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  1. #1
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    Kingston, Ontario, Canada
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    Fixed vs. Variable Aperture

    Good-day,

    For those of you not already familiar with the environment in which I will be photographing my subjects, a complete description is available under my post "Macro->Nikon, Canon, Pentax->Bodies, Lenses" in this forum (Digital SLRs) (though I do not believe knowledge of this is greatly important for the subject of this post).

    Background:

    i.) From my understanding, the main purpose of the aperture is for the control of lighting (hopefully I have this much right... ;) ). Now, as my subjects are in a very low light environment to begin with (i.e., the inside of my research furnace), too much light should not be a problem. In addition, I can, and will most likely, add more lighting to my system in order to improve the lighting to a sufficient level.

    ii.) It appears the price for a fixed aperture camera is generally more*** than that of a comparable variable aperture.

    iii.) I have the impression that a fixed aperture lens is generally of higher*** quality than a variable aperture.

    iv.) I am currently looking at acquiring a D100 or D70.

    *** Please correct me if this is not the case.

    Question:

    As I can control the lighting of my system fairly cheaply (i.e., CAN$50-100 halogen lamps) relative to the cost of a better aperture, would it most likely be more inexpensive to get a variable aperture lense with a suitable focal length (i.e., Sigma 70-300mm f4-5.6) and compensate for any difficulties through controlling my lighting?

    Thank you for your time.

    Auf wiedersehen,

    James
    "Don't take life too seriously; you'll never get out alive"
    - Bugs Bunny

  2. #2
    has-been... another view's Avatar
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    Rockford, IL
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    Too much light is rarely a problem! You are correct, aperture controls how much light gets through the lens to the sensor (or film). There are actually three components that make up exposure: Aperture, Shutter Speed and ISO. If you're in low light, you need fast lenses - that's just how it is. Turning up the ISO can fix one problem and cause others, but nothing beats lens speed (like 2.8 is faster than 5.6, etc).

    Also, from your previous posts, I think a consumer variable aperture lens is a step in the wrong direction. It's pretty rare to find a consumer lens made out of metal. They can be pretty sharp stopped down one or two stops from wide open but pro lenses are designed to be sharp wide open - which is already faster than the consumer lens. For example, the 80-200 f2.8 is shot wide open (I have the two-touch Nikon previously discussed and can tell you from experience it's sharp wide open). Say the consumer zoom is f5.6 at the 200mm end of the zoom range. Stop down even one stop (f8) and you've lost three stops over the pro lens. You've lost two stops even wide open and the image might not be sharp enough for you.

    A fixed aperture lens is generally higher quality than a constant aperture lens, but not because of that reason. Constant aperture lenses are bigger, heavier and more expensive. Variable aperture lenses are built to be light weight and inexpensive. Nothing wrong with variable aperture lenses, I'd rather carry a 1lb lens than a 3lb lens but just realize that there are tradeoffs.

  3. #3
    Junior Member
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    Jun 2004
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    Kingston, Ontario, Canada
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    No Longer Metal Lens

    Quote Originally Posted by another view
    It's pretty rare to find a consumer lens made out of metal.
    Good-day,

    Just for clarification for all those who may be reading this and following from my previous threads:

    Though I previously mentioned some interest in a metal lens, I am no longer interested in that route, as it should be much simpler to deal with any heat escaping the furnace though insulation, and other relatively inexpensive and simple means.

    Thank you for your time.

    Auf wiedersehen,

    James
    "Don't take life too seriously; you'll never get out alive"
    - Bugs Bunny

  4. #4
    has-been... another view's Avatar
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    If that lens is fast enough for your application, I've got a Tokina 80-400 which actually is made out of metal (although the hood is plastic just like the Nikon). I didn't mention it above because I figured that it wouldn't be the best choice for what you're doing - but it is quite a bit less expensive than a 2.8 zoom. It's very sharp until you get over 300, then it's a little soft - but 400mm is probably not useful to you anyway. Two large prints made with this lens in the 200mm range confirm this! I have the latest version which I guess is a big improvement over the first version. The current one has a tripod mount on the lens, and it's got a "II" in the part number. The minimum focusing distance (if I remember right) is about 6' or 7' though - if that doesn't work for you, you could add an extension ring to shorten that distance.

    Your other question - yes, you can add halogen lamps to increase brightness. That's one great thing about digital, you can adjust the white balance so that halogen light appears white in the finished image instead of yellow which is how it would normally (i.e. daylight film) be rendered. There would be some issues with heat with these too - but probably more for the internal wiring of the fixture than anything else.

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