[aegisphan]

When I said "perspective", I meant the relationship between the subject and the background/foreground. At the same magnification, longer focal length will bring the subject more foward, and thus, seperate the subject from the background. However, I don't know for sure if the perspective would be the function of focal length. But i know for sure, with the same medium, and the same magnification, they're correlated to each other.

Reach/magnification determines the FOV; however, that is only applicable within the same medium (i.e. the same type of film, or the same sensor). Reach dictates the ability to gather light from a given distance of a lens. So if you shoot a 300mm and a 200mm on a FF, the 300mm will optically move the subject closer. Therefore, it will resolve/show more detail of the object than the 200mm would.

Simply put, moving from 200mm to 300mm within a medium is like optical zoom, while moving from a FF to a crop sensor is like digital zoom. It's like you shoot an image, crop it, then blow it up to the original size.

[thePiRaTE!!]

Aegis is right, for some reason a lot of people think they are getting an advantage in the long end the smaller the sensor gets (partly due to misleading marketing on the part of manufacturers in reference to equivalent field of view as some sort of advantage. Its not).

To put it real simple - 200 mm only denotes how far the rear element is from the sensor. If you have a smaller sensor, you have a narrower field of view and a lot of light is wasted off the sides. Its no more magnified, you're just losing free real estate you'de otherwise have with a sensor that could capture that light. If you want the actual 'zoom' factor that a 300mm lens provides, you need a 300 mm lens, not a 200mm on a smaller sensor.

Otherwise you could create a 1x1mm sensor and a 200mm would have a 10000mm FoV and suddenly be able to see the dust on mars... not. You would have the equivalent FoV of a 10000mm but only the 'reach of the 200mm still.

[thePiRaTE!!]

If someone would do it, it would be cool to see Big Daves chart layed flat and represented with field of view angles shown graphically. Adding some measure of distance in feet along the side would be nice too. I'm at work right now, might do it later on if noone else has.

[rparmar]

Otherwise you could create a 1x1mm sensor and a 200mm would have a 10000mm FoV and suddenly be able to see the dust on mars... not.

You should have posted this as a product release blurb 24 hours ago.

[Kguru]

When I said "perspective", I meant the relationship between the subject and the background/foreground. At the same magnification, longer focal length will bring the subject more foward, and thus, seperate the subject from the background. However, I don't know for sure if the perspective would be the function of focal length. But i know for sure, with the same medium, and the same magnification, they're correlated to each other.

One APS-C person with 200mm lens and one FF person with 300mm lens shooting from the same spot will get the same FOV and the same perspective.

If the APS-C person then steps back (adds 50% more distance to the shoot object), changes to a 300mm lens, he gets the same object size as in the earlier shot, but different perspective behind the object.

Clear as mud?!

[Gooshin]

Gooshin, you can do what you want, but me personally, I give up when somebody starts telling me that I screwed up because I was stupid enough to apply the asymptotic formula when I should have used 2 arctan (d/2f) whatever. ;-)

Will
(who wonders why he wandered into this thread)

thats fine, i'm a gearhead/science buff myself

the only thing is that i know everythign in laymens, funny how that is.

[aegisphan]

One APS-C person with 200mm lens and one FF person with 300mm lens shooting from the same spot will get the same FOV and the same perspective.

If the APS-C person then steps back (adds 50% more distance to the shoot object), changes to a 300mm lens, he gets the same object size as in the earlier shot, but different perspective behind the object.

Clear as mud?!

Thank you for clearing that up. So perspective would depend on the the subject distance and not focal length.

[Kguru]

So perspective would depend on the subject distance and not focal length.

That's correct.
Easier to visualize this way -- if you stay at the same spot (= same subject distance) and change focal length: shorter fl gives wider angle, more are "squeezed" into the frame, but foreground and background both vary by the same proportions so no perspective change.

[moxfyre]

When I said "perspective", I meant the relationship between the subject and the background/foreground. At the same magnification, longer focal length will bring the subject more foward, and thus, seperate the subject from the background. However, I don't know for sure if the perspective would be the function of focal length. But i know for sure, with the same medium, and the same magnification, they're correlated to each other.

No, focal length and magnification do not affect perspective. One aspect of perspective is the rate at which lines appear to converge with each other in the distance: if you stand in the same place and take a photo of the same building with an 18mm lens and a 50mm lens, the lines will converge in the exact same way... it is just the size of the image that will change.

People *think* that focal length/magnification affects perspective, because you normally stand closer to your subject when using a wide-angle lens, and further when using a telephoto lens, in order to fill the frame appropriately. But there is no necessary, fixed relationship between the two.

Reach/magnification determines the FOV; however, that is only applicable within the same medium (i.e. the same type of film, or the same sensor). Reach dictates the ability to gather light from a given distance of a lens. So if you shoot a 300mm and a 200mm on a FF, the 300mm will optically move the subject closer. Therefore, it will resolve/show more detail of the object than the 200mm would.

Hmmm... I've never heard the term "reach" used in a precise context, but from what you're describing, the is a one-to-one correspondence between the notions of reach, magnification, and FOV.

Simply put, moving from 200mm to 300mm within a medium is like optical zoom, while moving from a FF to a crop sensor is like digital zoom. It's like you shoot an image, crop it, then blow it up to the original size.

That's not necessarily true. Let's say that your 35mm color film has an effective "optical resolution" of 5 megapixels... in a 36x24mm area. And let's say that your APS-C image sensor has an effective "optical resolution" of 5 megapixels as well... but in a 24x18mm area. (Both are pretty reasonable figures for modern film/sensors.)

In that case, taking a lens off the 35mm camera and putting it on the APS-C camera is not like digital zoom. It is like optical zoom. Assuming the lens can resolve as much detail as the smaller sensor is capable of producing, your image on the APS-C sensor will contain more detail than you would get from cropping the 35mm image.

Of course, the big assumption here is that the optical resolution (as measured by MTF normally) is limited by the film/sensor, and not by the lens. If the lens can't produce finer detail than what is needed in the 35mm format, then you will not get more detail by putting it on the APS-C camera.

This all explains why lenses have to improve as megapixels get higher. A lens that will provide as much detail as a 6MP sensor can record may not provide enough to take full advantage of a 14MP sensor. And it makes the megapixel race for compact cameras kind of pointless... they keep putting more and more megapixels on the sensor (and advertising it ) without improving the lens.

What it comes down to: if the sensor is limiting the optical resolution of the complete system, then switching to a smaller, finer-grained sensor will be like optical zoom. If the lens is limiting the overall resolution, then switching to a smaller, finer-grained sensor will be like digital zoom... the sensor will be capturing more "detail", but it will be details of lens aberration and noise, rather than details of the actual scene.

Also, it could go the other way... switching from a 200mm lens to a 300mm lens on a FF system will only get you more detail if the 300mm lens is capable of resolving it. A crop from a really fine 200mm lens might actually contain more detail than the complete frame from a crappy 300mm lens!!

[moxfyre]

Aegis is right, for some reason a lot of people think they are getting an advantage in the long end the smaller the sensor gets (partly due to misleading marketing on the part of manufacturers in reference to equivalent field of view as some sort of advantage. Its not).

Yes it is, it *is* a real advantage in optical resolution... *if* the *lens* is capable of imaging sufficient detail for the finer sensor/film granularity.

Of course in the real world this is not necessarily so, or not even often so, since digicam manufacturers often boost sensor resolution to advertise "MORE MEGAPIXELS!!!" without improving the lens.

To put it real simple - 200 mm only denotes how far the rear element is from the sensor. If you have a smaller sensor, you have a narrower field of view and a lot of light is wasted off the sides. Its no more magnified, you're just losing free real estate you'de otherwise have with a sensor that could capture that light. If you want the actual 'zoom' factor that a 300mm lens provides, you need a 300 mm lens, not a 200mm on a smaller sensor.

Otherwise you could create a 1x1mm sensor and a 200mm would have a 10000mm FoV and suddenly be able to see the dust on mars... not. You would have the equivalent FoV of a 10000mm but only the 'reach of the 200mm still.

With the 1x1mm sensor (having the same megapixel resolution as the larger sensor), you would have extremely small pixels, << 1 micron^2 in area. The lens couldn't project an image with sufficient detail to provide much contrast between adjacent pixels... so in this case you'd be "wasting" the additional area of the lens's image circle. (Also with a 1x1mm sensor you'd have massive noise issues, and difficulties due to diffraction at the pixel microlenses, but that's a whole 'nother can of worms.)

See my previous post for why EITHER the lens OR the sensor/film can ultimately limit the optical resolution of the complete camera system:

Case 1, "Cropping the sensor is optical zoom:" If your lens projects finer detail than your sensor can record, then you'll get more detail by using a cropped sensor with smaller pixels (assuming you can keep noise under control).

Case 2, "Cropping the sensor is like digital zoom:" If your cropped sensor can record finer detail than your lens can project, then you'll get more detail by using a crummier lens with a smaller FOV/longer focal length.

Anyone noticed how Photozone.de features the disclaimer that "lens performance data are only comparable within the same camera system"? That's because it's the combination of lens and sensor that limit the optical capabilities...

[thePiRaTE!!]

You should have posted this as a product release blurb 24 hours ago.

yes, for looking at the Virgle colony on Mars, hehehe...

(Virgle: The Adventure of Many Lifetimes)

[rparmar]

Moxfyre: great explanation!

My understanding is that the resolution of good lenses (say the limited series) is more than enough to cover the cropped sensor and even enough for film in the cases of the 31, 40, 43, 70 and 77. In fact the others may have enough resolution for film to be maxed out, if the light circle they produced would cover the physical area.

[moxfyre]

Moxfyre: great explanation!

Thank you. I work in a physics lab so I am thinking about this kind of crap and making graphs all day long

My understanding is that the resolution of good lenses (say the limited series) is more than enough to cover the cropped sensor and even enough for film in the cases of the 31, 40, 43, 70 and 77. In fact the others may have enough resolution for film to be maxed out, if the light circle they produced would cover the physical area.

Yeah. The actual optical resolution of 35mm film varies a lot, apparently, but Ken Rockwell seems to think it approaches 25 megapixels for top-quality low-speed slide film. Whereas it might only be equivalent to a few megapixels for cheap, fast, print film.

The resolution of the Limited primes is pretty darn high, as shown by the MTF50 figures in the Photozone reviews. But I don't think high resolution is their most distinguishing characteristic actually... many other lenses have nearly as high resolution (at least for optimal apertures).

[aegisphan]

No, focal length and magnification do not affect perspective. One aspect of perspective is the rate at which lines appear to converge with each other in the distance: if you stand in the same place and take a photo of the same building with an 18mm lens and a 50mm lens, the lines will converge in the exact same way... it is just the size of the image that will change.
People *think* that focal length/magnification affects perspective, because you normally stand closer to your subject when using a wide-angle lens, and further when using a telephoto lens, in order to fill the frame appropriately. But there is no necessary, fixed relationship between the two.

In my post, I didn't say perspective is a function of focal length. However, you are correct in this matter. Thank you for pointing it out. I've learned something new.

That's not necessarily true. Let's say that your 35mm color film has an effective "optical resolution" of 5 megapixels... in a 36x24mm area. And let's say that your APS-C image sensor has an effective "optical resolution" of 5 megapixels as well... but in a 24x18mm area. (Both are pretty reasonable figures for modern film/sensors.)

In that case, taking a lens off the 35mm camera and putting it on the APS-C camera is not like digital zoom. It is like optical zoom. Assuming the lens can resolve as much detail as the smaller sensor is capable of producing, your image on the APS-C sensor will contain more detail than you would get from cropping the 35mm image.

Of course, the big assumption here is that the optical resolution (as measured by MTF normally) is limited by the film/sensor, and not by the lens. If the lens can't produce finer detail than what is needed in the 35mm format, then you will not get more detail by putting it on the APS-C camera.

This all explains why lenses have to improve as megapixels get higher. A lens that will provide as much detail as a 6MP sensor can record may not provide enough to take full advantage of a 14MP sensor. And it makes the megapixel race for compact cameras kind of pointless... they keep putting more and more megapixels on the sensor (and advertising it ) without improving the lens.

What it comes down to: if the sensor is limiting the optical resolution of the complete system, then switching to a smaller, finer-grained sensor will be like optical zoom. If the lens is limiting the overall resolution, then switching to a smaller, finer-grained sensor will be like digital zoom... the sensor will be capturing more "detail", but it will be details of lens aberration and noise, rather than details of the actual scene.

Also, it could go the other way... switching from a 200mm lens to a 300mm lens on a FF system will only get you more detail if the 300mm lens is capable of resolving it. A crop from a really fine 200mm lens might actually contain more detail than the complete frame from a crappy 300mm lens!!
Yesterday 08:26 PM

I have to admit, you almost convince me right there . However, there is a whole lot of assumptions going on in your argument. I can't assume that today sensor has the same resolution as film. I have no say on whether or not the current lens (the top of the line for now) would/wouldn't out-resolve the sensor or film.

However, I know one thing for sure. Given the same registration distance, a 200mm lens is a 200mm lens, and the resolution of the lens can't be changed. Crop/film size wouldn't affect this fact. That's what we're trying to argue here, not other things.

I also want to overlook the optical difference between a given 200mm and 300mm. There is no point saying if a 200mm have more resolving power than a 300mm, then a 300mm FOV crop picture of a 200mm would look better. That's just an obvious fact. For our purpose, that just introduces unnecessary variable. So let us say a 200 and a 300 both have resolution of Z.


If we have the same subject to medium distance, a 200mm will have X magnification/reach to produce a Y physical projection size of the subject at Z resolving power. With the same condition, a 300mm will produce a new set of A, B, Z. Seeing that the 300mm can reach further to the subject, A would be bigger than X, B would be bigger than Y. At the same Z resolving power, the given object will have more details for being bigger (e.g. the same area was occupied by two discernible photons, is now occupied by 3 discernible photons)

To be fair, I will cut the same film down to the crop sensor size. The 200mm will still have the set of X, Y, Z since I establish the medium size wouldn't affect these. By doing this, however, the relative size of the the physical projection size Y to the medium size changes to the same ratio of the 300mm on full frame film. However, Y is still Y, and it's still smaller than B. In order to reach B's size, we have to do a digital zoom.


However, I believe if digital sensor reaches the same level of MP as film (and thus it has denser pixel density), then it all depends on whether the lens is the limiting factor or the sensor/film. And if the sensor/film is the limiting factor, then your theory is indeed true. But until both of these facts are known and well-established, I can't agree with you at the moment.

It has been a fun experience so far. I've to re-read some stuff. I also learned new stuff from you. Thank you.

Cheers

[moxfyre]

In my post, I didn't say perspective is a function of focal length. However, you are correct in this matter. Thank you for pointing it out. I've learned something new.



I have to admit, you almost convince me right there . However, there is a whole lot of assumptions going on in your argument. I can't assume that today sensor has the same resolution as film. I have no say on whether or not the current lens (the top of the line for now) would/wouldn't out-resolve the sensor or film.

Well, the resolution of image sensors, film or digital, can be quantified using MTF. The resolution of lenses can also be quantified using MTF, though since you have to "put" the image somewhere, it depends on which sensor you use to measure the lens's MTF The imperfect resolution of the lens and that of the sensor/film combine to limit the total resolution/sharpness of the system. It's not always clearly possible in practice to identify one or the other as most limiting... but sometimes it is.

For example: put a lens on the 6mp K100D, and then on the 10mp K10D, and take pictures of the same scene. Does the K10D's image resolve more detail? If yes, then the optical resolution is more limited by the sensor than the lens. If no, then the opposite.

However, I know one thing for sure. Given the same registration distance, a 200mm lens is a 200mm lens, and the resolution of the lens can't be changed. Crop/film size wouldn't affect this fact. That's what we're trying to argue here, not other things.

Actually, I thought we were arguing about whether a 200mm lens on an APS-C sensor would produce more/less/same resolution as a 300mm lens on a FF sensor.... ?

And I explained why any of those is possible, and why the sensor/film size does affect the resolution of the complete optical system. (You're right, the resolution of the lens itself does not change.)

I also want to overlook the optical difference between a given 200mm and 300mm. There is no point saying if a 200mm have more resolving power than a 300mm, then a 300mm FOV crop picture of a 200mm would look better. That's just an obvious fact. For our purpose, that just introduces unnecessary variable. So let us say a 200 and a 300 both have resolution of Z.

It's not an unnecessary variable. It's utterly crucial. As I've stated, if the lens's optical resolution is limiting, then shrinking the sensor will be like "digital zoom" (narrower FOV, no extra detail gained)... if not, then shrinking the sensor will be like "optical zoom" (narrower FOV with extra detail).

But sure, let's imagine 200mm and 300mm lenses which have equal resolution in terms of MTF50...

If we have the same subject to medium distance, a 200mm will have X magnification/reach to produce a Y physical projection size of the subject at Z resolving power. With the same condition, a 300mm will produce a new set of A, B, Z. Seeing that the 300mm can reach further to the subject, A would be bigger than X, B would be bigger than Y. At the same Z resolving power, the given object will have more details for being bigger (e.g. the same area was occupied by two discernible photons, is now occupied by 3 discernible photons)

I still don't know what "reach" means...

Leaving aberrations and distortion aside, the ability of a lens to reproduce a scene can be described by:
(a) the vertical and horizontal angles of view subtended by the sensor
(b) the level of sharp detail projected onto the sensor (quantified by MTF)

What does the notion of "reach" include that isn't covered by angles-of-view and MTF???


Also, you're talking about the resolution of the lens itself. I agree completely... if both lenses have the same MTF (let's call it 50% contrast at 30 lines/mm)... then the 300mm lens will produce more detail of a distant object, over the entirety of its image circle.

Which is why, again, it's important to decide whether it's really the lens or the sensor limiting the system's optical resolution (and it practice it will be a combination ). If all our sensors had infinite resolution, and all our lenses had poor resolution, you would gain nothing by putting a FF lens on a crop sensor... and in fact you would LOSE part of the image circle.

To be fair, I will cut the same film down to the crop sensor size. The 200mm will still have the set of X, Y, Z since I establish the medium size wouldn't affect these. By doing this, however, the relative size of the the physical projection size Y to the medium size changes to the same ratio of the 300mm on full frame film. However, Y is still Y, and it's still smaller than B. In order to reach B's size, we have to do a digital zoom.

However, I believe if digital sensor reaches the same level of MP as film (and thus it has denser pixel density), then it all depends on whether the lens is the limiting factor or the sensor/film. And if the sensor/film is the limiting factor, then your theory is indeed true. But until both of these facts are known and well-established, I can't agree with you at the moment.

Yeah, I think we basically agree here 8) Except that you are more skeptical about whether it is really the sensor that is ever limiting the total resolution of the system... Which you may be right about in many cases. Though with a sufficiently good lens (or sufficiently crappy film/sensor!!) the opposite can be true.

This can be tested quantitatively. Get a 200mm FF lens, a FF film camera with appropriate high-quality film, and an APS-C camera.
(1) shoot an MTF test chart with the FF camera, standing at a distance of 10m from the chart, and scan it.
(2) shoot the same test chart with the APS-C camera, standing at a distance of 15m from the chart.
(3) crunch the numbers to determine MTF50.
(4) If the FF and APS-C camera resolve equally fine details (in terms of object dimensions), then the cropped sensor is like optical zoom.
If the FF camera resolves details that are 1.5X smaller than the APS-C camera, then the cropped sensor like digital zoom.
If it's somewhere in between, well then it's somewhere it between

It has been a fun experience so far. I've to re-read some stuff. I also learned new stuff from you. Thank you.

Cheers

Likewise!!