Re: [OM] Astrophotography

[Chuck Norcutt]

Rather than building some some sort of equatorial thingamajig I'd 
suggest finding a used 4-1/4" Meade reflector telescope which can be had 
with equatorial mount and clock drive.  It's the sort of thing typically 
sold for kids at discount stores near Christmas time.  I bought one of 
these for about $100 new some 5 or more years ago and gave it to my 
grandchildren.  Bad decision.  With my son unable to instruct them in 
its use and me not around to do so it never (ever) got used.  I 
reclaimed it one day after realizing it never got used and never would.
I don't want to bother trying to observe with a 4-1/4" reflector but I 
have kept the scope in reserve for the day when I finally do what you're 
doing and strap my E-M5 on it for some wide field photography.  At this 
point I don't know if I'll strap it on the scope and use the scope for 
fairly precision guiding or dispense with the scope and just strap the 
camera to the scope's mounting plate.  The clock drive by itself is 
probably accurate enough for guiding a short focal length lens.
There are also simple guiding mechanisms you can make yourself.  It's 
been many years but IIRC it's called a "barn door mount".  It's 2 
boards, one on top of the other and joined on one side with hinges.  At 
the open end on the opposite side of the hinges you have a (say) 1/4-20 
T-nut in one board with a 1/4-20 screw passing through from the bottom 
and pressing against a small metal "wear plate" in the bottom side of 
the top board.  Attach a small knob to the bottom side of the screw such 
that turning the knob pushes the top board up and causes it to rotate 
about the hinges.  Put a camera mount on the top of the top board and 
then attach the whole thing to a tripod head with the head tilted to 
approximate the latitude of your location.
Do a Google search for "barn door mount" and you'll get lots of hits. 
Here are some images 
<https://www.google.com/search?q=barn+door+mount&lr=&as_qdr=all&tbm=isch&tbo=u&source=univ&sa=X&ei=lzrUU4jcLoycyATVl4GYCQ&ved=0CCsQsAQ&biw=1446&bih=904>
I couldn't find one on ebay with scope but here's a Meade (manual) 
equatorial head for $18. 
<http://www.ebay.com/itm/Meade-EQ-1-Telescope-Mount-Head-NEW-Head-only-no-tripod-cables-ctwt-bar-ctwt-/331265020559?pt=LH_DefaultDomain_0&hash=item4d20ef128f> 
 Note that it's lacking drive knobs and flexible cables.
Chuck Norcutt


On 7/26/2014 4:28 PM, Paul Braun wrote:
> On Sat, Jul 26, 2014 at 3:21 PM, Chuck Norcutt <
> chucknorcutt@xxxxxxxxxxxxxxxx> wrote:
>
> > Looks pretty good to me.  Better than anything I ever did with a
> > telescope.  The upper left of your image seems to show a bit of rotation so
> > maybe you need to move the camera more frequently.  I guess I need to study
> > how this is done.  I don't understand the need for so many "dark images" or
> > the very large number of light frames for that matter.
> >
> > As to hyperfocal distance for 100mm on 4/3 sensor
> > f/2.8 about 700 feet
> > f/5.6 about 300 feet
> >
> > You can cut those distances in half for use on small images like a 4x5
> > print or web images.
> Thanks, Chuck.
>
> I'm not sure about the number of dark frames - just going by what my friend
> suggested. I'm going to do some more research into the mechanics of the
> process.  The guys that are really serious also shoot a series of what are
> called "Flat frames" and one other type as well.  Not sure what all of them
> are.
>
> I think the series of 10 frames will go much faster with the cable release,
> so maybe less movement.  I may end up having to build some sort of
> equatorial thingamajig.
--
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