Looking for advice on new scope for visual and eaa

[engreric]

Hi everyone, I hope I'm asking this in the right place, this is my first post =)

Basically my current setup is an omni xlt 120.

I've done a lot of work on the cg4 mount including my own drive motors using eqmod and astroeq. I used large steppers and really went overkill to ensure I had good repeatable accuracy.

My main usage is visual on planets and EAA for cutting through the light pollution and for doing the monthly outreach by the beach in southern california where I live. I've been using the AVS DSO and love the fact that I can get near realtime dsos in my backyard in the city.

Although everything is pretty nice for me and I get a lot of usage out of this, I wanted to upgrade the ota for a few reasons.

I'd like to increase the FOV I get with my camera (I'm pretty much maxed out with a lot of focal reduction right now and it's still a little small), and I'd also like to cut out the CA.

Now my limitation is the CG4 mount, I don't want to drop money on a better mount and lose all the work I've put in to the CG4 with the motor modifcations. Currently the mount is claimed to do 20lbs but I feel the omni xlt 120mm is already pushing it at 12.5lbs, so I feel like I would gain by going smaller.

 

My idea at the moment is:

ES102ED Carbon Fiber Triplet APO

- Shorter FL gives me a big improvement on my current FOV with the DSO camera

- F7 instead of F8.33 so I get a little faster imaging (especially with a reducer)

- 7lbs instead of 12.5lbs which should improve the sturdiness of my CG4 mount and make it easier to use (less likely to hit the mount and more convenient from a size perspective)

- The only Draw Back of the 102mm instead of the 120mm is the aperture. But, I feel like the planets will still look good which is the main visual usage, plus no CA! And DSOs visually look terrible from my house anyways so the DSO camera should make up for the loss of aperature and give me a better FOV.

 

My other 2 options I'm thinking of are the

SW120ED Pro Doublet APO

ES120ED Carbon Fiber Triplet APO

Both of these bring the weight up to about 15lbs which I think is really pushing the CG4 mount, but I would hate to waste my money on the 102mm and wish I had bought the 120mm. Also, both of these scopes would only be a mild improvement on the FOV from my current setup. I could go this route anyways but It would be a very long time before I upgrade my mount.

 

I know that the real cost savings is in a larger reflector, but... I think I would have to go with an 8" astrograph like the orion in order to substantially beat the 120mm I have right now on FOV and light gathering ability. But again, I don't think the CG4 will support the 8" very well...

 

What do you guys think???

Thanks,

Eric

[Peter Drew]

Hello Eric, welcome to this forum.  You describe the usual dilemma, how to do different things with just one telescope without too much of the inevitable compromise. My advice, which of course what I would do rather than what might suit you, is to consider a 8" SCT OTA. It would have better light grasp  and better planetary potential than your alternatives, light enough and no CA. With a F3.3 reducer it would perform very well for EAA on most DSO's and your wider field AP could be covered with a photographic lens. 

[Timebandit]

Hi Eric and welcome to SGL. If it's purely for visual then a large reflector is the way to go. As the light gathering ability is stepped up making a considerable difference in the ability to magnify the target(under suitable atmospheric conditions). Also an increase in reflector aperture compared to refractor aperture on a like for like basis is mostly always cheaper, therefore a lot more bang for your buck with a reflector. scopes which seem to get good reviews are the skywatcher 200 if you are looking for something in the 8" range at a reasonable cost. If you wish a bit more quality with a high grade mirror then have a look at the Orion optics uk vx 8 with a 1/10pv good scope and quality mirror. I am not sure what the weight rating on your mount is. But remember it is not just the weight but the size of the scope that can upset the balance issue in regards the mount set up. Also a large area newt can be effected by the wind conditions as can catch gusts and upset balance and stability.

If you are going to upgrade then upgrade in a reasonable fashion or you will be disappointed and regret your decision IMO. So if a refractor is on your wanted list the a 120ed apo is a very good scope . I have a SW equinox 120ed apo and it is a great scope . So I would go for a 120 refractor without considering a smaller aperture. A good aperture for planetary and DSO and the quality of the sw 120ed apo is great. Some of the chaps on here have even put them in the same sort of ball park as the Taks which is an indication of quality ,but at a lot cheaper price. I have mine mounted on and AZ4 and this mount handles the weight and balance fine. 

I hope the above is helpful ? 

[Chris]

Hi and welcome to SGL  

I know the CG4 mount well enough to know that an 8 f/4 or f/5 reflector will be too much for it. A 6" f/5 reflector would be very good for your needs and very cheap though.

I also think Peter Drew's suggestion of a C8 is a very good one. I've had a couple of these (XLT and Edge HD) and they are amazingly light and compact for the aperture. This would probably be the most aperture you could sit on the CG4 I reckon. They give great resolution on the planets without any annoying diffraction spikes like what you get with a reflector. They can be reduced down to a really fast f3.3 which works well with small chips for EAA, or f/6.3 for larger chips, or even f/2 (for the brave and technically minded) with the hyperstar system if you get a hyperstar ready C8. The only drawback is they are dew magnets so a dew shield is a must, heated would be better in damp conditions.    

It does sound like you would benefit from two optics, one for planetary and one for widefield. A lens or a small apo would work very well to get you more FOV. Having said this going back to a 6" f/5 reflector idea, this would give you more FOV, no CA, a faster native system, not bad on planets, and would be very cheap! 

[RobertI]

Hi Eric,

I would agree with Peter/Chris that a C8 (or a C6) with an F3.3 (and F6.3) reducer would be a great way to go for EAA and visual planetary. 

For EAA I use a Celestron C8 SCT at either its native FL (for small DSOs such as small planetary nebs) or with a F3.3 or F6.3 reducer (for medium size DSOs such as galaxies, galaxy groups and open clusters). I also have an 72mm F6 refractor which I use with the above reducers for very large DSOs such as nebulae. This combination gives a nice range of focal lengths and fields of view with my Lodestar camera.

I do find the dewing of the SCT and mirror flop a slight problem in the SCT so more recently I have been using a RC6 (which I picked up cheap) which is very nice indeed as it has a crayford focusser and open tube, so no dewing, fast cool down etc. The down side is that it does not have the amazing range of focus of the SCT and so extension tubes are required, so only really suitable as a dedicated EAA scope, not for swapping between EAA and visual. But I would be quite happy with the C8 for EAA if I did not have the RC6.

Rob

 

[engreric]

Thanks, you guys are making a lot of sense to me!

For the cost of an es120ed triplet carbon fiber I can get a C8 SCT for most visual work and EAA outreach, and an at72ED for really large fov (also great for the small camping trips where I don't want tracking and all the associated gear). In fact, those 2 still come in cheaper and I might even be able to eventually get a hyperstar for the C8.

 The C8 would be about the same weight I have on the CG4 right now, maybe a little heavier but much shorter so it should balance better on the CG4. Thanks for the heads up on dew protection.

 

So if I may use your wisdom and ask 2 more questions:

- Any 8 SCTs you would highly recommend for my CG4 mount?  I'm looking for the lightest, and that would allow a hyperstar in the future.

 

- My other question is that I wouldn't mind upgrading my mount, but I don't want to lose out on my diy motor drives and eqmod setup. I've been looking for a solid CG5 or similar mount head that would be compatible with my CG4 tripod and would be manual controls only so that I can add my drive system, and would hold more weight than the CG4/EQ3/2 Mount Head.

I've looked and have done some google searches, but I haven't found anything that is reasonable and fits the bill. Any suggestions on where to look?

Thanks everyone!

 

[Peter Drew]

Eric.

 

The C8 is the lightest SCT and as far as I know the Celestron range has Hyperstar potential.  

[Waldemar]

As Peter just said: the whole Celestron range has HyperStar potential, but be warned:  it is not as easy done as said.  A hyperStar needs a super collimated scope and is very critical in backfocus. I owned a C-11 with a hyperStar, but never got it working properly.
A lot of spheric abberration (if very well collimated only a 25 mm flat imaging circle... APS-c needs 27). Focussing is VERY critical because of the steep light cone. At a point I started doubting my C-11, got frustrated and sold the whole set up. Maybe Murphy ( atronomer's patron)  was on it... 

Waldemar