Big Stopper Question

Mystery57

Mystery57

Suspended / Banned
Messages
1,811
Name
Andrew
Edit My Images
Yes
Just want to check something on calculating filter exposure times.


The Big Stopper is a 10 stop variance from the normal exposure - does it matter if you dont get this one hundred percent accurate ?

If a normal exposure read 1/500 at F11, what would the BS times be ?



With Graduated ND filters how do you go about calculating the exposure times for these as obviously not all of the frame is affected



thanks
 
Yes, although I make the F32 exposure 16 seconds myself (more if using film as you're into the realms of reciprocity failure) and you'd also be risking diffraction making everything mushy at f32.

That said 1/500th at f11 is pretty bright, you'll usually find in the UK that you're looking at two or three stops down from there in sunlight, sometimes more, and of course a lot less at dusk or dawn
 
Stuart M said:
When using a 10 stop filter, multiply your stated exposure time by 1024.

So, 1/500 x 1024 = 2 secs
Click to expand...

Cunning, and why 1024? Because it's 2 to the power of 10. And why 2? Because each stop doubles the exposure time.

Im sure most people know that anyway, just sayin like :)

For a 3 stopper, multiply by 8, or 2 to the power of 3 (cubed).

Ok, Im off now. :geek:
 
Dunno about the maths. I said 1024 because that's what it says in the chart I pointed the OP at and the chart was made up by a bloke who knows what he's talking about. Keep it simple I say. :lol:
 
Stuart M said:
Dunno about the maths. I said 1024 because that's what it says in the chart I pointed the OP at and the chart was made up by a bloke who knows what he's talking about. Keep it simple I say. :lol:
Click to expand...

Keep it simple, yes - x1000 is near enough. But of all the very dark ND filters I've tried, none of them has been exactly as marked and they're known to vary slightly from batch to batch, like 10.3 or 10.6 stops etc.

Furthermore, depending on the level of infrared present and the filter/lens/sensor combination, the effective density can vary a little on that score too.

Way to do it is to test your filter on a typical day. Work out what the actual exposure factor is, and do a custom white balance while you're at it. Armed with info, you should be able to get very close on the day but will almost certainly need to tweak the expose slightly and optimise the colour in post processing.
 
You must log in or register to reply here.
Back
Top