ABOVE - Me shooting the Nautica/Malibu Triathlon benefiting the Children's Hospital Los Angeles in Malibu, CA this past weekend with a curved blade aperture Nikon AF-S 500mm f/4 lens and my Nikon D4s.
Camera lenses all share certain design characteristics which are dictated by their function and the properties of light and more importantly capturing it. Aperture construction has remained similar for the past 100 years. Most sources you will find state that both curved and straight blade options have been around for just as long. The advantages of one over the other are debatable. It is a known fact of photography and light physics that the shape of the aperture is represented in the out of focus areas of the frame, especially in the representation of light sources. Straight blade apertures produce polygons. Rounded or curved blade apertures produce circles or circular shapes. In terms of aesthetics and the recent focus (sorry for the pun) on "Bokeh" - or the quality of out of focus elements of a photo (i.e. are they pleasing or distracting); the general consensus is that the more soft and rounded the bokeh highlights, the more pleasing the effect. The most common explanation for the use of straight blades over curved has to do with the cost of manufacturing (curved blades are more expensive to produce - thus the recent assertion that lenses with straight blade apertures are "cheaper" than a lens with curved blade apertures). I haven't seen any hard data confirming this; either way there are professional lenses which cost upwards of $10,000 US which utilize one or the other. In the case of professional Super Telephoto Lenses; none of these lenses are "cheap". This past weekend I shot coverage of the Nautica/Malibu Triathlon with two high-end professional Nikon Super Telephoto Lenses - the AF-I 300mm f/2.8D IF ED (straight blade aperture) and the AF-S 500mm f/4D IF ED (curved blade aperture). BELOW - A side-by-side comparison of two images at the same angle of view during the cycling portion of the triathlon - shot in the same location - HWY 1 (The Pacific Coast Highway).
WHICH IS BETTER? I can tell you that Bokeh aside the AF-S lenses (powered by focus motors inside the lens) are superior to the older AF-I (sometimes called AF-D) lenses which have to be powered by the body (through a port connection between the body and the lens). The tracking and focus speed is night-and-day different. That being said the optics in both are amazing sharp and crisp. The level of color representation and detail is unquestionably beautiful. The difference in the shape of the out of focus highlights may or may not be an issue for you aesthetically, so the difference in the lenses comes down to two factors - economics and speed of focus. The price difference between the two can only be compared on the used market - because both the AF-I and AF-S (non VR) lenses are no longer manufactured. With the AF-S used models running nearly twice the cost of the AF-I models; the difference in their price may be the difference in owning a professional Super Telephoto or not. If you can afford the AF-S, I'll tell you to always get it first. The frustration that you'll save in experiencing focus to shoot time over the AF-I is worth the price if you can afford it. If not there's absolutely no shame in getting the older AF-I /AF-D models. Just be careful. Some of the AF-I/AF-D lenses are nearly impossible to get replacement parts for since Nikon stopped manufacturing them (the dates are fuzzy with some sources saying they stopped making replacement parts in 2005 and others saying before). I own a pristine AF-I 300mm f/2.8 because it was the ideal lens for my Nikon F-5. The combination of this lens with any Nikon DSLR that has the internal focus motor (body) is stunning - polygon bokeh and all.
ABOVE - Earlier in the day at the 2015 Nautica/Malibu Triathlon (I hadn't broken out my "lucky" hat to keep the sun off me yet), shooting the first part of the day with my older but optically amazing AF-I/AF-D 300mm f/2.8D IF ED lens.
IN CONCLUSION - Which is better? The quality of the image where the point of focus is concerned is identical. Both the AF-I/AF-D lenses and the AF-S lenses are incredibly sharp and color representation is phenomenal. Where the two differ is in the handling of the bokeh (the out of focus elements of the frame). The AF-I/AF-D lenses produce a clear 9-sided polygon shape and the AF-S lenses produce circular (although they are more football shaped than round) bokeh. In the next card I'll do a thorough comparison of these two amazing lenses and get into the fine details of their construction, functionality, focus abilities, and overall image quality. What do you think? Of the two examples (the shots from the race showing the bokeh shapes), which is more appealing to you? I'd love to hear your thoughts!
© Copyright 2015, Jon Patrick Hyde, All Rights Reserved. Photography & Cinematography 101