As an example of Bob's description, here's what a Sinar lens shade (system) looks like in various configurations. Notice the 3rd picture, where almost all extraneous light can be removed, matching the actual ratio of the film or sensor. That's the real deal.
Last edited by Ken Lee; 25-Nov-2011 at 08:10.
Ken, both you and Bob are wrong. Even if you configure the shade's sides in such a way that they match the film format ratio and limit the lens view on the film area only it still doesn't mean that ALL image non forming light has been removed. It has only been reduced to the minimum given at that shade's length. The geometry of a lens shade is more complicated than you and Bob understand.Originally Posted by Ken Lee
As an example of Bob's description, here's what a Sinar lens shade (system) looks like in various configurations. Notice the 3rd picture, where almost all extraneous light can be removed, matching the actual ratio of the film or sensor. That's the real deal.
Last edited by Ken Lee; 25-Nov-2011 at 08:10.
A full pro compendium has the same bellows length as is used by the camera's for the exposure in qusestion and the opening in the front of the bellows is the same size as the image area. These are too large and bulky for field use so better field compendiums compensate for this by closing the masks down until they just manage to intrude into the image area. Then there is no stray light. They do it this way because a field compendium has less bellows length then the camera has.
Thank you for the correction.
I have revised my post to read "almost all extraneous light has been removed".
By the way, I have the lens shade shown in the first of the 3 photos. It's small and light enough to take into the field, and because it's a real bellows, can be used for additional extension with longer lenses.
I have and use the Sinar barn doors shade, but it only fits Sinar cameras.
Any reason why so many of these matte boxes lack bottom shading?
My old Cameflex matte-box is rigid and has masks for five lenses and a geared slot for glass wedge filters. I used to think it was a pretty sound idea - in those days there was a lot of shooting with overhead back-light and a lot of white backgrounds that were 2 stops over.
Ever since the 'natural light' revolution - one large source off to the side somewhere - the matte-box has been forgotten in favour of a 'Cremer' or tin flag attached to the tripod. I use the bottom of a an 8x10 box and a double clip most of the time.
The Matte-box got it's name because it was originally devised for special effects in the cinema - such as blocking out part of the picture for later insertion of scenery and such.
I have modified my Linhof compendium to accept 4x4 filters and it works reasonably well even with the ND grads; the Cokin shade has to be attached to the lens via adapters: readily usable for different cameras but a nuisance when you change lenses and you need the ring adapters for different lenses.
I have a beautiful Chrosziel Matte Box for a Super 16 camera: one filter stage rotates, additional flag clipped on top, BUT -it is bulky and too heavy for any of the front standards I have.
So, I'm still looking for the 'near perfect' shade/filer holder...
I have an old Lindahl bellows shade that I've fitted to my B&J, it has a geared thingy on the bottom that lets me push the shade 1" away from the camera so I can access the shutter, leaving me about 5" of shade if my memory serves. I say memory, because I've only ever taken it out into the field once. Since then, I just hold up my dark cloth as an improvised shade when I need one. If I did a lot of studio work, I would leave the Lindahl permanently attached but as-is, it's too much trouble to bring and set up each time.
Bob, your explanations show that you still don’t understand correctly the underlying geometry involved in a lens shade construction. It is erroneous to think that for the simple fact of the shade’s opening size being equal to the film format and at a distance of the lens focal length all extraneous light is eliminated.
I have indicated this error of yours in my previous post. Since Mr. Ken Lee have deleted the post I mention I won’t repeat the geometrical reasons proving you wrong. Instead I challenge you to investigate your error in a simple practical way.
Put a lens shade (the one you mistakenly believe being able to eliminate all the stray light) on a lens. Have an assistant place a torch 9 ft in front of the lens (the longer the distance the more obvious your mistake is), in the lens axis. Now tell him to slowly move the torch (while shining at the lens) away from the axis, perpendicularly to it. When you won’t be able to see the torch on the camera’s gg tell him to stop moving. Then ask him, if he can still shine with the torch on the lens surface. He will tell you that yes, he still can. That’s the light that you don’t see on the gg but yet it illuminates the lens - the stray light that was not eliminated by the lens shade.
Alternatively, you can use a laser, easier to see on the lens surface than a torch light. Another way to perform the practical proof of your error is to have the assistant be looking on the lens surface and move slowly in the way the torch did before. When you won’t see his eyes on your gg tell him to stop moving. He will still be able to se the lens surface - despite the lens shade on it! Hopefully this simple experiment will convince you that the full elimination of a stray light with a lens shade doesn’t work as you thought it does.
Yes, it is an overkill. Not because of the shading capacity but because of its ridiculous weight inadmissible on LF cameras for this kind of accessories.
Why not to make yourself such a shading "matte box" from black flocking paper and put it on your lens?
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