How we made our Technical Pan 3-color composite:

As telescope we used our Deltagraph, which is a very fast instrument with 300mm aperture and 990mm focal length. It consists of a parabolic mirror and a 3-lens corrector that is suitable for 6x7 format.

The Filters:
The blue and the green filter are dicroic interference filters. Volker Wendel drawed filter curves and discussed our needs with the company that makes such filters for non-astronomical purposes and it turned out, that they had suitable filters on stock. You can see the filter-curve for blue and for green by clicking on the text. For red, a Schott OG590 was used.

Getting the right exposure time
I do not know wether this is a good method, but we photographed color tables, grey-scales (illuminated by day light) and some flowers in Namibia. We found a exposure factor of 2 for blue and 1.7 for green (assuming 1 for red). This is a little bit surprising, since Technical Pan should be weaker in green than in blue. We planned to make a lot of 3-color exposures in Namibia. Unfortunately the weather only allowed for one full exposure. But even this was not very good since clouds passed through the field during the making of the green and the blue-channel. We exposed 70m with the OG 590. So therefore we should have needed 120m with the green-filter and 140m with the blue. Instead we could   (due to clouds in the last night) make 110m in green and only 75m in blue, which is much to short.
Furthermore the quality of the exposures is very bad due to the passing clouds. Also we had some problems with the hypering. This causes the negatives to be very uneven.

Stacking the exposures
The stacking has been done with PictureWindow 2.5. I really could not find the best way how to make this in the help-manual, but here is how I succeded (after some hours):

1. convert the BW-tiff image into a 48-bit color image (transformation, convert)
2. you will now still have the image displayed B&W. Take the red image and go into <transformation>, <color>, <curves>. Now select <b> in RGB and put the line to zero. Also select <g> and put this line to zero. The resulting image will be pure red (as shown in the left exposure above). The same has to be done with the blue and the green image.
3. stack the exposures with composite

Below you can see the final image.

Seagull-Nebula 3-color Technical Pan Composite Deltagraph 300mm f/3.3

Detail from the left exposure

There is still a long way to go until we will be satisfied with our composites, but regarding the fact, that it is our first try and we had very difficult weather conditions, we are quite pleased with the result.