Alt/Azi on Dobsonian base.

[tea_subtle]

I was going to print off a setting circle to put on the base of 200p dob. 
mainly so the grandson can understand more about findings things in the night sky. 
ive use a digital inclinometer with magnetic base on the tube to get the angles what I was pondering on is, is it possible to just use the iPhone compass set to true north and lay that flat on the base of the dob pointing forward or is there something I’m missing. 
 

[Corncrake]

4 hours ago, tea_subtle said:

inclinometer with magnetic base on the tube 

iPhone compass set to true north

Does that mean the tube is magnetic, as you dont mention attaching anything else ?
I dont know iphones, do they use gps to aquire north, or do they use the same fluxgate sensor found in (some>?)  android devices which get all upset and declare an alien influence,  like when my daughter tried to use her starchart app on her android thingy near my magnetically tubed 300p dob

Edited March 28, 2021 by Corncrake

[tea_subtle]

Steel tube on the dob. 
not sure what system apple use for the compass. They do use the inbuilt inclinometer and I believe Gps but anything else I’m not sure. 
I’m new to the hobby and just wondered if it was to feasible to use this method to find objects. 

[Corncrake]

Certainly the method of adding circles to it is feasible, at least for finding way about the sky on low and medium low powers. But the alt/az coordinates do change surprisingly rapidly with increasing powers of eyepiece !

I suppose you could find out if the iphone varies its sense of where true north lies as you approach it. In which case you could lay a mark(chalk?) on the ground against which to set the dob base ?

[Corncrake]

11 minutes ago, tea_subtle said:

I’m new to the hobby 

to use this method to find objects. 

Oh, caveat ! how new ? Sorry if I am about to teach eggs but ,

be aware that if you mean using the RA/Dec coordinates of an object as "this method" then no, not without a calculator, PC prog, or app to keep time vs. hour angle etc !

[Corncrake]

 and another addendum :-

just looked up your history so may I say a belated "Welcome aboard " !

and have you found the excellent freeware Stellarium ? That has a display mode that can maintain a running update on where an object is in Alt&Az.

 

 

[vlaiv]

You'll probably find it difficult to accurately use settings circles on 8" F/6 scope.

True field of view is simply too narrow. Maximum TFOV that you can get out of this scope is 2.2 degrees and you need 2" eyepiece with 46mm field stop in order to do so.

I doubt that phone based compass is accurate to 1° and settings circles are going to be difficult to use to that precision (you need very large settings circle in order to make room for 1° marks on it. Whole circle has 360° and if dob base is 50cm in diameter - that is ~157cm in circumference. Single degree will be only 4mm wide and you need to see that accurately in the dark.

If you use simpler eyepiece like 1.25" 32mm plossl - you'll be limited to only ~1.3° TFOV. Miss by 0.65° and target is no longer in the eyepiece.

[Corncrake]

Yes, all very good points @vlaiv  I was too fluenced  on the effect of the steel tube etc. and should have discussed red-dots and finders, and omitted eyepiece discussion.

But to get someone pointed in the right general direction, navigation,  with a concept of coordinates it could still be a useful aid especially if the Moon, Venus, Mars etc was involved ??   >"grandson can understand more about findings things in the night sky."<

I'll let you all know in a year or few, my 5y old g'daughter already knows Orion and had us all falling about when, upon pointing out the full moon, declared he had eaten too much

There are commercial variations on this theme,, or ought I not to mention them !

Perhaps a bit of a nit-pick but in times of yore astronomers did use setting circles, but strictly speaking the term was only used for RA/Dec circles, and not for alt/az, nor on Dobs

 

 

Edited March 28, 2021 by Corncrake

[CraigT82]

5 hours ago, vlaiv said:

True field of view is simply too narrow. Maximum TFOV that you can get out of this scope is 2.2 degrees and you need 2" eyepiece with 46mm field stop in order to do so.

You don't have to get the main scope right on target with the setting circles... that's what finders are for 😉

[vlaiv]

51 minutes ago, CraigT82 said:

You don't have to get the main scope right on target with the setting circles... that's what finders are for 😉

Fair point. I would not normally use settings circles for finder - but for educational purposes, why not.

[tea_subtle]

Thank you all for input on this. 
Plenty of food for thought.

 

[Spile]

I find a combination of techniques depending on what I am targeting and what mood I am in works for me...

Telrad

RACI

Wide angle, low power EP

SkEye Indirect mode