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R5 keeps reverting to F7.1 - manual settings


Hi All ,

shooting manual settings.  Want to use 4.5 (on 100-500 lens).  Keeps reverting to 7.1.  What am I doing wrong?

I want to control aperture, shutter speed and ISO all in manual settings.  Why is it locking me out of 4.5 or 5.6 etc?   I’m definitely in Manual mode. 

thanks for your help!




Are you using the RF 100-500mm f/4.5 to f/7.1 lens?   If so, note that when you're near or at the 500mm focal length, the minimum aperature will be f/7.1.   This lens is thus a variable aperture lens.   As you move throughout the focal length range of the lens, the minimum aperature will have different values (e.g. at some point it will be f/5.6).

In order to be at f/4.5 for your lens, you'll need to be at or near the 100mm focal length.

Lenses such as the RF 70-200mm f/2.8 would allow you to use f/2.8 at all focal length settings.


EOS 5D IV, EF 50mm f/1.2L, EF 135mm f/2L, 600EX-RT (x6), ST-E3-RT
EOS C70, RF 24-70 f/2.8L IS, EF-EOS R 0.71x

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There is no workaround to the aperture setting itself.  As you move closer and closer to the 500mm range, the minimum aperture will indeed change.  Lens manufacturer's create such variable-aperture lenses to lower the cost as well as typically lowering the weight of the lens.

Thus, correct in that you'll need to find ways to compensate such as raising ISO and/or slowing the shutter if that's doable.

In terms of another lens option, I'll let others weigh in as the only zoom lens I have is for my cinema camera (an RF 24-70mm f/2.8).  For my DSLR, I only have two prime lenses.   Thus, I cannot readily recommend zoom lenses in your desired focal length range. 


EOS 5D IV, EF 50mm f/1.2L, EF 135mm f/2L, 600EX-RT (x6), ST-E3-RT
EOS C70, RF 24-70 f/2.8L IS, EF-EOS R 0.71x

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The 100-500 is Canon's longest RF zoom. 

Screenshot 2022-02-02 195449.jpg

Canon will be releasing a 600mm f/4 prime, but that is a $9000 lens in EF mount and it seems that RF mount lens are costing more for equivalent lens.

You can download a trial version of Topaz Sharpen AI and see how that handles your higher ISOs. I have been pleased with what it does with my 1D X III files.

John Hoffman
Conway, NH

1D X Mark III, Many lenses, Pixma PRO-100, Pixma TR8620a, LR Classic

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@NancyMac wrote:

"Thanks for explaining that to me.  Causes a bit of a problem in low light situations.  I did have a 2.8 - 70-200 and the 100-300 so I’m bummed out about this?  What’s the work around?  Just bump up my ISO?   Dang!  Wish there was another lens option.  Any suggestions?  Appreciate your help.   Nancy" 

Hello, Nancy.

I've been using this combo for several months now to shoot birds and wildflowers. The R5 handles higher ISO's amazingly, in fact, I don't notice any noise when shooting in low light. Now, what I consider low light is early morning, late evening, forest canopy, and underbrush. I really like f/7.1 as a starting pont because it allows DOF to be a little better. However, by bumping up my ISO, I can get the lens in its "sweet spot". Since I shoot birds, they generally flit around or are constantly moving their body parts even when perched, so I like to keep my SS in the 1/500th to 1/1000th range. Even then, I can usually keep my ISO below 4000, which isn't a problem at all with the R5, or R6 for that matter. I can also keep my aperture where I want it by adjusting ISO. This is considered unconventional, but it works for me. We were all trained that low ISO is the goal, but the R5, IMHO, is an exception to that rule. I've been using high ISO settings since the 5D mark IV, so I'm used to taking advantage of it and frankly, don't see it as a "workaround" in low light. I've seen some shots on this forum from the people that are using the 1D X mark III with some really outrageous ISO settings, even with their f/2ish primes for sports, and they look really good. I'm sure they denoise to some extent, but the point is, high ISO shouldn't be feared with these newer camers, IMHO. I think if you bump up that ISO you will be happy with the results. This lens is fairly sharp at at f/7 but if you bump up the ISO and get it into the f/8 to f/16 range, it's hard to beat.

This Tufted Titmouse was shot at dusk. EOS R5, RF 100-500, f/7, 1/500th, ISO 4000. No post NR and NR in camer is at its default setting. Edited in DPP 4 and cropped for forum. I was approximately 35 feet away.

Tufted Titmouse-0000001a.JPG

Same bird and settings cropped in closer.

Tufted Titmouse Test-0000002a.JPG

Yellow-throated Warbler shot under the same conditions. EOS R5, RF 100-500mm, F/8, 1/500th, ISO 6400 (Note that I raised my ISO to get to f/8). Smaller bird (3"), but same distance. Same post settings (no NR).

Yellow-throated Warbler-000002a.JPG


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You're welcome!  It was so frustrating and I could not figure out why it was defaulting to 7.1.  Now I know and I can work with it to achieve my desired outcomes.  Glad it helped you too.  Take care!!  

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