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DPAC Test - Intes MN76

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#1 Jeff B

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Posted 13 February 2020 - 07:56 PM

So I've been on a DPAC binge during the miserable weather around here and this is my last one for a while.

 

It is my Intes MN76 Mak-Newtonian.

 

This scope has a much larger fully illuminate FOV relative to my APM/MW MN86 reported elsewhere in this forum, rocketing all the way up to maybe 5-6mm.  But still small in absolute terms and, like the MN86, only less so, will not allow me to image the entire aperture with my current DPAC Ronchi screen/LED holder.  So, I had to, again like the DPAC for the MN86, flip the holder over to see and image the other edge of the primary.  I also switched over to a white LED source which is much brighter than the green one I traditionally use.  This allowed me to lower the ASA (reducing grain) as well as increase the shutter speed to 1/3000 of a second (!), which basically "freeze frames" the image, removing any motion artifacts from hand holding the cell phone camera.  These came out pretty good.

 

And speaking of pretty good, these optics certainly are!  But again, I already knew that from my time spent over the last decade with this scope, except, I now have some actual DPAC data that correlates with my visual impressions and star testing.   A mild, uniform circular zone (not seen visually in star testing) but otherwise very smooth surfaces for the entire system.  A very nice edge and look how straight those bands are.  These images are from outside of focus.  I did not have enough in-travel left to image more than one fat line inside of focus but I really don't need to see inside focus to see what I want to see.  

 

Visually, this scope does indeed render very sharp images and takes high power with ease (but like all newts, you have to nail collimation and control the internal thermal conditions of the structure and optics to take full advantage of excellent optics like this).

 

As usual, hover your cursor over the images to read their titles, and, as always, comments are welcome. 

 

Jeff

Attached Thumbnails

  • MN76C.jpg
  • MN76 In DPAC.jpg
  • MN76 DPAC Holder.jpg
  • MN76, DPAC, Outside Focus, Rightside Up.jpg
  • MN76, DPAC, Outside Focus, upside down.jpg
  • MN76, DPAC, White, At Focus.jpg

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#2 JohnH

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Posted 13 February 2020 - 11:17 PM

4 faint zones and some radial spikes evident.

#3 stuart keenor

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Posted 14 February 2020 - 01:53 PM

Very interesting posts Jeff thanks for sharing

#4 precaud

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Posted 15 February 2020 - 08:43 AM

What? No color-focusing errors?  Boring...  :)



#5 Jeff B

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Posted 15 February 2020 - 09:31 AM

What? No color-focusing errors?  Boring...  smile.gif

Ha ha, actually there is.  You just can't see it.


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#6 starman876

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Posted 15 February 2020 - 09:38 AM

talk about a simple set up.  Shows how easy it is to do this.   If you get the scope better aligned with the flat you will get a nice round circle with the bands.  



#7 Jeff B

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Posted 15 February 2020 - 06:12 PM

talk about a simple set up.  Shows how easy it is to do this.   If you get the scope better aligned with the flat you will get a nice round circle with the bands.  

Actually, the bigger issue is the tiny fully illuminated FOV's with these Intes maks and compound scopes in general, like the SCTs.  With my present screen/LED holder, I just cannot see the fully illuminated aperture with theses scopes.  Now with a smaller diameter LED, carefully placed right up to the edge of its holder, I can bring the source and return beams closer to each other and maybe be able catch the full aperture.   I've been spoiled by my refractors with their big fully illuminated FOVs. 

 

Jeff


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#8 precaud

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Posted 15 February 2020 - 08:42 PM

 Now with a smaller diameter LED, carefully placed right up to the edge of its holder, I can bring the source and return beams closer to each other and maybe be able catch the full aperture.   I've been spoiled by my refractors with their big fully illuminated FOVs. 

 

I'm curious, how far off center is your LED?



#9 Jeff B

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Posted 16 February 2020 - 11:00 AM

I'm curious, how far off center is your LED?

Less than 1/8" as best I can measure.  Notice too that I place the return beam so that it lands right next to the LED and subtly bisects the holder.   Center to center separation of the two beams is maybe 3/16" or less when adjusted.  Now, I'm just assuming that the two beams should be symmetric about the center axis.

 

Jeff


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#10 scooke

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Posted 16 February 2020 - 11:55 PM

Actually, the bigger issue is the tiny fully illuminated FOV's with these Intes maks and compound scopes in general, like the SCTs.  With my present screen/LED holder, I just cannot see the fully illuminated aperture with theses scopes.  Now with a smaller diameter LED, carefully placed right up to the edge of its holder, I can bring the source and return beams closer to each other and maybe be able catch the full aperture.   I've been spoiled by my refractors with their big fully illuminated FOVs. 

 

Jeff

That is such as issue.  I tried to DPAC my Questar and Celestron 7" mak and I get these tiny not fully illuminated images.  Now I know I'm not alone and it not just my inexperience.  Both scopes are very sharp in use.  As an example, here is my Questar outside focus.  Straight lines but weird photo and I haven't figured out how to do better.  I can't get a full circle visually either so this isn't just a photo artifact.

Q Outside.jpg

Attached Thumbnails

  • Q Inside.jpg

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#11 precaud

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Posted 17 February 2020 - 09:03 AM

Hmmm.... I didn't have any problem getting the full aperture of my SW 180 Mak (same as your Celestron)...

Attached Thumbnails

  • dpacin.jpg

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#12 Jeff B

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Posted 17 February 2020 - 09:24 AM

That is such as issue.  I tried to DPAC my Questar and Celestron 7" mak and I get these tiny not fully illuminated images.  Now I know I'm not alone and it not just my inexperience.  Both scopes are very sharp in use.  As an example, here is my Questar outside focus.  Straight lines but weird photo and I haven't figured out how to do better.  I can't get a full circle visually either so this isn't just a photo artifact.

attachicon.gifQ Outside.jpg

Yup, all of my SCTs , Maks and even some of my refractors have tiny fully illuminated FOV's ,making it virtually impossible to see the entire aperture, yet alone image it.  So, what I've learned to do is to flip over my screen/LED holder to see "the other side".  

 

When you look at your pictures (and mine), you see the sharp edges, which are the real edges of the aperture and the fuzzy edges, which are the out of focus edges of the baffle tube end.

 

Keep at it and boy, that Questar looks great (!).

 

Jeff



#13 Jeff B

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Posted 17 February 2020 - 09:27 AM

Hmmm.... I didn't have any problem getting the full aperture of my SW 180 Mak (same as your Celestron)...

John,can we see your screen/LED holder?  Also seems like a good sized secondary.  A very nice scope!

 

What camera do you use?

 

Jeff



#14 davidc135

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Posted 17 February 2020 - 09:34 AM

Would something as simple as varying the back focus explain the two 180 Mak images? But I tried on my B&L 4000 and gave up.   David


Edited by davidc135, 17 February 2020 - 09:37 AM.


#15 precaud

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Posted 17 February 2020 - 10:41 AM

John,can we see your screen/LED holder?

 

What camera do you use?

 

I normally use a Canon S30, but this one was a Fujifilm F30. It didn't get the focus quite right.

 

Here's my DPAC "eyepiece".

Attached Thumbnails

  • DPAC2.jpg
  • DPAC3.jpg


#16 precaud

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Posted 17 February 2020 - 04:19 PM

Would something as simple as varying the back focus explain the two 180 Mak images? But I tried on my B&L 4000 and gave up.   David

 

It could. I left mine set at where it was with the stock 2" diagonal in place (but removed the diagonal for the test, of course...)



#17 G-Tower

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Posted 17 February 2020 - 05:11 PM

Hmmm.... I didn't have any problem getting the full aperture of my SW 180 Mak (same as your Celestron)...

What's causing the rough appearance? Meniscus or primary?



#18 precaud

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Posted 17 February 2020 - 05:41 PM

What's causing the rough appearance? Meniscus or primary?

 

Neither - focus. I forgot to put into Macro mode. And it was set for Aperture Priority @ F/5, not a smart choice. Maybe other camera settings as well. It was the first time I used the F30 (for anythng). I didn't catch the focus error until after I tore down. Too lazy to redo it  :)




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