cyclespeed wrote:
I know that lenses that open to F 1.8 and even bigger on some have an advantage when shooting in low light. Are there any other situations when this larger amount of light coming through would have an advantage.
I am about to try and use macro lens / settings to capture one of the fluffiest snow flakes we have seen in some time. So for example would a fast lens be better to use in this case?
Thank you for your thoughts.
No, a larger aperture is not necessary for photographing something like a snow flake at very close or macro magnifications. In fact, it's the opposite of what you want. Stop down for sufficient depth of field. Put the camera on a tripod and use a longer exposure if need be (to allow you to keep IOS low and minimize digital noise in images).
While "low light" is one use of a large aperture lens, I'd argue the ability to render shallow depth of field effects and blur down backgrounds is at least as important and maybe even more-so. This effect that's only possible with a large lens aperture helps make subjects stand out and is useful for sports, portraiture and other purposes.
But it's the opposite of what you need shooting high magnification close-ups, where depth of field is awfully shallow already. It's also not desirable for many landscape shots and may not be necessary if shooting in a studio where you can control the background and lighting to similar effect. In those cases, smaller apertures are likely to be "better".
Something else that a large aperture lens does is often overlooked: It can help autofocus work better under marginal lighting conditions. This also isn't something needed for most macro shooting, though, where focusing is often done manually anyway. It's most useful for action photography such as sports.
So, again, a large aperture "fast" lens isn't likely to be of much or any help shooting macro photos of snow flakes.
EDIT: Chg_Canon mentions another important consideration: While there are exceptions, often "fast" lenses aren't their sharpest wide open. They need to be stopped down a little if critical sharpness is wanted. An f/1.4 lens I use is usable, but slightly soft wide open. So I often stop it down to f/2 or f/2.2 when I want to assure sharpness. The same can be said of most lenses... They aren't at their sharpest wide open. So, does that make an f/1.4 lens a "waste of money", compared to say a less expensive f/1.8 or f/2 lens? In my opinion and for my purposes, there is still added value to the f/1.4 lens. I could have bought an f/1.8 lens (2/3 stop slower) for half the price... but for that lens to render its sharpest shots might require it to be stopped down to f/2.6 or f/2.8. This, plus the fact that there may be times when the extra 2/3 stop of light and/or stronger background blur possible with the f/1.4 lens wide open make the more expensive lens "worth it" for me, even if there's a trade-off off slightly less sharp images. Other image quality factors come into play, too. The "more premium" f/1.4 lens has more aperture blades for nicer looking background blur... and, more subtly, it has better coatings that make for better contrast and color saturation.
When it comes to macro shots of snow flakes, you're likely to want as much sharpness as you can get out of a lens... as well as optimal contrast and color rendition. Macro lenses are "flat field" designs, meaning that they use an optical design that will render edge-to-edge sharpness at very close focusing distances (non-macro lenses are likely to "go soft" in the corners of images, particularly at larger apertures). Most macro lenses also deliver great contrast and color saturation. Even illumination across the image is another typical feature of a macro lens... I.e., lack of optical vignetting.
It all depends upon what you want... how you want your images to "look". It isn't a "bad thing" for parts of images to be soft or for vignetting to occur. For the shot of a rose bud below I deliberately used a non-macro f/1.4 lens forced to focus closer (with macro extension tube) and at a larger aperture (f/2), because I knew it render shallow depth of field, would "go soft" and would vignette... I
wanted those things to occur in this shot. They may or may not be things you want to see in your snow flake close-ups.
Conversely, for the small product close-up shot below I used a similar focal length lens, but a tilt-shift design, at a smaller aperture (and longer exposure, on a tripod) to assure that the entire subject was in focus.
I'm guessing that snow flake shots will be at a lot higher magnification than either of the above... and because of that you have more issues with shallow depth of field. The freshly hatched snail below was shot at about 3.5X life size with an ultra high magnification macro lens... It was stopped down to the maximum possible (f/16), which in macro photography makes for an extremely small "effective" aperture (at 3.5X mag, effective aperture is approx. f/72).
In the image above you can see how shallow DoF becomes at very high magnification ... a plane less than one millimeter in depth is in sharp focus... even using an incredibly small effective aperture (which also risks softening the image due to an effect called "diffraction"). Of course, that snail is a 3 dimensional subject and a snow flake will likely be more 2 dimensional and that should help. Plus I don't know how high magnification you'll need. Depends upon the size of the snow flake. The snail above is maybe 4 or 5mm in length.