gaspar_bakos2

Dear all,

Thanks for the numerous messages helping us in solving the focusing

problem of this Autofocus lens.

To clarify a couple of issues:

- We have a large digital detector in the focal plane at the correct

distance (to Phil, S.)

- We have this autofocus lens (and not the MF version) just because

this is what the observatory could purchase - it is very difficult

to

buy FD versions of the 200mm f/1.8 nowadays. BTW, we have 5 of

those,

but used already on other telescopes giving beautiful images of the

starry sky (to Phil, S., Maureen, M)

- The lens, of course, is exactly like a telescope, there is no

fundamental problem here. If one attached an eyepiece to the end, it

would be possible to peep through with the naked eye. However, we

use

a CCD in the focal plane, and in this sense what we are doing is

exactly photography (to Mark, U.)

- The focus ring is not attached to the focus group mechanicaly

(thanks

for Scott Ferris et al., and message for Minh Thai)

- I was trying to locate Chuck Westfall, but could not - anyone has a

link how I could contact him (thanks for Jim Vanson)?

- To Chuck Dowling: THANKS A LOT! The pinout and pin functions are of

great help! Before we buy any camera body (not so easy in the middle

of the Negev desert) - any idea of the voltages (0.2V or 2V or 5V -

just the order of magnitude) emitted through the pins?

- To Bob Atkins: THANKS for clarifying lot os issues. You confirmed

what we are afraid of: this lens can't be focused manually without a

camera body attached, and power turned on.

Cheers,

Gaspar Bakos

Dear all,

We are desperately seeking the electronic

protocol of a Canon EF autofocus lens. Here is

the problem we are facing:

An EF 200mm f/1.8 Canon lens is used on an

astronomical instrument WITHOUT a Canon EOS body

attached. We would like to MANUALLY focus the

lens by turning the "manual focus ring" and

setting the lens focus mode switch to "manual".

However, the focus does not change at all with

the above approach; for example, the image of

stars remains exactly the same: rather blurred.

We are afraid that this "focus mode" switch works

only (thus, can be switched to manual) if the

lens is attached to an EOS body, and some kind of

voltages are applied to the little golden

'plates' (pins) on the bayonett of the lens. Here

comes the question: does anyone know the protocol

of these pins? Does anyone has a multimeter and

could do a 5 minute reverse engineering for us on

a Canon EOS body to see what voltages are set to

the pins?

If we knew this, we could apply the same

voltages, and focus the lens.

Any help is appreciated,

Gaspar Bakos