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!

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Making the Pitch Lap, and Polishing

I’m waist deep in the polishing process of the telescope making project, for me this is the final stage.  As I stated at the beginning of this project, I would omit the Foucault test as well as figuring of the telescope glass.

In truth, I had to make 2 pitch laps.  The first one was okay, but now very good.  The “channels” that were cut were far too shallow, and the lap came out lopsided.  Besides, I got a little anxious to finish this mirror and polished before fine grinding was done.  So I had to scrape off the lap with a knife and return to fine grinding.  How did I know? Well, the surface was more frosted than it should have been for starters.  Also, I found that there was a scratch that went unnoticed.

So another hour and a half of grinding is what it took to correct these few problems.  The new pitch lap is much better and it’s polishing!  Below is the setup of the area for the pitch lap making:

Lap making setup

Now, before I get into the whole process, because it is an involved one, let me state that this only one way of making a pitch lap.  There are probably hundreds of ways (no I’m not kidding) to make a successful pitch/wax lap.

All of the books I read on this stage were advising the beginner not to make a lap of pitch, but I didn’t listen, because of extensive research and tips of the actual process.  You may wonder why I said “wax” in the preceding paragraph.  That’s because a lot of people have made wax laps over the years, mainly of beeswax.  I’m not sure if you can purchase beeswax sheets anymore, but maybe some are still around.  The beeswax lap serves as an economic alternative to the traditional pitch and is easier to make (not anymore unfortunately).

On to my lap making process!

The first thing to do is to open up the pitch package, put it in an old pan, and heat it very slowly.  Because I am trying to be as economic as possible, I decided to purchase a synthetic lap, Acculap Pitch.  I bought the intermediate grade as it is best for laps of this sort, which can be purchased here.

While the pitch is heating, the surrounding area should be covered well in newspaper (see above photo).  Also, I got a large bowl and put hot water in it, then the two glass disks.  This is probabilistic one of the tensest parts of making the lap, for if even a single drop of cool water gets on a glass disk, it will crack it and it’s over.  Luckily, that did not happen.

Be sure to watch the pitch lap closely, and I meant it when I said to heat it slowly, because I became a little impatient and heated it too fast, and it started to bubble, which hardens the pitch.  Fortunately, the addition of turpentine can bring it back to it’s normal hardness.  But be careful if you do this to not get any in the flame, because of the explosive properties of turpentine.

The reddish hue is due to the Rouge from the previous lap.

The reddish hue is due to the Rouge from the previous lap.

While all of this is going on, I took a small bowl of water and filled it with warm water and a soap solution of dishwashing detergent, this will be lubricant to keep the mirror and lap from sticking while pressing is in progress.  Also, when the pitch is poured, a cardboard damn will need to be made to retain the pitch on top of the tool.  This was made out of a cereal box, and the glossy, printed side was facing in as its able to retain the moisture of the pitch.

When all of this is finished, the pitch should be very liquidy, though still thick as pitch is.  Then I removed the tool from the water bath, dried it very thoroughly to promote good adhesion of pitch and slowly poured the pitch onto the tool.  I decided to have this lap much thinner than the previous lap, because if I have to scrape it off again, it will be much easier to accomplish.

Freshly poured pitch

Freshly poured pitch

Now I let it sit for 5 or six minutes, for the pitch to harden enough to peel off the cardboard dam.  This is my favorite part.  There’s just something about the lap that really looks sharp, or as sharp as a slab of pitch on glass can look.  I did not get a photograph of it, but it still remains in my mind.  Now one of the most critical parts- pressing.

Now the soapy water comes into play.  I poured a liberal amount of the stuff onto the warm lap, then slowly set down the mirror.  Now I move the mirror slowly around a half an inch to 1 inch in different directions, also rotating the mirror.  I thought I made good contact and it feels smooth when I polish, but the edge is polishing before the center, which means the dreaded turned edge.  This can be fixed, but I need to cold press, which is a process where a rouge lubricant is put between the mirror and lap and a weight is put on top of the tool to sit for 30 minutes or more.  The only problem is that the lap dries rather quickly and I don’t want to get them stuck together.

Getting back to the lap making, I slid the mirror off after I though good contact was made, and let it cool off for a couple of minutes, and then proceeded to cut the channels.  In Amateur Telescope Making, they recommend using a razor blade to cut these large channels.  They even have pictures of  someone cutting a perfect, flawless lap from a razor blade.  This is however, not the case.  What follows is jagged, uneven impressions, and almost every time chipping off large pieces out of the face of the lap.  Me and my Dad learned this making the previous lap, which by the way, my Dad is a huge aid to me during this process.

So just to see, we tried a couple of lines, and it came just as described.  So my Dad came up with a genius way to make good channels, a small handheld grinder.  This served perfect for making neat, and good looking channels.  What was most amazing to me during cutting these channels is the effect of the ground up pitch.  I grinds it into this very fine fuzz, the closest thing being cotton candy.

A finished pitch lap

A finished pitch lap

It is not the best lap I’ve ever seen, but it does it’s job like it should.  For polishing, I decided to use Red Optical Rouge.  I would prefer to use the faster polishing Cerium Oxide, but it’s more than triple the price for the stuff and like I said, this is a budget project.  I have heard that Rouge gives a better polish that Cerium Oxide though.

The main difference between grinding and polishing is that in polishing, you have to be very careful when you have the lap on the stand.  It should be dust free, and the work is so delicate that dust will scratch the polished surface.  You wouldn’t think there would be any chance to get dust between the disks, but there are actually many.  For example, you expose the lap when you go to renew the charge of rouge.  So to stop this, I put a piece of plastic or a sheet of paper over the exposed lap to keep dust to a minimum.

One thing about using Rouge is that is is abominably messy.  The stuff gets everywhere! And it’s all over your hands most of the time, so when you go to wash your hands with a bar of soap, the bar will be covered with rouge.  It gets on clothes, doors, doorknobs, towels, even in your hair!

My new goal is to be finished with the entire project by the end of the year, which is not a whole lot of time.  I probably won’t get the mirror aluminized, but everything else (I’m hoping) will be finished.

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!

 

More Mirror Grinding: Books

When I first got the idea of actually building a telescope in my mind, the first book I read was Amateur Telescope Making.  To many this represents the pinnacle of telescope making books/guides.  However, there are more out there than I once thought.

For example, here is the book on mirror making that my grandpa wrote back in the 60s.  It was typed with a typewriter and the drawing were all made by him, which were really great drawings.  This book is the simple way on how to build a 3 inch F-12 reflector.  But don’t search for this book, because I have the only one.

Another good book for telescope making is Building Your Own Telescope, by Allen Thompson.  I have not read it myself but many have said it is a very good reading, and can had for around 10 dollars (here).  Look around, you’ll find countless books on this subject, they are not very recent, but still have the same valuable information to build a telescope from the ground up.

So, the question is, which book to buy?  This depends on how far you want to go as far as precision for the telescope.  I reccomend a simple technique that does not require the foucault test, because it just makes telescope making a whole lot simpler.  Plus, a mirror’s figure does not need to be perfect in order to observe celestial objects with satisfactory results.  It has been said time and again that a considerably less than perfect mirror will perform as well as a perfected mirror, it is just a matter of conscience.

Before I got really serious about building my telescope, I was demanding for perfection.  I had to do the focault test, had to have a parabolic surface, and I wanted at least a 6 inch diameter mirror.  It turns out that I did not do/get any of those, and that is fine with me based on what it said in Amateur Telescope Making.  Sometime in the near future, I will be putting my grandpa’s book on this website as a page, along with all of the pictures, sketches, and references.

This weekend, I had been pushing some glass myself- only 2 more grades of abraisive left to go!  I ground through the 12 micron today, and and hour was enough.  Last weekend (and the previous post), I had thought of something that would be simple and effective in cleaning house for the next finer grade of abraisive.

A simple idea really, all I did was cover the top of the grinding stand in clear plastic wrap, then set the tool in place as normal.  I tried it, and it really works!  Cleanup was easy as ever, all I had to do was simply pull up the tape, and lift the wrap off.  Then the new wrap can be laid on and taped, ready for action.

As I am progressing through these finer grades, the glass has started to lighten up a bit, and it is not as frosted as it previously was when I ground the first grade (#80 silicon carbide).  I have been told that when the final grade has been finished, the glass should almost be transparent, though not quite, as polishing will remove the final grade of pits.

While progressing through the project, I’ve been planning ahead for gathering the finishing materials (diagonal, diagonal mirror, mirror cell, etc) and found a place to get mirrors aluminized cheap, as well as pretty inexpensive secondary mirrors, and other components.

On Friday morning, I was able to take out my 70mm refractor for a good hour and a half.  I was able to get an extraordinary view of the Orion Nebula, which is saying something, because I have seen this diffuse cloud through a 14 inch reflector, so I know what I am talking about.  I’d say that the view at 56 power is pretty close to the view through a 6 inch reflector.  I hope to have this sketch on Astronomy Sketch of the Day, just like when I had my M31 sketch on there.

Here is my sketch of M42 :

All I can say is, I hope to be sketching this through my 4 inch soon.

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.