Page 2 of 2 FirstFirst 12
Results 21 to 26 of 26

Thread: f1.8 on full frame = f1.8 on crop frame?

  1. #21

    Default Re: f1.8 on full frame = f1.8 on crop frame?

    Quote Originally Posted by miaoteh View Post
    thanks for the reply, yes i understand about the FOV.

    but my question here is, as what bro aspenx said in his previous reply, taking photo from exactly same spot (same subject distance?), with exactly same settings, same lens (same focal length?), one on FX and on on DX, will give you same DOF. of cause the FOV from both camera will be different in this case.

    but the data from DOF calculator says the DOF will be different.
    Quote Originally Posted by aspenx View Post
    Actual focal length DOES NOT multiply.

    Assuming you have 2 cameras, one full frame and one with a cropped sensor that are both 10MP, have 2 exact same lenses on both cameras, taking the same photo from the exact same spot and settings will give you the same DOF.

    However, if you step forward with your fullframe setup such that the subject takes up the same number of pixels in the pictures as it would on the cropped sensor at the previous position, you will get a more shallow DOF then.

    This topic has been discussed to death several times already. Try doing a search next time...
    Hi,

    I have similar question. I'm using canon so suppose I shoot with a crop sensor (1.6 crop factor) at 10mm compare with shooting with full frame at 16mm; all at same settings. Will DOF be the same? One friend told me that full frame will have shallower DOF relative to crop in such case.

  2. #22
    Member
    Join Date
    Aug 2008
    Location
    here
    Posts
    1,350

    Default Re: f1.8 on full frame = f1.8 on crop frame?

    Quote Originally Posted by miaoteh View Post
    erm, but when i use the online DOF calculator, at same focal length, aperture and subject distance, DX camera will have less DOF than FX camera.

    anyone can explain?
    "Depth of field calculations only involve focal length, distance and the value chosen for circle of confusion and do not include format. Format is only involved insofar as it's a factor in choosing the circle of confusion value."

    Why a cropped sensor and a full frame sensor will have different COC values is beyond me.

    Because of this difference in value, you supposedly get different DOF values with the online calculator. But from what I've tried with D200/D40 and D700...

  3. #23
    Member
    Join Date
    May 2007
    Location
    Florida
    Posts
    1,984

    Default Re: f1.8 on full frame = f1.8 on crop frame?

    Quote Originally Posted by aspenx View Post
    "Depth of field calculations only involve focal length, distance and the value chosen for circle of confusion and do not include format. Format is only involved insofar as it's a factor in choosing the circle of confusion value."

    Why a cropped sensor and a full frame sensor will have different COC values is beyond me.

    Because of this difference in value, you supposedly get different DOF values with the online calculator. But from what I've tried with D200/D40 and D700...
    This is because DOF calculators have to decide on a standard threshold where they can decide what is in focus and what is OOF. This website: http://www.bobatkins.com/photography...al/dofcalc.html gives the standard CoC size
    # 35mm - 30 microns
    # 1.3x DSLR (EOS 1D) - 23 microns
    # 1.5x DSLR (D100) - 20 microns
    # 1.6x DSLR (EOS 10D) 18.75 microns
    # 2x DSLR (E-1) 15 microns

    which means that a spot larger than roughly 1/1200 of the longer dimension is considered OOF. This is actually somewhat arbitrary, and will scale with the FOV and therefore the crop factor. This website gives a more flexible calculator which involves print size and viewing distances: http://www.cambridgeincolour.com/tut...calculator.htm.

    Relating back to the original question of this thread, the same lens used at the same object distance and same f-number will produce exactly the same image on any sensor/film. But depending on what the in-focus criterion is, the calculated DOF will change, even though the image captured could look exactly the same (minus differences in FOV).
    My photos - see just some or all of it =)

  4. #24

    Default Re: f1.8 on full frame = f1.8 on crop frame?

    No it stays at 1.8, I'm to tired to get into the physics of it all.

  5. #25
    Member
    Join Date
    Aug 2008
    Location
    here
    Posts
    1,350

    Default Re: f1.8 on full frame = f1.8 on crop frame?

    Quote Originally Posted by Gengh View Post
    This is because DOF calculators have to decide on a standard threshold where they can decide what is in focus and what is OOF.

    ...

    which means that a spot larger than roughly 1/1200 of the longer dimension is considered OOF. This is actually somewhat arbitrary, and will scale with the FOV and therefore the crop factor. This website gives a more flexible calculator which involves print size and viewing distances: http://www.cambridgeincolour.com/tut...calculator.htm.

    ...

    But depending on what the in-focus criterion is, the calculated DOF will change, even though the image captured could look exactly the same (minus differences in FOV).
    Thanks. I've actually read up on the topic a few times but only understand now.

  6. #26

    Default Re: f1.8 on full frame = f1.8 on crop frame?

    Summary
    If same distance to subject and same focal length, then the dof of apsc and ff will be same (but fov different)

    If same distance to subject and same fov (focal length different), then ff will hv shallower dof than apsc.

Page 2 of 2 FirstFirst 12

Bookmarks

Posting Permissions

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