Film area

[KristerH]

Hi.

I did a search but can not find an answer. When estimating the amount of developer the data sheet talks about a amont of films. How do you calculate this for 8x10 negatives?
I have calculated that a 8x10 is 1,4 a 120 film. Could that make sence?

[smithdoor]

The old Kodak Master Darkroom Guide has this data

Dave

[Jac@stafford.net]

If 8x10 is 1 film, then
4 4x5 is 1 film,
1 120 roll is 1 film,
1 36 exposure 35mm is 1 film

More here: http://www.largeformatphotography.in...ing-Sheet-Film

[Jim C.]

You need to know the sq inches of film a given amount a developer will work.
Kodak has this info on the sq inches a given film size is, and the development capacities of their chems
I started a thread on this subject a few years ago -
Mixed film size developing capacities
It's for C41 color but it should apply to BW also.

[Harold_4074]

Regarding the "amount of developer", there are at least two concerns: chemical and "mechanical".

Chemically, if there is too little developer present (concentration multiplied by volume) it will be exhausted during development. If the total volume is too small, there may still be enough developer present to create the image, but the buildup of reaction products (bromide, iodide, chloride and oxidized developer molecules) will cause the result to be different from what you would get in a larger volume.

From a mechanical standpoint, there needs to be enough solution for the intended agitation, which may range from continuous through intermittent to almost negligible ("stand" development). Many developers would need impractically short development times for some films, so they are diluted until the working time is reasonable; HC110 is one of the better examples of this. (This is sort of halfway between a chemical issue and an mechanical one, so maybe it is the "temporal" question.) Also, with developers which are very susceptible to oxidation by air, the amount of surface exposed can be an issue; tray development may dictate more solution than would be required for the same amount of film in a deep tank, just because of the difference in surface area.

The most common rule of thumb is the one given by jac@stafford.net; this used to show up in developer instructions in connection with the amount of replenisher to add after each use, and is in all cases equal (or close enough) to 80 square inches.

Beyond this, all of those other factors have to be accounted for, so once you have "enough" developer for one film, format, container and agitation, you still have to make allowances if you change one of the factors

[Leigh]

A standard "sheet" of film is an 8x10 sheet or anything that can be proofed on a single 8x10 sheet of paper.

BTW, actual image area has nothing to do with this calculation. It's the gross surface area that's important.

- Leigh

[Heroique]

Let's have some fun here.

For Tri-X 400 in a tray of D-76 1:1, Kodak's table says useful capacity for 8x10 sheets per G/L in a tray = 16/4.

Kodak's sentence requires some interpretation before it makes sense, but it can be done.

Practice makes perfect:

You're in sixth grade. The teacher says "Pop Quiz!" and hands-out a test that gives Kodak's information above, and asks the following question:

If you start with a fresh tray of 64 oz. of D-76 1:1, and you develop seven 4x5 sheets and nine 5x7 sheets of Tri-X 400, how many 8x10 sheets can you next develop in the same tray of solution before you finally exhaust the developer's useful capacity?

If you're not allowed to use your i-pad to login to the LF forum and ask for an answer, what are you going to do?

[Leigh]

seven 4x5 = two 8x10 (conservative)
nine 5x7 = five 8x10 (also conservative)

64 fl oz is 1/2 gallon, so capacity = eight 8x10 sheets.

Conservatively you could develop one 8x10 sheet, or two if you want to push the system to its limits.

- Leigh

[ROL]

Pop's quiz may be the only (semi) reliable way of ciphering fixer longevity as well, film or paper, the OP may take note (…if they can make cents of it ).

[KristerH]

Thanks.

If I understand you right it is not the exposed area that is the thing, its the total film area. Right?

So if my developer and film states that I need 30 ml / film its safe to assume that this is equal to
30 ml / 8x10.

I am still a rocky in the film world. On almost all the negatives I have developed so far there is this thing



What do you think ? Mechanical, drying process?