Additional factors I had in mind were that the lens must be of a large aperture, decent focal length, outstanding resolution, minimal aberration and image circle to cover a full frame DSLR. I wanted the largest image scale practical given these extensive criteria. AND not expensive - that ruled out Zeiss immediately, despite the copious salivation…There was no Sigma 135 Art yet.
The focal length I had in mind that would work would be around 100mm f2 or faster, so looking around, the best reviewed lenses were the venerable Canon 135f2 and this nkotb Samyang 135f2. The Canon had the advantage of being autofocus and established, but the new Samyang 135 had rave reviews upon its launch then. So I took the risk of ordering it unseen from Amazon, as it was not available locally yet being a newly launched lens then.
What can we take with 135mm? It will cover an FOV of 15 by 10 degrees on the full frame, so the Eta Carina complex, vela SNR, LMC etc are suitable targets. 135mm also is wide enough to get away with doing a quick polar alignment for 2-3minute subs. Other focal lengths such as 85mmm are also good, but there was no 85s on par (again…NO Zeiss, Milvus or otherwise – just too expensive to justify
).With a weight of about 2kg for the DSLR and lens, it is quite a decent load for a basic tracker like the SWAT. Searching for objects is also quite straightforward with direct vision. No need for red dots or finderscopes. Manual focus is fine for AP. The manual focus ring is very firm yet smooth with no noticeable backlash. The aperture at f2 is 67.5mm and the resolution tested excellent wide open, improving at f2.8. Ideal for holidays and casual AP!
As far as AP is concerned, stars are tight all the way to the corners on a 50MP DSLR, CA is almost invisible; there is some noticeable vignetting at f2 which goes away at f2.8, but then there are spikes on the brighter stars from the closing aperture blades. It is a matter of preference which evil to pick, - I usually do f2 and Adobe will do lens profile corrections on the RAWs (I just use the equivalent Canon specs) so the image is cleaned up a bit. Easier to remove vignettes than multi-spiked stars!
After using this for a few trips, I feel this lens is the most value for money lens for this range per mm of aperture. Not only does it excel at AP (and general portraiture I suppose), it is very well built and the mechanics are top notch. If you are considering which lens for a holiday AP kit, do give this one some serious thought!
Update: The samyang, sigma and zeiss mtf charts are shown.
https://www.lensrentals.com/blog/2017/0 ... e-curtain/
PS: As the images are too big to load, do have a look at them on my flickr page (other scopes are also used) -- https://www.flickr.com/photos/clintonhazel/
