As a vendor in the astrophotography business I have access to a lot of premium gear for my use. But I do have to use my own money for much of my passion, and being that I’m not independently wealthy, I often have to be careful and go the “budget” route. I’ve rented and enjoyed using some high quality lenses for wide field photography and finally realized I was spending more money renting than if I’d just outright buy one. So I looked around and after some failed attempts to snag a high end lens off eBay at a steal, I went with a recommendation made by many a talented (and far more experienced than I) wide field photographers have suggested, a Rokinon lens.
Rokinon, Samyang, Bower… these are all the same manufacturer but branded differently for reasons I do not know. The well-regarded lens review site www.photozone.de gave the Samyang lens excellent marks on sharpness, and I had borrowed a friends on a vacation trip out west and compared it to a Zeiss lens I rented. I did like the Zeiss better for landscape photography (never had cloud free skies for stars!), it just felt better and it had focus confirmation. A bit out of my budget however and aside from all the literature, two personal friends had Rokinon lenses and recommend them so I took the plunge and ordered one via Amazon just before my Alaskan vacation where I hoped to shoot the Aurora outside Fairbanks (see my previous blog about this).
As everyone knows when you get new equipment, it attracts clouds. It was days before I could get starlight to do a proper test of the lens at a small lake near my home. I put the lens on my Canon 5D Mark III, grabbed my tripod and despite the moonlight was determined to get some stars to see how things went. I used live view to focus on the back and took several test shots. They all had this disappointing asymmetry across the field. Sharpish stars in the middle, large bloated out of focus stars on the right, and elongated distortion on the left. I was heart broken, and it was only a couple days before my Alaskan trip. I did what most people do, which was doubt myself. Perhaps I was out of focus? I even stopped the lens down as much as f/5.6, no change except perhaps slightly less distorted stars on the left hand side of the field.
I took it anyway to Alaska thinking to refine my skills and make sure it wasn’t user error. I even setup and used a laptop and the camera software I work on in my day job to make sure I had good focus… alas, the same asymmetry was readily apparent. At a wide enough angle, you can’t hardly tell. I could see it though. My aurora photographs were quite satisfactory for many reasons, but looking closely I could see that the stars on the left were smaller and brighter than the stars on the right hand side of the field, and I knew why even if you couldn’t tell once the image was down sampled small enough.
When I returned home I declared the lens a lemon and friends on Facebook counseled me that they too had returned their original lenses, then evaluated another. One said he had gone through three lenses before finding a good one. It seems they can be good, but the quality control is such that you had to look for them in the pile. For the money, they are excellent values… but you might have to pick through a few like bypassing bad apples at the grocery. So, rather than return the lens for a refund, I asked for an exchange. To Amazon’s (or Amazon Prime’s) credit, this was hassle free. They sent me a replacement lens immediately before I had even returned the bad one.
This time the wait for clear weather was not so long. The day after I received the replacement I took it to the “duck pond” and tried it out again. This time the stars were good all the way across the field with the edges showing some distortion as you’d expect from a lens this fast, but it was symmetric all across the field. I took it down to my observatory the following weekend and did some milky way test shots. I was quite pleased as you really can shoot at f/2.8 with this lens with minimal distortions in the corners.
In fact, short of a high quality flat field astrograph, I’ve never shot through a camera lens that didn’t have some distortions off center without having to severely stop them down. The image shown here is actually quite impressive really as it was shot wide open at f/2.8. These stars at the far edges show some distortion when zoomed in about 400%, but this is far better than I’ve seen on my more expensive lenses.
There is a bit of barrel distortion of the entire field that these lenses are well known for. Your not likely to be able to tell on a starscape or wide field landscape shot, but Adobe Photo Raw can fix this with a downloadable lens profile that will warp the entire image back to flat. I found this too to be not really objectionable, and with the improved field and really quite exceptional performance at the edges and corners, I’d declare this lens an excellent value… possibly the best available, for wide field nightscape photography. Just make sure you don’t pick up a rotten apple when you get yours…