How the heck do bellows work?

Treymac · Oct 20, 2010

Hey guys.
Since I`ve started using the 4x5 camera, I`ve wondered how bellows work. Now that I`ve seen bag bellows, I regard it as magic.

How does the light not get all scrambled up hitting the the corrugated foldings? With bag bellows this gets even more confusing, how does light not just start going all over the inside of the bag, how does it get directed onto the film? Insane.

mjs · Oct 20, 2010

The color of the inside of the bellows is a clue.

Mike

domaz · Oct 20, 2010

If your bellows were made of shiny fabric from the 70s I think the internal reflections would be a problem. It's nice that nature provided us with a color that does not reflect light and instead absorbs all light- called black.

Treymac · Oct 20, 2010

So basically the light is just a stream that goes though the bellows that ends at the film. Fairly obvious, kind of thought about that, but also thought that the light when inside could potentially hit the edges of the bellows and maybe then get some vignetting.

holmburgers · Oct 20, 2010

Light travels in a straight line from the lens and from that point anything is possible, including hitting the bellows. But they wouldn't make a bellows that blocked the light from hitting the film now, would they?

Simple wonders, eh

Vaughn · Oct 20, 2010

It is magic! Magic is the only way to keep the darkness from leaking out of one's camera.

BetterSense · Oct 20, 2010

They work pretty good.

Ottrdaemmerung · Oct 20, 2010

For light to make an image onto the back of the camera once it passes through the lens, it needs some distance in order to achieve focus. The length of the bellows provides this distance. Of course it has to be protected from extraneous light entering, therefore it is black and consists of an enclosure. And because the distance needs to be variable without the enclosure getting in the way, it's a bellows design. Simple!

lxdude · Oct 20, 2010

The corrugations also help by scattering away from the film the part of the light they don't absorb. The light bounces around in there, getting absorbed by the bellows with a little bit scattered each time. The further the light travels by being scattered multiple times, the weaker it gets. A little bit of the scattered light makes it to the film, but it isn't enough to cause problems. This occurs inside any camera, which is why cameras are dark colored inside, and often have some sort of textured material inside.

Photo Engineer · Oct 20, 2010

The lens focuses a direct image on the film plane. The black bellows absorbs any possible reflection. So, what you have is a beam of light (the image) similar to the beam from a flashlight, with most all of it directed at the film with some little bits being scattered around and being absorbed.

Don't forget the lens!

PE

totalamateur · Oct 20, 2010

Yep, figured this all out when I made a pinhole out of a tin can with a shiny inside - got the weirdest "lens flare" on the negative you could imagine. covered the inside with black gaffer's tape and problem was solved.

My Calumet 4x5's bellows are gray on the inside, but I guess the corrugated nature of the bellows helps scatter and absorb internal reflections. I can't help but wonder if I could lower the base fog of my Negs by spraypainting the insides black or something. Probably jsut ruin my bellows.

lxdude · Oct 20, 2010

totalamateur-
What are the bellows made of? There are dyes for vinyl, leather, etc.
I'd be wary of paint as it would probably flake off.

bobwysiwyg · Oct 20, 2010

Also, depending upon the type of paint used, the solvent/vehicle might destroy the fabric or material.

hpulley · Oct 20, 2010

I say let sleeping phodogs lie...

totalamateur · Oct 21, 2010

I was mistaken, looked inside again last night and they're black. THey're gray on the outside - sorry, I'm stuid.

Steve Smith · Oct 21, 2010

Vaughn said:
It is magic! Magic is the only way to keep the darkness from leaking out of one's camera.

I like that. It's a much better theory than keeping the light out.

Steve.

lxdude · Oct 21, 2010

totalamateur said:
sorry, I'm stuid.

No, you're definitely not stuid.

Joe VanCleave · Oct 22, 2010

I've seen advertisements of LF cameras, with the bellows fully extended and twisted up like a pretzel (not a Petzvel), and sometimes I have to wonder if the "droop" in the top of the bellows is enough to interfere with the projected image. I suppose this would only be a problem with long-focal length lenses.

Q.G. · Oct 22, 2010

lxdude said:
No, you're definitely not stuid.

At the risk of sounding stuid: how would you know?

Q.G. · Oct 22, 2010

Joe VanCleave said:
I've seen advertisements of LF cameras, with the bellows fully extended and twisted up like a pretzel (not a Petzvel), and sometimes I have to wonder if the "droop" in the top of the bellows is enough to interfere with the projected image. I suppose this would only be a problem with long-focal length lenses.

It is. Also in close-up work.
Something remedied by putting an extra standard plus bellows 'halfway'.

lxdude · Oct 22, 2010

Q.G. said:
At the risk of sounding stuid: how would you know?

Because I am!

How the heck do bellows work?

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