44 replies to this topic

[curtisleo]

I finally got a working eTTL circuit from Aquatica for my A300 housing. What is the proper way to "test" the TTL.

I been playing around with the camera (300D) settings and the ttl appears not to be working.

Thanks,

Curtis

[marriard]

I finally got a working eTTL circuit from Aquatica for my A300 housing. What is the proper way to "test" the TTL.  

I been playing around with the camera (300D) settings and the ttl appears not to be working.  

The quickest TTL test is as follows:

1. Cover the lens or put the lens cap on. Take a shot - the strobes should do a full power dump (as it should never get enough light to close the shutter)

2. Now take the lens cap off and take a shot where there should be plenty of light (I normally just open up the f-stop). The strobes should not perform a complete power dump

This will show whether TTL is at least trying to work.

Also remember if there is a LOT of light, the strobes may not be able to quench fast enough and you may have to choose a high f-stop for it to provide a good exposure. The opposite for real small f-stops.

M

[Alex_Mustard]

You will also be able to tell by the results!

Set the camera and strobe to TTL and then shoot the same subject at a range of apertures and they should all be correctly exposed.

This is an example of a dTTL test I did with my D100:


Alex

[marriard]

You will also be able to tell by the results!

Good example - you can also see an example of where TTL 'worked' at F2.8 but the aperture was too wide for the light to quench fast enough.

From this sort of test you can also see what kind of TTL compensation you may need when shooting TTL.

M

[whitey]

Please let us know if your eTTL works! I haven't seen a single eTTL shot from an Aquatica camera anywhere yet. I did mail Aquatica earlier today to get their thought on this. Aquatica "cracking the eTTL code" has been mentioned many times on this site as fact (since March this year), but where are the working ICU-equipped housing photos?

[bvanant]

Alex: What strobe were you using?
BVA

[satura]

Please, to compare the eTTL better with the exellent TTL from Olympus do some tests with different light levels, as well. I have heard that ETTL does not work fine with very high ambient light levels.

[curtisleo]

Here's my test results. Let me know what you think.

Test Setup.
Aquatica A300 eTTL Housing
Canon Rebel 300D
Canon EF 100mm Macro f2.8
2 Ikelite DS-125

http://www.leo-tech....A300-eTTL-Test/

[satura]

Thanks for sharing your tests. Are you sure you ordered the ICU? :| I cannot see any TTL at all....

[curtisleo]

Forgot to add to the test setup, Blinded Duck....

[curtisleo]

Yes I ordered the ICU circuit. It's the 2nd circuit that I got. The first one didn't work at all. It would cause the strobes to go haywire and not cycle. the second circuit doesn't do it anymore and allows it to sorta "work" but no ttl.

[whitey]

Curtis, what mode are you shooting in? (eg P, Av etc)

Hey your eTTL works fine at f/3.5! I like the idea of an eTTL circuit that only gets the correct exposure when you set the shutter speed and aperture correctly...I think I'll call this new concept "Manual TTL"

[curtisleo]

I set the camera to "M"
ISO 100
Shutter - 1/200s
Apeture - f2.8 to f32 <- this is what I changed.

Is there another way to test this?

[whitey]

OK Curtis, I see you're online. I've just been testing my 90mm and 10D with similar shots.

1/Setting Camera to 'M' is correct.
2/ 1/200th is probably your max sync speed - you might want to retest at 1/125. Having said this, eTTL should definitely work fine at max sync speed unless you're at the limit of your flash's power. Let me know what your distance from the subject is. It looks quite close, but perhaps that's a very large duck you're shooting.
3/ I'd advise testing with your subject further away from the background, this lets you see that eTTL is working properly as the background will darken but the subject will be easily illuminated. Alex's Nikon shots above didn't really show this well. I'll post a couple of shots and show you what I mean.

[whitey]

Here's a test I've just shot for you. This shows you if Canon eTTL is functioning properly. You need a well lit background far enough away that the flash is not illuminating it. The above pictures show general exposure, but it's difficult to distinguish flash from ambient as the subject is too close to the background.

You need to choose settings so that at least one exposure is properly exposed (check the light meter). Correct exposure means the background (ambient light) is properly exposed. The flash should expose correctly regardless of settings (exceptions to this noted in a moment).

[whitey]

Shot in "M" mode.
Shutter 1/125
Aperture from 2.8 to 32
Speedlite 420EX as flash, no exposure compensation.
ISO 100

This shows eTTL function. The f/2.8 exposure is correct on the light meter, and the background is properly exposed. As the f-stop is increased, the camera meter reads that it is underexposing, and the background darkens. Note that the cup (subject) remains correctly illuminated - the flash increases its output to compensate for the smaller aperture (larger f stop).
At f/22 the background is very underexposed, but the foreground subject is still correctly exposed by the flash.
At f/32 the flash is not powerful enough to expose the subject and underexposure of the subject results. The 420EX indicated on this exposure that it was unable to obtain the correct exposure. A larger flash or higher ISO would allow me to take this photo with correct flash exposure.

So that's Canon eTTL in M mode. The effect of aperture on exposure will vary between modes - so keep that in mind when testing. FWIW, underwater I've been shooting Av and M.

I'd suggest running a test as above so we can see what your ICU is actually doing. It cetainly doesn't seem to be performing anything resembling Canon eTTL function.

[satura]

...I think I'll call this new concept "Manual TTL"

"mTTL" , sounds very professional :-) :-) :-)

[scorpio_fish]

Alex's test is a good test for TTL. The entire scene is lit by strobe. Each change of aperture should result in the same exposure. If it isn't, something is wrong. The histograms can be easily compared to examine overall exposure.

Whitey, while your test is a good demonstration of the effect of aperture change on ambient exposure, it is not a good TTL test.

Note that the cup (subject) remains correctly illuminated

1. Is it? How do you know it is exactly the same? It's close, but it doesn't appear to be exactly the same.

2. If it isn't, is TTL "wrong"? Not necessarily, because the TTL calculation may or may not be trying to get the cup correctly exposed. When TTL evaluates the scene to determine the proper flash amount, what do you think it is evaluating? Is it the entire frame, the cup, the things in the cup, the cup and everything in proximity to the cup (e.g. foreground tablecloth)?

This is one of the reasons TTL is not a perfect thing for wide angle photography.

[james]

Whitey: Ever heard of balanced fill flash? It's what your camera and the Canon EX speedlite are trying to do.

To do a proper test of TTL you should NOT let ambient light factor into the test.

Curtis: Thanks for posting your test results. They are not encouraging.

Cheers
James

[whitey]

Sigh.....

Alex's test is a good test for TTL.  The entire scene is lit by strobe.  Each change of aperture should result in the same exposure.  If it isn't, something is wrong.  The histograms can be easily compared to examine overall exposure.

Whitey, while your test is a good demonstration of the effect of aperture change on ambient exposure, it is not a good TTL test.

Note that the cup (subject) remains correctly illuminated

1. Is it? How do you know it is exactly the same? It's close, but it doesn't appear to be exactly the same.

2. If it isn't, is TTL "wrong"? Not necessarily, because the TTL calculation may or may not be trying to get the cup correctly exposed. When TTL evaluates the scene to determine the proper flash amount, what do you think it is evaluating? Is it the entire frame, the cup, the things in the cup, the cup and everything in proximity to the cup (e.g. foreground tablecloth)?

This is one of the reasons TTL is not a perfect thing for wide angle photography.

Scorpiofish, what does the sigh represent? Excuse me if I'm wrong, but it sounds a bit condescending to me. You'll note the question was about eTTL (Canon's flash system), which I've attempted to explain in practical terms with an example which I shot specifically to illustrate this to those who might be interested. Your comments 1 and 2 suggest that you're not clear on what eTTL is and how it works. Please read my post again, and if still in doubt there are many good posts on the internet about how the eTTL system functions.

The practical reason for using eTTL in nature photography is to BALANCE the exposure between flash - which illuminates the subject, and ambient light. You control subject exposure with flash exposure compensation, you control background/ambient exposure with exposure compensation, or in the case of 'M' mode with aperture.