Fatford Loc: Rock Hill, South Carolina

Is there a place that I can learn what the conversion is between the digital lens focal length and the focal length of the traditional film camera lenses?

Linda From Maine Loc: Yakima, Washington

Here is one article. Someone else will probably find a better one.

http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm

Full frame digital cameras have the same angle of view as 35 mm film. It's the point n shoot, bridge cameras, and APS-C cameras (crop sensor) that make us crazy :)

SharpShooter Loc: NorCal

There is no difference. They are one and the same.
The focal length of a lens is not tied in any way to its actual physical length. Teles are shorter than simple long lenses, but by design, not by whether they are film or digi.
A lens' focal length is actually the field of view seen by that lens as compared to ISO std. master optics fields of view, nothing more.
Or maybe I misunderstood your question?! ;-)
SS

SnappyHappy Loc: Chapin, SC “The Capitol of Lake Murray”

The focal length of a lens is identified on the lens, that is the exact focal length. Some digital cameras are full frame, some are smaller "crop" sensors. A lens mounted on a full frame camera has an effective focal length equal to the focal length marked on the lens. The same lens mounted on a crop sensor camera will have an effective focal length of the lens focal length multiplied by the crop factor of the camera sensor. The lens remains the same on both cameras, but the reduced image size of the crop sensor forces the image to be enlarged by the amount of crop factor when viewed.

As I re-read my statement I sounds as much like a legal disclaimer as an answer to your question. I hope it helps.

f8lee Loc: New Mexico

I am going to try to take a different tack here...

In the good old days of film, you had 35MM and 120 roll as well as sheet film cameras, right? And depending on the size of the film format, a "normal" lens could be a 50MM (on 35Mm film), or an 80MM on your Hasselblad or even 150MM on your 4x5 view camera.

The reason for this is that it is the combination of focal length and imaging area that defines the angle of view, and that's what matters.

When DSLRs first came along, due to the manufacturing limitations of making the imaging chips, they took the form of film SLR cameras but essentially used smaller "film". But so many photographers were familiar with the notion that a 50MM lens is "normal" that the marketing flacks decided to keep thing simpler by creating a term called "crop factor", which is merely a way of guesstimating the angle of view of a given focal length (which does not change in a lens) on a different sized chip.

So, on a so-called "full frame" digital camera, which has a sensor that is the same 24x36MM dimension that a frame of 35MM film exposed in days of yore, that 50MM lens still has the "normal" angle of view.

On the smaller-chipped cameras, which Nikon calls DX (I forget what Canon calls theirs), this "factor" is 1.5 due to that smaller size imaging chip. So multiple that 50MM by 1.5 and it tells you that on the DX camera, that same 50MM lens will give the angle of view of what a 75MM lens will show on the full frame model. Or a 300MM lens will give an angle of view that would require a 450MM lens on a full frame camera.

Micro 4/3's cameras have a crop factor of 2, so on that kind of camera that same 50MM lens would "see" the equivalent of what a 100MM lens would view on a full frame digital camera.

I hope that makes some sense.

BHC Loc: Strawberry Valley, JF, USA

It might be easier to say that the perceived focal length of any lens is nothing more than a difference in the field of view of that lens based on sensor size. We both know, and I'm sure we agree, that a 100mm lens is a 100mm lens is a 100mm lens - no matter what camera its on. I'm glad you used the term "effective focal length"; too many people ignore or do not understand the importance of the word "effective"!

And your reply was not nearly long enough to be mistaken for a legal disclaimer.

rmalarz Loc: Tempe, Arizona

The focal length of a lens doesn't change, regardless of whether you use in on a digital or film camera.
--Bob

Fatford Loc: Rock Hill, South Carolina

Thank you all for your replys.
This information was very helpful, as was the Cambridge Colour website.

aellman Loc: Boston MA

As usual, Wikipedia comes through. Scroll down to the "Common Crop Factors" table. https://en.wikipedia.org/wiki/Crop_factor

jerryc41 Loc: Catskill Mts of NY

Yes, it can be confusing. Since everyone thinks in terms of 35mm lenses, camera makers should describe their focal lengths in those terms. "20X" mean nothing.

wilsondl2 Loc: Lincoln, Nebraska

Are you talking 35 mm film cameras? If so you need to check whatever camera you are using for a crop factor. Then multiply the true focal length of the lens by that factor and you will get the field of view that the lens would have on a 35 mm camera. I would recommend just putting the different lenses on the camera and see what the view is and then when you need that view use that lens. - Dave

boberic Loc: Quiet Corner, Connecticut. Ex long Islander

You mentioned- normal lens. In 35mm cameras "normal" is a 50mm prime lens. The reason 50mm is "normal" because it aproximates the eye's angle of veiw. For full frame digital cameras normal is still 50mm, For crop sensor cameras, normal would be 35mm. For Nikon(1.5 crop) that would equate to about 52mm and for Canon (1.6 crop) about 56mm. Butas has been said a 50mm lens is the same redardless of which camera it is attached to.

amfoto1 Loc: San Jose, Calif. USA

I agree with much of the above...

Focal length doesn't change from one format to another. What does change is how any given format "behaves"... the angle of view it renders will differ, depending upon format.

Here's a little secret... If you only ever use one format (such as so-called and common "APS-C crop sensor" )... IT DOESN'T MATTER. All you need to do is learn what serves as wide, standard and telephoto for that particular format, won't need to do an math at all, and can simply forget about the other formats.

It only becomes important if, say, you are switching from one format to another. For example, perhaps you shot 35mm film in the past and now are buying an APS-C camera and want to determine what lenses to buy that will most closely match those you used with your old camera. It also can be important if you use more than one format, such as APS-C and so-called "full frame" digital, which is possible because some systems offer both (currently Nikon, Canon and Sony) and a lot of the lenses available can be shared back and forth between them.

In general, if you have an APS-C crop sensor cameras, you can use BOTH lenses made especially for those AND full frame capable lenses on the cameras. On the other hand, if you have a full frame camera, you'll be a little more limited, only able to use that camera with, or to its fullest potential with full frame capable lenses (Note: some camera systems allow using crop-design lenses on their full frame cameras, but that's like shooting yourself in the foot... you bought full frame for it's imaging capabilities, which become seriously limited when it's restricted by putting a crop only lens on it).

BebuLamar

Fully agreed except that the M4/3 and 4/3 were not designed based on the 35mm SLR and thus we shouldn't say that it has a crop factor of 2 but rather the normal lens for M4/3 is 25mm. Just like you said the normal for 6x6 is 80mm and 4x5 is 150mm. By the same token the medium format digital since they have sensors smaller than 6x6 or 6x4.5 but using the lens system based on 6x6 or 645 then we can say those have a crop factor.

anotherview Loc: California

Agree: