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jimegger
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Reged: 12/22/05

Loc: Palmer,Alaska
Re: 9.25 inch refractor project new [Re: Jeff B]
      #5675153 - 02/12/13 01:45 AM

well, the polishing of 8 hours per side is not enough after cleaning off all the lenses I saw a definite milky sheen so I put in 2 more hours per side. We will see if that does it but I may have to go another 2 hours per side. Gotta make the glass take on a good polish before trying it out !!!

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kfrederick
Carpal Tunnel
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Reged: 02/01/08

Re: 9.25 inch refractor project new [Re: jimegger]
      #5675381 - 02/12/13 08:12 AM

Jim Great thread thanks for posting .Are you folding the telescope . Could be mounted like a newt with the flat where the primary goes .Or a window setup with your big flat mounted ahead of the lens . Very cool how ever you do it .

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Sean Cunneen
Let Me Think
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Reged: 08/01/07

Loc: Blue Island Illinois
Re: 9.25 inch refractor project new [Re: kfrederick]
      #5675726 - 02/12/13 12:16 PM

How do you know you are done polishing? Is there a "super-duper" polish you could put on an objective? I know that Zambuto and Ziess polish a certain amount of time after they should be done, but I am curious as to your perspective?

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Mike I. Jones
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Reged: 07/02/06

Loc: Fort Worth TX
Re: 9.25 inch refractor project new [Re: Sean Cunneen]
      #5675732 - 02/12/13 12:21 PM

A severe test for polish is to shine a laser pointer through the glass at several different places. If you can see the beam spot on either surface, you ain't done polishing.
Mike


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jimegger
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Reged: 12/22/05

Loc: Palmer,Alaska
Re: 9.25 inch refractor project new [Re: Mike I. Jones]
      #5676816 - 02/12/13 11:37 PM

The laser test seems like a good one Mike , it makes sense, any pits would make the scattered light obvious.

I have 12 hours on both the crown sides now and 11on the flint. I am going to put them in the scope tomorrow for a look see at the mountain here. The polish looks close to done if not done but I have not done the laser pointer test on them. The first go around I had about 16 hours on the flint and 20 on the crown while attempting to correct the figure before I gave up and went back to fine grinding. All the surfaces looked pretty polished out at that time but I did notice that the 12 hour mark seemed to be the start of the full polish period. I only went to 5 micron grit for the final size in fine grinding but maybe next time I'll go to the 3 micron size to help expedite polishing.


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Mark Harry
Vendor
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Reged: 09/05/05

Loc: Northeast USA
Re: 9.25 inch refractor project new [Re: jimegger]
      #5677057 - 02/13/13 06:07 AM Attachment (53 downloads)

Laser works good, and so doesn't holding it up with foreground light coming thru at different angles looking at a dark something-or-other with low contrast. Either is a dead give-away to a lack of polish. When I use a laser, I shoot it thru straight on to the surface. Greenies are even better with a divergent beam.
My 8" crown dialyte, I polished about 2 hours each side with pads on the grinding tool, then an hour each with pitch, NBK7. Completely transparent.
M.


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Mike I. Jones
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Reged: 07/02/06

Loc: Fort Worth TX
Re: 9.25 inch refractor project new [Re: Mark Harry]
      #5677247 - 02/13/13 09:02 AM

Beautiful, and FAST there, Mr. Barkie! Sure sign of excellent work during fine grinding. Makes me wonder if Jim didn't smooth long enough earlier in grit stages, way before 5 micron, like even at 30 microns or larger. 12 hours of polishing on buttery-soft flint glass like F2 seems way overkill, and should have only taken a couple of hours or so. He may be trying to get out the bottoms of Carbo pits! I think I spent maybe 3 hrs/surface on my F4 flint for my 6" f/10 achromat.

But hey, Jim's a hard worker and if 12 hours does it, then GOOD! Go have fun with that lens!
Mike


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jimegger
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Reged: 12/22/05

Loc: Palmer,Alaska
Re: 9.25 inch refractor project new [Re: Mike I. Jones]
      #5677621 - 02/13/13 12:42 PM

I went 45 minutes per grade starting with 120 grit on the flint and crown. The 320 grade and 30 micron grit I followed it with are nearly the same size for a total of an hour and a half on that. It always polished out my pyrex mirrors well in less time than I have in this lens now. I am using my original pitch laps to which I had added some beeswax which may have slowed the polishing down somewhat. From what I see now at 12 hours it still needs some more time - but it is close ! I have to take a break here from all the polishing for a day or so to do some machine work but I may make new pith laps after that and continue on.

I did put the lens elements in their cells and will be taking a peek through the scope later on today. I see that the lenses need more polishing. A new lap may just be the ticket to finish up !


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Mike I. Jones
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Reged: 07/02/06

Loc: Fort Worth TX
Re: 9.25 inch refractor project new [Re: jimegger]
      #5677778 - 02/13/13 02:23 PM



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jimegger
Pooh-Bah
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Reged: 12/22/05

Loc: Palmer,Alaska
Re: 9.25 inch refractor project new [Re: Mike I. Jones]
      #5678096 - 02/13/13 06:00 PM

The scope is together and a per-cursory peek shows a very good image even before the cool down of the lens. The elements do need more polishing time but they are getting closer. I believe a new series of laps may be the solution for more rapid polishing action. The old ones I am using are getting the job done but I suspect the constant use has allowed the wax to be not as polishing agent en training as new pitch will be. The spacing of the lens elements needs to be increased by .008 inches also to make it to your specs Mike. I am not going to do the double pass until polishing is complete as it would probably change the lens forms anyway. I can say with certainty though that the image I see is definitely sharper than the first go around so on that note I will stay the course.

As soon as the sun gets off to one side and the glare goes away , I'll attempt a picture through the scope and post it here.


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Mike I. Jones
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Reged: 07/02/06

Loc: Fort Worth TX
Re: 9.25 inch refractor project new [Re: jimegger]
      #5678174 - 02/13/13 06:54 PM

Great news, Jim! Can't wait to see your picture(s).

Just curious: what pitch and polishing compound are you using? Could either be slowing you down? I've been working for years out of a gallon jug of ZOX and really like it. CeO2 is fast but can sleek unless you ball-mill it. CeO2 is better for dummy shining mirror backs, sides, etc. Red rouge is SLOW!

Using Acculap or Gugolz 64, I find that if I slop on too much slurry the lap surface gets overcharged and the polishing also slows down, along with the figure getting hinky. Taking a wire brush to the lap occasionally to scrub the hard surface glaze off gets you back to native pitch.

Whatever, your perseverence is certainly paying off!

When you get to double-pass testing, test in green light like from a green LED, that spectrum should be narrow enough, and a properly corrected lens will give you nice straight fringes. Just a suggestion: before going to a figuring session, try a few different airspace shims first - the airspace I gave you assumes all measured data is exact.

Standing by,
Mike


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jimegger
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Reged: 12/22/05

Loc: Palmer,Alaska
Re: 9.25 inch refractor project new [Re: Mike I. Jones]
      #5678303 - 02/13/13 08:26 PM Attachment (54 downloads)

Mike, I do have a glaze on my lap that I suspect is not doing a good job with the Cerium Oxide. I bought some Gugolz 64 pitch which I aim to make into new laps if the wire brushing of the present laps doesn't speed things up. On the first go around I made some laps from Burgundy pitch and got a real nice polish at 14 hours with the Cerium Oxide. At any rate , it will get done if it takes me 20 hours! It is almost there.

Here is a picture I just took of Pioneer Peak on a windy cloudy day with my Canon 20 da. Focus may not be perfect but to my eye the images look good. Color correction seems very good as well.


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Mike I. Jones
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Reged: 07/02/06

Loc: Fort Worth TX
Re: 9.25 inch refractor project new [Re: jimegger]
      #5678567 - 02/13/13 11:15 PM Attachment (43 downloads)

Hmm, I'll take your word for it at this point - low contrast, no sense of scale, and unknown level of horizontal path turbulence, so it's hard to tell. Can't wait to see a clear day shot, followed by lunar terminator shots!

Here's a test suggestion for double-pass autocollimation testing (assuming you have like a 10" optical flat?). Get a Radio Shack 5mm Green LED, Model 276-022 , Catalog #: 276-022, for a whopping $1.99. Website is here. Spec sheets says its spectral centerline is 570nm, with half-power points at 550nm and 590nm. Perfect spectrum for double-pass testing with Ronchi and slitless knife-edge (do both!). I simulated your lens in double pass with these wavelengths and weightings.

It says the forward voltage is 3VDC, and operating current is 20 milliamps. You have to put a resistor in series with the LED or you'll burn it up. If you use a 9V battery, the resistor should be (9-3)/0.02 = 300 Ohms. A quarter-watt fixed resistor is plenty. To vary the LED brightness you can also put a little 0-1K pot in series with it as well. But the 300 ohm resistor must stay in the circuit path.

If you're a master electronics guru, I apologize!

Mike


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Mike I. Jones
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Reged: 07/02/06

Loc: Fort Worth TX
Re: 9.25 inch refractor project new [Re: Mike I. Jones]
      #5678618 - 02/13/13 11:49 PM Attachment (43 downloads)

I processed some on your picture to see if I could bring out any detail. Still can't tell scale, but you're right, it's still an RGB color picture, but I don't see much in the way of secondary spectrum in the fine details.

More pictures!
Mike


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jimegger
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Reged: 12/22/05

Loc: Palmer,Alaska
Re: 9.25 inch refractor project new [Re: Mike I. Jones]
      #5678708 - 02/14/13 02:10 AM

What i usually do Mike for comparison is look through my APO which I know to be excellent at the same power at the same time to get a better picture of how badly the atmosphere is behaving. I did not do it this time. The part of the peak you see here is about 5 miles distant and a Raven would be just about the size of that point you see at the very top. The lenses are still milky enough when used together to ruin the contrast as well as the sky being cloudy with a slight haze.

Tomorrow comes more polishing possibly with new laps. I am trying to weigh the time spent making a new lap to just using the old ones again for a bit. The glass is so close to being polished out another run of a couple hours on each side just may do it.


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jimegger
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Reged: 12/22/05

Loc: Palmer,Alaska
Re: 9.25 inch refractor project [Re: jimegger]
      #5680393 - 02/14/13 11:15 PM

Okay, so I wire brushed the laps and guess what.... it polished like a fiend !! Right now they appear fully polished but just to be certain I will be putting in 1 more hour on each lens surface. By wire brushing the pitch surface it made the lap "bite" much better - one could feel the lap working its magic with more of a grabbing feel during the stroke. Now the lenses look clear. If I had done this in the beginning I would have been done quite a ways back. I was not sure wire brushing the laps would be something one could do without hurting the laps until you told me you did it with no trouble Mike. Thanks for the advise !

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Mike I. Jones
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Reged: 07/02/06

Loc: Fort Worth TX
Re: 9.25 inch refractor project [Re: jimegger]
      #5680464 - 02/15/13 12:07 AM

Glad to help! Wire brushing shatters off the surface scab glaze and makes billions of little microchannels that the polishing slurry can more easily flow through. Be sure to brush lightly, and just enough to get rid of the glaze. And, you still have to press in a little afterwards, as the lap profile is definitely changed by brushing. Rinse the lap well in lukewarm to slightly warm water before pressing to get rid of the powderey brushed-off mess. Wire brushing is far superior to pressing petticoat material, scratching up with a razor blade, etc., but you have to develop a feel for how hard and long to brush, and how quickly the microchannels will press out while working the lap and it starts to get too "grippy" or "draggy".

You do know about pressing in after brushing with just clean water, no slurry, and a single layer of a polyethylene trash bag stretched between lap and glass, right? The freshly brushed pitch will re-form to the glass shape almost perfectly, and the two parts will never stick together. Using only water keeps the lap from charging up too much and needing another scrubbing. Another old cool optics shop trick I picked up along the way.

Mike


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jimegger
Pooh-Bah
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Reged: 12/22/05

Loc: Palmer,Alaska
Re: 9.25 inch refractor project new [Re: Mike I. Jones]
      #5680520 - 02/15/13 01:08 AM

The laps I have are pretty hard from use, being old and the fact that I added the beeswax in the very beginning. I cold press the laps overnight by letting the lenses sit on them with no weight to keep their shapes. The wire brushing was just enough to leave scratches on the hard pitch surface. It was just perfect for good polishing action. The other trick is to press a fine mesh into the pitch and get many small facets for increased action. The scratches were just enough to do a really good job in my case though. I use a fairly watered down slurry of Cerium Oxide for most polishing and at the end just use water as the lap leaves a smoother polish that way.

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MKV
Carpal Tunnel
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Reged: 01/20/11

Re: 9.25 inch refractor project [Re: jimegger]
      #5680599 - 02/15/13 02:38 AM

Mike you're right - wire brushing is so much better than microfacets. Also quicker. I use brass wire brush only, but I imagine a very hard tooth brush may do the job too. Worth investigating. The bag and clean water pressing is another good shop technique. You can't overemphasize the need for such methods, along with the final figuring slurry concentration of 1:100, 1-minute figuring spells, and cold pressing after each.

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jimegger
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Reged: 12/22/05

Loc: Palmer,Alaska
Re: 9.25 inch refractor project [Re: MKV]
      #5681631 - 02/15/13 02:19 PM Attachment (46 downloads)

Here are a couple of pics of the final polishing results. The crown is on the polishing stand in this one.

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