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Re: [APML] 35 mm Camera & Focuser
Serge Theberge wrote:
>
> Thanks Bill. Looks like I got myself into a really interesting focusing
> challenge with this f/4.
Not really Serge ! :^) It is a *adventure*
> 1. Stiletto and Hutech
> I got the picture, factory setting is theory, reality requires that I do my
> own testing/calibrating/testing... I looked at the Hutech web site and a
> do-it-yourself calibration procedure is provided. Can I calibrate the
> Stiletto or does it have to be sent back to STI?
Both can be calibrated by anyone possessing the proper implement to do
so. The STI requires a digital depth gauge with a narrower profile.
There are other subtle differences between the two. The STI enables you
to get "close" to focus very quickly. From that point the ronchi screen
is used like a knife edge to refine your focus. The Hutech is simply a
knife edge. Personally I would opt for the Hutech because its cheaper
IIRC. But thats opinion so YMMV.
>
> 2. Impact of unmounting/remounting camera on whole focus procedure
> In a nutshell, what you are saying is that this is a non-issue if one is
> careful (I thougth Murphy's laws applied here too!)
>
> 3. Viewfinders
> >From your experience, viewfinders would work for slower scopes but for an
> f/4 setting they can't be trusted. So solutions based on the viewfinder are
> not recommended. I got the point although I still would like to give it a
> try it though just in case I am lucky enough to have a camera where all the
> distances match (I can hear you say that this guy believes in miracles!). In
> any case, it would help make me get hands-on understanding of the value of
> knife-edge focusing over other methods.
Can't hurt to try Serge. When I started out I had just enough good
results to keep me interested in continuing <laughs> But the bloom fades
off of that Rose pretty quick and I would prefer to get a higher chance
of success given the effort that lugging all of the paraphenalia to a
dark site is.
>
> 4. Nikon, Olympus
> You are saying here that it doesn't really matter since knife-edge focusing
> is available for both cameras. Olympus though is lighter, Nikon has more
> flexibility...
Or the camera that you currently have too .... Personally (since you
asked) I like Nikons. The are built like a tank and I have dropped mine
and it survived without a scratch. But the Oly's are fine too. I just
prefer the Nikon's for prime focus work.
> 5. Off-axis vs guidescope
> Your experience is that guidescope limits useful exposure to 10-15 minutes
> due to flexure problems, etc. Do you have any specific off-axis guider that
> you would recommend? What are the limitations that I should be aware of?
> Thanks for your advice Bill,
Lumicon 2 inch Newtonian Off Axis Guider. *But* you might need something
different because at f/4 you will need the coma corrector and I am not
sure what the Vixen specifics are on theirs and how it mounts. Lumicon
has a coma corrector that threads into the bottom of the OAG. You can
still put filters into the imaging patrh without interfering with the
guiding path which is a nice feature. Especially if using a Ha filter
because you will not be able to guide through it. I have a very strong
opinion on this subject so take that into consideration Serge. I wasted
a year and half trying to use a seperate guidescope before I wised up.
Others have gotten good results. The Vixen 203 f/4 has a robust
secondary and I believe that Herm images using a seperate guidescope so
it can be done. Perhaps someone can fill in the blanks on the Vixen coma
corrector and the appropriate spacing to optimise results and that would
help. I am certain it can be done though ....
Are you planning on manually guiding? or will you be using an Autoguider
?
Regards
Bill
--
William R. Mattil |
wrmattil@ix.netcom.com | http://celestial-images.com
(972) 399-4106 |
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