View Full Version : Exposure Compensation - horseman vhr

Hugh Sakols
21-Jun-2005, 08:19
I finally have a horseman vhr - my first field camera. When I extend the bellows how do I know what exposure compensations I should use.? When using a mamiya c220 there is a scale to follow. Also if I tilt the front standard do I have to make any aditional compensations?

Ted Harris
21-Jun-2005, 08:37
In my experience with the Horseman FA there is no exposure compensation required, even at the longest bellows extension. Same likely applies with the smaller format VH series.

Emmanuel BIGLER
21-Jun-2005, 08:40
quick answers :

1/ the quick disc
www.salzgeber.at/disc/ (http://www.salzgeber.at/disc/)
www.salzgeber.at/disc/down.html (http://www.salzgeber.at/disc/down.html)

2/ by simple computation

approx formulae valid for most view camera lenses :
e = extension w/respect to the infinity-focus position, f focal length
bellows factor = ((total bellows length)/(focal length))^2 = (1+e/f)^2

General expression for bellows factor, non-symmetrical lenses, with non-unit pupillar magnification ratio P_M :
bellows factor = (P_M+e/f)^2/(P_M)^2aperture stops = log_2(bellows factor) = 3.32*log_10(bellows factor)

Tilt angles with a field camera for landscape use are usually small, typically less than 10 degrees. there should not be any additional compensation to be added to the bellows extension factor.

Leonard Evens
21-Jun-2005, 09:01
You wouldn't normally be in situations where you have to do any exposure compensation. That is only necessary in the close-up range which is usually defined to be less than 10 times the focal length. And even for 10 X, the correction is so small, it can be ignored. The rule is that you take the ratio of bellows extension (film to lens distance) to the focal length. You have to multiply the f-number by that ratio to gwet the effective f-number. Alternately, you multiply the exposure time by the square of that ratio.

Here are some examples. At 10 X the focal length, the desired ratio works out to 10/9 ~ 1.1. which amounts to about a quarter of a stop difference. At 5 X the focal length, the desired ratio is 5/4 = 1.25 which amounts to about 2/3 of a stop.

For the lenses you have, the bellows extenstion should be measured from the film plane to the lensboard. You don't have to be specially precise in the measurements.

I don't know about the VHR but the maximum extension of my Horseman 980 is a bit over 250 mm, but to make use of it you have to put down the infinity stops and use the gg to focus.

Tilting the lens has a complicated effect. Some of the film plane is closer to the lens and some is further away, so some film gets less exposure, and some more . This is not unsimilar to the untilted case except that in that case the light intensity drops off symmetrically from the center. Exactly how the tilt affects exposure would also depend on the position of the image frame in the tilted image ellipse. In most cases, the amount of the tilt isn't large enough to make a signficant difference. Don't be misled by pictures of view cameras with exaggerated movements. In practice one seldom uses large tilts. For 6 x 9, because the greater inherent depth of field, tilts are quite small, and I doubt if you will ever encounter a situation where any exposure compensation is called for. But if you do, you will have to deal with it by experimentation.

I didn't do much close-up photography with my Horseman and in the few cases I did, I didn't use any tilts. But I don't remember every having a problem with exposure compensation.

Hugh Sakols
21-Jun-2005, 10:12
Thanks for all the help. I'm glad for the most part that I don't need to think about compensation unless I'm doing some exteme macro. Now I just need to get out and develope a feel for the system.