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eyepiece to make telephoto lens into telescope


I wonder if you can help me. I posted the following on the EOS Digest mailing list the other day but have not had any helpful replies yet. A friend recommended your site & it seems to be the sort of place to ask these questions:

I am trying to get hold of an "eyepiece" to put on my telephoto lenses, in place of the camera body so that I can use them as telescopes, in order to save weight (not to mention money) when out photographing & watching wildlife.

My first question is - does anyone know where I can come by such a device in a Canon EF fit? WJM has told me that he has seen such items advertised in the past but not recently.

I have obtained a "Minolta Lens/Monocular Converter" & found a company called SRB Film in Luton, England who are very helpfully prepared to convert the mount on it to Canon EF but I would also like to be able to take advantage of the image stabiliser on my 100-400. I found the lens contact pin-out details (below) on WJM's site but I am not an electronics expert. Can anyone tell me what is likely to be needed to turn on the IS?

Martin Wiseman wrote the following on 10/8/98:

"Looking at the front of the camera body and reading from left to right, the signals are:

  1. VBAT
  2. P-GND
  3. P-GND
  4. VDD
  5. DCL
  6. DLC
  7. LCLK
  8. D_GND

Pins 2 and 3 are combined into one large contact on the lens. My interpretation of these signal names is as follows:

VBAT - Battery power for driving motors etc.
P_GND - Power ground - the return path from motors to battery negative.
VDD - Power for the logic circuitry
D_GND - Digital ground for the logic circuits
DCL - Data from Camera to Lens
DLC - Data from Lens to Camera
LCLK - Data clock

Other people have suggested that the data protocol is probably 8 bit serial at 62.5 kHz and possibly based on the Motorola SPI interface."

I have not tried simply putting 6 volts across pins 1 & 2 yet but I imagine that there will be something more complicated than that needed to activate the IS.

I have mailed MW who says that this may work however, especially if I add the correct data voltage across pins 4 & 8: Since early bodies were not aware of IS there can be no signal specifically sent to activate the IS but there may be a general "wake-up call" sent to the lens. Does anyone know what data voltage is used, to save me much effort with my multimeter & trying to fool my EOS 3 into believing the lens is on when it isn't?

WJM has suggested using the Novoflex Lens Reversal Adapter (that maintains electrical contacts to the lens when it is detached from the camera body) & using the camera body itself to activate the IS. This would certainly do the trick, however it would be a bit cumbersome for bird watching to have the camera body suspended nearby all the time, & the eyepiece would have to be used with the Novoflex adapter even on non-IS lenses because it would have to be suitably shortened. I would far prefer to find out what signals need to be sent to the lens to switch the IS on, & try to incorporate a battery & a device to give these signals into the eyepiece, or mounted on it.

Anyway, this is all I have managed to find out so far & I would greatly appreciate it if someone can enlighten me further before I risk blowing up my treasured IS lenses! Can anybody help please?

Dave Knott
Sat Dec 8 10:50:21 PST 2001


I'm looking at converting my 75-300 IS lens into a spotting scope. Did you have any luck in your project?


Mon Feb 7 06:20:34 PST 2005

I was looking for more information on the EF lens communication protocol when I found the EF232 Lens Controller for Canon EOS Lenses, a device similiar to what you want to make from Birger Engineering. The adapter is not cheap, but seems to provide a lot of functionality. Their mechanical drawing (which I attached here) provides a good source of mechanical information for the EOS EF mount.

Attached File: EF232-RING_mechanical_drawing.pdf

Chieh Cheng
Mon Feb 21 01:27:15 PST 2005

You could simply use a SLR body and adapt a high quality flip mirror to be used like a teleconverter. I once saw mirror for telescopes.
The problem with rebel XT is that the lens mirror is not very bright.

joaquim Muchaxo
Mon, 06 Nov 2006 12:04:03 -0800

I manufacture objective lenses for telescopes refratores in a simple laboratory that set in the background of my house.
I would also make eye lenses so simple. Could you send me information about and also some linkes about it?

Eu fabrico lentes objetivas para telesc�pios refratores em um laborat�rio simples que montei no fundo de minha casa.
Gostaria de tamb�m fazer lentes oculares de forma simples. Poderia me enviar informa��es a respeito e tamb�m alguns linkes sobre o assunto?

Francisco Jos� Silva
Tue, 04 Mar 2008 15:46:15 +0000

What kind of information are you looking for? If you tell us the specifics, I might be able to give you specific information.

Chieh Cheng
Tue, 04 Mar 2008 18:44:22 +0000

I bought a Sunagor PATP 54038748 OP Telephoto lens adapter for my Canon Olympus telephoto lens with a 3 x converter. I don't know if they still make them. It is very powerful, and almost impossible to use to track high altitude objects like birds or planes- but it's fun to try. I can, however, get good definition images of the moon.C.

Tue, 11 Aug 2009 17:26:16 +0000

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