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R-41 40mm DPAC

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234 replies to this topic

#1 CharlieB

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Posted 18 August 2017 - 05:38 PM

I finally pieced together a DPAC setup - mostly.  The objective & tube are resting directly on the flat.  Photographing is not easy.  I managed to get a somewhat decent shot of the Astro Optical R-41, 40/500mm.  It looks OK to me, but I need input from others.  I think this was outside of focus, but I'll take better notes next time.

 

Charlie

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#2 Chuck Hards

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Posted 18 August 2017 - 06:06 PM

That looks great, Charlie, as good as they come.  waytogo.gif

 

The LED is too bright, one of the problems of my setup that I'm fixing.



#3 CharlieB

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Posted 18 August 2017 - 06:20 PM

Yes, but it's an artifact of the camera I used, a point & shoot.  I'll have to get the Nikon out.  Visually, it was just about right.



#4 Chuck Hards

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Posted 18 August 2017 - 06:26 PM

For the same reason, I've abandoned the cell-phone camera and will use my own DSLR in the future.  Are you going to test all of your 40mm & 50mm?  



#5 CharlieB

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Posted 18 August 2017 - 07:47 PM

Yes, once I get the setup finalized.



#6 Chuck Hards

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Posted 19 August 2017 - 12:10 AM

I'd like to see a 40mm Jupiter objective, sans erector.  I looked at my home made 40mm f/20 (old Edmund objective), and it wasn't fantastic.    Not terrible, but a noticeable turned edge.



#7 CharlieB

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Posted 19 August 2017 - 08:04 AM

I was pondering the same.  I have both a Jupiter and Asahi. The Asahi always seems to be the better of the two.



#8 rolo

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Posted 19 August 2017 - 08:52 AM

Not the best idea to put the scope on the flat but that looks dang good!



#9 starman876

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Posted 19 August 2017 - 09:01 AM

i guess that would take out of the quation just about any alignment factors



#10 rolo

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Posted 19 August 2017 - 09:58 AM

With enough weight you can distort the flat.



#11 DAVIDG

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Posted 19 August 2017 - 12:46 PM

 It is great that people are testing their optics ! The lens looks very good. In theory it should because of the small aperture , which are easier to make. They block up the blanks into a  larger disk and grind and polish them spherical. If the elements are away from the edge of the blocked disk, then odds are better that they will be optically smooth and spherical. 

  When you start to go up in aperture it then becomes harder to make a surface that is zone free and figured correctly without additional testing and correcting. So the larger the aperture the greater the chance that something is going to show up.

   Keep on testing and posting the results !

 

                         - Dave 


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#12 CharlieB

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Posted 19 August 2017 - 06:09 PM

Two 50mm scopes (I know, I said 40mm, but bear with me).  First, a Jupiter 50/600.  Inside & outside focus.  Not as good as I'd hoped for, but it reflects what I see at night.

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#13 CharlieB

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Posted 19 August 2017 - 06:13 PM

Asahi Pentax 50/600.  Essentially the same scope.  Again, the results reflect what I see through the scope.  The secondary reflection you see in these photos is from a ND filter I put in the holder.

 

Much better than the Jupiter.

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#14 DAVIDG

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Posted 19 August 2017 - 06:25 PM

 The Jupiter is showing a large amount of undercorrection. That is  a classic sign of a possible flipped element or the lens being backwards in the cell. So double check that is not the problem.

 

                    - Dave 


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#15 CharlieB

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Posted 19 August 2017 - 09:39 PM

Will do.  Thanks!



#16 CharlieB

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Posted 19 August 2017 - 10:40 PM

Well, as much as I'd like to say otherwise, it appears the objective is undercorrected to that degree.  I've tried every possible permutation and the best outcome is what was pictured above.  

 

Charlie


Edited by CharlieB, 19 August 2017 - 10:42 PM.


#17 CharlieB

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Posted 19 August 2017 - 10:43 PM

Would it be worth adjusting the lens spacing?  



#18 CharlieB

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Posted 23 August 2017 - 09:12 AM

A few more.  First, a 50/500mm Bushnell SkyRover.  Visually, it puts up great images.  Sorry for the excessively bright image, but I'd forgotten to put some tape over the back side of the LED.  Inside, then outside of focus.

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#19 CharlieB

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Posted 23 August 2017 - 09:19 AM

Next, a Unitron 127 - 40/700mm.  I had a tough time getting the reflection centered - not sure why.  Looks pretty good, though.

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  • Unitron 127 inside.jpg
  • Unitron 127 outside.jpg

Edited by CharlieB, 23 August 2017 - 09:20 AM.


#20 CharlieB

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Posted 23 August 2017 - 09:22 AM

Last one - one of the SPI 40/800mm scopes.  There was clearly something amiss. 

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  • SPI 40mm inside1.jpg
  • SPI 40mm outside1.jpg


#21 CharlieB

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Posted 23 August 2017 - 09:25 AM

Thanks to the insights from DAVIDG, I tried flipping the crown with this result.  Much better, but still not perfect.

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  • SPI 40mm inside2.jpg
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#22 CharlieB

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Posted 23 August 2017 - 09:26 AM

I still have a lot to learn and a lot of scopes left to test.



#23 CharlieB

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Posted 23 August 2017 - 10:29 AM

Lest I forget the 3" scopes -- a great Optica b/c 76/1200 RAO.

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#24 CharlieB

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Posted 23 August 2017 - 10:31 AM

Lafayette 384 76/910.  Another RAO.

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  • Lafayette 384 inside.jpg
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#25 CharlieB

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Posted 23 August 2017 - 10:33 AM

And this is why I love my Swift 831.  A 3" scope of this vintage just doesn't get much better.  The views through the scope confirm this.

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  • Swift 831 inside.jpg
  • Swift 831 outside.jpg

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