While (mostly π) patiently waiting for my 183 to arrive, I've been exploring some lightweight, cheap and portable lenses to experiment with once it arrives. I've got a beautiful WO z61, but don't have access to a garden and have to do most of my astro out in public spaces - where I am, the most I've managed before something sketchy has spooked me into packing up and getting out of there was about 45 minutes, so am looking for something a bit more inconspicuous until my garden situation changes!
To that end, after a little reading and some eBaying, I saw a Canon FD 300mm f/5.6 going for Β£30 in great condition and thought it was a good place to start. I have ordered the ZWO EF-T2 adaptor, and I am trying to puzzle out if I will need to get an FD-EF adaptor designed to focus to infinity using a built-in lens (most of which I've found provide an additional crop factor and from reviews tend to degrade the image a bit at wider aperture), or if I can use the basic FD-EF conversion ring without the infinity focus element I would need for a DSLR, given I can manipulate the distance the ZWO sensor is from the FD lens with extension tubes? That would be much cheaper, and wouldn't have the annoyance of additional and average glass in the train (plus the impact on the focal length).
If I can make this work, I'll have something in size and weight akin to a RedCat, but with a bit more punch in focal length (albeit I am sure with an image quality that doesn't compare, but neither does the expenditure)... I just really am a bit lost among the diagrams, formula and varieties of builds.
Any advice or pointers welcome - this is my first dedicated astrocam, I am very familiar with DSLRs, but definitely need a hand with image trains!