ISO3200 film + ND filter question

[Graham_Martin]

I have a roll of 3200 film in my RB67 that I was using for some indoor shots. There are still a few frames left which I will have to shoot in sunlight. In order to get my shutter speed at or below 1/400 I am planning on using an ND filter (Cokin P154) which has a 3 stop effect. I figured that a 3200 speed film with a 3 stop ND filter would have the effect of acting like ISO400 so far as exposure settings are concerned.

To check this out I tested my digicam with and without the filter. At ISO400 it showed a shutter speed of 1/8 @ f/2.8. (I am indoors at night testing this out). At 3200 the shutter speed increased to 1/50 which is a 3 stop variance. I then put the 3 stop ND filter on the lens and at ISO3200 it gave me a shutter speed of 1/10 @ f/2.8 which is about 2 1/2 stops down in shutter speed from 1/50. However the results were close enough to validate my original theory.

Are there any other factors I should be taking into account when setting the exposure?

 

[Shawn Dougherty]

Keep in mind that RB67 shutters are notoriously slow at the high speeds. I mean some of them can be extremely slow, such as 1/400 and 1/250 being closer to 1/125. Obviously this can vary from shutter to shutter and the slower speeds can remain accurate despite the top end problems.

Maybe trying shooting in the quiet light before dawn and after sunset?

 

[Graham_Martin]

I did not know that. Now I'm wondering how my indoor shots will come out. I can see if I can get in some shots after sunset. Maybe some city lights or something like that.

 

[polyglot]

Your assumptions are all good except for reciprocity failure, but that won't be an issue unless your exposures are several seconds long; absolutely not relevant in your daylight situation. It'd only matter if the ND changed a 1 minute exposure into an 8 minute exposure or something like that.

One stop of overexposure on Delta3200 is absolutely not going to hurt anything. In fact, the usual recommendation around APUG seems to be to shoot at 1600 and follow the development instructions for 3200. If it's any other negative film, it'll still be fine with an extra stop.

 

[Jeff Kubach]

I didn't know that any RB lens are at 2.8.

Jeff

 

[Dr Croubie]

Are there any other factors I should be taking into account when setting the exposure?

The only other thing to watch out for is if you use TTL metering. Putting an ND in front of a lens, and/or stopping down a lot with stop-down metering can lead to incorrect metring due to stray light coming in through the eyepiece.
It's easy enough to get around it, press your eye really hard-up against the eye-piece, use the view-finder blind if your camera has one, or use an external meter. Otherwise, no issues that i can think of.

I also just devved a Delta 3200 last week, I exposed at 3200 and used the times from the MDC at 3200 (Xtol 1+0, 20C, 7.5 mins). Actually, I was closer to 8 mins at 21C, I always add a bit because I prefer shadow detail and I still never manage to blow highlights when pushing (delta/tmax/trix in xtol), next time I'll go a bit longer again.