PHRubin Loc: Nashville TN USA

Semantics. It would have the FOV of a 16 but would still be a 24. It would have the DOF of a 24. All you do is crop when going from larger format to smaller. All light characteristics stay the same. The FOV changes only because you are looking at a different % of the projected image.

speters Loc: Grangeville/Idaho

I absolutely agree and I never said that anything that suggest's different!

wdross Loc: Castle Rock, Colorado

Although it does work in reverse, the circle of image does not. Most lenses are designed with a specific angle of view in mind, even if it is a zoom. In the case of a prime lens, where the angle of view is 10° for the diagonal, the angle of the projected image circle would be ~11°. Then the square or rectangular image is cropped out of that. But when a smaller format's lens is put on a larger formats body, the smaller image circle is not big enough to cover the diagonal distance of the square or rectangular larger format sensor.

kymarto Loc: Portland OR and Milan Italy

It's really simple: a 24mm lens is a 24mm lens. The AOV of a 24mm lens on 6x4.5 is around 110 degrees diagonal. Put that lens on an APS-C camera the image circle remains the same, but a much smaller portion of the center of that circle hits the sensor. So the AOV for that lens on APS-C would be around 61 degrees diagonal.

If you are asking the opposite, i.e. what is the AOV of a Pentax APS-C 24mm lens on a 6x4.5, then answer is that a 24mm lens is always a 24mm lens, so the size of the elements in an image focused on the sensor will be the same as for the APS-C camera. Unfortunately, that lens is only made to cover the smaller sensor, so you will get a circular image in the center of the frame surrounded by a lot of black.

Lenses are designed generally to cover a slightly larger area than the sensor's diagonal size, so the full image circle on the 6x4.5 file may give you slightly more angle of view if you crop it down to exclude the black parts of the image, but basically you won't get more than you get on the APS-C sensor after you crop the black off.

User ID

This is the OP query
"If I put a 24mm from a Pentax 645
on my K20D does the FOV expand?"

If thaz what you're answering [should be !]
then the new FoV would be equivalnt to a
36mm on FF, cuz he's putting a 24mm lens
on an APSC body.

You generally know your stuff. So how did
you wind up with that 16mm equivalent ?
Where did you get that from ?

.

User ID

Semantics ? LOL !

Are you able to state something clearly ?
Then state it clearly, in WHAT applications
will a 24mm lens have the FoV of a 16mm.
Cuz what you have written so far is simply
a conjoined pair of incomplete statements.

.

PHRubin Loc: Nashville TN USA

The word equivalent was too broad for me.

PHRubin Loc: Nashville TN USA

Really? Are you an English teacher? SHOW ME ONE INCOMPLETE SENTENCE! How is any of those not a complete statement?

With a camera having a sensor 1.5 time larger than a 35mm slide, the sensor would be illuminated by the 24mm lens with an field of view as large as a 16mm lens would illuminate on a 35mm sensor (if the lens could, in fact, cover the bigger whole sensor with the projected image.)

User ID

Thank you for a more complete and disambiguated version
of your previous post.

-------------------------------------------------------------

Never said your sentences were incomplete. I did say that
your statements were incomplete, which acoarst creates
ambiguities. Your adherence to good grammar is not any
guarantee of clarity or continuity. Learn to read what you
wrote as if someone else had written it to you.

.

PHRubin Loc: Nashville TN USA

I think the original was not ambiguous and each statement WAS complete.
"acoarst"???

BebuLamar

So I would suggest not to use it at all. Whenever we use the word equivalent focal length we use the 24x36mm as reference. I dislike this because I think today fewer people use the 24x36mm format than the APS-C format and others.

rcarol

We didn't seem to have all of this confusion with film cameras. It was understood that a normal lens on a 35mm camera was a lens with a focal length of 50mm, 2 1/4 square was 80mm, 4" X 5" was 150mm, etc. It was also understood that you could adapt a Hasselblad lens to a Nikon and you still had an 80mm lens but the image would be smaller on the Nikon than what you would get on the Hassie. Not hard to understand at all. The focal length of the lens never changes only the size of the film (or sensor) changed.

User ID

Very true. The frame of reference [24x36mm]
is obsolete. It was handy for marketing during
the transition from 24x36 film to APSC and H
digital formats. Today it [soooo obviously] just
generates more confusion than clarity.

A corollary would be to dump the "crop factor"
notation as well, since that is also based on a
24x36mm format.

==========================

Question arises as to what should replace the
"equivalent" and "crop factor", and I believe
the least confusing solution to be to rename
format in the traditional manner, the old 6x6,
6x9, 24x36 and 18x24 [etc] method. Result
would be 13x17, 16x24, 24x36, 33x44 and
44x55mm. Minor deviations can be ignored.

13x17 is realistically the smallest format with
interchangeable lenses. All-in-one "bridge" or
zoom cameras can be simply marked as 15X,
40X etc etc. The argument about how wide is
the wide end can also be ignored. Geeks can
google the specs. No one else cares to know.

--------------------------------------------

Altho it will never fly, another simple option
to renaming formats is the TV and monitors
scheme. Just name it by the diagonal. Little
things like aspect ratios are, again, only for
geeks. No need of confusing everyone else,
who just wanna know "Whatzit cost, whatzit
weigh, and can it do Snap Chat ?".

.

BebuLamar

That because back then we didn't use the equivalent. We simply know the focal length of lenses for each format.

BebuLamar

I am all for that and we can just remember the normal focal length of each format. So for the longer or shorter lens is simply compared to what is normal.