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How do the old Cave Newtonians compare to today's Modern Newtonian Reflectors ?

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#1 Rollo

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Posted 17 March 2017 - 08:20 PM

Hi,  looking for someone who has experience comparing the old Cave reflector telescopes to today's modern newtonian telescopes.  How do they compare in optical performance ?

 

Thanks   smile.gif

 

 


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#2 Joe1950

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Posted 17 March 2017 - 08:58 PM

I had a Cave Astrolla, 10", f/7 around 1974. It was a superb instrument. The optics were top of the line and really left nothing to be desired. The build was likewise with a fiberglass tube made by Parks and a very heavy duty equatorial mount.

 

At the time they were the top of the line. The final figuring was done exclusively by hand.

 

I believe it cost me about $800. Today that would amount to about $4200 (But what people don't account for is that we had more spendable or savable income relatively speaking. It isn't apples vs. apples).

 

I've had a modern 6" f/8 made by Skywatcher. A DOB. It cost me $275. That's about $35 in 1974. Smaller scope and a different mounting system. I gave it to my adult son. I found it to be a fine telescope. The build was very impressive and I found no real fault with the optics.

 

I'm not saying it was comparable to the Cave optically or mechanically, but I, not being an optics expert who could evaluate the wavefront error or Strehl ratio, found the Skywatcher to be very good! It gave a good star test and a very nice Airy disk and understated diffraction ring pattern.

 

Two things are important to consider here.

 

1. Seeing at my location is rarely very good to excellent. So any scope would have a hard time reaching it's full potential.

 

2. The biggest issue in recent times has been consistency and quality control. It has gotten better, but there are still variations in what you may receive. At the time, all Cave scopes were excellent just as are the premium names of today. The production scopes of today are mostly good, some excellent and some lemmons.

 

So I would say the Caves of yesteryear were consistently excellent. No one worried about getting a scope with poor optics back then with Cave. And they were built like a masonry waste facility. No plastics or weak points anywhere.

 

Just my take.

 

joe


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#3 bremms

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Posted 17 March 2017 - 09:03 PM

From my experience, modern premium mirrors are a little better. Used about five Caves, one was superb, two were good and two were just OK.

I had a 10" F6 made by Alika Herring after he left Cave, but it was a custom mirror. It was Superb as well.

The Two Zambuto's I looked through were stunning.  The Caves ( other than the superb one)were more similar to the Orion dobs. Sorry, but that's the way it looked to me. The Caves were good but not like a top notch mirror of today.


Edited by bremms, 17 March 2017 - 09:04 PM.

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#4 Joe1950

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Posted 17 March 2017 - 10:12 PM

Agreed, Bremms! I was comparing the Cave mirrors to the 'production' Newtonian optics of today. Never having the pleasure of viewing through a Zambuto  or any of the other premium brands, I couldn't comment.

 

I will also agree that from my experience with my Cave scope, the views were very good but not as jaw dropping as one might expect. I don't know if that was an effect of average seeing or optical quality.

 

After the Celestron revolution started, Cave, as did so many other telescope makers found it more and more difficult to compete, and the overall quality suffered before they eventually shut the doors.

 

But at their peak, from a consumer standpoint, they produced a consistently good quality instrument and was the big name in the industry. 


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#5 starman876

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Posted 18 March 2017 - 09:17 AM

I agree that the caves I have had were good, but no where as good as some of todays mirrors that are available.   I think all this hype about Cave mirrors is a bit over the top.


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#6 DAVIDG

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Posted 18 March 2017 - 09:26 AM

I'm help teaching our yearly mirror making class and a12" Cave f4.5 was brought in to be tested. It is no better then a 1/2 wave. If I get free minute I'll post some images of the test results from double pass autocollimation. 

            Dave


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#7 terraclarke

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Posted 18 March 2017 - 10:10 AM

I agree that the caves I have had were good, but no where as good as some of todays mirrors that are available.   I think all this hype about Cave mirrors is a bit over the top.

Like the Dynamax Deluxe, I think a lot of the hoopla then and now about the Caves was all about the style, their look and feel! It was like a big old shiny Cadillac. Big, heavy, lots of chrome, and a ride like you were riding on air- just floating along! Nothing like it! But who wants to go back to eight miles to the gallon. Certainly not everyone. The Caves, like the big old Caddy's just aren't efficient by today's modern standards. But oh what a ride!


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#8 Joe1950

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Posted 18 March 2017 - 10:45 AM

It certainly may have been an overly hyped situation, since most users then were not as optically sophisticated and educated as people are today.

 

There was much less information on how to perform a star test, and virtually no one had any idea of what a Strehl ratio was. If anyone did test a scope it was usually to the extent of putting a Ronchi eyepiece in the focuser, which is not a highly sensitive test with just one pass. A double pass autocollimation was having the front end of your muscle car aligned - twice.

 

So I don't dispute at all the possibility of the optics being mediocre, especially in the latter days of operation. 

 

Terra makes a very valid point. It was in great part name and image that made the legend. Again, I think they went through a good period and then declined. But people never questioned what they were getting, it was just a given. 

 

The level of information back then was puny compared to today. Very little on star testing or collimation aside from eyeballing it... you just believed what the established companies said because very few of us had any qualitative optical knowledge or access to it except the ATMers - and communication was nothing as it is today.

 

One side note. About 1972 or so, I had one of the early C8s. I saw a display of it at the Franklin Institute one day, and had to have one, which eventually I did. It had the small base with the spur gear drive, but okay for me.

 

There was a very good opposition of Mars, I believe the 1973 event where it reached 21.2" diameter, and all of us in the club set up outside with our scopes. I happened to setup next to a guy with an 8" Cave. I don't know if it was the quality of the Cave, the weakness of the C8 or a combination of both, but the difference was astounding.

 

I think the Cave owner felt sorry for me and the view I had with the C8 and mentioned the secondary obstruction issue - but it was much more than that lol.gif .

 

A year or so later I got the 10" Cave but wasn't overwhelmed with it and it was way too heavy for take out and ins. Another club member bought it and put it in a dome.

 

Those are my best recollections of those days.


Edited by Joe1950, 18 March 2017 - 10:49 AM.

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#9 Richard Whalen

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Posted 18 March 2017 - 11:07 AM

I think they were hit or miss as are most of today's production scopes. Never looked through a really bad one, or a truly excellent one. If I had to guess I would say today's are probably more consistent, with better coatings etc. Not picking on Cave, from my experience Meade, Parks, Celestron etc. had the same problem with consistency back in the day.


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#10 Rollo

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Posted 18 March 2017 - 11:20 AM

Thanks for all the reply's to my question !  Very interesting and good info !! 

 

I guess we might be living in the Golden Age of Amateur Astronomy.

 

Never had so many good choices as we have right now.  

 

I feel better knowing this and you guys have confirmed my gut feelings.   bow.gif 


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#11 CHASLX200

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Posted 18 March 2017 - 12:07 PM

My 8" F8.5  1970 Cave was as good as you can dream for.  Also my 10" F/7 from 1968 was super.


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#12 tim53

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Posted 18 March 2017 - 12:42 PM

I'm help teaching our yearly mirror making class and a12" Cave f4.5 was brought in to be tested. It is no better then a 1/2 wave. If I get free minute I'll post some images of the test results from double pass autocollimation. 

            Dave

That's incredible!  (incredibly bad, that is).  I wonder if it's because it's a fast one.  I know Cave was fond of long-focus newts.  So maybe he didn't put the effort into the RFTs?  

 

=Tim.


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#13 tim53

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Posted 18 March 2017 - 12:44 PM

 

I agree that the caves I have had were good, but no where as good as some of todays mirrors that are available.   I think all this hype about Cave mirrors is a bit over the top.

Like the Dynamax Deluxe, I think a lot of the hoopla then and now about the Caves was all about the style, their look and feel! It was like a big old shiny Cadillac. Big, heavy, lots of chrome, and a ride like you were riding on air- just floating along! Nothing like it! But who wants to go back to eight miles to the gallon. Certainly not everyone. The Caves, like the big old Caddy's just aren't efficient by today's modern standards. But oh what a ride!

 

While that made for a good story wink.gif , I'm not with you on the efficiency compared to today's plastic computerized gizmoids.  Thousands of years after the ICs in the modern toys fail, those synchronous motors will still be chugging away!

 

-Tim.


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#14 starman876

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Posted 18 March 2017 - 01:25 PM

try and get a replacement IC some years from now.  These IC's are out of date only a few years from their birth.   The whole industry is having this problem.  You need to buy whole new system every so often to keep your equipment running.


Edited by starman876, 18 March 2017 - 01:26 PM.

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#15 CHASLX200

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Posted 18 March 2017 - 01:28 PM

Every fast Newt i had back in the 70's and 80's gave sub par images.  This was before collimation tools and the Paracorr. 


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#16 Bomber Bob

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Posted 18 March 2017 - 02:08 PM

These IC's are out of date only a few years from their birth.

 

I imagine that'll be an issue even if you buy a top-tier computerized mount.  A saving grace for the telescopes is that we're in an a la carte system - buying scopes & mounts separately rather than as a bundle - so the better made OTAs should survive.  As I found out with the Orion XT12g go-to Newtonian:  When a cheap component fails, the design doesn't allow for manual / push-to use.  That type equipment won't be around nearly as long as the vintage scopes we currently collect & use.


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#17 Bonco

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Posted 18 March 2017 - 03:35 PM

I owned a early 70's vintage Cave 10 inch f/6 for over 20 years. A fine scope and because it was so much better than my C8 of the same vintage, I sold the C8.

As much as I loved my Cave I did need an optician (Richard Fagin) to perform some corrections to the primary. This turned the Cave into an excellent performer. Due to lack of garage space I sold the Cave in the 90's. Recently I've purchased a Zhumell 10 inch f4.7 Dob. The mirror is on Par with my corrected Cave mirror. So  my experience with new mirrors is very good.

Bill


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#18 CHASLX200

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Posted 18 March 2017 - 04:27 PM

Just about all the cheaper stuff is junk today and will never out last the older scopes made in the 50's thru the 70's.  All plastic today.  


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#19 Bonco

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Posted 18 March 2017 - 05:03 PM

Th OP's 2nd sentence asked how does the old compare with the new optically. My answer is they compare favorably. I don't think my pressboard Zhumell Dob is in the same class mechanically to my beautiful Custom classic deluxe Cave.

However I think the optics are on par.

Bill 


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#20 starman876

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Posted 18 March 2017 - 07:13 PM

a lot of the newer tubes are steel.  Makes them a bit heavy, but not that bad.  Focusers are always upgradable. So I would say the newer syuff compared to the Caves is a bargain.  Not as pretty, but who cares if the optics are as good or better. After all, that is the main goal, the veiwing through the eyepiece.  Better mounts can also be bought.  


Edited by starman876, 18 March 2017 - 07:14 PM.

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#21 rolo

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Posted 18 March 2017 - 09:25 PM

My all time favorite is my 12.5" f/6 Cave. I've looked through and have owned a few Chinese Newtonian and none were stellar. Your basic over or under corrected mass produced and some that the mirror wasn't even a parabola. There was one Celestron 10" f/4.7 that was very good, hardly any SA and one very mild zone that probably didn't affect anything. The biggest issue is roughness.

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#22 Chuck Hards

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Posted 18 March 2017 - 09:44 PM

I own three Caves.

 

6" f/8 Student Deluxe:  Performance is at least almost equal to any other 6" Newtonian I have ever owned, including a 6" f/8 Jaegers and 6" f/8 Edmund.  My home-made 6" f/8 is superior, however, by a small margin, but that mirror cost me a premium and was considered "the best of the lot" at the time.  Some 18 years ago, and it has an enhanced coating which the Cave, Edmund, and Jaegers do not have.  Also it has a 1" secondary, considerably smaller than the commercial scopes.  

 

10" f/6 Custom Super Deluxe:  Although I have the stock mirror, it was refigured commercially decades ago by the prior owner and now has a Galaxy mirror installed.  Performance with the Galaxy mirror is superb.  I have not re-installed the stock, refigured mirror because the interferogram from the refiguring optician isn't encouraging.  I plan to have it re-re-figured sometime in the future.

 

12.5" f/7 Observatory model:  Only used once by myself, but performance from this 1967 mirror was without complaint.  On the bench, it shows perfect Ronchi lines.  

 

That's about all I can tell you.  


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#23 terraclarke

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Posted 18 March 2017 - 10:13 PM

 

 

I agree that the caves I have had were good, but no where as good as some of todays mirrors that are available.   I think all this hype about Cave mirrors is a bit over the top.

Like the Dynamax Deluxe, I think a lot of the hoopla then and now about the Caves was all about the style, their look and feel! It was like a big old shiny Cadillac. Big, heavy, lots of chrome, and a ride like you were riding on air- just floating along! Nothing like it! But who wants to go back to eight miles to the gallon. Certainly not everyone. The Caves, like the big old Caddy's just aren't efficient by today's modern standards. But oh what a ride!

 

While that made for a good story wink.gif , I'm not with you on the efficiency compared to today's plastic computerized gizmoids.  Thousands of years after the ICs in the modern toys fail, those synchronous motors will still be chugging away!

 

-Tim.

 

No actually that was far from what I had in mind. But thank you for misinterpreting my words. I was talking about the efficiency of using photons in todays modern apos and higher end Newts. Cave's were high end instruments back in the day, just like Unitrons were. A much better comparison would be the Royce and Zambutos of today, along with Televues and Taks. There is a lot better milage in the new models. Moreover, a TV101 or an FS102 is a whole lot easier to set up than a Unitron 152. Oh yeah, and how about the weight/performance ratio of a modern 25" Obsession compared to a 50 year old 12.5" Cave Observatory model. All modern telescopes aren't junk or "plastic computerized gizmoids".


Edited by terraclarke, 18 March 2017 - 10:18 PM.

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#24 Chuck Hards

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Posted 18 March 2017 - 11:07 PM

Terra, respectfully, weight doesn't enter into the equation in a permanently-mounted telescope such as a Cave Observatory model.  If it's the transportable version, and transportation is needed, that's another story.  But it isn't really fair to compare weight between portable telescopes and observatory instruments.  Apples and oranges.


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#25 terraclarke

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Posted 19 March 2017 - 10:06 AM

I was making a comparison of what was available to amateurs as a large, high end Newtonian telescope in 1967 compared to 2017. I think that is a very valid comparison. What you get today weighs less, is more transportable, collects four times as much light, and costs very roughly the same dollar for dollar, adjusted for inflation. How is that not more efficient both interms of light energy collected and mechanical energy expended. And how is that any different than comparing a large luxury sedan of 50 years ago to a luxury sedan of today, that cost the approximately the same amount in dollars, but use very different amounts of fuel, produce different amounts of emissions, and have longer lifetimes in term s of road miles? I think your math has an emotional quotient that mine does not. Respectfully.


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