The Right Mount

[Genehelsel]

Hi All;

I have now been armed with a bit of knowledge for others on this site,  I realize that I need to first consider a mount that achieves something close to 2 arcseconds/pixel.

There are 3 possibilities to consider which are all within my budget. I am hoping that readers who understand the subtle but important differences can provide some guidance.

First is my current equipment and intended purchases: 

Have now: Celestron 8SE, skysync GPS, starsense autoalign, color burst CCD camera, Nikon D5500, Celestron F/6.3 field reducer and flattener

Near term purchases: Stellarvue 90mm APO, Celestron 9.25 EdgeHD, Orion Starshoot autoguider, QHY PoleMaster EQ Mount Polar alignment camera (if needed), ZWO ASI174MC Color CMOS, or Celestron Nightscape color CCD

Given what equipment I have, and what I intend to buy, which of the 3 mounts would be best, or is there something better for under $US1800?

Celestron Advanced VX mount & tripod

Celestron CGEM mount & tripod

Celestron CGEM DX mount & tripod

Thanks for your input,

Gene

 

 

[ollypenrice]

It's the camera-scope that might be best working at about 2 arcsecs per pixel.

This means you need a mount that can deiver an average error of 1 arcsecond (unconnected with pixels) or better. This is not an impossible order (you might get to an average error ov 0.5 arcsecs) but will need an autoguider to accomplish. I wouldn't expect much difference in accuracy between these three mounts but the stiffness and payload will vary. 

There are also the mounts sold as Orion in the USA. We know them as the Skywatcher HEQ5 and NEQ6 in the UK.

Olly

[Ken82]

Personally I'd buy the best mount you can afford so for me it would be the dx . You want to future proof your purchase and as you've probably heard many many times the mount is more important than the scope ! That's becoming a cliche ! 

[RT65CB-SWL]

Hi Olly & Ken,

Apologise in advance for hijacking the thread but I was going to ask the similar question as I have a Vixen GP. My interests are Lunar, Solar & Planetary. Is the GP good enough?

[ollypenrice]

25 minutes ago, Philip R said:

Hi Olly & Ken,

Apologise in advance for hijacking the thread but I was going to ask the similar question as I have a Vixen GP. My interests are Lunar, Solar & Planetary. Is the GP good enough?

Yes. Fast frame imaging involves lots of short subs aligned afterwards, so you can consider the 'autoguiding' to be retrospective and done by the stacking software.

Olly

[gorann]

One thing,

Why do you go for the EdgeHD 9.25? You cannot get a dedicated focal reducer for that one and it is twice the price of an EdgeHD8 (for which you can get a focal reducer). With a scope of that focal length you really want the option of a focal reducer for AP. The difference in light gathering power between 8 and 9.25 " is trivial so I suggest you spend the difference on the best mount you can afford.

[RT65CB-SWL]

1 hour ago, ollypenrice said:

Yes. Fast frame imaging involves lots of short subs aligned afterwards, so you can consider the 'autoguiding' to be retrospective and done by the stacking software.

Olly

Thank you.

[Genehelsel]

3 hours ago, ollypenrice said:

Yes. Fast frame imaging involves lots of short subs aligned afterwards, so you can consider the 'autoguiding' to be retrospective and done by the stacking software.

Olly

 

1 hour ago, gorann said:

One thing,

Why do you go for the EdgeHD 9.25? You cannot get a dedicated focal reducer for that one and it is twice the price of an EdgeHD8 (for which you can get a focal reducer). With a scope of that focal length you really want the option of a focal reducer for AP. The difference in light gathering power between 8 and 9.25 " is trivial so I suggest you spend the difference on the best mount you can afford.

Excellent point. I guess I feel that getting another 8"SCT even though its an EdgeHD as opposed to 8SE is not much of a step up. However if the  8" EdgeHD is far superior to the 8SE than it makes sense to get it instead of the 9.25 EdgeHD. Besides I already have a f/6.3 reducer flattener for  the 8SE.

So I am going with the cGEM DX

[Waldemar]

8 hours ago, gorann said:

One thing,

. The difference in light gathering power between 8 and 9.25 " is trivial so I suggest you spend the difference on the best mount you can afford.

I am sorry, but trivial?? the light gathering difference is 33%... to me that is not trivial.

[ollypenrice]

44 minutes ago, Waldemar said:

I am sorry, but trivial?? the light gathering difference is 33%... to me that is not trivial.

It isn't trivial for visual observing but aperture isn't the big issue for deep sky imaging. For DS imaging the key differences are in focal length, which you may or may not want to be longer, and in the disastrous lack of a focal reducer for the 9.25 Edge. As things stand the C9.25 Edge is treading water until the focal reducer appears. At F7 it would be a tempting scope.

Olly

[gorann]

I also calculated 33% and I assume that it could be discussed if it is trivial or not. Both scopes are f/10 so exposure times will be the same without reducer but with a reducer the 8" would win. The difference in focal length is only 16 % (2032mm vs 2350mm) so you get a little bit closer with the 9.25, but that also means that the mount has to be very good and very well aligned. As often pointed out in other threads here, astrophoto with the long focal lengths of SCTs is very demanding and not really anything to recommend for a beginner. I would suggest that Genehelsel tries this with the 8" SCT he already has to see if he can master it with the new mount.

Before ordering the scope(s), have a look at the review of the Vixen R200SS in this month's Sky at Night Magazine. It was given five stars which does not happen often. That one has a lot of light gathering power (200mm of it, giving an f value of 3.8 with the new PH corrector) compared to the 90 mm APO, so exposure times will be very manageable, and the optics are apparently excellent (Vixen even claims it does not need to be collimated and that seems to be the case according to the review):

http://www.pressreader.com/uk/sky-at-night-magazine/20160121/283046938487156/TextView

[ollypenrice]

5 hours ago, Waldemar said:

Can't delete this box! Sorry

The business of F ratio and aperture is a bit more complicated than it seems. You cannot just say that a focal reducer speeds up capture. It doesn't do so for objects which fit on the chip without the reducer because it does not bring in any new photons. However, this was a mount thread so we shouldn't discuss it here.

Olly

[Scott]

19 minutes ago, ollypenrice said:

The business of F ratio and aperture is a bit more complicated than it seems. You cannot just say that a focal reducer speeds up capture. It doesn't do so for objects which fit on the chip without the reducer because it does not bring in any new photons. However, this was a mount thread so we shouldn't discuss it here.

Olly

@ollypenrice not sure if it was you trying to delete the box but if you click ctrl+right click it'll give the option to delete  HTH

[gorann]

Olly is right, so back to mounts.

The Skywatcher AZ EQ6 has received good reviews and an advantage with that one is that it is belt driven which reduces backlash as I understand it. The quality is probably similar to the Celestron mounts (both Skywatcher and Celestron are own by the Synta Technology Corporation of Taiwan). Here is a review on SGL:

 

In the USA it is sold as Orion Atlas Pro AZ/EQ-G.