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Generally speaking, telephoto lenses are not particularly prone to flare - since FOV is fairly narrow, one needs to point the lens effectively directly into the sun to make it flare. Leica APO Telyt-R 180mm f/3.4 might be one of few telephotos that actually does show a rather nasty flare and not only in most extreme situations. The two shots below compare the amount of flare you'd get with this lens with the sun positioned close to the picture frame. In both cases, the sun rays were hitting the front lens element at about 60 degrees. Both wide open as well as stopped down, the lens shows flare as well as ghosting. Lower contrast and patches of color shifts come along as well across all aperture levels.


ISO 320, 1/4000, f/3.4, 180mm (Canon 5DMk2)

ISO 320, 1/800, f/8, 180mm (Canon 5D)



Generaly, vignetting (or light falloff) is not a major problem for telephoto lenses of this focal length. Even more so for a lens with such a relatively slow maximum aperture. To my surprise, :Leica APO Telyt-R 180mm f/3.4 did actually show vignetting on a full frame body at f/3.4. Of course the level of light falloff is not particularly alarming at ~0.7EV, but it is still not particularly welcome. Vignetting drops a little bit at f/4 and then drops some more by f/5.6, where it becomes basically not an issue at all. And on APS-C body, vignettign is a non-issue throughout the aperture range.



What that basically means is that you would end up with slight darkening in corners if you have light colored scenery around corners, i.e. a clear blue sku. To most this is probably not going to be a major issue, but if it is, you can easily correct it in post-processing, or even within your camera.  personally would not stress much about it. Vignetting did not seem to increase with the use of built-in lens hood.


Vignetting @ f/3.4 - full frame vs 1.6x crop



The lens showed minor degree of barrel distortion. At 0.33%, distortion is unlikely to cause any problems in general photography, and would not even be noticeable to the human eye.


Distortion (FF) @ 180mm
Distortion (FF) @ 180mm