15 replies to this topic

[leonard]

 

 

       

I have wondered what this thing was , now we all know . It’s the Unitron 40mm

 

 

 

    Leonard

Edited by leonard, 01 March 2018 - 07:36 PM.

[leonard]

 

 

 

 

 

   Its an Erfle.

[MartinPond]

Looks like a singlet and two doublets to me,  1,2,2

 

Erfles are 2,1,2

 

Not sure why, with two doublets, it would be called "monochromatic".

 

I have 5    1,2,2 examples , what I call "top-expanded-plossls".

Their main purpose seems to have been higher field width

  and enhanced contrast with uncoated elements.

 

Not putting it down..... the 1,2,2 is really nice, and really remarkable for

deflecting scatter without coating.

It's fine with me if someone wants to call it "Erfle".

Edited by MartinPond, 01 March 2018 - 07:18 PM.

[leonard]

Hello ,

 

 

        Has two achromats with dome in , and a singlet in its own casing with the dome facing in also. The singlet is the eye lens .

 

 

 

 

 

Leonard

[BillP]

Is this the Unitron 40mm Monochromatic eyepiece?  Love that the spacers appear to actually be metal!!

[leonard]

          In Lords eyepiece evolution chart , the Erfle called the Erfle 3 looks like our boy here but if you look close the whole eyepiece is shifted field lens to eye lens .

[leonard]

   Hi Bill ,    Yes its the 40 mm sorry I missed putting that in .   Far as I know its he only eyepiece called monochromatic ever !

[MartinPond]

Hello ,

 

 

        Has two achromats with dome in , and a singlet in its own casing with the dome facing in also. The singlet is the eye lens .

 

 

 

 

 

Leonard

 

 

Ah...yes.

And I believe it's well color-corrected, so why it was called 'monochromatic' is still a mystery.

 

It does look uncoated.

And...I'm willing to bet the contrast is nevertheless quite good...colors saturated, black is black.

 

I see that in the highest grade binoculars from Paris , 1914----1930.

In that case, they sacrifice field down to 50 degrees and have excellent contrast.

 

In some wide 8x30s from Japan, it surfaces as a 55--60deg afov with very good

(but not excellent) contrast.

Edited by MartinPond, 01 March 2018 - 07:44 PM.

[MartinPond]

          In Lords eyepiece evolution chart , the Erfle called the Erfle 3 looks like our boy here but if you look close the whole eyepiece is shifted field lens to eye lens .

Yup.

Or...one of the 42 Konigs.   Might depend on the values used.

 

The way the scaterring is deflected is awesome.

A big beneficiary of edge-blackening, if you have a Sharpie.

My examples are ~18mm.  Eye relief gets a little close; ~10mm

 

The 2,2,1 has similar traits.    Very easy eye placement.

Edited by MartinPond, 01 March 2018 - 07:50 PM.

[SandyHouTex]

090.JPG

 

 

 

 

 

   Its an Erfle.

None of the “monocentrics” amateurs have are actually monocentrics (all lenses having curves with a single focal point).  The TMBs and the $1000 Zeisses are all 3 elements in one group Hastings triplets that you can buy from Edmund Optics for $95 to $115 in lots of 1.

 

Link: https://www.edmundop...romatic-lenses/

Edited by SandyHouTex, 01 March 2018 - 09:30 PM.

[Peter Besenbruch]

Is this the Unitron 40mm Monochromatic eyepiece?  Love that the spacers appear to actually be metal!!

The Unitron Monochromatic 40mm I owned had two, closely spaced achromats, plus a larger, double convex lens toward the bottom of the eyepiece tube. The spacing was much greater for that third element.

Edited by Peter Besenbruch, 01 March 2018 - 10:26 PM.

[Jim Curry]

Unitron branded Nihon Seiko 40mm eyepieces came in at least 3 lens variants over the years.  You can see the eye lenses changed diameter.  Also, the crosshair ep has another one or two lenses at the bottom in addition to the wire crosshair.  Looking through the Xhair ep it also appears to have an etched crossing, not visible unless you're looking thru the ep.  A hand magnifier may show the surface with the etching.  This one needs cleaning so I'll track down this apparent etching.

 

 

Jim

Edited by Jim Curry, 03 March 2018 - 10:40 AM.

[SandyHouTex]

 

Is this the Unitron 40mm Monochromatic eyepiece?  Love that the spacers appear to actually be metal!!

The Unitron Monochromatic 40mm I owned had two, closely spaced achromats, plus a larger, double convex lens toward the bottom of the eyepiece tube. The spacing was much greater for that third element.

 

Sounds like a Symmetrical eyepiece with the two achromats.  Why there's a double convex element at the bottom, I have no idea.

[leonard]

Hello , Martin wrote :

Looks like a singlet and two doublets to me,  1,2,2

 

Erfles are 2,1,2

 

      ....................................................................................................

 

Lots of Erfle were 2-2-2 , and other designs with lenses arranged in different  ways but lens count seems to stay at 5 or 6 in 3 groups .

 

         Looking at older posts here , Starman 1 talking about Konig eyepieces a few years age mentions a Konig design that is 1-2-2 with the singlet being the eye lens .  So this looks like the Monochromatic as the lens are in the correct orientation seen in my sample .

 

                                                So let’s call it Konig  , what ever it’s called it’s not going to replace anything I use on a nightly basis .

                          

                                                                                                                        Leonard

[Peter Besenbruch]

 

The Unitron Monochromatic 40mm I owned had two, closely spaced achromats, plus a larger, double convex lens toward the bottom of the eyepiece tube. The spacing was much greater for that third element.

Sounds like a Symmetrical eyepiece with the two achromats.  Why there's a double convex element at the bottom, I have no idea.

That makes two of us. The eyepiece performed like your basic 1.25", narrow field 40mm Plössl.

[VVObserve]

I just picked up a Unitron Monochro. 40mm I will use to round out my Unihex.

Can't wait for clear skies here in Central Pa, a fairly rare event.