>> Forums home page
 Practical BTZS
 The BTZS System in Practice

Announcements | General Discussions | Plotter | ExpoDev Palm | Film & Paper Testing | Practical BTZS | ExpoDev for iOS

  Messages since    View    Per page
 [Compose New Message] Messages 381 to 387 of 387 (Total: 387) First | Prev | Next | Last 
Light sensitivity of the stopped negative 
David B. Mark  12:07 24 Sep 02 
Re: Light sensitivity of the stopped negative 
Phil Davis  17:58 24 Sep 02 
Roll film use and BTZS 
Phil  12:25 1 Sep 02 
Michael --

I see that I didn't answer your second questiion in my first note so how's this:

You can't transplant much of the BTZS data to sheet film because of the restraints on development control. Unless you're willing to commit an entire roll to subjects of similar contrast it's probably best to provide "normal" exposure and development, and leave contrast control up to paper filtration.

Since ISO ratings are based on development that results in abnormally high negative contrast, it's almost always prudent to de-rate the film speed in normal use. If you check one of the Plotter's EFS/G charts you'll see that there's usually a 1/3 to 2/3 "loss" of film speed at the "normal" G of around 0.5, compared with the speed for G=0.62 (approximately the value that the ISO rating is based on). If you're using the Expo/Dev program that speed adjustment is made automatically, based on the film/dev combo you're using, the paper ES you've chosen, and the SBR (and reciprocity, if that's a factor). If you're working manually. and if you know what the appropriate EFS is for the subject you're shooting, then it's wise to set that speed into your meter before calculating the exposure.

As far as I know, small camera metering systems aren't smart enough to make this speed adjustment because they can't know your target ES, or what film/developer combination you're using. For that reason, I guess I'd recommend checking the "normal" (7-stop SBR) EFS of your roll film/developer pair, setting that into the meter, then going with whatever exposure the camers calculates. Then develop "normally" (for a 7-stop SBR). Obviously, if you're prepared to expend a whole roll of film on a subject of some abnormal SBR, then calculating exposure and development for that SBR makes sense.
[Reply] [Email author of message] [Compose New Message] [Modify] [Delete]
How to Use Personal Speed Point 
M E CARBOY  0:02 1 Sep 02 
Re: How to Use Personal Speed Point 
Phil Davis  8:40 1 Sep 02 
Re: How to Use Personal Speed Point 
M E CARBOY  11:26 1 Sep 02 
Re: How to Use Personal Speed Point 
Phil  11:53 1 Sep 02 >> Forums home page Last Updated: 22 Aug 2002