topic Re: Tinkering with aperture priority and Auto ISO in EOS DSLR & Mirrorless Cameras

Tinkering with aperture priority and Auto ISO

stevet1 — Sat, 02 May 2026 15:57:36 GMT

Normally, I shoot in Manual, but The other day I was adjusting the settings, and accidentally put my camera in aperture priority and Auto ISO. When the photo came out, I went "Whoa. That's kind of a nice picture."

Since then, I've taken a couple of other pictures, and I think my T8i is actually doing a better job at selecting a better exposure than I do manually. If I set an aperture, the camera is selecting a shutter speed roughly twice what my focal length is and ISO to match or balance what my higher shutter speed is. Psychologically, I'm trying to adjust to that higher ISO value. If the camera overexposes the picture a little, I'll use a negative exposure compensation of a 1/3 of a stop or so to darken it up a little. Normally, I shoot with lower ISO values like 100 or 200.

I realize that in lower-light situations, this might not work, as the shutter speed would need to be slower and the ISO numbers would be unacceptably high, and Manual might be the better choice, but it's been interesting.

Steve Thomas

Re: Tinkering with aperture priority and Auto ISO

Waddizzle — Sat, 02 May 2026 18:37:12 GMT

“Hello There!”

I think you’re onto something there. When I shot with my DSLRs, I almost always had -1/3 EV of AEC dialed in. I also shot as RAW.

Those Av settings could be problematic in low light conditions. It really depends on the lighting and the lens.

I think you should get satisfactory results at ISO 800. Don’t be afraid to try it my But, I would suggest not allowing the camera to control more than one leg of the Exposure Triangle at a time,

Isn’t your T8i capable of allowing Auto ISO in M mode? If so, does it allow for AEC?

Re: Tinkering with aperture priority and Auto ISO

stevet1 — Sat, 02 May 2026 21:16:06 GMT

Waddizzle,

You asked about EC in Manual.

Yes, you can, but since the other two settings are fixed, the only thing that gets compensated for is ISO.

For the last couple of days, I've been alternating between Aperture Priority with Auto ISO and Manual with Auto ISO. It could be my imagination, but I'm thinking the camera is picking a better shutter shutter speed than I am.

Noise doesn't seen to be a problem with this T8i. That's always been something that has really surprised me.

Steve Thomas

Re: Tinkering with aperture priority and Auto ISO

jrhoffman75 — Sat, 02 May 2026 21:44:53 GMT

in Program or Av mode the camera is programmed to select a shutter speed about twice the focal length because that is the rule of thumb for avoiding motion (camera shake) blur for crop sensor cameras.

Re: Tinkering with aperture priority and Auto ISO

stevet1 — Sat, 02 May 2026 22:13:10 GMT

John,

Yes, and that's why I think my camera is better at it than I am.

Part of that, I think, is due to the markings on my lens. I'm using an 18-135mm lens, and the markings on my lens jumps from 50mm to 85. It's hard to tell up front if you are shooting at 60 or 77 or whatever. In Manual, I'll rock back and forth trying to get the metering needle to zero out, but if you change your position even slightly, that needle is prone to shift.

I'm beginning to think I'll just let the camera handle it.

Steve Thomas

Re: Tinkering with aperture priority and Auto ISO

Waddizzle — Sat, 02 May 2026 22:32:37 GMT

“ Yes, you can, but since the other two settings are fixed, the only thing that gets compensated for is ISO. “

Exactly! It’s a popular way to use the camera under varying lighting conditions. I reminds me of shooting with film the most. With film, you had to live with the film speed you had loaded in the camera until you used up the entire roll.

Using “Ev” mode allows me to change “film speed” on the fly automatically. I can even override the camera by dialing in AEC, changing exposure by as much as +/- 3 Ev.

Continue to exploring the camera. I used to spend weekends in an urban setting looking 👀 to only photograph subjects that looked a certain way.

it was a great composition drill. I would only photograph square or rectangular things. Round things. Triangles. Parallel lines. Red, blue, or green things. Etc.

Re: Tinkering with aperture priority and Auto ISO

stevet1 — Sun, 03 May 2026 01:07:15 GMT

In some cameras, you can set a minimum shutter speed, below which you cannot go. I think this would be helpful in dim light conditions, where the camera might want to go down to 1/4 or 1/13th, or 1 or 2 seconds, and you cannot shoot a picture handheld at those kinds of speeds.

My T8i does not have that feature, so I just have to tell myself when I hit 1/30th or so, "You cannot do that. Better get the tripod."

Steve Thomas