Any way to put prefered f-stop in AV mode?

EDIT: error in the title, sorry. Shutter speed. Not F-stop.

Hi, is there a way, on a t3i in AV mode, to tell the camera to stay around a range of shutter speed?

I was trying to shoot a butterfly on a weed. Windy and all. My camera tried to stay at around 100/ 160ms which give me a bit of motion blur. I would prefer that the camera raise the ISO rather than lower the shutter speed.

I shoot in AV mode because I like to control my DoF. Quite important for macro subjects.

Sorry for the newbie question...
thanks

Manual mode in auto ISO. Not sure if your camera supports that

kwando wrote in post #14775655
Manual mode in auto ISO. Not sure if your camera supports that

^^^^^ It does....Set SS and aperture in M mode with Auto ISO.

With flash you can trap SS between 1/60 and 1/200 or lock it at 1/200 in Av mode with Cust. func-3.

Manual mode with auto ISO. Ok thanks!! I'll try that!

That's all well and good, and will be a great start for you, however, the T3i only supports full-stop ISO speeds; so Manual with auto ISO could give you a slightly underexposed or over exposed image depending on what the camera thinks is best.

To be clear, when in Av mode, the shutter speed can be adjusted in increments of 1/3; similarly when in Tv mode, the aperture can be adjusted in increments of 1/3... Unless you have a camera that can adjust the ISO in increments of 1/3 also then you might not get the best exposure.

For example... if the correct exposure was achieved with f4, 1/160, and ISO 200 and you dial in f4, 1/200, ISO Auto then the camera will have to decide whether to give you ISO 200 and risk underexposing by 1/3 of a stop because the shutter speed is faster than the best settings, or giving you ISO 400 and risk over exposing by 2/3 of a stop because ISO 400 is more sensitive and the shutter speed becomes too slow... A camera that had intermediate ISO speeds would give you ISO 250 for example.

This isn't a massive issue, however, it's something worth bearing in mind when you're shooting. For example, if it's slightly under or over exposed when you take a shot, you might have to dial in a little more or a little less shutter speed to get it spot on. Once you get more experience you will be able to think about the ISO you require based on the conditions you're shooting in... don't forget there's nothing wrong with having a really high shutter speed for macro work, so you could set ISO 800 for example in Av mode and see what shutter speed it thinks is correct... if it's too slow then try ISO 1600, if it's really fast then try ISO 400 to get a bit better image quality as a result.

Hope that makes sense, Chris

The easiest way is set your aperture to what you want on av mode. Then manually set your ISO to a high enough value that give you an appropriate shutter speed. If the light is changing, make sure your ISO is set high enough for the shady areas to maintain a sufficient shutter speed. You can use EC in this mode too.

Setting aperture and shutter in manual mode with auto ISO is good, but you can run into situations where it will over and under expose. This isn't because of only supporting full stop ISO's though. The light meter can be easily fooled by backlighting, very dark or light colors filing the frame, etc. there isn't a way to dial in EC. If I was gonna go the manual route, I would just go full manual instead of relying on auto ISO.

chrismarriott66 wrote in post #14776493
... however, the T3i only supports full-stop ISO speeds; so Manual with auto ISO could give you a slightly underexposed or over exposed image depending on what the camera thinks is best.

Auto ISO will set finer increments; see page 80 of the manual.

Manual with Auto ISO is how I always have my 60D set up except in rare circumstances when the metering is off.

oldvultureface wrote in post #14776732
Auto ISO will set finer increments; see page 80 of the manual.

Even on the T3i? I used to have a 450d, which I'm pretty sure didn't do that... but if it does, I stand corrected!

I'm glad I asked the question. Lots of valuable answers. Thanks chrismarriott66, it's very clear. I did try the manual mode today, a bit. It was a bit awkward at first. Fixing the ISO a bit higher before hand is a great idea. I think I'll go with that for a while. I dont know why I didn't though of it.

I notice that I get worst handheld results with the t3i than with my old 20D. (with the 50mm 1.8 and the 85mm 1.8). Could there be any difference in the shutter speed calculation between the 2?

On the 20D, it was rare I had a blurry pic. Now 50% of my pics have some motion blur. Maybe it's just me after the years long break I took.

chrismarriott66 wrote in post #14776774
Even on the T3i? I used to have a 450d, which I'm pretty sure didn't do that... but if it does, I stand corrected!

T3i DOES choose finer increments for actual exposure, when using Auto ISO in manual shooting mode...Viewfinder may show ISO 800, but Exif shows 640 for example.

More camera motion might be evident on T3i's higher pixel density sensor than with the 20D's lower density sensor, at equivalent shutter speeds.

Personally I would stay away from the Auto ISO mode period. Just keep on bumping up your ISO in short increments. When you focus I believe it will show you the shutter speed in the view finder.

Your going to want to keep bumping up that ISO until your reading possible 1/250 or 1/300 or whatever it totally depends on how fast the object is moving and the distance. 1/250 is not too shabby at all for slow moving objects.

Just bite the bullet and shoot full manual. It might be a little scary at first, but you'll get it.

Auto-iso has changed over time. Generally speaking, it's gotten better after each generation of camera that came out- so if it is a newer model over another-it's auto-iso implementation usually got better. I've had a t1i, 7D, 5D3, t4i, and you can see the improvements ( T4i and 5d3 are basically the same generation- but the 5D3 is more functional.. ). Older cameras like the 450D would be more limited because their ISO wasn't that high to begin with.

I use a auto-iso function to set a shutter speed for rotor blur- set the shutter speed, an aperture, and let the auto-iso fill in the rest. On the t1i- autoiso was limited to 1600 iso- I think. 7D- 3200 ISO. Neither could be changed ( I think ) . the newer models allow you to specify the upper end of auto-iso. It's helpful when manual is too much of a pain- like when you are going from extremes of exposure- like bright sky- to darker areas like tree lines, etc..

As soon as the firmware version 2 is announced for the 7D, you'll be able to change the upper limit for auto ISO on that camera too. 400-6400 range.