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Boller and Chivens 16" Cassegrain

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#26 starman876

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Posted 08 August 2023 - 08:16 AM

Rand made it easy to carry around a 32" Cass. It was called RAMO.

Are you talking about the RAMO scopes that were on a trailer that could be pulled around by a car or truck?  I do not think they were carried around.  


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#27 CHASLX200

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Posted 08 August 2023 - 06:17 PM

Are you talking about the RAMO scopes that were on a trailer that could be pulled around by a car or truck?  I do not think they were carried around.  

Ya. That is what i mean by carry - towed.  I stopped to vist them in 1987 in Atlanta.



#28 starman876

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Posted 08 August 2023 - 08:27 PM

Ya. That is what i mean by carry - towed.  I stopped to vist them in 1987 in Atlanta.

They do look like they were interesting scopes.  I cannot imagine put a scope like that on a trailer and then go 60 mph without having some protection for the scope.  what do you think?



#29 CHASLX200

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Posted 09 August 2023 - 05:54 AM

They do look like they were interesting scopes.  I cannot imagine put a scope like that on a trailer and then go 60 mph without having some protection for the scope.  what do you think?

Sure as heck not gonna tow one with my Vette doing 140mph. But i have heard some of these scopes were total mush bombs. There was a Ealing 16" that was pretty sad that somone bought.



#30 Peter Ceravolo

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Posted 09 August 2023 - 12:03 PM

The Boller and Chivens instruments are massive, including the 16" version, the baby of the group.

 

Designed at the dawn of the space age, the instruments were clearly intended for institutions and were capable of handling a heavy payload directly bolted to the scopes backplate/mirror cell.

 

I've always wondered why the 16's focal ratio was soo long, perhaps it has something to do with photometric instruments of the day.

 

Sandiego State 16 5-S.jpg

 

This unit, originally at Kitt Peak then Georgia State, eventually wound up being surplussed and probably junked.

 

BC.16in.KPNO_.1964.600dpi.1-S.jpg

 

Georgia State U 16 1.jpg


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#31 Peter Ceravolo

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Posted 09 August 2023 - 02:58 PM

Understandably, observatory class telescopes elicit high expectations of image quality, often they are disappointing.

Many decades ago, during a star party, I looked at M13 through the 74" Cassegrain reflector at the David Dunlap Observatory in the Toronto area.

I didn't think much of the image. Outside the view through a 12" f/5 Newt at 75x was a lot more inspiring. Looking back on the experience, we were looking through the center of the globular through the big scope because of the ludicrously high power. The globular look like an open cluster...

 

"Everything is big in this telescope!" said my wife as we poked around the sky with the B&C 16". At f/18 and 7,300mm focal length the lowest power I can get is about 200x with my 35mm TeleVue Panoptic.

That's very high power for most people, and it will reveal all the telescope's deficiencies and amplify any mediocre seeing effects. One can hide a lot of sins at 50x. Originally this instrument was mounted atop a five story science building so the seeing conditions were rarely good enough to show off it's optical quality. Fortunately, now it lives in a well ventilated mountain top observatory with often ideal seeing conditions. As I mentioned before, we often use Ludicrous Power on appropriate targets with good results.

 

The optics are of the classical Cassegrain type: F/3 parabolic primary and a 4" dia secondary to amplify the focal ratio 6x.

 

B&C16_optics_layout.JPG

 

In the drawing above the optical quality is specked to be 80% of the light within 1/2 arc second.

That's a bit strange because to the best of my knowledge the Airy disk produced by a 16" instrument is about 0.7 arc seconds across. The B&C is not limited by the laws of physics! Let's assume the speck was a cut and paste error from the 24" drawing.

 

Here is a drawing with details of the Pyrex (I assume) mirror dimensions and radii:

 

Attached File  16_B&C_prim_sec_drwg.pdf   27.36KB   33 downloads

 

Naturally one of the first things I did was to assemble the OTA and test the optics. They weren't too bad, a little under-corrected and a little rough.

 

The clipped aperture was a bit weird, the baffle tube must be out of alignment. More on that later.

 

OTA test 1.jpg

 

Berea_16.jpg

 

 

 


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#32 ccwemyss

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Posted 09 August 2023 - 03:39 PM

Seeing that 16" full thickness flat supported by a couple of wood dowels certainly gave me pause. But the high tech use of masking tape rolls to support the ronchi grating holder is something I can personally relate to. 

 

It's hard to know what an observatory scope has gone through. They are workhorses that get constant use, with the heavy loads changed out regularly for different instrument packages. Although maybe not so much at a small college. When we did the open cluster photometry run on the 36" at Kitt Peak, we found a plastic garbage bag laying on the mirror (the wind had apparently picked it up from the trash can under the desk and dropped it into the tube). Nobody had any idea of how long it had been there. It was just because one of the students really wanted to climb the ladder, not just far enough to pull off the cover, but to satisfy their curiosity by actually taking a look at the inside the scope, that we discovered it before our session. 

 

Chip W.


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#33 MassiveRedTelescope

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Posted 09 August 2023 - 05:02 PM

As a student I actually lived in this building as a student monitor.   I could once boast that I had a Boller and Chivens on my roof.  The telescope pier did not go to the ground. Rather, the observatory was supported by a series flying buttresses that reached from the floor to outside walls.  Getting up there required agility which I had more of when I was a student.

 

The building pictured above is, of course, gone.  It's been replaced by a new building tipped by one of those silly prefab copulas that are common on old-looking new college buildings.

 

Below is a pic of the 4 rescuers once the equipment was safely on the ground.  I'm the one in the hard hat and suspenders.  Mark Sproul is at left.

 

Group Shot_s.jpg


Edited by MassiveRedTelescope, 09 August 2023 - 05:06 PM.

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#34 Peter Ceravolo

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Posted 09 August 2023 - 08:02 PM

The primary had the usual bird crap and dust on it, but the surface was not otherwise damaged. Both mirrors needed recoating.

 

Once stripped of the old aluminum I set up independent autocollimation tests for both mirrors to see which of the two was causing the roughness and undercorrection.

No surprise, it was the secondary.

 

For the primary I used a double bounce (off the flat) autocollimation set up. In the photo below the Ronchi tester is behind the primary.

The big f/3 mirror has a wonderfully smooth and well corrected parabolic figure right out to the edge. A pro job.

Unfortunately I could not record the test results because the camera could not accommodate f/3 beam.

 

16BCprimary test.jpg

 

For the secondary I happened to have a 14" Hindle sphere of just the right radius to be able to test the secondary by autocollimation.

The job was made easy because I have a lot of lab stages for precise positioning, but one could have fashioned mounts from wood just as well.

 

16BCsecondary Hindle 1.jpg

 

16BCsecondary Hindle 2.jpg

 

Here you can see the test results, the figure is undercorrected and kinda rough, no doubt from the "spin" polishing used to induce the hyperbolic surface.

This is the kind of thing I usually see in SCTs (at least the old ones).

 

16 BC secondary Hindle s.jpg

 

Despite the less than optimal secondary, I think the system as it was would have offered very pleasing images and would have been seeing limited most of the time.

But the problem is the roughness, it would scatter a lot of light so I decided to touch up the secondary. Looking back on it now I should have just made a new secondary and left the original alone.

When one "touches up" an existing optic, the figure rarely gets better right away. Often the figure gets worse first and you have to bring it back. One of the reasons is the fresh polishing tools that need to be "broken in".

This job went as expected, I should have started fresh. But I did manage to smooth out the figure a little but there is a bit of a roll at the edge. I decided to leave it and see how it works out on the stars.

 

16 BC secondary refigured.jpg

 

The overall image quality is quite good, the 0.57 src second separation double star, Eta Crb is cleanly split with sky between the Airy disks. But there is an objectionable haze, most obvious around 5th magnitude stars like the Double Double that will definitely affect planetary contrast. I suspect it's the still too rough secondary figure, but I am surprised at the haze's extent and brightness.

 

But there's more!

 

The rolled edge that didn't look too bad for visual use turns out to be not acceptable for astrophotography. There are spikes in bright star images that would be hard to deal with. They disappear when the scope is stopped down to 15".

 

So I've started work on a new secondary!

 

Edge roll.JPG

 

 

 


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#35 Peter Ceravolo

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Posted 10 August 2023 - 06:08 PM

The Boller and Chivens instruments were designed by opto-mechanical engineers so you one would expect finesse design through and through.

And that's what you get, except for the 16" primary's mirror cell...

 

primary installed.jpg

 

I was expecting a typical nine point flotation cell, but I was surprised to see the 3.1" thick (edge) primary was supported by a simple annulus of Bakelite (I think) about 6" diameter.

 

mirror support plate.jpg

 

That's a lot of mass to have hanging over the edge of the annulus. I would expect it would affect the primary's figure, causing a bump in the central area, when pointed at the zenith.

If it is happening I haven't noticed it yet, because I have not had a good view of the relative intensity of the diffraction rings. I think the secondary roughness is affecting their visibility.

 

The mirror is supported radially by four adjustable pads.

 

IMG_3605.JPG

 

The pads are actuated via set screws, a push rod and ball bearings. I like this design as it makes centering the primary in the cell easy.

 

mirror centering.JPG


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#36 CHASLX200

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Posted 10 August 2023 - 06:30 PM

The Boller and Chivens instruments were designed by opto-mechanical engineers so you one would expect finesse design through and through.

And that's what you get, except for the 16" primary's mirror cell...

 

attachicon.gif primary installed.jpg

 

I was expecting a typical nine point flotation cell, but I was surprised to see the 3.1" thick (edge) primary was supported by a simple annulus of Bakelite (I think) about 6" diameter.

 

attachicon.gif mirror support plate.jpg

 

That's a lot of mass to have hanging over the edge of the annulus. I would expect it would affect the primary's figure, causing a bump in the central area, when pointed at the zenith.

If it is happening I haven't noticed it yet, because I have not had a good view of the relative intensity of the diffraction rings. I think the secondary roughness is affecting their visibility.

 

The mirror is supported radially by four adjustable pads.

 

attachicon.gif IMG_3605.JPG

 

The pads are actuated via set screws, a push rod and ball bearings. I like this design as it makes centering the primary in the cell easy.

 

attachicon.gif mirror centering.JPG

Don't look like much air flow. I have yet to ever look thru a good Cass all these years. Always the same as 90% of the SCT's i have owned. Just not anywhere near Zambuto like.



#37 deSitter

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Posted 10 August 2023 - 06:43 PM

The Boller and Chivens instruments were designed by opto-mechanical engineers so you one would expect finesse design through and through.

And that's what you get, except for the 16" primary's mirror cell...

 

attachicon.gif primary installed.jpg

 

I was expecting a typical nine point flotation cell, but I was surprised to see the 3.1" thick (edge) primary was supported by a simple annulus of Bakelite (I think) about 6" diameter.

 

attachicon.gif mirror support plate.jpg

 

That's a lot of mass to have hanging over the edge of the annulus. I would expect it would affect the primary's figure, causing a bump in the central area, when pointed at the zenith.

If it is happening I haven't noticed it yet, because I have not had a good view of the relative intensity of the diffraction rings. I think the secondary roughness is affecting their visibility.

 

The mirror is supported radially by four adjustable pads.

 

attachicon.gif IMG_3605.JPG

 

The pads are actuated via set screws, a push rod and ball bearings. I like this design as it makes centering the primary in the cell easy.

 

attachicon.gif mirror centering.JPG

Is that ocher material the same stuff as in my Tasco and Sears mounts? :) And what is it called? I think I remember fishpaper. Fiber board. Very good stuff, I need some now.

 

-drl



#38 starman876

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Posted 10 August 2023 - 07:05 PM

Don't look like much air flow. I have yet to ever look thru a good Cass all these years. Always the same as 90% of the SCT's i have owned. Just not anywhere near Zambuto like.

Look at the CFF cassegrain.      Awesome scopes.  Perfect optics.  Very expensive.  I am about to close the deal on the one I have.   All carbon fiber scope.  



#39 davidmcgo

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Posted 10 August 2023 - 08:23 PM

Phenolic sheet.  Basically resin on a paper or cloth core.

 

Dave

Is that ocher material the same stuff as in my Tasco and Sears mounts? smile.gif And what is it called? I think I remember fishpaper. Fiber board. Very good stuff, I need some now.

 

-drl



#40 firemachine69

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Posted 10 August 2023 - 09:16 PM

Rand made it easy to carry around a 32" Cass. It was called RAMO.

 

 

You mean RAMbO? grin.gif lol.gif



#41 Peter Ceravolo

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Posted 11 August 2023 - 05:24 PM

The B&C's secondary assembly is the polar opposite in terms of apparent finesse when compared to the primary support.

 

IMG_6964.JPG

 

IMG_6928.JPG

 

The focusing is accomplished by changing the secondary to primary spacing, like a conventional SCT.

But unlike an SCT's the secondary moves, not the massive primary.

The secondary cell is mounted to a piston supported by 8 bearings, very much like a Crayford focuser.

 

IMG_6961.JPG

 

The mirror sits in a ring with plastic support pads bolted to the cell.

 

IMG_3631.JPG IMG_6914.JPG

 

 


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#42 Peter Ceravolo

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Posted 13 August 2023 - 08:11 PM

One thing about the primary assembly warrants special attention, the long and apparently small diameter baffle tube.

 

IMG_6911.JPG

 

At first glance one wonders how much vignetting there must be given the 3" diameter baffle tube is so long.

After making all the appropriate measurements I laid out the system in CAD software and found that, because of the F/18 convergence cone, there is minimal vignetting over a 1/2 degree field of view.

A 1/2 degree field may not sound like much, but at 7,300mm focal length it will cover a large format CCD detector like the 4kx4k KAF16803.

 

But what really sets this baffle tube apart form anything I've seen before is the fat that one must "collimate" it so it does not clip the converging light. This is what I saw when I first assembled the scope:

 

Berea_16.jpg

 

Something was blocking the light converging to focus on axis, it turns out it was the baffle tube. Normally I would expect the baffle tube to bolt onto the cell with no adjustments required to center or align it, instead counting precision machining to position the tube properly. But in the case of this B&C telescope the baffle is bolted to a adjustable force retaining ring holding the primary in place.

 

primary installed.jpg

 

Primary retainer.jpg

 

As one tightens the bolts to apply force, the retaining ring's top surface tilts. This is the surface the baffle tube rests on and that tilt will knock the tube out of alignment as seen below.

When you place your eye at the mirror's center of curvature the baffle tube should be centered as well. In this case it's not.

 

baffle 1.jpg


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#43 Peter Ceravolo

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Posted 13 August 2023 - 08:20 PM

To align the baffle tube I found I had to make an adjustment to the retainer, mount the tube and assess the centration at the primary's center of curvature.

 

IMG_6905.JPG

 

IMG_6908.JPG

 

IMG_6909.JPG

 

I had to go through this three time before the tube was lined up.

 

Now, I know the telescope primary has been re-aluminized, at least once. I suspect that when the primary was reinstalled this "collimation" procedure was not done.

And I do not see any note about this requirement in the assembly drawings or any other documents that exist online.

 

 


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#44 deSitter

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Posted 13 August 2023 - 08:31 PM

To align the baffle tube I found I had to make an adjustment to the retainer, mount the tube and assess the centration at the primary's center of curvature.

 

attachicon.gif IMG_6905.JPG

 

attachicon.gif IMG_6908.JPG

 

attachicon.gif IMG_6909.JPG

 

I had to go through this three time before the tube was lined up.

 

Now, I know the telescope primary has been re-aluminized, at least once. I suspect that when the primary was reinstalled this "collimation" procedure was not done.

And I do not see any note about this requirement in the assembly drawings or any other documents that exist online.

So I assume that slotted arrangement on the retainer is what allows for collimation.

 

-drl



#45 Peter Ceravolo

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Posted 13 August 2023 - 08:36 PM

So I assume that slotted arrangement on the retainer is what allows for collimation.

 

-drl

 

The slotted retainer is essentially a springlike device. Perhaps the mechanical engineers out there could offer some input.

 

Peter



#46 kgb

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Posted 13 August 2023 - 09:45 PM

The material for that retainer almost looks like ABS in the picture. Is that anodized aluminum?

Edit: BTW Peter, thanks for sharing your restoration. You are handling this skillfully and I'm really enjoying following along.

Edited by kgb, 13 August 2023 - 10:00 PM.


#47 Peter Ceravolo

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Posted 13 August 2023 - 10:05 PM

The material for that retainer almost looks like ABS in the picture. Is that anodized aluminum?

Edit: BTW Peter, thanks for sharing your restoration. You are handling this skillfully and I'm really enjoying following along.

 

Thanks!

The material is anodized aluminum.

Peter
 



#48 Peter Ceravolo

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Posted 15 August 2023 - 07:53 PM

I thought I'd take a break from all the opto-mechanical talk and mention how much fun I'm having using the telescope!

 

Day and Night!

 

I've been following Venus for a few weeks now, at first I was observing the inner planet at full aperture with no problems. Yesterday I viewed and imaged Venus at inferior conjunction, about 7 degrees from the sun.

 

Venus_23_08_13.jpg

 

The image is a stack of 100 images taken with a QHY174 monochrome camera and processed by my wife Debra. She added the slight blue color to the black and white image. If the image seems soft it's because the seeing was horrible. We're in the middle of a heat wave so the thermals from the hot local terrain caused a lot of turbulence.

 

Surprisingly, these old super slow Cassegrains are ideal for solar/daytime imaging and observing. The key is the long, relatively small, central baffle tube which keeps stray light from reaching the focal plane, even at full aperture. I've had fun observing Mars, Mercury and numerous stars in broad daylight at large solar elongations.

 

IMG_6911.JPG

 

In the B&C the baffle is about 3" diameter, but the opening is about 38" from the focal plane. For observing very close to the sun the addition of a full aperture mask with a 5" off axis aperture is required. I simply taped it in place... lots of tape!

 

 


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#49 deSitter

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Posted 15 August 2023 - 08:51 PM

I thought I'd take a break from all the opto-mechanical talk and mention how much fun I'm having using the telescope!

 

Day and Night!

 

I've been following Venus for a few weeks now, at first I was observing the inner planet at full aperture with no problems. Yesterday I viewed and imaged Venus at inferior conjunction, about 7 degrees from the sun.

 

attachicon.gif Venus_23_08_13.jpg

 

The image is a stack of 100 images taken with a QHY174 monochrome camera and processed by my wife Debra. She added the slight blue color to the black and white image. If the image seems soft it's because the seeing was horrible. We're in the middle of a heat wave so the thermals from the hot local terrain caused a lot of turbulence.

 

Surprisingly, these old super slow Cassegrains are ideal for solar/daytime imaging and observing. The key is the long, relatively small, central baffle tube which keeps stray light from reaching the focal plane, even at full aperture. I've had fun observing Mars, Mercury and numerous stars in broad daylight at large solar elongations.

 

attachicon.gif IMG_6911.JPG

 

In the B&C the baffle is about 3" diameter, but the opening is about 38" from the focal plane. For observing very close to the sun the addition of a full aperture mask with a 5" off axis aperture is required. I simply taped it in place... lots of tape!

Wow that's what it is ALL about! Goose bumps! 7 degrees! You'll be able to do the ring plane crossing of Saturn - 10 degrees from the Sun, but closer to the horizon.

 

-drl


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#50 icomet

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Posted 16 August 2023 - 02:32 PM

I want onegrin.gif

 

Me too!

 

I'd put a bed and other necessities so I could live there 24/7 and still doubt I'd ever make full use of it.

 

Gary 

 

Are you kidding ? Have you ever observed thru one of these ? 

The one we have here is nothing short of amazing, from my 5 years of running it on weekends, it is still the best visual instrument I have ever had the pleasure...  Of course F16 helps a lot but it takes back seat to nothing !

CS

Bob

There's one about 220 miles from me.

 

Clear Skies. 


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