Just how important is speed?

Discussion in 'Pentax' started by robert_s|2, Mar 23, 2004.

  1. Question...
    when buying glass, just how important is speed?
    I have looked at a lot of lenses, it seems like you really do pay for
    speed when there are some real deals to be had on slower stuff, IE
    F2.8 costs a ton, but similar focal length in an F5 to 8 is cheap like
    hell...

    I have used some fast stuff, but to be honest, most of my shooting is
    done at f8 to f11 "ish" Chromatic abberation in really cheap stuff not
    withstanding, just how bigga deal is the speed?
     
  2. I shoot ISO 100 film most of the time and find myself using large apertures a lot. To me a fast lens is pretty important, it lets me shoot in much lower light. I'm only using primes right now and I buy them used on Ebay, so they're cheap...and fast. I assume you're talking zoom lenses maybe? With prime lenses I don't really consider f2.8 to be very fast; unless you're talking about telephoto lenses.

    Not only do they allow you to shoot in lower light, but they give you a brighter viewfinder as well...which makes that low light shooting even easier.

    Alan
     
  3. I use fast lenses for the extra shutter speed I can use when I handhold(I handhold 35mm almost exclusively) but really the faster stops are used for the minimal depth of field. Using the 77 limited at its maximum aperature really puts the background out of focus enough to give a nice mood, but doesn't make the shot distracting. Of course, shooting on a tripod and doing landscape work the opposite might be the case where I want everything to be sharp.

    If you are in the market for zooms, you can safe a couple of bucks and buy slower, but still optically good zoom lenses and pick up a 50f1.4 and another fast lens, either in the telephoto or wide category, depending on what you shoot.

    Come to think of it, most of my 35mm format lenses are relatively fast, probably because I prefer to use primes and I like to spend money. ;-)
     
  4. Someone please stop me if I'm wrong but.... Don't the faster lenses perform better even at smaller apertures? My thought is that all glass has imperfections. The faster lenses spread these imperfections over more glass so that individual imperfections are a smaller percentage of the glass that the image is being transmitted through. Add this to the fact that usually faster lenses are more expensive and made with better quality glass using better quality mfg processes. When I switched from f/4.0-5.6 to constant f/2.8 zooms, my shots became much crisper, clearer, and more contrasty, no matter what aperture I shot at (and I rarely shoot wide open). Anybody here actually know about lenses? These are just my impressions and should not be taken as anything to do with real life.
     
  5. Fast lenses give you greater focusing precision and a brighter viewfinder, so they're a pleasure to use even if you're actually using them at f/8 or f/11.
    If you're talking zooms, and I assume you must be, since you say f/2.8 costs a ton, there are other considerations. The f/2.8 zooms are often better built, better corrected, with constant aperture, and less distortion than their cheap slow consumer cousins. They're marketed at serious photographers, while the cheap slow stuff is marketed at people who don't understand much about lenses beyond focal length.
    Among single focal length lenses for 35mm cameras, unless it's an extreme focal length, f/2.8 is considered fairly slow and cheap. For example, the 35mm f/2.8 lens in the Olympus Stylus Epic costs around $90.00, including the entire camera and flash. And it's a sharp, well-corrected, relatively flare-free lens. There are only a few 50mm lenses for SLRs that are as slow as f/2.8, and those are usually for special purposes, such as macro.
     
  6. If you can't see,all is lost!!

    Richard G.
     
  7. stemked

    stemked Moderator

    Hi Robert.

    I think the phrase, "all things have their place" is appropiate here. For critical focusing, yes a faster lens regardless of the chosen f-stop will aid in focusing. Also the faster lenses generally have improved optics in the form of special glass optics which tend to be most notable on the longer end. However, I'm amazed at how excellent my super cheap-o 80-200 A f4.7-5.6 performs even wide open. I think improvements in faster film have really turned some of these lenses into much more attractive alternatives, especially when one considers weight of a f2.8 lens.

    So my $0.02, if you are shooting in low light conditions, are a Velvia 50 regular shooter, or really want a limited DOF go with the f2.8 lenses. Otherwise you have little reason to pine for a really fast lens- and your back will love you after a long day's travel!
     
  8. As another example of where speed pays...last night I was out shooting with some ISO 100 film and I brought along my 50 f1.4 lens only. It was about 15-20 minutes or so after sunset and I wanted to silouhette some nice looking branches against the sky, I also wanted the branches behind and to the side blurry. I had my tripod with me but I needed the camera to be higher then the tripod allowed. Not a problem since I was able to shoot at 125th at f1.4. Something I would have had a very hard time with with the zooms I used to use.

    Oh yeah, and the lens costs under $50 used.

    Alan
     
  9. With my manual focus bodys I like a Tamron 70-210 f3.5. Holding it with the *ist is close to pain. At the moment I'm hunting a slow AF-zoom for easy-going outdoors. According to photographic tasks and photographers needs I like to say it's no mistake to own both kind of lenses. A friend of mine 's got a 200 f2.0 Nikkor, wich might be a good lens but in real life there are nearly no results, because it's to heavy...
     
  10. I'm amazed how well my f18-f32 performs also!

    Yea But!!!
     
  11. The assumption that fast lenses are somehow "better" is a common - and expensive - misconception.

    They are easier to focus precisely due to the larger aperture ans the smaller DoF, and allow faster shutter times and less DoF. But if there is any difference at all at f:16 it will be small, and probably in favor of the slower lens.
    The faster lenses need to be more complex than the slower ones in order to be reasonably well corrected at full aperture, which increases the price proportionally. A slower lens can be a lot simpler, lighter and correspondingly cheaper. Also fewer compromises have to be made in the optical construction, and very good results can be achieved with few lens lements of low-cost glass. The classic Tessar construction is a case in point, at f:4.5 they are small and cheap, while the resolution at f:16 is second to none.

    Zoom lenses are compromises anyway, and the more expensive ones will generally be sharper and have less distortion - regardless of maximum aperture.
     

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