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**akptc** · 02-14-2015, 09:47 PM

I bought this lens for its look, without realizing that it did not have a focusing mechanism, which, turns out, resides in the camera body. Before I toss it, I thought I would try building a telescope with it. I woinde rif that is possible. Any advice would be appreciated.

LINK to Canon lens museum

The lens is easy to adapt to M42 or K mount, I have done that via 3rd party adapters from ebay. I even put the Pentax helicoid adapter on it, a teleconverter, the Pentax monocular, and every combo in between, nothing useful came out of it. So no I'd like try something that makes sense

Andy

JimmyDranox · 02-15-2015, 05:34 AM

I don't think it can be done. because of the short focal lens and short distance behind the lens. Even if you disassembly the lens, Looking at the construction, there is a positive frontal group of elements, which I'm sure it has a short focal distance, followed by a negative group. Most camera lenses are build like this, and from the shape of this, it is also.

wombat2go · 02-15-2015, 08:16 AM

Is that a complete lens?
Suggestion:
Use the "BookEnd" method to determine if the lens is positive, and then the distance of the focal plane behind the lens mount. ( first photo below)
I think it will need to be about 50 mm of clear space at minimum to use the lens as a terrestrial 'scope.

The reason is, you will need an erecting prism (second photo below) shown with a Kellner 20mm eyepiece.

The focal points of the eyepiece and the objective have to coincide, and that will be somewhere inside the prism tubes.

Have fun!

**Kerrowdown** · 02-15-2015, 09:25 AM

Originally posted by akptc

Can I make a telescope with the Canon 125/3.5 EX lens?

Just from the thread title alone, I was going to suggest a coffee cup like the these... but of seeing the shape of it, I don't think it would even be much use for that.

http://ecx.images-amazon.com/images/I/81xynBDIjEL._SL1500_.jpg

glasbak · 02-15-2015, 09:40 AM

Originally posted by akptc

I bought this lens for its look, without realizing that it did not have a focusing mechanism, which, turns out, resides in the camera body. Before I toss it, I thought I would try building a telescope with it. I woinde rif that is possible. Any advice would be appreciated.

LINK to Canon lens museum

The lens is easy to adapt to M42 or K mount, I have done that via 3rd party adapters from ebay. I even put the Pentax helicoid adapter on it, a teleconverter, the Pentax monocular, and every combo in between, nothing useful came out of it. So no I'd like try something that makes sense

Andy

This lens misses the rear group, because that was part of the camera.
Probably a rare lens, find a canon collector, before destroying it by adapting.
Maybe by selling it, you can buy telescope.

**akptc** · 02-21-2015, 10:57 PM

Well, a paper weight it will be

JimmyDranox · 02-21-2015, 11:11 PM

Sometime ago, I sold more then 100 lenses, elements, tu be correct in english. It is very hard to mach two groups, almost imposible.

Last edited by JimmyDranox; 02-22-2015 at 04:57 PM.

02-14-2015, 09:47 PM	#1
akptc Site Supporter Join Date: Feb 2008 Location: USA Photos: Gallery Posts: 771	Can I make a telescope with the Canon 125/3.5 EX lens? I bought this lens for its look, without realizing that it did not have a focusing mechanism, which, turns out, resides in the camera body. Before I toss it, I thought I would try building a telescope with it. I woinde rif that is possible. Any advice would be appreciated. LINK to Canon lens museum The lens is easy to adapt to M42 or K mount, I have done that via 3rd party adapters from ebay. I even put the Pentax helicoid adapter on it, a teleconverter, the Pentax monocular, and every combo in between, nothing useful came out of it. So no I'd like try something that makes sense Andy

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02-15-2015, 05:34 AM	#2
JimmyDranox Veteran Member Join Date: Oct 2012 Location: Ploiesti, Romania Photos: Gallery \| Albums Posts: 1,632	I don't think it can be done. because of the short focal lens and short distance behind the lens. Even if you disassembly the lens, Looking at the construction, there is a positive frontal group of elements, which I'm sure it has a short focal distance, followed by a negative group. Most camera lenses are build like this, and from the shape of this, it is also.

02-15-2015, 09:25 AM	#4
Kerrowdown PEG Moderator Join Date: Aug 2008 Location: Highlands of Scotland... "Hold Infinity in the palm of your hand" - William Blake Photos: Gallery Posts: 57,866	Originally posted by akptc Can I make a telescope with the Canon 125/3.5 EX lens? Just from the thread title alone, I was going to suggest a coffee cup like the these... but of seeing the shape of it, I don't think it would even be much use for that. http://ecx.images-amazon.com/images/I/81xynBDIjEL._SL1500_.jpg

02-15-2015, 09:40 AM	#5
glasbak Veteran Member Join Date: Apr 2009 Location: Netherlands Posts: 369	Originally posted by akptc I bought this lens for its look, without realizing that it did not have a focusing mechanism, which, turns out, resides in the camera body. Before I toss it, I thought I would try building a telescope with it. I woinde rif that is possible. Any advice would be appreciated. LINK to Canon lens museum The lens is easy to adapt to M42 or K mount, I have done that via 3rd party adapters from ebay. I even put the Pentax helicoid adapter on it, a teleconverter, the Pentax monocular, and every combo in between, nothing useful came out of it. So no I'd like try something that makes sense Andy This lens misses the rear group, because that was part of the camera. Probably a rare lens, find a canon collector, before destroying it by adapting. Maybe by selling it, you can buy telescope.

02-21-2015, 10:57 PM	#6
akptc Site Supporter Join Date: Feb 2008 Location: USA Photos: Gallery Posts: 771 Original Poster	Well, a paper weight it will be

02-21-2015, 11:11 PM	#7
JimmyDranox Veteran Member Join Date: Oct 2012 Location: Ploiesti, Romania Photos: Gallery \| Albums Posts: 1,632	Sometime ago, I sold more then 100 lenses, elements, tu be correct in english. It is very hard to mach two groups, almost imposible. Last edited by JimmyDranox; 02-22-2015 at 04:57 PM.