Are there any M4/3 or 4/3 lenses > 300mm (actual)?

[Hywel]

Just a thought, but if you genuinely need focal lengths above 300 mm actual, have you considered using a telescope?

Something like a Meade ETX80 has focal length 400 mm and f/5 focal ratio, for under 300 UK pounds. Or for real reach a Maksutov-Cassegrain like the ETX-90 or ETX-125 (which is what I have) with focal length 1900mm at f/15.

I've not actually shot through it with my GH4 but it worked just fine with a Canon 7D.

Sure, the prices go on up and up, and you might end up wanting an eye-watering Apochromatic for serious photographic use but telescopes often come with pretty stable, reasonably portable mounts designed to take the weight of the telescope plus a camera hanging off the back.

Cheers, Hywel

[Telecaster]

Via adaptor you can get some serious reach from m43 cameras if you want. I've attached a pic I took a couple years ago with an Olympus E-M5, Nikon 400/3.5 lens plus a pair of stacked 2x TCs. That's 1600mm.    Even then the pic is a full-res crop from the original. Saturn is a long ways away! My aim here wasn't to do serious astrophotography but merely to find out what an extreme combo—small sensor + very long lens—was capable of. It took me longer to find Saturn with such a small field-of-view than it took to photograph it.

I have to say the most enjoyable part of this exercise was watching Saturn at ~10x mag via the rear LCD as it moved through the image frame. I've done the same thing a few times this year with Jupiter and its major moons…usually haven't even bothered taking photos.

-Dave-