Archive for November, 2011

Sony NEX-5N with Voigtlander and Zeiss rangefinder lenses – part 1 – ultrawides

Wednesday, November 30th, 2011

f/11

There has been a lot of discussion about how well the new NEX cameras will work with wide and ultra-wide angle rangefinder lenses. Apparently the NEX-3 and 5 did not work well with many, resulting in color shifts and smearing in to the edges and corners.

With the release of the NEX-C3, reports trickled in of much better performance. Many naturally hope this will hold true for the 5N and the much anticipated 7. However, from early results posted by Steve Huff in his mini-shootout between the 7 and the Ricoh GXR with M module, the 7 definitely appears to have issues with some lenses, such as the Voigtlander 15mm f/4.5 Super Wide-Heliar. Coincidentally, the 15mm is also a difficult lens on the Leica M9 (B&H link – black, silver), also due to strong edge color shifts and vignetting (though much better now with the latest firmware).

So, what about the NEX-5N?

I had a 5N on loan for a few weeks and spent some time trying all of my rangefinder lenses on it.

To start off, here are results from my three super wide angles – the Voigtlander 12 (the Leica screw mount version) and 15mm and the Zeiss ZM 21mm f/2.8 Biogon.

As you will see from the images below, all work well on the 5N with no adverse color shifts and sharpness is retained into the corners (with some catches).

What surprised me though was that of the three, the Voigtlander 15mm (M mount version) trounces the other two until about f/8.

On my M9, it is the problem lens, yet not here on the 5N.

On my M9 the 12mm is pretty good, though with some edge softness/smearing. On the 5N it looks terrible along the left edge until about f/11. I should point out I’m using a Novoflex M to NEX adapter, which is probably the most expensive on the market, and one would expect, with its German manufacture, to be held to the tightest tolerances of any of the adapters currently available. However, based on these preliminary results, I’m a bit suspicious about the adapter because the 12mm looks so bad. On the M9 it is very usable even wide open, though I can detect a slight band of softness/smearing in the left third of the image. It’s possible that the 16MP 5N sensor is exaggerating this defect in the lens. FWIW, when I bought the lens in person (rather than online), I was able to test it against another one in stock, which was markedly worse with much stronger chromatic aberrations and much, much softer corners (though on the M9)… but it would seem it could still be better.

It could be possible that what works well on a full frame M9 sensor doesn’t translate exactly to the NEX APS-C sensor due to factors such as the NEX’s much higher resolution of the very central part of the lens’s image circle, as well as optical issue with the lens and misalignment with the adapter. It’s also worth stating that alignment tolerances are considerably more sensitive the more wide angle the lens.

The Zeiss 21mm f/2.8 Biogon is kind of a surprise on the 5N. I didn’t expect there to be as much sharpness issue into the corners as I see in my initial results, however, if one examines the Zeiss MTF for this lens, one will see it falls off in sharpness towards the edges at wider apertures (on full frame). And it has a fair amount of field curvature, from my experience. So this is probably coming to play against it on the NEX. Stopped down to 5.6 and higher though it’s really pretty good. And this is also my opinion of it on the M9. The Zeiss is a pretty good performer but I wouldn’t use it to photograph flat objects wide open, especially at closer distances, but past f/5.6 it’s very good across the frame.

It would be interesting to compare the Zeiss C-Biogon 21mm f/4.5. It’s technically a better performer than the f/2.8 version, however, like the Voigtlander 15mm, it’s notorious for extremely strong edge colour shifts and vignetting on the M9. In fact, the resulting characteristics are nearly identical. Given how good my 15mm is on this NEX-5N, I’m now very curious about the C-Biogon, though probably not enough so to spend about $1100 for what will be a 30mm equivalent field of view and not very usable on the M9.

UPDATE 2011.12.13

Zeiss has published an interesting piece about their wide angle lenses, which contains some relevant information explaining the poor performance of the ZM 21mm f/2.8 on the NEX on page 12 here (pdf). To quote directly:

Lenses with a very large beam tilt (from the rear element to the corner of the sensor) react in a much more sensitive manner to a change of refractive index in the image space caused by filter plates in front of the sensor (such as low pass and IR-blocking filters). If the filter plate is not considered in the design of the lens, the edge definition will suffer. The effect of the additional path through the glass grows exponentially with the beam inclination. A Distagon which never achieves more than 20° beam tilt in the corner of the image reacts more tolerantly than a symmetrical wide- angle lens, which might reach a 45° tilt. This is why filters in digital Leicas are very thin – to remain compatible with older optics.

If the filter is significantly thicker, the contrast transfer for the image edge becomes worse for tangential structures. In the graph of the curves, this looks like the old retrofocus lenses but is caused by astigmatism rather than lateral chromatic aberration. The focus is shifted to greater distances for tangential structures by the additional path through the glass. If the best edge definition is to be achieved, then all that can be done is to stop down further.

Advantages of nearly symmetrical wide- angle lenses (such as the ZM 21mm f/2.8):
• Small size and low weight
• Very good, uniform definition despite
moderately high effort required
• Usually excellent freedom from ghost
images
Disadvantages of nearly symmetrical wide- angle lenses:
• Cannot be used with every camera
• Require specially matched digital
sensors
• More sensitive to the change of optical
parameters in the image space
• Greater natural fall-off of brightness
toward the edge of the image

Based on samples in various photo forum discussions the ZM21mm f/4.5 seems to perform better on the 5N than the 2.8 version. Why it does, and the f/2.8 doesn’t, yet both are highly symmetrical lens designs, is a mystery to me. But one conclusion drawn by many is that the ZM 18mm f/4 Distagon is a better option than both 21s, though it is somewhat larger.

Below are sample images. Clicking on the image will point you to the full size, straight from camera JPEG file. The camera was set to the default settings – Standard color profile – and high ISO noise reduction was set to low (you can’t turn it off in-camera), though these were mostly done on a tripod at ISO 100. White balance was on auto, so some of the sequences show variations in white balance as a result.

Planar object (building) with the Voigtlander 12mm, 15mm and Zeiss ZM 21mm f/2.8, focus was set with magnified view, dead center:

12mm at f/5.6, 8 and 11:
f/5.6

f/8 f/11

|

15mm at f/4.5, 5.6, 8 and 11:
f/4.5

f/5.6 f/8 f/11

|

Zeiss ZM 21mm at f/2.8 through f/11 in one stop steps:
f/2.8

f/4 f/5.6 f/8 f/11

|

The same building from the side with the Zeiss ZM 21mm f/2.8 Biogon, again f/2.8 through f/11 in one stop steps:
f/2.8

f/4 f/5.6 f/8 f/11

Forest scene. The focus was on the near tree trunks at the left side of the frame.

12mm, f/5.6 through f/11:
f/5.6

f/8 f/11

|

15mm, f/4.5, 5.6 through f/11:

f/4.5

f/5.6 f/8 f/11

|

Zeiss ZM 21 from f/2.8 through f/11:

f/2.8

f/4 f/5.6 f/8 f/11

I should note that all images were focused wide open using the magnified view, without focus peaking to get the best visual idea of correct focus.

If you’re looking to buy any of this equipment, please consider using the following links to help support this site:

For all Zeiss lenses (ZM, ZE, ZF, etc.), please contact Rob Skeoch at Big Camera Workshops or his sister site the Rangefinder Store. Rob has been the source for most of my Zeiss ZM purchases and is a great guy to deal with. Free shipping within Canada is included, as is a B+W UV filter with each Zeiss lens purchase, and Rob will ship outside Canada. Due to the scarcity of many Zeiss lenses at this time, it is best to contact Rob for availability and please mention this site as a referral.

Otherwise, please consider using these B&H links:

Voigtlander 12mm f/5.6
Voigtlander 15mm f/4.5
Zeiss ZM 21mm f/2.8 black silver
Zeiss ZM 21mm f/4.5 black silver
Zeiss ZM 18mm f/4 black silver
Novoflex NEX-Leica M adapter
Sony NEX-5N camera only (black only) or kit with 18-55 in black or silver
Electronic viewfinder (EVF) for NEX-5N


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