Chromatic aberration is also so-so on the periphery, but that goes along with the suboptimal corner sharpness. If you have problems with it, it is easy to bump the aperture up a notch to f/4 and it will get noticeably better. Even though the corner sharpness isn't the greatest, it isn't particularly noticeable on images. The main downfall of this lens is its corner sharpness, varying from not-so-hot at lower magnification to good at higher magnification. It performs at its best at an aperture of about f/3.3 - half way between f/2.8 and f/4. This is an expensive bellows lens and at least for central sharpness and resolution, performs as you would expect a lens of this caliber - top of the heap. A mix of coated and uncoated elements, but it doesn't seem to hurt the performance of the Photar design. Aperture control marked in large white numbers in real f-stops. Leica 25mm f/2.5 Photar Lens: Magnification is between 2-10x. The smaller ones were changed slightly around 1984 and became a 50mm f/4, 25mm f/2, and 12.5mm f/2.4 14440. The specs for the smaller lenses were 50mm f/4, 25mm f/2.5. Photars were introduced around 1970 and originally six were offered, the three larger ones with a 40x1.0mm thread and the smaller three with the microscope thread W 0.8"x1/36". Excellent lens for 5x-20x shooting at f/4 with APS-C or sometimes use it around f/2.8 if I am shooting around 15x where diffraction kicks in. A dream to work with and is extremely sharp. There is a lot of potential using this old Leitz bellows lenses for some serious high magnification photography using a modern DSLR. Made for use on 4"x5" Aristophot Camera System with 25:1 - 60:1 magnification - On 35mm camera system with short bellows: 12.5 -16x magnification with long bellows 16 - 40x magnification. Image scales on 4x5" large format are massive 25:1 - 60:1 magnifications. Can be used from 4x5" medium format cameras through APS-C DSLR with bellows. Not aware of any other camera lenses made by any lens maker that will outresolve this lens in the magnification ranges specified above. Highly corrected for high magnification photography at 15x-30x. Recommended magnification range is 5 to 20 times life-sized. The 12.5mm Photar is for 15x to 30x magnification. An excellent lens used in macrophotography (5x-30x magnification) and can be used with large format cameras. Bellows RMS (Royal Microscopical Society) screw mount Macro/Micro lens. The Photars are very expensive but the best for achieving extremely high magnifications in macrophotography - the ultimate quality. Leica 12.5mm f/1.9 Photar Lens, Leitz Wetzlar Germany: Leitz Wetzlar Photar lenses are made for extreme close up photography and these are the best! - Photar photographic objectives are designed to be used by themselves without an eyepiece, unlike microscope objectives that are designed to be used in optical systems with two stages of magnification. Have to decide how much weight and expense is justified in a quest for optical perfection, which surprisingly has turned out to be a moving target with already amazing lenses repeatedly getting overtaken in image quality over the past decade. Leica R lenses first, then other brands, ordered by increasing focal length. Hope that the following notes are helpful to others. Sorry, didn't keep track of where each remark is quoted from, so please use an internet search engine to locate the original sources instead of quoting these mostly unattributed comments. Some personal notes accumulated over several years while trying to figure out what equipment might be of interest, summarizing what the internet thinks of various lenses and cameras to help compare. LENSES, CAMERAS, AND PHOTOGRAPHIC EQUIPMENT