22 replies to this topic

[25585]

So easy to use. Sturdy mount as part of the product. Eye at OTA top. Simple & cheap as I like. Choice of  manufacturers & specs. Parts can be replaced or upgraded, modification possible. No chromatic aberration. Entry size is not price prohibitive. 

 

John Dobson is in my Telescope Hall of Fame.

  

[spaceoddity]

Me too! 

[Chaz659]

100%. Have two, looking for a third. LOL. I might have a problem....

[rowdy388]

Point and shoot simplicity plus the ability to go deep. I love them too. 

[George N]

I **might** disagree if -- I could afford a 20-inch APO and the observatory it would need.....  

 

In the meantime -- I'll stay using my Obsession 20 that I've owned since 2004.

[stargazer193857]

Refractors are great for wide angle views. I prefer them mounted at the top of my dob, eyepiece near the main eyepiece.

[Codbear]

Refractors are great for wide angle views. I prefer them mounted at the top of my dob, eyepiece near the main eyepiece.

First question is, how small a refractor do you have at the top of your dob?

 

Second, how do you go about rebalancing the dob? I'm presuming some sort of weight system at the 

base of the dob tube or mirror box?

 

I would love to have my TeleVue NP101is with its almost 5 degree FOV at the top of my dob, but a 10 pound scope on the Upper Tube Assembly would probably require 20-30 lbs of weight at the bottom to balance due to leverage.

[junomike]

First question is, how small a refractor do you have at the top of your dob?

 

Second, how do you go about rebalancing the dob? I'm presuming some sort of weight system at the 

base of the dob tube or mirror box?

 

I would love to have my TeleVue NP101is with its almost 5 degree FOV at the top of my dob, but a 10 pound scope on the Upper Tube Assembly would probably require 20-30 lbs of weight at the bottom to balance due to leverage.

I use a 4" F4.5 Achro @ 7lbs mounted in the Finder Shoe

I require about 7lbs of CW (Welders magnets) which need to change depending on Dob position.

 

IME a 10lb OTA is pushing things however nothing is impossible with some creativity

[StarCurious]

I use a 4" F4.5 Achro @ 7lbs mounted in the Finder Shoe

I require about 7lbs of CW (Welders magnets) which need to change depending on Dob position.

 

IME a 10lb OTA is pushing things however nothing is impossible with some creativity

I have a Starblast 80mm achro (focal length 350mm) with a vixen dovetail without rings. Is there an adapter/converter than connects the vixen dovetail on this to a standard finder bracket?

 

The 80mm achro has a standard finder bracket onto which I can then connect the original 8x50 RACI finder.

[junomike]

I have a Starblast 80mm achro (focal length 350mm) with a vixen dovetail without rings. Is there an adapter/converter than connects the vixen dovetail on this to a standard finder bracket?

 

The 80mm achro has a standard finder bracket onto which I can then connect the original 8x50 RACI finder.

I removed the Vixen Dovetail and added a Svbony Finder Shoe.

[StarCurious]

Thanks, Mike.

 

This would be fun.  4.44° TFOV for the 80mm with 32mm Omni Plossl.  Add a 1.25" filter.  Observe ALL of the Veil, North America or California, and inspect portions with the Z10.

 

Only uncertainty is the width of the SvBony Dovetail Board Width (bottom): 32mm. An 8x50 finder scope trapezium base width is <30mm.  Worst case is replace the stock finder bracket on the Z10.  I may still proceed.

[stargazer193857]

First question is, how small a refractor do you have at the top of your dob?

Second, how do you go about rebalancing the dob? I'm presuming some sort of weight system at the
base of the dob tube or mirror box?

I would love to have my TeleVue NP101is with its almost 5 degree FOV at the top of my dob, but a 10 pound scope on the Upper Tube Assembly would probably require 20-30 lbs of weight at the bottom to balance due to leverage.

30-50mm f4-5 Plossl eyepiece. 68 deg would be better, but that is more weight and needs a bigger prism.

[Jon Isaacs]

Refractors are great for wide angle views. I prefer them mounted at the top of my dob, eyepiece near the main eyepiece.

 

I like having a 50mm RACI finder with a quality wide field eyepiece near the main eyepiece.  It's surprisingly good as RFT.  You give up a little magnification, a little exit pupil, get some nice wide fields.  With the 16mm Type 5 Nagler, it does about 6.2 degree at 12.5 x with a 4mm exit pupil. The Veil, the North American,  the big nebula are pretty special.

 

 

I prefer having my refractors separate from the Dob, I look at different things with the two scopes.  It doesn't make sense to be to tie the refractor down by mounting it to a large, cumbersome scope.  

 

The NP-101 with a diagonal weighs about 11 pounds. You would need some sort of rings or alignment arrangement.  Figure 15 pounds with the eyepiece. With a classic Dob, the center of gravity is low, the ratio between top and bottom is greater than 5:1.  That would be a minimum of 75 pounds of counterweights.  The upper cage isn't built for such weight.

 

If one want to add a 4 inch refractor, an 102 mm F/5 achromat with a TSFLAT2 mounted on the opposite side trunnion solves the balance problems and stays out of the way.. With the TSFLAT2, eyepieces like the 31mm Nagler will be quite sharp at the edge, the thing really works.

 

Jon

[stargazer193857]

I like 80mm f5 refractors too, separate from the scope. Maybe a 50mm needs to be transferable to a tripod. When I'm looking through a dob, I like being able to go back and forth.

[StarCurious]

30-50mm f4-5 Plossl eyepiece. 68 deg would be better, but that is more weight and needs a bigger prism.

Weight was a consideration.  That's why Omni plossl. I can put the ES 68 24mm, but it will yield the same TFOV with a smaller exit pupil.

 

I will use a 12.5mm reticle eyepiece to turn this into a larger aperture finder.  I won't piggy back mount my stock RACI 8x50 finder.  The ES 68 24, Omni 50 32, SvBony 40 40mm all yield practically the same TFOV with different exit pupils. The 80mm collects 256% more light than the 50mm.

 

This was the OTA:

 

https://www.telescop...pe/p/102792.uts

 

I added a WiFi adapter to the AutoTracker mount, and it became SynScan GOTO Mini-Dob, with SkySafari 6 Pro, now a grab and go setup with Meade 114mm F/4 Reflector. No hand controller.  

Edited by StarCurious, 23 January 2021 - 11:38 PM.

[25585]

First question is, how small a refractor do you have at the top of your dob?

 

Second, how do you go about rebalancing the dob? I'm presuming some sort of weight system at the 

base of the dob tube or mirror box?

 

I would love to have my TeleVue NP101is with its almost 5 degree FOV at the top of my dob, but a 10 pound scope on the Upper Tube Assembly would probably require 20-30 lbs of weight at the bottom to balance due to leverage.

I have an 80mm TS finder scope. Its light, is RACI, helical focuser & takes 1.25" eyepieces. I can see a great deal more with it than with a 50mm finder.

[Jon Isaacs]

I have an 80mm TS finder scope. Its light, is RACI, helical focuser & takes 1.25" eyepieces. I can see a great deal more with it than with a 50mm finder.

 

I have 70 and 80mm finders but I prefer the wider field of a 50mm, I see plenty of stars in the 50mm and the wider field lets me span great distances and use stars farther apart for pointing. 

 

The objects I am generally looking for are not visible in any finder...

 

Jon

[George N]

.....

I would love to have my TeleVue NP101is with its almost 5 degree FOV at the top of my dob, but a 10 pound scope on the Upper Tube Assembly would probably require 20-30 lbs of weight at the bottom to balance due to leverage.

I've observed a few times with a guy with an Obsession 25 F/5 with a TV-101 that mounts about half-way up the tube using triangle shaped 'base' that bolts to two of the truss tubes. He also has a massive 'tail' shelf on the back of the scope for a laptop, etc. Somehow - he got it not only balanced, but the StellarCat has no problems driving it. Nevertheless he admits that he's pushing the StellarCat 'to the edge' -- and one time it did eat up part of his ground board requiring a replacement.

 

If you order a Dob from NMT Ryan will provide up to about an 80mm attached to the UTA - with proper balance of course.

 

One friend for a while had his Explore Scientific 6" Levy Comet Hunter MacNewt on the mirror box of his 28" F/3.8 SDM 'classic' Dob. It was on a little mount of some type that allowed it to be easily collimated with the main scope. However -- he found he didn't use the 6" that much and was concerned that it was stressing his StellarCat drive - so after a year or two he removed it.

[rowdy388]

The only thing better than a dob is a small piggyback refractor sitting on top of one with the eyepieces next to each other. 

I use Jon's 70mm pieced together design using F/4.5 Carton optics on my 12.5" New Moon. That works especially well because

it is exceptionally light for the aperture. I don't like having to set up multiple scopes and work back and forth when they can be 

used together. I do like looking at the same targets in both scopes and the refractor becomes a super finder that can also switch out

eyepieces.

 

My Z12 used to have an 80mm ATEDT piggybacked but now I mostly use the New Moon scope so now the AstroTech usually sits on

a TV Panoramic mount and ash tripod.  The Z8 with piggyback ST80 is still my travel/outreach scope and is a lot of fun. For counterbalance

I use the Harbor Freight 7 pound magnet covered with tape to prevent scratches plus weights screwed onto the very bottom. I use the 

screw holes left after removing the mirror locking screws. Those screws are worse than useless anyway because they are 60 degrees

offset from the collimation screws. Tightening them down only makes collimation more difficult. Better to just replace the springs.

Edited by rowdy388, 24 January 2021 - 03:05 PM.

[GUS.K]

25585, on 24 Jan 2021 - 03:37 AM, said:

So easy to use. Sturdy mount as part of the product. Eye at OTA top. Simple &amp; cheap as I like. Choice of manufacturers &amp; specs. Parts can be replaced or upgraded, modification possible. No chromatic aberration. Entry size is not price prohibitive.

John Dobson is in my Telescope Hall of Fame.

Same here, rebuilt my EQ mounted reflector as a dob in the mid 80's and have been hooked ever since, for me, the best way to see the universe.

[MitchAlsup]

Having grwon up with equitorially mounted telescopes, and gotten my head around using the celestrial coordinte system, and using these kinds of mounts for 40 years before building my first DOB::

 

I completely agree!

 

If you are not astroimaging, Alt/As is the way to go !!

[vdog]

Big aperture for a (relatively) small price. What's not to like?  

 

If I could even get a 16" APO, it would probably cost as much as my house. 

[stargazer193857]

Big aperture for a (relatively) small price. What's not to like?

If I could even get a 16" APO, it would probably cost as much as my house.

You must have an expensive house. I think that was a humble brag.