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Thread: why toy cameras vignette

  1. #1

    why toy cameras vignette

    For those with an interest in vignetting and plastic cameras...

    there's a widespread myth that it's the plastic lens per se that causes the vignetting in "toy" cameras, I want to debunk this and tell you the truth.

    I strongly believe that the effect is caused by the placement of multiple internal apertures which progressively obstruct the light path as you get closer to the edge of the frame

    Here's a series of pictures which should illustrate how this occurs:

    pic 1 is the lens mounting off a diana camera that shows there's a small hole close behind the lens

    pic 2 shows the swing arm that you move to change the f-stop... it's either fully out of the way or else placing one of two small apertures into the light path. This sits between lens mount and shutter.

    pics 3 and 4 show the aperture formed by the shutter... in the original diana it's round and in the diana deluxe it's square. I'm not showing a pic of it but the holga is oblong unless you modify it.

    pic 5 shows that when you look thru the diana from directly behind, the aperture is round

    pic 6 shows how when you look from behind but off centre you see the aperture cut off by camera parts. this is what the film sees and you can see how easily you lose over an f-stop simply by the application of multiple internal obstructions to the light path

    [if you look at a diana deluxe it doesn't vignette as much because the square shutter opening doesn't cut off so much light]

    the point of this diatribe is that you should be able to reconstruct the vignetting effect with pretty much any[?] lens by placing maskes behind any lens.

    you can predict that the closer a mask is to the film the sharper the cut off will be and that a smoother cut off will be had from masks close together and close to the lens Attached files

  2. #2

    why toy cameras vignette

    Excellent food for thought! I read somewhere that sluggish aperture blades on an auto-aperture SLR lens can produce soft corners too--probably related.

  3. #3

    why toy cameras vignette

    You have it exactly, Andrew. I recently found that a 105 mm Agnar will just about cover 4x5 -- this is a lens originally sold on an inexepensive 6x9 cm folder, and when focused inside about 25 feet and stopped down to f/16 or smaller, it will cover film more than twice the size of its original format. Open it up a little, though, and you start to get falloff. Looking through the back of my Speed Graphic, it's easy to see why: when you open up the aperture a bit, the edge of the rear lens element starts to vignette the aperture in the corners, just as you can see in your final image above. Close down the aperture some, and you start to see the whole opening, so only the out-of-round shape due to foreshortening affects light falloff -- a much smaller effect.

    Got a Holga you want to "correct" to get rid of the light falloff? Just open up the inside a bit.

    BTW, my Baldixette has a baffle inside the rear, but it doesn't vignette at all -- the aperture in the baffle is square, the same shape as the frame mask, and doesn't shadow the film from any part of the original aperture stop.

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