Written by Grant
In the last post I made, I went over all of the native micro4/3 lenses that we have, which I feel do an excellent job of covering most of the focal range, although there really isn’t much there to cover anything wide angle, just the Rokinon 12mm and the kit lens. Since then, I decided to pull the trigger on something I’d been considering for awhile: a Metabones Speedbooster focal reducer, and now I can experiment with adapted lenses! The main lens that I had in mind to use with the focal reducer is the reasonably priced and very well regarded Sigma 18-35mm f1.8 made for APS-C sensors.
The main item I had to consider was to go with the regular speedbooster which provides a 0.71x magnification which is what would generally be recommended for APS-C lenses, or the more extreme 0.64x ‘XL’ option, which is intended only for condensing the image circle of a full frame lens down to micro 4/3 dimensions. If life were black and white it’d be a pretty straightforward decision, but the difference between the 0.64 and 0.71 is 1/3 of a stop of aperture, which would go a long ways to adding versatility to my camera: letting me keep a compact kit when I want, especially for the telephoto stuff, but giving me closer to full frame results when I’m willing to use the bigger/heavier lenses (bringing me up to 2/3 of a stop slower, instead of the 2 stop disadvantage without the focal reducer).
The primary concern for using the XL with a lens that is too small for it would be some severe vignetting. It was easy to look around and find a ton of people using the combination of the speedbooster XL and the 18-35, as it is extremely popular, and adapts to a 11.5-22.4mm f1.1 zoom, but almost everything I could find about it was specifically talking about video, and cropped down to a 16:9 aspect ratio, and the best I could find about stills was along the lines of “it vignettes at the wide end, but goes away pretty quick as you zoom in”. So after finding a good deal on a used lens, I wanted to do a bit of testing with it, and share the results of the lens at different zoom/aperture/focus positions. All the pictures are RAWs straight out of the camera, with no adjustments or corrections.
Vignetting:
First up, at the wide end, and minimum focus distance:
There’s some very strong vignetting in the corners, for whatever reason, the bottom right is the most severe. I’ll show full stops increments from f1.4 to f8, and then the smallest aperture f10
Next up, still all the way zoomed out, but focusing farther away (focused on the snowman):
So how about some other focal lengths? Zoomed in to an indicated 20mm (actually ~13mm/26mm in full frame terms:
And just for funsies, a quick check back at the minimum focusing distance:
So for focusing up relatively close, I feel like the lens is completely usable wide open and zoomed out, or stopped down a bit if I want to get rid of most of the vignetting. For more landscape-oriented uses, a 3:2 crop gives perhaps a more familiar aspect ratio, and takes care of most of the vignetting, as seen below. For astrophotography, which I expect this lens will excel at, I imagine it would be more or less case by case, whether composition would work alright with the vignetting, or to go to a 3:2 crop.
Image quality
First, a couple images I took of the cat indoors when I first got the lens:
I’m extremely impressed with what this lens does, in addition to being a nice wide zoom range at ridiculously fast aperture, its also extremely sharp wide open, and while a wide angle lens isn’t what you’re going to grab to get some blurry backgrounds, I find the door to be pleasingly soft and just out of focus enough for Penny to really pop out of the image. Next are some crops of a couple of the images from above.
Lastly, another image I grabbed of the snowman before heading inside:
Focusing
I opted for the Canon EF version of the speedbooster and lens, so autofocus does work with the combination, and it actually works just fine on the G9. It’s not as fast as the Panasonic lenses that I have, but it is by no means slow, and seems to be just as accurate as any of the other lenses I have. This is also a lens with nice manual focus controls (one of the nicer autofocus lenses to manual focus, that I’ve experienced, if that makes sense), it has an AF/MF switch on the barrel (although I use the lever on my camera body instead) along with a dedicated indication of the focus range, and the focus ring is well sized and turns with a nice weight, and you can feel when you reach the ends of the focus range.
Conclusion
Overall I’d simply put that I am very happy with the purchase of the speedbooster and the lens. It is an extremely sharp lens, and the vignetting can be significant and severe, but I think the 0.64x speedbooster is absolutely the way to go, the extra speed and wider field of view is worth the tradeoff of some manageable or croppable vignetting.
