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Old Jan 4, 2011, 10:14 AM   #1
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Default question about FA vs DA lenses

Hi everyone!

Just curious, if I buy a 35mm FA lens and use it on my KX, then I must multiply with 1.6 to get the "real" focal lenght? correct?
But if I buy a 35 DA lens, then it really is 35mm focal length?

Is this how I should think when buying lenses? so if I wanted a 400mm lens then I could buy a 300 FA lens instead?
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Old Jan 4, 2011, 12:50 PM   #2
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Originally Posted by CyberTron View Post
Hi everyone!

Just curious, if I buy a 35mm FA lens and use it on my KX, then I must multiply with 1.6 to get the "real" focal lenght? correct?
But if I buy a 35 DA lens, then it really is 35mm focal length?

Is this how I should think when buying lenses? so if I wanted a 400mm lens then I could buy a 300 FA lens instead?
Hi Michael,

The simple answer is that for DSLRs the FL specified on the lens is always the true FL. There is no "crop factor" automatically applied to the specs of any lens suitable for 35mm film, APS-C, or 4/3 DSLRs. All camera and 3rd party lens manufacturers only use true focal length to describe their lenses in all model series. Lenses that are either optimized for digital or designed for the APS-C image circle only differ in the coatings for digital sensors, or the size of the image that is projected at the sensor plane respectively. Focal length is not effected. Specifically, an FA* 300/4.5 will give you the same magnification and Field of View that your DA 55-300 does at the long end, and the DA35 will give you the same coverage as your DA 18-55 does when set at 35mm.

Unless you are very used to the Field of View provided by a 35mm film camera, or need reference to the 35mm equivalents provided by P&S cameras, I think you'd be best served forgetting about "crop factor" and use the actual focal length of the lens with your experience with how a given FL will look in your Viewfinder as reference. You have FL ranging between 18mm-300 at your disposal, so you know how all of that looks. . .

If you read old articles or books where the author is talking about lens FL suitability and his reference camera is a 35mm film camera, then the crop factor may be relevant -- You'd multiply by 1.5 to get the APS-C equivalent. The very general usage FL ranges for APS-C are less than 18mm is ultra wide, under 28mm is wide angle, 28-40 is "normal", and over 40 is telephoto, with over 200mm as ultra tele. The APS-C "portrait" range is generally considered to be 50mm to 85-100mm.

Though I shot 35mm film for close to 40 years, I haven't even looked through a 35mm viewfinder for over 6 years, and the reference no longer has any practical meaning for me -- I've standardized my reference to APS-C as that will be my shooting format for the foreseeable future.

"Crop factor" has been, and probably will continue to be, a major source of confusion. The FL "equivalents" are not really equivalent technically. The most apparent aspect -- the size of a given subject in relation to the frame captured, or Field of View is equivalent, but some other photographic factors like Depth of Field and Perspective/Depth compression are not.

There are some great articles on crop factor, DOF and photographic perspective on the Web which explain these much better than I could -- If you want to pursue these further, Google is your friend.

Scott

Last edited by snostorm; Jan 4, 2011 at 12:59 PM.
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Old Jan 4, 2011, 1:16 PM   #3
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Hi Michael,

The simple answer is that for DSLRs the FL specified on the lens is always the true FL. There is no "crop factor" automatically applied to the specs of any lens suitable for 35mm film, APS-C, or 4/3 DSLRs. All camera and 3rd party lens manufacturers only use true focal length to describe their lenses in all model series. Lenses that are either optimized for digital or designed for the APS-C image circle only differ in the coatings for digital sensors, or the size of the image that is projected at the sensor plane respectively. Focal length is not effected. Specifically, an FA* 300/4.5 will give you the same magnification and Field of View that your DA 55-300 does at the long end, and the DA35 will give you the same coverage as your DA 18-55 does when set at 35mm.

Unless you are very used to the Field of View provided by a 35mm film camera, or need reference to the 35mm equivalents provided by P&S cameras, I think you'd be best served forgetting about "crop factor" and use the actual focal length of the lens with your experience with how a given FL will look in your Viewfinder as reference. You have FL ranging between 18mm-300 at your disposal, so you know how all of that looks. . .

If you read old articles or books where the author is talking about lens FL suitability and his reference camera is a 35mm film camera, then the crop factor may be relevant -- You'd multiply by 1.5 to get the APS-C equivalent. The very general usage FL ranges for APS-C are less than 18mm is ultra wide, under 28mm is wide angle, 28-40 is "normal", and over 40 is telephoto, with over 200mm as ultra tele. The APS-C "portrait" range is generally considered to be 50mm to 85-100mm.

Though I shot 35mm film for close to 40 years, I haven't even looked through a 35mm viewfinder for over 6 years, and the reference no longer has any practical meaning for me -- I've standardized my reference to APS-C as that will be my shooting format for the foreseeable future.

"Crop factor" has been, and probably will continue to be, a major source of confusion. The FL "equivalents" are not really equivalent technically. The most apparent aspect -- the size of a given subject in relation to the frame captured, or Field of View is equivalent, but some other photographic factors like Depth of Field and Perspective/Depth compression are not.

There are some great articles on crop factor, DOF and photographic perspective on the Web which explain these much better than I could -- If you want to pursue these further, Google is your friend.

Scott
ok, so if I take my old rokina lens at 50mm and then take my DAL 18-55 and set it to 50mm it should look the same.

and if I buy the FA 50/1.4 it will be roughly the same as DA 50/2.0 (except for aperture)
The FA50 is cheaper and has gotten great review...

Thanks Scott for explaining it to me!! it helps alot when I will be buying lenses the next time!
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