Re: [APML] ELITE CHROME 200 EXPOSURE QUESTIONS

[Roland Roberts <roland@astrofoto.org>]

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>>>>> "g" == StarManGMH  <StarManGMH@aol.com> writes:

    g> My site is about 20 miles from the nearest city so the skies
    g> are fairly dark but I do have a few local light issues.  My
    g> equipment is as follows:

Well, you have to just just how dark is "fairly dark".  20 miles
barely gets me out of NYC :-)

My dark site has a ZLM of 6+ under good weather conditions, but it is
noticeably worse when there is snow on the ground.

    g> Stellarvue 80mm f6 Achromat
    g> Nikon FE2 
    g> Losmandy GM-8
    g> Lumicon Easy Guider
    g> Elite Chrome 200

    g> My questions are concerning exposure times.  First of all,
    g> should I push 1 stop or shoot at 200?  I've read that you
    g> should square the focal ratio of the scope.  Is this correct or
    g> does it depend on the darkness of the site?  Can anyone
    g> recommend a min. or max. exposure time for this film (pushed or
    g> not) using an 80mm Achromat.

I saw Stuart's response about trying 90 minutes, and all I can say is
he's a better man than I am if he can *manually* guide for 90 minutes!

My rule-of-thumb has been 2f(f+1) at my dark site with good
transparency using E200 with no push.  That's purely empirical and not
based on very large sample, but it seems to work and it close enough
to Covington's f^2 rule.  I've used push +1 on E200 with satisfactory
results, and I think others have used push +2.  If you are guiding
manually, I would consider push +2 just to keep your guiding times
below your fatigue limit.

regards,

roland
- -- 
                       PGP Key ID: 66 BC 3B CD
Roland B. Roberts, PhD                             RL Enterprises
roland@rlenter.com                            6818 Madeline Court
roland@astrofoto.org                           Brooklyn, NY 11220

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