[LargeFormat] Lens Shades

[Rich Lahrson]

Hi Clive!

      And thanks for your post.  I hadn't thought about the extra bellows
possible being
more of a problem in the wind.

      I just received the BTZS 5x7 Focus Hood, or cloth really, so I've had a
chance
to look through the camera.  The BTZS cloth is well designed, fits snuggly
around the
back of the camera and the Velcro strip is effective in cutting out nearly all
the extraneous
light. I'll recommend this focus cloth.

Cheers,

Rich Lahrson
Berkeley, California
tripspud@transbay.net

Clive Warren wrote:

> 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!)
>
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