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Unitron 150 restoration thread

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#51 PawPaw

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Posted 18 February 2020 - 07:40 PM

Edmund thickness measured:

 

Crown:  .358"

Flint: .450"

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#52 PawPaw

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Posted 18 February 2020 - 07:44 PM

Finally I put the Unitron Lens in the Edmund Cell.

 

And the Edmund Lens in the Untron Cell..  ( already tested this but what the heck)

 

These three pics are of the Unitron fitting in the Edmund......Like a glove!

 

 

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#53 PawPaw

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Posted 18 February 2020 - 07:49 PM

Now The Edmund in the Unitron Cell.....As stated previously the diamater fits just like a glove....The thickness however would require some type of modification to the retaining ring on the Unitron cell.  A spacer could be added between the retainer ring and the objective cell or the retainer ring could have some material removed to adjust for the Edmund objective thickness.

 

The diameter on either objective does not need modification to fit in either cell....At least for the two objective samples that I own.

 

First two pics are the Unitron cell with Edmund side by side.

 

Third pic....Unitron Newton rings in Edmund cell.

 

 

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#54 PawPaw

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Posted 18 February 2020 - 07:58 PM

I also purchased a Micrometer  (Thanks for the recommendation Robert)  I measured both the Edmund and Unitron Foil spacers.  I found them both to be the same at .004".

 

So I constructed new foil spacers out of straight Aluminum foil with no adhesive to .004"

 

The Newton Rings look finer on the Edmund objective than the Unitron but both are now concentric.   Looking forward to a star test next.  



#55 starman876

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Posted 18 February 2020 - 08:02 PM

I could be that when Unitron supplied Edmund lenses they ones they used maybe have been a different lens than what you have.   I got the information about the Edmund lenses and having to mill out the cell for the Edmund lens to fit from the vice president of Unitron.  



#56 starman876

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Posted 18 February 2020 - 08:10 PM

Unitron 4" lenses over the years had a different thickness.  I have about 5 of the 4" lenses and some will not interchange with into other cells.  I have found that lenses in the 60mm and 75mm were also a different thickness over the years.   I believe they were made by different shops over the years hence the varying thickness.  I would presume these shops also had the lens cells made to fit the different lenses. 



#57 CHASLX200

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Posted 19 February 2020 - 06:38 AM

Edmund had some killer lens here and there.



#58 AstroKerr

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Posted 20 February 2020 - 05:49 AM

Nice thread, PawPaw, on-hand factual. Good work, informative


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#59 clamchip

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Posted 20 February 2020 - 02:23 PM

I have this image in my electronic files.

Diameter 4.028"

The dates may indicate this is the Edmund 4 inch lens made 'in house' at Edmund.

I don't know if Dr. Rank was involved in this lens, or if the radii are standard recipe.

The note,

"All surfaces figured to 1/8 wave +- 15 rings"

I wonder if those are Newton's rings at the specified .004" air space.

I did find flint glass Type 649/338 but ran out of time researching it.

Robert

 

post-214027-0-46455900-1514037379_thumb.jpg


Edited by clamchip, 20 February 2020 - 02:38 PM.

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#60 PawPaw

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Posted 20 February 2020 - 07:02 PM

I have this image in my electronic files.

Diameter 4.028"

The dates may indicate this is the Edmund 4 inch lens made 'in house' at Edmund.

I don't know if Dr. Rank was involved in this lens, or if the radii are standard recipe.

The note,

"All surfaces figured to 1/8 wave +- 15 rings"

I wonder if those are Newton's rings at the specified .004" air space.

I did find flint glass Type 649/338 but ran out of time researching it.

Robert

 

attachicon.gifpost-214027-0-46455900-1514037379_thumb.jpg

Since the last Engineering revision date on this looks like 4/24/81?  My guess is a Rank objective.  I know the RKE eyepieces first appeared in Catalog # 781 Sept 1977 so by that date Edmund was working with Dr Rank.

 

Also interesting that this shows the air space should be .004 which is what I measured (Foil) on both the Unitron and Edmund lens I own.



#61 clamchip

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Posted 20 February 2020 - 08:49 PM

I've always used .005" on Edmund lenses Sam Brown in 'All About Telescopes' says

.005"

Could it be that I'm a thousandths off?

Is there another level of perfection beyond perfect? maybe so I may just try

.004"

The  plus or minus 15 rings is interesting.

Are you getting 15 rings with your Newton's?

 

Robert


Edited by clamchip, 20 February 2020 - 08:53 PM.


#62 starman876

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Posted 21 February 2020 - 11:26 AM

I have this image in my electronic files.

Diameter 4.028"

The dates may indicate this is the Edmund 4 inch lens made 'in house' at Edmund.

I don't know if Dr. Rank was involved in this lens, or if the radii are standard recipe.

The note,

"All surfaces figured to 1/8 wave +- 15 rings"

I wonder if those are Newton's rings at the specified .004" air space.

I did find flint glass Type 649/338 but ran out of time researching it.

Robert

 

attachicon.gifpost-214027-0-46455900-1514037379_thumb.jpg

The diameter on this spec sheet falls more in line of what I thought in that the Edmund lens is larger in diameter than the Unitron lens. 



#63 PawPaw

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Posted 21 February 2020 - 07:10 PM

After experimenting for 3 days on the Unitron cell and lens I had that Eureka moment.  Ok so I just reinvented the wheel but I was excited......

 

The main issue I was struggling with was the small clam chips on the edge made it difficult to find the optimum location of the foil spacers.  earlier I discovered the original thickness of the Unitron foil was .004 but that does not work when the edge is not uniform.  So the solution I found was two fold.   If I  used the 120 degree offset for the spacers I could not get the Newton Rings to be concentric...ie centered.  I finally found the sweet spot on the lens although not exactly 120 degrees the spacers are close.  This cell is the older one that does not have the push pull collimation built in just 3 screws to retain the lens.  The issue I was having is I could get the newton rings centered and concentric until I put on the retaining ring.  Even with out tightening the screws just the weight of the retaining ring would throw off the rings.  

 

I got out my straight edges and flat surfaces thinking the cell itself was not true but to no avail it was good.  So today after giving the lens a final hydrogen peroxide soak and complete rinse with distilled water I decided it is what it is.  I made my final adjustments leaving a very slight rattle in the lens but the newton rings still all over the place......Until.......I screwed it into the OTA assembly.  I guess trial and error is my motto, or reinventing the wheel.  My eureka moment finally arrived....The older unitron cell is not very thick or substantive but once it was mated securely to the OTA cell it trued up.  I did my best to get pictures of the newton rings as they are now solid, centered and secured.  I found you can even overtighten the lens cell to the OTA so there is a sweet spot there as well.  Next step is the star test.  I cannot get the pictures to show the rings very well.  In person they look much better.   With that said I am not an optician so I would like opinions on the Newton Rings pictured below with cell attached to OTA   Good, Bad,  Ugly, OK?

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Edited by PawPaw, 21 February 2020 - 07:22 PM.

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#64 starman876

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Posted 21 February 2020 - 07:17 PM

congratulations.  Looks good.  I wonder if that was by design that the lens cell trued up once put on the tube.  I have never checked for this and I have had a lot of Unitrons apart and then put them back together.  



#65 PawPaw

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Posted 21 February 2020 - 07:21 PM

Thanks...I count about 20 rings.  Is the number of rings a direct correlation to how good the lens curvature is?  



#66 davidc135

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Posted 21 February 2020 - 07:33 PM

Thanks...I count about 20 rings.  Is the number of rings a direct correlation to how good the lens curvature is?  

Probably but not necessarily. The fringes are a contour map of the airspace. If there were more than 30 then at least one surface would have to be off. But if both were wrong and over spec by around the same amount, but of opposite sign, there would only be very few fringes. 

 

I'm not sure how many fringes a surface would have to out by before it would be noticed in use. A lot more than 15, I think. I half remember Ellison saying, when grinding lenses, not to trouble too much about an spherometer error of .001'' or around 80 fringes. David


Edited by davidc135, 21 February 2020 - 07:51 PM.


#67 Stew44

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Posted 22 February 2020 - 08:04 AM

You might take a look at post #13 by DAVIDG in this thread:

 

https://www.cloudyni...0-newton-rings/

 

The rings are an interference pattern between R2 and R3 that are created by constructive and destructive differences in the thickness of the airspace between the lenses.  Certainly appropriate for alignment, but in a design with R2 equal to -R3 they likely will not show.  In the design above (#59) R2 is 24.669 and -R3 is 24.622.  It very well may be that the reference to 15 rings describes the characteristics of the Newton rings seen with appropriate spacing and for those two radii.  The rings are also affected by the wavelength of the monochromatic light used.  So if the mention above is related to a specific test used at the time, it would be helpful to know the setup for that.


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#68 PawPaw

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Posted 22 February 2020 - 06:39 PM

I've always used .005" on Edmund lenses Sam Brown in 'All About Telescopes' says

.005"

Could it be that I'm a thousandths off?

Is there another level of perfection beyond perfect? maybe so I may just try

.004"

The  plus or minus 15 rings is interesting.

Are you getting 15 rings with your Newton's?

 

Robert

I would probably try the .005 spacing but I feel very lucky so far to not have any mishaps so I am going to stay with .004.  DPAC is around the corner........Thanks Stew!

 

Not putting too much into the newton rings but comparing them between Unitron and Edmund (again for the ones I own) the Edmund has approx 3 x more rings that are very fine in width,  difficult to capture on camera.  

 

Since I was in the cleaning mode I decided to remove my 4 inch Edmund lens from the OTA due to some fungus starting to appear (I live north of the Swanp but still humid here). While cleaning I measured with calipers and it is the same diameter (4.00") as my spare Edmund lens with the #12 stamp.  My better Edmund lens has no #12 but has three register marks and two of these  very informative stamps on both the Crown and Flint.  

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Edited by PawPaw, 22 February 2020 - 06:41 PM.

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