Dobsonian Altitude Scale

[Clarry (Clayton)]

I decided to make an altitude scale for my 8" dob. After much experimentation I devised a method using a lightscribe CD. In Photoshop I made a 12cm circle then drew a 0 to 90deg scale around 1 quarter of it. I then burnt the image onto a lightscribe CD. Next I removed the thumb screw on the axle of the scope and fitted the CD between the washer & the hud. I used white out to put a mark on the mount near the spring. Using a spirit level I put the barrel on an even plane the losened the thumb screw slightly so I could turn the CD independant of the barrel. I set the 0 deg on the white mark then tightened the thumb screw. That's it, now the Cd turns with the barrel and the white dot indicates the altitude. Cheap and simple. Possibly not accurate to the fraction of a degree but good enough to let you know where your looking.
The only problem I have is the lightscribe is a bit faded looking, I have a friend who can burn white labels so he's doing one for me in clear black on white.

Some photos here plus the original .png file of the scale if anyone else wants to do the same thing.

http://members.optushome.com.au/clarry/1.JPG

http://members.optushome.com.au/clarry/2.JPG

http://members.optushome.com.au/clarry/3.JPG

http://members.optushome.com.au/clarry/4.JPG

http://members.optushome.com.au/clarry/5.JPG

http://members.optushome.com.au/clarry/6.png

[bmitchell82 (Brendan)]

Nice job, gives me a good idea for my setup

[Ian Robinson]

Be easier to attach an electronic inclinometer to the OTA I would think , and less bother .

[taminga16 (Greg)]

Nice work Clayton,

As Ian said an electronic inclinometer would be less bother, but at about $80.00 it's a lump and then there is the satisfaction of doing it yourself. How have you set up your azimuth scale?

Regards,

Greg.

[koputai (Jason)]

Originally Posted by taminga16

an electronic inclinometer would be less bother, but at about $80.00 it's a lump

I bought mine off Ebay for $65, which I thought was pretty good, but I was at McBunnings on the weekend and they have them for $37 !!

That said, I think Clarry's done a lovely job, certainly looks better than a digi inclinometer!

Cheers,
Jason.

[stevejack (Steve)]

Nice work, I considered a method like this also.

I ended up with an inclinometer from Carbatec ($60ish dollars?) as I would have needed to buy a spirit level and build something to adjust the level of my scope (more money and effort) so I justified it that way.

But that said - most times it's enough to be pointing roughly at the correct region of sky and pan around there with a wide field/low power EP. Unless it's a really faint object it's not a problem. Have a blast with it!

[astro_nutt]

Great job Clarry!..I have done a bigger version and have it lit up with a red LED..very easy to read!
Cheers!

[Clarry (Clayton)]

Yes an inclinometer would be good too, but $60 to $80 as opposed to a $1.50 blank CD kills it for me. I also recorded some 60's music onto the CD, so if the clouds come over, I can take it off and slip it into my stereo to entertain me. Try that with an inclinometer, lol.
For my azimuth, I've ordered a digital compass from eBay. I'll just attach it to my base, lined up with the front of coarse. It only cost about $15 delivered. I haven't got it yet but hopefully it will do a reasonable job. If not I haven't lost much.
Look here http://members.optushome.com.au/clar...592ba03b_b.jpg

[stevejack (Steve)]

Originally Posted by Clarry

Yes an inclinometer would be good too, but $60 to $80 as opposed to a $1.50 blank CD kills it for me. I also recorded some 60's music onto the CD, so if the clouds come over, I can take it off and slip it into my stereo to entertain me. Try that with an inclinometer, lol.
For my azimuth, I've ordered a digital compass from eBay. I'll just attach it to my base, lined up with the front of coarse. It only cost about $15 delivered. I haven't got it yet but hopefully it will do a reasonable job. If not I haven't lost much.
Look here http://members.optushome.com.au/clar...592ba03b_b.jpg

I like the idea of a digital compass! I looked into this briefly but for some reason abandoned it... and I have no idea why... it makes much more sense! Now you've got me thinking

[taminga16 (Greg)]

Clayton,

The only problem that you may find with the compass method is deviation, the needle chasing or deflecting from the steel OTA.

Good Luck.

Greg.

[Clarry (Clayton)]

Thanks taminga, I was going to mount it on the wooden base as opposed to the OTA so maybe that will help things. Once again, at $15 its worth a try.

[taminga16 (Greg)]

Clayton,

The digital compass seems like a great solution and I hope that it works, but if you find that you are constantly frustrated by odd outcomes then it my well be deviation (the compass need not be in contact with the OTA for this to occur, infact the altitude angle may affect your compass readings).

Good Luck,

Greg.

A boat builder that I know tells a wonderful story of swinging a compass (calibrating the compass according to it's surroundings) onboard a large pleasure craft, on returning a second time at the insistance of the owner, who was claiming that the compass was not accurate he decided to spend a day on board to determine the cause of the problem. As the day progressed he noticed a considerable amount of beer being consumed by the guests and came to the conclusion that on the two occassions he had swung the compass the fridge was full of beer in readiness for a day on the water and empty of same on the way back to the harbour creating deviation.
His solution was simply to have the owner half fill the fridge with beer and swing the compass accordingly.

[Clarry (Clayton)]

I remember reading somewhere that the bottom of Australia was sometimes called the Magnetic Coast. Apparently there's lots of iron in the cliff faces & it causes compasses to play up. Hence the proliferation of ship wreaks there.

[bmitchell82 (Brendan)]

this is my idea to the situation Put the OTA in the horizontal position, move your base till its at the required angle, then swing your ota into position.

Like this device has been created for, i belive that is just a "ball park" figure. And isn't too much different than using the star hopping method. pick that star then that star use a thumbs width to get it about in the right spot, then hey there ya go. pan around and find it.

If you always use the same method for getting something 9 times out of 10 it will have repeatable proformance, eg, it should hit approximately the same spot if all other variables have been contained.

[taminga16 (Greg)]

Brendan,

Once calibrated (two known objects) for a nights viewing I can hold my own with my mate's Argo Navis, the only difference being that I require a laptop. The system puts most DSO's inside the FOV of my 35mm TV Panoptic.

Clayton,

The South West coast has magnetic anomalies that are recorded on nautical charts as such, (apparently compasses perform in very odd ways in these areas).

Regards,

Greg.

P.S. Peter Batchelor writes about his system in the "how to" threads under Mods to his 16" Lightbridge.

[JethroB76 (Jeff)]

Originally Posted by taminga16

Brendan,

Once calibrated (two known objects) for a nights viewing I can hold my own with my mate's Argo Navis, the only difference being that I require a laptop. The system puts most DSO's inside the FOV of my 35mm TV Panoptic.

Agree, they work very well. They're no "ball park" method

[taminga16 (Greg)]

Thanks for the support Jethro,
I feel that the tale of the old bull and the young bull might not be wasted on Brendan.

Regards,

Greg.

[bmitchell82 (Brendan)]

mmm tale of the old and young bull? interesting.

I wasn't talking about a argo navis, man if i paid the money to get one i would want it to work 100%. Im talking ball park with using manual methods inclometer and digital compass. these are ball park tools!

Sall good.

[JethroB76 (Jeff)]

We weren't talking about the Argo Navis either.