Canon RF 45mm f/1.2

Tom_W
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p.7 #1 · Canon RF 45mm f/1.2

takowasa wrote:
Depends on what you mean by "light gathering". For the same scene and shutter speed, f/1.2 on FF will put 2.5x more light on the sensor than it will on crop. However, the FF sensor has 2.5x the area, so the amount of light per area will be the same. With regards to the ISO setting, then, it's the amount of light per area that matters, not the total amount of light on the sensor. But with regards to noise, what matters is the total amount of light on the sensor, not the amount of light per area (regardless of...Show more →

I'm going to have to work through this for a minute, because I'm sure you're not saying what I think you're saying. And I'm not quite sure what I even think you're saying, but that's on me.

I'll use a practical example (and the basis of me using the 200-800 on the R5 versus the 100-500 on the R7)

800 on the full frame body gives a pretty close framing to 500 mm on a crop body.

So I use 800 on my R5 for birding rather than 500 on my R7 which would frame equally so the bird makes up a similar amount of the final image.

Now, at 800, the 200-800 gives a maximum aperture of f/9
at 500 mm, the 100-500 gives a maximum aperture of f/7.1

So, a win for the 100-500 based on max aperture, but hang on.

We want equivalent exposure, obviously, and we want a shutter speed of 1/2000 so the twitchy little bird stands a chance of not having motion blur. (we can tweak that shutter speed to help out with ISO if the subject is in too dark an area, of course).

Let's say it's a bright, shadowy area where the bird is located, so we will have the following settings to achieve 1/2000 shutter speed with the respective cameras, the R5 at 800 mm f/9 and the R7 at 500 mm f/7.1.

For an EV of, say, 12, at f/7.1, the ISO setting would be approx 2500
For an EV of 12 at f/9, the ISO setting would be approximately 4000

So, as we already had figured, a 2/3 stop difference in aperture results in a 2/3 stop difference in ISO setting.

Now, we think that the R5 loses here, higher ISO = higher noise. BUT....

If we look at the DR chart vs ISO on Photonstophotos.net comparing the R5 and R7, we see that the R7 has a photographic DR of about 6.3 at ISO 2546, so roughly 2500, whereas the R5 has a photographic DR of 6.93 at 4022, or roughly ISO 4000. In fact, to match the PDR of the R7 at 2500 ISO, the R5 can be at ISO 6400.

So while I lose 2/3 of a stop of aperture with the 800, the R5 is about 1 1/3 stops cleaner in terms of PDR compared to the R7, resulting in a somewhat cleaner image.

We can throw a lot of abstracts in there, a lot of variables (if we crop to match framing, etc.) but in practical use, the R5, as long as the entire sensor is used, gives a cleaner image than the R7.

Aug 09, 2026 at 11:46 AM

takowasa
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p.7 #2 · Canon RF 45mm f/1.2

Tom_W wrote:
I'm going to have to work through this for a minute, because I'm sure you're not saying what I think you're saying. And I'm not quite sure what I even think you're saying, but that's on me.

I'll use a practical example (and the basis of me using the 200-800 on the R5 versus the 100-500 on the R7)

800 on the full frame body gives a pretty close framing to 500 mm on a crop body.

Should be exactly the same, actually.

So I use 800 on my R5 for birding rather than 500 on my R7 which would frame equally so the bird makes up a similar amount of the final image.

Yes.

Now, at 800, the 200-800 gives a maximum aperture of f/9
at 500 mm, the 100-500 gives a maximum aperture of f/7.1

So, a win for the 100-500 based on max aperture, but hang on.

We want equivalent exposure, obviously, and we want a shutter speed of 1/2000 so the twitchy little bird stands a chance of not having motion blur. (we can tweak that shutter speed to help out with ISO if the subject is in too dark an area, of course).

Let's say it's a bright, shadowy area where the bird is located, so we will have the following settings to achieve 1/2000...Show more →

For the same scene and shutter, yes.

Now, we think that the R5 loses here, higher ISO = higher noise. BUT....

If we look at the DR chart vs ISO on Photonstophotos.net comparing the R5 and R7, we see that the R7 has a photographic DR of about 6.3 at ISO 2546, so roughly 2500, whereas the R5 has a photographic DR of 6.93 at 4022, or roughly ISO 4000. In fact, to match the PDR of the R7 at 2500 ISO, the R5 can be at ISO 6400.

Quick note: [P]DR is a tricky subject in and of itself. Many conflate DR with noise, but, while related, they are the same. Anyway, that's a whole other discussion.

So while I lose 2/3 of a stop of aperture with the 800, the R5 is about 1 1/3 stops cleaner in terms of PDR compared to the R7, resulting in a somewhat cleaner image.

It's possible the R5 sensor is a little "cleaner" than the R7 sensor, and that gives the R5 a slight advantage for equivalent photos.

We can throw a lot of abstracts in there, a lot of variables (if we crop to match framing, etc.) but in practical use, the R5, as long as the entire sensor is used, gives a cleaner image than the R7.

I would like to say at least as clean (and detailed) so long as you use a lens that is just as sharp, gives the same angle of view, and has the same (or faster) equivalent f-stop. But if using the same lens on both cameras, the R7 would most likely come out on top if cropping the R5 to get the same framing as you'd get with the R7.

Aug 10, 2026 at 12:04 AM

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