Guidescope Suitability Calculator

[FLO]

Years ago we built our own collection of astronomy tools and calculators so we could more easily answer questions and advise customers. In 2014 we made it available to all as the Astronomy Tools website. 

In 2015 we added a CCD suitability Calculator (was a bit controversial but has proven popular).

We are now working on a Guidescope Suitability Calculator to help you assess imager / guider combinations. 

This new calculator is a work in progress so we will be grateful if you would please kick it's tyres then let us know how it might be improved. 

In particular, what is considered a good ratio these days?  We are thinking anywhere between 1:1 and 1:4 will work well but with improved software even up to 1:10 can produce good results? 

We will be grateful for your feedback  

Steve & the FLO team

[souls33k3r]

That's a really good addition. I look forward using this

[FLO]

Currently there is no explanatory text, we will add that when enough people have kicked it's tyres  

[souls33k3r]

2 minutes ago, FLO said:

Currently there is no explanatory text, we will add that when enough people have kicked it's tyres  

Yes, text would most certainly help. Or maybe some sort of an indicator (Traffic light system) or even better a legend to suggest what the numbers mean. 

[tooth_dr]

Skywatcher finderscope as guider?

[souls33k3r]

3 minutes ago, tooth_dr said:

Skywatcher finderscope as guider?

I guess you missed the memo mate

 

[Demonperformer]

My result is 1:1.17

Sorry, got that wrong - it's 1:0.99.

Edited April 16, 2018 by Demonperformer

[pipnina]

Does only pixel scale matter for guidescopes, or is a guidescope of certain size relative to main telescope aperture also required?

[tooth_dr]

8 minutes ago, souls33k3r said:

I guess you missed the memo mate

 

No no I'm using one, I just cant see it on the drop down list

[souls33k3r]

1:10.8 for me. Been using this with my SCT with 3 min exposures and no issues. Well when i say no issues, that's to the naked eye of course

[scitmon]

7 minutes ago, tooth_dr said:

No no I'm using one, I just cant see it on the drop down list

I see it as "Sky-Watcher 9x50 Finder".

[tooth_dr]

7 minutes ago, scitmon said:

I see it as "Sky-Watcher 9x50 Finder".

Ooops, carry on!  (Cheers )

[geordie85]

Mine says 1:0.33

Not sure what it means but guiding always seems fine in real world action

[Jessun]

Tricky one, since guiding traditionally relied on a human turning little wheels to keep a star in the cross hairs. These days with various software calculating centroids to a fraction of a pixel it's perhaps a different story.

Any too precise theoretical calculations might perhaps tempt you to chase the seeing rather than stay put and guide on an average position - which is something that software can do for you over a vast range of scope 'ratios'.

 

[Ouroboros]

Great idea. I'd love to know what ratio is 'good enough' too. 

Mine is 1:4.6   I get guiding of 1" RMS or better as long a s there's no wind. That seems to be just about acceptable for my set up on most frames. I did once try testing the guiding by putting the guide camera into the main scope just to see what was the best I could get. That improved guiding by about a factor of 2.  So I could gain a bit by using a longer guide scope.  Trouble is I'm using a Lodestar X2 guide scope, which has 8um pixels in a 9x50 finder scope. 

Just a note on the software interface. On iPad I can't see all of the calculated numbers like resolution. So for example I can see the resolution is 2 point something but not what the two digits are after the decimal point. 

Heres a pic. 

 

 

Edited April 16, 2018 by Ouroboros

[James]

If it helps I'm easily guiding (famous last words ) at a ratio of 1:4.75 - the resolution of my imaging camera is 1.43" per pixel, the guide camera is at 6.77", that's on an HEQ5 Pro.

I don't feel brave enough (nor have enough clear nights) to see just how far I could push that ratio

James

 

[Stub Mandrel]

Not hugely important, but the 130P-DS isn't listed and  '0.9' is missing from the barlow reducer list so i can't get my exact setup (130P-DS with 0.9 CC)

130P with no reducer is close enough, but adding those values makes it into a more useful general porpoise calculator

[Anne S]

I could have done with this earlier in the year when I was using a Sx guidehead to guide with giving me a ridiculous image to guider scale! Now I use my new Superstar and I get 1:2.6, though I’m having to use a 0.8 reducer when it’s actually a Planostar 0.79.

Anne

[bottletopburly]

ratio of 1:5.05 is that good ? +1 for a traffic light ? on the result figure 

Edited May 24, 2018 by bottletopburly

[michaelmorris]

Looks great. ?

[Shibby]

I like the tool. FYI, I have a ratio of 1:5.1 and have no problems guiding.

[RayD]

Depending on my main/guide scope/camera combination, I have a ratio of anything between 1:1.37 and 1:5.43 and I don't seem to struggle with guiding or, more accurately, poor images related to guiding as a result of the higher figure. 

There has been a couple of interesting posts on CN about this, and the generally agreed consensus appeared to be a maximum figure of 1:10, with several people noting successful guiding at around this, but with a target figure of 1:4.  However, I think much also depends on your mount and software, and the ability to smooth out corrections etc.

From my images I would say 1:5 is absolutely fine, with higher figures increasingly perhaps needing a little more care and attention in other areas.

[iapa]

Celestron C8, ASI-1600, Startravel 80, Touptek mono

1:5.01 without .63 reducer, 1:3.16 with

This also matches with my spread sheet.

+1 for traffic light

Removing the full stop after the ratio would make it cleared

[Skipper Billy]

This is what the calculator is giving me - looks like I need a shorter guide-scope or bigger pixels !! Having said that I am VERY happy with my guiding ~0.4" Total RMS and nice tight round stars!

I would agree that a simple traffic light system for bad - borderline - good would be an excellent addition.

[Stub Mandrel]

33 minutes ago, Skipper Billy said:

This is what the calculator is giving me - looks like I need a shorter guide-scope or bigger pixels !! Having said that I am VERY happy with my guiding ~0.4" Total RMS and nice tight round stars!

Ignore it, no point trying to do better than that!

I used to get 0.6 and results were spot on.

New setup and now struggling to get these levels, I've just written out all of my old settings to copy across.

(Edit) Hopefully I've found it - backlash compensation was switched off, also minor differences that probably wouldn't cause issues, but I've changed them to the 'known good' values anyway.

Edited January 23, 2020 by Stub Mandrel