A Proper Amateur Refractor!!

[Rusted]

I used to borrow the "Fairy liquid" for cleaning off mini bits after using the Gunk. [Mini Marcos.]

[John]

2 hours ago, Rusted said:

Patrick Moore's 5" refractor had a Charles Frank mounting.
Recognisable by the spherical housings. It also had a nice, solid pier by the look of it....

 

My secondary school had an 8 1/2 inch Frank newtonian in a dome on the same mount. The very first telescope of any type that I observed with. I was about 12 years old !

 

[John]

2 hours ago, Rusted said:

Nice instruments John.

The T-Rex needs an offset counterbalance by the look of it.  Berry, offset fork style.
You'll need a large clamp which doesn't mar the surface of the mounting cylindrical section.
With a threaded rod, [stud/all-thread] on the opposite side to the telescope, to carry the counterweight.
Work out the weight of the telescope and its offset to calculate the moment required.
Lead is dense and compact.

What about a black, gutter downpipe clamp in PVC?
They are set up to have a sturdy screw fixing to the wall.
Some are about the right size too...

 

Thanks

The joy of the T-Rex is that it is really solid and steady without any need to counterweight the scope. If a counterweight was needed I would have gone for an AZ100 instead. I needed two of Rowan's 3.75 kg counterweights to balance the 130mm F/9.2 when I used the AZ100 but none at all with the T-Rex and that is one of the main appeals of the latter for me - keeps the overall weight of the setup down by 7.5 kg which is very important to me in my observing circumstances.

 

 

[maw lod qan]

With these large refractors, do the lenses get ground where they are convex on both sides?

I cant imagine the difficulty of grinding a lenses on both sides.

[chiltonstar]

...and I thought my 4" f13 was a monster! Clearly after looking at some of these pics of gorgeous big 'fracs, mine is just a babe and has a long way to grow!

Chris

[Rusted]

4 minutes ago, maw lod qan said:

With these large refractors, do the lenses get ground where they are convex on both sides?

I cant imagine the difficulty of grinding a lenses on both sides.

You carry the biconvex lens blank in a matching concave holder packed with a soft cushion.
You work each grade of abrasive both sides of the lens before moving on to the next.
I taped the edges of mine to the holder to avoid having clips or a raised rim on the lens holder.
You can pitch the lens to its holder but it is very messy to clean up afterwards.
In my youth pro optics labs used a low melting point metal holder [boiling water melting point] and varnish as an adhesive.

[RT65CB-SWL]

Mine is more like 'pea-shooter' for comparison. 

[LukeSkywatcher]

I love this scope. Do you use a shroud?. Is stray light an issue?.

[Rusted]

10 hours ago, LukeSkywatcher said:

I love this scope. Do you use a shroud?. Is stray light an issue?.

Thanks for your interest.

It was a desperate attempt to make a very long scope light and manageable.

The beam was made up of heavy channel sections [alu.] holding builder's straight edges.

Unfortunately the design was almost completely unusable on an equatorial mounting.
The mass of the full thickness, 10" f/8 mirror was seriously offset from the twinned beam.
So it applied heavy torque to the beam when not physically "upright."
i.e. Not pointing to the Pole as in the posed picture.

The mirror cell twisted visibly on the beam as soon as it was leaned to either side.
It was awful to handle because the mirror cell always wanted to be hanging downwards.
So I had to give up despite my best efforts to stiffen the design with extra brackets.

I have tried several new tube designs but each lacked stiffness.
Or were far too bulky and too heavy. I had no interest in mounting it as an altazimuth.

The image shows some rough mock-ups of potential new tubes for scale.
I have a steel duct 30cm [12"] in diameter x 6'6" [2m] long but the bulk and weight makes it too unwieldy.
Yet ironically it weighs much the same as all the other materials I tried. Over 20lbs for the bare tube.

I laminated the cardboard tube from thinner and shorter concrete piling forms.
It was heavy and hopelessly flexible. Another dead end.

The completed OTA has to fit up between the rafters of my shed as it stands on its mirror cell.
It was just too much of a struggle to make it worth the effort.

Ideally such a long OTA needs to be housed in a dome or roll-off.
So it never needs carrying in and out by a [fit] septuagenarian.
 

[Roy Challen]

On 08/11/2020 at 13:13, RodAstro said:

 

Yep I love the Zeiss Orthos I have the full set and two of each for the bino head and a 40mm and a 63mm Zeiss huygens that is fantastic. 

I had a few CZJ orthos a little while back, and have to say that they were the best eyepieces I've used in any telescope. And I still have a 25mm Zeiss Huygens, which is a fantastic ep in my f/16 (one of Dave's old scopes!).

[RodAstro]

Hi Roy

Does your F16 have a Carton lens I think that's what Skylight use?

I have a 76mm F16 with a Carton lens it is superb, just in the middle of restoring the tube then fitting on a Unitron 145 head. I have a set of T circle ortho eyepieces for it but I don't think they will get much use with the CZJ orthos about.

People don't realise how good and bright a well made Huygens is, all comes down to the least amount of glass interrupting the beam. Very rare items since Tasco gave them such a bad name.

Rod

[Roy Challen]

Hi Rod,

As far as I'm aware, it's a Kenko lens. The scope itself is based on a Prinz 660 which is also 76mm aperture.

 

[F15Rules]

56 minutes ago, Roy Challen said:

Hi Rod,

As far as I'm aware, it's a Kenko lens. The scope itself is based on a Prinz 660 which is also 76mm aperture.

 

Hi Roy (+Rod),

Yes, it's a Circle K Kenko objective in the Prinz 660, and very nice they are too. The scope can take high magnifications, the weak link was the tripod and to a lesser extent the mount..when solidly mounted they can really fly!

My own Meade 339 80mm F16 scope which was modified by Mark Turner of Moonraker is a  Circle T (Towa) lens, the rest of the scope apart from the original finder was rebuilt, it was effectively a prototype for Moonraker's long focus range. It was commissioned originally as a project by Neil English, in the days when he was a big fan of long FL achromats.

The original Circle T  scopes were most common in the UK under the Brand name "Topic" ( a naff name if ever I heard one!)..

In my humble experience the Kenko lens had a slight performance edge, but both, when well mounted, and used with decent eyepieces/diagonal could/can deliver superb views - especially on Lunar and double stars👍😊.

Dave

[F15Rules]

During this Summer's lockdown I decided to mount the Moonraker F16 on my Tak EM2 mount for fun..solid as a rock.

There's more on the "Show us your frac thread" if anyone wants to see more photos of the setup 🙂.. just click the link and scroll down a little...

https://stargazerslounge.com/topic/245216-show-us-your-frac/page/112/

Dave

Edited November 12, 2020 by F15Rules

[Roy Challen]

A lovely setup Dave! I don't have any fresh photos of mine, but here's a link to a thread I started when I first got my Tak mount.

Everything is clean and working now (has been for ages actually), except for the LCD screen on the control box. I also found a more suitable counterweight. I did refit the original black dew shield though as it better matches the rest of the components.

My garden looked tidier back then too😁

[F15Rules]

That's a lovely mount Roy!..but we need more pictures please!!👍😊

Dave

[RodAstro]

Hi all

Just thought I would bump this thread.

I bought a new camera a couple of weeks ago Opticstar DS-616C-XL+ and a Astro Physics CCDT67 telecompressor (reducer) to use on my Meade SCT.

I have seen some pictures taken with the Zeiss B 150mm f15 Apochromatic and the AP reducer made for f9-f18 scopes, so was wanting to try it on my Zeiss 150mm f15 Semi Apo scope to see if it all worked.

Well to say I am pleased is an understatement.🙂

The image is of M3 using 19 x 5 min subs with 50% gain in Bortle 6 sky's.

From the image with the APS chip the reducer seems to be giving me around f8-f10.

Good result F15 rules