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Re: (meteorobs) Normal lens
>George Zay wrote:
>I got another question about the box you made for your lens and 4X5 film
>holder...how do you focus it? Is it pre-focused for one spot on your film
>holders film plane? Can you somehow make minor adjustments? That is does the
>lens somehow move back and forth? Do you have a fresnel lens mounted somehow
>to see what your focusing?
Mount the lens on a lens board. Use a ground glass to find the approximate
focus position of the lens. The moon is good to use for this purpose as it
is bright. Examine the focus with a magnifying glass. Measure the distance
from the rear of the lens to the ground glass and build your box to fit
this. Take some pictures to see how good the focus is. You can always shim
the plate holder to find the best focus position. Once found, lock or
secure everything in that position. Everything of course should be squared
up so you have good focus across the entire plate. The focus should not
change after that.
You wrote:
>
>What kind of film you use? You mentioned in a previous post about using Pan
>1250 I believe? I think this is the same thing as black and white Plus-X 125
>in the 35mm format? Would you recommend another film with a little faster
>film speed...such as HP-5 developed in Tmax as ASA 400? Have you ever tried
>Light Hypering film for spectra purposes?
>
You can use any panchromatic film. I have used Kodak Tri-X Pan Pro 4164,
320 ASA, Kodak Royal Pan 4141, 400 ASA, Kodak Royal X-Pan 4166, 1250 ASA,
ILFORD H.P.-4, 400ASA. T-MAX 400 is probably a good choice also. Plus-X
125ASA is a good fine grain film but abit slow. (Great for spectra of
fireballs) I wouldn't Hyper film for spectroscopy. Spectra of faint
meteors arn't of much use, unless that's what you are going after. High
dispersion, high resolution spectra are what is needed. Unfortunately, they
are hard to get but that's life! D-19 is a good high contrast developer but
I have also used HC-110.
-----------------------------------------------------------------
Edward Majden epmajden@mars.ark.com
1491 Burgess Road Meteor Spectroscopy
Courtenay, B.C. CCD's - P.E.P.
CANADA V9N-5R8 Amateur Astronomy