Popping the Myth of the Focal Length Multiplier I

At the same DOF I believe any size lens/sensor complication will have the same diffraction limits. A smaller sensor needs a wider aperture to keep the same DOF of field the same.

Therefore, even considering diffraction limits "large" and "small" len designs scale well.

Chato wrote:
[snip]

Chato said:

Of course Peter, but then again I don't know the "lingo."

But I will say this. Resolving power in a lens is a result if it's
ability to gather and focus light. There's a reason why these
astronomers spend millions of dollars grinding out their glass and
not just making larger sensors.

Click to expand...

Totally, and resolution is not the main reason -- at least not for Earth-bound telescopes. Light-gathering power is.

Chato said:

The ability to distinguish between two close objects is the ability
to resolve these two objects as being seperate and distinct.

Click to expand...

Yup. And currently this is limited by the sensor's pixel count, not the lens. Both on small-sensor digicams and on digital SLR's.

Chato said:

Now
I've seen many fine images taken with these little digicams. But
these shots cannot be cropped without the detail being lost. While
the same shot from a true telephoto can be cropped to reveal even
more detail.

Click to expand...

Examples, please.

Another question you've repeatedly failed to address is what you consider to be a "true" telephoto.

Chato said:

Interpolation is a great thing, wherever it is being used, but as
you know, it doesn't provide additional detail - It merely
clarifies whatever detail is there in the first place.

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And, yet again, it has absolutely nothing to do with the question under discussion.

By the way, on clear days the sky tends towards the blue in daytime. Therefore, you're wrong. Right?

Petteri
--
http://www.prime-junta.net/
http://www.flickr.com/photos/primejunta/

...please explain what you mean by a "true" telephoto.

Normally, "telephoto" means "lens with a field of view narrower than the diagonal of the image circle (give or take a few degrees)."

You're the first person I hear tacking on "true" in front of it. What exactly do you mean by it?

Petteri
--
http://www.prime-junta.net/
http://www.flickr.com/photos/primejunta/

Not to beat up on you any more : ) but you're right and wrong. It's true that the focal length of a lens doesn't change with sensor size. That's what the guy is trying to say in his 10,000 words or whatever. I don't think anyone disagrees with that - focal length is a mathematical function of the lens properties alone.

But (and it's a very big but), to the photographer, who is only concerned with end results, the resulting photo is exactly the same as if the focal length did change. photographers might call it a focal length multiplier, bui strictly speaking, it's a FOV multiplier. However, since photographers have worked with FL for so long, and we intuitively know what a 500 MM lens does, we've used the little white lie of calling it a FL multiplier, so we can stick with terms we're familiar with.

Get it? The FL doesn't change - but the end results are EXACTLY the same as is it did - so we stick with the familiar and call it a FL multiplier.

Petteri Sulonen said:

...please explain what you mean by a "true" telephoto.

Normally, "telephoto" means "lens with a field of view narrower
than the diagonal of the image circle (give or take a few degrees)."

You're the first person I hear tacking on "true" in front of it.
What exactly do you mean by it?

Click to expand...

Surely a 'true' telephoto is a reference to the lens design - as in the opposite of retrofocal to produce a lens that is physically shorter than its focal length.

Using telephoto to describe any long lens is not wholly inaccurate wrt photography but is often wrong in other fields.

I doubt that this is the case here.

Chato said:

Chato said:

Chato said:

While
the same shot from a true telephoto can be cropped to reveal even
more detail.

Click to expand...

Cropping doesn't magically make detail appear that wasn't there in
the first place.

Click to expand...

My point...

Click to expand...

You seem to be making the opposite point, that "true telephoto" (whatever that is) can be cropped to reveal more detail.

The plain fact is that a sensor has a certain resolution, and the lens in front of it also has a certain resolution. If the lens manages to outresolve the sensor, you get the sensor resolution.

So are you trying to say your A540 gets 1/3 the resolution of your D1x?

Chato said:

Chato said:

We aren't talking about interpolation.

Click to expand...

No, we are talking about me zooming in on an image taken with a
digicam and comparing that to zooming in on the same subject from
the same distance taken with a real telephoto.

When that is done, the apparent detail, that our eye/brain fills in
on the digicam shot vanishes into an incoherent smear...

Click to expand...

Then I suggest there is something wrong with your digicam or your methodology. Post an example with full exif.

--
Seen in a fortune cookie:
Fear is the darkroom where negatives are developed

Andrew dB said:

Surely a 'true' telephoto is a reference to the lens design - as in
the opposite of retrofocal to produce a lens that is physically
shorter than its focal length.

Click to expand...

A retrofocus lens is physically longer than its focal length.

--
Seen in a fortune cookie:
Fear is the darkroom where negatives are developed

For the same DOF you will need a wider aperture for the smaller lens, which makes the angular resolution the same.

All cameras, from a huge viewfinder to tiny point and shoot, have the same diffraction limited sharpness at the same DOF.

I suspect that even sensor noise is the same for all formats at the same DOF. Consider a FF dSLR and a point and shoot w/a 5:1 crop factor sensor. If you shot at F8 w/the FF sensor, you'd have to shoot at about F1.8 w/the point and shoot for the same DOF. At the same shutter speed, you'd get 25 times the light.

The real reason point and shoots don't work like dSLR's is that the tiny CCD's can't handle the increased light density needed - not enough well depth.

Chato said:

CBenson said:

Chato said:

Chato said:

This seems rather misleading. Surely a lens of a particular focal
length designed for a particular format will have different
physical attributes than a lens of the same focal length designed
for some other format.

--
Regards,
Carl

Click to expand...

If I stick a 50mm lens on my Nikon, I should be getting the
"magnification" of a 75mm lens. Should I not?

Click to expand...

Click to expand...

Chato said:

This question is much too vague for me to understand.

Click to expand...

The Nikon D1x has a cropping factor ot 1.5, meaning according to
proponents of the FLM, that it should provide a 1.5 magnification
of whatever lens is being used. Does this clear up what I am saying?

Click to expand...

No. You have merely placed words in the mouths of the "proponents of the FLM." I do not know what you are trying to say.

Chato said:

Chato said:

Chato said:

But oddly enough if I switch my eye from the viewfinder to eye ball
the subject, I see no such magnification - None. Zip. Nada. I see
the exact same scene even though It looked Larger in the viewfinder
then using my FF SLR.

Go figure...

Click to expand...

Are you trying to say that you do not agree with the statement that
a lens of a particular focal length designed for a particular
format will have different physical attributes than a lens of the
same focal length designed for some other format?

Click to expand...

I have no idea what the above means. If your saying that the 50mm
prime designed for a FF camera therefore does not provide any
magnification when placed on an APS sized sensor I would agree.

Click to expand...

I don't know what your guess at what I am saying means. What does "does not provide any magnification" mean?

I don't know what you are saying - you don't know what I am saying. Maybe this thread isn't very helpful.
--
Regards,
Carl

nickleback said:

Andrew dB said:

Surely a 'true' telephoto is a reference to the lens design - as in
the opposite of retrofocal to produce a lens that is physically
shorter than its focal length.

Click to expand...

A retrofocus lens is physically longer than its focal length.

Click to expand...

The statement should have read:

Surely a 'true' telephoto is a reference to the lens design (the opposite of retrofocal) to produce a lens that is physically shorter than its focal length.

Well done at spotting the deliberate mistake - you can have a gold star ;-)

OK, so it is pretty easy for even a feeble-minded person like me to understand lenses will always project the same image, and I can even understand that when I bring whatever thing I am projecting against "closer" to the backside of the lens, the part that gets the image will look smaller. I can EVEN understand that if I use a "thing" (sensor for example) that is larger that what the lens will project I'll end up with "nothing" around the edges, which is why things look vignetted using, for example, a Nikon DX lens on a 35mm film body.

I have this all right so far, correct?

So, here comes the BUT. I use a 400mm f2.8 AFS-1 Nikon Prime Telephoto on my D200 which is one of those APS-C sized sensors, 1.5 crop, 1.5 FLM, 1.5 FOV whatever you want to call it. This tells me that a bunch of photons that come through the lens don't get used, all of those ones around the edges. Well, since the camera is "closed", where the heck did all those photons go? Are they somehow just bouncing around inside my camera? How the HECK are these camera makers smart enough to flush these out so they don't cause problems? I'd think they, the photons, would be pretty darned annoyed at just being ignored ......

Enquiring minds and all that.

Frankly, I think all the "explanations" are important for only one reason, and that is to dispel the Marketing Hype that surrounds all of this. Why doesn't this occur with 8x10, 4x10, 6x7cm, 2-1/4 square, 6x4.5cm, 35mm. My guess is that those are all use primarily by folks with a grounded base of knowledge, and now the Marketing can Mass Market, hey, time for new and confusing ways to give us a way to prove that whatever "we" have is far better and bigger than whatever it is that "you" have.

Oh, yeah, by the way, my question above while it may sound silly is really quite serious. Where the heck DOES all that light go???????

--
Bill Dewey
http://www.deweydrive.com

Nobody listening to the other. The basic problem is there is no myth and one side is insisting there is. And not understanding the reason why there's no myth.

--mamallama

Bill Dewey said:

Oh, yeah, by the way, my question above while it may sound silly is
really quite serious. Where the heck DOES all that light go???????

Click to expand...

Soaked up by the inside of the lens and the camera body. That's why lens internals and camera insides are flat black. Reflections are bad. Flat black doesn't reflect (much).

--
Seen in a fortune cookie:
Fear is the darkroom where negatives are developed

Lenses are designed for specific frame sizes and shutter designs, and this is the point at which your argument starts to lose linearity.

1) Smaller glass elements can be formed to much finer tolerances at much lower cost (but are they?).

2) Your argument works where the same lens is placed on different cameras is designed for the larger of the two sensors.

3) However, taking the 38-380 (35m equiv FL) lends from my wife's camera will give you no better images on a FF DSLR than it does on the Canon S1, and probably a lot worse.

So in short, to summarise, recapitulate and in conclusionment: it is the NET result of the entire photographic tool that determines image quality and effective image resolution. My wife's 380mm (equiv.) might not match your 380mm (actual) - I'm keeping my equipment out if this argument - but it sure as heck is better than your digitally zoomed 38mm (possibly, you'd need to check that)...

mamallama said:

Nobody listening to the other. The basic problem is there is no
myth and one side is insisting there is. And not understanding the
reason why there's no myth.

--mamallama

Click to expand...

I've had a long discussion with Dave (Chato), and I think I understand his position - more or less. He read some papers (mostly about microscopes), and learned that a microscope's resolving power grows with the focal length of the lens.

Based on that, he came to the conclusion that the amount of detail a digital camera can resolve is determined by - and only by - the lense's focal length.

Now, all my objections (that the digital camera's resolution is not the same thing as microscope objective's resolving power, and that the notion of microscope's magnification doesn't apply to a camera, and that different sensors and different lenses can have different resolutions, and that small-sensor digicams actually work, and that Phill measured their resolution) fall on deaf ears.

If Dave replies at all, it's "so, do you think all those scientists [who wrote the microscope articles] were wrong?"

Chato said:

But I will say this. Resolving power in a lens is a result if it's
ability to gather and focus light. There's a reason why these
astronomers spend millions of dollars grinding out their glass and
not just making larger sensors.

Click to expand...

Astronomers (and I do have a PhD in astrophysics) make large telescopes to: 1 gather more light and 2 be able to resolve, say, two stars very close together. Maybe this second reason is what is making you confused Chato. By increasing the aperture, not the focal length, you decrease the diffraction (ignore the fact that the atmosphere is making a normal telescope seeing limited rather than diffraction limited for now...).

Chato said:

The ability to distinguish between two close objects is the ability
to resolve these two objects as being separate and distinct.

Click to expand...

Yes, "being separate" is however a question of definition I believe, but thats probably a different discussion

Chato said:

Now I've seen many fine images taken with these little digicams. But
these shots cannot be cropped without the detail being lost. While
the same shot from a true telephoto can be cropped to reveal even
more detail.

Click to expand...

Maybe Im missing your point here (haven't read all the posts) but I think what people are trying to tell you is that with your telephoto lens your bird will form a large and nice image which you then sample with a large detector of 10 million large pixels. With your small digicam you get an identical image, but much smaller, which you sample with a small detector of 10 million small pixels. Your bird will look identical in the two images within reason, no?! The beak will cover 5 pixels in both images for example...

Petteri Sulonen said:

...please explain what you mean by a "true" telephoto.

Normally, "telephoto" means "lens with a field of view narrower
than the diagonal of the image circle (give or take a few degrees)."

You're the first person I hear tacking on "true" in front of it.
What exactly do you mean by it?

Click to expand...

It's a heck of a lot easier to type "true" as opposed to "the focal lenght equivalent telephoto" ...

Dave

Petteri Sulonen said:

Petteri
--
http://www.prime-junta.net/
http://www.flickr.com/photos/primejunta/

Click to expand...

CBenson said:

CBenson said:

The Nikon D1x has a cropping factor ot 1.5, meaning according to
proponents of the FLM, that it should provide a 1.5 magnification
of whatever lens is being used. Does this clear up what I am saying?

Click to expand...

Click to expand...

CBenson said:

No. You have merely placed words in the mouths of the "proponents
of the FLM." I do not know what you are trying to say.

Click to expand...

I didn't place these words in YOUR mouth. I am repeating what is being said. The cropping factor provides magnification based on the degree of the crop. So that a 1.5 Cropping factor provides 1.5 magnification. If that's not what they are saying, there would be no argument.

CBenson said:

CBenson said:

I have no idea what the above means. If your saying that the 50mm
prime designed for a FF camera therefore does not provide any
magnification when placed on an APS sized sensor I would agree.

Click to expand...

Click to expand...

CBenson said:

I don't know what your guess at what I am saying means. What does
"does not provide any magnification" mean?

Click to expand...

I am seeing the same magnification with the APS sized sensor as with the FF sensor - which is to say - None.

CBenson said:

I don't know what you are saying - you don't know what I am saying.
Maybe this thread isn't very helpful.

Click to expand...

Who knows? Maybe its possible to reach understanding...

CBenson said:

Regards,
Carl

Click to expand...

nickleback said:

nickleback said:

nickleback said:

No they are not. Measure across the horizontal lines at 20. I get
about 46 pixels on each image. The reason the lines look thinner
on the Canon shot is that you are looking at the range 1800 - 2600,
whereas on the Pany image you are looking at 1200 - 2200.

Click to expand...

Click to expand...

Click to expand...

My bad, I measured at the point where the lines are cut off and compared them to where the lines actually ended.

nickleback said:

nickleback said:

At the end of the horizontal run, where the lines expand, on the
Panasonic image the lines are almost EXACTLY twice as large -
Meaning the verticle space occupied by all the lines on the
Panasonic are twice as high as the vertical space occupied by the
Canon

Click to expand...

I hate to break it to you, but this is a res chart. The lines are
expanding all the way across your screen. What counts is size at a
particular range. I picked 2000 (i.e. 20). They are the same.

Click to expand...

(snip)

Not only did I have the measurement wrong, but the vertical line on the Canon (above the "20" ) is in fact almost twice as long as the vertical line on the panasonic.

But my point is still valid - the lines should be roughly the same size, even though I mixed up the cameras. I gave that as an example that we don't know all the parameters that Phill used, and in THAT sense I was correct.

Dave

CBenson said:

Chato wrote:

Click to expand...

(snip)

CBenson said:

CBenson said:

What you’d then see is this smaller crop of
the image expanded to fill the original lighted rectangle. Since
the field of view was smaller, this process would make the image
look like it was taken with a telephoto lens!

Click to expand...

What is your definition of a telephoto lens?

CBenson said:

In fact, it would
make it look like it was taken with a telephoto lens with a focal
length of about 75mm.

Click to expand...

It wasn't clear to me until now that the slide put in the projector
and projected on the wall was taken with a 35mm camera and a 50mm
lens.

Click to expand...

Surely you know that each post we make here is limited to 6000 characters? The poor guy above was forced (by me) to have his essay "cropped." Indeed, I had to crop even MORE to post my reply...

Which is why I provided a link...

CBenson said:

CBenson said:

So why can’t we just say that the focal length was multiplied? Are
we being a bit too much of a purist here? No we are not, and
here’s why.

First, did you ever see one of those pictures that showed a coyote
baying on a hilltop with a moon the size of a Buick behind him?
Clearly nobody can move the moon to the coyote, and you similarly
can’t get howls out of a coyote three-quarters of the way between
earth and moon. What happened was that a photographer was sitting
down at the base of the hill with a telephoto lens, and shooting
the picture. The telephoto lens changes the perspective of the
scene; far objects seem magnified more relative to near objects
than we’d see with the eye. You may also have taken a picture of
someone lying on the beach, using a wide-angle lens, and found
their feet looked about three times as big as their head.
Wide-angle lenses also change perspective; the near objects are
magnified more than the distant ones relative to what the eye sees.

Click to expand...

This seems rather misleading. Some could take the statements "The
telephoto lens changes the perspective of the scene" and
"Wide-angle lenses also change perspective" to mean something other
than "the perspective is based on the position of the subject
relative to the camera."

Click to expand...

Once again, I cropped his work...

And in these kind of cases there is no Full length multiplier to telephoto his essay back to the point where it can "resolve" what I cropped out...

CBenson said:

CBenson said:

How does this apply to our digital camera? Well, the perspective
of a lens is based the position of the subject relative to the
photographer. Wide-angle lenses make close stuff appear big
relative to far stuff because “close” stuff is really close to the
camera, so it’s relative size is large. A coyote baying at the
moon taken with a wide-angle lens with the coyote filling a third
of the horizontal frame would show a really little moon, because it
would be taken close to the coyote and the moon’s size relative to
the coyote’s size would be small. The same combination shot with
the same coyote size taken with a 500mm lens would show the moon
larger relative to the coyote, because from the position of the
photographer (now farther away), the moon is larger relative to the
coyote and the lens magnifies the angel of each equally. Throw
that lens on a digital camera, again keeping the same in-frame size
of the coyote, and you’ll be moving farther from the subject again,
so now the moon looks larger compared to the coyote.

http://www.cimicorp.com/DI/DTipLenses.html

Early marketing literature, and the articles in the press based on
them, described the chips in digital SLRs as 1.5x and 1.6x chips.
The formula, said the marketing folks, was that you multiply the
focal length of your lens by 1.5x or 1.6x (depending on the brand)
to get the length of your lens when mounted onto one of their
digital SLRs. The implication being that these chips provided some
kind of magnification.

Click to expand...

This hardly seems a sin. You in fact stated "the system
magnification from subject to print is increased."

CBenson said:

Image chips in digital SLRs crop the image provided by the lens.
They don't offer any magnification. Is this really an advantage?

In the above example the image on the left was shot using a 300mm
lens on a standard SLR. The image on the right shows the effect of
mounting the same 300mm lens on a digital camera with a 1.5x chip.
The result is the equivalent of a 450mm lens. This is a good thing
right? This was a good thing said the marketing folks. What they
didn't say was that it is more accurate to describe that 1.5x chip
as a 2/3rds chip !

These chips are smaller than the area covered by a frame of 35mm
film. There is no extra magnification, as is implied, and has been
erroneously reported by journalists in any number of articles.
These smaller chips crop the image rather than magnify it. So the
"gain" is in fact no gain at all, it is a loss, and that loss
occurs equally throughout the entire range of focal lengths from
wide-angle to telephoto.

Click to expand...

What is the loss?

Click to expand...

Well, HE is saying that losing the rest of your image is a loss. I would disagree, in the sense that while there may not be additional magnification, the cropping factor DOES provide additional clarity to whatever the lens is capable of resolving. At least on digital where the recieving structure is not film buy pixels.

CBenson said:

CBenson said:

http://www.vividlight.com/Articles/3814.htm

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Click to expand...

Dave

CBenson said:

Regards,
Carl

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