How good does your mount need to be for a particular telescope?

[Jerry Barnes]

 

I shall go to the Practical Astronomy Show in a couple of weeks and may accidently have to buy some new gear (!).  Could I make sensible use of a 1000mm focal length scope on my mount?

Alternatively do you get good results from something like a Skywatcher 200 PDS on something like a EQ6R?

Or to put the question a different way if I know the guiding error in arc seconds and the arc seconds per pixel of my scope and camera what ratio can I push it to?

My camera has a pixel size of 3.8 and astronomy tools calculates 0.78” per pixel at 1000mm focal length which it considers ok for average seeing.  If the guiding error was also 0.78”RMS does that affect the answer?

I’ve found some reference to similar questions elsewhere that would merit some proper study but will take some time to get my head round properly.

[barbulo]

I've been using the 200PDS on my EQ6-R Pro with fairly good guiding results: 0.5-0.7"RMS depending on the day. But 1000mm was too much FL for my cameras, so bought a 130PDS (good quality/price must say).

IMO, 0,78 arcsec/px ratio is oversampling, regardless what Astronomy Tools says. You would like to go above 1,5. 

Guiding performance helps, but there are other factors like optics, filters, seeing, LP or wind that will affect the quality of your images.

[AstroMuni]

1 hour ago, Jerry Barnes said:

Alternatively do you get good results from something like a Skywatcher 200 PDS on something like a EQ6R?

Its all to do with are you getting the best out of your current equipment IMO.

This is how I would go about it - by checking the following:

- Is my mount capable of handling the weight of the scope etc.comfortably

- Can I improve areas like backlash etc. by doing any upgrades to mount OR do I need to change whole mount

- Are there improvements I can make to the scope (eg.focuser, collimation, flattener, Coma corrector)

- Is guidescope of correct size etc.

- Are my cameras suited for the objects that I wish to image

- Will filters help me (UV/IR cut, specialist filters for enhancing nebula etc.)

- Do I need to upgrade my processing software

HTH

[ONIKKINEN]

The Astronomy.tools CCD calculator is hardly helpful with what it considers good sampling rate for a given system. Its best to think of the higher estimate as the better choice than the lower one. For example the higher estimate of 2'' per pixel is perfectly fine for my 8''  scope, but the lower estimate of 0.67'' is without a shadow of a doubt oversampled. I would have to live on a mountaintop, or a desert, or better yet a desert mountaintop to be able to sample at this rate and not oversample. Guiding would also have to be epic for this to work. By binning 2x2 you get a very reasonable resolution with your scope and camera combo.

But for the mount question i think the EQ6 would do just fine with the 200PDS. I have an AZEQ6 and have no major complaints with my 8'' F4.5 newt. It can be a little bit windy and will work just fine, but if there are sudden strong gusts it can still be problematic, but that's just how it is with long scopes, especially newtonians. So far i have gotten 0.7'' and 0.65'' RMS guiding in mild wind and less than great seeing with mine guided by a 60mm F4 guidescope.

[Jerry Barnes]

Thats an interesting thread quoted above, thanks for that ONIKKINEN.  It will take some study...

[Stu Wilson]

I used a 200pds on neq6pro for a few years. Great results.

Upgraded the mount to belt drives. Guiding 100 percent better.

Upgraded ota to ts optics 8 inch f4 astrograph and works great.

[ollypenrice]

On 09/03/2022 at 13:10, Jerry Barnes said:

 

My camera has a pixel size of 3.8 and astronomy tools calculates 0.78” per pixel at 1000mm focal length which it considers ok for average seeing. 

 

If this is the case then Astronomy Tools is bonkers. 

On 09/03/2022 at 16:25, ONIKKINEN said:

For example the higher estimate of 2'' per pixel is perfectly fine for my 8''  scope, but the lower estimate of 0.67'' is without a shadow of a doubt oversampled. I would have to live on a mountaintop, or a desert, or better yet a desert mountaintop 

 

True.  I do live on a mountain top and, though it's not a desert, it's pretty arrid and I never get anywhere near to resolving at 0.67".  Double it at best.  I've imaged at about this sampling rate with a 14 inch scope (which had the resolution to support it) and with a mount tracking with an RMS of about 0.3 arcsecs. Even so I resampled every image downwards by a large margin. (The camera did not work properly when hardware binned for reasons unknown.)

Olly

[900SL]

Thanks to this thread I found the excellent videos by James Lamb on youtube about resolution etc.