Physics for the Brainiacs

Okay, ladies and gents, put your thinking caps on and educate me, the village idiot.

As the focal length of a lens increases, the field of view narrows.

Have I got that right?

If I do, what, if anything, can be done to eliminate that?

Hold the kudos, as I came up with this in my sleep and woke up to run down here and post it.

Would it be possible to have, say, a 300mm lens with the same field/angle of view as, say, a 24mm lens?

What field of view does the Hubble have? Does it see a swath as wide as a 16-35?

Have at it, peoples.

me

The whole point of having longer lenses is to narrow the field of view. Thus giving a higher resolution to a smaller area which is what alows the magnified view.

Well, there is a way but it's kind of goofy. You can accomplish what you speak of bu having a variable size sensor. Then as you focal length increases, your sensor size increases as well to match. That way you can have a 100mm lens on one camera match a 50mm lens on the other.
But, your quickly going to get to the edges of your optics in the process so, You'll also have to invent variable size glass as well. So, then when you zoom out from 50,, to 100mm, not only does you sensor grow, but your lens grows as well.
But wait, this won't really work then all you'll have is a bigger camera and lens. dang!!!

gjl711 wrote in post #2446302
...So, then when you zoom out from 50,, to 100mm, not only does you sensor grow, but your lens grows as well.
But wait, this won't really work then all you'll have is a bigger camera and lens. dang!!!

hehe

MDJAK wrote in post #2446130
Okay, ladies and gents, put your thinking caps on and educate me, the village idiot.

As the focal length of a lens increases, the field of view narrows.

Have I got that right?

If I do, what, if anything, can be done to eliminate that?

Hold the kudos, as I came up with this in my sleep and woke up to run down here and post it.

Would it be possible to have, say, a 300mm lens with the same field/angle of view as, say, a 24mm lens?

What field of view does the Hubble have? Does it see a swath as wide as a 16-35?

Have at it, peoples.

me

Assuming the lens is for use with a given camera, the short answer is NO!

Field of view, or more accurately angle of view, is a property of the focal length of the lens and the size of the sensor. The equation for angle of view is:

A = 2arctan(d/2f)

where:
A = angle of view;
arctan = "the angle whose tangent is";
d = the dimension of the sensor/film in the measuring plane ("d" is from "diameter of the image circle"); and
f = the focal length of the lens.

For a full-frame 35mm sensor (or 35mm film), the image is 36×24mm. This produces a diagonal of 43.27mm. This 43.27mm is the size of the image circle.

For your 300mm lens on an ff35 camera, the angles of view are:

36mm (horizontal) plane = 6.87° (most useful AoV)
24mm (vertical) plane = 4.58°
43.27mm (diagonal) plane = 8.25° (least useful but most cited AoV)

If you put the same lens on an EOS-1D MkIIn, which has a sensor size of 27.8×19.1mm, with a diagonal of 33.73mm, these angles of view become:

27.8mm (horizontal) plane = 5.31°
19.1mm (vertical) plane = 3.65°
33.73mm (diagonal) plane = 6.44°

Again, if you put the same lens on an EOS 30D with a 22.5×15mm sensor, with a diagonal of 27.04mm, the angles of view become:

22.5mm (horizontal) plane = 4.30°
15mm (vertical) plane = 2.86°
27.04mm (diagonal) plane = 5.16°

The smaller the sensor, the smaller the angles of view for a given lens. This is the basis of the so-called "crop factor," which is 1.2544 for a 1D (NOT the published 1.3) and 1.6 for a 30D.

I don't happen to know either the focal length or the sensor size for the Hubbel telescope. It is, however, not a "telescope" in the traditional meaning of the word, but rather one hell of a digital P&S camera.

I'm missing something. Why do you want, for example, a 300mm lens with a 24mm fov? Just use a 24mm, you goof.

The Hubble telescope has a focal length of approximately 58.6m (58600mm) and a circular sensor with a diameter of 2.3399m (2339.9mm). This gives it an angle of view of 2.2875°

This is approximately the same angle of view as a 1083mm lens on an ff35 camera.

The Hubble telescope is a super-telephoto fixed-focal-length digital P&S camera.

A little big for birding, though.

I wonder how many megapixels are in that 2.3399m diameter sensor. Think it's as sharp as a 1Ds MkII?

20droger wrote in post #2446646
The Hubble telescope has a focal length of approximately 58.6m (58600mm) ....

A nifty fifty on the Hubble. Isn't that just like NASA. Spends all the money on the body and tosses on the cheapest lens. Maybe it's time for NASA to upgrade to a red ring.

Look more closely, that nifty fifty has a focal length of 58.6 meters.

Remember the trouble the originally had with the mirror? Well, what did they expect! The mirror was made by a division of GM, the same folks who give you car mirrors with the etching, "Object in mirror may be closer than they appear."

MDJAK wrote in post #2446130
Would it be possible to have, say, a 300mm lens with the same field/angle of view as, say, a 24mm lens?

Easy. Get further from the subject.

Spielberg loves this technique. I first noticed it in Jaws, where chief Brody sees (or thinks he sees, I forget which) the shark amid all the holiday swimmers there is a shot were the camera zooms in on his face, but the FOV remains the same.

In film it is called a "Dolly Zoom", and was invented sometime in the late 1940's or early '50's. It is accomplished by simultaneously zooming in AND pulling back (on a dolly to insure smooth motion). By increasing the focal length and increasing distance you keep the same field of view on the subject, but, the background changes quite unsettlingly.

Rad

20droger wrote in post #2446895
Look more closely, that nifty fifty has a focal length of 58.6 meters....

Whoa!!! Thats a bit different. So it's one great big nifty fifty.

you can get a bigger field of view by using a bigger sensor, with the same focal length lens.

Radtech1 wrote in post #2446914
Easy. Get further from the subject.

Spielberg loves this technique. I first noticed it in Jaws, where chief Brody sees (or thinks he sees, I forget which) the shark amid all the holiday swimmers there is a shot were the camera zooms in on his face, but the FOV remains the same.

In film it is called a "Dolly Zoom", and was invented sometime in the late 1940's or early '50's. It is accomplished by simultaneously zooming in AND pulling back (on a dolly to insure smooth motion). By increasing the focal length and increasing distance you keep the same field of view on the subject, but, the background changes quite unsettlingly.

Rad

In Jaws they were already zoomed in and were going wide AND moving forward.

RAD & Zepher....Thanks guys, brought back old industrial movie days. I liked the Chapman series of dollies (they seem smoother ) I had a special "dollie dwarf" I worked with by the name of Dave Reynolds (good gaffer too). We worked up some pretty complex shots that still have people asking 'how'd they do that?

By the way the term 'dollie dwarf' is not a demeaning term, but rather one of status. It basically comes from their croutching down to avoid any chance of spoiling the shot. And yes they are FIT. With a 16/35mm film cam and gear + the PA on an outrigger with monitor in lap and a focus puller on the other side, it takes a tremendous amount of strength and skill to bring that load to a precise stop and no camera backlash at the end.

That avatar really suits you...