Sony 35mm f/2.8 Sonnar FE - 13 Sep 2018

I've been recently reading up on the new Sony a7iii Full-Frame camera when I came upon the Zeiss 35mm f/2.8 Sonnar FE ZA pancake lens. This lens is similar in size to my current Sigma 30mm f/2.8 DN lens that I'm using on my Sony Alpha a6300 APS-C camera for digiscoping.  At $800 the Zeiss/Sony 35mm f/2.8 Sonnar is expensive, especially for an f/2.8 lens. Reviews, however, have rated the lens as outstanding in quality and great as a compact travel lens.  I had the opportunity to pick up a brand new copy for only $200 so I decided to purchase and compare it with my Sigma 30/2.8 ($169).

Since I received the lens literally a day before we left for Newfoundland, I decided to use it exclusively on the Sony a6300 and give it a test run as both travel lens and digiscoping lens. On the crop-censored a6300 the 35mm gives an effective focal length of ~52mm. Images from the camera are the same as real life, and I found no evidence of distortion at the edges. The quality of images was impressive, especially when I generated panoramas from vertically-stitched image series. On the Sony a6300 the 35/2.8 Sonnar made for a great travel camera.

I then tried using it for digiscoping. On the Digidapter™the lens had the same profile as my Sigma 30, so I didn't have to make any adjustments to the mount. That said, after a week of digiscoping with it, I was frankly disappointed.  I found a Swamp Sparrow at Cape Spear Lighthouse and thought I had  great digiscoped images. They were a bit soft, even when I focus-peaked. Of the 2-dozen images I took only 1 was considered acceptable.

So, I thought I'd spend some time checking the setup and giving it more work. At Elliston, NL I had the opportunity to concentrate on a Great Black-backed Gull, and I was much more satisfied w/ the quality of images. Sharp, and little-to-no chromatic aberration in high-contrast white feathers.

Robin and I then drove to the Atlantic Puffin colony just a short distance away.  I spent some time in the mid-afternoon sun digiscoping puffins from about 150' away, and, once again, found myself disappointed in the quality of the images. I had some nice keepers. I had more losers; soft-focus birds with distinct CA that tells me that I was either front- or back-focusing on the birds.  I could possibly place some blame on time of day, wind, moving birds, and possible heat shimmer, but I did not feel good about the lens after this visit.

When I got home I decided I really needed to compare the Sony 35/2.8 with the Sigma 30/2.8 in a more controlled environment. This evening I set the scope up about 20' away from the thistle feeder and digiscoped some American Goldfinches with both lenses. To normalize results I not only digiscoped both lenses at 25X zoom on the scope (EFL~1125mm with the Sigma 30 vs. 1300mm with the Sony 35), but then shot the Sigma 30 at ~30-35X zoom (EFL ~1300mm).

Sony 35/2.8 @ 25X Zoom 

Sony 35/2.8 @ 25X Zoom

Sigma 30/2.8 @ 30X Zoom

Honestly, I could not see any difference in image quality between the 2 lenses under the same lighting conditions. All were taken at 1/800 sec at f/2.8 (Aperture-Priority) and ISO 3200. Feather detail is sharp in all instances and the amount of grain was similar in all. Images are all straight out of the camera.

Perhaps most telling, however, was during focus-peaking. When I focused the scope on the bird I then attached the Digidapter™ and camera setup, then used focus-peaking to get maximum sharpness of head feather detail. The balding male goldfinch really helped here. I found that focus-peaking with the Sigma 30 optimized just before infinity while the Sony 35 optimized right at infinity. This is kind of critical since I found at some moments I could not focus-peak w/ the Sony and get a super-sharp image unless I did some additional focusing w/ the scope! As a result, I ended up getting slightly softer captures more often than not.

The bottom line? When it comes to digiscoping with the Sony a6300 the Sigma 30/2.8 DN lens ($169) is every bit as good (and perhaps more reliable) as the Sony 35/2.8 Sonnar under the same conditions. I would expect the Sony to show better edge sharpness and less CA at the edges than the Sigma 30, but frankly, the Sigma 30 gives reliably sharper images, even when zooming the scope to 30-35X.

So, my advise would be to purchase the Sigma 30mm f/2.8 DN and save the extra $600 to buy something nice for your significant other. The Sony 35mm f/2.8 Sonnar is an excellent lens, and reliable as a travel lens and digiscoping lens, but in my case the extra $600 does not result in significantly better image quality. That said, if I do get my hands on a Sony a7iii the Sony 35/2.8 Sonnar may be a killer combo.

In the meantime, here is one of my resident Ruby-throated Hummingbirds that is still hanging around. I digiscoped this little beauty hand-holding the scope!

Sigma 30/2.8 1/1000 sec f/2.8 ISO 3200