The
focus is a bit of an issue but I do my best. I use a loupe (x10) that gives me
a useful star image. I am sure it can't be the best solution but so far it has
worked. I have a Polaroid Land 55 back and I will do the trail method with
that film because I get an instant result in the field to conform the focus is
correct.
So you can use a Hartmann mask with the Polaroid
to nail the focus? With your helical focuser this is an option. On
my lens, I would have to fool with jack screws on each corner, making that
more dificult.
As for the tube, I had it cut in a large lathe
by some well meaning professional guy who did me over because I was silly
enough to admit it was for something scientific. That added a 30% premium to
the job. However I am sure the ends are parallel.
Next time, just tell him you are making a
Bar-B-Q and maybe he will knock off 30% <G>.