How do i know how wide my lens is??

Discussion in 'Photography Beginners' Forum' started by shorty6049, Mar 21, 2007.

  1. shorty6049

    shorty6049 TPF Noob!

    Joined:
    Mar 8, 2007
    Messages:
    1,906
    Likes Received:
    1
    Location:
    Minnesota
    Can others edit my Photos:
    Photos OK to edit
    So i was talking to a friend and we were discussing lenses (wide angle more specifically) and i came apon the realization that the focal length doesnt necessarily determine the "wideness" of a lens. for example, my sony 18-70 is not as wide as a 20mm Sigma lens... the difference is about 45 degrees to 90degrees , respectively, so can anyone explain how to figure out how wide a lens is? or do i just have to look in the specs for each lens to get that info?
     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

    Joined:
    Dec 16, 2003
    Messages:
    33,821
    Likes Received:
    1,811
    Location:
    Edmonton
    Can others edit my Photos:
    Photos NOT OK to edit
    What do you mean by 'wideness'? The field of view?

    It is determinded by the focal length and your 18-17mm should have a wider view (at 18mm) than your 20mm...(assuming both are on the same camera).
     
  3. shorty6049

    shorty6049 TPF Noob!

    Joined:
    Mar 8, 2007
    Messages:
    1,906
    Likes Received:
    1
    Location:
    Minnesota
    Can others edit my Photos:
    Photos OK to edit
    yeah, by wideness i meant field of view, sorry i forgot to specify that... I ask that because on sony's website, it says that my 18-70 has a FOV of 45 degrees at its widest, and the sigma site says thier 20mm has a FOV of 94.5 degrees.... it says its made for digital, so i would assume that means that the FOV that they give is for a common digital sensor? i'm so confused
     
  4. shorty6049

    shorty6049 TPF Noob!

    Joined:
    Mar 8, 2007
    Messages:
    1,906
    Likes Received:
    1
    Location:
    Minnesota
    Can others edit my Photos:
    Photos OK to edit
    i emailed Sigma , so they should help me get this straightened out, if anyone else knows anythign about this please give me your advise though, thanks!
     
  5. HASHASHIN

    HASHASHIN TPF Noob!

    Joined:
    Mar 1, 2007
    Messages:
    414
    Likes Received:
    0
    Location:
    NYC
    Can others edit my Photos:
    Photos OK to edit
    :thumbup:
     
  6. shorty6049

    shorty6049 TPF Noob!

    Joined:
    Mar 8, 2007
    Messages:
    1,906
    Likes Received:
    1
    Location:
    Minnesota
    Can others edit my Photos:
    Photos OK to edit
    is there any crazy way that that could be wrong though? i dont get why sony's site would say their lens only had a 45 degree FOV if all of sigmas lenses in that area are around 90 degrees.... its not common for them to give FOV isn one direction from the normal (perpendicular) is it?
     
  7. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

    Joined:
    Dec 16, 2003
    Messages:
    33,821
    Likes Received:
    1,811
    Location:
    Edmonton
    Can others edit my Photos:
    Photos NOT OK to edit
    I see the confusion...the Sony is designed for digital camera with a smaller sensor (APS-C)....while the Sigma 20mm is designed to be used on 35mm film SLR cameras (but of course it can also be used on the digital cameras as well).

    So actually, the Sigma does have a much wider field of view...but you won't see that on your camera because your camera (with it's smaller sensor) will effectively 'crop' the image that comes though the lens.

    That's why I said "assuming both are on the same camera". So to figure out the effective field of view of the Sigma, on your camera, you have to figure in the 'crop factor'...it's 1.5.
     
  8. shorty6049

    shorty6049 TPF Noob!

    Joined:
    Mar 8, 2007
    Messages:
    1,906
    Likes Received:
    1
    Location:
    Minnesota
    Can others edit my Photos:
    Photos OK to edit
    well 94.5/1.5 is still 63 , so that still would suggest a larger FOV ....
     
  9. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

    Joined:
    Dec 16, 2003
    Messages:
    33,821
    Likes Received:
    1,811
    Location:
    Edmonton
    Can others edit my Photos:
    Photos NOT OK to edit
    The 1.5 factor is applied to the focal length, from there you should be able to calculate the field of view. The 1.5 is the comparison factor...it compares 35mm film to your camera.

    Really, I don't think it matters...the fact is that a shorter focal length has a wider view (on the same camera).
     
  10. shingfan

    shingfan TPF Noob!

    Joined:
    Dec 29, 2006
    Messages:
    569
    Likes Received:
    0
    Location:
    Toroto, ON
    Can others edit my Photos:
    Photos OK to edit
    the crop factor is not a linear factor to all aspect of a lense.....dont overuse it.....it is merely use as a represention of the focal lenght on digital cameras compare to 35mm film cameras......as mike said.....18mm should provide a wider FOV compare to a 20mm on the same digital camera......

    if you compare a picture taken at 100mm and a picture taken at 200mm.....you wont see a 2x dimension on the 200mm.....instead.....what difference you see would be the change in overall area....i suspect the area is 2 times as big compare to the 100mm (i have not verify this)
     
  11. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

    Joined:
    Aug 25, 2003
    Messages:
    7,021
    Likes Received:
    34
    Location:
    Lawrence, KS
    Can others edit my Photos:
    Photos NOT OK to edit
    Google "FOV calculator" or "field of view calculator", and look for one that allows you to choose various formats or cameras. You also have to pay attention to whether it is giving you the field of view horizontally or from corner to corner.
     
  12. shorty6049

    shorty6049 TPF Noob!

    Joined:
    Mar 8, 2007
    Messages:
    1,906
    Likes Received:
    1
    Location:
    Minnesota
    Can others edit my Photos:
    Photos OK to edit
    ok, thanks everyone
     

Share This Page

Search tags for this page
how do i know how wide my lens is?
,
how do i know my lens is a wide angle lens?
,
how do i know what is my lens is
,
how do u know how wide your lens is
,
how to tell how wide my lense is
,
how to tell how wide your lens is
,
how wide is my camera lense
,

how wide is my lens

,
how wide is my lrns
,
what size lans is the jc penny p 42 macro lens