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Light sensitivity of glass plates?
Aug 13, 2018 14:16:27   #
clickety
 
Occasionally a more senior friend and I discuss photography. I always find his stories of his SpeedGrapfics days interesting. Today he showed me a large (16x20) digital print made from scanning one of his Grandfather's 5x7 glass negatives. The detail was impressive. His memory of his grandfather (a pro photographer with a studio in the early 1900s) adjusting exposure time by removing and replacing the lens cap or even his hat was interesting. This led to a discussion of the necessarily long exposure times and thus the question:

What would be the ASA /ISO equivalent of the light sensitivity of a glass plate?

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Aug 13, 2018 14:22:08   #
Longshadow Loc: Audubon, PA, United States
 
ASA 2?

https://www.freestylephoto.biz/180450-J.-Lane-Pre-Coated-BandW-Glass-Dry-Plates-ISO-2-4x5-10-Pack

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Aug 13, 2018 14:43:26   #
ricardo7 Loc: Washington, DC - Santiago, Chile
 
That's pretty slow film. Around 7 stops slower than Kodak Plus X.
Hence the long exposures of photos made in the late 1800s,

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Aug 13, 2018 22:41:45   #
clickety
 



Thank you for the quick reply and link to the plate information. Now we can continue our discussion at next week's coffee. I'm amazed they can still be purchased.

UHH is an amazing storehouse of knowledge and experience.

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Aug 14, 2018 07:55:22   #
chem
 
There are many variations of the emulsion used on glass plates, each of which had a different sensitivity. Also, since the photographer, or his/her assistant, poured the emulsion onto the glass to dry, film thickness played an important role. As did storage conditions, grain size, etc.

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Aug 14, 2018 12:39:44   #
Ron Dial Loc: Cuenca, Ecuador
 
I concur with others that the speed was very slow. That is one of the reasons that studio portraits used metal head holders, to keep people from moving even an inch during an exposure in a dimly lit room. I would think the average speed was 1 or 2. Sure not the sunny 16 rule.

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Aug 14, 2018 17:04:29   #
ecurb1105
 
clickety wrote:
Occasionally a more senior friend and I discuss photography. I always find his stories of his SpeedGrapfics days interesting. Today he showed me a large (16x20) digital print made from scanning one of his Grandfather's 5x7 glass negatives. The detail was impressive. His memory of his grandfather (a pro photographer with a studio in the early 1900s) adjusting exposure time by removing and replacing the lens cap or even his hat was interesting. This led to a discussion of the necessarily long exposure times and thus the question:

What would be the ASA /ISO equivalent of the light sensitivity of a glass plate?
Occasionally a more senior friend and I discuss ph... (show quote)


Well the attached photo was shot on 4x5 film, but the exposures were controlled by the film holders dark slide. I pulled the darkslide after closing and setting the f-stop (f32), I held the slide in front of the lens, waited for the camera to settle and lifted the dark slide to start the exposure. Halfway through the thirty second exposure the clump of people stopped in front of me so I covered the lens and waited. They weren't moving, so I uncovered the lens to complete the exposure. So i got ghost travelers.



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Aug 14, 2018 22:37:52   #
James R. Kyle Loc: Saint Louis, Missouri (A Suburb of Ferguson)
 
clickety wrote:
Thank you for the quick reply and link to the plate information. Now we can continue our discussion at next week's coffee. I'm amazed they can still be purchased.

UHH is an amazing storehouse of knowledge and experience.


============

ISO-2 (Two) is about right.

I am making Photo-Paper Negative. By making use of over 3000 - 8X10 sheets of the stuff from my film printing days. I did not just want to toss it in the trash, so I got out the two old cameras that I had (Ansco 8X10 and a Crown Graphic 4X5) and began to make orthochromatic photographs from the old stock.

I am having a really fun time in doing this. AND as I am doing something that was used with the "Sliding-Box" design - I made the decision to build two cameras myself, and use lenses from about 1870 to 1900. No Shutter (except for the one built in 1900) just a lens cap. The Aperture adjustments on these lenses were made by "Waterhouse" Stops (Sheets of brass that have appropriate holes in the center).

Since 2013 I have been using Photo-Paper to make Negatives that I scan and bring into Photoshop to Invert to Positives. I have done Contact printing as well. Also, I have acquired MORE photo-paper from other photographers that have seen my work and donated their stock to keep me going.

Experimenting with different ISO possibilities I have found that not every photo-paper is the same the ISO can range from Three (3) to that of 100 - (So far that 100 ONLY is done with Kodak "Industrex" paper. This was (is) used for making Positives from X-Ray negatives in "Radiography" (The X-Raying of Welding joints.) I was flat amazed that I would even to be using a photo-paper that would allow me to expose an image at f-11 at a shutter speed of 1/50th of a second.

The Glass Plates described here interest me a great deal. I am going to look into this - Thank You for posting.

=0=





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Aug 14, 2018 22:57:35   #
Darkroom317 Loc: Mishawaka, IN
 
Depends on the emulsion and the process. Wetplate colloidion is usually around ISO 1. Silver gelatin emulsion speeds vary greatly. With the commercial emulsion I use for my plates the ISO is about ISO 1. Emulsions can initially gain speed and contrast with moderate age. ISO 2-3 is generally standard paper speed. I know of some of that have created home made emulsions in the ISO 25-50 range.

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Aug 15, 2018 05:28:35   #
A.J.R. Loc: Devon, UK
 
I did a Photography Course at Guildford School of Art (UK) 1958 to 61. We used glass quarter plates (3 1/4in x 4 1/4in in Gandolfi Cameras). As far as I can remember they were about 100 ASA (now ISO), but were also used either side of this sensitivity by adjusting the development time depending on the contrast of the subject matter, something difficult to do with roll film or 35mm.

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