Everyone Needs Some Good Glass (pt-2: Prime vs Zoom)

Los Angeles's El Ray Theater

 Last month, I was in San Francisco. I took some time to go shoot the Golden Gate Bridge with an L-series 24mm lens, and a standard Canon zoom. I compared the photos shot with the different lenses, and wrote a blog about it. (You can view the original post here). It was pointed out to me that since I had manually set the L-series lens, and left the zoom on auto, the differences may have had more to do with the f-stop then the glass. I decided to re-visit the subject with a new post, and this time both lenses would be set to f/16 with the camera set at an ISO of 200. I set the my Canon T2i  to aperture priority so it would choose the best shutter speed. I set up my tripod, and shot both sets of pictures from the same position.The two lenses I used where the standard (comes with the camera) Canon EF-S 18-55mm  zoom, and an old FD L-series 24mm (f1.4). I adapted it to the camera with a Fotodiox Lens Mount Adapter . This particular adapter has an element to adjust for the difference in flange depth between the FD and EF mounts (thus allowing a full range of focus). This element however, appears to magnify the image a bit, as well as cause some light loss. (As is evident by the different exposure times.)

Beverly Hills City Hall

It also deserves to be noted that the L-series lens is a prime lens, and the standard lens is a zoom. The additional elements in the zoom are most likely the culprit for the additional refraction evident in the photos shot with it. This is most visible around light sources such as the street light in the above photo of the El Ray Theater in Los Angeles. However, in the photo on the right (of the Beverly Hills City Hall) Their is an odd refraction in the center of the image of the photo taken with the 24mm. I suspect that is caused by the additional element in the Fotodiox adapter. The star pattern that you see around light sources is coming from the blades of the iris. (I am stopped down to f/16) If I had shot these same images wide open, all of the light sources would appear round. The images from the 24mm lens are sharper then the ones shot with the 18-55mm. The color also looks better to me. A big advantage to the L-series lens that these photos do not demonstrate is the speed. the 18-55mm zoom is f3.5-5.6 (changing a bit through the length of the zoom). The L-series lens is an f1.4. That is 4 full stops faster. Considering each stop is "a halving of the light intensity from the previous stop", you can shoot in lower light conditions without the long exposures I've used in these photos. (maybe a comparison for pt 3).

Paramount Pictures Front Gate

What is clear in these photos is the usefulness of a prime lens. Just because you can get a 24mm shot with your zoom, doesn't mean it will be the best choice of lenses. Every piece of glass between your subject and your image collector (be it film or a digital sensor) degrades your image. Prime lenses have less glass in them, and therefore give you a better image with less refraction, and less light loss.
The refraction is particularly evident in the photo on the left of the front gates to Paramount studios in Hollywood California, and the picture below of Wilshire Blvd.

*You may notice light streaks in most of the photos on this page. Those light streaks are the lights on the cars that drove by while the shutter was open (in some cases over 30 seconds). with a long exposure, anything moving quickly through the frame (like a car) will not be seen. However if that quickly moving object has a light source (like headlights or tail lights), they will register in ever position they were in while the shutter was open. This produces the glowing streaks in these shots.

Wilshire Blvd, Los Angeles

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