teast
professor emeritus
Reged: 11/10/07
Posts: 500
Loc: Kentucky
|
|
Quote:
I haven't looked at the R&P focuser but is rolls down from the mid-point. i assume there is a shim or pressure pad of some material to tighten it?
If the RV-6 has a weak point, it's the R&P focuser. It does the job, but just barely. I shimmed mine with some thin cardboard (cereal box) in order to get more traction but it still had a lot of slop in it so I replaced it with a JMI RCFMini1 which works great. If you can get yours snugged up using shims then go for it.
Quote:
I have focused on some fir tree needles at 2000' (so clear and bright!) but only with the focus racked out, the brass sleeve pulled out, and the ep just in the sleeve. Does that seem about right?
The brass sleeve is actually two brass sleeves, one inside the other. Did you have both extended or are they flush with each other? You can extend the drawtube by pulling the inner sleeve out from the outer one.
By the way, the electrical tape was probably put on the finder to prevent marring the tube with the adjusting screws. Some clear bumper pads might do the trick and not take away from the looks as much.
-Tom
|
strdst
scholastic sledgehammer
Reged: 03/23/08
Posts: 830
Loc: Oregon USA
|
|
Quote:
"Anyone have a theory why I have a second set of screws in the tube. The mirror is held by the set closest to the end. The other set isn't doing anything at the moment."
I'm no expert but I did stay in a Holiday Inn Express. Someone please correct me if i'm incorrect.
Wow, I need to start getting out more.
|
strdst
scholastic sledgehammer
Reged: 03/23/08
Posts: 830
Loc: Oregon USA
|
|
Hi Tom,
There is the brass focuser with the grooves cut in, and a 2 3/8" brass sleeve that slides into the focuser. Looking out about 3 miles to some trees I need the focuser fully extended, the brass sleeve pulled out to near the falling out point, and then the 18mm eyepiece can be flush to the sleeve. Anything closer, and I need to slide the eyepiece up as well. Not a good move in the dark over a hard surface! I'm on grass, still in the light. Are you saying there are 2 sliding/removable sleeves?
|
teast
professor emeritus
Reged: 11/10/07
Posts: 500
Loc: Kentucky
|
|
Now that CN is back online I can answer your question  .
No, I was referring to the outer brass tube (the "rack") as one of them and the inner brass sleeve as the other. In my mind I envision the focuser as the black crinkle housing attached to the tube. Just a terminology glitch in my mind.
For near focus (3 miles as compared to infinity) I recall having a similar situation although perhaps not quite as extreme as your description. Newts aren't typically used for terrestrial viewing since they invert the image so the drawtube won't be as long as you might be used to with a refractor.
Are you sure that the primary mirror is being held in by the set of screws closest to the back end of the tube? If it's actually held in by the upper set that could explain a bit of your situation. I think once you turn it to the sky you won't have a problem. Keep us posted.
-Tom
|
Bonco
Carpal Tunnel
Reged: 04/17/06
Posts: 2297
Loc: Florida
|
|
Quote:
Anyone have a theory why I have a second set of screws in the tube. The mirror is held by the set closest to the end. The other set isn't doing anything at the moment.
If I read your comment correctly, the second set of screws are likely there to fill the holes that someone drilled to move the mirror forward for prime focus photography. They moved the mirror back to the original position to facilitate visual use. Cheers, Bill
--------------------
RV6
Meade 2045
6 inch f/4 RFT R. Fagin Optics
TV Genesis
2.4 inch Lafayette Equitorial
3 inch Polarex/Unitron Equitorial
10 inch Zhumell
PST 40mm Solar scope
4 inch F/15 Antares
2.4 inch Unitron Equitorial
Tasco 10K 80mm/1200mm
Towa 339 Restored
|
strdst
scholastic sledgehammer
Reged: 03/23/08
Posts: 830
Loc: Oregon USA
|
|
OK focuser, rack, sleeve, eyepiece... got it. I had a few moments to catch Jupiter through the clouds last night. Yes the mirror is attached closest to the end (farthest from the secondary). At infinity, the B&L 18mm eyepiece that came with was just focusing, using most of the available (rack out) travel. A 12.3 mm Meade Plossl had plenty of movement in and out to focus. The image of Jupiter wasn't real crisp, but I'm sure the mirror needs collimating. Not bad for starters! I'll have to be looking for used tools to do that.
|
teast
professor emeritus
Reged: 11/10/07
Posts: 500
Loc: Kentucky
|
|
IIRC, the inner brass sleeve has vertical slots cut into it to permit a kind of "compression" (for lack of a better term) adjustable fit, to hold the eyepiece in place without a set screw. You should be able to lift the eyepiece up slightly, exposing a bit of the barrel without danger of it falling out too easily. This may give you a bit more draw for focusing. Do your eyepieces fit snugly in the sleeve or do they automatically slide down flush with the top of the sleeve?
-Tom
|
strdst
scholastic sledgehammer
Reged: 03/23/08
Posts: 830
Loc: Oregon USA
|
|
Tom,
The eyepieces are quite snug. I was lifting the ASP 18mm to get a far off terrestrial image. Looking at Jupiter last night I was able to leave it flush with the sleeve and just rack out fully. Although the first light wasn't sharp, I was pretty impressed with how bright things were... you know compared to my 3" and 4" toy refractors. I also remembered I have a classic orange C-8 in the spare bedroom I never even think to take out anymore. I remember I've never been impressed with the C-8 for planetary sharpness, but it's pretty great for the globulars. Maybe this RV-6 can bridge the gap between my refractors and the 8" SCT.
other keith
|
BRisley
sage
Reged: 09/04/06
Posts: 345
Loc: SW Florida
|
|
Glad it arrived in good shape.
Brian
--------------------
3 C-8's (2 OT 72/80 and SPC-8)
8" f5 Dob
Meade 4450 on EQ-2
Meade 4501 on EQ-2
Tasco 4.5" on EQ-2
Tasco Starguide 60GT
C-90/Cometron Sky Scanner 80 mounted tandem in a C-8 Fork
Cometron CO-62
Meade 11x80 Bino
|
teast
professor emeritus
Reged: 11/10/07
Posts: 500
Loc: Kentucky
|
|
Keith,
Keep in mind that newts will perform better after some cool down time. Set it up an hour ahead of time to let it start stabilizing to the ambient temperature. Tube currents can dull an image and make it "swim". Collimation is also important, as you've already mentioned.
It'll take some learning on your part since you've mostly used refractors in the past. Once you get a feel for it though, I think you'll be amazed at how well it can perform. My RV-6 at a dark site has given me some absolutely stunning views of the Orion nebula, Andromeda, planets and even some comets. Have fun, ask questions and keep us posted!
-Tom
|
StarmanDan
sage
Reged: 08/27/07
Posts: 391
Loc: China Spring, Texas
|
|
Welcome to the RV-6 crowd! Looks like your newest addition is in better shape than mine. I acquired mine from a friend whose grandfather had his stashed in the garage for the past 30 odd years. The bakelite tube was cracked in a couple of spots, the focuser was seized up, mount was rusted, mud daubers and spiders had made home in the tube and the mirror coatings were nearly non-existent. To my amazement, the clock drive still worked! Had the mirrors recoated, cleaned up the focuser, tube and the rust, replaced the cork in the clutch and I'm now working on restoring the tube. Even in its present state, the scope is usable and delivers excellent images for being a spherical f/8 mirror. I'm sure you won't be disappointed.
--------------------
"Starman" Dan Doyle
Texas Astronomical Society of Dallas
Central Texas Astronomical Society
8" LX200GPS w/ST80 guidescope, Canon 350D+DSI Pro
150mm f/8 Sky Watcher Refractor
10" f/4.5 Homemade Dob
RV-6 Criterion Dynascope
http://darcstar.wordpress.com
|
deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2926
|
|
StarmanDan,
The mirrors were parabolic - a 6" f/8 sphere would have noticeable SA, and mine had none - NONE. It was a great mirror.
-drl
|
Bonco
Carpal Tunnel
Reged: 04/17/06
Posts: 2297
Loc: Florida
|
|
Ahhha...The old RV6 spherical vrs parabola raises its head once again. I've never tested my original mirror due to its excellence. However I bought a 2nd RV6 mirror and it tested spherical with an excellent smooth surface. The test facility said a 6 inch at f/8 is very forgiving with little detectable SA. Haven't tried the mirror yet visually. The guy doing the testing said he "believed" most if not all RV6 mirrors where spherical at least the ones he's tested.
Bill
--------------------
RV6
Meade 2045
6 inch f/4 RFT R. Fagin Optics
TV Genesis
2.4 inch Lafayette Equitorial
3 inch Polarex/Unitron Equitorial
10 inch Zhumell
PST 40mm Solar scope
4 inch F/15 Antares
2.4 inch Unitron Equitorial
Tasco 10K 80mm/1200mm
Towa 339 Restored
|
DAVIDG
Carpal Tunnel
Reged: 12/02/04
Posts: 1986
Loc: Hockessin, De
|
|
My RV-6 that I purchased new in 1976 had basicly a spherical mirror with a broad turned edge. I refigured it to an excellent parabola. I've test many a RV-6 mirror and handful of RV-8's. The RV-6 are almost always undercorrected and every RV-8 was a sphere.
The reason why the RV-6 give nice images is because a 6" f/8 sphere is just over a 1/4 wave, and if you polish on it for about 5 minutes and put a little correction on it, the wave front will drop below a 1/4 wave.
A spherical 8" f/8 is well above a 1/4 wave and needs to be parabolized to produce a good image.
- Dave
--------------------
Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics
Engineering = Taking what you have and making what you need.
|
teast
professor emeritus
Reged: 11/10/07
Posts: 500
Loc: Kentucky
|
|
Criterion advertised the RV-6 as parabolic with 1/10th wave accuracy. Considering this was during the 50's, 60's and 70's, the claim could be interpreted in several different ways. I am assuming that the description applied to the mirror surface but who knows  ?
I believe this was pretty standard terminology before Strehl ratios came along. Some who have their mirrors tested find that they are spherical while others find them parabolic and exceeding the specified standard. What really matters most is does it perform well. Mine sure does !
-Tom
|
rmollise
Post Laureate
Reged: 07/06/07
Posts: 4575
|
|
Quote:
Ahhha...The old RV6 spherical vrs parabola raises its head once again. I've never tested my original mirror due to its excellence. However I bought a 2nd RV6 mirror and it tested spherical with an excellent smooth surface. The test facility said a 6 inch at f/8 is very forgiving with little detectable SA. Haven't tried the mirror yet visually. The guy doing the testing said he "believed" most if not all RV6 mirrors where spherical at least the ones he's tested.
Bill
At f/8, a spherical mirror will function tolerably well. It will certainly not be a barn-burner. Just OK.
It can ALMOST meet the 1/4 wave criterion (you really need to be at f/10 to do that with a sphere), but CANNOT be better than that, no matter how smooth and well-made the sphere. The 4.5-inch Tasco (Towa) reflectors all had good spherical mirrors, and did OK--good on the deep sky, quite useable on the planets. That is not "blow your doors off," though... 
I would guess that those RV-6s that perform well on the planets (one of the scope's hallmarks) are parabolic. Lots of weird stuff went down over the long run of these scopes, between the glory days and the B&L debacle, but I do know Upco, Criterion's supplier through at least the sixties, made some good mirrors. 
--------------------
Uncle Rod
Rod's New Book:
Choosing and Using a New CAT
Available now!
Edited by rmollise (08/05/09 06:27 PM)
|
rmollise
Post Laureate
Reged: 07/06/07
Posts: 4575
|
|
Quote:
The reason why the RV-6 give nice images is because a 6" f/8 sphere is just over a 1/4 wave, and if you polish on it for about 5 minutes and put a little correction on it, the wave front will drop below a 1/4 wave.
An undercorrected mirror is an undercorrected mirror, which does not mean it was left a sphere. A plain sphere at f/8 will produce average images.
--------------------
Uncle Rod
Rod's New Book:
Choosing and Using a New CAT
Available now!
|
deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2926
|
|
Rod has an excellent point. I'm sure the parabolizing on these was perfunctory, but they probably had real masters who knew how to do it fast without overcorrecting. A perfect parabola can be made in an hour or less by a master from a 6" f/8 sphere. I have a 4.5" f/8 sphere and I can see the residual SA in this otherwise perfect mirror, and I don't remember seeing any in my RV-6, so that was one they probably hit out of the park.
-drl
|
Steve40
member
Reged: 10/15/06
Posts: 24
|
|
Just to chime in---
I purchased an RV-6 in the late 1960's as a high school graduation gift to myself! It was terrific! Many years later, as a high school physics and astronomy teacher, I guided many students through grinding, polishing, and figuring 6 inch mirrors.
Just for fun, I put my RV-6 mirror on the foucault tester. It blanked out evenly and smoothly all over---a beautiful sphere! No hint of parabolization I could see.
Steve
|
Bonco
Carpal Tunnel
Reged: 04/17/06
Posts: 2297
Loc: Florida
|
|
The thread is becoming very interesting! I've written this many times before so I'll be concise this time:
I had my 6 inch f/8 triple element oil spaced 1989 vintage Astro Physics refractor set up in my yard viewing Jupiter. I loved this scope and wish I still had it. A kid in the neighborhood brought over a 70ish RV6...The RV6 side by side to the refractor provided a more contrasty, clear view of the planet. Gulp... Long story short, sold the AP and restored my 1960's vintage RV6. Spherical or paraboloid the RV6 delivers fantastic performance at a very economical price.
Bill
--------------------
RV6
Meade 2045
6 inch f/4 RFT R. Fagin Optics
TV Genesis
2.4 inch Lafayette Equitorial
3 inch Polarex/Unitron Equitorial
10 inch Zhumell
PST 40mm Solar scope
4 inch F/15 Antares
2.4 inch Unitron Equitorial
Tasco 10K 80mm/1200mm
Towa 339 Restored
|
Previous
Index
Next
Threaded
[Re: 
Edit
Reply
Quote
