Richard Ashrowan Posted September 25, 2012 Share Posted September 25, 2012 I have a Vario Switar POE on a Bolex. The film speed dial on the lens only goes to 200 ASA, but I am shooting using Kodak 7222 daylight stock at 250 ASA. Does anyone know what kind of exposure compensation I might need to apply to get a correct exposure using the over-fast 7222 film for this lens? Link to comment Share on other sites More sharing options...
Chris Millar Posted September 26, 2012 Share Posted September 26, 2012 Stop down an extra 1/3 stop To be exact: Log2(250/200) ...or more generally Log2(filmSpeed/meterSetting) positive results infer you need to stop down - negative that you need to open up Link to comment Share on other sites More sharing options...
Richard Ashrowan Posted September 26, 2012 Author Share Posted September 26, 2012 Thanks Chris - a perfect reply with a useful math tool! Much appreciated. Link to comment Share on other sites More sharing options...
Chris Millar Posted September 26, 2012 Share Posted September 26, 2012 Actually, the math is a bit upside down. If you use: Log2(meterSetting/filmSpeed) the results might be a bit more intuitive - positive means open up, negative = stop down Whichever way your head works ;) Link to comment Share on other sites More sharing options...
Robert Lewis Posted September 27, 2012 Share Posted September 27, 2012 I have a Vario Switar POE on a Bolex. The film speed dial on the lens only goes to 200 ASA, but I am shooting using Kodak 7222 daylight stock at 250 ASA. Does anyone know what kind of exposure compensation I might need to apply to get a correct exposure using the over-fast 7222 film for this lens? This is the Mark I POE lens by the sounds of it. The highest ASA setting it could take was, as you say, 200ASA. The Mark II version of the lens could be set to 400ASA. So, if you wish to use the auto-exposure function of the lens you can't really use manual exposure settings unless you are shooting a picture which has a steady light reading because the auto exposure will contually vary the exposure as the light reading changes. You can't do that in any event unless you have an exposure meter and unless you know how to take into account the Bolex prism factor which one has to have regard to when using a conventional exposure meter. A Bolex exposure meter takes the prism factor into account, and so if you had one of those you could lock the exposure control on the lens and use manual settings. To use the lens you have on auto setting, you need to reduce the light going through to the film by 1/3 of a stop. You could use a 1/3 of a stop filter behind the lens. The lens will, on its 200ASA setting, allow 1/3 of a stop over exposure. So you use your POE lens on 200ASA setting and use a 1/3 of a stop filter behind the lens. That will then reduce the light going through to the film by 1/3 of a stop. That having been said, however, having used EK 7222 film myself, I am not so sure that 1/3 of a stop over-exposure would be significant. I hope this is helpful. Link to comment Share on other sites More sharing options...
Chris Millar Posted September 27, 2012 Share Posted September 27, 2012 As you've pointed out, if we choose to he concerned about 1/3rd stops with neg film stocks the prism will be a factor. Funny thing is the 250 to 200 offset would work out kind of well, it would over-expose about what the prism under-exposes Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now