Canon 5D + Samyang 135mm. Worth it in the long run?

I use my Samyang 135 with 533/1600/2600 cameras. I also have an stock Canon 6D full frame DSLR. I have never used the Canon because of the cooling and using true astro cameras. The Rig itself (lens, camera, zwo eaf, small 30mm guide scope,120mini, dovetail bar and hardware) is heavier than I would like on my Skywatcher camera tracker. I use it on an Orion Sirius (HEQ-5) mounting instead. 

The combo is wonderful. I use it often. Image scale is an eye-watering 6+ arc sec / pixel with a 3.76micron pixel camera. Never a high resolution solution. However, it is extremely fast, good stars to the corners, anything not perfect is easily fixed with BXT. I would still make the same purchase today even after using it now for close to a year.

CS Tim

I don't have the 135 Samyang but a Nikkor 180mm F2.8.  I never get tired of it. Mounted on my astro modded 6Dii, my stock R6, my 533 and now my 2600.  I have it on a star tracker often while my main rig runs or mounted atop my main rig.  

I have thought about the 135, but honestly the Nikkor is also a great lens. I would doubt you would tire of it.

I have the Samyang 135mm F2 lens which I use with an old Canon 5D MKII and combined with a ZWO adapter, with my 2600 MC Pro camera. It is a lovely set up. The lens is sharp even wide open and is flat to the edge. I picked up the Astrodynium ring set for it and added a ZWO autofocuser. This is my goto rig for widefield shots of Orion, Rho Ophiuchus, the Vela region and many others. If I could only have one portable rig, this would be it. You do need to take good flats with it but this is very simple to do. For the price it is very hard to beat.

Giulio Ercolani:
The quality of Samyang 135 lens varies greatly from specimen to specimen. I tried two and they were terrible. Upon analysis carried out with ASTAP and CCD Inspector, the two objectives were affected by very severe tilt and heavy coma. The stars were so elongated and distorted at the edges that it was not possible to correct them even with BlurXterminator. These problems arose when using the lens with a QHY268M, therefore a camera with an APS-C sensor. With a larger sensor the problems would be even more serious.

Please, beware that these issues often arrise from the adapters used to connect astrodedicated cameras to the lens and is not inherently a problem of the lens itself. You can exchange the camera adapter to a standard M48 and screw in the rest of the imaging train to minimize tilt. And even then, at f2 especially, you need to dial down backfocus in the range of micrometers. I use the lens in combination with an Ogma O'tilter and Ogma APS-C camera and it dialed down all the above mentioned issues.

Once you have a working system, dont touch it 😄

For OP: If you are using the intented camera with your lens, you most probably won't encounter these problems. I love the simple setup with a simple star tracker, it even procured me a IOTD!

Go for it.

Samyang (or Rokinon) 135mm F/2 is a must-have astrophotography lens. That said, in my experience, it does have some issues to consider (some duplications with what have been said already):

• QC is not very even. As others said, the quality (esp. optical axis tilt) varies from unit to unit.
• Has strong vignetting, especially for full-size chip cameras. It works very well (after applying flats) for APS-C chips.
• Focus (and the star shape) is very sensitive to the backfocus distance. With my dedicated astro cams (ZWO ASI 071MC PRO and 2600MM PRO), even 0.1mm makes a big difference. Not sure how accurate EOS cams' backfocus is.
• Need a special tripod collar to hold the lens. This may be important when used with a Canon/DSLR, because the camera or lens weight may bend the bayonet joint slightly, causing optical axis tilt. Ideally, support both lens and camera.
• Related to the above, there are 3D printed products available these days for this lens. (available from sellers on Etsy.com)
• The elongated and seagull shaped stars at the edge of the field are annoying, but, these days, BlurXterminator very effectively can correct them (if you are ok with such "manipulation").
• If you are using a dedicated astro cam or a modified DSLR, sharp narrowband filters (3nm, 5nm etc.) are not very effective when the lens is used wide open at F/2. I use a stop-down ring to make the lens F/2.8 (to avoid diffraction spikes from the iris blades) . This also improves the resolution slightly. You can also use  spectrum-shifted NB filters (for fast systems)  that seem to be popular these days.
• The 3D printed tripod collars also come with gears and brackets for a  motorized focuser that you can use to focus the lens manually (I am thinking of the manual focus version of the lens). This would be very useful for fine focus control. With a dedicated astro camera, automated focusing is a bit trickly, because it usually requires going beyond the infinity mark. You would need to have a bit of "surgery" to shift the focus limit to go beyond infinity. You can find how to do this on forums and YouTube.
• Because the stars are very sharp and 135mm is a rather short focal length, the sensor need to have fine pixels. My 2600MM worked well (pixel size 3.76 um) , but 071MC (pixel size 4.78 um and with a Bayer matrix) did not do so well for imaging the star-rich Cepheus area in RGB.

Hope this helps. I am still learning how to use this lens in my system effectively myself. 

Seiji

Thank you for that detailed explanation! I might make an order and try it out atleast =)

It's as everyone has said. Very good lens. I recommend stopping it at 2.8 and keeping exposure time in line with the sensitivity of your camera. Ie for 533 mc pro its best at 3 min exposure. Any more than that i find lens flare on bright stars