I am now completely confused (DReb, 420EX, and 50 f/1.8)

[FlipsidE]

Ok, so I got this new lens tonight, and I figured I'd give it a try.

I mounted the lens, put the flash on the hotshoe, and went downstairs to see what I could find to shoot. Things were going great. On Program mode, everything was coming out just perfectly. Shutter speeds of 1/60 and aperture of f/2.8.

Then I got fairly close to an airplane model I have, fired a shot, and noticed the extremely tight depth of field (to be expected). So, I switched to Av mode, and set the aperture to around 3.5. Oddly enough the Shutter speed slowed down drastically when I did this...to around 1/8 to 1/3. So, I pushed the aperture back up to 1.8, and the shutter speed didn't really change much. Put the camera back in P mode...perfect again. Put it in Tv, no problems (could do 1/60 easily with what looked like proper exposure). Back into Av mode...same thing again. Very slow shutter speeds...some as much as 1 second. It's almost like the camera just didn't think the flash was there. I tired it with the built-in flash...same results.

What's up?

Edit: Forgot to include the fact that the flash was firing the whole time. That I made sure of.

FlipsidE

[robertwgross]

First of all, let me ask: How did the shots come out?

The camera body will not tell you, in advance, what settings it is going to do with the flash firing. The camera body will tell you what settings it wants to do as if the flash is not there and it is only using ambient light.

Now, I suggest you try your experiment again. This time, take note of what the camera body is telling you in advance, then take the shot, then look at the EXIF data to see what settings really got used.

All of this stopped me dead in my tracks for about three days when my camera was new.

---Bob Gross---

[FlipsidE]

Well, the shots are coming out as if there was no flash. The flash is firing, but the shots are coming out as if only taken by ambient light. Same with both my 420EX and the built in flash.

Now, I'm not sure I follow what you say about the body telling you what info it will use w/out the flash there. Is that only in Aperture Priority? Or is that in all settings. Because it seems in P mode, the correct shutter speed and aperture are shown before the shot is taken.

And now going tback to check the Exif, it seems the camera used the exact settings it showed me before the shutter button was pressed.

FlipsidE

[FlipsidE]

FYI, I just went back and reverified. The Exif showed me exactly what I was seeing in the viewfinder before the shot was taken. The flash is firing, but the camera doesn't seem to be picking that up. And, as I said, the shots look as if they were taken with ambient light only.

FlipsidE

[FlipsidE]

Let me add one more piece of info...this occurs with the 28-105 f/3.5-4.5 also. It's not just the 50 f/1.8.

FlipsidE

[cmM]

The Drebel uses different metering modes in P and AV mode. I think matrix in P, and partial in AV mode.
That might explain the difference in shutter speeds.

[robertwgross]

FYI, I just went back and reverified. The Exif showed me exactly what I was seeing in the viewfinder before the shot was taken. The flash is firing, but the camera doesn't seem to be picking that up. And, as I said, the shots look as if they were taken with ambient light only.

FlipsidE

Hmmm. I would have to think about that. I agree that it does not sound like it is lens-related.

(1) Does your 420EX ever fire properly and give you a decent flash exposure? Make it simple and set it to Green Box mode, if you want.

(2) Verify that if you are shooting with flash, that you are not exceeding the flash sync speed (of the body).

(3) Verify that your 420EX is set up normally, and not in some weird mode.

---Bob Gross---

[FlipsidE]

In full auto mode as well as P mode, everything works just fine...exposures look great...built in flash and 420EX. But, in Av, even at the widest aperture, I get shutter speeds that are just far too long to be workable.

What's the deal? I even went into the menu and chose the "Clear Camera Settings" option to make sure I hadn't messed something up earlier by pressing a button I didn't mean to. But, that didn't change anything.

What's the deal? Is this yet another bad camera?

FlipsidE

[slin100]

Go to the EOS Flash Sticky and click on the link to the Flash Bible and read about the differences between Av/Tv and P when flash is involved. In short, you'll find that in Av/Tv the camera will meter for ambient exposure. In P, it will usually default to 1/60 @ f/4 in low light, ambient exposure be damned.

[Paul_B]

hi ya Flipside,

I had a simalar post here again. I was out last Sunday, nice sunny day taking shots in Av of various things in the Park. All perfect.
The kids get in front of the camera, so I put flash up (pop up on rebel) for fill flash. Just making sure shadows are not on the face.
Same thing, shutter speed was way to slow. Tried smallest to largest aperture. Any with the flash was to slow to hold still.
So, I'll copy/paste a few responces I got -

Focus isn't determined by shutter speed but you could be confusing camera shake with a focus problem (it's hard to tell sometimes.) Your flash does have a maximum sync speed but it's high enough that I doubt that is your problem. The EOS flash system is "interesting". In the automatic modes it makes all kinds of interesting decisions based on the situation and the mode you choose. (ie P, Tv AV, and M each have their own logic.)


When you use flash, the shutter has to completely uncover the sensor before the flash fires. This "X-sync speed" is about 1/200 sec. on the DR. If your aperture setting wanted a faster shutter speed (if you were using the camera at f/5.6, for instance in bright sun and ISO 100, the correct shutter speed for the available light would be about 1/800. When you turn on the flash on the DR, it slows the shutter speed to the X-sync speed. So you'd be getting a longer exposure than you would without the flash, even though you're adding light.

and here is link to EOS Flash - http://photonotes.org/articles/eos-flash/
Long read, but I've read others say they "understand now" after reading it all.
I'll be reading it all this weekend.
Anyhow, I don't think anything is wrong with your camera, just the way the Rebel handles Av with Flash.

[FlipsidE]

Go to the EOS Flash Sticky and click on the link to the Flash Bible and read about the differences between Av/Tv and P when flash is involved. In short, you'll find that in Av/Tv the camera will meter for ambient exposure. In P, it will usually default to 1/60 @ f/4 in low light, ambient exposure be damned.

I *believe* I'm following now. According the the EOS Flash Bible, in Tv and Av modes, the camera meters for fill flash. In other words, it will try to match the foreground with the background...properly exposing both. If you are in low light, then the background will already be dark, so you'll need a long shutter speed to properly expose the foreground even with fill flash.

In P mode, it automatically picks 1/60 for the shutter speed, no matter what. And it'll set the aperture based on that particular program.

I *believe* I understand now. But, someone please tell me if I'm wrong on this one.

Edit: So, I guess my question is this... How do you compensate for the slow shutter speed? How can I increase depth of field while still having a hand held shutter speed? Is this where a flash meter comes into play? Or can a histogram be used to find the correct exposure when using a flash for the main source of light versus just fill?

lol...wow...this is a lot harder than I wanted to think tonight.

FlipsidE

[PacAce]

Go to the EOS Flash Sticky and click on the link to the Flash Bible and read about the differences between Av/Tv and P when flash is involved. In short, you'll find that in Av/Tv the camera will meter for ambient exposure. In P, it will usually default to 1/60 @ f/4 in low light, ambient exposure be damned.

I *believe* I'm following now. According the the EOS Flash Bible, in Tv and Av modes, the camera meters for fill flash. In other words, it will try to match the foreground with the background...properly exposing both. If you are in low light, then the background will already be dark, so you'll need a long shutter speed to properly expose the foreground even with fill flash.

In P mode, it automatically picks 1/60 for the shutter speed, no matter what. And it'll set the aperture based on that particular program.

I *believe* I understand now. But, someone please tell me if I'm wrong on this one.

Edit: So, I guess my question is this... How do you compensate for the slow shutter speed? How can I increase depth of field while still having a hand held shutter speed? Is this where a flash meter comes into play? Or can a histogram be used to find the correct exposure when using a flash for the main source of light versus just fill?

lol...wow...this is a lot harder than I wanted to think tonight.

FlipsidE

If you don't want the camera to set the shutter speed for you in Av mode when using the flash, you can tell it not to by setting custom function CFn-03 to 1. What this will do is set the shutter speed to 1/250. The only problem with this is that you won't get much ambient lighting and the background will be relatively dark compared to, say, shooting at 1/60.

[FlipsidE]

Well, I'm curious. In low light conditions like these, is a flash meter preferable? Or can this be judged by the histogram? Seems this would be one place where a flash meter would be a very nice thing to have.

FlipsidE

[robertwgross]

If you don't want the camera to set the shutter speed for you in Av mode when using the flash, you can tell it not to by setting custom function CFn-03 to 1. What this will do is set the shutter speed to 1/250. The only problem with this is that you won't get much ambient lighting and the background will be relatively dark compared to, say, shooting at 1/60.

So, it is back to the photographer's mood. Do you want to illuminate the subject only, or the subject with background also? There is no right or wrong. It is just different options.

---Bob Gross---

[Quinn Porter]

[quote=slin100]Edit: So, I guess my question is this... How do you compensate for the slow shutter speed? How can I increase depth of field while still having a hand held shutter speed? Is this where a flash meter comes into play? Or can a histogram be used to find the correct exposure when using a flash for the main source of light versus just fill?

You will find manual mode to be very helpful. In manual mode, you select shutter speed and aperture, while ETTL metering will determine the correct flash output. Generally, if flash is to be your primary light source, manual mode is the way to go.

[DaveF]

The standard to read when new to Canon flashes is

http://photonotes.org/articles/eos-flash/

Has helped many folks understand what happens in various modes when using EX flashes

Edited to direct your attention to #10 of "Top Ten Frequently Asked EOS Flash Questions".

[daveh]

Edit: So, I guess my question is this... How do you compensate for the slow shutter speed? How can I increase depth of field while still having a hand held shutter speed?

Set the camera to M.

[daveh]

Well, I'm curious. In low light conditions like these, is a flash meter preferable? Or can this be judged by the histogram? Seems this would be one place where a flash meter would be a very nice thing to have.

Flash meters are great - especially with studio flashes. You don't need one to fix this though.

[boone]

If you don't want the camera to set the shutter speed for you in Av mode when using the flash, you can tell it not to by setting custom function CFn-03 to 1. What this will do is set the shutter speed to 1/250. The only problem with this is that you won't get much ambient lighting and the background will be relatively dark compared to, say, shooting at 1/60.

I think you need the Digital Rebel firmware hack to do this. I have the hack and I can tell it to use a shutter of 1/200 when using flash in Av mode. Works great. The default Av mode with flash is just about useless without a tripod or an already well-lit subject.

[DocFrankenstein]

I was getting the same results when using rebel Av mode and 550 EX

Dunno why

[pcasciola]

I was under the impression that in Av mode with a flash, the camera will set the shutter speed as if there was no flash connected and use flash fill for the foreground subject. This would explain the slow shutter speeds, no? Or am I missing something?

Did you read the EOS Flash Bible that's on the sticky post in this forum? It's GREAT, and helped me understand a lot of the oddities about EOS flash photography.

"If that means the shutter speed is some really low value so that you need to use a tripod to avoid camera-shake blur, so be it. In dark conditions, therefore, Av mode works in slow sync mode."

EOS Flash Bible (Av information) (http://photonotes.org/articles/eos-flash/index2.html#avflash)

[FlipsidE]

Flash meters are great - especially with studio flashes. You don't need one to fix this though.

- I am curious, though. Seeing that I'm new to photography and really don't have any experience when it comes to EOS flash exposure in Av, how would I know what exposure is best? I know that you can just continually snap off pictures with a digital camera. But, for the sake of argument, let's say I was using a film camera. Seems like a flash meter would almost be a necessity unless a single shutter speed (like 1/60, 1/200, or 1/250) will work no matter what.

FlipsidE

[daveh]

The flash will still be in auto even though the camera is in M. Try it. (Same for EOS film cameras.)

[rkoshy]

Edit: So, I guess my question is this... How do you compensate for the slow shutter speed? How can I increase depth of field while still having a hand held shutter speed? Is this where a flash meter comes into play? Or can a histogram be used to find the correct exposure when using a flash for the main source of light versus just fill?


I think I have a pretty decent solution for you:

#1 - Use M mode and manually set the shutter speed/aperture. It will take time to get used to it, but I find that with a flash I can vary my speed between 1/40-1/100 without any shake at close quarters (<20 feet or so). This works on my 50mm, 28-75mm, kit lens, and my 70-200mm.

#2 - The DRebel tends to underexpose, when using the external flash anyway. The solution that I found through experimentation (read about 200+ shots with diff settings), which is confirmed by other threads/sites/FAQ's etc, is that it's usually required that you use FEC... push it up by a few stops... I find that anything from about 2/3 to 1 is required to give good lighting for most pics that the DRebel takes.

I hope this helps...