Recently I had a chance to swap some of my old Pentax lenses for a very interesting lens. It makes a mirror-less Fuji X-T1 camera into a mirrored one. This is a Sigma 600mm f8 mirror lens.
The principle of this type of lens is quite simple. It works as a reflector, with a big mirror at the back of the lens focusing at another mirror in the front (that little black circle in the middle) and into the camera. This design allows the lens to be very compact compared to an equivalent standard lens.
Lets talk first about the advantages of this. It's 600mm, and on a crop sensor it gives you a very nice 900mm field of view. It's well build, with with smooth focus ring. Minimum focus is about 2m, which is quite close. Sigma has printed 1:3 Macro at that position :) . The lens is quite light, and can be used handheld, plus it is cheap. This one cost $175cdn. Not bad....
Now lets talk about bad... The aperture is constant f8. This means that with out a tripod and lots of light the lens is almost unusable. I had to switch to manual shutter of 1/1000 to be able to shoot handheld, and let the camera choose ISO. Many times the ISO would be around 1600-3200 or even higher. Fuji deals with noise very well, and I did not mind it. The depth of field is very shallow, which in turn makes proper focus a little challenging. Again Fuji comes to the rescue, with it's arsenal of manual focus aids. I found that digital split image focus worked best.
As you can see in the above image the highlights are a little different than we are used to. Some like it, some don't. To me it looks different and interesting.
Overall, it is an interesting lens to use. It's challenging and I found it fun to use. It's easy to hold, and even though it is a mirror, it fits the mirror-less camera world quite well. Here are some images I took with it.