Need ND Filter--Help Me Calculate Exposure

[wjlapier]

OK, so I'm looking at a exposure calculator and I'm a bit confused. I want to use a Canon 50/.95 wide open ( testing for sharpness after conversion ) during the day and I know I need a ND filter, but not sure which one to get. I'd prefer one. Film speeds from 100-400. Anything from full sun to slight overcast. Used on my M3. Anyone? I bet this shouldn't be difficult :bang:

Thanx--Bill

 

[bolohead]

You just need to figure what your exposure would be without the ND filter and then how many stops of ND you would need to get an exposure in the range of your M3's capabilities.

For instance, if you're shooting at f.95 and 100 speed film and your exposure would be 1/8000 of a second, you could use a 6 stop ND (i.e. ND64) filter to get down to 1/125.

Part of the confusion with ND filters is the naming. Many times the names don't necessarily equate to the number of stops. Check out the Wikipedia on ND Filters. Towards the end is a table with the names and the related f-stop reduction.

Also, if you have an android phone, check out the Exposure Calculator application, which has built in capability to calculate effects of ND filters.

 

[raytoei@gmail.com]

here's one possible explanation, using Sunny 16 and iso 100 film

on a brightest day, sunny 16 rules say to shoot at iso 100 and 1/125 (nearest to 1/100) speed and f16 aperture.

1/125 f16 - No ND - Original
1/125 f4 - ND8 - 4 stop compensation
1/125 f2.8 - ND8 + ND2 - 5 stop
1/125 f2 - ND8 + ND4 - 6 stop
1/125 f1.4 - ND8 + ND4 + ND2 - 7 stop

Increasing speed to 1/250:
1/250 f1 - ND8 + ND4 + ND2 - 7 stop

Another method with only one ND8 and increasing speed:

1/125 f16 - No ND - Original
1/125 f4 - ND8 - 4 stop compensation
1/250 f2.8 - ND8 - 4 stop
1/500 f2 - ND8 - 4 stop
1/1000 f1.4 - ND8 - 4 stop (max for M3).
1/2000 f1 - ND8 - 4 stop

 

[Roger Hicks]

This is the basic problem. There at least three 'standards' for marking NDs.

ND 8 = 8x (3 stops, simple multiplier -- quite comon)

ND 0.9 = 8x (3 stops, log -- about equally common)

3-stop ND = 8x (3 stops -- rarer, but not unknown)

Get an ND10 (stops) or ND1000 (simple multiplier) or ND 3.0 (log) and the sums are easy: 1/1000 second = 1 second.

I think that's right but it's late and I'm falling asleep.

Cheers,

R.

 

[wjlapier]

Thanx for everyone's help. Roger, I don't need more confusion 🙂

Looks like I need at least 6 stops, for 100ISO film. I guess I wait until tomorrow afternoon to place my order. I'll have to shoot in the dark in the mean time 😉