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New RKE Collection

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#26 John Rogers

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Posted 07 November 2020 - 12:49 PM

 

Also: I'm not reading anything in those ad pages that indicate the RKE eyepieces were designed specifically for the Astroscan telescope.  I have not yet had my coffee today, and so excuse me if I'm simply overlooking it.

 

Ah, a little more Edmund history is in order: https://www.cloudyni...ays/?p=10625184


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#27 REC

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Posted 07 November 2020 - 02:34 PM

It has been a long time since I re-assembled an eyepiece line that I used to have.  I usually do not.  But decided that I really want a classic minimum glass design that is also only single coated as these usually excel on planetary and double stars.  Recently tested out an RKE in the planetary role with Mars and it was quite impressive, even next to the likes of my ZAO and XO.  So that sealed it for me.  But there is more too that makes the RKEs a little more special for me.  I grew up in south Jersey and when a young kid would often have my brother drive me to the Edmund Scientific showroom in Barrington, NJ.  That place was an absolute playground of science stuff and they had a huge surplus room filled with old optics and odds and ends.  Could stay there for hours it was so much fun.  Plus I got several of my first telescopes from there as well.  So have a lot of history with that brand.

 

Today just received the last focal length I have been waiting for.  I already had the 28 RKE and I have 2 for binoviewing.  The 15mm I recently got used as this focal length is now discontinued.  The rest I purchased new from Edmund Optical.  These will now become part of my primary observing eyepieces that I keep in my small grab case.  I replaced the anodized aluminum barrels they came with with nice chromed brass ones.  These give the little RKEs a lot nicer heft, plus looks good as well.  The 28 RKE is the only one where the field stop is part of the barrel, so for that one I got a rubber o-ring from Home Depot and cut it to fit and works perfectly as a field stop; the seam is very difficult to notice and you have to search for it.

 

To round out the two ends of the focal length range I placed a Celestron 30mm Pre-Ultima and then a classic single coated Celestron 6mm Ortho that is an amazing performer as well (had to go thru a number of these classic Abbes to find an exceptional one).  Btw, the AFOV on the RKEs, even though the data table says is 45 degrees, is really 51 degrees, so not so constraining of a view smile.gif  They are pictured below on the new 2nd edition of the S&T Jumbo Pocket Atlas that just arrived yesterday!  Can't wait for Orion to make its appearance now laugh.gif

 

attachicon.gifFull Set (web).jpg

 

Wow, what a great collection! I would think the 28mm RKE would be a very cool view of the Saturn, Jupiter conjunction in December!


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#28 Thomas_M44

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Posted 07 November 2020 - 06:24 PM

Wow, what a great collection! I would think the 28mm RKE would be a very cool view of the Saturn, Jupiter conjunction in December!

 

My gal and I recently (near opposition) observed Mars using the 28mm RKE with the 5X Powermate plus a 1.5-inch extension tube between the Powermate and the eyepiece. The 1.5-inch extension increases the 5X Powermate magnification to 6.2X.

 

The effective focal length of the combination above was 4.6mm, which in conjunction with my 600mm FL TV85 provided a 130X view, which was about optimal given our seeing conditions.

 

We were looking straight-through, no diagonal,  via 3.5-inches of 2" extension tube inserted between the focuser and Powermate.

 

Although the exit-pupil behavior made eye-positioning a bit challenging to initially acquire, once positioned, the view of Mars through the 28mm RKE was really nice, with excellent contrast and sharpness and without vignetting.

 

The "floating in space" view added a nice aesthetic too --it was fun!  My partner Esther particulary liked the Powermate-amplified view of Mars with the 28mm RKE.

 

We both kept thinking, however, that the experience would have been much more relaxing with the benefit of a polar mounting with RA drive. Trying to keep good eye positioning while readjusting the alt/az mounting for drift was a bit of a hassle.

 

Also: we tried out a 'Baader 570nm Orange Longpass Filter' with the above setup. The view with the 570nm filter was captivating, as the planet took on a very rich tangerine glow. The dark albedo features jumped-out strongly, surprizingly. The South polar cap also became very clearly defined, portrayed in a bright light-yellow caste. So, not very true-to-nature, but a very revealing and engaging view nonetheless.  We now call the 570nm lowpass filter our "orange sunshine psychedelic fun filter" smile.gif

 

A problem we did encounter with the 570nm filter was that it darkens the sky background glow severely, and so one has difficulty seeing the field-stop boundary. It thereby becomes challenging to acquire the proper eye positioning for the RKE 28mm when searching for the target.  Again, RA clock drive would make this combo much more relaxing and enjoyable.

 

I see the purchase of a used GM-8  polar mounting in my future...


Edited by Thomas_M44, 07 November 2020 - 10:52 PM.

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#29 luxo II

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Posted 08 November 2020 - 03:08 AM

 

We both kept thinking, however, that the experience would have been much more relaxing with the benefit of a polar mounting with RA drive. Trying to keep good eye positioning while readjusting the alt/az mounting for drift was a bit of a hassle.

This is why I switched from a push-to rig (Losmandy AZ8 and encoders) and bought an AZEQ6. Altaz, and it tracks beautifully even at 500X.

 

An RKE28 with 3X barlow could be interesting in my beast...


Edited by luxo II, 08 November 2020 - 03:09 AM.

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#30 BillP

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Posted 08 November 2020 - 10:47 AM

A 28 RKE binoviewed with Barlow is a wonderful setup.  The ER lengthens some with Barlow and makes bino observing even more natural feeling.

 

Juppiter Opposition 2010.jpg


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#31 Thomas_M44

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Posted 08 November 2020 - 04:21 PM

This is why I switched from a push-to rig (Losmandy AZ8 and encoders) and bought an AZEQ6. Altaz, and it tracks beautifully even at 500X.

 

An RKE28 with 3X barlow could be interesting in my beast...

That hybrid alt/az-polar Skywatcher mount is quite interesting.

 

I'm going to have to do some thinking and researching.

 

I absolutely want a convenient and robust RA driven mount. Having additional built-in alt/az capability would be great also.


Edited by Thomas_M44, 08 November 2020 - 04:22 PM.

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#32 izar187

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Posted 08 November 2020 - 04:27 PM

I web searched it too after reading that.

I'm not in the market, but that is really cool.



#33 Thomas_M44

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Posted 08 November 2020 - 11:22 PM

This is why I switched from a push-to rig (Losmandy AZ8 and encoders) and bought an AZEQ6. Altaz, and it tracks beautifully even at 500X.

 

An RKE28 with 3X barlow could be interesting in my beast...

 

I have not yet tried the RKE 28mm with my TeleVue 2X and 3X Barlows.

 

I have used the TV Barlows with the 21mm and the 12mm RKE's, however, and had good results.

 

Using the 12mm RKE with the TV 3X Barlow for an effective 4mm FL is a nice pairing. The 12mm RKE has reasonably comfortable 9.68mm eye-relief, and the combination gives a very crisp view indeed.

 

I look forward to obtaining the 15mm RKE, so I might achieve a very useful 5mm effective FL with the TV 3X Barlow.

 

Mostly I've been using the 21mm and 28mm RKE's with the 5X Powermate ( sometimes with the addition of a 1.5-inch extension tube to increase magnification of the 5X Powermate up to 6.2X) and thus far these have been my favored combinations. Ample eye-relief, and very clean FOV.

 

But yes, with a classic Barlow plus RKE eyepiece there is a total of only 5-elements in 3-groups. This is a nice "minimal glass" route.


Edited by Thomas_M44, 08 November 2020 - 11:29 PM.


#34 BillP

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Posted 09 November 2020 - 12:28 AM

Very nice conditions tonight, to did some RKEing with the TSA-102.  Observed M1, M35, M45, STT64 in M45, TU Gem (Carbon), Double Cluster, and of course Mars.  Very much enjoying them across all targets.  They even brought in M1 quite excellently unfiltered with the 4".  Star colors rendered very nicely, including the carbon star.  Details showed extremely well on Mars -- for that had 15 RKE + 2.5PM and 12 RKE + TV2x, both yielding 6mm effective and both showing Martian features equally as etched and contrasted.  Star points excellent with classic airy disks (I forgot how nice the 8mm was).  But in all of them one of the standouts was just how inky black the background sky was which made the open clusters really vibrant.  And absolutely zero EOFB. 


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#35 Thomas_M44

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Posted 09 November 2020 - 02:14 PM

Very nice conditions tonight, to did some RKEing with the TSA-102.  Observed M1, M35, M45, STT64 in M45, TU Gem (Carbon), Double Cluster, and of course Mars.  Very much enjoying them across all targets.  They even brought in M1 quite excellently unfiltered with the 4".  Star colors rendered very nicely, including the carbon star.  Details showed extremely well on Mars -- for that had 15 RKE + 2.5PM and 12 RKE + TV2x, both yielding 6mm effective and both showing Martian features equally as etched and contrasted.  Star points excellent with classic airy disks (I forgot how nice the 8mm was).  But in all of them one of the standouts was just how inky black the background sky was which made the open clusters really vibrant.  And absolutely zero EOFB. 

Nice tour of objects!

 

An encouraging preliminary report of viewing DSO's with the RKE's  waytogo.gif 

 

It's also heartening to hear that your 15mm plus 2.5PM is performing approximately on-par with the 12mm plus TV2X.

 

The more I use my 5X Powermate, the more I like it. I also like my 2.5X Powermate, but have much less time on it.

 

I'm eager to do some more viewing of my own with the 21mm RKE and 5X Powermate.



#36 BillP

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Posted 09 November 2020 - 04:51 PM

An encouraging preliminary report of viewing DSO's with the RKE's  waytogo.gif

I was also comparing the single coated RKEs against the top shelf XWs which are some of the best on transmission.  Looking at M1 I could not see any notable difference between the 21.5mm RKE and the 20 XW.  When I did the math of a 4 group 8 element multicoated eyepiece (20XW) vs. a 2 group 3 element single coated eyepiece, they were within 2 or 3 % theoretical transmission, so fairly on-par with each other.  Given the thickness of the larger elements in the XW probably closer to the same.  Just goes to show that the classic 3-4 element 2 group eyepieces, multicoating is not really needed.  RKE and Brandons have remained single coated all these years.


Edited by BillP, 09 November 2020 - 04:53 PM.

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#37 Thomas_M44

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Posted 09 November 2020 - 08:40 PM

Some of the most engaging and "tactile" telescopic views I ever recall seeing were had via an extremely old brass ocular which was included with an ancient 6-inch f/9 to f/10-ish Newtonian (almost certainly no newer than 1940's vintage, perhaps much older) my stepfather obtained in the early 1980's.

 

That old Newtonian was a very nice instrument. Brass mounting rings were still attached to the aluminum optical tube, but we had to fashion a DIY mounting to work with them.

 

The eyepiece had a large eye lens, and was very "haunted". The ghost of Jupiter was prominent. I'm not sure if the glass was even coated at all, but base upon how I remember the appearance of the glass, likely not.  I'm guessing it was a Kellner of some sort, perhaps 20mm FL. It was obviously quite carefully made.

 

I remember the view of M42 was gorgeous, and the general view felt quite "3D" . Excellent contrast.

 

I only wish he had retained that scope. I would have loved to have restored it, and had the opportunity to better analyze it --particularly that hefty old eyepiece.

 

Moral of the story: often, quite simple designs, thoughtfully executed, can perform unexpectedly well wink.gif


Edited by Thomas_M44, 09 November 2020 - 09:32 PM.


#38 Astrojensen

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Posted 10 November 2020 - 01:02 PM

 

Moral of the story: often, quite simple designs, thoughtfully executed, can perform unexpectedly well wink.gif

Especially (or, perhaps in most cases, only) if they're paired with a long focal ratio objective. At f/19, even a drop of water on a microscope slide can provide wonderfully crisp views of the Moon. 

 

 

Clear skies!

Thomas, Denmark


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#39 Thomas_M44

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Posted 10 November 2020 - 01:37 PM

Especially (or, perhaps in most cases, only) if they're paired with a long focal ratio objective. At f/19, even a drop of water on a microscope slide can provide wonderfully crisp views of the Moon. 

 

 

Clear skies!

Thomas, Denmark

No doubt! --Ha!

 

The 'ball singlet' the *ULTIMATE* in optical simplicity wink.gif

 

Once I obtain a polar mount with RA drive *then* I'll likely obtain a 7.5mm ball singlet to experiment with in conjunction with my Barlows.

 

For now, I'll be playing more with these RKE's


Edited by Thomas_M44, 10 November 2020 - 02:21 PM.

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#40 BillP

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Posted 10 November 2020 - 02:29 PM

The 'ball singlet' the *ULTIMATE* in optical simplicity wink.gif

A 7.5mm BK7 sphere will have an effective focal length of 5.5mm and ER of 1.8mm.  Sure you want to Barlow a 5.5mm eyepiece??

 

Here's the formula for sphere singlets:

FL = nD/[4(n - 1)]
n=glass index (N-BK7=1.515089)
D=diameter of sphere
ER=FL-D/2


Edited by BillP, 10 November 2020 - 02:31 PM.

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#41 luxo II

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Posted 10 November 2020 - 06:05 PM

... and remember the index of refraction varies by wavelength - hence a ball eyepiece has chromatic aberration - the centre of the field is not as good as some might think.

 

A super-polished steinheil monocentric, or a modern variant of it, is probably as good as you could wish for.


Edited by luxo II, 10 November 2020 - 06:07 PM.


#42 SandyHouTex

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Posted 10 November 2020 - 07:42 PM

A 7.5mm BK7 sphere will have an effective focal length of 5.5mm and ER of 1.8mm.  Sure you want to Barlow a 5.5mm eyepiece??

 

Here's the formula for sphere singlets:

FL = nD/[4(n - 1)]
n=glass index (N-BK7=1.515089)
D=diameter of sphere
ER=FL-D/2

Now that’s some short eye relief.



#43 BillP

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Posted 10 November 2020 - 07:53 PM

Now that’s some short eye relief.

Yes it is.  But since the ball pertrudes above the top housing surface, it really does not feel that tight.  I have a 5.9mm FL Sphere and a 4.4mm FL Sphere.  On-axis is absolutely superb and more contrast than any multi-element eyepiece.  When the contrast is this high, any other aberrations are simply inconsequential.


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#44 DeWynter

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Posted 10 November 2020 - 08:09 PM

A 28 RKE binoviewed with Barlow is a wonderful setup.  The ER lengthens some with Barlow and makes bino observing even more natural feeling.


I'm absolutely thrilled by binoviewing with 28 RKE. My 2.6x GPC gives roughly the same x100 magnification in my ED100 so I prefer to observe planets with a bit higher magnification (~150x & 0.66mm exit pupil), but when I'm using 1.7x GPC and RKE 28mm (~ 50x) for DSO the view is absolutely magnificent. Almost like a 3D view. Simply amazing!


Edited by DeWynter, 10 November 2020 - 10:31 PM.

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#45 Thomas_M44

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Posted 11 November 2020 - 12:38 AM

A 7.5mm BK7 sphere will have an effective focal length of 5.5mm and ER of 1.8mm.  Sure you want to Barlow a 5.5mm eyepiece??

 

Here's the formula for sphere singlets:

FL = nD/[4(n - 1)]
n=glass index (N-BK7=1.515089)
D=diameter of sphere
ER=FL-D/2

 

Thanks for the formula Bill waytogo.gif

 

Yes, in fact I'm thinking my 1.6X Nikon EiC Barlow would  be a good match for a 7.5mm ball singlet.

 

An effective FL of 5.5mm plus 1.6X Barlow would net a 3.44mm FL which would give 174X in my 600mm FL TV85.

 

I'm thinking such a ball singlet I would use mostly for critical lunar observations at times of excellent seeing. I particularly enjoy extended viewing of finer lunar features,  watching the shadows and illuminations slowly changing --just zoning out, taking a mental break from Earthly affairs...

 

With an extension tube between the singlet EP and the1.6X Nikon Barlow, I can also easily make the Barlow achieve 1.9X, and so 207X when using the 7.5mm singlet in my scope.

 

I'm thinking the addition of a Barlow *might* incrementally increase the singlet's very small eye-relief and possibly decrease CA due to the slower light cone exiting the Barlow. I'd certainly be interested to hear comments regarding this conjecture.

 

But alas --*first* I need to obtain a good RA tracking mount wink.gif

 

I'm not too keen on the idea of hand-guiding a scope that is at 200X or more when viewing through a 10-deg AFOV.

 

For now, my Edmund RKE's and Masuyama 85-deg EP's should keep me well enough occupied...


Edited by Thomas_M44, 11 November 2020 - 12:41 AM.


#46 Thomas_M44

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Posted 11 November 2020 - 12:45 AM

I'm absolutely thrilled by binoviewing with 28 RKE. My 2.6x GPC gives roughly the same x100 magnification in my ED100 so I prefer to observe planets with a bit higher magnification (~150x & 0.66mm exit pupil), but when I'm using 1.7x GPC and RKE 28mm (~ 50x) for DSO the view is absolutely magnificent. Almost like a 3D view. Simply amazing!

That sounds like a fantastic combination --good show!

 

I'm envisioning a  Baader Bino Viewer in my future  --at some point after I first manage to secure a decent tracking polar mount.



#47 25585

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Posted 11 November 2020 - 06:58 AM

I'm absolutely thrilled by binoviewing with 28 RKE. My 2.6x GPC gives roughly the same x100 magnification in my ED100 so I prefer to observe planets with a bit higher magnification (~150x & 0.66mm exit pupil), but when I'm using 1.7x GPC and RKE 28mm (~ 50x) for DSO the view is absolutely magnificent. Almost like a 3D view. Simply amazing!

Totally agree. Inexpensive and rewarding.



#48 Peter Besenbruch

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Posted 11 November 2020 - 05:17 PM

I find life is just plain easier above f/6

Absolutely!waytogo.gif

 

You really need the 32mm RKE to complete the set.

 

attachicon.gif1989_Catalog_32mm_RKE.jpg

I have one of those. It really needs a field stop to make it behave.



#49 Thomas_M44

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Posted 12 November 2020 - 01:57 PM

Absolutely !waytogo.gif

 

I have one of those. It really needs a field stop to make it behave.

That's funny! lol.gif

 

Yeah, the definition of  'RKE' eyepiece was clearly -s-t-r-e-t-c-h-e-d- a bit by the Edmund marketing department to include what appears to be a relatively conventional Erfle.

 

I wonder if Dr. Rank had was not perhaps a bit displeased by that?


Edited by Thomas_M44, 12 November 2020 - 01:58 PM.


#50 BillP

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Posted 13 November 2020 - 10:54 AM

Yeah, the definition of  'RKE' eyepiece was clearly -s-t-r-e-t-c-h-e-d- a bit by the Edmund marketing department to include what appears to be a relatively conventional Erfle.

 

I wonder if Dr. Rank had was not perhaps a bit displeased by that?

 

Interestingly, a few nights ago I decided to do a critical examination of my 28.7 RKE vs. a conventional 30mm Plossl.  I was using my TSA-102 f/8.  I was not expecting the RKE to do a better job in the off-axis, but lo and behold yes it did!  Both eyepieces have approx the same AFOV, extremely close.  The RKE only had some FC near the field stop, whereas the Plossl had both FC and Astigmatism.  With a small refocus the star point of the RKE at the field stop were razor sharp.  I could find a half way point that my eyes could accommodate too.  The FL of my TSA being only 816mm I'm sure most of that FC was probably from the main objective and not the eyepiece.  Quite unexpectedly nice performance!  I've never given the "respect" to the 28 RKE as a critical observing eyepiece as have only used it for its ornamental fun floating view.  But with my acquisition now of a full set for routine observing along side my XWs, I have been giving them some critical observing time and have been quite pleasantly surprised!
 

Also...interestingly the advert in Post #21 for the 2" Edmund "RKE Wide Field Erfle" it says that it contains "3 precision fully-coated achromatic elements".  An "achromatic" element can only be a doublet!  So it is saying that this 2" RKE Erfle has 3 doublets, which is akin to the Kaspereit design, which is an Erfle variant.  Interesting that David Rank called this obviously quite different design from his 28mm to 8mm RKE eyepices also an "RKE".  Makes it more understandable now that he stated that the acronym RKE means "Rank-Kaspereit-Erfle" and he might have been using it as a catch-all for multiple designs he put out.

 

From https://www.handprin....html#kaspereit --

"Kaspereit – The modification of the Erfle design by Otto Karl Kaspereit adds a sixth lens to create a 2-2-2 design of three corrected doublets. It is currently offered by Edmund Optics as the "RKE Wide Field eyepiece", a design modified by David Rank. It expands the apparent "wide field" of view to 68° and provides eye relief of about 10mm (at ƒe = 28mm)."


Edited by BillP, 13 November 2020 - 11:11 AM.

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