How good in the Rokinon 135mm? What else is in it's class?

I really really love my Samyang/Rokinon 135mm. It was a huge boost to my AP, because I am now at least 10 times faster in acquisition copared to my last tele lens. It is so sharp that you can compare it with cheaper 200mm lenses regarding resolution.
Sometimes I use it at f/2, just for the speed, but I recently tend to use it at f/2.8 to get slightly smaller stars.
All I can say is that it is an amazing addition to my mobile setup and nicely works on the Star Adventurer.

I have heard a lot about this lens, can anyone provide a sample single unprocessed  (RAW if possible) shot at F2 with full frame DSLR camera or similar sized CCD.

The images look very good at about APS-C  (QSI583 is just a tad smaller). Thanks.
Now I have something to compare with the Zeiss 135 f2 APO sonar T*, but I think the Rokionon appears to be much better. My opinion is just from memory of seeing ice cream cones for stars at f2 in the corners of a full frame camera (D810A). Unfortunately I did not save the images. Waiting for some clear skys to shoot some samples.

I use Canon 200mm f/2.8L IS USM ll and Samyang (Rokinon) 135mm f/2. I was inspired by the Lloyed's images to purchase the latter. The lens gives me very sharp stars at F/2, but my unit appears to have a slight misalignment of the optical axis in the lens or in the lens-camera adapter, resulting in blurred/elongated stars along one edge of the field. This may indicate some QC problems (I did try to adjust for the sensor tilt). Both Canon and Samyang/Rokinon lenses give me very good narrow-band frames too, but the S/R's F/2 light cone would be too steep for 3nm-6nm filters due to the spectrum shift (I use an aperture mask to tame it to F/2.. Canon at F/2.8 gives me superb images in narrow band, but RGB images are not as sharp due to its rather severe CA. I would stop it down to F/4 for that (Rokinon/Samyang does not seem to have this problem).

I've used 5nm Ha (Astrodon) with no issue.  I  haven't done the others simply  because the camera only has 5-position filter wheel.  The system is remote which makes it tough to switch out ;-)  I could have the local tech do it, but for now Ha is good enough.

Can you post a link to a raw frame?  I'm curious how well it does across the entire frame.  I'd like to get a range of lens to cover different fields of view.  For now the 135 Roki (effective 127mm on my rig is very good.  Would be nice to find a good performer at 200mm at a reasonable price.  The Roki is < $500

Lloyd:
Can you post a link to a raw frame?  I'm curious how well it does across the entire frame.  I'd like to get a range of lens to cover different fields of view.  For now the 135 Roki (effective 127mm on my rig is very good.  Would be nice to find a good performer at 200mm at a reasonable price.  The Roki is < $500

Have you thought about just using different sensors with different sized pixels instead of different lenses?

Lloyd:
Not a bad idea.  Getting different lenses is a bit on the more economical side than new cameras though.  Still something worth considering.

Yes, more economical depending on the cameras you use...   Maybe a wash with some other brand cameras.  I'll keep you posted on experimentation and testing due to start in the next week or two

Will the Rokinon come to focus with the QSI WSG? Or is the WS version required?

I use a single telescope ring to stabilize the system that keeps the belt from pulling the system.  I also make sure the belt it not too tight.  One other thing that should be tested is the frequency of focusing needed for this lens and your system.  I have yet to determine definitively, but I believe the Rokinon is relatvely insensitive to temperature change.  Assuming this is true then two things come to mind:1) focus is infrequent and thus will pull on the lens infrequently, 2) imaging does not occur during the focusing process.  So if there's tilt, then I question whether or not the belt is the source while imaging.  It could be the source if it's generally too tight, or it the lens is not otherwise supported as in the case with a ring.

http://deepskywest.com/rokinon_astrophotography/

Thank you Lloyd and Bill.
I'll try loosen my belt and add mount ring to hold my lens.
Bill I already bending the leaf sting so there are so little wobbles. but there are still elongated stars up-right-side of my image.
Because my focusing motor located at down-left-side of my lens, I think it may caused by belt-driven system.
Rokinon does not have internal focusing motor so I use the system.

I think it's the best lens for all astrophotography beginners. It's cheap , sharp, has low CA and has an newbie friendly focal length.No big mounts are needed, no guiding needed.

There may be some QA issues, but I guess I was lucky with my piece.

My  findings:
- In case of T2 adaptation a proper distance is crucial ,especially for shorter wavelenghts (OIII)
- Going for f2.8 may help to increase the quality.
- The lens seems to hold focus pretty good

The Samyang/Rokinon lens is a great piece of hardware. I would buy it all over again.

I couldn't agree more!  We  have it on a PME which I should clarify:  the mount is definitely not required for good images.  It happened to be unused at the time.  I will go up to at least 10 minutes unguided in this way over-mounted configuration, but even a modest mount will do well at such a short FL.  Overall, very highly recommended "starter scope".