Re: [APML] Raw NGC7000

[steve banbury <banburys@sonic.net>]

Hi Steve and Chris--I was the one who posted about trailing and thumbscrews.

I have 3 cameras mounted on a single platform guided with an STV thru a
135 mm  f2.8 telephoto.  Two cameras are OM-1's attached respectively
to a TeleVue Oracle with a 0.8X Reducer, and to a TV101. The 3rd camera
is a Nikormat attached to a 400 mm f6.3 telephoto.

On June 1 I was photographing the Veil simultaneously through all 3 cameras.
Twenty minutes into the shot, I realized that I had the long axis of the OM-1
cameras oriented N/S instead of E/W, and realized the edges of the nebula
might be cut off. I finsished 30 minutes of exposure, and then rotated the 2
OM-1's 90 degrees by loosening and tightening the single set screw on the
TV scope drawtubes. I then shot 60 minute exposures on all 3 cameras.

In the resulting prints from that night the 400 mm shots are untrailed.
The 20 minute shots are significantly trailed, and the 60 minute shots
are a disaster.

On June 30 I repeated shots of 60 minute duration with all equipment
the same--except I added a second thumbscrew to the TV scope drawtubes.
No trailing.

If you skim thru the "Ask Al" TeleVue FAQ's, you will find a response
from Al in which he says something to the effect that "Its hard to hold
2-1/4 lbs of cantilevered gear steady with a single set screw".

Now, my 3 inch long 2 inch diameter extention tubes are not made by
TeleVue.  That may make a difference in overall system slop--
necessitating a second thumbscrew for my application.  I tried
everything I could think of including adding a second clamshell to the
TV101 to try to eliminate elongated stars before taking a big gulp and
drilling my drawtubes.  I've been fighting this battle for 11 months.

Maybe stopping down your camera lens will solve all your problems.
But if it doesn't, I'd sure give this experience some thought.

Happy trails---Steve


Steve Lindsey wrote:

> Thanks Chris.  I'm hoping you're right.  My friend and I have been through a
> lot in the past to get pretty good at drift alignment and I'd like to be
> solving a different and more straight forward problem for a change.  Like
> stopping a lens down a setting! ;-)
>
> Glad you didn't have a problem with the thumb screw but my buddy Dan's ST8 +
> colorwheel + 0.8 reducer is pretty beefy and I'm sure a few pounds heavier
> than my Nikon body and the 0.8 reducer will be when I shot film with it.
> BTW - I'm setting up a modified Lumicon NEG to guide with the ST4 off-axis
> like John Boudreau does for film work on the TV85 to avoid the guidescope.

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