Can anybody answer my question about the pincushion distortion on the SLC?
Is it part of the design?
Yes, I'm sure I will be corrected if I miss a detail of Swarovski history, but until the SV series most Swaro roofs (SLC and the original EL series) had a "traditional" distortion pattern with pincushion, which seemed to be typical of the era (e.g. Leica Trinovid + Ultravid have always had pincushion) other than the Nikon HG/LX with their "field flattener" eyepiece lenses.
Swarovski changed this when they introduced the "Swarovision" EL models, which have extreme "flat" fields (almost no distortion or curvature). The side effect of eliminating pincushion to such an extreme level is that you trade off one distortion for another, namely "angular magnification distortion" (AMD) which causes the "rolling ball" effect where objects appear compressed at the edges.
The SLC never got this update, and have continued with a traditional design (pincushion w/o field flatteners). Some (myself included) believe the pincushion approach yields greater "3D depth" in the image compared to a binocular with field flatteners, which can give the impression of compressing the depth in the image. Tobias Mennle
mentions this effect when contrasting the Leica Ultravid 7x42 vs the Nikon EDG 7x42. I have an EDG 10x32 as well as Leica Trinovid 10x42 (slightly more pincushion) and Ultravid HD 8x32 (a lot more pincushion) and I clearly see what he's talking about when comparing them, the Leicas have a greater sense of depth and feel more "3D" to me whereas through the EDG perspective of depth feels more flattened out.
Looking at Allbinos reviews, which rate distortion as the approximate % distance from the center to where the lines begin curving, and thus is a decent proxy for the degree of pincushion:
- Original Swaro EL 8x32 = 36%
- Original Swaro EL 10x42 = 31%
- Swaro SLC NEU 10x42 = 45%
- Swaro SLC HD 10x42 = 39%
- Swaro SLC WB 10x42 = 42%
- Zeiss Victory FL 8x32 = 56%
- Zeiss Victory FL 8x42 = 34%
- Zeiss Victory FL 10x42 = 37%
- Leica Ultravid HD 8x32 = 36%
- Leica Ultravid BR 10x42 = 59%
- Leica Ultravid HD 10x42 = 74%
- Leica Ultravid HD 8x42 = 45%
As you can see the 1st gen EL and the SLC all have good amounts of pincushion and are relatively in line with Leica Ultravid and Zeiss FL.
Now some "flat field" binoculars:
- Swaro SV 8.5x42 = 91%
- Swaro SV 10x42 = 88%
- Nikon MHG 10x42 = 92%
- Nikon EDG 10x42 = 88%
- Zeiss SF 10x42 = 98%
So, yes, there's a clear design difference between the SV models and the SLC in this respect, the SLC do not have any field flatteners and will show a more pincushion and probably also field curvature than the EL SV series.