How come I get different min/max Aperature settings?

Discussion in 'Beyond the Basics' started by GerryDavid, Mar 22, 2004.

  1. GerryDavid

    GerryDavid No longer a newbie, moving up!

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    Ive noticed that I get different minimum and maximum aperature settings depending on what film iso I use and what length of lense I use, and I was wondering shouldnt I get the same aperature amounts for all ISO's? With Ilford 125 and I think 28mm lense I can get an aperature of f38, but with Ilford 400 I think the most I got was f28 or something like that.
     
  2. Skyeg

    Skyeg TPF Noob!

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    the film speed shouldn't change your lenses min and max aperature.
     
  3. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    Aperture isn't affected by film speed.

    Focal length affects f/stop relative to aperture (f/stop = focal length divided by aperture diameter).

    I'm not really understanding what you are asking?
     
  4. GerryDavid

    GerryDavid No longer a newbie, moving up!

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    Just asking why the aperature max/min changes with different iso's and different focal lengths. :0).
     
  5. markc

    markc TPF Noob!

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    I'll echo the others. The max f/stop will be affect by the focal length, but not film speed.

    The actual physical size of the hole (aperture) remains the same, but the ratio (f-stop) changes with focal length.

    My 22-55mm lens maxes at f4.0 at 22mm, f4.5 at 35mm, and f5.6 at 55mm.
    The min remains at f22 through the entire range due to rounding.
     
  6. GerryDavid

    GerryDavid No longer a newbie, moving up!

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    Thanks for everyone's replies. Im goign to have to keep track of the min/max aperature's with different iso's at different focal lengths, im sure it changes on my camera, hehe. That or I wasnt paying closer attention before.
     
  7. markc

    markc TPF Noob!

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    Hrm. I think I just came up with a way that this might happen. If you are in an automatic exposure mode that is particularly point-and-shootish and are pointing the camera at a very bright scene, it might not let you overexpose the image. If this is the case, then raising the ISO will force the f/stop to close down. This won't happen in dim light, however.

    This isn't the usual behavior for cameras, as they normally just let you know that the image will be too bright.
     
  8. GerryDavid

    GerryDavid No longer a newbie, moving up!

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    Ive only been using my canon rebel 2000 on manual mode since ive been using it for class, and learning how all the manual stuff works. So I dont think it would be limiting me cuz of to much light, then again I did notice this difference in the studio which isnt as bright as the outdoors as I have been using the camera. Perhaps the rebel 2000 has biult in annoyances. :0).
     
  9. Jeff Canes

    Jeff Canes No longer a newbie, moving up!

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    :scratch: How can film speed not have effect on the aperture. If you have two cameras with the same lens, but different speed films of 100 and 400,
    With the same light EV those films would have different min & max range of both the f-stop and shutter speed not the aperture for that EV :scratch: :scratch:

    Edited to cover up my stupid ness :wink:
     
  10. GerryDavid

    GerryDavid No longer a newbie, moving up!

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    To me the aperature shoudlnt be limited, just like the exposure isnt limited. On the extreme's, it would be complete washout or complete unexposed. Like if you can set it to expose for 1/2000 in very dark situations or bulb for 4 hours during extremly birght days. It would be nice to have the option for f38 on a very bright day with higher iso if im able to do it with lower iso. :0)
     
  11. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    You are talking about exposure; of course ISO would change the meter recommended f/stop if the shutter speed were set the same for each ISO.

    As I said, I may be misunderstanding the original post, but I took it to mean that GerryDavid thought that his 28mm lens would stop down to f/38 when the camera was loaded with ISO 125, but would only stop down to f/28 when loaded with ISO 400.

    Here's the quote, "With Ilford 125 and I think 28mm lense I can get an aperature of f38, but with Ilford 400 I think the most I got was f28 or something like that."

    This I do not understand. ISO does not change the range of available apertures on a lens. If the smallest f/stop is f/22, then it doesn't matter what speed film you put in the camera. It's still going to be f/22.

    On the other hand, if you set your 28-105mm zoom on f/22 at 28mm, as you increase the focal length and zoom in the f/stop number will increase. At least this is how most consumer zooms work. Some pro lenses adjust the actual aperture size so that the f/stop remains the same no matter how the focal length is changed.
     
  12. Jeff Canes

    Jeff Canes No longer a newbie, moving up!

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    I fell stupid
    :oops: :oops: :oops:
     

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