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A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe

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#1 Datapanic

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Posted 22 January 2013 - 03:07 PM

Taunting me for the past couple years has been this little Cave 8" sitting by the entrance of my favorite used telescope shop, Stellar Visions, in downtown Tucson. It kept saying "Take me home! Buy Me!" every time I visited. So, since lately, it's been kind of dry for any kind of Classic around here, I made up my mind Saturday to make a deal and go get it.

Once at the shop, we rolled it on out from behind a bunch of other scopes to pull the mirror and have a look. I wanted to be sure it was a Cave mirror before I bought it. Turns out it was made in 1972, with a 35 1/4" FL - f/4.4. For a long time, I thought this was an f/5 scope, but this is actually the Cave 8" f/4.5 RFT Lightweight Deluxe model as advertised in the early 70's catalog. It was also advertised as a Dual Capability scope - an RFT at f/4.5 and f/14 with a barlow. The only eyepieces or accessories that came with this one was an older Japan Teleview 40mm Plossl.

The 38" long fiberglass OTA sits on a Lightweight Deluxe mount with Clock Drive, 1" shafts and rotating rings. The scope is painted the grey and wrinkle black scheme. There are no Cave Labels on the OTA or mount and no signs that there every were any.

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#2 Datapanic

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Posted 22 January 2013 - 03:09 PM

The Focuser is actually pretty nice, a 1 1/4" Carle II Photo/Visual that has a push/pull adjustment as well as fine focus. With a 32mm Brandon, the focus point is out far enough that I think the in-focus travel will allow a camera to be used. I have not tried a camera on it yet.

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#3 Datapanic

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Posted 22 January 2013 - 03:10 PM

The Finder is an unbranded 50mm with a 1 1/4" diagonal, but no eyepiece.

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#4 Datapanic

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Posted 22 January 2013 - 03:11 PM

The Tube End Rings are the thicker type from that time period. The Secondary is somewhere between 2.1" and 2.4" - I haven't taken it out to see what the size really is. The inside of the tube is really dirty and coated with dust, just like the rest of the scope.

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#5 Datapanic

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Posted 22 January 2013 - 03:12 PM

Nice 4" Magnusson aluminum setting circles with aluminum block pointers.

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#6 Datapanic

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Posted 22 January 2013 - 03:12 PM

On the top of the rotating rings are what look like mount holes for guidescope rings.

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#7 Datapanic

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Posted 22 January 2013 - 03:13 PM

The Pier Cap has 4 set screws (2 on either side) to keep the latitude adjustment in place. I've seen this on the heavier mounts before, but not on a Lightweight.

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#8 Datapanic

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Posted 22 January 2013 - 03:14 PM

The mirror was coated in dust. Since it was already removed at the store, I went ahead and cleaned it up before re-installing it, but as you can see, the coating is nearly gone! The good news is that I found a place in Tucson, Composite Mirror Applications, that coats smaller mirrors with about a 1 week turnaround time!

This is a photo of the mirror surface after cleaning - that's not dust, that's light passing through!

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#9 Datapanic

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Posted 22 January 2013 - 03:17 PM

The next day, I started to collimate it (it was way off), but the secondary would not budge! So, I zoomed up to Ace Hardware, got some fasteners and stuff and did my non-destructive collimation screws mod with it as well as replaced the 5/16" threaded rod and re-installed it. Then, rolled it out of the garage and plugged in the Clock Drive. But, no motor sound! So, I pulled the Clock Drive cover off and sure enough, it's a dead motor that I'll have to deal with later. But I was able to get a nice sharp view of the moon from center to edge, even though probably more than 1/2 the light was passing through the bad coat on the primary.

I plan to start overhauling this one soon, keeping the original paint scheme and hopefully repair the motor since replacements are hard to find. The OTA can always be set on my 8" f/7 Lightweight Deluxe mount for photography. At low power, with about a 2-degree FOV, a Clock Drive is nice, but not mandatory for wide-field observing.

#10 Dave M

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Posted 22 January 2013 - 03:30 PM

Nice scope, Congrats!

#11 mdowns

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Posted 22 January 2013 - 04:18 PM

How much did you give for this one? I'm jealous!

#12 mustgobigger

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Posted 22 January 2013 - 05:56 PM

nice dan,
i didn't know cave made mirrors that fast.
learn somthing new...

#13 droid

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Posted 22 January 2013 - 06:35 PM

Given that you said it was focuser made for photo visual, is it usable for visual work???

#14 Datapanic

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Posted 22 January 2013 - 07:38 PM

How much did you give for this one? I'm jealous!


Well, kind of close to Retail :bigshock: But, not really because I traded in a Meade ETX90 and Tripod to get the cash side of it down. Of course any time I get a scope, my wife must get something too, so it's hard to say how much I had to give :)

#15 Datapanic

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Posted 22 January 2013 - 07:59 PM

Given that you said it was focuser made for photo visual, is it usable for visual work???


It works for both. Since it's not ready for photography yet because of balance, I pointed it horizontally towards the Santa Rita mountains, about 20 miles from here to get an idea of eyepiece and camera focus travel. Overall, the out-focus is a little over 4" and in focus is 7/8". In the picture, you can see where focus is for visual and photo. There's about a 1/2" to spare with the camera. I will run the tube layout through the Newt program soon to get an idea of any vignetting that might be going on.

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#16 Datapanic

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Posted 22 January 2013 - 08:01 PM

nice dan,
i didn't know cave made mirrors that fast.
learn somthing new...


Thanks Brian :) The catalogs show a whole lineup of f/4.5 scopes, but I have know idea how may they made.

#17 gelkin

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Posted 22 January 2013 - 08:28 PM

Looks like a great Cave project. Congrats Cave master. :bow: Love the Magnusson circles. Wish my lightweight had them. Interesting how there are 2 counter weights. Are they smaller than the usual one weight on most?

#18 PiSigma

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Posted 22 January 2013 - 08:58 PM

Sweet Dan.

Take a look at the April 1972 S&T Cave ad. It shows this OTA on a heavy duty mount (and even with the 360 degree dec drive). It also shows a guide scope on very high mounts on the rotating rings.

My Lightweight Deluxe doesn't have any set screws to hold the latitude adjustment. It actually holds just on the clamping force between the pier cap and RA shaft housing.

I'm curious about the paint scheme. I thought when they went to the grey and black scheme it was actually a sort of pewter silver and black like my '74 Model B and not the earlier equipment grey. This is the first one I've seen that is equipment grey and black.

#19 Datapanic

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Posted 22 January 2013 - 09:02 PM

Looks like a great Cave project. Congrats Cave master. :bow: Love the Magnusson circles. Wish my lightweight had them. Interesting how there are 2 counter weights. Are they smaller than the usual one weight on most?


The OTA weighs in at about 28lbs and each of the counterweights are about 14lbs. With the short Dec Shaft, I guess the extra weight is needed to counterbalance the missing guidescope and it would also work with a camera. Normally, a longer shaft with less weight would be better since that adds up to less weight overall. Remember the weight X distance = weight X distance thing. If there's not a lot of distance on the Dec Shaft for counterweight travel, then more weight is needed for less of a distance to counterbalance the OTA and what's on it.

#20 Datapanic

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Posted 22 January 2013 - 10:09 PM

Sweet Dan.

Take a look at the April 1972 S&T Cave ad. It shows this OTA on a heavy duty mount (and even with the 360 degree dec drive). It also shows a guide scope on very high mounts on the rotating rings.

My Lightweight Deluxe doesn't have any set screws to hold the latitude adjustment. It actually holds just on the clamping force between the pier cap and RA shaft housing.

I'm curious about the paint scheme. I thought when they went to the grey and black scheme it was actually a sort of pewter silver and black like my '74 Model B and not the earlier equipment grey. This is the first one I've seen that is equipment grey and black.


I took a look at the April 72 S&T ad - noted that the Finder rings are painted that grey color instead of black. I think the guidescope rings were higher so they could clear the obstructions from the Finder and Focuser. It doesn't look right to me, and with the guidescope that far away from the center of gravity, it would require more weight on the Dec shaft for balance. Also, in the ad, the Guide Scope rings are black. Looks like it's just barely fitting in there too! From my experience with a 60mm f/15 guidescope and film photography and what looks like a 50mm f/10 or so guidescope in the ad, that would have been really hard to work with - finding a guide star near the object to photograph, centering it under high power and doing a long exposure would have taken a good 30 mins or so to setup! Ah, the old days!

When I bought my 75 Lightweight Deluxe, I thought I was getting what was in the catalog photo - grey and black with 4" circles, but much to my surprise, it was the pewter and black scheme and 6" circles instead - the newer design. That was alright by me :)

#21 turk123

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Posted 22 January 2013 - 10:29 PM

Wow! Outstanding Dan. Perfectly balanced size for a large scope. You have too many scopes, want to sell it????

#22 Rich (RLTYS)

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Posted 23 January 2013 - 06:14 AM

The 38" long fiberglass OTA sits on a Lightweight Deluxe mount with Clock Drive, 1" shafts and rotating rings. The scope is painted the grey and wrinkle black scheme. There are no Cave Labels on the OTA or mount and no signs that there every were any.


Beautiful scope. :ooo: I still have the tube assembly for mine (sold the mount years ago, dumb, dumb me :foreheadslap:) which measures 40" in length. I guess a slightly longer focal length. I also remember only a single counter weight. Good luck with yours. :jump:

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#23 Grava T

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Posted 23 January 2013 - 08:50 AM

Nice telescope Dan. You should be able to get some nice widefield views with that baby.

#24 Datapanic

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Posted 23 January 2013 - 11:53 PM

I talked with the owner of Composite Mirror Applications in Tucson and am setting up to have this mirror as well as my 8" f/7 and the Horsetrail Cave mirror stripped and recoated there next week. It costs a wee bit more but the turnaround is 1-2 weeks and there's no risk of damage from shipping.

It'll be kind of interesting to bring in these old school 40 year old mirrors to a high tech composite mirror/telescope making place. I'll bring a camera and try to get them to let me take a peak at the scopes they are making. Take a look at their website, it's pretty cool stuff!

#25 Datapanic

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Posted 10 February 2013 - 10:40 PM

It was bright and sunny today here in Tucson, a little cold, but I managed the 50 degree temps okay :lol: So, I commenced to take the scope apart and get the mirror ready to go for recoating at Composite Mirror Applications later this week.

Jon had mentioned earlier that the color scheme was unusual, and he was right, the mount used to be pewter and wrinkle black at one time and somebody painted over with a grey color.

As you can see, they did a mask-n-paint instead of taking all the mount apart and painting it. Surprisingly, they did not even remove the Dec Pointer, which would have been easy. Here you can see the original paint beneath the pointer. (I sure do like my Canon 3Ti)

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