Imagon Exposure

I'm using a 200mm Imagon with bellows on my Hasselblad, but I'm not sure how to make exposure calculations. Would you add a "bellows factor" based on the bellows extension? Can I use the exposure taken off the ground glass with a Hasselblad metered prism?

Any suggestions would be helpful. Thanks.

If you're not doing extreme close ups I wouldn't worry about a bellows factor. An easy rule to remember is M+1 squared, where M = magnification on film or ground glass. At life size on film (1X magnification) +1 =2, squared =4x more exposure than your hand held meter indicates. I'm not familiar with your Hasselblad metering prism, so I don't know if it will compensate for extension. If it reads a stopped down lens then it should.

As long as your subject is a meter or more away from the lens, you do not need an extension factor. Your bellows is just substituting as the focus helicoid.

 

If you have a standard "ground glass" matt screen (ie the old screens), your meter prism will measure correctly, as it reads TTL regardless of the extension factor. I do find that the acute matte screens read a bit off due to amount of uncorrected spherical aberration in the lens (which gives the soft focus effect). The prismatic surface of the acute matte screen directs a variable amount of light towards the eye (and meter sensor) depending on focus and amount of spherical aberration set. In also find it easier to focus the imagon with a regular screen than the acute matte for the same reason.

 

However, the Hasselblad meter prisms reads out in EV, and requires you to set the lens aperture on the meter. It's doable but complicated, especially with the non-standard H values of the Imagon. The Kiev meter prisms are easier as they are balance circuits. A handheld meter is also good, and less complicated.