Skylux 70/700 - rings/dovetail?

[kiloran]

I'm looking to put my son's Bresser Skylux 70/700 on a Nexstar 4SE mount. A pretty crazy idea but he loves the scope as it is "his" and wants to continue using it but benefit from GoTo.

The problem is that the mount on the scope is too thin to fit the dovetail on the Nexstar mount. Its a sort of dovetail (trapezoid at the base of a plastic collar which goes around the OTA) and fits the cheaper Celestron GoTo mounts used on the LCM series but not the Nexstar.

What are the options? I couldn't find 70mm telescope rings. Would rubber strips epoxied to scope collar be good enough? Its only a few mm short of mounting up tight. Thinking of using bicycle inner tube.

[Cornelius Varley]

I don't think attaching a 700mm refractor to a mount designed for the celestron 4se is going to work. The longer tube of the refractor is going to hit the base of the mount when elevated. Setting the limits on the mount to reduce the amount of elevation will stop this from happening but is also going to restrict the usability of the mount. The mount has a built in wedge so using that should work.

[kiloran]

Ah, good point, I hadn't thought of that. I'm thinking perhaps the SLT mount might be the better option (it's designed for a 102mm refractor - not quite as long as the Bresser). Will check and see what FLO can do.

[Cosmic Geoff]

It seems you don't have the GoTo mount yet-am I correct? I have seen the SLT and the Discovery mounts offered separately. The latter has clutches so that it can be pushed around without the power - good for a child? It is usually offered with a 6" reflector.

You could perhaps get a complete GoTo outfit with refractor and hope your son can be weaned off the Bresser when he looks through the replacement.

You should be able to buy 70mm tube rings and a dovetail bar. I can't guarantee that the rings will be of the exact internal diameter required. Also I suspect that the total cost may be as much as a Bresser OTA is worth. 

I can't remember what the Bresser dovetail looks like (used to have one) but a bit of DIY with screws or Araldite might pack it out so that a standard dovetail clamp will grip it.

HTH.

[kiloran]

Hi Geoff,

You're correct - we don't have an existing GoTo mount. The 4SE was an overstock bargain from FLO - similar price to the various SLT & Star Discovery bundles offered and so I went for it based on the mount being more versatile/robust.

I see you have the SLT and SE mounts - is the clamp the same on both?

I think packing out the dovetail will work but now I need to check for tube clearance. Its a simple plastic wedge which tightens with a thumbscrew pushing against an indentation in the middle of one side. Mounts to the OTA collar with two screws/pegs which annoyingly don't appear to be removable. 

My dilemma is that ease of use and setup time is important. Having used both GoTo systems Celestron's is so much more flexible than Skywatcher. SkyAlign is simple enough that I think my 7yo could do the alignment on his own. Having said that, if I went for the 6" Sky-Watcher the view might convert him - not least because his favourite colour is red  

 

[Cosmic Geoff]

8 hours ago, kiloran said:

I see you have the SLT and SE mounts - is the clamp the same on both?

No, they're not. Most small telescopes these days mount with a standard size dovetail bar approx 44mm wide, angled on both sides, but the method of clamping varies.  Some go in from one end, as on the SLT, which has two angled clamping faces.  Some go in sideways, as with my Sky-watcher kit. These may have protruding screws that prevent end-loading. The EQ-5 mount from Sky-waycher has a side mount saddle which holds the dovetail bar in place with a screw rather than an angled clamp. These clamp variants have names which I won't give here, to avoid confusion.

Celestron's SE6/8 mount appears to have a sideways entry clamp. I have only used it once as  the OTA is intended to be permanently attached to the mount.  The SE 4/5 mount is not necessarily the same. 

So far as I recall the 70/700 Bresser dovetail was non-standard, with the dovetail squared on one side and a recess for a big nut in the mount.

[kiloran]

Thanks. Going to experiment with packing the dovetail out today. If not, I guess it will be time to return the 4SE and look at the SLT mount options.

[happy-kat]

Could change the dove tail on the bresser to a more standard fitment. 

[kiloran]

Well, Cornelius was right - the tube of the refractor is just too long, even with the tube cradle slid all the way back to the focuser. And that's without a star diagonal installed. Ah well, there goes my plan of sneaking a "daddy telescope" into our kit

 

[happy-kat]

There is a member who used an ed80 on a 8SE mount. @paralaxx I think that was the telescope.