A more accurate inclinometer?

[Ratlet]

Listening to the Actual Astronomy podcast recently as the covered setting circles, I realised how incredibly easy they are (in theory) to operate, especially given the ease of finding coordinate on your mobile.

I've not test got the azimuth printed up for the dob base, but I made a start on the alt.  This is inspired by Dakota Starry Nights on YouTube where they did something similar.  Essentially it's a small jig that allows you to adjust the inclination of you inclinometer to allow better calibration.  It attaches to the tube using two embedded neodymium magnets.  The base is 3d printed andhas a layer of flock to avoid scratches.

Say you point at a star that is supposed to be 35.5° but your inclinometer says it's 34°< you simply adjust one of the nuts to get the inclination to match.

Not tried it in anger yet, but thought I'd share.  My hope is that by the time I have actually tried the full setting circle business I'll have spent at least twice as much as a Starsense unit and still not been able to get it to work.

[CraigT82]

Nice idea…. I guess that removes the need to level the tube to zero it.  Be better with wingnuts though? 

[Ratlet]

26 minutes ago, CraigT82 said:

Nice idea…. I guess that removes the need to level the tube to zero it.  Be better with wingnuts though? 

Indeed.  The hardware shop did not have any, and I mostly made do with what I had at hand.

[Mr H in Yorkshire]

If you needed to start from a known horizontal you could just fix a short spirit level, or just the bubble tube, alongside the unit. That way you would not need to mechanically adjust the inclinometer, merely zero it. Don't forget they have an error which is somewhat greater than the reading 'resolution'.

Edited March 9, 2023 by Mr H in Yorkshire

[Ratlet]

I think this project perhaps more aptly demonstrates why I became a chemist and not an engineer 🤣

[Mr H in Yorkshire]

Hi Ratlet, I think I can withdraw that comment I made. A tiny bit of reading indicates that the repeatability of these is pretty good - 0.1 degrees. So once you have calibrated against your known altitude target the device should continue to read +/- 0.1 of that value. That has to be good enough for a dobsonian because pushing to a tenth of a degree is not that easy. So it's all a question of 'digital' (your hands) input versus digital output!

[Ratlet]

1 hour ago, Mr H in Yorkshire said:

Hi Ratlet, I think I can withdraw that comment I made. A tiny bit of reading indicates that the repeatability of these is pretty good - 0.1 degrees. So once you have calibrated against your known altitude target the device should continue to read +/- 0.1 of that value. That has to be good enough for a dobsonian because pushing to a tenth of a degree is not that easy. So it's all a question of 'digital' (your hands) input versus digital output!

They seem reasonably popular on Cloudy Nights with the dob squad, although I'm not sure I get behind the people who proclaim it makes goto and Digital Setting Circles obsolete.  I did consider the fully digital option as there is a set designed for the stellalyra, but this seems fairly low cost, low risk.  If it manages 0.1 degree repeatability that will be perfect.  Even without the azimuth circle (need to get it printed) getting the altitude correct to that accuracy should make it easier to find faint fuzzys.  I'll be giving it a test tonight hopefully.

I will say that I made a fairly large failure of logic in the whole process because I should be making sure the dob base is level which means that I have a level surface to calibrate the inclinometer on.  Assuming it still reads good on a star then the adjuster is redundant.

Edited March 10, 2023 by Ratlet

[Guest]

I have a setting circle and angle gauge on my 10 inch dob and i would not be without either of them on a manual dob.  My setting circle is fixed so i have to adjust the base instead of the circle.  The angle gauge  i level on the base and then move it to the tube.  Now.... How accurate is it is the question.  Well that comes down to many things.  How accurate the circle is made, the more level your scope is the more accurate it will be.  I have no issues at all getting my target inside of a 32mm eyepiece most of the time.  If i have done everything just right i can get it inside of a 26mm and if i miss it is usually just up or down a bit.  Is it a more accurate system then a DCS or full on go to, well in my experience with my XX16G I am just about as accurate manually with my 10 inch as the computer is with the 16.  As a matter of fact i am going to add a setting circle to the XX16G for the nights i dont feel like messing with the go to and just go manual.   

[Macavity]

The inclinometer (altitude) should be accurate... Few tenths of a deg, if "bench" calibrated?
(See ABOVE!) But then it could be useful to have the *adjuster* you made. There are SMALL
things like "cone errors" - The scope optical axis may not be aligned with the rings/mount? 😏

The Azimuth circle (Usually on the Base of Dobsonians) depends on "aligning with North"?!?
But you can significantly improve this accuracy by calibrating, using a... "One Star alignment".
Just centre a star of *known* coordinates and adjust the scope settings to match up with this.
- Personally, rather than attempting to HEAVE the *whole* scope around, I make the azimuth
graticule/reticle "line" adjustable (erasable pencil/marker?) for use against a *fixed* Scale. 🙂

[CraigT82]

5 minutes ago, Macavity said:

The scope optical axis may not be aligned with the rings/mount?

Good point. Optical axis may be off from the long axis of the tube if it’s been collimated with a focuser that’s not quite square to the tube. Or if the secondary isn’t quite central, I think. 

[Ratlet]

The plan for the azimuth is the circle will go on the rotatable section of the base.  I'm thinking a small magnetic strip on the proper base and then some thing I can stick on that that will reach up and point to the azimuth scale.  Will allow me to zero it accurately (hopefully).

I found a design someone did for the az5 and I'm going to upgrade it with setting circles all going well for the 130pds.  I get 2° FOV with my 32mm so it has a fairly large scope for getting close enough.

[Mr H in Yorkshire]

2 hours ago, Ratlet said:

I did consider the fully digital option

On a motorised binochair (described here on SGL) I have used encoders, part of the DobsonDream equipment designed especially for dobs, I didn't need to the attachment hardware. They work well with Skysafari on an Android tablet (app shows an arrow for the direction to move towards target) or on a PC tablet with Stellarium and David Ek's encoder driver which paints a big red box with numbers on screen. You reduce the numbers to zero to find the target.

Obviously a much more expensive option, but if you ever consider it I can vouch for the kit and the helpfulness of Alexander the company head - AstroGadgets.

[Ratlet]

Just now, Mr H in Yorkshire said:

On a motorised binochair (described here on SGL) I have used encoders, part of the DobsonDream equipment designed especially for dobs, I didn't need to the attachment hardware. They work well with Skysafari on an Android tablet (app shows an arrow for the direction to move towards target) or on a PC tablet with Stellarium and David Ek's encoder driver which paints a big red box with numbers on screen. You reduce the numbers to zero to find the target.

Obviously a much more expensive option, but if you ever consider it I can vouch for the kit and the helpfulness of Alexander the company head - AstroGadgets.

This is the beauty of the hobby imho so many ways to do the job.  I'll keep that in mind.

[Mr H in Yorkshire]

 

 

If you accurately level your base then glue a few of these on in the desired orientation you will have a calibrated level. A. couple of quid on ebay.

[Ratlet]

A wee bit of follow up.

I used the dob and inclinometer last night.  Leveled the base using a cheapy circular bubble from AliExpress and then zeroed the inclinometer.  Worked excellently.  Dial in the altitude and then pan in azimuth in the rough area.  Object always ended up in the FOV of the 30mm 70° eyepiece.  Worked best for larger objects since they were easier to spot.

I could probably have used the adjuster plate, but I didn't need it with the dob.

[JeremyS]

I’m inclined to believe you

[rojay]

On 11/03/2023 at 16:00, JeremyS said:

I’m inclined to believe you

Yes, I think he's on the level.