FX1 Lens REALLY 4.5 mm-54 mm F/1.6-2.8 ?

[Dave Allen]

I have an FX1, and I am fairly familiar with the field of view and zoom/lens strengths.

I often put a .6 wide angle adapter on it, other times a +4 magnification diopter.

But numerically, 4.5 mm seems ridiculously wide angle, yet zoomed all the way in, there is no way I am getting a field of view equivalent to a 4.5mm lens, which would seem fisheye wide.

I am trying to match field of views and zoom strengths from the FX1 to the new FS700.

[Adam Gold]

Well, no, 4.5mm is the wide end. Zoomed all the way in, it's 54mm.

According to the manual, the wide end is the equivalent of a 32.5mm lens on a 35mm still cam, which is hardly what you'd call fisheye. I used a 28mm WA on my 35mm film still cams all the time because we always considered them the limit to how wide you could easily go without showing any distortion at all.

The tele end is the equivalent of 390mm in 35mm terms.

P. 98.

Remember, focal length isn't the only variable.

Anyhow, the answer is yes.

[Adam Gold]

Just noticed your question about this lens on your other thread:

Originally Posted by Dave Allen

I am not sure why they call the FX1/Z1 lens a "4.5-54mm", then list this; "for 35mm Conversion 32.5-390mm"

Then add "12x zoom" into the mix.

...so it appears maybe you don't quite understand zoom lenses and field of view (and their relationship to chip size) as much as you think.

The actual physical focal lengths of the lens on the FX1 are 4.5-54mm. It is a zoom lens, which means the focal length is variable from 4.5 to 54mm as you turn the ring.

4.5 x 12 = 54 (or more accurately, 54/4.5 = 12, or 54:4.5 = 12:1), so it is a 12x Zoom. "Zoom" is simply a word used to describe any variable-focal-length lens, and the "12x" is the way all lens mfrs describe the ratio of the widest end to the most telephoto end.

But these number are meaningless because much also depends upon the sensor or film size -- basically the size of the actual imaging device or image itself projected by the lens onto the focusing plane -- the actual picture. 35mm film is a much bigger image than the relatively small image on the 1/3" sensor on the FX1 or any vid camcorder of its generation, so the differing image sizes relative to the chip thrown by every lens of a given focal length has to be put into apples to apples terms. Because an image that might look very wide on a full 35mm frame would look very telephoto tight if projected at the same size onto a tiny 1/3" chip, right? Only a small portion of this large image would fit onto this smaller chip, right?

Picture it this way: You are looking at a projected image on a screen. Overlay a tic-tac-toe frame over it. The whole screen is a 35mm film/chip, and the center "square" is your FX1 chip. It's 1/9 of the total picture but appears to be hugely zoomed in. Your lens has the same focal length but appears to be hugely telephoto.

So Sony and many other mfrs express the focal lengths in 35mm terms as an equalizer so you can compare them. Why 35mm? Because for a million years it was the standard for still photography and everyone had a camera that shot 35mm film (and pros shot 35mm movie film too [although it goes through the camera differently and the frame isn't exactly the same], and many still do) and it was a common frame of reference and everyone understood it and the lenses that went with these cameras. That's why they list the 35mm equivalent. If a lens with the same field of view as the FX1's were on a 35mm still camera, it would be a 32.5-390mm lens, which is still a variable focal length 12x zoom lens.

If you were comparing your FX1 to, say, the FX7, you'd see that the latter has a 20x 3.9-78mm lens. Cool, you'd say, the 7 goes both longer and wider, right? Maybe yes, maybe no, because the 7 has a 1/4" chip, so now you don't really know, do you? But a look at the manual further reveals that the 35mm equivalent is 37.4-748mm. So while it does go hugely longer at the tele end (in fact it's one of the longest native tele ends ever made, but remember you didn't know that until you looked at the 35mm eq number -- the "20x" figure means nothing really unless you know where it starts) you can now see it isn't really wider after all, even though the focal length is physically shorter, because it's being projected onto a smaller chip.

Originally Posted by Dave Allen

... zooming to the far end of a 27-50mm equivalent zoom does not even come close to reaching out far. I know there is a mathematical reason why they use conflicting figures, and probably some marketing reasons too, lol.

In the 35mm world, a 50mm lens is considered "normal"; that is, neither tele nor wide. 32mm is wide but not very. As we note above, 27mm is pretty wide but not close to fisheye; you shouldn't have much if any distortion. Really wide, for group shots and such, would be below 25mm (in my experience, unless you want to have to back up a lot outdoors or keep bumping into walls inside). "Portrait" lenses -- where you can get a little closer so their torsos fill the frame but you're not creeping them out because you're standing too close -- are 85-115mm. Real tele doesn't begin until 200mm and if you're doing sports, I haven't found much useful less than 500mm eq. But these are just my personal preferences.

So based on what we now know about 35mm eq, this is the closest you're going to find to your FX1's lens:

http://www.bhphotovideo.com/c/product/913563-REG/sony_selp_18200_18_200mm_f_3_5_6_3_pz_oss.html

...which is obviously the one referred to in the other thread.

Originally Posted by Dave Allen

I just can't figure out why Sony can make a 32-390 lens for their FX1/Z-1 that always nails autofocus, the lens does not rotate, the lens does not extend upon zoom, and focus is internal. Why can't they make a lens like that for the FS700?!

Because the lens is permanently attached to a huge camcorder body, which is where both the brains and the mechanics/power for the lens mostly reside. With interchangeable lenses, they don't know what cam it's going to be paired with so the design is completely different and much of those functions have to be onboard the lens itself. It's completely unrealistic to think they can perform the same in that regard. On the other hand, the optics are quite likely better.

To add yet another layer of complexity and answer a question you didn't ask, the f-stop is variable because while they try to maintain the same stop as the lens zooms, at a certain point the aperture can't physically go wide enough to maintain the same f or t number as the focal length gets really big. This is why nearly all zoom lenses have a range with smaller f-stops/t-stops (larger number = smaller aperture) at the longer end. F-stops are real numbers, not theoretical; they are an actual ratio of the physical aperture size divided into the actual physical focal length. So the diameter of the lens barrel limits how wide the aperture can physically go when focal lengths get up to, like, a million. So your FX1 lens can go as wide ("Fast") as F1.6 at the wide end but only F2.8 when zoomed all the way to the tele end. The aperture is physically wider when zoomed in all the way, but as a ratio of the diameter of the opening into the focal length, the opening is a smaller fraction.

Hope this doesn't come off as too pedantic and condescending, and hope it clears up the confusion for you. The figures aren't really conflicting any more than feet and meters are. They're complementary -- just different ways of expressing the same thing.

Want to see a really cool lens? Here's what they use at Sporting Events:

http://www.bhphotovideo.com/c/product/887615-REG/Canon_xj100x9_3b_af_lo_XJ100X9_3B_Digital_Zoom_Lens.html

Now THAT'S a lens.

[Dave Allen]

Adam

A more accurate statement would have been: "I know even less than you think I do"! lol. I figured if I laid my soul bare as unworthy, someone who actually knew the math would reply at some point somewhere.

I can just picture it now: "One just needs to take the 4:4:4 pull down and debayer it before the pulldown conversion algorithm as according to REC709...." at which point my eyes start to glaze over into a porcine like stupor and all I can get out of my lips is a barely audible; "Uh, yeah, what he said". ;)

You did outdo my expectations though as that was a very helpful and appreciated reply. Now if only an A or E mount lens in that zoom range existed that does not barrel extend upon zoom as I sure can't find one. Oh, and preferably not priced nor sized like that Canon $200k low budget wonder!

Thanks again! :)

[Adam Gold]

I think that if what you are asking for were possible, the lens would already be in the "extended" form and would only appear to be not extending externally when zooming.

Why does it matter?