Lens quality

The quality of the camera lens is the most crucial quality factor in your camera system. Therefore, you should be careful in making your choice of lens, especially when money is an issue and you are limited to lower-quality lenses. Factors to take in consideration are:

• Surface coating: there should be a coating on all lens elements to reduce internal reflection. Coatings are easily recognized by a colored hue when looking at the lens in sunlight. Coatings can be blueish or greenish, or brown, depending on the type of lens. Do not buy a lens without coating, or any impurities or scratches in the coating. If it has, the seller will probably say something like 'you won't notice it'. Let me tell you, you will notice it, because weather photography asks much more from your equipment than standard landscape or portrait photography.

• Lens construction: this refers to the optical design of the lens. A lens usually consists of several elements, like 3 or 4 lenses grouped together in the lens. Zoomlenses should be aspherical, especially when covering a wide range of zoom. Fixed focal length lenses are usually better (less distortion and sharper image) than zoomlenses, but are not always practical.

• Distortion: some cheaper lenses, especially at wide-angle sizes between 24mm and 35mm focal length, can create a distorted image, like a barrel-shape or pincushion. Wide-angle lenses will always create distorted images to some degree, but good 20, 24 and 28mm lenses and longer should not.

• Aperture range: typical apertures for a wide-angle (28mm) lens are from f/2.8 to f/22 (or similar), standard lenses (50mm) range from f/1.4 to f/16 or so, and 135mm telephoto lenses can be had with range from f/2.8 (or lower) to f/22 also. Zoomlenses should at least have a range from f/2.8 to f/22 for 28-200 zoom ranges. Less expensive zoomlenses have smaller ranges (from f/3.5-5.6 to f/22 or so).

• Coma: some lenses show coma when used with their aperture fully open. Coma looks like a blurriness towards the edges of the frame. The amount of unsharpness depends on the aperture setting. Very cheap lenses have a lot of coma and should be avoided. Particularly with lightning photography, which sometimes even requires low aperture numbers such as f/2 or lower, coma can really ruin a photo.

Lens focal lengths

The lenses used for weather photography range from all-sky (180 degrees) fisheye to telescopic tele-photo lenses of up to 2000 mm. Depending on the subjects you want to photograph, you may only need part of this range of focal lengths. The following table lists some different focal lengths and subjects where these are useful for.

focal length (mm)	FOV (deg., diagonal 35mm frame)	Subjects
fish-eye 8mm fish-eye 16mm	180, full circle 180, rectangular	halo displays, twilight arch/wedge, extensive crepuscular rays, thunderstorm clouds, all-sky cloud photos
16-24	107-84	halos, twilight arch/wedge, crepuscular rays, zodiacal light, aurora, thunderstorm clouds, complete rainbow
24-28	84-75	rainbow, clouds (esp. alto- and cirriform), zodiacal light, gegenschein, aurora, meteors
28-80	75-30	close lightning, wide-sky astronomy, aurora, zodiacal light, clouds, sunrise and sunset, crepuscular rays, glory, rainbow, most halos, heiligenschein, fog
80-200	28-12	glitter path, light pillars, comets, sunset close-up, smaller clouds, iridescence, corona
200-500	12-5	mirages, solar eclipses, misc. astronomy
500-1000	5-2.5	mirages, solar/lunar eclipses, low-sun distortion, green/red flash
1000-2000	2.5-1.2	mirages, sunspots, lunar eclipses, low-sun distortion, green/red flash, deep-sky astronomy

[Lens focal lengths, field-of-view (FOV), and photography subjects]

I plotted the relationship between FOV and focal length of lenses, to visually demonstrate that in the wide-angle range of lenses, every mm counts, as they say in the photography business. That is, every small change in focal length in that region makes large differences in FOV. This really begins to matter for lenses shorter than 35mm.

[Field-of-view (FOV, in degrees) as a function of lens focal length (in mm), for the most common focal lengths. The graph gradually diminishes to zero for an infinite focal length. Note that a lens with 180 degrees FOV should have 0mm focal length (which, in practice, is impossible to achieve - that is why such small focal lengths are designed as fish-eye lenses, which are actually two lenses in one).]

I can't possibly name every phenomenon associated with the weather and specify which lens should be used for what effect. Anyone attempting to photograph the different phenomena will soon discover the merits and limitations of lenses. I can give two tips, however, when selecting lenses:

• For the 28-80 and 80-200 ranges, buy two zoomlenses, as you will frequently use these. For all ranges, including the above, additionally buy fixed-focal length lenses. Do not buy zoomlenses with a large zoom range such as 28-200. These are lower-quality than smaller zoom ranges. Even better would be to use fixed-focal lenses exclusively, although sometimes this is less practical when composing your photo. But for all specialized photography, i.e. the green flash, zodiacal light, macro photography and so on, use fixed focal length lenses.

• Buy bellows or macro rings, as these will allow you to do macro photography (useful for snowflakes, hailstones etc.). Don't be fooled by any lens which says "macro" on it - that won't be enough. What I mean with macro is getting as close as a few cm (1") with a standard-lens (50mm) to the subject to photograph. That will open up a wealth of possibilities!