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Russell Optics 50mm Super-Plossl XLC

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#1 chemisted

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Posted 10 February 2021 - 04:40 PM

As part of my efforts to explore the utility of 1.25" eyepieces for afocal use with my NVD Micro, I approached Gary Russell with a request to make his 50mm 1.25" eyepiece with filter threads cut next to the eye lens.  He was not anxious to attempt this as it hadn't been done before but I am very grateful to him for agreeing to take on the challenge.  This exquisite lens is now in my possession and I have some early results to report.  The threads at the eye lens allow me to hard couple it to my Micro directly using 1.25" spacers.  Last night I was out with a scope that hasn't seen a lot of use by me.  It is a Short Tube 80 that was marketed by Bresser and I acquired in a thrift shop while on vacation to the west coast.  The optics and focuser are quite fine and I had the new eyepiece coupled to them through a TV diagonal.  This new eyepiece has a very long eye relief and I used a total of ~35mm of spacing between it and the ENVIS lens of my Micro.  After screwing on my 12nm Astronomik H-alpha filter to the 50mm I trained the setup on the Heart & Soul nebulae with the Double Cluster right next door.  Now here is the amazing part.  I could not detect any edge of field aberrations.  Stars were pinpoints throughout the entire FOV.  I was so surprised I would let stars drift into and out of the FOV to see if anything changed but they did not.  This is a 3.70 FOV at f/2.65 and it was beautiful.  Clouds rolled in before I could move on to other targets.  I just had to make this post as these ST-80 scopes are cheap and ubiquitous and with this new eyepiece can provide an exceptionally fine view of deep sky objects.


Edited by chemisted, 10 February 2021 - 04:42 PM.


#2 GeezerGazer

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Posted 10 February 2021 - 05:11 PM

Excellent find on the ST 80 and great results with your experimental 1.25" 50mm eyepiece.  For those who are limited to 1.25" eyepieces or filters, this certainly sounds like a viable afocal option.  

Ray


Edited by GeezerGazer, 10 February 2021 - 05:12 PM.

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#3 joelin

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Posted 14 February 2021 - 04:15 AM

is there some light loss or vignetting or something else that happens when you use long focal length eyepieces in the 1.25" format instead of 2"? 



#4 chemisted

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Posted 14 February 2021 - 07:19 AM

Every telescope and eyepiece combination is unique to itself so I can't generalize.  I can say I used the Celestron 45mm Plossl with my ST-80 and edge of field aberrations were very apparent.  That is why I was so surprised by the RO 50mm result.  The 50mm is brighter than the 45mm because the combination provides f/2.65 vs. f/3.0 for the 45mm Plossl.  The FOV is the same with both of them since they have essentially the same field stop.  As you know, the advantage of a 2" format is the larger field stop that gives a larger FOV for a given magnification.  I really like the 8X magnification that this RO 50mm/ST-80 combination provides and the 3.7o FOV is still big enough to cover major showpiece nebulae.  I have other combinations that give bigger FOVs at the same magnification (Nikkor 200mm, Sky 90 and TV-140 setups where 2" eyepieces are used) and I like those as well.  A wonderful aspect of the combination described in this thread is that it can be carried outside with one hand at a moments notice.



#5 BJS

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Posted 15 February 2021 - 08:29 PM

Can you post a picture of this setup and of the eyepiece?  TY.



#6 chemisted

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Posted 15 February 2021 - 09:57 PM

There is nothing remarkable about the setup or eyepiece.  The main body of the eyepiece is 75mm long.  My spacers are five old 1.25" filter shells which measure 36.5mm in total length  So combined the eyepiece and spacers are ~4.4".  The eyepiece slips into the diagonal and the NV device screws onto the top spacer.  The body of the cylindrical eyepiece has a diameter of 50mm.  I use a 1.25" male/male gender changer at the top of the eyepiece so that male threads terminate the spacer stack to screw directly into the ENVIS lens of the NVD Micro.

 

One more thing:  The Russell Optics 50mm Super-Plossl XLC is almost exactly the same size as my venerable Nagler 9mm Original eyepiece but is a fraction of its weight coming in at 186 grams.


Edited by chemisted, 16 February 2021 - 08:09 AM.


#7 chemisted

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Posted 04 March 2021 - 07:56 AM

I was out last night before the moon came up to try to evaluate this setup a little bit more.  It is really quite remarkable seeing the Horsehead and Flame clearly visible with an 80mm achro.  I spent the most time on the Rosette as it is perfectly framed in this FOV.  Stars were everywhere within and outside the very nuanced nebula.  Sure, it isn't as bright as some of my more expensive setups but clear and detailed it was.  I could go on but I will finish with one of the main features of this approach - looking straight up.  IC 405/410 was bright and inviting with wispy nebula extending beyond some images I have in my reference books.  This complex was easily found and comfortably viewed sitting all the while.  When I quit I felt a little bit like I had just broken some law of physics.  Sky gazing really shouldn't be this good with such modest equipment.




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