My first post after reading many many posts for support over the years.
I use Canon lenses, often with teleconverters and often with stacked teleconverters.
Using a Canon DSLR is all good re focusing as a number of programs give you control of the lens’ built in focusing system.
Using an astro CCD camera however is a different story and I’ve come to the conclusion, after trying a few methods, that manual focus is not the way to go. After all, these lenses have state of the art USM focusing systems built in, you just have to take control of them whilst not using a Canon DSLR for imaging.
Searched the internet and various solutions are out there however a bit complicated and some a bit expensive. Then I thought of a hybrid system that seems quite straight forward.
Basic idea is to run an 8 core cable (eg LAN cable) between the pins of a teleconverter to the pins of an extension tube. Extension tube with camera cap is attached to an EOS camera and the teleconverter is in place with the lens and CCD camera.
Connect EOS camera via normal USB cable and use EOS Utility or BYE or …… and you have control of the lens focusing system. Different program is controlling and showing Live View of the CCD camera.
There are cheap extension tubes out there that have metal rods connecting their camera end pins to the lens end pins.
A teleconverter such as the Yongnuo YN-2.0X II has the same type of metal rod arrangement between pin sets. In theory you don’t even need to solder any wires. Just use wire shrink tube on each metal rod with the stripped wire inside. I did this with my Yongnuo but put in too much heat and melted the plastic holding the rods. Place the plastic in ice water and use more care, all should be fine. Be careful of all the pins and springs, pins different sizes etc.
If you have success using shrink tube method, teleconverter should work with either DSLR or CCD attached to the teleconverter / lens system. That is, still has connection straight through or via cable to ‘secondary EOS focusing’ camera.
I’m half way through this “project”, now waiting on some deliveries and away on holidays in January.
Nevertheless, I thought I would share my idea and I believe in theory this should work.