How many rolls for a batch of developer?

[kykr]

I've been using Ilford DD-X (1:4) with Kentmere 400 as I get back into the world of film, but I didn't have a ton of experience with all of this years ago.  I usually develop two rolls of 35mm in a stainless tank, and then throw out that batch of developer.  But occasionally I'll shoot a roll of 120 or some other type of 35mm b&w.  

I have re-used the developer for a third roll of 35mm done right after the first two and everything worked fine.  Right now I've got two rolls of Tri-X 35mm, one Foma 400 120 and an HP5+ 120, so I'll develop them in three batches in a two-reel tank.  Can I use the same 1:4 batch of DD-X for all four rolls developed all in the same day (so storage times aren't relevant)?  I have read about increasing development time 10% for additional rolls but I'm wondering if that's a myth or solid advice.  I do have some old powder D-76 included with a box of darkroom stuff bought recently, so I'm wondering how this works for other developers too.  Yes, I'm an admitted cheapskate... 

[808 Photog]

IMHO you are flirting with film fatality! Stick with one time use. I use a pyro staining developer and even at retail purchase price it cost less than 25 cents (USD) per 450ml Nikor tank run. (2) 35mm or a single 120 film.  Aloha,  Bill

[conrad_hoffman]

Have to agree. If you want consistency, use once and dump. Somewhere in the manufacturer's literature there should be the number of square inches of film a given amount of developer can develop, but I only worry about having enough, not maximizing it. Time and film are way more expensive than developer.

[kykr]

1 hour ago, conrad_hoffman said:

Time and film are way more expensive than developer.

So true. Thanks for the replies!

[You Plidou]

Foma Retro Special Dev is made to be used many times. Otherwise, your might want to push your luck with paper but not with your films.

[glen_h]

The official Ilford data sheet is here:

https://www.ilfordphoto.com/wp/wp-content/uploads/2019/08/ILFOTEC-DDX-AUG19.pdf

 

As above, they recommend one-shot use, but allow for up to 10 rolls (135-36 or 120)

per litre of diluted developer, with increased times for later rolls. 

That would allow for 2.5 rolls for 250ml, or 5 rolls for 500ml.

 

So, if you do two rolls of 135-36 in 500ml, that counts as four rolls/L.

According to Ilford, you could do another roll at 40% longer time.

 

I would do one roll per 250ml, or two rolls per 500ml.

That is, two rolls of 120 in 500ml, with 20% more time for the second roll.

 

Doing a 120 roll and two 135-36 rolls, it might be better to do the 120

roll first, and then the two 135-36 rolls at 20% longer time.

Much of the development is done in the first minute, so starting

the second batch with stronger developer helps.

 

[allancobb]

Of course, Diafine plays by its own rules.

[glen_h]

11 hours ago, allancobb said:

Of course, Diafine plays by its own rules.

My favorite for over 50 years, since I learned about it from my grandfather.