Tv mode question

Sorry for having to ask this, but I have a question about the workings of Tv mode (I have a dRebel, but I think it's the same for all cameras).

When I select a shutter speed to shoot in, and half-press the shutter release, the camera selects an appropriate aperture. This much I know. What it doesn't tell me is if the exposure will be good. The exposure meter stays centered. Then sometimes, the picture is underexposed, sometimes it's completely black. I then have to go back and crank up the ISO, but I still don't get anything useful from the exposure meter.

My question is: why doesn't the camera adjust ISO to achieve good exposure? also, should I just be shooting in Manual mode? There are a lot of implications that go with that as well.

We can use baseball as an example. I want to shoot 1/4000 to freeze the action. I *thought* that simply using Tv mode would do the trick. In full manual, I will have to be constantly adjusting ISO and/or aperture with every passing cloud, which makes it hard to stay on top of the action.

Maybe I'm just whining, but I'd appreciate other viewpoints because I'm probably missing something.

The camera does not adjust ISO, because it is not meant to do so.

If you set for Tv, 1/4000, etc., and the camera picks an aperture, then that ought to be good (assuming that you have a normal metering pattern that will give a good result for that subject). If the aperture indicator is flashing, then this is not good.

Suggestion. Switch from Tv to Sports mode, view the subject and see what shutter and aperture are chosen by the camera. Now switch back to Tv and use those settings. Now what do you get?

I used Tv 1/4000 the other day to "freeze" the main rotor of a helicopter in flight, and at that shutter, the aperture was wide open. As soon as I moved off the subject slightly, the aperture was all wrong.

---Bob Gross---

That "meter" you see in the viewfinder is NOT the exposure meter. It is the exposure compensation scale. It tell you how much, if any, exposure compensation you have selected. If none is selected, it will stay in the middle.

The thing that tells you whether you are going to get a good exposure or not is the aperture value if shooting in TV mode. If exposure if fine, the aperture will be lit steadily. If not, it will blink. So, when the aperture is blinking, you will need to adjust the shutter speed until the aperture selected stops blinking.

Pac Ace, actually that is the camera's exposure meter. It is a graphical representation of the camera meter reading. In Manual Mode it is what you use to get the exposure correct as you adjust shutter and aperture. Yes, when you use flash and exposure compensation it is a graphic representation of that as well, but when you are metering a scene, that is the meter.
The issue the original poster is raising is the difference between the Meter Reading by the camera and a Correct Exposure. In most situations, where the lighting is even, or the tones in the image average out to 18% grey(12% on some), the two readings, Camera and Correct are the same. But as you know when shooting a white dress or snow, you have to adjust the Camera Meter's reading up by 1-2 stops, or if your shooting a black tuxedo, down 1-2 stops. Evaluative metering is good but not perfect. It can be fooled by backlighting as well, or scenes with lots of shade and sun.
In addition, changeing the ISO wouldn't solve the problem. The problem is due to the limitations on the meters ability to decide on the exposure. That requires someone to thoughtfully guide the exposure in the right direction, a photographer.
Regards,
Scott

Maybe i'm off here but...

Make sure when you pick a shutter speed that the apateur
in the viewfinder isn't BLINKING. If it is, then the lense you
are using doesn't open up enough for the shutter speed you
picked to expose correctly. This would cause DARK pics.....

Just a guess on the dark pics part of it.

Rod

Yes, but that's only true in Manual mode, no? Not in the auto modes such as Tv, Av, P, etc., right?

It's always the meter. When you dial in exposure compensation your telling the camera to expose more/less then the meter would on its own. For Example: You select Tv Mode. 1/125. The camera selects an appropriate f stop and the meter reads dead center. The camera has selected an f stop that when combined with your shutter speed and ISO, gives a combination that puts the needle in the center of the meter. That's how the camera would expose that scene. You being a smart guy and not wanting your snow to look grey, use the big dial to overexpose beyond what the camera chose by two stops. The meter will now show that you are overexposing by two stops. You may call it exposure compensation, but what you are doing is over/underexposing what the camera meter recommends and that's why the needle is where it is. The same is true for Av. The only time that this isn't true is FEC(flash exposure compensation). In that case your telling the flash to over/underexpose from what the preflash tells it to do, or the manual setting tells it to do. So it's not really a meter reading.
Regards,
Scott

OK, I have my 10D set to Tv and the shutter at 1/400. I have 0 exp.comp. and I have the lens cap on. When I half press the shutter, my Aperture is set to 4.5 because that's the widest it'll go and it's blinking. But the "meter" is still in the middle. Are you saying that my setting of 1/400 with f/4.5 is the correct exposure as indicated by the "meter"?

I then set the shutter to 30 seconds and the aperture is set to f/32, this time with the lens cap off and pointing at a bright object. Again the "meter" is in the middle but the aperture is blinking. Is this the correct exposure, too, according to the "meter"?

The fact that the f stop is blinking tells you that the camera cannot give a correct exposure and there is no meter reading. The Av, Tv,P, Auto modes are designed to give you a correct meter exposure using the camera meter without your help. If it can't do this, it blinks and gives you no other information. The auto modes reduce the utility of the meter to the point where it only tells you good/bad like the idiot ligts on a car, but it's still the meter. I think your getting too hung up on what a meter is. The camera meter is always there. The mode you choose alters the way the meter is reflected in the viewfinder. Many point and shoots have a little green light that goes on when the exposure/focus is OK. That's the reflection of the meter reading on that camera.
Scott

As Scott indicated, you aren't thinking right on what the camera is telling you. When either the shutter speed indication is blinking, or the aperture indication is blinking, that means that the camera does not have an exposure solution. Depending on which mode you are in, you'll have to adjust either ISO, or shutter, or aperture until there is no blinking.

Exposure compensation is generally something to do once the camera has a basic exposure solution (no blinking) and then you want to modify that slightly to account for a very dark or very light subject.

This is more like a user error than a meter error.

---Bob Gross---

I'm not going to belabor the point because obviously we have different notions of what a meter is.

The point I was trying to make with my first reply to the original poster was that, in the TV shooting mode he was using, that thingamajig he was looking at in the viewfinder would NEVER tell him whether his exposure is good or bad, because, in TV mode, it will NEVER go off center if EC is 0 and, if using a flash, the FEC is 0. The only way he would be able to tell if his exposure is going to be good (or what the camera thinks is good) is if the aperture number is not blinking.

'Nuf said by me. Peace.

OK, thx for the replies. blinking aperture = bad.

Does this sound like a good solution for my baseball situation: I set shutter speed (1/4000), then work up the ISO until I get a solid aperture. If I can't make it by ISO, then I start cutting shutter speed down.

Seems simple to me. BTW, I'm working with my 70-200 f4L on this. I'll post a sample later tonight.

Thanks again, Bill

I guess my only question is do you need 4000 for baseball? Sure, the ball can travel fast but does it go that fast. I would think you could get away with 2000 or less depending on sunlight and other lighting. This way you have much more room to play with in terms of aperture and ISO settings. Of course I could be wrong because I've never photographed baseball.

Cordell

OK, so here's what I'm talking about:

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Oh, yeah, and this shot was taken at 1/1000, and shows why I want to get up to 1/4000. (It was earlier in the day, so the shadow hadn't made it across the field yet.

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