Exposure!

[Ash]

Hey everyone,

I rarely post, as my half-plate has sat quite upset in his case for months now! I've made a promise to myself to make good use of it, using masks to allow 4x5 film in the camera... oh and manufacture/source a cheap 4x5 enlarger too!


Anyways, the page here is boggling my mind!!

Basically I want to successfully take some photo's, but the whole large format thing is still quite daunting! Currently I've been using my Leica/Contax rangefinders, and Rollei TLR's, so I can successfully meter with an old Leningrad handheld meter, but I'm not sure whether the Leningrad will suffice for large format.


So far I'm only talking an easy intro, a bit of a play around to get comfortable with the format. What are the tips you'd give to get a rough exposure time?

Say, 5inch lens, 14inch of extension (at a guess) and f/16? (literally numbers picked out of the sky there). Hmm and film at 100iso (I'm thinking of getting some cheap Era film), the meter reading is 2' at f/16.

focal length
f/stop
film speed
meter reading
bellows extension


So what would I do next?



My first neg I made with the camera was on kodalith ortho a couple months ago, with a 4.5inch wray enlarging lens, close focusing on my kiev camera, I guessed at around 3 or so seconds late afternoon at I think 5.6, and developed on a whim for a couple mins in highly diluted rodinal. I got a bit of a thin neg out of it, but a neg all the same. I'm keen to really improve on a technique. Bear in mind I'm using the lens-cap-as-a-shutter method in absence of a real shutter.


Any help on a blatant, outright simple step by step would be really great!


Thanks!

[Colin Robertson]

First of all- with a LF camera you focus by extending the bellows.To focus on infinity you will extend by the focal length- for 5 inch lens (about 120mm) you'll need 5 inches (or 120mm) from lens to ground glass.
As you go closer you need more extension. To get life size ( 1:1 , macro) you'll need twice the focal length. So, with a five inch lens, you'll get life size at 10 inches of bellows. Now- as the lens moves away from the GG it begins to project a bigger and bigger image, but using only the same amount of light. So the light gets spread out and 'diluted'- dimmer.
With a 5 inch lens at 10 inches of extension the image covers 4 times the area.
With a 5 inch lens at 15 inches of extension the image covers 9 times the area.
(Take the TOTAL extension, divided by focal length, and square it.)
How much extra exposure do you give?
1 stop extra = x2 exposure
2 stop extra = x4 exposure
3 stop extra = x8 exposure
There is aother way. Search here for the QuickDisc. You download and print two parts. One is a disc which you include in the scene. The second part is a ruler with which you measure the size of the disc on the GG- the ruler then tells you how much extra exposure to give. Good luck.

[Colin Robertson]

PS (just to make life even better). Remember reciprocity failure. If you use 100 asa film, with small apertures like f16 or f22, you'll find you get long exposures. Probably into several seconds. Many films need extra exposure. Although you can use your Leningrad meter no problem, you may need to alow extra exposure. I use Ilford FP4, and on their website Ilford give a graph to help you. So, for example, if my meter says 15 seconds the graph warns me to actually give 50 seconds. Sorry, can't help with Era film.

[Rakesh Malik]

During the spring Smokies workshop, Danny Burk showed me how to use the QuickDisc to compute exposure for closeups... it works like a charm. And it takes about 30 seconds to figure it out.