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wsmith96 · May 29, 2026

Mekos said:
After having changed to mirrorless (owning now the Canon R6 Mark II and Canon R7), last week I decided and bought the fullframe Canon 5D Mark IV (I own the APS-C Canon 7D). Out of the box, battery and memory card ready, I turned upset/nervous with something: Only in Av (or also in Tv mode), choosing an aperture (i.e. f/8), no matter the different brightness I pointed the camera to, the shutter speed (or the aperture in Tv) remained always the same, turning the file underexposed or overexposed! never that had happened before with any Canon camera I had owned. So, or there's a real problem with the upper left dial only in Av or Tv modes (not in P or M), or... for the first time I feel dumb with the menu of a Canon camera! (No, no exposure limits reached, nor ISO problem: tried setting to 100 and also in auto). Something else to try? Please help! Thanks, guys!

check the shutter speed settings in custom functions 2 to see if it is set to a particular speed.

David - Sydney · May 29, 2026

Chig said:
Be nice to see Astro versions of cameras again like the eos Ra or no AA filter versions like the 5Dsr maybe an R5a or R5sr based on the R5ii ?

Given the "reasonable" pricing to mod your camera sensor using companies like Spencers (https://www.spencerscamera.com)
provides many options (IR, full spectrum, visible+Ha, etc) then it might not be profitable for Canon. Spencers also offer new or even used bodies from their site.

Clip in filters from Astronomik means that the camera remains "normal" and yet narrow band when you want it - albeit fiddly to install at night with gloves.
You can even add back a "clear" clip in filter to restore the camera to normal after removal of the AA/IR filter

Front filters like https://capturetheatlas.com/capture-the-night-filter/ can also provide some more subtle Ha which I prefer but have a slight transmission loss.

I can't see Canon releasing another one. I think that they had an option with the R5 but decided against it.

David - Sydney · May 29, 2026

MikeGalos said:
Diffraction is based on the size of the photo site. For the same resolution sensor the site on an APS-C is always going to be the same proportion smaller and give one stop worse diffraction issues. That's physics. As resolution increases the size of those sites is smaller. If the sensor is smaller the size of the sites is smaller. The size of the Airy disc is tied to the aperture. When the photo sites are smaller than the Airy disc you are losing resolution. When they're less than half the size of the Airy disc you start getting noticeable resolution loss. The only ways to fix that are to go with bigger sensors or lower resolution sensors.

I do wonder how diffraction in practice seems to be less of an issue for higher mp sensors than the maths would indicate.

I like f16 for having deliberate diffraction spikes for light point sources at night for instance... especially with odd numbered aperture blades.
For underwater macro work with powerful strobes, f16-f18 is common for a single shot as nailing DoF focus when moving around is really hard.
For macro on land whether on a rail or stepped in-camera then f11 seems to be a common option which should still show diffraction theoretically but in practice is more than acceptable once stacked.

exkeks · May 29, 2026

Canon Rumors said:
Unrelated, but I've been slacking with the site a bit. I'm in the process of moving countries again at the end of June. The moving process is still awful, even with experience.

In case you didn’t notice: The Twitter postings have stopped in mid May.

MikeGalos · May 29, 2026

bloblom said:
With higher resolution sensors, this difference between FF and APS-C is getting slimer with each new generation of camera and in a few years we probably won't compare FF and APS-C on diffraction.

Diffraction is based on the size of the photo site. For the same resolution sensor the site on an APS-C is always going to be the same proportion smaller and give one stop worse diffraction issues. That's physics. As resolution increases the size of those sites is smaller. If the sensor is smaller the size of the sites is smaller. The size of the Airy disc is tied to the aperture. When the photo sites are smaller than the Airy disc you are losing resolution. When they're less than half the size of the Airy disc you start getting noticeable resolution loss. The only ways to fix that are to go with bigger sensors or lower resolution sensors.

Chig · May 29, 2026

Be nice to see Astro versions of cameras again like the eos Ra or no AA filter versions like the 5Dsr maybe an R5a or R5sr based on the R5ii ?

bloblom · May 29, 2026

neuroanatomist said:
The long end of the 100-500, when used on APS-C, gives an FoV equivalent to 800mm on FF, but the f/number remains f/7.1. Thus 800mm f/7.1.

I’ll leave the rest of the explanations to @AlanF if he chooses to reply, but his numbers and reasoning are completely correct.

For FoV but it's not the core of the message here.

Regarding the "2 stops more" I sincerly doubt his numbers are correct.
You let more light with a bigger pupil, true, but you spread it over a greater surface (focal length/magnification), that's the entire point of having f-stop (focal length/entrance pupil) as a universal value for exposure, it's already taken into account.

If we take the total light gathered formula (light intensity * exposure * sensor size), how can reducing light intensity by 2/3rd of a stop increase the dynamic range by another 2/3rd of a stop?

Let's simplify to total light to ignore exposure, assuming it's the same on both systems.

Light intensity at the focal plane is defined by 1/N² where N is the aperture of the lens (this is directly derived from the formula that allows you to calculate the F-number of said lens)

For the R7:
Intensity = 1/7.1² = 1/50.41 = 0.01984
Sensor size = 22.3 * 14.8 mm = 330.04 mm²

0.01984 * 330.04 = 6.547

For the R5:
Intensity = 1/9² = 1/81 = 0.01235
Sensor size = 36 * 24 mm = 864 mm²

0.01235 * 864 mm² = 10.67

10.667 / 6.547 = 1.6298

That's log2(1.6298) = 0.7047 stop more light

neuroanatomist · May 29, 2026

Bob Howland said:
That's where Neuro is coming up with 1.3 stops loss, although I think it's 1.0.

1.6 squared is 2.56. The base 2 log (i.e., stops) of 2.56 is 1.356144.

I round that to 1-1/3 so it translates to camera-based 1/3-stop exposure settings.

bloblom · May 29, 2026

Bob Howland said:
When using a FF lens on an APS-C sensor, the light intensity on the APS-C sensor is correct for the selected F-Stop. But that extra light around the edges is simply wasted, just like if the FF image was cropped in post processing. That's where Neuro is coming up with 1.3 stops loss, although I think it's 1.0. The speed booster takes the output of a FF lens and reduces the size of the sensor onto which it projects and reduces the apparent focal length of the lens.. The light intensity on the APS-C sensor is now 1 stop higher than it would be with a FF lens. The speed booster is why my 100-400 f/5-6.3 becomes a 71-284 f/3.5-4.5 and why my 150-600 f/5-6.3 becomes a 106-424 f/3.5-4.5. The EXIF data sent to the camera reflect that fact. With the 150-600, the result is so good that it's just plain eerie.

Yes, for total light gathered (light intensity * exposure * sensor size). If aperture and exposure are the same, that's log2(1.6²) = 1.3561 stop of difference.

neuroanatomist · May 29, 2026

bloblom said:
Aren't you mixing up things? Where does 800mm f/7.1 come from here?

The long end of the 100-500, when used on APS-C, gives an FoV equivalent to 800mm on FF, but the f/number remains f/7.1. Thus 800mm f/7.1.

I’ll leave the rest of the explanations to @AlanF if he chooses to reply, but his numbers and reasoning are completely correct.

Bob Howland · May 29, 2026

bloblom said:
Aren't you mixing up things? Where does 800mm f/7.1 come from here?

Where does that come from? Aperture dictates light intensity (photons per surface area), even if the entrance pupil is bigger, the focal length is bigger too, we're still talking about f9 vs f7.1 so that's 0.67 stops against FF.
APS-C doesn't work like a teleconverter. You're not taking half the light and projecting it onto the same surface like a TC does, you're taking half the light and projecting onto half the surface, light intensity at the sensor plane remains exactly the same. So it's not 1.3 + 0.67 but rather 1.3 - 0.67 = ~0.67 in favor of FF.

Initially I was talking about the measured DR between the R5II and the R7. At 6400 the R7 has 5.09 stops, at 12800 the R5II has 5.
I see that 1.3 stop figure repeated in this thread. Not saying it's wrong, in a perfect world, with perfect cameras, there would be a flat 1.3 stop delta across the entire ISO range due to sensor size difference between FF and APS-C. In reality, it's almost never 1.3 stops, and it's not constant across the entire ISO range. Physics are real, but physics also say cameras aren't isolated systems.

When using a FF lens on an APS-C sensor, the light intensity on the APS-C sensor is correct for the selected F-Stop. But that extra light around the edges is simply wasted, just like if the FF image was cropped in post processing. That's where Neuro is coming up with 1.3 stops loss, although I think it's 1.0. The speed booster takes the output of a FF lens and reduces the size of the sensor onto which it projects and reduces the apparent focal length of the lens.. (A teleconverter works in exactly the opposite way.) The light intensity on the APS-C sensor is now 1 stop higher than it would be with a FF lens. The speed booster is why my 100-400 f/5-6.3 becomes a 71-284 f/3.5-4.5 and why my 150-600 f/5-6.3 becomes a 106-424 f/3.5-4.5. The EXIF data sent to the camera reflect that fact. With the 150-600, the result is so good that it's just plain eerie.

bloblom · May 29, 2026

AlanF said:
In terms of signal/noise a 800mm f/7.1 is equivalent to a 500mm f/5.6, ie 0.7 stops faster than than 500mm f/7.1.

Aren't you mixing up things? Where does 800mm f/7.1 come from here?

So, in fact the signal/noise advantage of the RF 200-800mm on FF is greater than 1.3 stops, not less, and is actually up to 2 stops better than 500/7.1 on crop.

Where does that come from? Aperture dictates light intensity (photons per surface area), even if the entrance pupil is bigger, the focal length is bigger too, we're still talking about f9 vs f7.1 so that's 0.67 stops against FF.
APS-C doesn't work like a teleconverter. You're not taking half the light and projecting it onto the same surface like a TC does, you're taking half the light and projecting onto half the surface, light intensity at the sensor plane remains exactly the same. So it's not 1.3 + 0.67 but rather 1.3 - 0.67 = ~0.67 in favor of FF.

Initially I was talking about the measured DR between the R5II and the R7. At 6400 the R7 has 5.09 stops, at 12800 the R5II has 5.
I see that 1.3 stop figure repeated in this thread. Not saying it's wrong, in a perfect world, with perfect cameras, there would be a flat 1.3 stop delta across the entire ISO range due to sensor size difference between FF and APS-C. In reality, it's almost never 1.3 stops, and it's not constant across the entire ISO range. Physics are real, but physics also say cameras aren't isolated systems.

blackcoffee17 · May 29, 2026

Skyfall said:
I agree, or even 150-600 f4.5-8 if the weight would be the same.

Yeah, i think making it 100-500 instead of the usual 100-400 was a brilliant idea.

blackcoffee17 · May 29, 2026

What i want is "cheap" PowerShot with a decent lens with at least 200mm at the long end. Doesn't have to have big sensor, something like a 1/1.7" would do, just like the old G series but with modern tech and modern processing. Would love to buy a camera like this and take it with me on some trips.

AlanF · May 29, 2026

Bob Howland said:
Have you ever used a Metabones or Meike speedbooster with EF lenses and your R7? I own both and use them (mostly the Metabones) with Canon 70-200 lenses and Sigma 100-400 and 150-600 lenses. They work best with the 150-600 but are more useful to me with the 100-400. I shoot motocross motorcycles (sometimes in flight) and the 71-284 f/3.5-4.5, that the 100-400 becomes, is perfect. The 100-300 would probably work just as well without the Speedbooster but I'm not spending that kind of money for one.

No, and I use native RF lenses now.

AlanF · May 29, 2026

bloblom said:
...In the same situation, if the 100-500 allows me to shoot at 6400 on the R7, the 200-800 on the R5II forces me to be at 12800. At that point there is actually less than a stop of difference between both cameras with the ES.

In terms of signal/noise a 800mm f/7.1 is equivalent to a 500mm f/5.6, ie 0.7 stops faster than than 500mm f/7.1. So, in fact the signal/noise advantage of the RF 200-800mm on FF is greater than 1.3 stops, not less, and is actually up to 2 stops better than 500/7.1 on crop. There are several ways of rationalising this if you don't know the maths/physics. A simple explanation is that the front element of the 800mm f/9 is larger than that of the 500mm f/7.1 and shines in more photons per duck - it is the number of photons that determines the S/N (= square root of number of photons) and not the dialed-in iso. It's the same reason that a 50mm f/2.8 lens on a crop camera set at the same iso and speed as an 80mm f/2.8 on an FF loses 1.3 stops in terms of S/N despite having the same field of view.

(There are complications in calculations for different amount of cropping, but the take home message is the physically wider 800/9 lets in more total light than the 500/7.1, and it is total light that is important, not light per unit area. I did a thread on this 5 years ago https://www.canonrumors.com/forum/threads/extenders-and-high-iso-with-the-r5.40575/)

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