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Thread: Lens issues

  1. #1
    Member Frieda's Avatar
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    Lens issues

    Hi

    I hope someone can help
    I have a canon 6D and have bought a samyang lens-14 mm f2.4 want to do some night sky.
    There were no instructions in the box. When you change the aperture looking thru the view finder is goes light/dark. The focus is very minimal as we'll. The focus ring moves and I can see it focusing only slightly

  2. #2
    Administrator ricktas's Avatar
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    when you change the aperture it will go dark. The larger the number you select, say f22, the smaller the actual aperture, to reduce the amount of light coming through the lens. This is what apertures do. So it appears the aperture is working as it should. Focus ring should have distance numbers on it? starting with smaller numbers and going out to infinity, often depicted on lenses as ∞ . You could use these to set focus distance. Remember that often ∞ is actually slightly back from the symbol. So dial the lens all the way out to its extreme and then move it back from that just a tiny wee bit.

    Are you trying these out during the night? If so, try testing the lens during the day to start with, and you will see the scene better. You can always dial focus out to infinity and take a shot, then dial it back and take another one and compare them on your computer.
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  3. #3
    Ausphotography Regular swifty's Avatar
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    I'm not familiar with the actual lens but it sounds like its a 'manual everything' type of lens.
    In the case of your aperture ring, turning it physically stops down your aperture diaphragm whereas native lenses hold the aperture at its maximum value (brightest) for AF and viewfinder brightness purposes and only stop down the aperture to the set value at the time you press the shutter button. This would explain why your viewfinder gets darker as you stop down.
    Look into the lens and you should see the aperture size change as you rotate the aperture ring.
    So do your focusing at max aperture, then stop down to your desired aperture once you've obtained focus before shooting.

    As for the minimal movement when you turn the focus ring, it just means the lens has a short focus throw. Most manual focus lenses actually have more focus throw (more turning distance) to allow for more accurate manual focusing but this is a wide angle lens and the lens could just be designed that way.
    Like Rick suggested, make sure you test it in day light and check that it is indeed focusing from its minimum focusing distance all the way to infinity within the short turning range of the focusing ring.
    Nikon FX

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    A royal pain in the bum! arthurking83's Avatar
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    It sounds as tho this lens is not electronically coupled(has no CPU communication whip to the camera).

    Like Swifty said, if you want to focus this type of lens the best way to do so, is to keep it wide open(as much as needed .. f/4 should be a reasonable setting) focus and then stop down to your desired aperture value before exposure.

    I don't think that keeping the lens all the way open will be beneficial, as it may render a loss of contrast having it fully wide open which could limit the ability to see fine detail properly.

    Somewhere between f/4 and f/5.6 on the lens shouldn't produce any loss of light to the viewfinder.

    But it may(actually it should!) if using liveview mode tho(as the focusing screen is bypassed).
    So for Liveview focusing, f/4 or f/2.8 on the lens would probably be the best settings to use(depending on available light).

    If the lens was electronically coupled, it should allow the use of the camera's aperture control mechanism.
    I'm not entirely sure if any CPU accessories can be purchased (for your camera system) to allow this ability.

    Alternatively, there may be a setting available on the camera to allow this with full manual lenses and Canon cameras(I don't know .. I'm not a Canon person).
    Last edited by arthurking83; 11-09-2014 at 1:55pm.
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    Ausphotography Regular
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    Quote Originally Posted by Frieda View Post
    Hi

    I hope someone can help
    I have a canon 6D and have bought a samyang lens-14 mm f2.4 want to do some night sky.

    When you are shooting "night skies" with this lens, then, probably most of the time for that task you will be using the lens (wide open) at F/2.8 (it's probably a Samyang 24mm F/2.8 lens).

    The reasons (either one or both) that you'd likely choose F/2.8 are:

    > To get the necessary SHUTTER SPEED to arrest STAR MOVEMENT (you might like to research the "Rule of 600" / "Rule of 500" for Astrophotography)
    > To get the lowest ISO to arrest NOISE


    Focus the lens at infinity ( ∞ ) for this task – that will be quite OK.

    WW

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    Ausphotography irregular Mark L's Avatar
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    So hows it going Frieda?

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