Newborn Lens for Canon 80D

Discussion in 'Beyond the Basics' started by alex_ethridge, Jan 5, 2018.

Tags:
  1. Cortian

    Cortian No longer a newbie, moving up!

    Joined:
    Jan 1, 2018
    Messages:
    503
    Likes Received:
    207
    Location:
    S.E. Michigan, USA
    Can others edit my Photos:
    Photos OK to edit
    If that'd suit her needs, I note somebody's got one of them listed in buy & sell. Looks like a good price for what appears to be a NIB lens. (N.B.: Cursory research only.)


     
  2. TCampbell

    TCampbell Been spending a lot of time on here!

    Joined:
    Mar 31, 2012
    Messages:
    3,495
    Likes Received:
    1,493
    Location:
    Dearborn, MI
    Can others edit my Photos:
    Photos OK to edit
    In lenses... there's such a thing as a "normal angle of view" ... that's the view that provides roughly what your eyeball expects for "1x" magnification (no magnification at all).

    Anything "wider" or "narrower" will change the perspective. An undesirable thing about "wide" angle lenses is that it isn't just that the view is "wider", it's also that it stretches the sense of depth. Things seem farther away than they really are... and it's all proportional... some moderately far things seem a little farther away... and slightly more distant subjects seem even farther way. You can thinking it as "stretching" your scene.

    The reason this matters in portrait photography is because if you imagine someone's face staring directly at the camera, their nose closer to the camera than their eyes... or their ears. So when you "stretch" the sense of depth in the image, you actually "stretch" the look of their face. Their eyes and ears seem farther away from their nose than they really area. This makes the nose seem bigger (relative to eyes and ears) and it's not a flattering look.

    For this reason, photographers like to choose lenses that are moderately narrow for portraits because they have the opposite effect... "compression". Their eyes and ears seem to be not as far from their nose... it's a more flattering look.

    So if we've got "wide" and "narrow"... what's just "normal"?

    It turns out anytime (for any camera) that the focal length of the lens is EQUAL to the diagonal size of your imaging sensor, you've got a "normal" angle of view.

    The diagonal measurement of your camera is just fractionally over 27mm.

    It turns out nobody actually makes a 27mm lens... there are 28mm lenses. Even 35mm lenses is pretty close (on the fractionally narrower angle). This would give you an angle of view which is not as tight as your 50mm... but still technically not a "wide" angle of view because it hasn't dropped below that 27mm magic value of the "normal" focal length.

    That's possibly a bit more than you wanted to know... but now you know.

    Use anything 28mm or up and you'll get good looking images. If you start to drop below 27mm then you start to get the wide-angle distortions that are unflattering for portraits (although you probably wont notice until you drop down enough.)
     
    • Informative Informative x 2
    • Like Like x 1
  3. Cortian

    Cortian No longer a newbie, moving up!

    Joined:
    Jan 1, 2018
    Messages:
    503
    Likes Received:
    207
    Location:
    S.E. Michigan, USA
    Can others edit my Photos:
    Photos OK to edit
    I certainly can't speak for Alex, but I sure found that explanation enlightening, Tim. Thanks!

    I would only request a clarification.

    When we speak of lens' focal length and APS-C cameras we always have to keep in mind the "1.6 multiplier." Thus a 28mm lens is really nearly 45mm on my 20D or Alex' 80D. When you talk about the sensor's diagonal measurement and focal length, this is "real" as opposed to "equivalent" focal length?

    E.g.: When you suggest a 28mm FL would likely be "ideal" for portraits (on Alex' APS-C camera), you really mean a 28mm lens, not an 18mm lens?
     
  4. TCampbell

    TCampbell Been spending a lot of time on here!

    Joined:
    Mar 31, 2012
    Messages:
    3,495
    Likes Received:
    1,493
    Location:
    Dearborn, MI
    Can others edit my Photos:
    Photos OK to edit


    One qualification... it isn't that a "28mm" is "ideal". It's that in order to avoid wide-angle distortion (even a very tiny amount) you would not want to go shorter than 28mm (most photographers seem to prefer using a slightly longer focal length for portraiture). But honestly... if you used a 24mm lens... most people are not going to notice the distortion (even though technically it is there.)

    My comments were mostly to help those unfamiliar with how to find the "normal" angle of view for their camera and wasn't meant to get into the crop-factor and equivalent focal length confusion.

    As for crop-factors... this is a very common point of confusion. A 28mm lens really is a 28mm lens and the rules of physics and all math would need to be done based on a 28mm lens. It doesn't matter if the lens is on a full-frame vs. crop frame camera (the lens doesn't "know" how large the sensor is).

    A "full frame" camera has a sensor measurement of 36 x 24mm. That creates a diagonal measurement of 43.27mm. Nobody actually makes a 43mm lens... and 50mm is the next size up. This is why the 50mm is considered the "normal" lens for a 35mm film camera or a full-frame DSLR. A "medium format" camera (such as a 6 x 6cm) would have a diagonal of 84.85mm (about 85mm) and a 6 x 4.5cm medium format has a diagonal of 75mm. So the "normal" lens for those cameras turns out to be an 80mm.

    What IS true is when you use a 28mm lens on a crop-factor camera... you'll see less in your frame then you would if you had used a 28mm lens on a full-frame camera (it's as if someone cropped in on your image... hence the name "crop frame"). And it turns out if you want to see the same area in your frame as a full-frame camera then it would compare to a full-frame camera using a 45mm lens. (btw, if you use the true "normal" for the APS-C camera at 27mm... and multiply that by 1.6x, you get 43mm... which is the true normal for a "full frame" camera... the math works.)

    You *could* take the image shot with the full-frame camera and the 45mm lens... and then just crop the image down to the size that would occupy the middle 27mm of the sensor. And if you did this, you'd get exactly the same image that the crop-camera captured.

    The "crop factor equivalence" is a bit of a misnomer because they aren't really "equivalent". What you end up with is similar framing (and it's not even identical framing because it technically alters the angle of view.) When you compare two camera with different sensor sizes using the "equivalent" lenses (based on crop factors) those lenses are not the same focal length and that means the "circle of confusion" size is different as is the "depth of field". If they were really equivalent then everything would be the same... turns out only the framing is similar.

    The depth of field of a 28mm lens focused to a given distance and using a given f-stop is whatever it is... it doesn't change based on sensor size. If I use a slide projector to project an image onto a projection screen... my "projector" doesn't "know" how large my screen is. But if I swap a larger screen for a small screen, while the "projector" doesn't know I did this... a "human" DOES know I did this. So now the image no longer fits the screen. The "human" compensates either by moving the projector (so the image fits the screen)... or if the projector has a zoom-adjustment on the lens, they can adjust the projection lens (and also re-focuses). If you do this with a crop-frame camera vs. full-frame camera, and either change lenses... or just change how far away you stand from your subject, then you change the depth of field.

    Suppose you wanted to take a shot with the hypothetical 28mm lens at f/2 and your subject is 5' away. You'd expect a certain depth of field. Points of light in the background make little bokeh balls and now you want to get that IDENTICAL shot with the "full frame" camera. You do have to use the a 45mm focal length to get the "normal" angle of view. But now the full-frame camera has too much in the frame, so you compensate by moving the camera closer. When you do this, you change the DoF and focusing on a closer subject results in a shallower DoF. So if you shot that at f/2 you'd have much stronger background blur. The bokeh balls wont be the same size. But if you multiple the f-stop by the crop-factor (1.6x) then 2 x 1.6 = 3.2. If you set your full-frame camera to "f/3.2" and take the shot, you'll get EXACTLY the same look... even the bokeh balls will appear to be precisely the same size (assuming you show the two images side-by-side where the whole frame is the same size.)
     
    • Like Like x 1
    • Informative Informative x 1

Share This Page

Search tags for this page

canon 80d set up for newborn photography