Analog Setting Circles

[stevejack]

Hi All, long time reader first time poster - this is a great site!
A while ago I bought my first dob - a 10" Bintel. I have used it quite a few times in my small backyard in Perth, and I have a great dark sky site a few hours away where I take it sometimes.

I started with the basic scope and eyepieces and eventually worked my way up to new eyepieces, a laser collimator and just recently a cheshire collimation eyepiece to make sure everything was right.

I was frustrated at not being able to view objects from my backyard that I knew were there - I just couldn't find them in the finder scope and only occasionally stumbled across them by sheer luck with my wide-angle EP.

There is no way I could afford Digital Setting Circles so, following the advice of others on this and other forums, I set about making Analog Setting Circles. First I tried printing them out on A4 sheets and sticking them together using a printed protractor.... needless to say it wasn't accurate enough. So I took my Jpeg into a local print shop and for $3.80 he printed out my circle. I used clear contact (the same stuff kids use on their school books) to "laminate" the print, and then cut out the circle and stuck it to the base of my scope with sticky tape. Its rough but don't you worry - it goes alright!

I picked up a digital angle finder at Carba-Tec and hooked up my laptop with stellarium next to the scope and BANG i'm panning right onto dozens of clusters and galaxies that I never had a hope of finding before. The faintest galaxies I could see were mag +8 (small and fuzzy but I was pleased!).
The angle was always spot on, and with the azimuth I was placing all objects within the field of view of my wide angle EP.

I'm still very new to all this, but I can definitely recommend to anyone with a dob who can't afford DSC's to organise some analog circles and a digital angle finder - you won't regret it!

Bring on the new moon and my dark sky site!!

[kinetic]

Hi Steve,

What a great contribution!

You could also make circles by getting an old retractable
tape measure blade that is broken.....cut it to a workable length
so it becomes the circumference of a disk that will be a practical size to
read from.
Turn the disk (aluminium or wood) down until the tape blade wraps
completely around the disk and the start meets the end.
Lets say you have an old tape blade with 360 cm.....
When wrapped around the disk, each cm represents 1 degree.
You could then either glue that to the circumference or mark it off
with felt pen and graduate each cm even with half or 1/4 degrees
even further if you wanted.
The bigger you make the disk, the more accurate the circles.

Then just fit the disk somehow to the alt axis of the dob and fit
a pointer and red illuminator LED as an option.

As for the Az axis, I suppose you could wrap a tape blade around the whole circle of the Dob base and increment the circumference measurement by calculating out the degrees.
If you're lucky, the measurement might be an exact multiple of
360 .

I've got aluminium disks on my homemade GEM that are the original
'cheapie' entry into setting circles.
http://mywebsite.bigpond.com/astrosteve/decncod4.jpg
Then when I added GOTO motor control to the scope, the same disks
became a roller surface for encoders for 'cheapie' digital setting
circles....the encoders were just a mouse pulled apart.
http://mywebsite.bigpond.com/astrosteve/decncod2.jpg
The accuracy and repeatability of this setup is about 1/10th of a
degree.

Alternatively, if you're up for a bit of soldering, you can make
a David Ek digital box VERY cheaply.
http://digicircles.eksfiles.net/index.php
His encoder project plugs in to a few planetarium software packages
to give you VERY accurate positional control.

regards,
Steve B.

[stevejack]

Hi Steve, thanks for the great reply.

I think homebrew encoders might be the next step - the mouse idea is something that I'll look into for sure.

You've highlighted many options for creating the analogs and it just goes to show how many different roads there are all leading to the same point.

The next trick for me is finding a way to power my laptop all night long from the middle of an open field.... where's Tesla when we need him??

[bmitchell82]

First of all i would like to say a very big :welcome: to the great site. :D ahh Home brew thats the thing that we all love.

Im thinking that we should all get to gether from this site for all of us in perth to meet greet and gaze :D hehehe should be good fun i thinks.!

Brendan

You must live around the morley area :D

[Ian Robinson]

Check out Berry's Amateur Telescope Making - he explains how to do it.