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Replacement Refractor

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#1 orlyandico

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Posted 18 August 2014 - 12:02 AM

I currently have an AT90EDT, of which I have no complaints except its massive weight and not-quite-Feathertouch focuser, and an SV80ED (doublet), which has a lot more sins (lots of CA out of focus and even in-focus, a not-so-good focuser, etc).

 

However my skills aren't so great that these scopes don't meet my expectations.  But I have always been curious about "premium" stuff, but have been unwilling to put out the $6000-odd to get an AP130EDF or similar (used).

 

It seems that the least costly "premium" optics is the Lomo 80mm.  These got for $1200 to $1300 give or take.  I can flip my SV80ED and AT90EDT and get the Lomo.

 

Does that make sense?

 

I got the SV80ED as a fancy guide scope, and also as a not-so-good imaging scope that I can put on my Star Adventurer - the AT90EDT is just too darn heavy for the little mount.

 

I mostly image with the AT90EDT - so in theory it's not much better than the Lomo 80mm.  I also have an 8" reflector that I use for imaging (believe it or not, with a Paracorr, that reflector equals the AT90EDT for imaging at my pixel scale).

 

 



#2 Ken Sturrock

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Posted 18 August 2014 - 12:54 AM

No argument from me. I've got a LOMO 80mm taking pictures outside as I type this.

 

As I said in another thread, the only complaint I ever have with the 80mm relates to image scale, but you  well know about that.



#3 orlyandico

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Posted 18 August 2014 - 01:27 AM

Hm.. food for thought.  What sort of flattener are you using?  I have the Televue TRF2008, but the undercut on the barrel causes it to get shifted out of orthogonal with compression-ring focusers.

 

I understand about the image scale, the thing is no refractor is going to give good image scale for galaxies.  What is the weight of the LOMO? do you have the William Optics tube? and is your focuser the Feathertouch or something else?



#4 Ken Sturrock

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Posted 19 August 2014 - 10:16 PM

I have a Stellarvue sv80s with a 2" Feather Touch focuser. I also use a TRF-2008 (on an ST-2000xm) and experience the exact same undercut problem that you describe. I have to hold the telescope, lens down, between my knees and press the camera into the draw tube while tightening the focuser set screws until they feel like they are about to snap. It holds pretty good after that. I despise under-cuts....

 

I couldn't tell you the all-up weight because I'm out of state right now but, when I get back on Friday, I'll weigh it. The Stellarvues have the reputation of being on the heavy side.


Edited by Ken Sturrock, 19 August 2014 - 10:19 PM.


#5 orlyandico

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Posted 19 August 2014 - 11:39 PM

Thanks Ken.  So you have the Feathertouch-equipped version.

 

What is the size of the tube rings you are using? I got the APM in WO tube on the mart, now I'm looking for appropriate tube rings and probably an FT retrofit.

 

I tried your method (scope with lens down) on my SV80ED but the TRF2008 still ends up getting tilted.

 

On the Feathertouch, you're supposed to rotate the compression ring so that one of the set screws is poking out (e.g. behaves as if there is no compression ring). This is for the low-profile 2"-to-1.25" adapter.  I can confirm that using only the poking set screw (with my Paracorr on my FT-equipped newtonian) results in better orthogonality. So in essence you have no compression ring.


Edited by orlyandico, 20 August 2014 - 12:05 AM.


#6 Starhawk

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Posted 20 August 2014 - 09:25 AM

I would suggest looking at a used NP-101, perhaps.

 

-Rich



#7 orlyandico

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Posted 20 August 2014 - 10:26 AM

I already paid for the Lomo.   :D

 

A friend has an NP101 with the Feathertouch pinion, he got it for $2000 but I cannot find such deals!

 

The Lomo is half the price, but I'll probably have to pony up for a Feathertouch retrofit.


Edited by orlyandico, 20 August 2014 - 10:40 AM.


#8 Ken Sturrock

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Posted 23 August 2014 - 11:25 AM

Orlyandico -

 

I have returned home and measured the telescope. The outside diameter of the Stellarvue sv80s is 90mm. It weighs 6.7kg complete with the telescope, TRF-2008 FR, ST-2000XM camera, CFW-8 filter wheel, focus motor, lens cap, rings and Losmandy-style dove tail plate. It's heavy for its size. I do not know if other manufacturers used this size of tube or not.

 

I will try your suggestion of sliding the band inside the focuser and see if that improves the connection between the FR and the focuser. My next camera setup will certainly use a threaded connection. Under-cut barrels and set-screws for a camera are a fool's game.

 

Take care.


Edited by Ken Sturrock, 23 August 2014 - 11:38 AM.


#9 orlyandico

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Posted 23 August 2014 - 12:18 PM

Got a quick query Ken.   According to "the internets" the best reducer/flattener for the Lomo 80/480 is the Borg 7887.  It covers 35mm to the corners and is threaded on both sides.  I already have the TRF2008 however, and aside from the undercut I have no complaints with it. So I wonder if it's worthwhile to look at.

 

BTW that's one heavy 80mm.   :p   Looks like the Star Adventurer won't be able to carry it.  Maybe the William Optics tube weighs less.



#10 WebFoot

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Posted 23 August 2014 - 04:15 PM

A used Takahashi Sky90 would blow the doors off what you're now using, both for visual and (with the flattener) imaging.

 

And you can "increment" your way up from there, to the typical 4" real Apo refractors, to the FSQ106, all the way to the AP130 f/6 Starfire.

 

Mark



#11 orlyandico

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Posted 24 August 2014 - 12:05 AM

Blow the doors off my SV80ED, yes, fully agree.  I am not so sure a Sky90 would "blow the doors" off a Lomo triplet, considering it's a fast doublet (FSQ85 is another story.. I have no doubt that is a superior optic).  In any case, an AP130 (or TEC140..) are indeed on my wish list / long term plan, but not at this time. As I said, I'd like to see what a "premium" optic is like but don't want to spend too much.


Edited by orlyandico, 24 August 2014 - 12:32 AM.


#12 rainycityastro

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Posted 24 August 2014 - 02:20 PM

Got a quick query Ken.   According to "the internets" the best reducer/flattener for the Lomo 80/480 is the Borg 7887.  It covers 35mm to the corners and is threaded on both sides.  I already have the TRF2008 however, and aside from the undercut I have no complaints with it. So I wonder if it's worthwhile to look at

Orly, I have the Borg 7870 which produces perfect stars edge to edge on KAF8300 with the lomo 80/480. I am sure it will work on larger sensors too but I have not tested.

 

The stars with this combo are as tight or even tighter than the FSQ 106ED + reducer. Focus shift is minimal with falling temperatures unlke the Tak which needs refocusing every 10 mins.(or so it seems.


Edited by rainycityastro, 24 August 2014 - 02:23 PM.


#13 Ken Sturrock

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Posted 25 August 2014 - 01:41 PM

I'm glad Rainycity chimed in Orly, as I couldn't begin to tell you. The only FR I've used is the TRF-2008 and I'm going to stick with it, at least on the sv80s, because it generally works and it's paid for.

 

Also - I took a look, as you suggested, at my Feather Touch focuser draw tube. The focuser on my sv80s *does not* have a metal strip under the set screws. The same focuser (2" Crayford) on a newer sv102t *does* have the metal strip. I think I"m going to have to just tightly dig those screws into the TRF barrel and hope for the best.








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