I don't think I've really covered this lens in a review up until now. It must be a rarity (the lens I mean), because I can find a few bits of information on a Rexagon 28mm f2.8, but there is nothing out there about the 23mm. So here I go with an Internet Exclusive!
I'm not equipped at all to do lab style lens reviews the way the well known Bloggers are, so I can't measure sharpness, distortion or corner-shading - all I can do is show some samples and give it a pass / fail from what my eyes tell me.
I am also conducting the eye-test review using a printed 8" X 10" of the above photo, as the printed product is more revealing of what's really happening in the picture. This lens seems to have similar characteristics to my Bushnelll 28mm f2.8, mainly being a low contrast and subtle colour lens. I don't know if thy share the same optical formula or not - I'm guessing that it must be close. Both lenses are nice and sharp, - there is certainly no lack of detail and texture here. Colour is somewhat low key - again similar to the Bushnell. Outer construction and markings are also identical. There are two huge differences however. The Bushnell has an 8-blade aperture, with the blades cut to a "star" shape, while the Rexagon has a conventional, slightly rounded 6-blade configuration Also, the Rexagon's focus and aperture rings turn in the opposite direction to the Bushnell, making it's control rotation like that of Pentax lenses, whereas the Bushnell is similar to Practika and Zenit (and Canon for that matter).
The "real" focal length on a Canon Rebel DSLR like mine is 23mm X 1.6, which is 36.8mm, making it close enough to behaving like a 35mm lens on a full-frame DSLR, or a film camera. The actual 23mm focal length would be super-wide on a film camera. I don't mind using the 35mm focal length, but it's really about as wide as I like to go, and then only sometimes. It's perfect for car show photography - I got up close to this old Bimmer to get a couple of nice shots:
Again, these are straight from camera JPG's. You can see the lens struggles a bit from strong noon sunlight, but still the detail is very nice, but there is enough barrel distortion to be visible in the white parking lines, which should be showing up straight here - but they're not. I suspect the effect we're seeing is from the optics of an extreme wide angle lens, but the field of view is cropped to that of a moderate wide angle. I'm not sure if it really works this way or not. From all the reading I've done about the APS-C crop factor on non-full-frame cameras, I'm still not convinced that the lens' actual optics don't contribute extreme wide angle distortion in comparison to similar focal lengths on lenses that are actually built for the APS-C image circle.
So, given rather shitty distortion, low contrast and bad flare resistance, can I actually say that I like this lens? I do prefer the low contrast / faithful colour rendering, and the lens has good, but not great sharpness. I don't care for super sharp lenses either. This lens has a great retro look to it which scores real high with me.
Another question might be "why bother"? My answer is that these old lenses, unlike newer electronic lenses, have a depth-of-field scale on the barrel, which makes it super easy to set them up for pre-focusing. Just set the aperture at f11, move the Infinity marker over the f11 mark on the DOF scale, and then you know, in the case of this lens, everything from 2.5 feet to infinity is in focus. This way, you can literally shoot any picture without having to focus - either manually or having to rely on Auto-Focus, which everybody seems to complain about. Put another way, there are actually three focusing methods available to the photographer - Manual Focus and Auto Focus everybody knows about. The third way is to Pre-Focus and forget about it. This is also known as pre-setting the lens for it's hyper-focal distance, and aside from the nice retro look I get from old lenses, this is the main reason I prefer using them.
On another matter, you'll probably notice that I've put my Labels on this blog, to the right. There are way too many, and I'l be working to scale these down to something more reasonable looking. And as always, don't forget to look at my Print Catalogue. You can reach me by email at firstname.lastname@example.org