Monday, June 27, 2011

Nikon AF-S 50mm F1.8G vs. AF 50mm F1.8D

There have been many reviews of the Nikon AF-S 50mm F1.8G, but how does it compare to the AF 50mm F1.8D that it replaced? Over the course of a week I took a number of photos to compare the two lenses under the same or similar conditions. While most of the test images were taken while the camera was mounted on a tripod, some were not. The purpose of shooting from a tripod was to reduce any discrepancies that might result from movement, as movement could affect the angle of view and depth of field between the test shots. This is by no means a scientific comparison, rather the idea of this post is to show how the two lenses act real life situations.

Physical Comparison:
The first comparison between the two lenses is physical; the new AF-S 50mm F1.8G is a larger lens, being at least twice the size of the 50mm F1.8D. Part of the reason behind the larger size of the newer lens comes down to the need to create space for the silent wave focusing motor (SWM in Nikon Speak). Depending on your point of view the increased size of the new F1.8G could be a good or a bad. I find the F1.8G to be more comfortable to shoot with when mounted on the D700, while others might like the smaller profile of the older AF-D lens.

Another notable change is the size of the filter thread between the two lenses. The AF-D lens has a 52mm filter thread, while the G has a slightly larger 58mm filter thread. The physical size of the glass elements themselves do not appear to have changed much at all, so the change in filter size is likely due to the in the  design of the lens body itself.

In terms of build quality the F1.8G feels to be made of superior materials, whether or not that is true could easily be questions. Both of the lenses are made with higher quality plastics, but the plastic on the 50mm F1.8G is more tightly assembled. This tighter assembly gives the user a more reassured feeling while handling the lens.  The newer lens also features a rubber gasket on the mount to help prevent dust and moisture from entering the F mount on the camera body.

There are a few other physical changes as well, although the rest are internal. The AF-D can be stopped down to F22, while the G only stops down to F16. This is noticeable in the images above, as the aperture blades on the AF-D leave a much smaller gap when fully closed. For the most part this change is irrelevant, due to diffraction past F16 on the AF-D model.

The AF-S 50mm F1.8G features a totally new optical formula, including an aspherical element, making it the first 50mm lens Nikon has made that has one. The AF-D uses a design that can be linked back to manual focus Nikkor lenses from the late 1970's, featuring 6 elements in 5 groups. The 50mm F1.8G on the other hand, uses an optical formula of 7 elements in 6 groups. Last but not least, the new F1.8G weighs slightly more than the F1.8D, but you wont notice the difference in practice. Even when mounted on the Nikon D3100 the F1.8G doesn't make the combo noticeably front heavy.

Auto Focus:
The next difference is in the area of auto focus. The 50mm F1.8D relies on the focusing motor in the camera body, which means that it cannot auto focus on entry level Nikon cameras (D40, D40x, D60, and all D3x00, series, D5x00 series cameras). Due to the use of the camera body focusing motor, the 50mm F1.8D is somewhat loud in use, at least when moving from one end of the focusing range to the other. This is more apparent when the lens hunts for focus, something that the lens does more of from my testing. The F1.8G on the other hand is nearly silent, although not completely. The F1.8D seems to focus fast, but the F1.8G focuses in a smoother fashion, and is generally more accurate. In the field the difference in focusing speed, if there is any at all, was not relevant, even with moving subjects.

The biggest advantage of having a AF-S motor is that you can manual focus at any time. With the AF-S lens you can grab the focusing ring while focusing, without causing any ill effect. On the other hand, if you grab the focusing ring on the AF-D lens while it is focusing you could damage the focusing gears in the lens, not to mention the cameras focusing motor. 

Optical Comparison:
Now that all the technical and physical differences are out of the way, what about the optical performance? There are several areas were the AF-S 50mm F1.8G is superior to the 50mm F1.8D, and the first of those is sharpness at F1.8, were it has a edge. The area of focus in the images below is between the third and four cans closest to the viewer. (Right click on images to see larger view).

Nikon AF 50mm F1.8D

Nikon AF-S 50mm F1.8G

Also if you look at the first set of photos again, you'll notice that the bokeh from the AF-S lens is less nervous. Meaning that there is less off center or double blurring of bright spots in the out of focus areas of the image. That leads us to the second area where the new AF-S lens shows better performance, bokeh. Thanks to using 7 rounded aperture blades, bokeh is less hexagonal in nature. This becomes more apparent as you stop the lens down.

Nikon AF 50mm F1.8D

Nikon AF-S 50mm F1.8G

The photos above show the bokeh of both lenses when stopped down to F4. As you can see the AF-D lens has a far more hexagonal shape in the of out focus light. Although the bokeh of the AF-S lens is still not perfectly round, it is an noticeable improvement. Overall the bokeh of the F1.8G is smoother, and simply more pleasant to look at.

Another optical difference is colour rendition. If you look closely at the samples you can see a slight difference in colour between the two lenses. The F1.8G produces slightly more contrasty and more pleasing colour, at least to my eye. The difference once stopped down is reduced, but still there, as you can more easily see in the samples below. These two samples were taken at F8, to see if there was any noticeable resolution or sharpness differences between the two lenses once they were stopped down. 

Nikon AF 50mm F1.8D

Nikon AF-S 50mm F1.8G

These shots were taken a short time apart, at the same shutter speed and aperture (F8), yet there is a difference in contrast and colour. The AF-S 50mm F1.8G produces an image that more closely matches reality. The image from the F1.8G also appears brighter, although there was no actual change in the lighting conditions. The above image also shows that the increased barrel distortion of the new F1.8G, that some reviewers have talked about, is not field relevant.

To get a better idea of the kind of resolution that these lenses can achieve, here are crops from both images, taken off center.

Nikon AF 50mm F1.8D

Nikon AF-S 50mm F1.8G

These are 2MP crops from each image (original shot is 12MP), and I cannot see any noticeable difference in resolution or sharpness once both lenses are stopped down to F8. The 50mm F1.8D is slightly better at smaller apertures (beyond F8), while the 50mm F1.8G does better at larger apertures (F1.8-F2.8).

Are there enough differences in optical performance between these two lenses to justify the nearly $100 price premium of the AF-S 50mm F1.8G over the AF 50mm F1.8D? If the quality of bokeh, sharpness at F1.8, having more natural colour and improved contrast in your images are important to you, the answer could be yes. If you are shooting with one of Nikon's entry level cameras without a built in focusing motor, the 50mm F1.8G is a no brainier, as nailing focus manually through the tiny viewfinders of cameras like the D3100 or D5100 at F1.8 is difficult to say the least. If you have a tight budget, or don't mind the slight optical flaws of the 50mm F1.8D, do not feel cheated when you save nearly $100.

To me the AF-S 50mm F1.8G is the winner, although not by much. I prefer using AF-S lenses, having sharp images when shooting wide open, not to mention the superior colour rendition. Using this new lens has truly revived my love for shooting with a nifty fifty, while the older F1.8D always left a slightly bad taste in my mouth (not that I actually tasted either of them).

I'll have more to say about the optical performance of the AF-S 50mm F1.8G when I finish my full review of the lens. Full Review Of Nikon AF-S 50mm F1.8G