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D-SLR Maginfication Fallacy

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Hello johnny

I guess You missed one small thing. In the crop process You gain % of the frame.

Eg. A thing that is 1cm on a 35mm film takes less % of the frame than in the D30. So, if You takes it this way You can say You got a magnification.

But i share You points in general.

Roine
johnny said:
OK. I Know that this is an issue that has been discussed often,
however, I feel it has yet to be clarified. So here I am revisiting
the issue of the D-SLR “magnification” ratio.

I have read numerous times that the images created on D-SLR
sensors, are crops. This process of capturing a smaller image is
said to “improve” the quality due to the sensor only
“seeing” the center portion of the image. Thus, this is
not a true “magnification” of the original image, and
just an illusion.

Another detail that gets overlooked way too often is the
perspective one has with any given focal length. Everyone knows
that a Tele “compacts” the perspective, while a Wide
angle “stretches” the view. This is very important when
creating an image. Moreover, this is also a misconception with the
“magnification” ratio of any given D-SLR (any with a
smaller than 35mm sensor). What the perspective in an image will
look like with a 100mm lens on a D-SLR is NOT the same as what you
will see on a traditional 35mm and 150mm lens. Am I wrong?

So, which is it? Is the image captured by a D-SLR sensor a crop,
and thus an illusion of “magnification” is created? Or,
is the Focal Plane “re-directed” in order to fill the
D-SLR Sensor, and thus a “True” magnification is
created?

Here is a diagram I have created to illustrate these principles.



Which is the reality of the Focal Plane when focused onto a D-SLR
Sensor?

Focal Plane “A”: This explains the “crop”
and thus the given Illusion of a “magnification ratio”

Focal Plane “B”: This shows the Focal Plane
“adjusted” to fit the smaller sensor and thus truly
creating a Higher Focal Length Lens.

I have come to the assumption that D-SLR manufactures are marketing
the “magnification ratio” in order to mislead the
consumers. It seems that the photographer is NOT gaining anything,
and in all reality “losing” a fair amount of
“image”.

Please feel free to add any thoughts or enlighten me on any
possible error on my ideas.

Thanks for your time,

johnny
Click to expand...
 
johnny said:
So, which is it? Is the image captured by a D-SLR sensor a crop,
and thus an illusion of “magnification” is created? Or,
is the Focal Plane “re-directed” in order to fill the
D-SLR Sensor, and thus a “True” magnification is
created?
Click to expand...
In an ideal world, both of the above would produce identical images except for depth of field. Magnification is just the ratio of size of the image to the size of the subject. There is no such thing as "true magnification" or "false magnification," just like there can be no such thing as a "true ratio of feet to meters" and a "false" one.

Your insticts tell you that the smaller imager on a D30 will yield inferior quality to 35mm, but you're wrongly concluding that cropping vs. magnification via longer focal length is the culprit. It isn't. The smaller imager yields two differences in the non-ideal case:
  • Less area to squeeze in more light receptors. There are 4MP digital cameras with image sensors 1/10th the width of a D30's, and they produce images just fine. So I think we can conclude this isn't a factor.
  • Resolution limits of the optical system. This can be due to diffraction at small apertures, but in most cases is limited by the design of the lens. A good 35mm SLR lens is generally regarded as yielding 60-100 line pairs/mm.
A D30's sensor is 22mm in width, so with a good lens you'd need 2880-4400 pixels horizontally on the sensor to record everything the lens can resolve. OTOH, a full 35mm frame receives 4200-7000 "pixels" of information horizontall. This is the source of quality loss due your intuition was pointing out.

On the flip side, most lenses are sharper near the center than at the edges. Since the smaller sensor on a D30 doesn't even pick up a lot of the image on the edges, the average resolving power across the entire final image will not be as bad as the above math would say.
el junior said:
I have come to the assumption that D-SLR manufactures are marketing
the “magnification ratio” in order to mislead the
consumers. It seems that the photographer is NOT gaining anything,
and in all reality “losing” a fair amount of
“image”.
Click to expand...
Like I said, magnification is magnification. The camera manufacturers are just using the correct optical terminology when they say a D-SLR has a 1.x magnification ratio relative to 35mm. As long as the sensor is capable of capturing and the lens is capable of resolving the image to that level of detail, you're not losing anything.

I'll add that it may not always stay this way. The cheap telescopes you see sold in department stores advertise 500x-600x magnification, when they're only capable of resolving about 150x magnification at best.
 
Larry,

If you were refering to my post as being in the 3rd group, you missed my point. In bothers me not to have people discussing whatever they wish to discuss. In this particular instance, it can be an interesting subject and I can understand why there are those who are interested in learning more.

However, what I was responding to was what I felt Johnny was trying to implicitly state. In readin his posts, I was left with the impression that he thinks everybody NEEDS to understand these issues. I felt that he was stating that if you don't understand this, you or your photography are somehow being harmed or damaged. Granted, these are my interpretations of what he was saying and I could be very wrong. But my position was and is, whether you understand this or not, it need NOT be a detriment to your photography, professional or amatuer. In no way am I arguing for ignorance. I only posted because of my impression of what was implicitly being stated. Which I disagree with.
lhsmith said:
Someone, presumably having interest-in, and wishing to
comment/question on a subject, posts their thoughts, often
requesting responses.

Others,wishing to respond out of interest-or-willingness-to-help,
do-so, ...and discussion ensues.

And inevitably, a third group appears, stating something
to-the-effect that those involved in the discussion are being
foolish to even discuss the topic, which is really "pointless" (and
presumably, a waste of everyone's time).

No matter what words the criticism is put-in, It always sounds (to
me) like "I AM SATISFIED WITH MY understanding of this subject, so
why don't all the rest of you stop discussing it,...are ALL of you
so much less intelligent/perceptive than I am?"

If there were really any-such-thing as a "know-it-all", I would
like to be one, ...it would probably be very useful. But If I WERE
one, I assume that one of the things I would "know", is that not
everyone-else knows-it-all, and I would not be offended by their
attempting to learn some-of-it.

I always wonder if the mouse-fingers of such "shut-up!" posters are
broken, so that they can't just "keep-on-clickin'", and spare
themselves any involvement in the (pointless/repetitious/really
stupid/obvious-to-a-child/etc.) discussion that so-antagonizes them.

I would think any "just-don't care" feelings on a particular topic
could be more-perfectly expressed by lack-of-participation and
indifference.

My thoughts of course, not necessarily anyone else's, ...but
something just seems "wrong-with-this-picture" to me.

Larry
the Chris Brown said:
Mike Greer said:
John,

What about those that simply don't care? All of this focal plane,
perspective, cropping, etc. is extremely interesting from an
academic standpoint.
Click to expand...
[snip]

Very well said. I don't understand why people get so het up if you
use the word "crop" in place of "magnification", or vice versa. It
doesn't matter a jot. For the "cropping is not magnification!"
crowd, I would ask why do you inist on pointing out this largely
meaningless distinction at every oportunity? What is the D30 a
"crop" compared to? It's not like you can fit a bigger sensor in
the D30 with the same resolving power, so what on Earth does it
matter?

Why not just get used to reclasifying your lenses along the
following lines?

28-35mm = standard
Larry H. Smith said:
35mm = telephoto
Click to expand...
Larry H. Smith said:
But as for me, I could really care less from a
practical standpoint. I'm with Scott on this one. It seems as
though many people want to marry digital photography to 35mm
photography and show how this or that differs from 35mm. I simply
do not care.
Click to expand...
Precisely. The D30 is not a 35mm camera. It doesn't use 35mm film
and all those who keep wittering on about D30 pictures being
"crops" of 35mm pictures are engaging in a completely pointless
argument - they are simply what they are - 3 megapixel images taken
on a camera which uses Canon EF lenses.
Click to expand...
Click to expand...
 
The effect is to take a 1.6 ratio crop on a regular 35mm canon camera. The plane of focus is the same as their 35mm cameras, but the sensor covers an area 1.6 smaller. This is identical to cropping down to this size on a 35mm negative.

The practical effect of this is that the field of view is 1.6 smaller on the d30 as compared to 35mm film. This can be equally described as a crop or a magnification in that the angle of view covered on a 50mm lens on the D30 is the same as the angle of coverage of an 80mm lens on a normal camera.

This change in the field of view, does not change the effect of the focal length in terms of DOF. I was skeptical of this till in an earlier thread someone posted excellent examples showing the other effects of focal lenth remain - thus the term "cropping" factor began and continues to be coined (and used by Phil) since this is a more accurate way of thinking of it.

Some D30 users like it because the effect of a narrower angle of view is that a given lens acts like a more powerful telephoto for a given cost (the magnification factor and effect). If you always crop down a 35mm film to 1/2 the area you but print the same size print - you would be at 2x magnification as compared to not using 1/2 the area.

So one can say cropping or magnification - cropping is the reason for the magnification effect.

No one is being misleading as the bigger sensors with less magnification and cropping are more expensive - so advertising a 1.6 factor is not misleading - it is a factual statement of the smaller size of the CMOS sensor compared to film. This helps on the telephoto end of photography, but hurts if you want a single zoom lens to cover a wide angle through telephoto view. It also makes it an expensive proposition to get wide angle coverage in a lens.

It is interesting that if they did indeed change the position of the focal plane on the D30 they might have avoided the cropping factor altogether, but this also would have changed all the focus distance scales on their lenses which is probably why they dont.

To summarize - the 1.6 cropping factor results in a magnification effect but does not actually affect the focal length effect in terms of DOF.

John Mason - lafayette, IN
 
While John is mostly right, I would make a technical corrections about the DoF. I have seen people get this wrong both ways.

If one shot a picture with a D30 with say a 50mm lens and then from the identical spot with an 80mm lens (1.6X 50mm) on a 35mm film camera and then printed them out at the same final size one would have exactly the same framing and perspective would be exactly the same but the Depth of field would be different.

The short answer is that the D30 image will have a 1.6X greater DoF but will be slightly softer (by 1.6X) overall.

The Longer Answer:

There are two factors in the Depth of Feild equation that get effected, the Circle of Confusion and the Focal length. The less understood effect is CoC. Since one would have to magnify more with the D30, the "Circle of Confusion" on the D30's "negative" goes down by 1.6X. The trite comment is that the circle of confusion is confusing, but it is simply just a measure of how much a point can blur before a person notices it (the more you blow and image, the more the blur will be more noticable -- a lens is "analog" and thus the amount of blur is a continuous function). The DoF goes down linearly with the Circle of confusion.

The more well understood part of the equation is that Depth of Feild goes DOWN by the Square of the Focal Length.

The net effect of "cropping magnification" versus using a longer focal length lens is that the DoF get greater by the Cropping Factor. This is because the DoF goes up (since the focal length is shorter) by the square of the difference in focal lengths but goes down by the CoC (since there will be more maginification of the "negative"). In the Case of the D30 versus a 35mm film camera using 50mm versus 80mm lenses respectively the result is (1.6X1.6) 1.6 = 1.6.

Karl
John Mason said:
The effect is to take a 1.6 ratio crop on a regular 35mm canon
camera. The plane of focus is the same as their 35mm cameras, but
the sensor covers an area 1.6 smaller. This is identical to
cropping down to this size on a 35mm negative.

The practical effect of this is that the field of view is 1.6
smaller on the d30 as compared to 35mm film. This can be equally
described as a crop or a magnification in that the angle of view
covered on a 50mm lens on the D30 is the same as the angle of
coverage of an 80mm lens on a normal camera.

This change in the field of view, does not change the effect of the
focal length in terms of DOF. I was skeptical of this till in an
earlier thread someone posted excellent examples showing the other
effects of focal lenth remain - thus the term "cropping" factor
began and continues to be coined (and used by Phil) since this is a
more accurate way of thinking of it.

Some D30 users like it because the effect of a narrower angle of
view is that a given lens acts like a more powerful telephoto for a
given cost (the magnification factor and effect). If you always
crop down a 35mm film to 1/2 the area you but print the same size
print - you would be at 2x magnification as compared to not using
1/2 the area.

So one can say cropping or magnification - cropping is the reason
for the magnification effect.

No one is being misleading as the bigger sensors with less
magnification and cropping are more expensive - so advertising a
1.6 factor is not misleading - it is a factual statement of the
smaller size of the CMOS sensor compared to film. This helps on
the telephoto end of photography, but hurts if you want a single
zoom lens to cover a wide angle through telephoto view. It also
makes it an expensive proposition to get wide angle coverage in a
lens.

It is interesting that if they did indeed change the position of
the focal plane on the D30 they might have avoided the cropping
factor altogether, but this also would have changed all the focus
distance scales on their lenses which is probably why they dont.

To summarize - the 1.6 cropping factor results in a magnification
effect but does not actually affect the focal length effect in
terms of DOF.

John Mason - lafayette, IN
Click to expand...
 
Chris,

Strictly speaking you are correct.

It's like talking about centrifugal force-- physicists know it doesn't exist. Yet there's a word for it; that's because, from your perspective you "feel" a force pushing you out as your car rounds the corner.

Similarly, objects that are farther away from the viewer appear smaller and closer together-- even though we know that a person far away is really not an inch tall.

But the part where I'd disagree with you is to say that there's "no such thing" as a compression effect when using a telephoto lens. Very clearly there is a difference in perspective offered by a specific focal length combined with the same camera-subject distance. When using a telephoto lens, this effect is commonly referred to as telephoto compression, and it's an effective photographic tool (despite the fact that it is true that the effect is not "caused" by the lens.)

bradley phillip
 
Mike Greer said:
I appreciate the fact that there are people who are concerned about
things like this so that they can provide answers for those that
desire to know. But to suggest that professional photographers
should "know better" isn't quite fair.
Click to expand...
I don't care what your profession is... if you consider yourself a professional, then it is your business to "know better."

Further, although this is a dead horse well beaten, it's good to refresh everyone's memories or enlighten newcomers to the forum. I encourage the discussion.

JCDoss
 
This was a good thread aside from the bashing that took place...lots of good learning material within.
Karlg said:
If one shot a picture with a D30 with say a 50mm lens and then from
the identical spot with an 80mm lens (1.6X 50mm) on a 35mm film
camera and then printed them out at the same final size one would
have exactly the same framing and perspective would be exactly the
same but the Depth of field would be different.

The short answer is that the D30 image will have a 1.6X greater DoF
but will be slightly softer (by 1.6X) overall.

The Longer Answer:

There are two factors in the Depth of Feild equation that get
effected, the Circle of Confusion and the Focal length. The less
understood effect is CoC. Since one would have to magnify more
with the D30, the "Circle of Confusion" on the D30's "negative"
goes down by 1.6X. The trite comment is that the circle of
confusion is confusing, but it is simply just a measure of how much
a point can blur before a person notices it (the more you blow and
image, the more the blur will be more noticable -- a lens is
"analog" and thus the amount of blur is a continuous function).
The DoF goes down linearly with the Circle of confusion.

The more well understood part of the equation is that Depth of
Feild goes DOWN by the Square of the Focal Length.

The net effect of "cropping magnification" versus using a longer
focal length lens is that the DoF get greater by the Cropping
Factor. This is because the DoF goes up (since the focal length is
shorter) by the square of the difference in focal lengths but goes
down by the CoC (since there will be more maginification of the
"negative"). In the Case of the D30 versus a 35mm film camera
using 50mm versus 80mm lenses respectively the result is
(1.6X1.6) 1.6 = 1.6.

Karl
John Mason said:
The effect is to take a 1.6 ratio crop on a regular 35mm canon
camera. The plane of focus is the same as their 35mm cameras, but
the sensor covers an area 1.6 smaller. This is identical to
cropping down to this size on a 35mm negative.

The practical effect of this is that the field of view is 1.6
smaller on the d30 as compared to 35mm film. This can be equally
described as a crop or a magnification in that the angle of view
covered on a 50mm lens on the D30 is the same as the angle of
coverage of an 80mm lens on a normal camera.

This change in the field of view, does not change the effect of the
focal length in terms of DOF. I was skeptical of this till in an
earlier thread someone posted excellent examples showing the other
effects of focal lenth remain - thus the term "cropping" factor
began and continues to be coined (and used by Phil) since this is a
more accurate way of thinking of it.

Some D30 users like it because the effect of a narrower angle of
view is that a given lens acts like a more powerful telephoto for a
given cost (the magnification factor and effect). If you always
crop down a 35mm film to 1/2 the area you but print the same size
print - you would be at 2x magnification as compared to not using
1/2 the area.

So one can say cropping or magnification - cropping is the reason
for the magnification effect.

No one is being misleading as the bigger sensors with less
magnification and cropping are more expensive - so advertising a
1.6 factor is not misleading - it is a factual statement of the
smaller size of the CMOS sensor compared to film. This helps on
the telephoto end of photography, but hurts if you want a single
zoom lens to cover a wide angle through telephoto view. It also
makes it an expensive proposition to get wide angle coverage in a
lens.

It is interesting that if they did indeed change the position of
the focal plane on the D30 they might have avoided the cropping
factor altogether, but this also would have changed all the focus
distance scales on their lenses which is probably why they dont.

To summarize - the 1.6 cropping factor results in a magnification
effect but does not actually affect the focal length effect in
terms of DOF.

John Mason - lafayette, IN
Click to expand...
Click to expand...
 
BA said:
This was a good thread aside from the bashing that took
place...lots of good learning material within.
Click to expand...
I'm having a deja vu about this topic...NIGHTMARES, AGAIN!!! ;)

To be serious, I also think that this is an interesting subject and pops up every now and then. The bashing is probably result of the fact that usually the person who brings the subject up, has some important fact wrong but still has made a great effort (usually with diagrams or pictures...) to prove what he has to say. The "compression of distance" is probably the most common misconception. It is of course a good thing that people try to understand these issues, I try also. But the war begins when we are discussing like: "I'm right, you're wrong, you moron". So lets ask "stupid" questions (well, I think there are no stupid questions) and lets try to answer them politely!

But hopefully we now realize how the cropping affects the image produced by D30. I think there should be a FAQ explaining this.

Severi
 
bradley phillip said:
bradley phillip said:
It'll be acting like a 480mm would on the EOS 30.
Click to expand...
what I meant more precisely was you'll get the FIELD OF VIEW of a
480mm on an EOS 30 by using a 300mm on a D30 . You will not get
the higher telephoto compression, or more limited depth of field of
a 480mm lens on an EOS 30, just the same field of view as a 480mm
on an EOS 30.

Image-wise, it is in all ways, equivalent to a crop.
Click to expand...
Amazing how people seem to argue over this - this thread is running in at least three forums - that's spamming in my book.

Your explanation has already been attacked when I said it on another thread -- but what do I care I only use the equipment, you also seem to use the equipment and I think somehow we are just a tiny bit correct. ;-)
 
bradley phillip said:
what I meant more precisely was you'll get the FIELD OF VIEW of a
480mm on an EOS 30 by using a 300mm on a D30 . You will not get
the higher telephoto compression, or more limited depth of field of
a 480mm lens on an EOS 30, just the same field of view as a 480mm
on an EOS 30.
Click to expand...
There is no such a thing called "telephoto compression". When you use longer lens, you can think of it as cropping and magnifying a part of an image from wider angle lens. The perspective remains the same.

There is only FOV and DOF, no other quntities. With a 300mm lens on D30 you'll get a FOV of an 480mm lens on Eos 30 but with a 1.6x larger DOF. Everything else is identical if the distance is kept the same. (Assuming that there was a 480mm lens available...).

Severi
 
As Phil now often uses the term "cropping factor" and all digital cameras that are based on 35mm designs have this effect - a faq on this site would be most helpful to people.

I'm still confused on the various effects of focal length. In otherwords is their any intrinsic effect of focal length that makes a 50mm cropped to give the angle of view of an 80mm not make the 50mm act in all ways like an 80mm - things like DOF. I thought I had recalled an earlier presentation of exact comparison photos that showed the 50mm was not acting like an 80mm in terms of DOF and perhaps other factors. I remember the thread directed people to a photo calculator that calculates paremeters of lenses based on various lens factors and it did indeed show the the conversion of the lens from a 50mm to a 80mm did not change things like DOF.

Like the wise people say:

The only stupid question is the question that is not asked.

John Mason - Lafayette, IN
 
John,

For a particular lens;
The DOF characteristics remain the same.
The minimum focusing distance remains the same.
All intrisic characteristics (MTF, barrel distortion, etc.), remain the same.
The only things that change are;
Field of View
Magnification (because minimum focusing distance REMAINS THE SAME)

I know it seems confusing because people continue to refer to a 50mm as an 80mm, but it is only an 80mm in terms of FIELD OF VIEW!

Whew. Hope this helps. Phil is correct in referring to it as a cropping factor.

Everyone continues to harp on how bad this is for wide angle. But it really can be turned to an advantage. For instance, if you want to do a wide angle near/far shot (main subject is very close to lens, with panoramic view of background), you can actually fill up more of the frame with near subject because your minimum focusing distance DID NOT CHANGE. Creative opportunities abound. I don't know anyone who thinks medium format is restrictive (lens wise), because an 80mm on that format really behaves differently than an 80mm on a 35mm camera. You must just think differently for that particular tool, and take advantage of each one's optical idiosyncracies.

Sincerely
Mastrianni
John Mason said:
As Phil now often uses the term "cropping factor" and all digital
cameras that are based on 35mm designs have this effect - a faq on
this site would be most helpful to people.

I'm still confused on the various effects of focal length. In
otherwords is their any intrinsic effect of focal length that makes
a 50mm cropped to give the angle of view of an 80mm not make the
50mm act in all ways like an 80mm - things like DOF. I thought I
had recalled an earlier presentation of exact comparison photos
that showed the 50mm was not acting like an 80mm in terms of DOF
and perhaps other factors. I remember the thread directed people
to a photo calculator that calculates paremeters of lenses based on
various lens factors and it did indeed show the the conversion of
the lens from a 50mm to a 80mm did not change things like DOF.

Like the wise people say:

The only stupid question is the question that is not asked.

John Mason - Lafayette, IN
Click to expand...
 
Mike Greer said:
Mike Greer said:
I was left with the impression that he thinks everybody NEEDS to understand these issues. I felt that he was stating that if you don't understand this, you or your photography are somehow being harmed or damaged.
Click to expand...
Click to expand...
Mike,

People need to understand these issues if they've gotten it wrong and are making decisions based on the error. Otherwise, they'll never figure out why they're not getting the pictures they think they should be able to take.

Will
 
In real life the actual output from the camera with particular lens leads to different results with DC using 1
Mastrianni said:
For a particular lens;
The DOF characteristics remain the same.
The minimum focusing distance remains the same.
All intrisic characteristics (MTF, barrel distortion, etc.), remain
the same.
The only things that change are;
Field of View
Magnification (because minimum focusing distance REMAINS THE SAME)
I know it seems confusing because people continue to refer to a
50mm as an 80mm, but it is only an 80mm in terms of FIELD OF VIEW!
Click to expand...
But hey, if you are standing on the same spot and want to make a same framing (take the same picture) with digital body (1

That is the difference of the effective real life output, not the theory of the lens itself. It is confusing if the lens and its characteristics are examined apart from the camera bodies.

The term of cropping is adequate for the photographer from the output point of view. Focal length multiplier is not correctly describing the phenomena.

Cheers,
Matti J.
 
bradley phillip said:
Chris,

Strictly speaking you are correct.
Click to expand...
[snip]
bradley phillip said:
But the part where I'd disagree with you is to say that there's "no
such thing" as a compression effect when using a telephoto lens.
Very clearly there is a difference in perspective offered by a
specific focal length combined with the same camera-subject
distance.
Click to expand...
Your earlier post seemed to imply that you feel that a 100 mm lens on a D30. does not offer the same "telephoto compression" as a 160 mm lens on a 35mm body. Assuming you want the same composition with both cameras, you would have to stand in the same place. You would therefore get precisely the same "telephoto compression" with the shorter lens on the D30. As you yourself acknowledge, it has nothing to do with the lens.

A D30 shooter with a 100 mm lens would stand in the same place as a 35 mm shooter with a 160 mm lens, ergo the same perspective.
 
I will be happy to post an FAQ on my website if someone wants to take the time to write detailed info. Diagrams and whatnot would be cool as well. I would want it to be factual obviously and not based on how someone "thinks" it works heheh.
Severi Salminen said:
Member said:
This was a good thread aside from the bashing that took
place...lots of good learning material within.
Click to expand...
I'm having a deja vu about this topic...NIGHTMARES, AGAIN!!! ;)

To be serious, I also think that this is an interesting subject and
pops up every now and then. The bashing is probably result of the
fact that usually the person who brings the subject up, has some
important fact wrong but still has made a great effort (usually
with diagrams or pictures...) to prove what he has to say. The
"compression of distance" is probably the most common
misconception. It is of course a good thing that people try to
understand these issues, I try also. But the war begins when we are
discussing like: "I'm right, you're wrong, you moron". So lets ask
"stupid" questions (well, I think there are no stupid questions)
and lets try to answer them politely!

But hopefully we now realize how the cropping affects the image
produced by D30. I think there should be a FAQ explaining this.

Severi
Click to expand...
 
lhsmith said:
This thread follows a pattern that many do, and which I find
interesting, ... re. the participants.

Someone, presumably having interest-in, and wishing to
comment/question on a subject, posts their thoughts, often
requesting responses.

Others,wishing to respond out of interest-or-willingness-to-help,
do-so, ...and discussion ensues.

And inevitably, a third group appears, stating something
to-the-effect that those involved in the discussion are being
foolish to even discuss the topic, which is really "pointless" (and
presumably, a waste of everyone's time).
Click to expand...
I think this isn't really a fair characterisation. The point I was making is that there are those who will argue the toss whenever someone dares to suggest that the D30 somehow has a "focal length magnifier", and will stomp up and down until everyone agrees with them that it has nothing of the sort, and is just performing a "crop". An earlier poster even gave an account of how he was angry with someone in a camera shop for saying he regarded lenses as being longer on digital SLRs. The silly thing here is that the two views are effectively no different in their consequeces - it doesn't matter if you regard it as focal length magnification or cropping - there is no practical difference in the outcome.

I would view those who insist on harping on about a meaningless distinction as being the most damaging to the debate. They create confusion where none need exist and serve to lower the "signal to noise" ratio in these threads.

What determines whether a lens is wide angle, normal or telephoto is the field, or angle of view it offers. On the D30, a 50mm lens is telephoto wheras it is not on a 35mm camera, for example. No amount of demanding people talk of "crops" rather than "magnifications" is going to change that, and I would argue that it does nothing to help the confused understand that either.
 
Matti,

No disrespect meant, but think again. This is NOT a real life phenomenom, only a perceived problem. The answer? Change position and aperture. There ya go. All images are nothing more than addressing physical limitations by applying creative solutions. Distressing over format differences will never be a big problem. At least, not for me. There is NO image I cannot replicate on any format. Aperture settings are not the same (in ref to DOF) on large format cameras, (which is why the lenses go to f64), so why make it a big thing here? Sensor size is nothing more than one more equation in the problem solving arena. I personally would take an 8mp sensor @ 1.5 cropping over a 5mp full frame any day. This "cropping problem" appears to mostly concern those who have never worked in formats other than 35mm. My point is, there is no REAL LIFE problem.

Sincerely
Mastrianni
Matti J. said:
Mastrianni said:
For a particular lens;
The DOF characteristics remain the same.
The minimum focusing distance remains the same.
All intrisic characteristics (MTF, barrel distortion, etc.), remain
the same.
The only things that change are;
Field of View
Magnification (because minimum focusing distance REMAINS THE SAME)
I know it seems confusing because people continue to refer to a
50mm as an 80mm, but it is only an 80mm in terms of FIELD OF VIEW!
Click to expand...
But hey, if you are standing on the same spot and want to make a
same framing (take the same picture) with digital body (1
factor) and 50 mm focal length setting comparing to 35mm film body,
you have use 31 mm focal length setting with the DC. That results
more or less different characteristics to the image e.g. different
effective DOF etc. The difference in the field of view (cropping)
leads us to use different zoom ranges for the same framing and thus
getting different results.

That is the difference of the effective real life output, not the
theory of the lens itself. It is confusing if the lens and its
characteristics are examined apart from the camera bodies.

The term of cropping is adequate for the photographer from the
output point of view. Focal length multiplier is not correctly
describing the phenomena.

Cheers,
Matti J.
Click to expand...
 
Does that mean that if the angle of coverage of a 50mm 1.4 is 46 degrees that it will then be reduced if used on a D-30 to 46/1.6 or 28.75 degrees?

Canon doesn't currently have an 80mm prime, but I looked up the angle of coverage of the 80-200 at 80mm and the angle of coverage is 30 degrees, which is very close to 28.75, but not exact.

dave
 
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