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# Thread: Dilution question

1. ## Dilution question

So I am a little confused. So I am going to try developing my first roll of b&w film with Rodinal. The dilution recommended is 1:25

I have a Patterson Universal which I understand holds 500ml. How do I calculate 1:25 for 500ml?

Is it like this?
500/25 = 20
500 -20 = 480

So that would mean 20ml of Rodinal go into 480ml of water?

Or am I totally missing something here?

2. There's a million threads on this, but in short...

devel = 500 * 1/25 = 20
water = 500 - (500 * 1/25) = 480

And at these dilution levels, the disparity between 25 or 26 total parts is not going to make or break things.

I recommend you use 1:50 for your first time, though.

3. OK cool, thanks Clayne. I will take your suggestion and do a 1:50.

Sorry I know its been covered but I kept seeing conflicting answers...but your explanation about the disparity eases my mind.

I developed film a very long time ago but that's when I was in school so all is forgotten

4. Whenever you see 1:50, within photo-circles and depending on who you're talking to, it could mean anything from 1 part dev, 49 parts water or 1 part dev, 50 parts water. That's why you'll commonly see 1+49, because it's clear it's 1 part dev, 49 parts water. In reality though we're talking .2ml variation - not enough to matter.

5. Originally Posted by shuttershane
So I am a little confused. So I am going to try developing my first roll of b&w film with Rodinal. The dilution recommended is 1:25

I have a Patterson Universal which I understand holds 500ml. How do I calculate 1:25 for 500ml?

Is it like this?
500/25 = 20
500 -20 = 480

So that would mean 20ml of Rodinal go into 480ml of water?

Or am I totally missing something here?
Simple anwser, divide the total required I:E 500 by the dilution +1, in your case 25, so divide 500 by 26,round it up very slightly, and you have your dilution, 20 to 480, this works for any dilution, and came from Patterson many years ago. one suggestion, when using Patterson tanks it is better to put a bit more developer in the tank, I would suggest 600, which at 1/25 works out at 24 developer to 576 water,as patterson reels can slip very slightly up the center colum, and leave a fraction of the film out of the chemicals,
Richard

6. Originally Posted by R.Gould
Simple anwser, divide the total required I:E 500 by the dilution +1, in your case 25, so divide 500 by 26,round it up very slightly, and you have your dilution, 20 to 480, this works for any dilution, and came from Patterson many years ago. one suggestion, when using Patterson tanks it is better to put a bit more developer in the tank, I would suggest 600, which at 1/25 works out at 24 developer to 576 water,as patterson reels can slip very slightly up the center colum, and leave a fraction of the film out of the chemicals,
Richard
Agree with Richard, and will add that if you have a multi-reel tank, use both reels (set the empty one to take up the slack on the column), put the reel with film at the bottom of course. This will reduce the chance of the reel coming up out of the fluid.

7. Originally Posted by clayne
Whenever you see 1:50, within photo-circles and depending on who you're talking to, it could mean anything from 1 part dev, 49 parts water or 1 part dev, 50 parts water. That's why you'll commonly see 1+49, because it's clear it's 1 part dev, 49 parts water. In reality though we're talking .2ml variation - not enough to matter.
excactly!

8. Originally Posted by shuttershane
I have a Patterson Universal which I understand holds 500ml. How do I calculate 1:25 for 500ml?

Is it like this?
500/25 = 20
500 -20 = 480

So that would mean 20ml of Rodinal go into 480ml of water?
Yes, that's correct. And it is a 1:25 dilution or, what I prefer, 1+24.

9. Originally Posted by clayne
Whenever you see 1:50, within photo-circles and depending on who you're talking to, it could mean anything from 1 part dev, 49 parts water or 1 part dev, 50 parts water. That's why you'll commonly see 1+49, because it's clear it's 1 part dev, 49 parts water. In reality though we're talking .2ml variation - not enough to matter.
That's perfectly fine for large dilutions, but when one talks about D-76 at 1:1 (undiluted) vs. 1+1 (1 part D-76 and 1 part water; i.e., 1:2 dilution) it is two very different things in chemistry parlance.

10. Originally Posted by Tony-S
Yes, that's correct. And it is a 1:25 dilution or, what I prefer, 1+24.
So is a 1:1 dilution 1+0?

I think it's only chemists who think of 1:25 as one part in a total of twenty five. The rest of us think of it as ratio i.e. one part to twenty five parts.

So 1:1 would be the same as 1+1 i.e. equal quantities of developer and water.

Steve.

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