Double exposure on a ´Blad 500 C...!!!

Hi there!
I ´m going out soon trying some doubles exposures. I have done some of them before but just with my Fe2, but never with my Hassy.
Take the first exposure, insert the dark slide, remove back, crank it, attach the back on the body, slider out and take the second exposure.
Now film choice...!!! B & W . I have a 4 different choices: Neopan 400, Kodak Tri-X 400, T-Max 100 or Acros 100. I´m going to shoot flowers on a first afternoon day-ligth. Setting proper shutter speed and blend. Ex: let´s say ligth-meter on a 100 asa with a 250 speed at f8 , how many t-stop I have to underexpose, I would say shot at F11 both exposures. And how can compensate that with my development times, (shot at f8 and push the film).
I have a T-Max developer and a Iflord rapid fixer.

Post here your magic potion so I will foward it to Panoramix..!!!!!
LOL
Peace

I'm just looking at this from first principles, but it seems that if you "underexpose" both shots by one stop, you'll be certain that the range of values in the double-exposed negative will be no *more* than it would be in the two component negatives if they had been exposed normally.

I'm going to use Zone System terminology because it gives a vocabulary for different levels of exposure.

Think about highlights---say you have a highlight area in the same place in both component images, which you would place on, let's say, Zone IX in a "properly" exposed version of either one. For the double exposure, you're going to underexpose both shots, as if you were instead placing that highlight on Zone VIII. But you're putting both exposures in the same place, and two Zone VIII exposures gets you back to the original Zone IX.

Mutatis mutandis if you have a shadow in the same place on both components.

Of course, depending on the compositions, you might not have a lot of shadows and highlights falling in the same place on the two images. That means that, if you underexpose both shots by a stop, you'll get a slightly compressed tonal range. But at least you know you won't end up accidentally blowing out a place where two highlights collided.

-NT

As Nathan says just underexpose by one stop for a double exposure. It's just a guide but if you take your metered exposure & divide it by the number of multiples you'll be close.
If you use a dark background, your images will stand out more brightly.

You really have to consider both separate exposures, and how they combine.
For instance, if you have lots of featureless darkness in both shots, with the brighter parts that do hold at least some detail of each appear where the other is featureless dark, you don't underexpose either shot at all.
And you don't always want both shots to appear equally prominent. So it's not always a matter of equal distribution/division in exposure over all contributing exposures.

Thanks
I´m back from the shooting...I´ve used the Acros 100, I´ve preatty much underexposed of one stop every exposure...Now I´m going to develop it ...Like in an hour or 2 I will post some results....
Later

Multi-exposure is simple. Take a light reading and divide it by the number of exposures, and that gives the proper setting for each exposure. Example, if double exposure, divide by 2. If triple exposure, divide exposure by three. If you are using a black background, and none of the exposures overlap, you can give each exposure full value.

Here is the result... Acros 100 , 500 C, 150mm f4 Carl Zeiss Sonnar..self developed tmax dev ...
THIS DOUBLE EXPOSURE