10 Stop ND - getting the right exposure?

[rhubarb]

Hopefully going out this weekend with a 10 stop ND filter. Never used it before. Its completely black - infact looks like a lens cap. Because its so dark I think I need to frame the sot I want first then screw on the filter.

So this I think is a really basic question but to get my exposure right what do I need to do. Get it right without the filter and then I need to do some sort of calculation based on the light exposure and knock 10 stops off of it, so say I'm at f8 at 1/640 and I want to remain at f8 what's the calculation?

Or is it best just to take a whole load of test shots to see what happens (my normal approach !!!)

[chris.mapey]

I'm going to get flamed for this I'm sure, but 10 stops is easily checked by turning the shutter speed dial 10 clicks round.

I can never remember the numbers for each "stop"! I use AP mode and choose the DoF and leave the camera to sort out the shutter speed.

Don't forget a tripod - you'll need it

Also, as you mention, frame & focus before attaching it - have fun & don't forget to post the results.

Chris

[GetCarter]

What I do with my infra red filter is : tripod > frame > focus > into manual > put filter on > think DOF & set aperture > test shot at 2 seconds / bracket at 4, 8, 1 and .5 > look at the results and work from there.

Edited by GetCarter on Friday 9th May 10:10

[Jenx]

chris.mapey said:

I'm going to get flamed for this I'm sure, but 10 stops is easily checked by turning the shutter speed dial 10 clicks round.

That's OK if your dial works in whole stops, but it's much more usual to work in half stops or one third stops...so 20 clicks and 30 clicks respectively.

Once you're close, carpet bomb

Martin.

[chris.mapey]

Jenx said:

Once you're close, carpet bomb

Martin.

That's my theory - shows what I know about "stops" - I only "stop down" when the CF card is full



Chris

[rhubarb]

Cheers guys, I was chatting to someone at work who started to explain manual calculations for things, and just read these replies, I think yours is a much better idea. Try out get somewhere close and carpet bomb away

[CVP]

I used to have a little card I carried in my camera bag that had two columns, shutter speed and aperture and just had them listed out in whole stop movments. That was an easy way to work out the movements required to your settings. This was in the days of film though when I didn't want to burn that many frames for each shot.

Chris

[C&C]

rhubarb said:

So this I think is a really basic question but to get my exposure right what do I need to do. Get it right without the filter and then I need to do some sort of calculation based on the light exposure and knock 10 stops off of it, so say I'm at f8 at 1/640 and I want to remain at f8 what's the calculation?

Or is it best just to take a whole load of test shots to see what happens (my normal approach !!!)

Calculation would be to work out what 1/640th of a second is in decimal - so with a pocket calculator, divide 1 by 640 (equals 0.0015625 seconds). Then multiply by 2, repeating a total of 10 times. This gives the shutter speed in seconds - in this case 1.6 seconds. It's actually the equivalent of multiplying the exposure length by 2 to the power 10, or 1024 (roughly 1000).

You can do a table in excel to work it out for a range of values, but as a rough guide, the following may be of some use (first column is shutter speed without filter, second column is speed with 10 stop ND filter):

1/8000 - 1/8
1/4000 - 1/4
1/2000 - 1/2
1/1000 - 1 second
1/500 - 2 seconds
1/250 - 4 seconds
1/125 - 8 seconds
1/60 - 16 seconds
1/30 - 32 seconds
1/15 - 64 seconds
1/8 - 128 seconds
1/4 - 256 seconds
1/2 - 512 seconds
1 sec - 1024 seconds

Maybe use this as a start, and then as Martin suggests, carpet bomb around there!

Hope this helps, and please post up some of your results.

Cheers,

Conrad.

[RobDickinson]

Does your camera meeter through the lens? if so who cares.

Frame, focus (manual mebe) put filter on, get the camera to meeter, see how it turns out (and bracket).

[stigmundfreud]

RobDickinson said:

Does your camera meeter through the lens? if so who cares.

Frame, focus (manual mebe) put filter on, get the camera to meeter, see how it turns out (and bracket).

i think ttl is going to struggle at 10 stops!

[RobDickinson]

Why , does it struggle at night or dusk?

[C&C]

TTL metering should work fine with the filter in place - obviously focus would have to be set manually without the filter there.

The only thing to make sure about would be to ensure that the eyepiece was properly covered, as if left uncovered, light getting in there would affect the reading and lead to underexposure. This obviously isn't such a big issue without a filter at night, as the overall light level through the lens and via the eyepiece is likely to be similar.

[Jenx]

[quote=C&C]
Calculation would be to work out what 1/640th of a second is in decimal - so with a pocket calculator, divide 1 by 640 (equals 0.0015625 seconds). Then multiply by 2, repeating a total of 10 times. This gives the shutter speed in seconds - in this case 1.6 seconds. It's actually the equivalent of multiplying the exposure length by 2 to the power 10, or 1024 (roughly 1000).

You can do a table in excel to work it out for a range of values, but as a rough guide, the following may be of some use (first column is shutter speed without filter, second column is speed with 10 stop ND filter):

1/8000 - 1/8
1/4000 - 1/4
1/2000 - 1/2
1/1000 - 1 second
1/500 - 2 seconds
1/250 - 4 seconds
1/125 - 8 seconds
1/60 - 16 seconds
1/30 - 32 seconds
1/15 - 64 seconds
1/8 - 128 seconds
1/4 - 256 seconds
1/2 - 512 seconds
1 sec - 1024 seconds

Maybe use this as a start, and then as Martin suggests, carpet bomb around there!

Hope this helps, and please post up some of your results.

Cheers,

Conrad.
[/quote]

Conrad...you need to get out more...Preferably in the Noble

Martin.

Edited by Jenx on Saturday 10th May 23:59

[C&C]

Jenx said:

Conrad...you need to get out more...Preferably in the Noble

Martin.

I think you're probably right there (says me replying from my desk at work on a Sunday!!)