Low F-Numbers

Question.
Why is it that most lenses are sought after for their low f-number, ie. those numbers below f/2.8.

I know they give better dim-light performance, BUT, is it real performance. Most fast lenses don't perform at their optimum until mid-range on their f-stops. Take your fastest lens and, from a tripod, shoot a star field at ISO 600 as fast as you can get a dim or decent star field. Then blow it up to 100% and watch the "comma" effect at the OUTER EDGES edges. Not there--well you have an excellent lens. Most will show a dramatic fall off in quality as the maximum f/stop is approached.

There are a few lenses, and I'm sure more than I know about, which are optimized for LOW LIGHT PERFORMANCE; [Noct Nikor, f/1.4 57 mm? ($3,500 range) and maybe the Nikor 14-24, f/2.8 ($1,800 range).

I'm sure Zeiss and others have theirs--I would like to see a list if available]

SO, THE QUESTION IS: Why are not ALL low f/number lenses optimized for their maximum aperture? Fast lenses are expensive and slow lenses less so, but...

Are we fooling ourselves when we pay extra for fast lenses, say for landscape photography? Perhaps usable photos for news reporting in dim light situations would be desired but for excellence in our efforts is it worth it in all instances to seek fast lenses?

Using them in dim light is NOT giving us the best photo. So shooting higher ISO with low noise camera with a medium f/stop lens seems to be the answer for me.

Just thinking out loud.

the fisch

Larry,

IMHO, yes, folks are paying too much for fast lenses for "landscape" photography. A number of points that I'm sure other, more savy folks will chime in on.
1. For landscape photography, in general, you're going for max detail and max depth of field. Why would anyone every use f/1.4? (see #4)
2. "Fast" lenses like f/2.8, f/1.4 etc. are expensive because of the glass, manufacturing and surface area required to gather more light. With today's digital camera with little or no noise at say ASA 400, 800 and higher, you can get the same results exposure wise with an f/5.6.
3. The "fast" lenses were very advantageous and sought after back when film speed was fixed at 50, 64, 100 or even 200. Yes, there were faster films, but they were more grainy than any dslr today at 3200! So, back in the day.... you needed speed if you wanted faster shutter speeds in dim light. it's that simple. Today, I don't see that as being necessary.
4. However, the other aspect to the very fast shutter speeds would be depth of field. We all know, the larger the aperture (the opening, not the number,) the less depth of field. An f/2.8 could be advantageous over an f/5.6 lens if you really want to emphasize a shallow DOF. Having the widest aperture can be very effective in macro, flora and even wildlife photography where you want to isolate a subject against a background.
5. Otherwise, with today's technology and techniques you can achieve great depth of field and detail in landscape photography (of course other genres as well) using a good lens at it's optimum aperture.
6. Also, in the end you get what you pay for. There is the quality factor as well and certainly some glass is manufactured to tighter specs and better quality than others and will produce sharper images with fewer aberrations, less flare etc. While very cheap lenses are just that and heck, might even use plastic instead of glass... who knows.

So in the end, your last statement didn't even make sense 20 years ago, but I think for todays cameras and technology your assessment is correct.

But I'm still using film and not even an electronic camera, so what do I know?

Lon

One other point : Due to design constraints, most lenses, even "slower" ones, are not necessarily at their best wide open. Therefore, if you like to shoot at, say, f/4, and you have an f/4 lens, it won't be at its best. But an f/1.8 lens, shot at f/4, just might be at its best.

Although it's true that one rarely uses maximum aperture setting to make a capture, you use maximum aperture every time you look through the viewfinder. The more light that passes through the lens the better in that regard. More importantly, the more light there is the faster and more accurate the autofocus will work on the camera. All of the camera manufactures specify maximum f stops for their cameras for that reason. Not as much of an issue for landscape photography but definately and issue for wildlife, particularly action shooting when fast, accurate AF is a must.

Summary:
depth of field in some circumstances--sometimes large and sometimes small--Overacker
viewfinder brightness for rapid autofocus--Roberts
having a decent lens at say f/4 one has to begin at f/2.8 or lower in most case--Bostedo
Good stuff.

Avian.

Small wild birds require long lenses and high shutter speeds. They look best in the soft light of early morning.

I use my Nikkor 300/2.8 AF-S with a Nikon TC20E 2x wide open almost all the time so I can get barely acceptable shutter speeds at an effective f/5.6.

If you're talking Landscape images a fast f/stop means little, but there is another consideration for buying faster lenses. Most of the faster lens (f/2.8, etc) are considered "Pro" lenses. This doesn't necessarily mean the optics are that much better than consumer lenses in most cases, but the build quality is usually a good bit better as far as weatherproofing, etc. goes. Here in Florida, and other extreme humidity states that can be a factor. I've had several instances where high heat mixed with high humidity killed (temporarily) non-pro electronics, both cameras and lenses. 95 degrees with 98% humidity can be rough on equipment (and people ), not to mention rain. After you take them inside and let them dry out, they work just fine again, but it's a real bummer when you're out in the field for 3 or 4 days and this happens on day 1. I've never had this problem with Pro lenses or cameras.

I also frequently work in minimal (or insufficient) light and use max aperture. Typically lenses performance suffers at max aperture and at the outside edges of the image. If you use lenses designed for full frame sensors (e.g. Nikon FX) mounted on a 1.5 or 1.6 ratio sensor (e.g. Nikon DX) then the portion of the transmitted image that suffers distortion at widest aperture isn't even used. That's another bonus of smaller sensor formats, better images with cheaper glass.

That said, there is NO substitution for good glass. Always heard that but never appreciated it until I 1) got picky about my images 2) changed my priorities and finally got some high quality glass.

(1) What Richard said.
(2) The best glass is in the bigger aperture lenses.
(3) No hard drive is too large; no lens has to low and f-stop.
(4) What Richard said, especially if you are shooting under a heavy forest/jungle canopy.

Another consideration not mentioned yet is that although fast lenses since they are considered "pro" lenses are usually more durable than a kit lense, along with that comes more weight. Medium and long telephotos can begin to get pretty heavy. Certainly a consideration for any nature photog that hikes miles with a camera bag on his back.

I don't agree that the "best glass" is necessarily in the large app lenses. With Nikon, anyway, the optics in their kit lenses is pretty much the same as the pro lenses. Maybe Nikon experts can prove differently, but in practice I doubt anyone can tell the difference between a print made from a kit lens with the comparable "pro" lens. The difference is the quality of the lens casing, mounts, etc which add a lot more durability (but also weight).

UPDATED SUMMARY:

Observations of low f/number lenses... necessary or not????

1) depth of field in some circumstances--sometimes large and sometimes small--Overacker
2) viewfinder brightness for rapid autofocus--Roberts
3) having a decent lens at say f/4 one has to begin at f/2.8 or lower in most cases--Bostedo
4) some non-landscape photos need fast lenses for dim light; perhaps even an advantage in some landscape attempts--Ditch
5) lens build is usually better on high dollar fast lenses, ie. waterproofing--Chambers
6) DX sensors might compensate for drop-off in lens performance in low light and wide apertures--Roberts
7) No substitution for good glass--Roberts
8) No lens has too low f/number--DeWitt
9) Better lenses often have low f/numbers are usually more durable in general but weigh more--Vangrov
10) Adequate "glass" is contained in Nikon 'kit' lenses or non-low aperture lenses and is 'pretty much the same as pro lenses'.--Vangrov

Maybe Nikon experts can prove differently, but in practice I doubt anyone can tell the difference between a print made from a kit lens with the comparable "pro" lens.

That may be true, but if you pixel peep, you can also usually find differences between kit lenses an higher end lenses in terms of flare and chromatic aberration. These relate to the type of glass used, and the coatings used on the glass. Whether or not you see these is pretty heavily image dependent of course - and you may have to print big.

Since I shoot both sports and wildlife, shooting "wide open" is important to me. They've been scheduling way too many night football games around here lately.

I will considering getting rid of my 300mm 2.8 lens and replacing it with the new 200-400 f/4, but only if I can upgrade to a pro body that handles high ISOs better in order to compensate.

Max

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That may be true, but if you pixel peep, you can also usually find differences between kit lenses an higher end lenses in terms of flare and chromatic aberration."
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I'm sure that's true - I'm far from expert on the technical aspects. My main point is the optics on the Nikon kit and "slower" lenses (can't speak for Canon or others) are very very good (astoundingly good really for the money as compared to the huge price jump to the "pro" lenses). So for most landscape photographers unless one really needs a pro lens for the one of the valid reasons listed above you might as well save the money for something else, especially if you don't print over 20x30+ -.

Agreed Barry... and anecdotally from what I've heard current "kit" lenses are world's better than they were even 10 years ago.

There are exceptions to every rule. Once in a while a really sharp "kit" lens comes along. I've go a Nikon 55-200mm VR lens that originally sold for about $250 and later dropped to $159 at the popular on-line stores. It is an absolutely wonderful lens. Up to an 8x10 print made from a full frame image I can't tell the difference when compared with an image captured with my 200-400 VR that cost over 20x as much. However, if you begin to crop heavily or the image is enlarged substantially beyond that, the sharpness between the two is evident and chromatic aberation becomes quite apparent. I have quite a few landscape images captured with the 55-200 that look quite good reduced for web display. Few of them would ever pass the scrutiny of a professional or skilled amateur looking at the full resolution version.

It's really all about "fit for purpose" equipment dependant on intended use. There is definately no need to drop big $$$ on a lens unless you are VERY serious about your photography. But if you are, and you just can't seem to figure out the "trick" to making that next step change improvement in image quality.... look into the glass.....