crtomkins wrote in post #4427136
I have a Canon 400d with the Sigma 70 - 300mm F4-5.6 lens. I'd previously bought the Olympus Tcon-17 and was wondering if there's a way to attach it to the Sigma lens? It doesn't just fit on (I suppose that's a given!), but does anybody know if there's an adaptor that would allow me to use it?
It seems to me a weird question.
The TC should be taken as inexpensive. The easy answer is to suggest you to buy a new TC. And if you buy a 1.4X TC and tape the reporting pins it will probably AF.
Now here it goes my weird answer.
To make this you will need an extension ring for EOS and a way to fix the optical elements of the TC inside the extension ring. Provisionaly you may try to do it with expanded polyestyrene or paper or whatever. But be careful of keeping the distances.
This remembers me something that some of you will find interesting:
HOW TO CHANGE THE POWER OF A TELECONVERTER
I had and still have the following MF material:
A Ricoh XR-X (it has a RK mount wich is a Pentax K modification).
A Hanimex 300mm f/5.6 catadioptric (AKA mirror) lens.
A Vivitar 2X (I bought it used).
A Pentax helicoidal extension ring.
Once upon a time I red at the old Modern Photography mag that you can change the power of a TC putting it closer to the lens or with a bigger space.
So I unscrew the nut wich fixes the optical elements from the TC.
After this, I unscrew the optical elements from the TC. At this moment I had the nut, the optical elements and the cylinder wich may be used as extension ring.
I found that the optical elements of the TC were assembled inside a cylinder covered with threaded metal, and the thread had the same screw size of the rear filter adapter of the Hanimex. They could share the same nut.
So I screwed half the depth of the nut of the lens, and screwed the TC on the other half.
In that way, I got the closest possible assembly with the lens and the TC elements. This is how you get the biggest power for a TC.
I had to extend a lot the Pentax helicoidal extension ring to get infinity focus again.
The result was something around a 4X TC, maybe even more.
Of course I lost a lot of light (4 stops, maybe even more).
Also I found that the focusing scale was "compressed": turning the ring very slightly the focusing distance changed from very close to infinity (or more than infinity) so it was very difficult to focus.
The idea in brief is that if you put the TC elements closer to the lens, you will get more power. But you will have to put a spacer between the-lens-and-TC-assembled and the camera mount, and you will have to adjust the distances. Maybe if you try it with a f/1.4 lens you will completely fool the AF, so think about it as a MF only possibility.
This is a very weird answer, maybe a bit out of the question, but not off topic. At least, that's what I hope. I'm sorry for the boring explanation.
