How a film camera superimposes the date onto photos - Page 1
Forum section: electronics / general

author: xrunner
author_rank: Super Contributor
timestamp: October 12, 2019, 01:09:39 pm
content: Amazing what people will invent when the need arises.

author: PA0PBZ
author_rank: Super Contributor
timestamp: October 12, 2019, 06:42:26 pm
content: Today I learned that you can expose a film from the back side

author: james_s
author_rank: Super Contributor
timestamp: October 12, 2019, 07:42:24 pm
content: That's neat, I always wondered how those worked, I'm not sure why I never looked into it. I had always imagined they were considerably more complex than that and built into the body of the camera.

author: tooki
author_rank: Super Contributor
timestamp: October 12, 2019, 10:41:15 pm
content: I always knew they were in the camera back, because in some cameras, you could purchase the data back as an upgrade after the fact. And knowing that, it is obvious why the numbers turn out orange, if you’ve ever looked at a piece of developed film!But the arrangement as a little projector, that is neat!

author: Red Squirrel
author_rank: Super Contributor
timestamp: October 13, 2019, 02:18:11 am
content: That's really neat. Never really gave that much thought but it makes sense. Also cool that it works from behind, did not think you could expose film on both sides. I guess it makes sense, that's why you never wanted to open the back of a camera unless the film was done and reeled back in. I remember that distinct rewinding sound when you took a picture and it was the last one on the film.

author: james_s
author_rank: Super Contributor
timestamp: October 13, 2019, 02:21:55 am
content: Never really thought about exposing the back of the film but it's not terribly surprising that it works. I mean you can shine a light through it, un-processed film is not completely opaque, so obviously light hitting the back is going to expose it, just through that rather dark filter.

author: soldar
author_rank: Super Contributor
timestamp: October 13, 2019, 07:14:23 am
content: You all realize the film HAS to be transparent. Right? Or else you could not make prints by projecting light through it.

author: PA0PBZ
author_rank: Super Contributor
timestamp: October 13, 2019, 07:48:20 am
content: Quote from: soldar on October 13, 2019, 07:14:23 amWhy? I think you can still make perfect pictures if the back is not transparent?

author: soldar
author_rank: Super Contributor
timestamp: October 13, 2019, 08:21:08 am
content: Quote from: PA0PBZ on October 13, 2019, 07:48:20 amReally? How do you think prints are made from the negative?

author: PA0PBZ
author_rank: Super Contributor
timestamp: October 13, 2019, 08:56:23 am
content: Good point, but the non-transparency could be disappearing in the development process. At least the film gets a lot more transparent in that process.

author: soldar
author_rank: Super Contributor
timestamp: October 13, 2019, 09:40:34 am
content: Film has a transparent substrate which holds the light-sensitive chemicals. That's all it needs and no one has found any reason to add an opaque layer that disappears when the film is developed. If there was a good reason it would have been done. Old film formats had a roll of black paper backing which was discarded before developing. I believe 135 (35 mm) was the first format to not have paper backing.https://en.wikipedia.org/wiki/120_filmhttps://thedarkroom.com/film-formats/120-film/https://parallaxphotographic.coop/guide-to-film-formats/I am old enough to have used all these old formats.

author: GlennSprigg
author_rank: Super Contributor
timestamp: October 13, 2019, 11:32:20 am
content: Speaking of "Exposure through the back of film"....I used to be a semi-pro photographer, with my own large dark-room at home.If you are ever 'playing' with theoldBox/Concertina cameras, (with modern film), the ones withthe littlered round 'window'at the back, to view the frame-number, you need to be aware!!TheOLDstyle B&W film used back then, was impervious to red light. So light coming through thatback 'window' did not affect the film. Just like using special Red lights in the dark-room, while makingB&W 'Prints', as it didn't affect the Paper. However, modern films, (including B&W), are susceptibleto a MUCH greater spectrum. As such, all images will be clouded, withoutBLACKING INthat Window!!P.S. If you want to know if your 'IR'Remote controlsare working?View them through ANY modern digital camera, or SmartPhone in photo/video mode...If working, you can see a bright light from the remote control, as the cameras can also see InfraRed !!

author: GlennSprigg
author_rank: Super Contributor
timestamp: October 13, 2019, 11:47:22 am
content: Come on........Don't tell me that at 'least' 10-20 people around the world, are not trying thiswith their Remote-Control & Digital Camera !!! But it's true...

author: soldar
author_rank: Super Contributor
timestamp: October 13, 2019, 12:03:05 pm
content: You could use pan or ortho film in those cameras. What shielded the film from the light was the black paper backing.https://filmphotographyproject.com/content/howto/2018/07/panchromatic-orthochromatic-film/Most "normal" film sold in the last 80 years was panchromatic and so sensitive to red. Orthodontic film was only used for specialty needs.

author: james_s
author_rank: Super Contributor
timestamp: October 13, 2019, 07:12:10 pm
content: Radiography (xray) film is not sensitive to red light. I actually need to trim a few types of that to size for my brother, he's a photography enthusiast who lately has been experimenting with some old cameras like that. Most of it has a double sided emulsion but mammography film is single sided and very fine grain.

author: soldar
author_rank: Super Contributor
timestamp: October 13, 2019, 07:40:07 pm
content: Orthochromatic materials, films and paper, are used when sensitivity to red is not necessary because those materials can be handled in the lab with red light. Normal black and white printing paper is orthochromatic and so can be handled in the lab with red light. The camera film, being panchromatic, needs to be handled in complete darkness.I used to develop my own films and I remember well loading them into the spool and the tank in complete darkness.

author: wilfred
author_rank: Super Contributor
timestamp: October 14, 2019, 12:26:36 am
content: Quote from: GlennSprigg on October 13, 2019, 11:32:20 amCameras that had a window on the back cover, red or not, had film rolled up with an opaque backing paper to stop light fogging the film. The backing paper was printed with exposure numbers to let you know where you were. This was used in cheaper cameras without inbuilt frame counters.