Article Index

Resolution

Resolution testing of ultra wide angles is always a hassle, particularly against an MTF target. Generally speaking, you need to leave enough space between the lens and the target so you don't measure the resolution of the target itself. That is not quite possible often with UWAs because at infinity focusing the lens captures so mach background that even the large ISO-12233 chart I use for testing, which by the way has the active area of 32 x 56in, does cover the entire image frame. And so either the camera has to be repositioned to separately measure the center and borders, or the UWA lens has to be tested at close distances - for the 15mm Super Wider Heliar, the working distance is up to ~2m on the APS-H sized Leica M8. Hene the need for a custom target, which helps increase the working distance to ~4m for the lens. Better, but still limited particularly if we move to even wider lenses like Ultra Wide Heliar 12mm f/5.6.

Anyhow, keeping in mind these limitations of the MTF50 tests for UWA lenses, let's take a look at how Voigtlander Super Wide Heliar 15mm f/4.5 performed. The simplified MTF50 chart below indicates that the lens is a capable performer. The resolution pattern is fairly uniform, with the center image quality remaining slightly better then borders throughout the aperture range. However, overall quality seems to be slightly degrading with stopped down aperture - f/11 seems to be the inflection point where diffraction starts to kick in, reducing the absolute resolution the lens can achieve.

 

Leica M8 (10Mp)

 

Looking at the chart crops, which compare image borders at f/4.5 and f/8, I see very little difference between the two, which, not for the first time, tells us that the MTF measurement algorithms are much more sensitive to slightest changes in quality that might not even be easily noticeable by a human eye. If you stare long enough at the crops, you will probably start seeing doubles, and so instead of spending any more time here, let's review the real-life shots.even

 

Leica M8 (10Mp)

 

The crops below demonstrate what you are likely be able to get out of the lens in the real life. The shots have been compiled using focus bracketing around infinity on 10Mp Leica M8. As is the case for all such tests, one shot with the sharpest center area per aperture is chosen and then crops from different frame areas are compared across different aperture settings. The most obvious and easiest conclusion we can make here is that center resolution is absolutely superb straight from the widest aperture. There is no visually noticeable variance from one aperture setting to another and while in absolute terms this might not be the best results I have seen out of all lenses tested so far, it is pretty darn good. It is also fairly obvious that border quality is not on par with the center. The difference is kind of noticeable even without blowing up the images to 100%, but under closer inspection the differences do become more pronounced. Still, while not absolutely perfect, the resolution even in extreme corners is quite acceptable and after a minor enhancement with an unsharp mask would cut the mustard so to speak for most users.

 

Center


f/4.5, Leica M8

f/8, Leica M8

L.L.Corner


f/4.5, Leica M8

f/8, Leica M8

L.U..Corner


f/4.5, Leica M8

f/8, Leica M8

R.L.Corner

f/4.5, Leica M8

f/8, Leica M8

R.U.Corner

f/4.5, Leica M8

f/8, Leica M8

 

Color Reproduction

The lens showed pretty minimal amounts of lateral chromatic aberration with center CA never exceeding ~0.3px and border CA hovering at around 0.4px throughout the aperture range. There is nothing particularly troublesome here as at these levels fringing should not be noticeable in real life situations, or require any extensive correction.

 

Leica M8 (10Mp)

 

Overall contrast levels were fairly modest - global contrast was not quite as high as with Carl Zeiss Distagon T* 18mm f/4 ZM I tested recently, but quite acceptable. Local contrast varied from moderately high in the center, to moderate/low in the periphery, which actually made images look slightly less crispy.

 

 

DOF & Bokeh

I am going to keep this section shorter then usual. Given the focal length of the lens, and its maximum supported aperture level, hoping to achieve a shallow DOF and nice bokeh is going to be naive. Even at close to the minimum focusing distances, where DOF is typically the shallowest, Voigtlander Super Wide Heliar 15mm f/4.5 shows too much detail in the background making it impossible to actually separate the foreground and background cleanly. Wide open or stopped down it is not that much different as can be seen from the images below.

 

ISO 320, 1/3000, f/4.5, 15mm (Leica M8)

ISO 320, 1/1000, f/8, 15mm (Leica M8)