Can anyone give examples of uses for 135mm in Astro? Astro is WAY outside of my normal shooting subjects aside from the stray Milky Way shot here and there. But I recently made friends with a guy that knows a lot about astro and am thinking about doing more of it. Is the Zeiss 135 APO useful for this purpose?
If you are to take Milky way and wide field astro imaging, this lens is not for you.
You would be a lot better to look at Samyang 14mm F2.8
where this lens excels is when you need to have more detail of smaller objects (Say detail of Andromeda/flame nebula at Orion or likewise dim but intermediate size objects) at best possible F stop that significantly shortens your time of night shooting or adds to your raw data acquisition per shooting session (Its hard to imaging but even a full cloudless night could be very short for a top of the line image, when shooting a dim object that is not so generous with photons. That is why many of the best images you see are actually the collection of images from many nights throughout the months).
This lens is one of the sharpest lens for the money and beyond.
I haven't seen compassion with the excellent Zeiss lens you quote (That BTW costs at least 3.5-4 times, yet a good comparison as similar to Zeiss, Samyang believes in providing the exceptional Image Quality, with Manual focus) but compare with Canon's L 135mm F2.0, that by many reviews, is considered as one the best Canon lenses ever made (Not an easy title by any stretch), this lens win the race, hands down, when shooting wide open. Usually even with best lenses you need to stop down more than One F to get the sharpest and best result (Significantly increasing your time of exposure for a dim object). Here you get it all at F 2 that makes it a wonderful choice for low light situations such as astrophotography. Then focal length 135 to 200mm is a perfect range of intermediate magnification, specially when significantly low payload of tools makes tracking and other aspects of shooting (Including mobility) like a silky smooth dream with no need of GuideScope or digging too much down into details of astrophotography that frustrate (If not permanently discourage) the new-to-field photographer. And its not only the sharpness that is superior with Samyang. Contrast and color saturation/Color accuracy, right off the camera is far superior compare with Canon L. Google and see the test results for yourself.
If in reality this lens is what tests show, a lot more people should seriously look into this undiscovered yet, gem.
And don't forget a lot of Samyang products have so far proven the concept of being "Best bang for the bucks" in past (Zeiss quality for the low budget). This lens might be a winner in that line, as more info is coming out.