Thursday, July 05, 2018

Conclusion about the Canon FD 300mm f2.8

The conversion is very easy, and could be done with off the shelf parts, and such conversion could be easily reversible.

When a 2x barlows is inserted before the diagonal, it could be used visually with an eyepiece.  It is not bad as a wide field telescope.

However, high power performance suffers especially with bright objects.  It is because it is a telephoto lens, so the flare and internal reflection renders it useless.

I've tried every effort to remove the internal reflection but in vain.  The problem must be in the unmodified part of the optical chain.  On looking at the inside through the objective, I believe that the internal unblackened parts could be the source, but I've no way to verify.  The protective element before the flourite lens could be another source as well... but again, I've no way to verify.

So this lens will be reserved solely for imaging purpose.  It is still a very nice 300mm f2.8 astrograph, it's very compact, light weight and thus highly portable.  It's also very well corrected.

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