Auto exposure, and the ND filter

[Piotr Wozniacki]

I've just noticed a sort of behaviour from my A1 that seems strange to me: being in Tv mode (keeping the shutter speed at 1/50th), engagement of ND filter did NOT cause automatic iris opening, to compensate for the limited amount of light! The picture in the LCD just turned darker, so I pressed the Exposure Lock button to see what the settings were - and to my astonishment, the exposure bar showed perfectly matched actual vs auto exposure marks! To get properly exposed picture, I opened the iris manually - with the picture bright enough, the 2 marks at the exposure bar were at substantially different positions!

Now, I thought the the Tv mode would automatiacally compensate for ND filtering (or lowering gain) with opening iris, but it doesn't. Why? And BTW, I had zebra on and it confirmed my impression of the picture not being bright enough.

[Chris Hurd]

I thought the the Tv mode would automatiacally compensate for ND filtering (or lowering gain) with opening iris, but it doesn't.

It certainly does on mine...

Tv 1/60 +12db = f/5.2
Tv 1/60 +6db = f/3.2
Tv 1/60 +0db = f/2.6

Tv 1/60 ND0 = f/8.0
Tv 1/60 ND1 = f/3.2
Tv 1/60 ND2 = f/1.6

[Piotr Wozniacki]

I couldn't reproduce the effect yesterday, because days are still so short...Anyway, we've had sunshine since today morning, so I experimented a little and can confirm, that indeed engaging ND filter (or decreasing gain) does open up the iris. I suppose what I did wrong yesterday was swithing the ND filter without a real need for it (the sunshine is not that bright at this time of year), which caused the iris to reach its maximum opening at the given focal length, which just wasn't enough to fully compensate for the decreased amount of light - hence the darkish picture. What I didn't notice yesterday was the shutter speed value blinking at me!

My point is that while blinking the shutter value is some indicator of insufficient exposure, I would expect the "ND off" blinking - and this never happens unless the AGC is switched on! I guess this is a rather unfortunate design feature, and I already was mentioning it in the "wishlist" thread. Since it wasn't included in the poll, I guess I may be isolated in considering it a problem - or does anybody agree the ND on/off indicators should work even with AGC on? If so, then please include it in the next issue of the wishlist - thanks Chris!

[Piotr Wozniacki]

BTW, please help me realize a difference (if there is ANY) between the A1 behaviour in Tv mode vs Av mode, with Exposure lock on - I guess they both equal Manual mode then? Or am I missing something?

I personally find myself mostly using the Tv mode, as I like having full control on all settings but - with light conditions quickly changing - it's useful to have camera find the correct iris automatically with one push of a button. Unless of course I need specific aperture value - then I start with the Av mode.

[Chris Hurd]

Originally Posted by Piotr Wozniacki

A1 behaviour in Tv mode vs Av mode, with Exposure lock on - I guess they both equal Manual mode then?

And in "A" Auto as well. So, the A, Tv, and Av modes plus Exp. Lock will all function exactly like the Manual program mode. I fully agree that of all these, Tv mode plus Exp. Lock is the best. I use it much more than the M mode.