Reverse T Adapter for EOS Lens

Hi all,

I've been looking everywhere for an adapter to connect an EOS lens to a camera with T-threads on the body and have not been able to find one. Anyone knows where I can buy one of these? I know they exist.

Thanks

Sorry if I am saying no but, they do not exist to go in that direction. I have lots of adapter but never seen that way.
You can make one but not likely to reach focus at infinity. That is why there is an adapter for FD to EOS with optics inline, but they are not great.

Here is a link where this is discussed.
http://photography-o...ad.php?t=980571

Here is a better link that gets into it from the otherside. What I mean is that in the camera world the Pentex screw mount has a flange to focal plane of 45mm and Canon EOS is 44mm. Therefore to the manufacturing world it is not a possible combination thus not made.

http://www.bobatkins..._focus_EOS.html

One of these adaptors may be of help. I am *guessing* that those cameras the adaptors are intended for are using T-thread and that the only difference between adaptors would be the the amount of spacing provided. You would probably want to ask Orion about that to be sure.

This assumes you are looking to use an EOS lens on an astro-CCD. If you are hoping to use an EOS lens on an old T-thread mount film SLR camera then I do not believe you would be able to focus to infinity.

Your right on the no focus at infinity. That is why I did not suggest that one.

BTW, the reason this is so rare is that camera lenses are designed for a very specific distance from the back of the lens to the sensor/film to focus properly.

The focus distance for EOS (EF or EF/S) lenses is *shorter* then the focus distance for standard "T-thread" or "T2" mount lenses. So a film SLR camera body designed to to accept T mount lenses would require the EOS lens to be mounted *INSIDE* the body of the camera - obviously impossible.

However in the astronomy world while we use T-thread all the time we do not maintain strict focus-distance measures. Most astro-CCD cameras will have the T-thread placed very close to the sensor rather then at the "T2 mount" official distance from the sensor - as a result there *IS* room for adaptors (like the ones I linked above).

Hopefully those linked adaptors are truly using T-thread, and that the camera you have will have a small enough distance from the thread to sensor to allow the lens to come to focus at infinity.

Thanks for the responses guys. One of those Orion ones will probably work but they're way too expensive. More than the old telephoto lens I bought to use with the camera
I've posted a wanted ad on AMart to see if I can find one cheap. If not I'm just gonna buy an EOS body ring and spacers. My chip to flange distance is about 15mm. As far as I know EOS flange spacing is 44mm. So I'm hoping I can make one with the spacers and the ring. Will post the results if I succeed

Is this what you are looking for?

This mates any EF-mount (EOS) lens to an SBIG camera, with the correct spacing, i.e. when the lens reads infinity you are very close to infinity focus. Unfortunately I am not aware of anyone selling them. The brass ring is custom-made. I sent this specific image to SBIG in 2005(!), trying to convince them to have them available for sale. Perhaps they now sell them? Check their website. Issues you should be aware of:

1. It is exceedingly difficult to custom-fabricate the Canon EF bayonet, hence you start off by purchasing cheap EF extension tubes and dismantle the front from the rear, usually by simply removing 3 or 4 watch-screws.

2. You then get any metal-worker with a small lathe to make the much-simpler brass tube that has a male T-thread on one end and a flat side the other end. The 3 or 4 watch-screws are then used to hold the brass tube to the EF female bayonet. One can also use aluminium instead of brass, whatever scrap metal rod is available. The lathe work is well within a hobbyist's ability, the most skill (not very challenging) being required to make the T-thread, straightforward if your lathe has a facility for machining threads.

3. EF lenses need to be stopped down on an EOS camera with the shutter set to B, then removed from the camera body with the shutter still open. The aperture will remain stopped down, say, to f4.0 or whatever you desire. You then attach it to the CCD camera+custom adapter. Sounds more complicated than the reality, which takes a few seconds. I believe this may be the reason why SBIG was not selling EF to T-thread adapters, but only Canon FD to T-thread. Of course, most Canon tele-primes 100mm or longer focal length do not need closing down for astro anyway.

Perhaps if you say what lens/OTA, precisely, you are trying to mate to what camera, you may get a more useful answer. Best wishes.

I have a canon eos 450d, and I connect a FD lens (old canon lens) using the adapter on ebay, came from india very quick. I did get focus using a 3x extender

http://cgi.ebay.com/...=item2eafad016c

Thank you Samir and Jose. I managed to put something together with an extension tube I got for 8 bucks and a step-up/down ring I had at home. I just checked by focusing on the farthest thing I could see from my window and it seems to be in focus right where it's marked infinity on the lens. Here's what it looks like in case anyone else wants to make one and an image I took with it from an electrical wire at infinity. The camera is an Orion SSAG.
I'm planning to use this as a light quidescope and will update again to let you guys know how it performs.
By the way the extension tube comes with 3 spacers so you can combine them and get the spacing about right.

And here's the image:

The mirror lenses actually work very well for autoguiding. My setup back in the days when I used to autoguide:

I think I was having flexure problems during my test with 10min subs last night. Any suggestions Samir?

My mirror guider-lens had support at 2 points, that bright ring surrounding the lens and the tripod foot of the CCD camera. I think you have to find some way of doing something similar to make everything very rigid. If you are guiding an SCT the common wisdom is that to do that properly most people end up using an off-axis guider because, even if your mounting is super rigid, the large primary mirror of the SCT is not, and the very long focal length is also sensitive to any very minor flexing of the tube+dovetail of the SCT itself.

Thanks Samir. I think my mistake was just using the single tripod mount on the lens. Will attach a ring to the guider itself and see what happens.

Ya I would go for rigidity even having to sacrifice the ability to adjust the guide scope , rock solid is how I have my finder guider on the C8 and it seems to work well.