Hmmmm...
I slipped a thin metal mirror into the film gate so light coming thru the lens from the front would illuminate the lens from behind.
No apparent fog or dusty bits front or back.
Next, I cut a little piece of 4x5 film and slipped it into the film gate and took an outdoor shot in some evening light.
Used the yellow filter, ISO 100 film, 1/30 second at f8.
Hand developed it by inspection.
Darn, the film slipped out of the gate.
Try again, but cut the film a bit wider so it wouldn't slide around.
The film curled a bit as I closed the camera, but the light is waning fast, gotta hurry.
Developed it and got a very nice, contrasty negative.
The curled film messed up the focus a bit, but the density and contrast is good.
That was kinda fun, a new experience with fingernail size negatives.
A hekkuva lot different than working with 8x20 negatives.
Reinhold
www.classicBWphoto.com