New Project: Criterion RV-6

Hi everyone, well it’s been a LONG time since I’ve posted, but now that school’s out, let the blogging commence! Anyway, I recently acquired a vintage reflector from a really nice guy, a Criterion RV-6 Dynascope.  I read up on these, and they apparently were top of the line back in the day (1950’s to the late 1970’s).  The RV-6 is a 6 inch F-8 Newtonian Reflector on an equatorial mount with a plug in motor drive for star tracking.  Top of the line back in the day, before the company’s demise with the rising popularity in the late 70’s.

So this is my summer project, restoration of this beautiful telescope.  I took it out for first light a few weeks ago, just as is (after of course cleaning the mirror as it was very dirty with all sorts of material I didn’t know what it was).  I got it roughly polar aligned.  The motor drive plugs into a standard outlet, and functions very well for it’s age (at this time, I did not know the precise date of this particular telescope). The view? Phenomenal.  My first target was Saturn, and plainly showed 4 moons, and this was not a very clear night.  Banding on the planet was obvious, as well as detail in Saturn’s rings.  Very pleasing, refractor-like images and sharpness. Collimating well is the key to better views in even cheap telescopes, but when you collimate well with a scope like this, it’s awesome.

My next target was M13, the famous sparkling globular in Hercules.  Now remember, where I live, there is very severe light pollution, and pulling detail out of deep sky objects, even bright ones is a challenge.  But, having good eyes has helped, I’ve pulled M81 and M82 out of my Observer 70mm from here in La Verne, which is quite an accomplishment I’ve heard.  Some people struggle with acquiring this in a 6 inch scope, but a 70mm? Wow.  Where were we? Yes! M13 with the RV-6.  My Orion Expanse 15mm eyepiece yields about 80x in this scope, and the view was spectacular. Very bright, round, on the verge of some resolution even at such a power as low as 80 (which is rather low for observing DSO’s. Averting my vision in various directions will make the glob “grow” and brighten, and make it very grainy.  The most satisfying part of the view was that it wasn’t moving! I’m sure I’ll discover that when seated (this scope’s designed to have the user remain seated) and tracking, I’ll pull out much more detail.  Mating the barlow lens with the 15mm yields about 160x.  Now it was getting interesting.  With direct vision,  the glob took up about 1/6 of the field.  Averted and direct showed numerous faint member coming out of the backround.  When it’s averted, the glob gets huge! So there you have it, my first light of the classic RV-6 Dynascope.

The RV-6 when I first received it

The RV-6 when I first received it

So, before I got into it, I knew I should make a scheduled plan of what to do and how to do it.  I made an immediate decision to refurbish the OTA before the mount, which would simplify things right from the start. First off, the condition the tube is in needed a lot of cosmetic help, meaning paint and hardware.  Some tape had been put on the tube as a marker to show where to put on the tube rings for balance.  Well, they were stuck on there good, I don’t know what kind of tape it was, but I pulled off a good amount of it, and sanded the rest down.  I had already decided to give the scope a brand new paint job, so I used the existing paint as a sort of primer, and sanded it really smooth.  The tube is a kind of cardboard, called bakelite back when it was first invented.  All in good condition, except for a small piece scraped off at the edge of the top of the tube.  For the paint, I did not want a bright glossy white, but rather I chose a glossy (not original) Vintage White color, from Rustoleum.  Took 2 cans to do, and also will be needing a clear-coat as a finish.  So right now with that, I’m making sure the white is completely dry for the last coat.


Post paint

I also painted the 6x30mm finderscope in the same color as the tube, and it looks great, but, the side of the tube is engraved with “Criterion”, and it might prove difficult to repaint this back to black.  If things continue going at this pace, expect to see a completely refurbished, put back together, working RV-6 by hopefully the beginning of July.  I think the tube will be finished rather soon as there really isn’t much to do there, just cleaning, and minor paint touch-ups here and there, nothing big, but I think it’ll look awesome when this project is done, and also, a great scope to use!


Fully Polished Mirror, and the Support

After 4 months of work, my telescope primary mirror is finished.  I started this project on the 18th of August and finished on December 31st, with a few hours to spare before the new year.  I thought that would be a goal, because I’m going to submit my work (a report basically) to win the National Young Astronomer Award, from the Astronomical League.

The winners (first, second, and third prize)  get an all expense paid trip to the ALCON (Astronomical League Convention) and of course the prize.  First place wins a five inch refractor telescope- a pretty good prize, see the details of this scope here.

Anyway, the telescope mirror is finished and that’s a huge part of the telescope.  For the reflective optical coating I chose Destiny.  My mirror will run a mere 30 dollars- after checking other companys, they averaged about 50 dollars for a mirror of this size.  I also bought a secondary mirror and spider for a small sum.  1/10th wave optics, 1 inch size, 15 bucks is pretty hard to beat.

Upon finishing my mirror, I counted up all the time working on my mirror, from start to finish.  Total time of the glass in motion was over 25 hours!  It may seem like not that long, but it feels longer because of the precision I had to maintain during the process.  Total polishing time clocked in at 6.7 hours- a little longer than expected.  But it’s rouge, one of the slowest polishing compounds you can buy.  And it was worth it considering that it is said to give a finer polish than Cerium Oxide, which is also three times the polish.  Oxide polishes faster, but the increased price was not worth it to me.

Finished Mirror

For me, one of the most important parts of the telescope making project is putting your initials and the date you finished it on the back of the mirror.  It was just as exciting as I thought it would be.  It may seem insignificant, but I liked doing it.


Also completed was the mirror support, or cell.  It consists of two circular pieces of wood, one the size of the mirror and one the size of the telescope tube.  The mirror sits on the upper piece, and is secured with “L” shaped clamps.  In between the pieces are 3 long screws, and attached are 3 springs.  Next comes the wooden piece for the tube.  Under that, the the ends of the screws are exposed, and wing-nuts are then threaded on.  By twisting on of the wing-nuts, it compresses the spring and moves the mirror on top slightly downward on that side of the mount.

IMG_3210 IMG_3209

mirror in the support

Pretty good huh? I bought an aluminum tube at the hardware store for 7 dollars.  It is five inches round, so the bottom piece of the support matches that.  Obviously, the “L” clips will need to be painted black and other stuff to eliminate reflections.  There’s not that much left to do on the scope really.  I had the bottom base for the Dobsonian mount finished- with a CD as the bearing material, which works really good by the way.

I'm building a mount similar to this.

I’m building a mount similar to this.

Well to wrap things up, I finished a big important part of my telescope and I’m glad I took my time with it.  Pretty soon I’ll be gazing upon galaxies and nebulae.  I think the biggest help will be the aperture.  If you’ve heard great things from Orion’s Skyscanner, my scope has the same aperture.  It also has a much longer focal length (f-12) and should, if collimated correctly, provide sharper images.

Telescope Polishing- Update

Almost polished mirror

Almost polished mirror

As you can see, the mirror is polishing pretty good but it is taking a long time to do, they weren’t lying when they said rouge is really slow, not to mention incredibly messy.  The large grey mass is on the back of the mirror- I got careless during the 3rd grade of abrasive and accidently set the mirror down face up. See post (here). All of the scratches you see are on the backside of the mirror.  Also, after repeated “cold pressing” sessions, the mirror refuses to polish from the center to the edge.  I have heard of this before, and it usually causes a turned edge.


As you can see above, the area in the middle is not polished yet.  This is often hard to distinguish from the ground surface on the back, but at the right angle, I can see it.  I was lucky enough to capture it in the picture.

Unfortunately, the lap in the previous post was ruined by dropping it, I am reckless sometimes.  Then I made a new lap, and let it sit too long after pouring it and it hardened before I could put in the curve.  The next lap polished a lot and then, for some reason, the lap started to crack around the edges.  It eventually came off so now I have to make another lap.  The books don’t lie, polishing with rouge and pitch are not easy.


Up close with Rouge and the polishing process.

Polishing operation, as always covered with Rouge

Polishing operation, as always covered with Rouge

Focal Length Test

As I progress through building my telescope, it is important to know and understand the focal length, or distance where all of the light from the star forms into an actual image at one point.  There is a simple yet effective way to do this.  You don’t need much, but a checklist is helpful.

When I perform this test, I use:

a bucket  halfway full with clean water

a tape measure that extends to about 100 inches

the mirror (duh)

a piece of chalk or card to mark the distance

and a white poster board (optional but it helps)

Here is the setup:

So here’s the steps from Building a Reflecting Telescope:


As you can see, the process is so simple and straight to the point that I will agree not to explain what is being depicted.  My results came out well as expected.  I was aiming for an f/12 telescope, which would yield a 48 inch focal length, and it came in at 47 inches.  No harm done, as an inch will not effect the performance in the least bit.

As I was grinding on the weekend, I am on the last 2 abrasives; aluminum oxide 9 and 5 micron.  It is said that when grinding has been successfully completed, the mirror will feel like the finest satin to the touch, and newsprint can be read through it.  It’s already unbelievably smooth, and not quite able to read through, but nevermind.

I caught a snag while finishing my abrasive: I scratched the mirror’s surface near the edge.  I’m not quite sure how it happened, but my best guess is that somehow, dirt of some sort got between the glasses, and scratched.  If this furrow was near the center, I wouldn’t be stressing over it as much.  It takes about 3 times as long to remove such a thing at the edge than one near the center, as the glass naturally grinds out fastest at the center.  Oh well.  I knew that I would get a scratch at some point, but I’m happy it wasn’t during polishing, or I would have been in some serious trouble.

Hope to be finishing this project soon, because I’m itchy to look through this telescope!


Project Update: Telescope Making 4

The continuation of my telescope making project is making headway.  I just got all of the abrasives necessary to finish all for the grinding .     I ‘m making good progress, but the going is slow.  I used my grandpa’s book that he made in the 1960’s-  Building a Reflecting Telescope.  Don’t try to look for this book, because it was never published.  It does have some very good drawings and explains a simplified way to build a telescope.

Well, I’m doing an even more simplified version of his book.  I found in the last chapter of Amateur Telescope Making.  Here’s a quote:

“For the first mirror we had to abandon Pyrex, the mirror handle, the pitch polishing lap, and the paraboloid.  We teach the beginner some of the rudiments of the Foucault test but only because we are present to coach the worker in its use.  Although pitch laps give finer polish and fewer zones, they are so difficult for the average beginner to make and alter that we regard them as the principal bottleneck in mirror-making.  They have discouraged more beginners than any one thing, or any ten things.  Although we get fewer fine mirrors with honeycomb foundation, it best suits our purpose, which is to finish the first mirror while the maker’s enthusiasm lasts.”

I pretty much agree with everything that they are stating here, and this “group” is the telescope making group from the Cleveland Museum of Natural History.  I checked out their website, and I’m pretty sure that they don’t make telescopes there anymore.  Apparently, there used to be a free program to build your own telescope from scratch, using a honeycomb foundation instead of regular pitch.  The only thing I don’t agree with is the part for a beginner not being able to make a successful pitch lap.

I guess that that this does not apply in my case as I have telescope making in my blood (thanks grandpa).    I’ve set up a grinding schedule and I plan to follow it quite closely.  I plan to grind through one grade every weekend.  I have 5 more grades to grind through, so I guess I won’t finish it by my birthday, but I’m not devastated.  Good mirrors take time, and that’s fine by me.

On Friday, I was really excited so i made some good progress through Saturday as well.  I ground my way through Silicon Carbide #320 and then on to White Aluminum Oxide 25micron.  It is very strange going from this muddy grey sludge to a white sludge.  The abrasive is becoming so fine that it doesn’t really feel gritty.  The only similar substance I can use to describe it is powdered sugar.

I have also thought about starting a new WordPress blog.  I want to do a blog that is like a sketch reference website.  But it has to be with at least 1 small telescope, as well as with a bigger telescope.  Of course, I have to have a lot of objects sketched in order to that, and I haven’t done that.  I have made many sketches, but not 110, yet.

Also, they would probably need to be black paper/background to really get noticed.  I have heard of running the white paper sketch through a scanner and then altering it to a negative image, but I don’t have a scanner, so I guess that means I have to use real black paper.  But that’s fine with me, I’ve been eager to use a different media for sketching.  Hopefully, sometime in the near future I can have a sketch on Astronomy Sketch of the Day.

Someday, I will make larger, more complicated telescopes as well.

Theory of Distance and Visual Limits

Early on in my astronomy career, I was looking at a rather nice astronomy book and it had wonderful high quality large photo prints.  They were obviously at the Hubble level, and they showed an excellent amount of detail.

I had left the book on my bed propped up, and upon my return, I noticed something.  I stood back a few feet, and noticed that there was less detail than being up close to it.  It seems like a rather oridinary thing, but I studied this for a while, and I started to formulate a scientific theory.

This theory states that there is a limit at which the human eye can detect color, and this varies to the person.  Plain and simple, at a certain distance, you can no longer detect color in an object.  I believe that this is possible in not just photographs, but as well live objects.

Step 1: Acquire a large, visual, preferably not very filtered astronomical picture.  The Orion Nebula and Andromeda galaxy are perfect.  Prop them up on a chair outside.

Step 2: Walk up to the photograph, and note the definite color and detail in the deep sky object.  Note and remember what you see.

Step 3:  Now walk back 10 feet, and study the photograph.  It now appears smaller, and with less striking colors and details.  What were beautifully detailed and cloudy objects are reduced to a smoother, mottled appearence.Note and remember what you see.

Step 4: Walk back another 10-15 feet and study the picture now.  It has most of it’s defined detail gone.  Now, when I got to this point, I came upon a problem.  Galaxies and nebulae emit their own light, and a photograph does not.  The solution I found was to have the picture be printed on a translucent piece of bendable plastic.  Now take a light, and shine it through the back, but scatter the light with a thin fabric sheet to make the light distribution equal over all diameters.  I probabily should have told you this before, so my apologies.

Step 5:  Now walk back again and again, repeating the process until which there is no more color detected by your eye.  This distance varies for everyone and generally, the view will be very similar to the view through a telescope.  You have now found your visual limit; but now what?

I am no math wizard, so there must be some kind of number system for the visual limit.  And if so, the object, distance of that object for real and the exposure time must also be accounted for.  This requires one big equation that I am definitely not up for.


This experiment actually works too! I tried it and there is something to this, try it yourself, it should only take a few minutes.  If you can’t have it printed on translucent plastic, another possible method is to print it out on regular paper or a poster and tape the paper to the plastic.  A decent astronomy poster that is somewhat large can be had for under 10 dollars on amazon.

Good luck and clear skies.