Page 4 of 18 FirstFirst 1234567814 ... LastLast
Results 31 to 40 of 178
  1. Collapse Details
    #31
    Senior Member
    Join Date
    Aug 2006
    Location
    Colorado Springs
    Posts
    473
    Default
    Actually, comparing a single dimension is the more valid way to calculate crop factor, you just have to pick the right one to compare. Decide on an aspect ratio, crop image area(s) to match that aspect ratio, and then take the ratio of the vertical, horizontal, or diagonal dimensions - all will yield the same answer. For example, if you crop 35MM FF (24mm x 36mm) to have a 16:9 aspect ratio you get an image size of 20.25mm x 36mm. Whether you compare the diagonals, the verticals, or the horizontals you get the same answer - a crop factor of 1.89. So the easiest way to do it is to compare whichever dimension - horizontal or vertical - which is not cropped to achieve a common aspect ratio (assuming you pick one or the other's native aspect ratio). If you are interested in 35mm FF aspect ratio (3:2) the crop factor becomes 2.24 because it is the vertical dimension which is not cropped (24/10.7). If you are interested in ND 16:9 aspect ratio the crop factor becomes 1.89 because it is the horizontal dimension which is not cropped (36/19).

    If you are comparing with an academy 33mm motion picture frame, you get two different answers depending on which aspect ratio you choose. If you want the academy 35mm aspect ratio it is calculated by comparing vertical sizes (because the horizontal one has to be cropped on the GH2); the crop factor is 16/10.7 = 1.5. If you want the HD 16:9 aspect ratio the ratio is calculated by comparing horizontal sizes (because the vertical one has to be cropped on the academy 35mm camera); the crop factor is is 22/19 = 1.16.

    Arguably, the worst way to calculate crop factor is to use the ratio of diagonals if the aspect ratios do not match.

    Let's do the comparison everybody is actually interested in - that is, what is the GH2 crop factor compared to IMAX? If you crop the GH2 sensor to match the IMAX aspect ratio of 1:1.33783 (I'm assuming you are interested in including GH2 footage in your IMAX movie), the GH2 crop factor becomes 4.92!
    Last edited by cbrandin; 12-31-2011 at 05:56 PM.


    Reply With Quote
     

  2. Collapse Details
    #32
    Default
    The dimension used to calculate a crop factor is ALWAYS the Diagonal because the diagonal defines the image circle and the angle of view and the focal distance of a lens relative to its sensor. So wneh comparing GH2 to a full frame STILL (not 5D for video) the crop factor will be 2x. the full frame STILL diagonal is 43,2mm and 43,2 / 21,6 = 2 So a 50mm still lens will be 100mm in GH2


    Reply With Quote
     

  3. Collapse Details
    #33
    Senior Member David W. Jones's Avatar
    Join Date
    May 2010
    Location
    La Petite Roche
    Posts
    6,742
    Default
    No a 50mm lens in a GH2 is still a 50mm lens.


    Reply With Quote
     

  4. Collapse Details
    #34
    Senior Member
    Join Date
    Sep 2011
    Posts
    188
    Default
    Quote Originally Posted by David W. Jones View Post
    No a 50mm lens in a GH2 is still a 50mm lens.
    I'm sure there is some sort of point you are trying to make here, but I think I missed it.

    My 50mm Nikkor on a GH2 has a vastly different FOV than it did on the camera it was originally designed and purchased for. Heck, on my old Canon it was roughly the equivalent of an 85mm- on the GH2 it is even deeper.

    I know you've been around long enough to know that, so I'm assuming there is some sort of point you are trying to make here- maybe I'm just not seeing it?

    Meanwhile, the point I think being made by others is that when comparing crop sizes on digital bodies, 35mm film has always been the standard by which they are judged. Because, when it all boils down, these are supposed to be replacements for STILL cameras. They happen to take excellent video, but anyone discussing adapters, lenses, crop factors, etc, will always be comparing to 35mm equivalents. Saying that we should be comparing to s35 cinema film is just going to create a lot of confusion.

    Maybe YOU only use your camera for video... but search for discussion about crop sizes on the internet, you'll undoubtedly stumble into a photography forum discussing the FOV of a 50mm on a cropped sensor. And I can guarantee you they are not comparing it to cinema film sizes. So why are folks trying to complicate the matter by using a completely different reference set? We should all be using the same universal language and just get along!


    Reply With Quote
     

  5. Collapse Details
    #35
    Default
    a 50mm lens will always be 50mm in all cameras, but what changes it the EQUIVALENT do 35mm STILL. In GH2 a 50mm lens is EQUIVALENT to a 100mm in full frame STILL


    Reply With Quote
     

  6. Collapse Details
    #36
    Senior Member David W. Jones's Avatar
    Join Date
    May 2010
    Location
    La Petite Roche
    Posts
    6,742
    Default
    Like I said, a 50mm lens is always a 50mm lens, it doesn't matter what camera you mount it to. It is always a 50mm lens! The field of view from said lens will be determined by the sensor size but the lens does not magically become a 100mm when mounted to a M4/3 camera.


    Reply With Quote
     

  7. Collapse Details
    #37
    Filmmaker's Mod
    Join Date
    Dec 2005
    Posts
    17,389
    Default
    I've always been confused on FOV and AOV, but I think even the FOV of a 50mm is also still the same, but the AOV changes due to the sensor size?

    I'm pleading ignorance on this one. Just can't remember.
    Comet Color Page
    Allow me: fanboy of great images.



    Reply With Quote
     

  8. Collapse Details
    #38
    Default
    both FOV (field of view) and AOV (angle of view) changes relative to sensor size. The rule is: take the lens focal lenght and multiply it by the crop factor.

    Example (for GH2 and 35mm STILL, crop factor 2)

    lens focal lenght = 50mm
    crop factor = 2
    50 x 2 = 100mm (equivalent to 35mm still when used in GH2)


    Reply With Quote
     

  9. Collapse Details
    #39
    Senior Member GrahamH's Avatar
    Join Date
    Feb 2010
    Location
    Knoxville, TN
    Posts
    950
    Default
    Quote Originally Posted by Apefos Adapter View Post
    a 50mm lens will always be 50mm in all cameras, but what changes it the EQUIVALENT do 35mm STILL. In GH2 a 50mm lens is EQUIVALENT to a 100mm in full frame STILL
    And just to be über-pedantic, we need to specify we talking about equivalent to the FOV of a 100mm. Some folk talk about "equivalents" in discussions of depth of field, which is different again.


    Reply With Quote
     

  10. Collapse Details
    #40
    Senior Member
    Join Date
    Jan 2006
    Location
    Studio City, CA
    Posts
    2,176
    Default
    Quote Originally Posted by dishan View Post
    I'm sure there is some sort of point you are trying to make here, but I think I missed it.

    My 50mm Nikkor on a GH2 has a vastly different FOV than it did on the camera it was originally designed and purchased for. Heck, on my old Canon it was roughly the equivalent of an 85mm- on the GH2 it is even deeper.

    I know you've been around long enough to know that, so I'm assuming there is some sort of point you are trying to make here- maybe I'm just not seeing it?

    Meanwhile, the point I think being made by others is that when comparing crop sizes on digital bodies, 35mm film has always been the standard by which they are judged. Because, when it all boils down, these are supposed to be replacements for STILL cameras. They happen to take excellent video, but anyone discussing adapters, lenses, crop factors, etc, will always be comparing to 35mm equivalents. Saying that we should be comparing to s35 cinema film is just going to create a lot of confusion.

    Maybe YOU only use your camera for video... but search for discussion about crop sizes on the internet, you'll undoubtedly stumble into a photography forum discussing the FOV of a 50mm on a cropped sensor. And I can guarantee you they are not comparing it to cinema film sizes. So why are folks trying to complicate the matter by using a completely different reference set? We should all be using the same universal language and just get along!
    Well, then I'd say you should go to the photography forums and discuss crop factor with full frame sensors there. The vast majority (meaning nearly all) discussion here is regarding shooting video, so therefore we should be talking about crop factor when shooting video and comparing to S35 not FF35.

    I don't think anyone is disputing the 1.9x 2.0x or 2.1x (or whatever it is) crop factor when comparing to the 5D or any other full frame-sized sensor. But really that crop factor has no bearing when you shoot with video because full frame is not the standard for shooting movies, Super 35 is. I really don't understand why no one gets this.

    And as far as the image circle of the lenses goes and a still lens having a different image circle than a cinema lens, yes that might be possible, but the image circle of lenses is vastly more difficult to find out than sensor or frame sizes. A lot, actually most, lens manufacturers don't publish the image circle size. However if you take a still lens and put it on a GH2 and a Scarlet, and then take a cinema lens and put it on a GH2 and Scarlet, both lenses will have the same crop factor when comparing the GH2 to the Scarlet. And plenty of people are using still lenses on larger sensor cameras than the GH2, and plenty (not as many as the other obviously though) of people are using cinema lenses on the GH2 and other DSLRs. So a still lens isn't just a still lens anymore. They are being used for shooting video and movies in great numbers now. So you really want to determine crop factors by comparing sensor size only, otherwise it gets tremendously more confusing for people than it clearly already is. Not every 50mm still lens has the exact same image circle, and not every 50mm cinema lens has the exact same image circle either.



    Reply With Quote
     

Page 4 of 18 FirstFirst 1234567814 ... LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •