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Equipment Discussions >> Classic Telescopes

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Datapanic
Post Laureate
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Reged: 10/17/09

Loc: Tucson, Arizona
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: Jeff Phinney]
      #5691519 - 02/20/13 06:46 PM

Quote:

Nice classic!

I'm not sure(which is to say, I don't recall) what motors Cave used on those mounts, but maybe you might find a suitable replacement here.

http://www.hansen-motor.com/ac-synchronous-motors.php?mm_campaign=e860a03aaeb...




After taking the mount apart and removing the motor, I found that it does indeed work!

Welcome to Cloudy Nights Classics, Jeff!


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Jeff Phinney
super member


Reged: 02/20/13

Loc: CA
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: Datapanic]
      #5691701 - 02/20/13 08:27 PM

Well that certainly makes things much easier.

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Datapanic
Post Laureate
*****

Reged: 10/17/09

Loc: Tucson, Arizona
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: Jeff Phinney]
      #5697455 - 02/23/13 10:16 PM Attachment (9 downloads)

After thinking about what color scheme this scope should be, I decided to just go for what it currently has and take it from there. Whoever and wherever it was originally painted and/or possibly painted later by the owner, I'll probably never find out, so, it's going to be Gray and Wrinkle Black. I'll follow the the usual scheme with the legs, pier column, RA and Dec shaft housings, clock drive backplate and outer rotating rings all painted gray. The pier cap, cradle, inner rotating rings, clock drive housing, shaft collars and knobs will all painted wrinkle black.

I found a nice gray with Ace's Rust Stop Medium Gray Gloss. I applied 2 coats of light gray primer and then 3 coats of the gray. It comes out as more of a greenish gray rather than a blueish gray, which was what I was after. Not too glossy either - somewhere between a satin and gloss shine.

Sky it blue


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Datapanic
Post Laureate
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Reged: 10/17/09

Loc: Tucson, Arizona
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: Datapanic]
      #5697473 - 02/23/13 10:24 PM Attachment (5 downloads)

I've become much better with the Eastwood Wrinkle Black. It requires 2 thick coats applied about 3 minutes apart. The quality of the wrinkle effect depends on the temperature and humidity as well as the thickness of the 2 coats. If the coats are too thin, the wrinkles wont come out during the cure, and if the time between the coats is too long, then there will be flat areas along with long wrinkles. Here in Tucson, the humidity is usually pretty low, so I've shortened the time between coats to about 2 1/2 minutes. Here's the Pier Cap about 2 hours after the application. It can take a good 12 hours for the wrinkles to fully come forth and another day before I even handle the part after it's painted.

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gfeulner
sage
*****

Reged: 11/23/07

Loc: Bergen county, New Jersey
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: Datapanic]
      #5697496 - 02/23/13 10:40 PM

0.113 pv is about 1/8th wave. Gerry

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Datapanic
Post Laureate
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Reged: 10/17/09

Loc: Tucson, Arizona
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: gfeulner]
      #5697522 - 02/23/13 10:58 PM

Quote:

0.113 pv is about 1/8th wave. Gerry




Yup, kind of disappointing, but not surprised. I had a long trail of PM's with DavidG about the test results and here's a summary (paraquoted):

The 0.113 PV is at 635nm which is in the red and the eye is most sensitive to around 540nm in the green. Since green light is shorter in wavelength than red the wavefront error is worse at shorter wavelengths.

The wavefront at the eyepiece is 2x 0.113 PV, or 0.226 PV, and 1/4 wavefront is 0.250...

On the Ronchi test, the images show some problems. They are not very good. The lines should be evenly and smoothly bowing. They should look like this (( )) and the closer you get to focus like this () On this mirror they start at the edges bowing inward then change direction and bow outward. This shows the figure is not smooth and this is also confirmed in the computer image showing the blue ring at around the 70% zone. From what I can see the mirror is just under 1/4 wave. Bob Romeo, the CEO at Composite Mirror Associates also mentioned this - the mirror has a turned edge.

It's interesting to note that in the series of Cave Catalogs out there, only in the early Red Catalog did Cave ever claim 1/10 wave accuracy in his mirrors. Subsequent Pink and the series of Blue Catalogs changed the wording to "highest quality". All Catalogs state the secondaries are 1/10 wave. Thanks goes to Jon "Pisigma" who probably has all the catalogs for following the claims of mirror quality as stated in the catalogs.

I intend to do a little more research on the 1/10 wave and "Highest Quality" claims. I have the '75 8" f/7 mirror at the shop now getting recoated and tested along with an RV-6 mirror and the Horsetrail Cave mirror, which might not be a Cave Mirror, but that might actually be a good thing! We'll find out next week.

Now I know a lot of people are going to say that Cave only made exceptional mirrors. Heck, they even made mirrors for Questar and the Government! Hmmm, what was that saying about "close enough for government work"?

I would like to hear from anyone who has had their Cave mirror on the bench and their test results.


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tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: Datapanic]
      #5697547 - 02/23/13 11:15 PM

Well, I haven't had my Cave mirrors tested. Probably should. But I did a shootout between my Cave 8" f/7 lightweight deluxe, the OC 8" f/6 Connoisseur, and the OC 8" f/6 Discoverer on Saturn. The discoverer was not very good, but the mirror might be pinched in the cell. Both the Connoisseur and the Cave were very good, though, with the Cave being ever so slightly better than the OC. I really wanted the OC to "win" because it's such a better telescope over all, with the 1.5" shaft mount and stuff.

My 12.5" f/7 Cave is also very good. Finest detail on Jupiter I've ever imaged. Real potential there.

My 10" f/16 Cave DK has Tinsley optics, so maybe it "doesn't count". I should probably test it, because all I've done is a visual assessment, and it might not have been performing up to snuff those couple nights.

My 6" f/8 Model A Deluxe needs a recoat worse than any Newt I've ever had! So the low contrast in it might be due to the awful coatings.

I would definitely not be afraid to refigure a mirror, even a Cave, if it wasn't a killer already. I'd bring it to a mirror class, like the one in Delaware next month that Dave works on, if it were me. Those classes are a blast!

-Tim.


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actionhac
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Reged: 08/09/08

Loc: Seattle
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: tim53]
      #5697643 - 02/24/13 12:25 AM

My 6"f8 Student Deluxe has a very good mirror and it was made March 1972, 238 mirrors before yours Dan.
I wonder how far Cave Optical was from the beach in Long Beach. Just thinking as the weather got nicer and with the glass store front and a sidewalk right there maybe Tom had more than one figure on his mind.

Robert


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tim53
Postmaster
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Reged: 12/17/04

Loc: Highland Park, CA
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: actionhac]
      #5697659 - 02/24/13 12:49 AM

Well, the Cave shop was pretty far from the beach!

-Tim.


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Datapanic
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Reged: 10/17/09

Loc: Tucson, Arizona
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: tim53]
      #5711746 - 03/03/13 11:38 PM

That would be cool if you could bring the best mirror over to David G's workshop and put it on the bench, Tim. I also wouldn't be concerned about re-grinding the glass of a Cave Mirror to get a better figure. But since this one has been recoated, I don't think that's going to happen any time soon!

Cave's shop was far from the beach, but there is that mystery Corvette parked in front of the shop from those old photos, so maybe he took a cruise on Fridays?


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Datapanic
Post Laureate
*****

Reged: 10/17/09

Loc: Tucson, Arizona
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: Datapanic]
      #5711754 - 03/03/13 11:42 PM Attachment (5 downloads)

Meanwhile, restoration continues... Mostly stripping off the old paint, applying primer and putting on the new coat of either "Instrument Gray" or Black Wrinkle Finish. It's a lot of work to do this - Aircraft grade paint stripper, sometimes two times, sanding off rust and blotches of paint, refinishing the Dec and RA shafts, and just the time it takes to apply a good coat of paint that will last a while is definitely a trial of patience. On the table are most of the major mount parts that have been reconditioned over the past 3 weeks. Once they have cured completely (a minimum of 1 week) then I'll start to put it back together. Can't wait!

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Datapanic
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Reged: 10/17/09

Loc: Tucson, Arizona
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: Datapanic]
      #5711774 - 03/03/13 11:58 PM Attachment (6 downloads)

Another shot of the staging area for the mount and rotating rings before assembly. The Wrinkled Black application has been the most challenging - unless done right, the wrinkles come out uneven and I start over again - stripping, priming and spraying it on once more. It takes a good 12 hours for the wrinkle paint to fully cure. I do each piece individually...

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Datapanic
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Reged: 10/17/09

Loc: Tucson, Arizona
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: Datapanic]
      #5711777 - 03/04/13 12:01 AM Attachment (3 downloads)

There are quite of few fasteners - nuts, washers, bolts and so on that put the scope together. I found it much easier to measure and inventory every one of them and put that info into an excel spreadsheet. I then place the order for those fasteners and when they get delivered, inventory them again, checking off each one on the spreadsheet and labeling each ziplock bag for which the fasteners are intended for.

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Datapanic
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Reged: 10/17/09

Loc: Tucson, Arizona
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: Datapanic]
      #5711792 - 03/04/13 12:19 AM Attachment (2 downloads)

Although the tube was already in very good shape to begin with, it still needed refinishing to match up with the fresh paint job of the rest of the scope. The fiberglass tube is waterproof, so with that in mind, after cleaning it up with some 409, I commenced to lightly wet sand by hand it with 600 and 1500 grit sandpaper, to smooth out any blemishes. This also helps subdue the spider cracks that tend to happen on the finder ring and mirror cell mount holes when they get bumped or tightened up too hard. Later, rubbing compound and a coat of wax will finish it off to a lustrous finish.

Wet sanding with such fine grades only takes off microns from the surface and does not intrude upon the coating enough to make a difference.

Any deeper gouges left are part of the assembly and covered up by the original parts that were there. In this photo, that would be the focuser edges, spider washers and finder base.


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Datapanic
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Reged: 10/17/09

Loc: Tucson, Arizona
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: Datapanic]
      #5711802 - 03/04/13 12:28 AM Attachment (4 downloads)

The inside of the tube was weathered with dust and grime and even after washing it, there was still a dull flat black that would not be acceptable for contrast performance. So, I coated it with Krylon Ultra Flat Black. But before applying the paint, I used blue painter's tape to cover up all the holes so that the black paint would not seep onto the white finish from the inside. It turned out to be overkill after I finished, but better to be cautious than loose time in the restore.

This tube is so short - only 38" long, that I was able to reach inside it with the rattle can of paint and get a good coating all the way up and down. The ends of the tube were not hit with paint very well, but that doesn't matter since they will be covered up by the aluminum end rings.


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Datapanic
Post Laureate
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Reged: 10/17/09

Loc: Tucson, Arizona
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: Datapanic]
      #5719738 - 03/08/13 12:49 AM Attachment (2 downloads)

The mount and tube are shown in this photo. First, the front end of the mount is complete. The RA and Dec Shafts have been refinished and shined up, along with the Dec Circle and its pointer. The Tube has been finished with a rubbing compound and wax. The Inner Rotating Rings have been reinstalled on the tube.

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Datapanic
Post Laureate
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Reged: 10/17/09

Loc: Tucson, Arizona
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: Datapanic]
      #5719745 - 03/08/13 12:57 AM Attachment (3 downloads)

The Inner Rotating Rings can be a bear to reinstall if the orientation is not noted before taking the scope apart beforehand. On this scope, I made pencil marks, small punch marks on the inside of the rings and even paper and pencil notes for the correct position of the rings as well as which ring was the upper and which was the lower on the tube when I took the scope apart. This is absolutely essential to do because the drill holes on the Inner Rings to the Tube are not perfectly 90-degrees apart; the rings only go back on one way.

So, after letting the wrinkle paint cure for a week, I slide the rings back on, used tooth picks to hold and verify that all the holes line up before fastening them back on.

It is important to be gentle with the fasteners and not force anything - because the tube is 40 years old and it can easily be spider-cracked if anything is forced against it!


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Datapanic
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Reged: 10/17/09

Loc: Tucson, Arizona
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: Datapanic]
      #5719747 - 03/08/13 01:01 AM Attachment (4 downloads)

The old tube still has some damage that we just have to live with - here is the worse of it where one of the finder rings mounts to the tube...

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Datapanic
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Reged: 10/17/09

Loc: Tucson, Arizona
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe new [Re: Datapanic]
      #5719754 - 03/08/13 01:07 AM Attachment (4 downloads)

When reassembling the scope, after painting, it's very important to clean out all the old threaded holes before putting things back together. Not only new paint, but any kind of crud can interfere with installation of new fasteners and a smooth calibrated elbow torque amount during reassembly. Here is a tap (3/8 - 24) being run through one of the Outer Rotating Ring Adjustment Holes before it is attached to the already installed Inner Rotating Rings...

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Datapanic
Post Laureate
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Reged: 10/17/09

Loc: Tucson, Arizona
Re: A 1972 Cave 8" f/4.5 RFT Lightweight Deluxe [Re: Datapanic]
      #5741901 - 03/18/13 10:02 PM Attachment (6 downloads)

When putting the Outer Rotating Rings back on, I try to evenly space the adjustment so the gap between the outer and inner rings are about the same all the way around and so that there is a smooth, but not too loose amount of tension when rotating the outer rings. Later, when performing celestial alignment the first time on the mount, there is a method to follow that will use these set screws to put the optical axis perpendicular to the Dec Shaft.

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