how many times can i reuse the same developer?

Im still fairly new to the darkroom. I have about two dozen rolls of 135 film developed under my belt. Each developed one at a time.

I recently purchased a paterson 3 reel tank that i will use for developing 4x5 film in. I plan to develop 4-6 sheets at a time. Also after my vacation, i have a lot of film i need to develop, about 50 sheets.

My question is, after developing and hanging 4 sheets of film, can i immediately reuse the developer for a second set? Will i need to increase the development time? Will i need to test this myaelf?

Additional information
film, hp5 400
developer, lc29. i plan on switching to ddx when the current developer is all gone

thanks

LC29 I don't use but it is based on HC which can be reused. Check the data sheet to see if it can be used replenished or non-replenished. DD-X has a non-replenish schedule for using 1L of stock up to 10 times by increasing dev time with each roll for example. The fact sheets are on Ilford's web page.

Thanks. Im looking at the data sheets now.

However my thinking is a little different. And possibly quite wrong. What im thinking is that, if the developer can develop 6 sheets or 4 sheets, can the developer be reused after 4 sheets have been developed?

I suppose it is the same situtation with tray processing. How many sheets can be processed before the developer needs to be changed?

4 sheets of 4x5" film (or 1 sheet of 8x10" film) are the same as 1 roll of 120 or 135-36 so the same rules for re-use will apply. It is simply a matter of film to chemical capacity and doesn't really matter if you use a tank or tray. From the Ilford data sheet:

1 litre films/litre
ILFOTEC DD-X 1+4 10
ILFOTEC LC29 1+9 10
ILFOTEC LC29 1+19 5

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So a 1L bottle of DD-X will make 5L with the 1+4 dilution and this will do 200 sheets of 4x5" film total. 1.25L will do your 50 sheets from your vacation.

If a series of individual films is being developed in
a spiral tank using either 1 litre of ILFOTEC DD-X
1+4 or ILFOTEC LC29 1+9 and 1+19,
compensate for the loss of developer activity after
developing the first film by increasing the
development time 10% for each successive film...

Click to expand...

More details are in the sheets.