10 replies to this topic

[City Kid]

I have a Moonlite focuser on my 12.5" reflector and it just doesn't seem to be up to the task of handling the heavy load of the Binotrons. The drawtube sags from the weight. Does anyone else with this combo have the same issue? Is it even an issue? What I mean be that is will that sag affect the sharpness of the view? Would a FeatherTouch handle the weight any better or do I just need to accept the fact that anything that heavy will push a focuser to it's limits and beyond?

[Eddgie]

Yes..  I reported this about three weeks ago when I tried using a pair of 22mm Panotics.  The focuser tube deflected so badly on the pinion shaft that it pulled away from the bearings.  Tightening the pinion supports would improve the deflection, but only at the high expense of making the focuser very stiff to turn.

 

I looked at re-orienting the focuser, but because the focuser tube is decentered from the mounting screws, this does not really look possible to me.

 

My ownly solution was to go back to the D21s.    With the D21s it is OK, but I still have to keep a bit of tension on the pinion screws.

 

Should have gonr with a Featerthouch in retrospect, but how could I have known that I would have this problem?  I guess it is one of those things you have to try to know.

 

Not sure what eyepieces you are using, but the only thing I can recommend short of changing the focuser would be to lighten the load as much as possible.

 

I have in fact been considering just moving to a Feathertouch because of this, but I doubt that the tiny bit of true field I would get with the 22mm Panoptics is worth the giant cost.

 

It is always something, eh?

Edited by Eddgie, 24 January 2015 - 03:09 PM.

[Eddgie]

As to the sharpness of the view,  in a way, yes.  Collimation changes when the focuser sags.    Mostly though, it is just aggrevating.

Edited by Eddgie, 24 January 2015 - 03:40 PM.

[City Kid]

I am using the D21's and it still sags quite a bit. I will try adjusting the tension. 

[City Kid]

Ok, I adjusted the tension and it made an improvement. The focuser is a bit stiffer now but not too bad. I can still see the drawtube sag under the weight but not nearly as much. I may try adjusting the tension even further to see if I can eliminate the deflection altogether and still have a smooth moving focuser but for now I'll see how this goes.

[City Kid]

I have in fact been considering just moving to a Feathertouch because of this ...

 

That was my first thought too but are you sure a Feathertouch wouldn't have the same issue? I mean these Binotrons are pretty heavy.

[Eddgie]

The Feathertouch on my 6" Apo seems impervious to deflection. 

 

This has been my experience with Crayfords in the past, and my gut intiution was to put a Feathertough on the dob to start with, but in the interest of saving a few bucks, I went with the Moonligth, and now kind of regret it.  Moonlight does a great job of publishing all their measurements though, and I knew I could get the exact right focuser height to reach power in all three modes with no extension of the OCS required. 

 

The issue with Moonlight (and all Crayfords to some extent) is that the pinion shaft has to carry the weight when it is oriented towards the gravity bottom, and the top bearings are not actually supporting any load.  All of the load is cantelivered from the bottom bearings and the pinion shaft acts as a fulcrum and bears all of the weight, which we know has a huge moment due to the binoviewers and eyepeices being so far out from the tube.

 

I do not know if the Feathertouch would be better on the dob, but on the 6" Apo, it never deflected even a little bit with binoviewers, and it always maintained a smooth motion.

 

Not that the Moonlight is not a good focuser.  It is a good focuser.  It would appear from both of our experiences though, that it is not capable of handling a load with a long moment.

 

My gut intuition was right, and next time (if there is a next time) I will know better and just get a Feathertouch.   For now, I have just increased the tension and accepted that I have to live with the stiffness. 

Edited by Eddgie, 25 January 2015 - 10:37 AM.

[David D.]

I have denk ll's on a 12" SCT with 24 pans and power switch with a feathertouch. It seams as though I could double the weight and still have no sagging issues. Not a bit.   

[bgi]

Motorized Moonlite on my old-school Meade refractor works fine with Denk 27's and not-so-heavy eyepieces.  I haven't tried a really heavy pair.  The heaviest EP pair I use weigh 190 grams each - just a bit lighter than Pan 24's.

 

I did have a problem prior to getting the Denk.  The older style focus motor assembly wasn't pulling the heavy 100 degree eyepieces up reliably.  I sent the focuser in to get the upgraded motor and clutch.  It has been fine since.

[scarubia]

I have a Moonlite focuser on my 12.5" reflector and it just doesn't seem to be up to the task of handling the heavy load of the Binotrons. The drawtube sags from the weight. Does anyone else with this combo have the same issue? Is it even an issue? What I mean be that is will that sag affect the sharpness of the view? Would a FeatherTouch handle the weight any better or do I just need to accept the fact that anything that heavy will push a focuser to it's limits and beyond?

 

A focuser board not designed to carry the added weight can deflect under the weight as well. Especially when racking out to higher mags. 

[Eddgie]

I did go ahead and put on the Feathertouch.

 

I had to put a lot of tension on the Moonlight pinion support to keep the focuser tube in contact with roller bearings, and this made the motion very stiff, and to be honest, there was still a little deflection when the scope was in high power mode (fully racked out).  I could see the collimation change going from mid to high power.

 

Put on the Feathertouch.   I re-collimated (it was all hosed because it kept shifting with the other focuser) and now collimation stays dead on at all three power settings.  The focuser motion so smooth that I can almost spin the knob and coast the inch and a half from low power to mid power when the scope is pointing near zenith.    There is zero play with this focuser. It is rock solid.

 

That being said, the rotation on the Feathertouch does not work well with binoviewers.  Best to get it into position and lock it down.  I complained about it, but don't expect a fix.  Maybe not an issue for the mono-viewer people, but pretty sloppy with the binoviewer.

 

Despite the rotation setup not working, the rest of the focuser is amazing. I regret not going to it sooner.

 

Can't wait to get the new Hyprion barrels without undercuts.  This was another area where I have had issues.    Kept having merge images because of the compression collets on the Binotron not locking up right on the barrel.  Every time I would zoom the eyepieces, they would shift in the collets and I would have merging issues.

 

Dob has been fantastic.  Have had some of my best Juptier views ever after putting on the new focuser.

Edited by Eddgie, 12 May 2015 - 05:55 PM.