I thought I'd provide a short review of the latest CV lens, the 75mm f1.8 (shown with the 75mm viewfinder that comes with the lens): First off, the lens design, construction and handling are like all CV lenses. It has great build quality, a much smoother focus movement than say the 50mm f1.1 or the 12mm f5.6, half f stops between each of the main stops (apart from f1.8-2) and the aperture is nice and round thanks to the 10 aperture blades (typical of CV). The kit comes with a sturdy feeling vented lens hood (with an unusual design in that a separate mount adapter is screwed onto the lens filter thread first, to which the hood attaches) and it also comes with a very tiny focus finder, that isn't of much use with m4/3s cameras and the like. Image quality is typically CV and while not up to the standard of Leica or Zeiss; it's still pretty good, depending on the situation. One thing that I've found with all of the CV lenses is that they don't like strong backlit/side lit situations and tend to exhibit pretty strong purple fringing under those conditions. The 75mm is no different and the effects can be very pronounced if the circumstances are right (or wrong in this case). I don't know why this is the case with CV lenses, but it seems to be common with all of them. CV 75mm f1.8: Crop of shoulder: Leica 135mm f4 (same position): Crop of shoulder: The thing is, it's not always evident and when it's not, the results are excellent. I don’t know why this occurs, as I would have thought that the coating technology would have been right up there at this stage and it should have been a footnote in lens design. But in the right conditions it shines and converting to B&W is very easy: Even Olympus Master can be useful with Art Filters: Cheers Ray
In my experience this purple fringing is a fairly common trait of fast lenses and it usually disappears on stopping down. It is certainly not specific to CV lenses, although I'm a bit shocked at the amount shown here. The old Nikkor 35/1.4 offered quite a lot of purple fringing around highlights, the Panasonic 20/1.7 shows it mildly, the Nikkor 35/1.8 DX also. On the net I've seen pictures of the famous Olympus macro 50/2 which shows a fair deal of it, even too much for my taste. The Panasonic/Leica MFT 45/2.8 is one of the very few lenses that doesn't seem to be plagued by purple fringing or longitudinal CA in the DOF zone (e.g. magenta cast before the focus point and green in the zone behind). Maybe that explains its high price and why its images look so clean. It takes extremely good and thus expensive fast lenses to avoid it wide open, but the good news is that it's usually gone at around f/4 to f/5.6.
i guess stopping down as far as 4-5.6 kinda suggests the money spent on the fast lenses for these purposes is possibly not worth it? depending on the optical qualities at that aperture in comparison to similar quality lenses of that focal length. ?
I haven't really looked at stopping down, but the entire purpose of fast lenses is getting quality at open apertures. I don't have any fast Lieca lenses, so I can't compare to the equivalent CV lenses. Also, I've never really seen a colour shot taken in difficult circumstances with a fast Leica lens to determine if there are radical differences (the 135mm f4 does count as fast). Cheers Ray
Yes... common with fast optics. My noctilux f/1 does show a little fringing at wide open. Due to its aspherical elements, the newer noctilux does show a bit improvement in this area (with a premium price). If my memory serves me the new CV 75 f/1.8 is nonaspherical.. am I correct?
It can still be money worth spent, but you just have to be aware of this issue. It doesn't affect every shot, just some, and once you understand where it is a problem, you adjust for the situation. I just did a test with the 75mm and at f2.8 is vastly reduced and by f4, the purple fringing is pretty much gone. Cheers Ray
An interesting factoid to pass on. I just upgraded to LR3, in the hope that it might provide better CA adjustments, but unfortunately not. On the other hand, I discovered if I left the WB 'As Shot', the purple fringing dissapeared. So I think that the issue isn't entirely with the lens, but also the sensor. The example of the Leica lens vs the CV lens may not have been entirely fair, as the Leica was showing the sensor a much smaller portion of the image and thus the lighting may not have been as big an issue for the sensor. I'm going to have to think about this some more and see if I can come up with other situations where the WB isn't as problematic as it was in the church (absolutely diabolical). Cheers Ray
Fast optics. To reduce purple fringing they either require ED glass or a complex lens system. The problem is, the faster the optics, the more spreadout the focus point for RGB is. I think, regardless of the CA, the pictures are outstanding. The last one I think is my favorite.
