many people. But that doesn't make it any less true. It's a basic fact, like F-stop or EV. Should be taught in any photography class. Just follow the rules to adjust ISO, F-stop, and FL between different sensor size systems. It's not perfect, but it's the best way to make similar images.

Guv Contributing Member • Posts: 779
Same here

I've been shooting film SLRs for over 20 years, cutting my teeth on my dad's old manual Minoltas and eventually building my own collection. The focal length equivalent is a convenient translation device for comparing formats. I don't consider it at all when thinking of DOF so that part is useless for me and, I suppose, where the OP is claiming the confusion enters.

rmhrmxyahoo Junior Member • Posts: 46
Re: All this talk about "equivalence" is silly

All this talk about "equivalence" is silly.
The concept "equivalence" is a crappy one.

Don't try to associate your cropped sensor size to 135mm sized sensor.
If you are talking about "physics", then forget about "equivalence".

Cropped is cropped, full sized is full sized. They are different in many ways.
Both can take good photos.

wihakowi Regular Member • Posts: 242
Re: Same here

Pultzar wrote:

I think that you are forgetting that the larger sensor allows you to bump the ISO up a stop and retain relatively the same noise characteristics and image quality.

200mm F2.8, ISO 100 on crop = 320mm F4.5, ISO 200 on FF

Huh? I don't get the eqaution.

Guv wrote:

I've been shooting film SLRs for over 20 years, cutting my teeth on my dad's old manual Minoltas and eventually building my own collection. The focal length equivalent is a convenient translation device for comparing formats. I don't consider it at all when thinking of DOF so that part is useless for me and, I suppose, where the OP is claiming the confusion enters.

I agree with this observation as well as the OP's take on it all. This thread certainly contains a lot of "absolutes" in re: ISO performance between all FF vs all crop factor bodies.

So a 5d or older 1 series body is always better in noise at the same ISO than a new crop body? Just asking ...
Steve

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Pultzar Senior Member • Posts: 1,512
Re: All this talk about "equivalence" is silly

Well said.

Pultzar Senior Member • Posts: 1,512
Re: Same here

Pultzar wrote:

I think that you are forgetting that the larger sensor allows you to bump the ISO up a stop and retain relatively the same noise characteristics and image quality.

200mm F2.8, ISO 100 on crop = 320mm F4.5, ISO 200 on FF

Huh? I don't get the eqaution.

The crop sensor produces a narrower field of view than the full frame sensor. So a 200mm lens on a crop sensor has the same field of view as a 320mm lens on a FF sensor (200*1.6 = 320)

So you put a 200mm on your crop and a 320mm on your FF. Now what?

It's time to get the apertures the same size. Aperture size = focal length / f-stop. So the aperture size of 200mm f/2.8 is 71. In order to get this same aperture size on the FF camera, it is 320/x = 71. x=4.5

Great, now we have the same field of view and depth of field. What about exposure? Since the FF is using a slower aperture, we need to bump up the ISO to compensate. I went from 100 to 200. This isn't 100% precise but it is ballpark considering that the next jump may be 400 depending on your camera.

The noise characteristics of the FF camera at ISO 200 are likely similar to the noise of the crop camera at ISO 100. So noise is the same. This is much more important than having the ISO be the same.

So now we have:

-Same field of view
-Same depth of field
-Same noise

If you stand in the same location and use the same shutter speed, you will have roughly the same image. Then aberrations like CA, lens sharpness, etc come into play but that is another topic.

bronxbombers Forum Pro • Posts: 18,226
Re: All this talk about "equivalence" is silly

Howard wrote:

Someone wrote a web page about "equivalence" some time ago. Let me first say that I perfectly understand the concept (it is really about perspective, DOF, framing, etc.), but I think all this talk about "equivalence" is silly, confusing and mostly bogus.

For example, the "equivalence" adherent will say that a 300 f/4 lens is "equivalent" to a 480 f/5.6 lens on a crop camera, or some such. But this has severely limited applicability -- that is, only if you are narrowly concerned about perspective, DOF and want to duplicate exactly the same image as on a FF camera. But this is not the only, or most important concern for most people. Actually, I want to argue that for most people, this is not a concern at all.

Well, for wide to moderate angle where reach is rarely a problem I think this is probably THE most important thing.

Some cases in point:

Case 2: if your primary concern is reach, then a 300 f/4 lens is decidedly similar to a 480 f/4 lens on a 1.6 crop camera, not 480 f/5.6.

Not really in that the crop has nothing to do with reach, it's the density. Case in point a FF 5D2 has more reach than the 1.3x 1D2 and the same reach as a 1.6x 20D.

bronxbombers Forum Pro • Posts: 18,226
Re: All this talk about "equivalence" is silly

Howard wrote:

Someone wrote a web page about "equivalence" some time ago. Let me first say that I perfectly understand the concept (it is really about perspective, DOF, framing, etc.), but I think all this talk about "equivalence" is silly, confusing and mostly bogus.

For example, the "equivalence" adherent will say that a 300 f/4 lens is "equivalent" to a 480 f/5.6 lens on a crop camera, or some such. But this has severely limited applicability -- that is, only if you are narrowly concerned about perspective, DOF and want to duplicate exactly the same image as on a FF camera. But this is not the only, or most important concern for most people. Actually, I want to argue that for most people, this is not a concern at all.

Some cases in point:

Case 1: if you want to stop action, in the same lighting condition, with the same ISO, a f/2.8 lens gives you the same shutter speed on a crop sensor or a FF sensor, so to same something like a 300 f/4 lens is "equivalent" to a 420 f/5.6 lens is completely misleading.

Well if you are not reach limited then the FF would have a larger surface area to capture over and would produce less noise so it would kind of fit. Although at long focal lengths like that you are often going to crop anyway so in that case the FF doesn't gain you any noise improvement.

Basically if use a 300 2.8 on a 7D and a 5D2 and shoot a distant bird then you can either get the bird with more reach but worse noise than the 5D2 or get the bird with a trace more detail a tiny bit less noise than with the 5D2.

If the bird is close and you can fill the frame with it a 420 2.8 then you can use a 300 2.8 on the 7D and also fill the frame but it will have worse noise than the FF shot since you are tossing the light onto a small collector compared to the FF. So the noise might be more like a 420 f/4ish vs 300 2.8 on the 7D.

bronxbombers Forum Pro • Posts: 18,226
Re: All this talk about "equivalence" is silly

Pultzar wrote:

I think that you are forgetting that the larger sensor allows you to bump the ISO up a stop and retain relatively the same noise characteristics and image quality.

200mm F2.8, ISO 100 on crop = 320mm F4.5, ISO 200 on FF

Basically if use a 300 2.8 on a 7D and on a 5D2 and then shoot a distant bird with both from the same spot then you can either get the bird with the 7D with more reach (more pixels per duck) but worse noise than with the 5D2 (when viewing at non-noarmalized size) or get the bird with a trace more detail and artifacts (due to careful downscaling and filtering) and a tiny bit less noise (due to slightly higher efficiency per area of sensor) than with the 5D2.

If the bird is close and you can fill the frame with it a 420 2.8 then you can use a 300 2.8 on the 7D and also fill the frame but it will have worse noise than the FF shot since you are tossing the light onto a small collector compared to the FF. So the noise might be more like a 420 f/4ish vs 300 2.8 on the 7D.

Erik00 Regular Member • Posts: 219
Re: All this talk about "equivalence" is silly

I think Howard knows what he is talking about.

The essence from his post - as I understand - is that we should say: a lense at f: 2.8 is 2.8 on all cameras both FF and cropped.

This is of course a fact not an oppinion and saying something else is also in my oppinion more confusing than helpfull.

Questions about how to obtain the same image quality (with same dof, at same shutterspeed and fov) is in my oppinion more interesting in a thread about the advantages and disadvantages of a FF camera ctr. a cropped.

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