AltAZ mount as an EQ?

[DrRobin]

Hi,

I have seen some dual AltAZ/EQ mounts available now and this got my thinking, couldn't all AZ mounts (including DOBs) be made to work as an EQ mount and then track or use GOTO?

If I took my Skywatcher Merlin mount for example, what if I mounted it on a wedge, counter balance if I need one, or just arrange the C of G to go straight down through the base.  Then I told the Synscan I was at the celestial north pole (Lat 90 would do as a start), surely then the GOTO would still work and it would track in AZ as if it was in RA?

Have I missed anything here?  Could this be a very cheap way to get an Alt/AZ (a Dob would be a great example) to work as an EQ and therefore improve the tracking for DSO imaging?

The GOTO might think some objects are below the horizon, but you can persist to get it to point to those.

Robin

[Zakalwe]

An EQ mount is nothing more than an Alt-az mount that's been tilted.

Some (if not all) Celestron and Skywatcher handsets allow you to tell the mount that it has been mounted on a wedge and to act in an EQ mode.

[Viewmaster]

Two points.....

If the Merlin thought it was at the north pole it would expect to have 2 stars for alignment as seen from the pole

and not from the UK as you would see them.

The tracking accuracy of these Skywatcher AZ mounts may not be accurate enough for any long exposures

for DSO work.

I use the Skywatcher synscan AZ mount, similar to yours and there are no accurate worm and gears,

just a stepper motor driving a large gear for Alt and Az. 

There is backlash in this arrangement which may show itself when trying to image over a period.

[Joseki]

Could this be a very cheap way to get an Alt/AZ (a Dob would be a great example) to work as an EQ and therefore improve the tracking for DSO imaging?

That's what equatorial platforms do.  

http://www.equatorial-platforms-uk.co.uk/

e.g.

http://www.equatorialplatforms.com/del.shtml

[ronin]

Quite a few Alt/Az mounts have an EQ option. You have the tell the system that it is in an EQ configuration.

If you use a wedge then these tend to be costly, as in as much or more then an EQ mount. A good wedge is often £200-300 you may as well buy an EQ5.

As to a dobsonian, the wedge has to be big enough to fit the base of the scope and a dobsonian base is big, if we say base = 2x scope aperture then you need a 16" wide wedge for a 200P, which I guess would cost £800-1000, probably have to be custom made. That then puts a manual dobsonian at some ungodly angle (sort of leaning back at 50+ degrees), and you have to put the wedge in something - a very solid even if short pier/base - add in another few hundred pounds for that, and if it is still manual either buy a goto dobsonian or a custom goto system - not going to even guess at the cost of that.

As most of these tend to add height then the eyepiece may be too high to be used on many occasions.

One vary simple aspect is:- Wedges have been around for a long time to convert Alt/Az to EQ, easily 15 years, if it were feasible, mechanically and monetarily, it would likely have been done many years ago.

[DrRobin]

Two points.....

If the Merlin thought it was at the north pole it would expect to have 2 stars for alignment as seen from the pole

and not from the UK as you would see them.

The position of the two stars visible from the pole would be in the same place at my 55N with the mount on a wedge.  The star is so distant from the location that the angular difference from the few thousand mile difference in position wouldn't be significant.

My Merlin mount tracks well enough in Alt/AZ, it has encoders so I don't see why it wouldn't track in EQ to the same level of accuracy?  Sure it isn't going to be as good, but with guiding why not?

That's what equatorial platforms do.  

http://www.equatorial-platforms-uk.co.uk/

e.g.

http://www.equatorialplatforms.com/del.shtml

Sure, but if you already have a Alt/AZ (or Dob) with GOTO why but a [expensive) tracking platform?

Quite a few Alt/Az mounts have an EQ option. You have the tell the system that it is in an EQ configuration.

If you use a wedge then these tend to be costly, as in as much or more then an EQ mount. A good wedge is often £200-300 you may as well buy an EQ5.

As to a dobsonian, the wedge has to be big enough to fit the base of the scope and a dobsonian base is big, if we say base = 2x scope aperture then you need a 16" wide wedge for a 200P, which I guess would cost £800-1000, probably have to be custom made. That then puts a manual dobsonian at some ungodly angle (sort of leaning back at 50+ degrees), and you have to put the wedge in something - a very solid even if short pier/base - add in another few hundred pounds for that, and if it is still manual either buy a goto dobsonian or a custom goto system - not going to even guess at the cost of that.

As most of these tend to add height then the eyepiece may be too high to be used on many occasions.

One vary simple aspect is:- Wedges have been around for a long time to convert Alt/Az to EQ, easily 15 years, if it were feasible, mechanically and monetarily, it would likely have been done many years ago.

I am sure I could knock up a chip board/plywood wedge base for a Dob for less than say £50.  As I don't have a Dob, I won't be giving it a try, but it is an interesting option for all of those GOTO Dobs out there.  I have just bought an iOpton mount and might give that a try, I reckon I could make a small wedge for it fairly easily, after all at my Latitude, I only need it to go over at 35 degrees.

As Zakalwe points out Celestron controllers are dual mode, they would have to be for the CPC series to function and I am willing to bet all they do is use a Latitude offset to change between Alt/AZ and EQ.

It is just food for thought.....

Robin

[Viewmaster]

The position of the two stars visible from the pole would be in the same place at my 55N with the mount on a wedge.  The star is so distant from the location that the angular difference from the few thousand mile difference in position wouldn't be significant.

That's very true, but the Altitude of stars is 52 degrees (too far north) in error when you enter them into Merlin in UK

as compared with what  Merlin expects them to be if at the pole.

As you travel north so all the stars sink down to the south, the Celestial Equator

 eventually finishing up on the horizon at both poles !

[Viewmaster]

OK I withdraw my analysis.....it's wrong

[Psychobilly]

As Zakalwe points out Celestron controllers are dual mode, they would have to be for the CPC series to function and I am willing to bet all they do is use a Latitude offset to change between Alt/AZ and EQ.

It is just food for thought.....

Robin

In alt/az mode the scope needs to move both axes simultaneously to track the star as it  traverses an arc across the sky..   However  in EQ mode only the  the az axis  - which becomes RA needs to be driven although guiding corrections can be applied to both ...

Peter....

[sgazer]

a while back I put EQ firmware on a Celestron SLT handset and made a wedge for the mount. It worked in EQ mode, although tracking wasn't brilliant, it was better than ALT/AZ mode (only 1 axis to move).