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Thread: Using fast lens

  1. #1

    Default Using fast lens

    I would like to know from those who uses fast lens. Do you use it wide open most of the time?

    I am an aperture priority shooter. I realise that even with a fast lens, I seldom use it wide open due to the shallow depth of field. It seems a shame to pay for a F/2.8 or F/1.8 lens and end up using it at F/4 or F/5.6 most of the time.

    What's your take on this?

  2. #2
    Moderator sebastiansong's Avatar
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    the purpose of a fast lens is the option (some might call it luxury) to use the full range of fstops. If you could afford it always go for the greater range of fstops.

  3. #3
    Pegasus
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    Default Re: Using fast lens

    Originally posted by limhousen
    I would like to know from those who uses fast lens. Do you use it wide open most of the time?

    I am an aperture priority shooter. I realise that even with a fast lens, I seldom use it wide open due to the shallow depth of field. It seems a shame to pay for a F/2.8 or F/1.8 lens and end up using it at F/4 or F/5.6 most of the time.

    What's your take on this?
    A brighter viewfinder. Optical view finder through the lens is always at its widest aperture. And not to mention for limited light photography.
    Last edited by Pegasus; 21st July 2003 at 11:34 AM.

  4. #4

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    and it will focus faster due to more light.....

  5. #5
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    1. Faster AF on most/all cameras.

    2. Easier to check focus bcoz of brighter viewfinder and smaller DOF when viewed thru finder. Human eye can judge more accurate where the focus plane is.

    3. On some Canon models need f2.8 or faster to use more sensitive AF cross sensors - faster n more accurate AF.

    4. i appreciate the low light options when flash is inappropriate. ISO 800 on an f2 or f1.8, at -2/3 ev, can help a lot in discretion. Focussing will still be a bit low bcoz of the poorer lighting.

  6. #6

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    sometimes shallow depth of field is good for subject isolation.

  7. #7

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    Nope I don't. Though if I need maximum shutter speed for sports (Amateur level) and if the light conditions are really really bad - I have absolutely no qualms in shooting them wide open.

    DoF is certainly a problem though the faster shutter speed does make up for the lack thereof. Nobody ever said low and available light photography was easy

  8. #8
    psyche
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    Default Re: Using fast lens

    Originally posted by limhousen
    I would like to know from those who uses fast lens. Do you use it wide open most of the time?

    I am an aperture priority shooter. I realise that even with a fast lens, I seldom use it wide open due to the shallow depth of field. It seems a shame to pay for a F/2.8 or F/1.8 lens and end up using it at F/4 or F/5.6 most of the time.

    What's your take on this?
    I have a 50mm f/1.4 but I never shoot it at f/1.4 apart fro one occasion to test it. For the simple reson as u've said, DOF is very shallow. Unless I want it intentionally that way. Usually, most of the time, if I can handhold reasonably at f/2.8, I see no reason why I should push it to f/1.4. Well, why did I get this lens then? Cos it was sold at quite a good buy, and also, I prefer the solid feel to it compared to the plasticky and more noisy f/1.8 version. But if not for these reasons, and if you're talking about getting good pics, yes, it's a shame cos the f/1.8 would be able to do the job exactly for me. If Canon had come up with a 50mm f/1.8 with USM and metal mount, and priced say at $300 or so, I'd have gotten it instead.

    As for brighter viewfinder and more responsive AF, I really can't tell that much diff between an f/2.8 and f/4. Maybe bcos I'm not a low-light photography enthusiast.

  9. #9

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    Sharper image. A 2.8 lens will give sharper images at f5.6 than say an f4 lens. And all the above that has been mentioned. The "Sweet spot" for most lens are usually 2-3 stops down so for a regular 4/5.6, you are looking at f 8 and above for sharp images and this means for indoor shots or dark surroundings...you are going to be seriously challenged

  10. #10
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    Default Re: Using fast lens

    Originally posted by limhousen

    I am an aperture priority shooter. I realise that even with a fast lens, I seldom use it wide open due to the shallow depth of field.
    It may not just be the shallow depth of field. From my experience, consumer fast primes do not give very acceptable results wide open. i have experienced this with the Canon 50/1.4 and 80/1.8. They need to be stopped down at least 1/2 stop for minimally passable results. The 'L' lenses are different - they are designed to give good results wide open.

    Generally, for wide angles, most ppl stop down for more depth of field. For the longer focal lengths, wide open apertures are used more frequently. i use my 70-200 wide open a lot, but below 35mm, it makes more sense to stop down. So for longer lenses, it's more worth it to pay for that extra one stop, but not so useful for WA.

  11. #11

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    perhaps for telephoto lenses, you hardly shoot at wide open cos of the very shallow DOF, but I'm sure there are times when f2.8 is useful. Especially when the subject is pretty far away, and you are in an indoor environment. F2.8 will give u good shutter speed, and DOF won't be too shallow as subject distance is further. E.g., fashion shows.

    for wide-angle lenses, wide open is useful for low-light photography. Being wide-angle, the DOF is deep thus shooting at wide open means u still get most of the subject sharp, provided u dun go too close to it.

    Furthermore, most lenses perform better when stopped down, so with a F2.8 stopped down, u still get useful fstops like F5.6. Not sure if this point is a "duh" though.

  12. #12

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    I'm a MF user with split image focus. If the lens is not bright enough, i'll have difficulty judging the focus. Fast lens helps a lot.

  13. #13

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    very insightful thread. good stuff.

  14. #14
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    I'm also a aperture priority shooter and has quite a number of fast lenses. I normally try and shoot wide open as I try and make use of the natural light instead of flash. I try and capture the mood, actual environment and ambience .. I'm only a starter.

    I have also shot at wedding dinner, especially the stage and it showed up well. My only gripe is that most of these 3rd party lenses at soft at F2.8 and it too happen to originals with the exception of my Nikon 80-200D F2.8 which is sharp throughout the ranges.

  15. #15

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    Could be helpful for low light conditions where you have to use the available light. This is especially true for concert photography where you tend to throw the lens as wide as possible to get every bit of light in. At the same time you need a reasonably fast shutter speed to prevent blur as the musicians are usually jumping around the stage In such a situation a faster lens will help as you can then use a slower film. The shallow DOF is something that is not something that you will mind too much in such situations.

  16. #16

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    Comparing the Canon 50mm f/1.4 and f/1.8, I read some say at f/1.8, the f/1.4 big brother gives a tad sharper images than the f/1.8. But after that, they are more or less on par in performance. Unless you're interested in minute numerical differences done in labs utilizing MTFs and what not. How much difference to the human eye anyway?

    Also, you can't quite 'blame' the lens designer for coming up with a lens that is 80mm f/1.8 or 100 f/2. Cos it's within their design limits that an 80mm can go as large as f/1.8 and yet still be reasonably priced. Is it worth it to limit the aperture to f/2.8 so that we have 80mm f/2.8 prime and get relatively sharp images? I don't think so.

    Lastly, I think shaprness is relative. How soft is soft and how sharp is sharp? If you need f/1.8 wide open to do the job, you gotta use it. U don't want to really risk camera shake by stopping down or frantically search for a non-existent tripod just bcos f/1.8 is "not usable" or soft. If you got to use f/1.8, you use it! That's what the lens is capable of.

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