mini guiding scopes numpty question

[powerlord]

Hi chaps,

I got myself one of these mini guide scopes - a 32mm svbony SV165 -pretty much the same as the ZWO ones but 1/2 the price.

optically nice and bright and works nicely with my new ASI224 (I know..not ideal for a guide camera but for now it's what I've got).

Question is - these mini guide scopes, just like the ZWO come with a mount which is not adjustable/alignable. Is this  just how guiding works ? I mean obviously fitted on an OTA it doesn't align to the viewfinder. But I suppose all the guider needs is some stars to plate solve - and if it keeps THEM steady, then whatever the actual OTA is pointing at  (moon and planets accepted) will also be kept steady ?

Otherwise it seems kinda dumb that they come with these mounts if I'm supposed to bin that and source a 30mm adjustable mount (though that seems to me would be a damn site better, as could be used for visual with an eyepiece.

Or have I got the wrong end of the stick here ?

stu

[Skipper Billy]

You have got the right idea.

As long as the guide scope is pointing somewhere close to where the imaging scope is pointing it will work just fine.

The last thing I would do is fit an adjustable guide scope mount - it's a sure way to introduce unwanted flexure.

 

[StevieDvd]

A finderscope is aligned with the main telescope so you can centre the same object in both, and use the wider feld of view of the finder to scan for an object then use the main scope to view.

It's easy to expect the guidescope to work the same, but it only needs to be 'fixed'  in relation to the main scope. You may be imaging a DSO but select a star to guide on (and normally the guide star chosen won't be central in the guidescope anyway. This more sense over time when you select a good star for a guide, which could be in any part of the field of view, of the guide window.

The 'fixed' part is the relationship between the imaging and guide scopes, if the guide star moves then so would the DSO, correcting one also corrects the other. If the guidescope was loose (flexure) that would ruin the relationship between them and screw up the corrections.

 

[michael8554]

On 19/04/2021 at 11:09, powerlord said:

But I suppose all the guider needs is some stars to plate solve

I expect you mean "all the guider needs is some stars to GUIDE on."

Plate solving uses images from the main camera, because that's the camera you want accurately pointed at the target.

Michael

 

[vlaiv]

There is one special case where it is beneficial to have guide scope and imaging scope point in same direction.

This special case should be avoided - so in most cases it should not pose a problem if your guider is not perfectly aligned with the main scope.

It is when either imaging or guiding low down close to horizon. Due to atmospheric influence - and rotation of the earth - apparent positions of the stars change when light is refracted thru a lot of atmosphere.

Effective speed of stars is higher than sidereal when stars are setting and lower than sidereal when stars are rising. If you guide on star that moves at sidereal but image stars that are rising or setting - you'll get trailing. Similarly when imaging regular stars and guiding on setting or rising stars - you'll again get trailing.

This of course is not a problem if you guide on the same star that you image - or when two scopes are aligned.

 

[Dinglem]

@powerlordI used an ASI224 as a guide camera and it worked very well.

[blameTECHIE]

58 minutes ago, michael8554 said:

I expect you mean "all the guider needs is some stars to GUIDE on."

Plate solving uses images from the main camera, because that's the camera you want accurately pointed at the target.

Michael

 

Michael - thank you!

Over the last year I've gone through several different combinations of auto-guider and the "power it on, it'll do the rest for you" (provided you have GPS and know what stars you're aligning to) and I've made a step to some better kit.

This included trying to get a setup for guiding and I hadn't thought about just needing an object to track with instead of the guide scope being perfectly aligned with the main scope - especially the bit about the plate solving being form the main camera, this comment has helped piece it all together for me.

Kev

Edited April 20, 2021 by blameTECHIE
typo

[StevieDvd]

13 hours ago, blameTECHIE said:

Michael - thank you!

Over the last year I've gone through several different combinations of auto-guider and the "power it on, it'll do the rest for you" (provided you have GPS and know what stars you're aligning to) and I've made a step to some better kit.

This included trying to get a setup for guiding and I hadn't thought about just needing an object to track with instead of the guide scope being perfectly aligned with the main scope - especially the bit about the plate solving being form the main camera, this comment has helped piece it all together for me.

Kev

Depending on what software you are using it is normally possible to load an existing image, which is then platesolved, to use to centre your current view - so you can do further images to improve on previous sessions captures. 

 

[michael8554]

Hi Kev

Just so there's absolutely no confusion.

Plate Solving determines where the mount is pointing, that's all, it doesn't Guide the mount.

The separate guidescope and guide camera guides the mount by looking for deviations of the guidestar position, and by sending correction pulses to the mount from the guide softwae, PHD2 for example.

Michael

[blameTECHIE]

That's the bit that I'd not got before and now the penny has dropped I'm looking forward to trying again.