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TTL

by Johan J Ingles-Le Nobel
Last updated August 31, 2017

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TTL stands for Through The Lens metering, and was the first rendition of a flash system that lets cameras measure light levels in a scene through its lens.

TTL has since moved onto a variety of other modes: ETTL (Canon), PTTL (Pentax) and ITTL (Nikon), and whilst they work differently to the original TTL method, the idea is the same, it enables the user to measure the light through the camera.

enables the user to measure the light through the camera

By using the relevant TTL mode for your make, essentially the camera does the thinking for you and fires a pre flash, which the camera uses to measure the light, and then varies its power to expose your actual photograph properly.

TTL For Extreme Macro

PTTL

Bumblebee shot of mine using P-TTL, the Pentax variant of TTL. With a Pentax AF160FC ringflash, P-TTL works extremely well, but with diffusers P-TTL is a thing of the devil, best avoided.

TTL is very nice and very convenient, but not always all that great for extreme macro. Insects have an extraordinary reaction time and the pre flash of TTL flash modes will scare some of them away before you've had a chance to take the actual shot. This is a downside of using *TTL for insect macro.

TTL just doesn't meter well using a diffuser. With extreme macro we're working at a very very short working distance, with a flash typically angled down on your shot with a diffuser.

Use of a diffuser has a tendency to confuse the light reading given back to the camera and underexposure using TTL modes is a frequent problem.

On the flipside though, PTTL works well for me using a ringflash with no diffuser.

TTL Consistency

Another issue worth noting is that by using TTL, you're letting the camera decide what flash power to use. This leads to inconsistent results as you maybe stacking your photograph, which has been known to cause issues (trying to stack different strength flash shots).

Pentax PTTL For Extreme Macro

The Pentax is basically rubbish for extreme macro. Pentax version of flash TTL is PTTL, and this is an especially annoying flash protocol to use for extreme macro. PTTL has the camera limitation that Pentax doesn't let it be used with anything other than a certain type of lens. This means that PTTL cannot be used with most of the optics we use for extreme macro, as these are classified as non contact 'manual' lenses, which are now since the K5 not supported. I have had email apologies from Pentax staff about this. Sadly the Pentax system is now rubbish for extreme macro. I've found a way round this but it's a bodge as you have to fool the camera. Stellar.

Comments (6)

Article: TTL
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Petrochemist says...
I often work handheld with off camera flash (Camera in Right hand flash in left) This gives me the ability to quickly change the direction/strength of lighting. TTL flash is essential for this sort of work as the flash subject distance is too variable for manual.
24th March 2014 10:09pm
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