AV mode weirdness

[MrCoffee]

Hey Everyone,

I have been using my Canon Rebel XSi a lot recently and I have noticed something very strange when putting in Aperture Priority mode. When I put the camera is full auto mode, and compose a shot, it will have correct settings, say 1/60th-F/2.8-400. But when I switch it over to AV mode it will jump the shutter speed up to like 3 seconds. Happens with all my Canon and non Canon lens. If I put it into full Manual mode, the shutter speed goes back to a correct speed. Since it is in AV mode, I can't adjust the shutter speed, And of course everything in a normally lite scene gets blown out. If I drop the ISO, the shutter stays long.

Ideas or suggestions? For now I have been using it only in full manual mode, but I would like to be able to use AV mode. I am kinda of stumped.

Thanks!
MrC

[Hill Country Hack]

MrC.

I have the same camera as you. Here is the best I can come up with.

In AV mode the camera adjusts the shutter and ISO to make the best possible exposure for the given light at the selected f-stop.

Next time you put it in AV mode check to see what apeture it defaults to. You can adjust the shutter speed by adjusting the apeture. Bigger apeture (smaller f number) the faster the shutter and the lower the ISO should be (depending on the amount light) the inverse is also true. Given the same lighting conditions, stop down the apeture to f13 and the shutter will slow down and the ISO will go up.

It is up to you to decide what apeture to use. Your choice of f-stop is dependent on the DOF you want, the amount of light you will use, how fast you want your shutter to be, how high you are willing to let the ISO go, to name a few.

In shutter priority (SV) the camera adjusts f-stop and ISO to get the selected shutter speed.

Not to sound flippant, google "exposure triangle" or check out the tutorial section here. A lot of good information there.
I hope this helps.

[inkista]

Assuming you know iso/aperture/shutter speed, the likely difference if you're at the same aperture in both modes is that you're shooting in very low light, but you haven't popped the on-board flash in Av mode. In full-auto the camera can turn on the flash by itself, so it can adjust the settings to be good for handholding.

[ArmySoldier777]

Originally Posted by MrCoffee

Hey Everyone,

I have been using my Canon Rebel XSi a lot recently and I have noticed something very strange when putting in Aperture Priority mode. When I put the camera is full auto mode, and compose a shot, it will have correct settings, say 1/60th-F/2.8-400. But when I switch it over to AV mode it will jump the shutter speed up to like 3 seconds. Happens with all my Canon and non Canon lens. If I put it into full Manual mode, the shutter speed goes back to a correct speed. Since it is in AV mode, I can't adjust the shutter speed, And of course everything in a normally lite scene gets blown out. If I drop the ISO, the shutter stays long.

Ideas or suggestions? For now I have been using it only in full manual mode, but I would like to be able to use AV mode. I am kinda of stumped.

Thanks!
MrC

Not sure if it's the same problem, but I had something similar happening to me when I first tried AV mode. On my 450d, If i hold down the "Av" button on the back so that it switches what setting is being changed, it allows me to adjust the bar below the shutter speed. This allows me to set what exposure I want with the aperture setting I chose, while automatically adjusting the shutter speed to match those settings. Hope that makes sense.

[MrCoffee]

Thanks everyone for the replies!

I understood the the concept behinds the AV mode, I use it quite a lot with my Nikon D70, and do not have this issue. It isn't that I am not getting enough light into the camera in AV mode, the exact opposite, I am getting way to much. Opening the lens to F/1.8 or F/2.8 should increase the shutter speed, it doesn't. The shutter actually is working in the opposite way. As I stop down to F/5.6 the shutter went from 3 sec to 1 sec. So as I am closing the Aperture, the shutter speed is increasing. Weird, eh? And the ISO remains constant.

I sent an email off to Canon about this and I haven't heard back yet.

I took the camera off Auto ISO tonight, because one of the known issues with the XSi is incredibly slow write speed to the SD card in Auto ISO. Canon says it is due to the camera trying to reduce the noise at higher ISO, but I have found that even at 100 it gets slow writing in RAW.

Other then this weird issue, I happen to like the XSi a lot.

[ArmySoldier777]

That is a weird issue. At first I thought it might've had to do with one of our two replies, but after reading your last post, I have absolutely no idea.. Just trying to get a feel for the entire situation, but what kind of lighting conditions are you shooting in? I'm just trying to figure out why the camera would feel the need for a shutter speed that long anyway. Even though it is being over exposed
David

[litenphrame]

That's a really strange problem and overexposure is always a shot killer. I'm still learning and probably off base, but have you done anything with the exposure compensation in the camera? I believe that particular setting stays the same in all settings just like the WB setting. If you have try setting it back to the default setting. I realized that I had changed mine and had to return it back to get better results in the Av mode. In some cases, I had to just use the manual mode.

[MrCoffee]

Originally Posted by ArmySoldier777

That is a weird issue. At first I thought it might've had to do with one of our two replies, but after reading your last post, I have absolutely no idea.. Just trying to get a feel for the entire situation, but what kind of lighting conditions are you shooting in? I'm just trying to figure out why the camera would feel the need for a shutter speed that long anyway. Even though it is being over exposed
David

Yes, now I think you understand the question a bit better.

I was/am shooting in normal room light conditions, my home office to be exact, and I was shooting a stuff animal, red and black lady bug. Not hugely bright light, but plenty so that in "PTBD" mode (push the button dummy), the pop flash was not needed.

In AV mode, I open up the Aperture, and as I do, the shutter speed decreases. At f/8, it dropped to 1/60, at F/2.8 it increased to 3 secs. Put it in full program or manual mode this doesn't happen. I first thought it was my Tokina lens, thinking that it was something to do with AV mode, and a third party lens, but it does the same thing with my Canon 50mm F/1.8 lens, so.......

Again thank you for the replies, and maybe I am just doing something stupid that is different on the XSi then my D30 or 10D was..... or maybe is it something with the camera itself....

Chuck

[ArmySoldier777]

Hmm, i have the 450d which is an xsi, and I haven't seen that happen. So I'd definitely have to say it's something wrong with that camera. But maybe I'm wrong and one of the "guru's" on here knows what's going on lol

David

[MrCoffee]

May have figured it out. It only happens when in Spot Metering. If I switch it to Evaluative Metering and the issue goes away, but happens in both Center weight and Spot metering. I didn't try Partial metering mode.

Tonight I am going to try it again, with a different test subject/object, and with different lighting.


Cheers!