41 replies to this topic

[ajkrishock]

All,

 

I am currently serving as President of my local Astronomy club. We have an aging 16" f/8 Cave-Astrola reflector that we just repaired the tracking drive on. It works now, but it's still showing its age.

 

What I mean to say is that it's.. limited. It's not a modern "go-to" scope, it's visual-use only since it can't achieve focus using a camera and it big & heavy. People have to climb a ladder and steady themselves at the eyepiece to look at objects which means it's unusable for the elderly and the wheelchair-bound. It's pretty badly scuffed up and it becomes a giant windsock whenever a light breeze kicks up.

 

There are some members of our board who seem to be of the opinion that we should leave the Cave alone and just let it do what it does best.. show nice images of the moon & planets to the interested public. My concern is that the old Cave isn't turning out the public like it used to. People seem to be (understandably) more fascinated with the EAA & astrophotography folks than with traditional viewing.

 

I have in mind a modernization project for our old scope, but before I put it to our board members, I'd like to hear your input.

Several of our club members (myself included) have really gotten into EAA and when we first started experimenting with doing EAA using the Cave, we.. failed. We learned that the camera could not achieve focus without either moving the focuser & secondary mirror assembly closer to the primary mirror by a few inches or moving the primary mirror forward in the tube by a similar amount.

 

I did some more research on this issue of focus distance in Newtonians and I came across an intriguing post that suggests a way of making that distance adjustable. When I proposed making a similar change to allow for EAA a couple years ago, I got some pushback about it on the grounds that it would complicate visual use of the scope (people would have to use an extension tube on the focuser for visual use). I suspect it was more a case of old folks not wanting things to change.

 

Since that time, EAA has become more popular and the old-timer's objections seem to have faded a bit, but there still seems to be a strong reluctance to alter the Cave.

 

My proposal is to transform our old Cave reflector into an open-tube design using plywood rings and aluminum struts that would allow the focuser and secondary mirror assembly to slide back and forth on the struts to accommodate both visual and EAA uses. My proposal would solve the following problems:

 

1. No tube. No more windsock behavior.
2. EAA! Images could be displayed on a monitor for better accessibility
3. Easily convertible back to visual use
4. More modern, more capable
5. We could broadcast our images

 

The possible downsides being:

 

1. More of a challenge to balance
2. More frequent cleaning would be required

3. Possible dewing issues?

 

Opinions? Has anyone attempted a rebuild like this?

Edited by ajkrishock, 10 May 2022 - 09:12 AM.

[John Rogers]

I would agree with your members who want to preserve the Cave in its current configuration.  The 16-inch Caves are rare.  There are only three in the current registry and only one at f8.  Do you know if yours is listed?

 

Have you considered selling the telescope to a Cave enthusiast and using the proceeds to purchase another telescope that meets your current requirements?  I know that shipping is probably not an option, but I would bet that there are some folks here who are willing to drive a considerable distance to preserve this telescope.

 

Unless you are doing lunar and planetary under good seeing conditions, I don't think the Cave would be ideal for EAA.  It is better to have a wide-field fast telescope to quickly allow the image to form on the screen.

[ajkrishock]

I would agree with your members who want to preserve the Cave in its current configuration.  The 16-inch Caves are rare.  There are only three in the current registry and only one at f8.  Do you know if yours is listed?

 

Have you considered selling the telescope to a Cave enthusiast and using the proceeds to purchase another telescope that meets your current requirements?  I know that shipping is probably not an option, but I would bet that there are some folks here who are willing to drive a considerable distance to preserve this telescope.

 

Unless you are doing lunar and planetary under good seeing conditions, I don't think the Cave would be ideal for EAA.  It is better to have a wide-field fast telescope to quickly allow the image to form on the screen.

Thanks for your response.

 

Do you have a link to the Cave registry? I'd be curious to know if ours is the f/8 on that list. 

 

Regarding my proposed changes, I'm not saying that the old cave tube should be discarded.. just replaced with an open tube design. We could restore the Cave to it's original state if necessary. I was also thinking that an f/7.5 focal reducer could be used to bring the Cave to f/6 which, though still not ideal, would be better for EAA. 

Currently, there are no plans to purchase a more capable EAA platform, so we're trying to find a way to check off all boxes with one instrument.

[siriusandthepup]

An old 16" f/8 Cave is a fine scope for an enthusiast willing to accept it's inherent limitations.

 

It is NOT the scope you need to do all the things you describe.

 

 

My proposal is to transform our old Cave reflector into an open-tube design using plywood rings and aluminum struts that would allow the focuser and secondary mirror assembly to slide back and forth on the struts to accommodate both visual and EAA uses.

This would be monumental in effort and would fail to achieve your objectives. - Don't do it!

 

 

 

Have you considered selling the telescope to a Cave enthusiast and using the proceeds to purchase another telescope that meets your current requirements?  I know that shipping is probably not an option, but I would bet that there are some folks here who are willing to drive a considerable distance to preserve this telescope.

I agree with this recommend. Let it go to a good home and move on. Use the funds to acquire a scope more suitable to do all the things you want from a good club scope. I would suggest a nice C14 or Meade 16" Schmidt Cass. Of course there are many other candidates as well.

 

good luck!

Edited by siriusandthepup, 10 May 2022 - 09:38 AM.

[John Rogers]

Here is a link to the latest spreadsheet: https://wiki.telesco...or_Registry.pdf

 

The CN documentary thread is here: https://www.cloudyni...irror-registry/

 

The serial number of the 16-inch f8 is 749508.  

[siriusandthepup]

If your club has interest in EAA - piggyback suitable EAA small refractors on the C14 platform and have fun.

 

lol

[lee14]

When I was doing outreach at the local observatory we had a 16" SCT working visually, a 10" SCT feeding a flat screen monitor, and a number of smaller scopes. The monitor presented big bright views of the moon, sometimes Jupiter or Saturn, and always had two or three visitors watching. The 16" always had a long line, even though the solar system views were 'less impressive', it could show a variety of other objects much better than the 10" with the monitor. People get more than enough screen time at home, it's hard to substitute the feel of direct viewing through a large scope.

 

If you can sell it and replace it with a 14 or 16 inch SCT, sure. They're very easy on visitors, the eye position doesn't change very much, and the viewer can readily tweak the focus if need be. But modify the Cave for EAA? Seems like a bad idea.

 

Lee

[Terra Nova]

I agree with the others here, wholeheartedly! A large Cave like that is rare and should most definitely be preserved. It wasn’t designed for EAA and wouldn’t be a good performer if adapted for such use. It was designed as a visual instrument and should be used as designed. There’s nothing like feeding a healthy dose of pure, unadulterated stellar photons directly from the stars to ones eyes and brain. People spend enough time stating idly at a tube or LCD while constantly twiddling their thumbs. They can look at better pictures in a book than they’ll see through your converted scope’s monitor and I think any novelty would soon wear off.

 

There’s an unmistakable thrill of actually seeing the Andromeda Galaxy and knowing that you are looking back in time two and a half million years.  A telescope is currently the only real and working time machine we have readily at our disposal. Maybe explaining it as such rather than merely telling people to step up and look at ‘M3’ would help. Tell them that if intelligent life on some planet orbiting a star in M31 is looking at us, they wouldn’t be seeing us, but instead, they would be seeing Australopithecus! Popularizing astronomy today is more a marketing/communications problem than it is a technical problem. Keep that wonderful old telescope, appreciate it for what it is, and use it!

Edited by Terra Nova, 10 May 2022 - 11:06 AM.

[Jim Davis]

Our club has a 12" Cave, and is one of our most popular scopes for public observing. The push-to mount doesn't really support imaging, though it has been used for that in the past. We normally use much smaller telescopes for EAA, since you don't need large aperture for a decent view of most objects we show the public. My advice would be to leave the scope as-is. If you really want something different, sell it and buy something more appropriate.

 

If you do change the Cave, please save the parts without modification so it can be changed back.

 

[apfever]

I have a regular wood and aluminum pole 16" truss with a Meade primary from their high QC in house days. Going to a truss won't solve any fast change issues for photo to visual. It would be just as fast to have a quick bolt system to move the primary cell between two sets of holes in the original tube.  A lot of vintage Newtonian tubes have multiple sets of holes for the primary location installed from the factory. 

A focuser extension is a good idea for a quick change system but do you need to do quick changes in a given session?  A 2" focuser reduced to 1.25" extensions will not vignette your eyeball. Don't ya hate when that happens?  

 

ajkrishock where are you, how complete is all the original stuff like mount/pier/legs/OTA. PM me with some details, serious questions to keep it together, I'm such a sap, I'm thinning, I hate you for temptations.

I'm not the only one in this forum perked by prospects. The Perseus Arm is kinda big for location.

Edited by apfever, 10 May 2022 - 03:11 PM.

[photoracer18]

Thanks for your response.

 

Do you have a link to the Cave registry? I'd be curious to know if ours is the f/8 on that list. 

 

Regarding my proposed changes, I'm not saying that the old cave tube should be discarded.. just replaced with an open tube design. We could restore the Cave to it's original state if necessary. I was also thinking that an f/7.5 focal reducer could be used to bring the Cave to f/6 which, though still not ideal, would be better for EAA. 

Currently, there are no plans to purchase a more capable EAA platform, so we're trying to find a way to check off all boxes with one instrument.

There are no focal reducers that work on Newtonians as far as I know. And I have been in this hobby since 1957.

[apfever]

There are no focal reducers that work on Newtonians as far as I know. And I have been in this hobby since 1957.

Now you tell me. I'll quit trying to put in my barlows backwards.

[CHASLX200]

I would pay big money for a scope like that. Just no way i am lifting a 180lb OTA onto the mount. If the optics are super it would be a killer planet scope in my seeing.

[1939Dodge]

OK, I’ll bite…..what’s EAA?

[ajkrishock]

There are no focal reducers that work on Newtonians as far as I know. And I have been in this hobby since 1957.

Here's just one:

 

https://starizona.co...-coma-corrector

[ajkrishock]

OK, I’ll bite…..what’s EAA?

Go forth and discover..

https://skiesandscop...sted-astronomy/

[Jim Davis]

OK, I’ll bite…..what’s EAA?

Electronically Assisted Astronomy. There is a whole CloudyNights forum on it.

 

https://www.cloudyni...-astronomy-eaa/

[Stevegeo]

I would kill for a cave that big,  when i was much younger my dream was a cave 12 .. and 16 ..

And you want to take it APART?? 

 

YOURE CRAZY,  fix it, restore it , enjoy it , but dont DESTROY IT.  

once the genie is out of the bottle , he never goes back in . 

Once you take a majestic scope apart for mods like that, it never goes back to its former glory ..

 

Ps. If your gonna wreck it, let me take it off your hands for a handsome  fee. ..

[ajkrishock]

I would kill for a cave that big,  when i was much younger my dream was a cave 12 .. and 16 ..

And you want to take it APART?? 

 

YOURE CRAZY,  fix it, restore it , enjoy it , but dont DESTROY IT.  

once the genie is out of the bottle , he never goes back in . 

Once you take a majestic scope apart for mods like that, it never goes back to its former glory ..

 

Ps. If your gonna wreck it, let me take it off your hands for a handsome  fee. ..

Steve -

 

You're located close to us. Darling Hill in Tully. Stop over and have a look at it sometime. I'm really just interested in making the Cave useable for EAA.

 

Maybe you could make some suggestions?

[Stevegeo]

Stop down to MY PLACE.  Otisco  valley rd. Down by Marina across from causeway 1662, 

Has LUNAR LANDER IN FRONT YARD NEXT TO THE ROAD. 1/2 SCALE. CANT MISS IT..

 

 

btw thinking of hosting an outreach for sundays lunar eclipse,, weather permitting.

I will bring out my C16 and C11 maybe the C8 if i get enough interest..

I have my own observatory close by as well with  a 12 in LX200....

 

PM  me.. im usually around 

[dgreyson]

If I had a 1925 Rolls Royce silver Phantom, I could rip out all the obsolete old junk parts and put in batteries and an electric motor. That way I would have the amperage to put in some ginormous base speakers in the back seats and saw a hole in the dash for a power Amp and a double din radio with blinking led lights. I'd have a most awesome ride then bro. But somehow, that seems like way more work and trouble than just selling off that old heap of junk and buying what I actually wanted in the first place. I think you could easily buy a used ess friendly scope and be a lot happier with the result.

[YourNotSirius]

Quick! Someone get that scope into the National Treasures Registry! That'll stop him from making a huge mistake and ruining it! BWAHAHAHAHAHA!!!

 

Really! Listen to those who are making more sense. Sell it and use the funds to get something that is better suited for your goal. Personally, I have no interest whatsoever in EAA or other such nonsense. To paraphrase a now rather infamous character "Let me see the Universe with my own eyes." (Yeah. It's a Star Wars reference for anyone who didn't get it. lol)

 

What you have really is a very niche item. It was designed for visual use only. Even astrophotography was challenging back then and was not considered when this instrument was manufactured. Although, by moving the mirror forward a bit it could have been done with minimal effort. Cave did make more elaborate and capable versions of this telescope for such purposes.

 

I am not currently in the position to make an offer on it. I'm swamped with work overload and too many projects to handle. In addition, with just relocating to new quarters and a partially disabled father to tend, I'm up to the gunwales with sharks circling the boat! LOL That really stinks because I would love to have that telescope here in the moderately dark skies of central western New Hampshire. (DRAT! I'm only 5 hours to the east of you, too! DOUBLE DRAT!)

 

Oh well. Please, listen to those offering good advice. In the long run, everyone will be much less stressed and much more satisfied.
 

Q

[Jim Davis]

If you can't use a camera due to not having enough in-focus, you could try moving the mirror forward in the tube. May lose a bit of the light cone around the secondary, but it could solve your main issue.

[Stewc14]

Just sell it to me.you can buy another more suitable scope for your needs. We will put it in our observatory when it done and it will be totally restored and used in our program…….l am serious 

[tim53]

If you can't use a camera due to not having enough in-focus, you could try moving the mirror forward in the tube. May lose a bit of the light cone around the secondary, but it could solve your main issue.

Most Newtonians of "the day" had a second set of mounting holes so the mirror cell could be moved up the tube an inch or so for use with an SLR.