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  1. #1
    Michel Hardy-Vallée's Avatar
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    Non-constant aperture zooms

    A small beginner's question that I can't fathom how to answer: when using a zoom that does not have a constant aperture (say, 3.5-5.6), is the aperture change for ALL f-stops or only for the widest aperture?

    In other words, if I use such a zoom at f/8, will it remain at f/8 when I zoom?
    Using film since before it was hip.


    "One of the most singular characters of the hyposulphites, is the property their solutions possess of dissolving muriate of silver and retaining it in considerable quantity in permanent solution" — Sir John Frederick William Herschel, "On the Hyposulphurous Acid and its Compounds." The Edinburgh Philosophical Journal, Vol. 1 (8 Jan. 1819): 8-29. p. 11

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  2. #2
    David A. Goldfarb's Avatar
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    No, all the stops change as you zoom. If you're metering through the lens, the meter will compensate. If you use a handheld meter or non-ttl auto flash, then you have to figure it out.
    flickr--http://www.flickr.com/photos/davidagoldfarb/
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  3. #3

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    The numbers (3.5, 5.6, 7, 11, etc) are a ration for the size of the opening in relation ship to the focal length of the lens. to make the math easier I will use f/2 as an example. if the lens is a 50mm lens, and it is at f/ 2 then the aperture opening is 25mm. if it happens to be a zoom lens, say 50-100, when you zoom in the focal length changes. the 25mm opening that was f/2 when zoomed out (50mm) is now f/4.

    Now to answer the question you asked. No. f/8 will change when you zoom in.

  4. #4
    Ian Grant's Avatar
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    That's a very good question but I just checked my Canon and Tamron 17-35mm f2.8-f4 metering off a plain evenly lit wall and the metering stayed constant as I zoomed at f5.6 and f8.

    I think the answer is with older mechanical lenses the apertures all vary as you zoom, but with most modern autofocus lenses where the camera body sets the aperture electronically it stays constant.

    Actually the constant aperture was a sales feature, now I think about it, with Canon lenses.

    Ian

  5. #5
    Michel Hardy-Vallée's Avatar
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    Thanks for the answers, it makes more sense now.

    I was planning a worst-case scenario at work that would involve a Nikon manual body, an AF zoom, and non-TTL auto flash. Mismatched trio, I know, but I'm waiting for an FM2n kit to arrive in the mail.

    Like a good young imbecile I did not take the shipping option bearing a tracking number (save money, yeah right!), so I'm anxious for it to arrive soon enough for a job I'm doing in mid-November (stupid! stupid! stupid!).

    Clearly, should the scenario be worst case, I will rent a body/flash that can deal with the zoom I have (as per Ian's explanation), unless my manual body and prime lenses arrive on time.

    BTW, I can't believe how cheap it is to rent an F5 for a week! 120$, plus a little extra for a lens. Rental is really the unsung hero of analog photo.
    Using film since before it was hip.


    "One of the most singular characters of the hyposulphites, is the property their solutions possess of dissolving muriate of silver and retaining it in considerable quantity in permanent solution" — Sir John Frederick William Herschel, "On the Hyposulphurous Acid and its Compounds." The Edinburgh Philosophical Journal, Vol. 1 (8 Jan. 1819): 8-29. p. 11

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  6. #6

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    With regard to Ian's suggestion that the variable aperture is compensated for by the electronics of the camera. It's not gonna happen unless the shutter speed changes.
    You've got a mechanical limit imposed by the design of the lens ie:variable aperture and unless there's some compensation somewhere.
    I guess the conclusion should be if it's working OK it doesn't matter how it does it.
    Heavily sedated for your protection.

  7. #7
    Ed Sukach's Avatar
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    It is a *FAR* more difficult design problem to keep the aperture constant as the focal length changes - more difficult, more elements/groups in question, but IMHO, indicative of a greater committment to quality.

    The one lens I have that seems to perform the *best* is an old(?) Olympus - Zuiko 75mm - 150 f/4 - with a CONSTANT aperture. That has fifteen (15) elements in eleven (11) groups.

    Somewhere along the line, it was decided to sacrifice lens design efforts and rely instead on "automatic" exposure, assuming that most (everyone?) would be deliriously happy not even knowing what the aperture was.

    Possibly the start of the "dumbing down" trend so prevalent in recent years?
    Carpe erratum!!

    Ed Sukach, FFP.

  8. #8
    copake_ham's Avatar
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    Quote Originally Posted by mhv View Post
    .....

    BTW, I can't believe how cheap it is to rent an F5 for a week! 120$, plus a little extra for a lens. Rental is really the unsung hero of analog photo.
    I dunno.

    As I write this, with 20 minutes to go - there's one selling on eBay for $620. Doubt it will go much higher than $700 so $120/week rental is m/l one-seventh of the sell price.

    If you got the need for seven weeks worth of F5 - you're better off buying one.

  9. #9
    Michel Hardy-Vallée's Avatar
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    Quote Originally Posted by copake_ham View Post
    If you got the need for seven weeks worth of F5 - you're better off buying one.
    I can't know I've got the bug before I get infected... That's how I found out about the FM2n, at any rate!
    Using film since before it was hip.


    "One of the most singular characters of the hyposulphites, is the property their solutions possess of dissolving muriate of silver and retaining it in considerable quantity in permanent solution" — Sir John Frederick William Herschel, "On the Hyposulphurous Acid and its Compounds." The Edinburgh Philosophical Journal, Vol. 1 (8 Jan. 1819): 8-29. p. 11

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  10. #10

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    Quote Originally Posted by copake_ham View Post
    I dunno.

    As I write this, with 20 minutes to go - there's one selling on eBay for $620. Doubt it will go much higher than $700 so $120/week rental is m/l one-seventh of the sell price.

    If you got the need for seven weeks worth of F5 - you're better off buying one.
    There is one on Craigslist for the princely sum of $400...not that I need another film camera, but that surely is tempting. Two F100s and the F5 and an N90s, along with the F4. I might never need to buy another film camera.
    Luke

    To create one's own world in any of the arts takes courage.

    Georgia O'Keefe

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