Help With Flash Photography - DPChallenge Forums

Canon EF 24-105mm f/4.0L IS

11/06/2003 12:09:15 AM · #1

Greetings...

//www.pbase.com/jmsetzler/420ex_flash

These are some test shots that I took to test out my new flash unit. The first shot was with the onboard flash on the 10d head on. The second was with the 420ex head on. The third was with the 420ex and the omnibounce diffuser. The 4th was with the 420ex, no omnibounce, bouncing the flash off the ceiling. The 5th was bounced off the ceiling with the omnibounce. The filenames describe the flash situation. These photos have no mods other than a resize and a sharpen... no level adjustments.

The 420ex shots seem to be underexposed compared to the onboard flash shot. Any ideas on why this may be? The camera was in point and shoot mode and the exif data is on the images. I would expect the exposure level to be a little higher than shown here with the 420...

Any thoughts?

Thanks :)

Natator

Canon EOS-5D

11/06/2003 12:14:30 AM · #2

I have exactly the same setup and although I have not done a direct comparrison I have not noticed that on an ongoing basis. I'll look forward to any answers here.

However, what it might be is ..... batteries.

I was suddenly getting underexposed (far worse that that) last weekend. Took off the 420 and back to correct exposure. I immediately started checking my settings, custome functions, AWB etc etc etc but to no avail.

I changed the batteres on the flash unit and everything instantly came good!

What I did not think to check at the time, but I suspect would have given it away, was the green "correct exposure" (or whatever) light on the back of the 420.

If it's not batteries then I have no idea, but look forward to seeing the answer. Certainly worth trying new batteries firth though, unless you already know they are good.

P.S. John, if you haven't got one I'd suggest getting the off shoe cord. I got mine a few weeks back and it is sensational, it has given me so many more options with flash (which may just be particularly exciting to me as I've never been able to do this before).

Message edited by author 2003-11-06 00:16:36.

kevinswope

Canon EOS-1D Mark II

Canon EF 70-200mm f/2.8L USM

11/06/2003 12:17:43 AM · #3

I cant remember but doesnt the on board flash only have one level of brightness when it flashes? becauseif it does than mabe the one shot with it, is overexposed just a little while the 420 compensates the level of flash needed to the situation. Im still very new at this - so just an idea.

jimmythefish

Canon EF 17-40mm f/4.0L USM

11/06/2003 12:24:54 AM · #4

Hi John,

Well the first thing I noticed about the onboard shot vs. the 420EX shots (which I have too and am just learning to play with it myself) is that the aperture and shutter speed is much the same, whereas the ISO is set at 400 on the onboard flash and 100 on the head-on external flash shots. Now, the E-TTL system should compensate for flash exposure regardless of which flash is used, but logically you're getting more of an ambient exposure with your onboard shot, which would do something to explain the exposure difference.

Popular photography had a flash photography article a few months back (I can scan it and send it to you if you'd like) where they recommended using manual exposure with flash photography as all flash photography is essentially a double exposure - ambient and flash. The trick is to use the ambient metering combined with the flash exposure compensation to get the desired look. The E-TTL stuff helps out a great deal in firing a pre-flash (that you can't really notice unless you're really looking for it) to meter the flash exposure. This works well if you have some time to set up a shot. For quicker work I seem to get consistent results by shooting bounce flash indoors with the sync locked at 1/200th (custom function) in Av mode.

James.

Originally posted by jmsetzler:

Message edited by author 2003-11-06 00:28:21.

Natator

Canon EOS-5D

Canon EF 24-105mm f/4.0L IS

11/06/2003 12:35:31 AM · #5

James .....

Can you explain the sync locked at 1/200th for me in simple terms. I haven't managed to get my head around that one yet, so don't use it. You may be able to shed (flash?) some light on it for me.

Seanachai

Canon EOS-20D

Canon EF 70-200mm f/2.8L USM

11/06/2003 12:39:11 AM · #6

Just a quick observation. Looks like you are shooting head on into a reflective glass surface with your flash. This might give you wacky exposure problems.

jimmythefish

Canon EF 17-40mm f/4.0L USM

11/06/2003 12:48:19 AM · #7

Well with the sync locked at 1/200th you can adjust aperture to suit your needs (shallow or broad depth of focus etc.) and rely most heavily on the flash metering to expose your subject. Aperture and shutter speed for exposure kinda goes out the window with flash photography. Instead, the camera uses the pre-flash to meter and then fires flash at varying intensities to expose properly. Sure you're getting ambient exposure with aperture and shutter speeds, but in most cases when you're using flash it's because there's very little light. The 10D will assume that the flash is to be used as the main light source in certain modes (the exception being Av with no sync speed set and Tv modes I do believe) and expose your subject with the flash rather than ambient light. 1/200th just sets a good fast shutter speed for ensuring that there's no situations where you get motion blur in shots, but can still adjust aperture and let the flash's intensity expose accordingly.

When you want to use fll flash to pump up a daytime exposure (backlit conditions etc) or want to properly expose a background in a nighttime portrait, you can use Av mode and the camera doesn't assume that the flash is the main light source. Instead, it takes ambient light into account when metering the shot. That is, the background will be exposed according to an ambient light metering and not a flash metering, with the camera selecting shutter speed rather than flash intensity to expose properly.

1/200th is the fastest shutter speed that the camera's E-TTL metering system can properly adjust exposure for. A good rule of thumb for indoor flash photography is f/5.6 and 1/200th with ISO 100. You won't screw up with those settings, if you're just after reasonable snapshots.

Originally posted by Natator:

Message edited by author 2003-11-06 01:23:25.

Natator

Canon EOS-5D

Canon EF 24-105mm f/4.0L IS

11/06/2003 01:40:38 AM · #8

Thanks for the excellent explanation there James :)

It is definately something I will have to experiment with.

Now, back to our regular program ... problems with flash photography .....

hortopth

Canon EOS-D60

11/06/2003 04:14:31 AM · #9

John, I noticed in your site that you have a Holga... did you get one as is, or one specially altered? Apparently, they are all gone now...
I wanted to get one rigged up for some fun with time exposures, but they can't be found new anymore (apparently)

Adrian Tung

11/06/2003 05:30:35 AM · #10

If I'm not mistaken, E-TTL measures exposures based on your active focus point. If you're in a habit of focusing and then re-composing (like most of us, I reckon), your active focus point would probably be pointing somewhere at the background (the white curtain in this case) which will cause the exposure to be wrong.

As a test, try this:
- Set M mode, shutter speed A5.6, 1/125s (just as a base for testing)
- Use only the centre focus point
- Focus on your subject, then, while keeping the focus point on your subject, hit * to AE/FE lock (assuming C.Fn 4 is set to the default value)
- Recompose, then take the shot.

Although I don't have a speedlite yet, I use this method with my 10D's internal flash and have always gotten good results (so far). I plan to get a 550ex in a month or two though.

Message edited by author 2003-11-06 05:33:51.

11/06/2003 09:10:06 AM · #11

Originally posted by hortopth:

//www.freestylephoto.biz/sc_prod.php?cat_id=&pid=2679

Mine is not modified and I haven't shot any film with it yet. I have only shot with the Ikonta so far. Talk to scab-lab about Holga stuff :)

11/06/2003 09:12:01 AM · #12

OK.. I overlooked the difference in ISO levels on those automatic shots. I sorta assumed that they would be close or identical, but that would definitely explain the difference in exposure levels on the test photos. What I don't understand is why.

There are several theories here that seem to make sense. The AF point could be playing a role. I will do some more test photos tonight and see what I come up with next...

Adrian Tung

11/06/2003 09:16:23 AM · #13

Think this will help:
//photonotes.org/articles/eos-flash/

(edit: testing new sig...)

Message edited by author 2003-11-06 09:25:33.

11/06/2003 09:28:03 AM · #14

I'm just a bit disappointed that the 420ex doesn't work as well as a point-and-shoot flash as the onboard flash does.

Adrian Tung

11/06/2003 09:33:55 AM · #15

Originally posted by jmsetzler:

I'm just a bit disappointed that the 420ex doesn't work as well as a point-and-shoot flash as the onboard flash does.

After reading the flash guide about E-TTL and all, I was quite disappointed too after getting used to the TTL capabilities of my C-750UZ and FL-40 combo. Oh well... different designs require different techniques.

"With great power comes great responsibility" ... LOL.

11/06/2003 09:45:04 AM · #16

My objective of flash photographer is primarily for point and shoot work. The 420 is definitely a better solution than the onboard flash but I will just have to get the hang of it :)

11/06/2003 09:54:04 AM · #17

One thing that I didn't see in this is mention of what mode you had the camera in. The Canon E-TTL system works entirely differently in P mode, Av & Tv mode or M mode - in each case the exposure is set for very different things, varying from foreground subject only to ambient background only. Being in the wrong mode for what you want and using E-TTL can quickly lead to disappointing results.

Looking at the pictures, the other thing that occurs to me is that you have a very reflective object, dead center of the frame - this will mean, particularly for the bounce shots, that you will get light reflected back too quickly which will confuse/ fool the auto-exposure system into under exposing (as it only measures reflected light) trying without pointing at a window/ mirror might help too.

Another important feature of the E-TTL canon system is learning how to use FEL (Flash Exposure Lock) particularly if you want to shoot 'off center' subjects like this.

Message edited by author 2003-11-06 09:57:19.

11/06/2003 09:55:42 AM · #18

The camera was in point and shoot mode for all of these test shots.

11/06/2003 10:05:47 AM · #19

Originally posted by jmsetzler:

The camera was in point and shoot mode for all of these test shots.

Which 'point and shoot' mode ? There are several and they each expose in different ways using E-TTL flash. The photonotes.org link mentioned earlier is a really good reference on the peculiarities of fully automatic E-TTL flash but basically:

P mode:
The overriding principle of Program (P) mode in flash photography is that the camera tries to set a high shutter speed so that you can hold your camera by hand and not rely on a tripod. If that means the background is dark, so be it.

(NB John - this is quite probably your problem here - I'm assuming f3.5 is your lens wide open- if you shoot in P mode, you'll never get a shutter speed slower than 1/60s) As it looks like you are shooting in doors, you are always going to underexpose, on camera or 420 flash used.

Tv Mode:
In this mode the camera lets you change the shutter speed. It then automatically chooses an aperture setting to expose the background correctly.

Av (aperture priority) mode flash.

Av mode lets you set the depth of field by specifying the lens aperture. The camera then chooses a shutter speed ranging from 30 seconds to the cameraâ��s X-sync speed, in order to expose the background correctly. 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.

Manual (M) exposure mode flash.

In manual exposure mode you specify both the aperture and shutter speed, and your exposure settings will determine how the background (ambient lighting) is exposed. The subject, however, can still be illuminated by the automatic flash metering system since the flash can automatically calculate flash output levels for you.

----- but basically it looks like the problem was you were shooting in a dark room, in program mode, with a slowish lens, so the camera could never get enough light, with the constraint you placed on it of using a shutter speed equal to or faster than 1/60s. In some cases you got better exposures and the camera was at f4 so there was just enough light, but in general it looks like you were skirting the boundaries of how much light was available, given the constraints of the shooting mode you selected.

Message edited by author 2003-11-06 10:15:49.

11/06/2003 10:36:20 AM · #20

I was using the 'green box' point and shoot mode... not the P mode. As noted earlier, the only difference in exposure was that, when in this mode, the camera with the onboard flash set the ISO to 400 and it only chose 100 with the 420 on the camera. That was my first curiosity after it was brought to my attention.

The way I had the camera setup, I would have expected the first and second shots in the set to be almost identical. The difference, however, is that the first one was ISO 400 and the second was ISO 100. Two stops of ISO difference explains the underexposure, but WHY the camera didn't choose ISO 400 for the second shot is the part that is confusing me.

jab119

11/06/2003 10:43:31 AM · #21

have you checked the flash level ( i thinks thats what its called) where you can tell the camera to use a strong flash or a weaker flash strength?? (or compensation)

I have a promaster flash I got for my 707, then bought the module for it to fit the D60. I have to adjust the in camera flash strength (compensation) to get the correct desired flash results using the promaster.

James

11/06/2003 10:47:52 AM · #22

Originally posted by jab119:

The output level of the flash here is supposed to be determined automatically by the e-ttl metering.

11/06/2003 10:49:16 AM · #23

Originally posted by jmsetzler:

The green box mode is even more basic than P mode. But essentially the problem is the same - you are shooting in a mode that limits your shutter speed to 1/60s or faster. You are shooting in essentially a dark room and the camera is trying to use the flash as the sole exposure source. Your lens is quite slow for that situation and the exposures are all pushed right up against the limits of your equipment.

The fact that you shot straight at a highly reflective subject probably further confused the camera meter. You might get better results if you use flash exposure lock/ pre-flash, but I doubt it.

11/06/2003 10:51:58 AM · #24

Originally posted by Gordon:

I understand this part completely. What I don't understand is why the camera did not choose a higher ISO with the 420ex like it did with the onboard flash in the same camera mode... That's what I'm investingating at this point. It may be that the 420ex is requesting that ISO setting. This will be part of my next test photos tonight.