Photo Jottings

Here’s a brief look at the Sony Carl Zeiss 24mm F/2 SSM lens.  Scroll down for the main review.

Slightly bulbous front element

Side shot with included hood

Metal mount with rear element at near infinity focus position

Sony X-ray view and MTF chart

The Sony A700 and Sony A900 were used for this review.  For a better understanding of terms and methods used in this review, go here.

 Sony introduces a new (2010) Carl Zeiss wide-angle (called “Distagon” by CZ) full-frame lens (made in Japan) featuring a fast aperture of F/2 with an excellent fit and finish.  Not noticed by many, but it’s actually the first prime lens for a Sony Carl Zeiss that uses SSM, or “super-sonic wave motor” that Minolta designed.  Typical for a ZA Carl Zeiss lens, it has a slightly different finish than the standard Sony lens, being more speckled with a different sheen, along with a very smooth machined metal mount.  Also of note; a MF/AF switch on the side, and in the middle of the switch is a focus hold button which can be changed to DOF preview on certain Sony cameras.

This lens will work great on your Sony full-frame digital camera, that’s what it was designed for.  It can also be used on an APS-C camera, and becomes a very usable 36mm (equiv) focal length.

Size-wise, the Sony Carl Zeiss 24mm F/2 is slightly heavier, longer and wider than the Sony Carl Zeiss 16-80mm F/3.5-4.5 zoom.

Sony claims this lens uses two aspherical elements, and two “ED” element; the former to help control coma at the corners, among other things too, the latter to control color fringing.

Focusing.  The focusing ring is at the front of the lens, and does not turn during auto-focusing.  The focusing ring on my copy seems just a little stiff, but is almost perfect for one-finger focusing adjustment.  You can override the auto focus at any time by just turning the focus ring.  SSM utilizes an over-drive type manual focusing system, that is, if you turn the focusing ring a certain amount, the distance numbers in the window will turn a lesser amount.  This allows for more precise manual focusing.  The Manual focusing ring turns just over 1/3 of the way around the barrel from Close-in to infinity, and doesn’t add any length to the lens.  Auto-focusing is quick, quiet, and very accurate, although some of the accuracy depends on your camera body calibration.  There is no infinity focus hard stop, so you’ll need to take care not to turn the focus ring all the way over (out of habit) if you manually focus for long distances without looking.   Also keep in mind I’ve found this lens to have noticeable wavy field curvature, and some folks will see fuzzy portions of their images and come to the conclusion that they aren’t focusing properly, or the camera missed the focus, but that’s probably not the case.  More on this issue at the conclusion.

In the box is the lens, caps, felt lined plastic petal hood, vinyl carrying pouch and owner’s manual with a warranty card.

Lens flare/ghosting.  Below average control of ghosting among prime lenses.  When using a full frame camera, I see a large red blob if the sun is at the edge, or just outside the image, but a hood or hand will help tremendously to prevent this.  Also look for a green arc and/or blob which is common when bright lights are part of the image.  APS-C cameras show plenty of ghosting also.

Color fringing (CA).  Above average control, look for minor amounts of lateral color fringing near the image edges on a full frame camera, and generally only visible at large viewing sizes.  I see very little CF using an APS-C camera.  There is some moderate axial color fringing at F/2, diminishing greatly at F/4, and nearly gone at F/5.6.  See examples in the full frame section.

Bokeh.  Smooth at F/2, but stopping down results in ringed outlines.  The aperture shape starts to show up between F/4-5.6.  Look below for sample crops.

Color.   Same as other Sony lenses, but maybe slightly more green.

Close up filter.  N/A.

Coma.  No real coma on APS-C camera, and minor to moderate coma at F/2 with full frame use.  See samples below.

Regular filters cause virtually no additional light fall-off problems on APS-C or full frame.

Filter size is 72mm.  Other Sony lenses that use 72mm filters are; 135mm F/2.8 STF, 20mm F/2.8, and the 85mm F/1.4 CZ.

Distortion.  Minor barrel distortion on both APS-C, and full-frame.  Check out the cropped sample in each section below.

Distortion example directly below.

Minor barrel distortion.

Bokeh, or background highlight blur is smooth when the lens is wide open, although as you stop down I see a slight ring around the highlights.  I see a very small amount of spherochromatism, meaning green tinged out of focus highlights in the background, and magenta tinged in the foreground.  This isn’t something to worry about.  Crops above were taken from the center of the image, focused about 6′ (1.8m), with the background about 18′ (5.5m) away.

Lens flare/ghosting examples

I see a magenta streak (left shot near upper left of image) when the sun is close to the edge of the image, at certain angles.  I also notice some typical arrow/arc shaped ghosts opposite the sun or very bright light source.  Flare problems are more apparent on an APS-C camera, so watch out when the sun is anywhere near the image.  Make sure you use the included hood, or your hand to block the sun if possible, examples of this are in the full frame section.

Light fall-off.

When using an APS-C camera, there is no real light fall-off to worry about.  Results are about the same when focusing close-in, or far away.

APS-C coma.

Coma is when bright points of light in the corners of an image become odd shaped blobs at large apertures, usually occurring in the range of F/1.4 to F/2.8.  When using an APS-C camera, there are no problems with coma on the Sony Carl Zeiss 24mm F/2.  These crops were taken from the extreme lower right corner of the image, from about 15′ (4.6m) away.

Center sharpness.

Below are crops from the image centers.

I see insignificant veiling haze at F/2, (but still plenty sharp), although it doesn’t show up unless viewed at huge sizes, and side-by-side as you see here.  The centers are tack sharp from F/2.8-8.  Diffraction causes minor softening at F/11.

The mid sections are soft, especially with a wide aperture.  If you stop down hard, you’ll get back some detail; this is the result of “wavy” field curvature, and not a focus-miss issue.

Corners.

The extreme corners look slightly sharper than the mid sections at wider apertures, due to the issue mentioned above.  Although you don’t gain much as you stop down, the crops still look fairly sharp at all apertures.  All crops above were taken at infinity focus, about 300′ (90m) away.

Let’s check out the macro capabilities of this lens.

Below, check out the cropped image (568kb) of the stamp.  The sample shot was taken with the Sony A 700 12.2MP camera.  The subject is a standard US stamp, 0.87″x 1.0″ or 22mm x 25mm.  Also, note the macro shot was taken as close to the subject as focusing allowed; in this case a very short 2.6″ (66mm), measured from the front of the lens barrel to the subject.

As close as you can get, F/5.6. Click for full image.

 

Full frame section next.

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Full frame results using the Sony A900 below.

Check out the differences when using a film or full frame camera below.  I’m only pointing out the noticeable issues as compared to the APS-C bodies, so if I don’t show it here, the results are not significantly different enough to warrant posting an additional set of images in this section.

Light fall-off

Light fall-off is definitely stronger with full frame coverage.  I see moderate to heavy levels at F/2, however, by closing the aperture just one stop, the dark corners brighten up nicely.

Full image below illustrating light fall-off from A900.

This full scene shows actual-use light fall-off.  It is noticeable, and causes a bright middle, but; this bright daylight scene would normally be shot around F/5.6-8, so light fall-off would be gone and the exposure would be more consistent.  If you shoot at F/2, try using -0.70 eV to keep the centers from being too bright.  Data for the image is; F/2, 2500sec, ISO 200.

Full frame distortion.

Minor barrel distortion on A900

It looks like full frame distortion is similar in amount to an APS-C camera, although the signature is different; the ends flatten out when viewed on a full frame camera, while APS-C is only showing the middle section.

Lateral color fringing.

F/5.6 color fringing, from left middle edge of image to 700 pixels in.

I see minor amounts of lateral color fringing along the edges of the image, mostly magenta is visible along the light colored columns.

 Center sharpness.

Below are crops from the image centers.

Again, center sharpness is very good wide open, but this time I’m using the full-frame A900.  I see very minor veiling haze at F/2 but it doesn’t show up unless viewed at huge sizes.  You can hardly notice the difference in sharpness between F/2.8-11!!

There is some softness in the mid-sections unless stopped down hard, that’s a bit disappointing as the super sharp centers make it more noticeable.  Things look good by F/8-11.  I’m shooting across a golf fairway, and I messed up and forgot to check for golfers on the F/2 shot.

Corners.

The full frame corners are soft and dark at F/2, but brighten up at F/2.8, although they don’t gain in sharpness.   You’ll need to stop down to F/8-11 for the extreme corners to sharpen up, which is easy to do in good light.  Crops taken from the last 300 pixels of the lower left corner.  Exposure differences are from light fall-off.  Notice the magenta color fringing around the window frames.  Images here were taken at infinity focus, about 400′ (122m) away.

When using a full frame camera, there is minor coma at F/2 in the far corners, but it disappears quickly by stopping down the aperture.

Lens flare/ghosting examples

I see a green arrow/blob (top left shot) when the sun is close, or inside the image at certain angles and exposure values, and obviously more visible depending on background.  The top right shot shows a somewhat different ghosting result.  There is a very noticeable red blob that shows up when the sun is near (but not inside) the corners, at certain angles, it’s mostly avoidable if you watch for it.  Make sure you use the included hood, or your hand to block the sun if possible, examples of this on last row.

You’ll see some purple color fringing when using a wide aperture, especially at F/2-2.8.  Thankfully this type of color fringing goes away as you stop down.  This car wheel shows the typical amount you would see in a picture, but if you shoot a bright sky through tree leaves (or something like that) it will show up more than this.

 

The Sony Carl Zeiss Distagon 24mm F/2 SSM is actually the first Carl Zeiss ZA wide angle prime lens, and the first with SSM focusing, did you know that?  If you didn’t, that means you didn’t read the introduction at the top!  As usual, the CZ build quality is superb, along with super quiet SSM focusing.  Just remember; focusing accuracy depends in-part on your camera body.  My A900 wanted to focus a tiny bit behind the subject, but only noticeable at F/2.  It could easily be corrected using micro adjustments, so that’s no problem, unless you don’t have that on your camera.

As far as sharpness is concerned, there are absolutely no problems in the centers at any aperture, including F/2.  Your(or your camera’s) inability to properly focus the lens will be the only reason your pictures aren’t sharp in the centers, especially at F/2.  However, once you stray from the centers, the image softens noticeably, especially at wide apertures.  This lens has what I’d call “wavy” field curvature, and may cause some confusion if you aren’t familiar with it.  For instance; you correctly focus on something at infinity, and take some pictures, but you look at your images later on your computer screen and only the distant centers, and maybe some details that are physically much closer to your position appear in focus.  It doesn’t seem to make sense, and can be exasperating.  This is not caused by you or the camera; it’s caused by the lens design, which makes it focus along a curve.  The only thing you can do is stop down the aperture to get consistent sharpness throughout the whole image.  It’s somewhat typical for a wide angle lens to behave like this, although I believe it’s much more noticeable on this lens because of the super sharp centers, and as a result, it makes the mid-sections look less sharp.

Landscape shooters will probably not be bothered by the field curvature issue, as they can stop down pretty hard, but if you’re using an aperture of F/2-5.6 and look at your pictures at huge sizes on the computer screen, you’ll notice the variations in sharpness across the image.  On another note; some folks will really like the super sharp close focus performance, although you have to get real close!  Interior shooters will want to look closely at this lens too, as 24mm is the interior defacto standard, and the distortion curve is pretty flat, but you’ll want to stop down to F/8-11 if you demand a high degree of sharpness across the entire frame.  Also make sure you watch for ghosting, as this Zeiss lens does not have the best control.  Be wary of high-wattage accent lighting when it’s somewhat close to the lens.  Hand held, available light street shooters may consider this lens too, as Coma is controlled well at F/2; way better than theMinolta AF 28mm F/2, which has so much coma wide open it almost ruins the image.  You also won’t notice the soft mid-sections in low light so much.

The Sony Carl Zeiss 24mm F/2 lens is expensive, but is it worth the price?  As I explained above, it has some really good qualities, and a few flaws for a very expensive lens, it all depends on what’s important to you.  Based on some preliminary tests, I’d say if you own the CZ 16-35mm and/or CZ 24-70mm, and won’t need F/2, then you probably won’t benefit from the CZ 24mm.  However, F/2 is a whole stop faster than F/2.8, that’s a big part of the additional expense, and very important when doing hand-held shooting in low light.  Also, if you’re a person that likes 24mm, and aren’t interested, or not in need of a zoom, then by all means, go ahead and try it out, it’s a lot lighter and smaller than the CZ zooms mentioned.