[LargeFormat] Lens Shades

[Clive Warren]

At 09:36 13/10/2002 -0700, you wrote:
snip

>My question is in regard to the necessity for a lens shade with  a wide 
>angle lens,
>do I need it?  Perhaps, I can fudge the matter with the dark slide or 
>using black craft
>paper and tape when needed.
>
>How do other large format uses deal with cutting off extraneous light?  I
>see pictures of large format workers using lens shades and not using lens 
>shades.
>
>Also, I recall reading in AA's Basic Photo series, that a larger camera
>with bigger bellows has less flare due to it's size.  That is, an 8x10 
>camera would
>have less flare than a 4x5.
>
>Thanks!
>
>Rich Lahrson

Well Rich, as you may have expected, you  are probably going to receive a 
raft of different answers to your questions.

A lens shade is always useful if there is potentially flare making light 
falling on the front lens element - I use a black hat made in the US of A 
and it works also as a camera cover when you are waiting for that decisive 
moment with the film holder in the camera.

The usual flare problem alluded to by people using lens bellows (shades) is 
derived from the circle of illumination of the lens being much larger than 
the format it is being used to cover.. The idea is to restrict the size of 
the circle of illumination by extending a lens shade in front of the front 
lens element to ensure that no more light than is absolutely necessary 
makes it past the front element.

There are a couple of reasons for this:

1. It can be argued that the light baffling in multi-element lenses is not 
100% effective and there may be bounced light from the edges of the lens 
elements or their barrels that introduces non-image forming light (flare) 
that reaches the film, reducing contrast amongst other things.

2. It can be argued that the inside surfaces of the camera along the path 
between lens and film reflect some light. If the circle of illumination is 
larger than the film format then non-image forming light may be reflected 
back onto the film plane.

Now, your 135mm WF Ektar covers 5x7 but not a lot more. So the only thing 
to worry about here is the internal lens baffling - which is also pretty 
efficient. So, the bottom-line is that the above two points will not be an 
issue for your 135mm WF on 5x7.

I use a 305mm G-Claron on 4x5 which has a huge image circle. I'm sure that 
in a studio situation that it would be possible to demonstrate some effects 
of flare from point 2. above. However it would probably not be too 
noticeable on general landscape work using a camera that is flat black 
internally from tip to stern :-)  Another set of bellows on the front of 
the camera would be something else to act as a sail in the breeze - may 
cause more problems than any potential flare on the particular camera it 
generally finds itself attached to......

Cheers,
            Clive  (on a laptop and mobile phone having just escaped 
hospital - the medical kind not the psychiatric!)