How to calculate exposure settings with bellows not extended

[dlschultze]

Is it the same as my standard light meter reads or do I need to calculate something to account for the space between the lens and the film in my 8x10?

[Greg Lockrey]

Yes it is the standard light meter reading. When you get around 1 1/2 times the length of the lens as when you are doing lose ups then you have to start taking bellows extension as a factor.

[johnielvis]

the f/stop setting on the lens is the thing that accounts for the distance on your camera---it is a ratio of the focal length---so you'll see that the longer the lens is, for the same size glass, the higher the f number---or the smaller the quantity of light.

[Leigh]

The light meter reading is the correct shutter setting when the camera is focused at infinity.

As the subject moves closer, and the lens moves away from the film, you need to compensate for that additional extension.

This doesn't become significant until you get pretty close.

Some examples, based on the distance (d) the lens moves from its infinity focus position:
d = 1/4 focal length: increase exposure by 1/2 stop
d = 1/2 focal length: increase exposure by 1 full stop
d = 1 focal length: increase exposure by 2 full stops

- Leigh

[johnielvis]

summarize--the correction IS based on bellows draw....

you take your bellows draw and DIVIDE by your focal length...multiply this number by the number indicated on your lens aperture--..

so at infinity...your bellows draw IS the focal length

so for ininity focus, your bellows is AT the focal length---so the ratio is exactly 1.

so your correction factor is 1...multiply this by your aperture setting to the the EFFECTIVE aperture for that lens/focus setup. NO correction for infinity focus is needed.

for a bellows draw = squrt(2) times the focal length--sqrt(2) = 1.414....

you would get the ratio to be sqrt(2) = 1.414

sqrt(2) times your aperture scale moves it exactly ONE stop...for example at f11, the correction would now be 11*1.414 = 16

at f45 the correction makes it now 45*1.414 = 64.....

like that see....the correction factor at infinity is ONE...no correction

[Bob Salomon]

I do it differently.
At infinity there is no correction,
At 1/4 life size (1 " object is 1/4" on the ground glass) open up 1/2 stop.
At 1/2 life size (1" object is 1/2" on the ground glass) open up 1 stop.
At 1:1 life size (1" object is 1" on the ground glass) open up 2 stops.

Somtimes I just meter directly through the gg after finding out how much light my gg and fresnel absorb and make a correction for that. To do that meter a grey card and then meter the grey card through the gg and Fresnel. The difference is the absorbtion of the gg and Fresnel if you are at infinity.
You must use a Fresnel and a gg for this system to work propoerly at all points on the gg.

[Vaughn]

A great while ago I was playing with a process camera. It had this neat scale thingy that you put at the plane of focus, then compared the image on the GG with another scale: which in turn gave you the factors for adjusting your exposure.

Otherwise I tend to just double the exposure...

[Leigh]

A great while ago I was playing with a process camera. It had this neat scale thingy that you put at the plane of focus, then compared the image on the GG with another scale: which in turn gave you the factors for adjusting your exposure.

Calumet sells that product, although it may not be the same one that you used.

- Leigh

[Bob Salomon]

A great while ago I was playing with a process camera. It had this neat scale thingy that you put at the plane of focus, then compared the image on the GG with another scale: which in turn gave you the factors for adjusting your exposure.

Otherwise I tend to just double the exposure...

We had built that scale into the overlay glass for the Linhof Super Screen but both pieces are now long discontinued but it is easy to DIY. Stick a ruler in the scene and measure any length on the ruler on the gg. If 4" on the ruler is 2" long on the gg you are at 1:2 and need to add one stop. 4" on both the ruler and on the gg you are at 1:1 open 2 stops, etc.

[Jimi]

Another variation on this theme is the QuickDisc:
http://www.salzgeber.at/disc/