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1965 Cave 10" f/16 Dall-Kirkham OTA

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#51 jrcrilly

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Posted 06 March 2011 - 11:15 AM

Is it possible the extremely high focal ratio can cancel out and overcome the 30% CO?


No, it has the same negative effect on contrast no matter what the F ratio is. It never affects resolution, though.

#52 tim53

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Posted 06 March 2011 - 11:29 AM

All I had to work with was Sirius. Jupiter was down by the time I set it up, and clouds were swallowing up a bunch of other stuff.

I still had a "flat spot" in the way out of focus star images, particularly looking up the drawtube without the diagonal in place. I could see two of the three primary mirror clips easily, but not the other. I did some adjustment of the focuser (I am delighted that this scope has these adjustments, unlike my SCTs), but I need to see things in the light of day to understand what I'm accomplishing (if anything, LOL).

It is a huge central obstruction, though. And the spider vanes must be 1/16" steel, welded to the center hub and with nuts welded on the tube end. It's actually very cleverly designed and robust. That secondary isn't going to move!

I had cogitated about making a smaller secondary for it at the Delmarva class next weekend, but the spider is already near the end of the tube and I'd need to be able to mount the secondary farther out than it currently is.

I think this scope is fine the way it is. I may take it out to our dark sky property in Utah and leave it there so I only need to bring my cameras and computer with me to do some deep sky astroimaging.

-Tim.

#53 jrcrilly

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Posted 06 March 2011 - 12:01 PM

It is a huge central obstruction, though.


It's not really so large. All the other Cass reflector designs (Classical Cass, RC, etc.) utilize obstructions of 40% to 50%. Only the relatively slow D-K variant permits such a small obstruction. Look at it this way - contrast will be similar to that of a 7" refractor. Most folks would consider that to be pretty good! ;)
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#54 tim53

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Posted 06 March 2011 - 12:47 PM

Hi John:

I'm not really complaining, thought it may sound that way! My 9.25" SCT has a bigger obstruction, and it does well on planets, where I like to hang out.

My 12.5" f/23 Classical Cass has a 20% obstruction, and works so well I'd really like to go longer for a dedicated planetary instrument one of these days soon - like f/30 or so!

-Tim.
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#55 DAVIDG

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Posted 06 March 2011 - 01:47 PM

Hi John:

I'm not really complaining, thought it may sound that way! My 9.25" SCT has a bigger obstruction, and it does well on planets, where I like to hang out.

My 12.5" f/23 Classical Cass has a 20% obstruction, and works so well I'd really like to go longer for a dedicated planetary instrument one of these days soon - like f/30 or so!

-Tim.


Tim,
I quick calculation shows that you can make a new secondary of about 1.5" in diameter that will get you a f/30 system. The only issue is that the figure will not be spherical but an oblate spheroid.
I think a better plan would be to make sure these optics are dead on the money and use a 2x barlow to get you to f/32.

- Dave
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#56 tim53

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Posted 06 March 2011 - 02:03 PM

Hi Dave:

I was hoping you'd chime in here. I think this scope is good enough as is for me to use it as my galaxy imager when I go to my dark sky site in Utah, so I'm planning on building a box for the OTA to store it in. I already have a scopeguard case for the mount. That way, I'll only need to bring my cameras and computer with me. I also think the coatings are serviceable as is, so I don't think I'll have the optics recoated.

So, the question is, what to do next weekend when I finish my 8" f/9? And I guess I'm leaning more toward wanting to refigure that 12.5" f/7.25. I may even put it on the big Springfield mount, but I might also just make a nice split ring mount for it. Either way I go, I'll likely make the tube in sections for transport and storage.

After using this Cave 10" last night, I relize that another 10" Cassegrain wouldn't add enough diversity to my "collection" to make it worthwhile at this point in time. The 10" Cave isn't a whole lot easier to move around than my 12.5" Cass, though it is lighter and does ride on the NJP well, whereas the 12.5" is a bit much for the NJP.

A 12.5" f/7.25 Newt on a Springfield mount would be crazy to move around unless I make it come apart (maybe WAY apart!, I can still picture the Simpson 12" f/8.4!), so probably a split ring with a truss tube makes more sense.

In related news (to the class, that is), I've got this cool 12" cubic case that looks like a scopeguard with the metal edges and plywood sides, that I thought I'd use to bring mirrors and tools back and forth from Delaware next week. But it's not quite big enough for a 12.5", though. So, I can bring my 8" kit, and maybe a couple other 8" mirrors to test that need recoating anyway, but if I finish that 12.5", I'll need to find a shipping box for it.

-Tim.

#57 tim53

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Posted 06 March 2011 - 02:53 PM

Sun came out, so I took another wholescope pic:

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  • 4430322-In_Daylight.JPG


#58 tim53

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Posted 06 March 2011 - 03:52 PM

Hey cool! Collimating this thing in daylight was actually pretty easy!

First thing I did was to loosen the focuser setscrews and reorient thefocuser so that the focus pinion shaft was parallel to the saddle plate! I hate it when it's not! (unless the focuser is rotatable on purpose, and this one isn't.)

Next, I made sure the secondary hub was centered in the tube. It's not quite, but it's only off by a couple mm in either x-y direction, and it's designed to be tightened snug against the inside of the tube.

So, I next adjusted the block holding the focuser and baffle, until the secondary was concentric with the walls of the baffle tube.

Then, I went back and forth a couple times between the primary and seconary adjustments until everything was concentric - aka, my waterfowl are now coaxial!

Too bad it's clouding up, and it's supposed to be cloudy tonight. I'd like to hunt for Jupiter before it gets too low. I may leave the scope set up just in case, then take it down if it's a bust.

-Tim.

#59 clamchip

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Posted 06 March 2011 - 04:29 PM

I was just over at Phil's site and noticed this:
http://www.philharri...n.net/cave3.jpg

Interesting because advertised as "the new" 10" Cass and "send for new 1963 catalog".
I wonder if this was when Cave introduced this model around 62'-63.

Robert

#60 tim53

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Posted 06 March 2011 - 04:32 PM

The Tak saddle plate that I mounted this thing on came with my Em-500 mount. Seller had a 5 or 6" Tak APO on it. I've still got the rings, but they don't fit anything I own. So I took them off the plate.

I actually prefer the plate to a Cassidy saddle and dovetail plate in the case of a big cass that needs to be mounted on the saddle at like head height. My 12.5" Cass has a dovetail plate on it, and it's pretty scary while I try to make sure it's seated right before I tighten the saddle clamps.

I bought a bigger saddle plate a year or so ago off amart to replace the Cassidy plate with for mounting the 12.5".

I really like that I can see how I'm doing, aligning the studs up with the holes in the saddle, and that supporting the tube with one hand while I put the nuts on with the other isn't so frightening as working with a dovetail at that height.

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#61 tim53

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Posted 06 March 2011 - 04:35 PM

Incidentally, I forgot to mention that, when I re-did the collimation today in the light, I realized I was pretty darned far off last night!

So, I still don't have a good idea yet how good these optics might be!

-Tim.

#62 tim53

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Posted 06 March 2011 - 06:55 PM

Robert:

They found me! Hopefully, my little diversion accomplished the desired result and you're cloud-free still!

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#63 clamchip

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Posted 06 March 2011 - 07:55 PM

I still have heavy cloud cover. I think we need to drop an expensive eyepiece or crack a corrector or something.

Robert

#64 tim53

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Posted 06 March 2011 - 08:26 PM

I'm totally socked in. I put everything away and am figuring on just doing stuff on the web tonight.

-Tim.

#65 tim53

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Posted 07 March 2011 - 02:16 PM

I was just over at Phil's site and noticed this:
http://www.philharri...n.net/cave3.jpg

Interesting because advertised as "the new" 10" Cass and "send for new 1963 catalog".
I wonder if this was when Cave introduced this model around 62'-63.

Robert


Hi Robert! I somehow missed this post yesterday. I've been wondering something similar, like maybe the 762 means July, 1962?

-Tim.

#66 clamchip

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Posted 07 March 2011 - 04:27 PM

Wouldn't that be something! July 1962 #2. Hopefully Clint's Tinsley friend will have some information.

The pictured portable is quite a bit different than yours with mounting rings, the finder and GS mounts, which you would expect on a portable telescope. If yours is a bolt on possibly Cave also had a permanent/observatory model also. Some of the early Cave's were bolt on tubes.

Robert

#67 tim53

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Posted 07 March 2011 - 04:45 PM

It seems unlikely that Cave would have made the scope in 1962 and not to order when the seller got it in 1965. Unless it was a showroom model? Mine never had rings on it and there is no evidence of other holes in the tube having been patched up. So, the finder and guidescope were likel always mounted onto the tube. Also, no tube counterweight, which must have been for balancing cameras.

The tube is similar, and the end rings are identical (though the seller painted over them, since they are riveted on).

I wonder if the tube is gray underneath the paint? I should ask the seller when I ask about the details about the mount and how he ordered it (and if he has the paperwork!!).

-Tim.

#68 clamchip

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Posted 07 March 2011 - 10:29 PM

Look at the tube mounting/stiffening? rings in this picture, I wonder if they are through bolted and only to keep the tube round at the mounting points. They look approx same location as your bolts.
http://www.frobenius.com/cave28.gif

I could see a display model sitting unsold for a couple years, at $1795.00, a new car was only a few dollars more or the average house was $12000!

Robert

#69 swh

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Posted 07 March 2011 - 11:47 PM

Tim, It appears the tube assy looks right at home on that hugh mount. The Cave has found a good home!

The cave mount shown on the rear cover is identical to the one I had. But only a single counterweight was delivered. When I purchased the scope, (less the tube rings shown on the Cave sales cat.) the tube assy was completed prior to the mount, so I took delivery of it and mounted the assy on my Galaxy Treckerscope mount.
The original color of the tube was white, but the parks tube yellowed over time (45 years)
If needed Im sure Parks has a replacement tube.
Tim, Thanks again
Steve

#70 tim53

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Posted 08 March 2011 - 12:16 AM

Hi Steve:

I just sent you an email ;oD

I think you may have answered some of my questions here, but I am curious if you ever took any pictures of the scope on the Cave mount?

Man, I was hoping to get a look at Jupiter with it tonight, but when I got home it was already getting windy. Now, all the windows in the house are rattling!

Must be why the Clear Sky Chart showed the seeing as "Bad" tonight!

-Tim.

#71 tim53

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Posted 26 May 2011 - 10:47 AM

Well, it's been a long time since my last update on this.

I had the scope out over the weekend, to finally collimate it on the sky. I pointed it at Saturn and tweaked one of the primary adjustment screws, as it was out enough to deliver poor views before I did.

But when it was collimated, it was surprisingly good. Mostly, I used the planetary Orthos I'd picked up at the swap meet a few months back. These were nice, but they were rather dirty. It looks as though a couple of them must have a film on the lenses in addition to some dust, like the plastics in the box (itself plastic) outgassed over the years in the heat.

By the time I switched to my Swan 9 and 15mm eyepieces, the sky was starting to cloud over, so I never did have a clear, contrasty view during this session. I suspect the contrast through the scope on a clear night might still be a little compromised, but probably due to the mirrors needing recoating more than the 30% obstruction.

Overall, I was pleasantly surprised by the definition it delivered.

I won't have a chance to try it out again for a few weeks at least, as RTMC is this weekend, and a field test of the Curiosity rover (simulated, not the flight rover!) starts next week and goes through the following week.

-Tim.

#72 tim53

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Posted 26 May 2011 - 11:21 AM

(...though I am cogitating about maybe taking it up to RTMC with me)

#73 tim53

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Posted 26 May 2011 - 10:51 PM

Whelp, don't know if it's the optics or the coatings, but my 10" f/6 delmarvascope (optics by yours truly) beats the heck out of the cave on Saturn for contrast. Jet black background!

Seeing isn't as good tonight as it was on the weekend, o'course, but the sky is more transparent.

Still, I think the cave is good enough to deserve a recoat.

Bots to put stuff away and get packing for Rtmc in the morning!

-Tim

#74 tim53

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Posted 24 July 2011 - 11:48 PM

Rats! Cave mount for 10" Cassegrain

...only the seller wants $1200 for it! No pics, either.

I may email him, though.

-Tim.

#75 tim53

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Posted 25 July 2011 - 12:20 AM

Same seller, similarly astronomical price: Cave 12.5" Cass

-Tim


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