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M75C Elbow Telescope

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#1 Chuck Hards

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Posted 03 November 2013 - 01:02 PM

I accquired this on Friday. In perfect working order, the filter wheel works, optics are clear and sharp. The prior owner built a power supply/dimming circuit for the illuminated reticle using 4 C cells. He had used it as a finder on a large classic Dob. It was mounted on an aluminum plate that allowed pivot & tilt movement for alignment with the main OTA.

I remember Jaegers selling these for years and years.

Really too heavy for most scopes these days, but I may find a use for it. Just fun to see one again after several decades.

Anybody else ever use one of these as a finder, back in the old days?

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#2 richard7

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Posted 03 November 2013 - 02:30 PM

Oh Wow. I can't quite read what the plate says but it looks very promising.
I wonder if he ever took it apart and cleaned it?

#3 Chuck Hards

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Posted 03 November 2013 - 02:48 PM

The top plate is the filter selector switch. CLEAR, NEUTRAL, AMBER, RED. None of the filters are useful for astronomy, IMO, even the neutral filter is way too dark for even the moon.

It looks amazingly clean on the interior, despite the worn external appearance. A few dust flecks on the reticle.

The focusing action is smooth.

#4 StarStuff1

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Posted 03 November 2013 - 04:29 PM

About 25 years ago I had one of these. Decent optically but as you say, pretty darn heavy. And bulky. Originally I was going to remove the optics and re-mount in a PVC tube but I wound up selling/trading it at a swap shop. I really hate to destroy original military gear to make it into an astro toy. Altho this WWII surveyor's tripod did clean up pretty well to make a sturdy tripod for a small refractor.

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#5 BillB9430

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Posted 03 November 2013 - 05:46 PM

Chuck - The M75C is an interesting scope for sure. A M75C I have needed to be disassembled for cleaning - so I had a chance to examine the eyepiece lenses. The M75C ocular is a two achromat arrangement that would likely be called a Plossl today. While the lenses were out, I compared them to an old 28 mm "Kellner" purchased from Edmund 40 years ago. The lenses seemed identical and would even exchange in the barrels. Quoting from page 129 of Edmund Catalog 651 about their 28 mm "Kellner": " . . . Has the same set of lenses used in quality military telescopes. We put them into a new metal cell and extension for 1 1/4" holders . . . ". This Edmund "Kellner" was very popular and showed the "floating image" effect like the RKE 28 mm does now. I recall using one for my first look at Jupiter's bands through a 6" f/8 Newtonian in 1960 - I was hooked! In the original M75C ocular mounting there is a wide metal rim around the eye lens (check your scope), so no "floating" effect is seen when viewing with the elbow scope. - Bill

#6 Chuck Hards

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Posted 03 November 2013 - 05:49 PM

Yeah, you could make a much lighter finder, with better coatings, from modern surplus optics. Although the eyepiece has possibilities, I agree with you. It's better kept intact as a military collectible. If it doesn't end up on a permanently mounted observatory scope, it will go on display indoors.

#7 Chuck Hards

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Posted 03 November 2013 - 05:51 PM

Chuck - The M75C is an interesting scope for sure. A M75C I have needed to be disassembled for cleaning - so I had a chance to examine the eyepiece lenses. The M75C ocular is a two achromat arrangement that would likely be called a Plossl today. While the lenses were out, I compared them to an old 28 mm "Kellner" purchased from Edmund 40 years ago. The lenses seemed identical and would even exchange in the barrels. Quoting from page 129 of Edmund Catalog 651 about their 28 mm "Kellner": " . . . Has the same set of lenses used in quality military telescopes. We put them into a new metal cell and extension for 1 1/4" holders . . . ". This Edmund "Kellner" was very popular and showed the "floating image" effect like the RKE 28 mm does now. I recall using one for my first look at Jupiter's bands through a 6" f/8 Newtonian in 1960 - I was hooked! In the original M75C ocular mounting there is a wide metal rim around the eye lens (check your scope), so no "floating" effect is seen when viewing with the elbow scope. - Bill


Thanks for the background info, Bill. I'll check it out next time I'm down in the shop and look for the eye lens rim.

#8 GlennLeDrew

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Posted 03 November 2013 - 07:25 PM

I wonder if this scope uses the same Amici prism I use in my home-made right angle bino? Mine have a clear aperture of 33mm, and are made to very high precision. The way the substrate is shaped for mounting, and the mount itself, are marvels. This pair of prisms is highly prized by me, and will have to be pried from my cold, dead hands. :grin:

#9 orlyandico

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Posted 04 November 2013 - 05:35 AM

man I had one of these when I was eight years old... probably an original from World War II left behind by you Americans in my home country.

my dad bought it for me for the equivalent of $6 in the early 1980s.

i was amazed at how clear the stars were through it, compared to naked-eye. this was before i discovered that i needed specs... :tonofbricks:

mine was still at home, but had completely corroded and froze up. my mom donated it to the local museum.

#10 Chuck Hards

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Posted 04 November 2013 - 08:59 AM

A very limited web search this morning only got two real hits with pics, one on the M75C and one on it's brother, the M17.

Looks like in both cases, they were originally used on anti-aircraft guns.


http://www.usmilitar...escope-elbow...

http://www.usmilitar...-m17-telescope/

#11 badback

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Posted 07 August 2015 - 10:39 PM

Concerning "Anybody else ever use one of these as a finder...: Well, I was given a well worn 8" OTA Newt years ago and this was used as a finder on it. It was mounted it in much the same way as you have described here. Unfortunately the optics are hmmm... cruddy, or perhaps better put, betrayed by the elements and time.. Looking down the "barrel" you can see a rather large chip and damage to the mirror or prism? Too top it off the entire shebang was painted with enamel house paint.

 

I accquired this on Friday. In perfect working order, the filter wheel works, optics are clear and sharp. The prior owner built a power supply/dimming circuit for the illuminated reticle using 4 C cells. He had used it as a finder on a large classic Dob. It was mounted on an aluminum plate that allowed pivot & tilt movement for alignment with the main OTA.

I remember Jaegers selling these for years and years.

Really too heavy for most scopes these days, but I may find a use for it. Just fun to see one again after several decades.

Anybody else ever use one of these as a finder, back in the old days?

Elbow1_zpsc42c5194.jpg

 

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#12 figurate

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Posted 08 August 2015 - 12:15 PM

I picked up a M75D model not long ago, intending to use the eyepiece on a finder if that was possible. While the EP and the other parts in the rear section are in pristine condition, there was something fishy about the objective, but no matter, it was cheap. To answer Glenn's question, the prism aperture  is much less than 33mm, more like 22mm (7/8").

 

Fred



#13 Gordon Rayner

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Posted 09 August 2015 - 05:39 PM

The  M6 , IIRC,  has  a much wide field eyepiece, and a larger  Amici  prism, IIRC.    A late 1950's   thru   1960's (?)   Jaegers   catalog shows  those and the ones of this thread, as well  as others.    Have .

not looked at mine in decades.

 

Had or have the one of this thread,  and had or have   at least one of the  larger, wide field  model   (M6).

 

The  Moonwatch  scopes   prepped for   US Vanguard   satellites   in the Sputnik   era,   were hybrids  of the M-17  with  objectives 5inch  f/5  from the USN  copies  of the WW II   Nikko and Toko   20 x 120 x 3 deg binocular with 45 deg inclination of the line of sight.




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