Lens hood required when using large coverage lens on small format?greenspun.com : LUSENET : Large format photography : One Thread
I have heard that when using large coverage lenses, such as 400mm on a samller formats, say 4x5 or even 6x9, that a lens hood or compendium shade is necessary to reduce the amount of light that is entering the camera, so that it is limited to an image circle slightly larger than the film being used. Supposedly all this extra light that bounces around indside the camera causes loss of contrast and sometimes creates some strange flare. The theory is, the inside of a bellows, does not absorb 100% of the extra light, so therefore the non absorbed rays bounc around, allowing some to get on the film or interfere with the light rays being absorbed by the film.
Before I try to run some test shots of this, I was wondering if anyone has any experience with this. Of course if you are using lenses that are suited for a given format, than I guess this is not a problem. However, all my lenses will cover 8x10 with plenty of movements, but I shoot mostly 4x5 and 6x9. Any input would be appreciated.
-- Bill Glickman (Bglick@pclv.com), July 31, 1999
If the interior of the view camera in question is finished in matte black, as I would hope is the case, the only concern I would have would be avoiding lens flares caused by direct sun or specular highlights that strike the front element itself. This kind of flare comes from within the optics and can affect the contrast of what comes out the back end. The actual projection outside the minimum circle of coverage needed for the target in question should't contribute anything that would be easy to measure. Where this kind of problem is common, is when lenses from larger format cameras are adapted to be used on smaller hand cameras whose mirror box might contain reflective surfaces that lie just outside the image circle of lenses designed for that camera. This used to a problem in the motion picture business when folks were adapting 35mm still lenses for use on 16mm cameras.
I have found that by shading the front of any lens I use with a piece of darkly colored card stock, I can observe just the right amount of shading necessary to keep oblique sun rays off the glass and avoid flares of any kind. I'm sure others prefer to use one of the many universal shades available to accomplish the same thing. I just hate to fiddle with more attachments when I'm busy trying to make an exposure.
Here's an idea if your still concerned. Maybe you could set the camera up with the back removed and devise a cardboard baffle around the camera to create kind of a camera obscura set up. You could try creating some wild ass flares from the front and measure, with a light meter, the reflections off the bellows! I'm betting you won't measure much. The film you're using is probably far lighter in color than anything else in your camera. What do reflections off the film contribute to loss of contrast?
-- Robert A. Zeichner (firstname.lastname@example.org), July 31, 1999.