35 mm Equivalence
 

I think in terms of 35 mm cameras for a "feel" for the angle of coverage for a lens of a given focal length. Here is a table that gives zoom values (Z), zoom ring focal length values (FL) and their 35mm equivalents.

This is based on the camera specs from Panasonic that the shortest focal length, 4.5 mm, is equivalent to 32.5 mm in a 35 mm camera, and the zoom is 10X.

On edit, zounds, I assumed the relationship between Z and focal length is linear. It's not. Back to drawing board, sorry.

Note: This is an edit of the previous post so it makes sense after I discovered my original assumption of a linear relationship between Z (display zoom values) and focal length in mm was wildly wrong.

Moving right along...

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I think in terms of 35 mm cameras for a "feel" for the angle of coverage for a lens of a given focal length. I thought it would be useful to me and perhaps a few others to create a little table of these values. For example, it would be useful to know what DVX100 focal lengths or Z values are the equivalent of the 80-110 mm lenses that are thought to be most flattering to the face for 35 mm portraiture. Little did I know...

I assumed I could take the focal length readings from the zoom ring and Z values from the display and find a fairly simple mathematical relationship that would let me calculate focal length from any Z value so I could present a table that showed not only the focal lengths engraved on the zoom ring but focal length for every ten unit increment of Z values, for example.

Alas, I have plugged the values from my camera into Excel and tried every non-linear equation for curve-fitting readily available in the program and can't find any of them that produces a good fit. Somebody here is probably better at this than I so feel free to jump in, please.

In any case, it is still useful just to present a little table based on the focal lengths engraved on the zoom ring. So here is one from my camera. I would be interested to have others check my data against theirs.

Here is a table that gives zoom values (Z), zoom ring focal length values (FL) and their 35mm equivalents.

The 35 mm equivalence is based on the camera specs from Panasonic that the shortest focal length, 4.5 mm, is equivalent to 32.5 mm in a 35 mm camera, and the zoom is 10X. Thus, the factor to get from the DVX100 focal length to the equivalent in 35 mm is 32.5/4.5 = 7.22

From my camera:
FL---- Z-----35mm

4.5----0-----32.5
6-----18-----43
10----49-----72
20----77----144
45----99----325

I'll print out a graph and manually interpolate some intermediate focal lengths at other Z values later. Looks like Z=52-68 will be good for faces.

BTW, if anybody has already done this little exercise please post so I won't embarass myself further ;-)

BBTW if there is a way to format a table here to make it pretty please let me know since I could not control columns, etc.

Many thanks Steve -- I apologize for the lack of a table format tool on our message boards here. Your data is much appreciated!

Steve,

I actually compiled a similar chart for my own use a few months ago, incorporating the equivalent focal lengths in both the 35mm still and cine formats, using the formula you've used (35mm still lens equivalent = DVX focal length times 7.222, 35mm cine lens equivalent = DVX focal length times 5.55), but then discovered the very handy focal length converter at the Panavision New Zealand site, and got slightly different figures from it, which left me wondering which was more accurate; the Panavision converter or Panasonic's own 32.5-325mm figure. An American Cinematographer article also cites the Panasonic figure, as well as a 25-250mm 35 cine lens equivalent, which doesn't quite reconcile with the figures from Panavision.

Here's the Panavision link:

http://www.panavision.co.nz/main/kbase/reference/tblelenseqvform.asp

The converter allows you to compare focal lengths from umpteen different film, video, and still formats, in whatever increments you choose, plus Angle of View. (Be aware, the Panavision NZ web site is for some reason frequently down, so if the link doesn't work, keep trying).

My big problem was that when inputting the information into the converter, converting the DVX 1/3" chip focal lengths to standard 4:3 35mm, and also to 35mm still lenses, the focal lengths were noticably (though not wildly) different from those cited by Panasonic (32.5.-325), which refer to still photography lenses.

The focal length converter also provides Angle of View information, though how this manifests itself in video lenses, I haven't the slightest idea.

As you'll see, the DVX to 35mm still lens comparison shows the DVX lens to be equivalent to a 30-300 lens, rather than the 32.5-325 lens Panasonic's figures claim. I've heard before that focal length figures for any given lens, particularly with regards to lower-end equipment like consumer video cameras and digital cameras, are accurate to within 5mm, which I guess could explain that variance between Panasonic's figures and those from the focal length conversion. Or perhaps I made some mistake.

When you input Panasonic's figures and compare them to 1/3 video, you get a 5-48mm lens, which is slightly off from the DVX's 4.5-45 marked focal lengths. How much of a practical difference this makes, I couldn't say. I would like to know for sure which figures are correct, or whether there is indeed some expected deviation, plus or minus the stated figures.

Anyone with more information on this issue, please chime in.

Here are the results for the 1/3" CCD to 35mm Academy aperture 4:3:

Video 1/3" TV 4:3 4:3 CCD Sensor AOV
Diagonal Std 35mm TV 4:3 TV Trans

DVX--------AOV-------Std. 35
4.5 mm----67.4°-----18.9 mm
9.5 mm----35.1°-----39.8 mm
14.5 mm---23.4°-----60.8 mm
19.5 mm---17.5°-----81.7 mm
25 mm-----13.7°-----105 mm
30 mm-----11.4°-----126 mm
35 mm------9.8°-----147 mm
40 mm------8.6°-----168 mm
45 mm------7.6°-----189 mm

And here are the results of comparing the DVX to 35mm still lenses:

Video 1/3" TV 4:3 4:3 CCD Sensor AOV
Diagonal Photographic 35mm Negative Image

DVX----------AOV------35mm still
4.5 mm------67.4°-----30 mm
9.5 mm------35.1°-----63.3 mm
14.5 mm----23.4°-----96.7 mm
19.5 mm----17.5°----130 mm
25 mm------13.7°----167 mm
30 mm------11.4°----200 mm
35 mm-------9.8°----233 mm
40 mm-------8.6°----267 mm
45 mm-------7.6°----300 mm

All focal lengths greater than 20mm rounded to nearest whole number.

Finally, here's my own chart featuring the DVX focal lengths and their equivalents to both 35mm film and still lenses. I haven't yet filled in the LCD readout numbers corresponding to each of the lengths marked on the lens itself (as well as some intermediate unmarked lengths to correspond to standard 35mm focal lengths, like 50mm). As you can see, this chart uses the figures I got from the Panavision converter, and not the 32.5-350 figures Panasonic quotes.


DVX----DVX lcd---35mm cine--35mm still
4.5-----50------------18.9--------30
6---------------------25----------40
10--------------------40----------66.7
12--------------------50----------80
18--------------------75----------97.5
20--------------------83.8-------133
24-------------------100---------160
36-------------------150---------240
45-----99------------189---------300


Hope all these numbers are of some use to someone :)