How Could i get it so wrong

[leon]

Hi All, Thought i would just share this with you Me and My 12" SCT

Ever had a time in your life when all of a sudden the penny drops, and everything is so clear.

Well that's what happened to me just recently when i was attempting polar aligining with my home made wedge.

I figured, well i know where true south is. yep, that's ok, latitude of the wedge, yep, Ballarat is -37, that's spot on, gee i'm cooking.

Now i'll get smart and take a couple of pics through the ED80 mounted on the wedge, parrallel to the center of the wedge, gee, they came out great, just about spot on, cant go wrong here i thought.

Boy was i wrong, oh so wrong,.

Upon asking a few people on this site, what do you think of my accurate line up, even graced with some pic's of the SCP, i was astounded that i was told not right, it will never work, they then gave me some suggestions.

Rubbish i said to myself, of coarse it will, look at pic of the SCP it is dead center.

Anyway i thought about it a bit and then it hit me, the buggers are right, it's all back to front.

The wegde was pointing South instead of North, the Latitude should have been 53 Degrees, so that when it put the SCT on the wedge it would be pointing directly at the SCP, which is -37 degrees, my latitude.

I was told by some, that to get the latitude right you had to point the scope directly up at 90 degrees and minus my latitude of -37, but did i listen, no, how could that be i said, the SCP is -37, and iv'e got the pic's to prove it.

Well i got it bloody wrong alright, so thanks to all who responded to my requests for assistance, i will heed your advice next time.

It all came together now, and all is now well, the penny has dropped.

Cheers Leon

[matt]

Glad it's all sorted Leon

Don't worry mate, being certain we're right when we're actually wrong is all part of the human condition

[janoskiss (Steve H)]

Originally Posted by leon

I was told by some, that to get the latitude right you had to point the scope directly up at 90 degrees and minus my latitude of -37, but did i listen, no, how could that be i said, the SCP is -37, and iv'e got the pic's to prove it.

It does not sound right to me either. When you're on the south pole, the SCP is straight up at zenith. For every degree you move north of the south pole the SCP moves one degree closer to the horizon. At latitude 37S you are 53 degrees from the pole so polar axis needs to point 53 degs away from zenith or 37 degs up from the horizon. No? Or are Meade SCTs under some strange curse?

[leon]

Hi Steve, yea i know it sounds crazy, but when you do it that way it ends up being right, now you know why i was confused,.

But if you think about it, and mentally vision the wedge pointed North at 53 degrees, and then you attach the SCT base to the wedge, and then center the tube between the forks it will be pointing directly at south and at -37 degrees.

Sounds pretty weird i know.

Cheers leon

[janoskiss (Steve H)]

Who's pointing at the what now?

I love my dobs.

[jjjnettie (Jeanette)]

When you start talking about this sort of stuff, my ears start buzzing and I need to have a little lie down.
I have to agree with Steve, I love my dob.

[Dennis]

Originally Posted by janoskiss

It does not sound right to me either. When you're on the south pole, the SCP is straight up at zenith. For every degree you move north of the south pole the SCP moves one degree closer to the horizon. At latitude 37S you are 53 degrees from the pole so polar axis needs to point 53 degs away from zenith or 37 degs up from the horizon. No? Or are Meade SCTs under some strange curse?

The wedge is not the polar axis, so that's why you do not set the wedge angle to your Latitude or point the open end of the wedge to the South. Think of the polar axis (SCP direction) as being defined by the forks with the OTA sitting in between the Forks (parallel to the forks) so the eyepiece is pointing down to the base. Then, the corrector plate is pointing at the SCP and the eyepiece pointing N.

With the Forks at right angles to the base, and with the base sitting on the wedge, then we can see the open angle of the wedge must “point” N at an angle of 90 deg minus your Latitude.

Cheers

Dennis

[leon]

Yea, JJJ, those SCT's are tricker than i thought, however i have it sorted now. I think, at least it now points to were i tell it to so, that's a start.

Cheers Leon

[leon]

Thanks Dennis, I know that now after it put it all together backwards, ah well, as i said to JJJ, at least it is working correctly, but i did learn a lot with that little episode.

Cheers leon

[Dennis]

Me too Leon, me too. I had the same misunderstanding as you 'cos I have always used a German Equatorial Mount which does point at the SCP, at my Latitude of 27.5 deg. Never having owned or operated a Meade, I had to sit down with pen and paper (inside a previous post) to work out the Meade wedge/fork configuration.

Cheers

Dennis