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Old Mar 10, 2006, 9:55 AM   #91
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DBB wrote:
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The cropping power magnifys the image without in any way increasing the resolution.

The crop doesn't magnify anything. The sensor records the image from the lens at the resolution of the sensor.

As long as the lens is capable of resolving the detail the sensor will record it.

The angle of view that is recorded will depend on the sensor size and the focal length of the lens.

In order to describe the lens sensor combination in terms most photographers will be able to relate to manufacturers state the 35mm equivalent focal lengths.
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Old Mar 10, 2006, 10:03 AM   #92
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The crop doesn't magnify anything. The sensor records the image from the lens at the resolution of the sensor.

As long as the lens is capable of resolving the detail the sensor will record it.

The angle of view that is recorded will depend on the sensor size and the focal length of the lens.

In order to describe the lens sensor combination in terms most photographers will be able to relate to manufacturers state the 35mm equivalent focal lengths.
Somebody give this guy a cookie! :-D
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Old Mar 10, 2006, 10:12 AM   #93
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Ok guys...

If you talk actual versus theoritical limits, as already pointed out numerous times in this thread, you get the same detail with a 100mm lens on a DSLR with an APS-C size sensor compared to a DSLR with a 35mm size sensor wearing a 150mm lens, for the same subject framing, provided the sensors are of equivalent resolution and image processing is equivalent.

You want a controlled conditions sample? I don't like to post links to other sites, but I'll make an exception this time.

If you look at the resolution charts for Phil Askey's review of the Canon EOS-5D, you'll see an 85mm f/1.8 lens used, stopped down to f/9. This is a 12 Megapixel sensor.

You'll also see resolution charts for a Nikon D2x, wearing a 50mm f/1.4, stopped down to f/9, setup for the identical framing with a much shorter focal length lens.

Guess what? The resolution charts are almost identical because both cameras have a sensor that's the same resolution. Any differences between them are probably due to image processing versus lens limitations, and if you shot raw with both and processed the images the same way, they probably would be the same.

The D2x actually outresolved the 5D shooting in jpeg.

http://www.dpreview.com/reviews/canoneos5d/page31.asp

There are other examples, too.. where even a prosumer model with a *very* short focal length lens can outresolve some DSLR models with about the same resolution.

In real world use, we haven't reached lens limitations that would show a difference yet, unless you buy poor quality lenses.

Also, it's not a crop if you have lenses designed specifically for a given sensor size. But, you'll still have angle of view differences, based on the sensor size, for a given focal length.

You have the same thing with different film sizes. You'll need a longer focal length for the same angle of view if you use film that's larger than 35mm. You'll need a shorter focal length for the same angle of view if you use film that's smaller than 35mm.

You see more benefit when going to larger film sizes, because you're increasing resolution of the film with surface area (given equivalent film characterstics, grain size, etc.).

But, with sensors that have the same number of photosites, regardless of whether it's an APS-C size sensor, or a sensor the size of 35mm film, it really doesn't make any difference whether you use a 100mm lens on the APS-C size sensor, or a 150mm lens on the 35mm size sensor for the same framing.

The detail captured will be the same with good quality lenses.


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Old Mar 10, 2006, 10:58 AM   #94
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You guys are THICK! :-) :lol:

One of those cheap little point and shoots with a 10x power zoom uses the cropping factor to "magnify" the image. And this kind of magnification IS GOOD, because it allows more pixels on the target. But it doesn't increase "resolution" in the scientific meaning of that word.

It resolves details that are already there to be resolved.

When you purchase a professional microscope you get TWO ratings. The apparent magnification AND the TRUE resolving power.


*****************************





Magnification and Resolution

Magnification is how much an image is enlarged under a microscope. Resolution is the amount of detail you can see. If you can magnify an image without increasing its resolution, that's empty magnification. We usually think in terms of the magnification of a microscope, but resolution is even more important. A greatly enlarged blur is still a blur.

Resolution is usually expressed in terms of the minimum distance observable between two objects. The smaller the distance that can be seen between two objects, the better the magnification. The resolvable distance for an objective lens is 0.61 l/N.A., where l is the wavelength of the light and N.A. is a property of the lens called the "numerical aperture."

Numerical aperture is a measure of the angle of the cone of light that can enter the objective lens. The bigger the N.A. the better, since N.A. is in the denominator of the equation. But each lens has a limit to its N. A. The objective lenses of many microscopes has the maximum N.A. inscribed on it.

To Demonstrate Resolution, Use Diatoms

1. Obtain a slide with diatoms on it. Special "test slides" of diatoms are available from scientific supply companies. Many diatoms have patterns of tiny dots on their surfaces, and some of the dots are near the limit of resolution.

2. The simplest thing to do is to look at the slide with the iris diaphragm way open and again with the iris diaphragm stopped way down. Stopping down does help increase contrast, but it also lowers N.A. way down by narrowing the cone of light. When N.A. gets smaller, the resolution gets to be a bigger number. So it's better to leave your condenser nearly wide open and then adjust the light level at the light source or put neutral density filters between the light source and the condenser.

3. Another way to see the relation of N.A. to resolution is to obtain eye pieces of two distinctly different magnifications. Suppose you had a 10 X and 5 X ocular or eyepiece. Then combine these with different objectives to get close to the same magnification. (40 X objective and 5 X ocular gives 200X; so does 20 X objective and 10 X ocular.) You will see the same magnification but different resolutions. Look at the numerical apertures of the objectives (often inscribed on the lenses) to see the reason for the difference in resolution.

4. If you don't have diatoms, a slide with many fine lines or with circular perforations will do also. A section of a testis with sperm tails in it will do. Ambystoma (salamander) testes are quite good.

http://www.classtech2000.com/nsta01/magres/magres.htm

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Old Mar 10, 2006, 11:08 AM   #95
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DBB wrote:
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You guys are THICK! :-) :lol:

One of those cheap little point and shoots with a 10x power zoom uses the cropping factor to "magnify" the image. And this kind of magnification IS GOOD, because it allows more pixels on the target. But it doesn't increase "resolution" in the scientific meaning of that word.

It resolves details that are already there to be resolved.
Dave:

What difference does it make in real world use with these cameras?

Who cares how they resolve the detail if the results you can get are the same using a shorter focal length on a smaller sensor, versus a longer focal length lens on a model with a larger sensor?

As long as the lens is capable of resolving the detail a sensor is capable of capturing, it doesn't make any difference which solution you use for detail purposes.

Now, if you look at other differences (for example, depth of field), then one solution may be preferrable versus another, for what you are trying to accomplish.

Heck, Steve shoots with a Nikon DSLR most of the time. But, do you know what camera he uses to take the closeups you see in the reviews? A Nikon Coolpix 4500. Before that, he used a Nikon Coolpix 995. Before that, he used a Nikon Coolpix 990...

Why? Dramatically greater depth of field for any given aperture and angle of view, with virtually no distortion because the "sweet spot" for macro use with these cameras is at around half zoom. That's a benefit of using a much shorter focal length lens with a smaller sensor if you want more versus less depth of field.

You use the best tool for what you're shooting. But, for detail purposes, it really doesn't make any difference if you're using a solution with an APS-C size sensor with a shorter focal length lens, or a solution with a 35mm size sensor using a longer focal length to get the same framing, provided the sensors and image processing are equivalent for resolution they are capable of capturing.


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Old Mar 10, 2006, 11:17 AM   #96
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JimC wrote:
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Dave:

What difference does it make in real world use with these cameras?

Who cares how they resolve the detail if the results you can get are the same using a shorter focal length on a smaller sensor, versus a longer focal length lens on a model with a larger sensor?

As long as the lens is capable of resolving the detail a sensor is capable of capturing, it doesn't make any difference which solution you use for detail purposes.

Now, if you look at other differences (for example, depth of field), then one solution may be preferrable versus another, for what you are trying to accomplish.

Heck, Steve shoots with a Nikon DSLR most of the time. But, do you know what camera he uses to take the closeups you see in the reviews? A Nikon Coolpix 4500. Before that, he used a Nikon Coolpix 995. Before that, he used a Nikon Coolpix 990...

Why? Dramatically greater depth of field for any given aperture and angle of view, with virtually no distortion because the "sweet spot" for macro use with these cameras is at around half zoom. That's a benefit of using a much shorter focal length lens with a smaller sensor if you want more versus less depth of field.

You use the best tool for what you're shooting. But, for detail purposes, it really doesn't make any difference if you're using a solution with an APS-C size sensor with a shorter focal length lens, or a solution with a 35mm size sensor using a longer focal length to get the same framing, provided the sensors and image processing are equivalent for resolution they are capable of capturing.

Right, on the 5D the pixel size is 8.2µm but on the 20D/30D it is 6.4µm. The 8.2MP is spread over a smaller area than the 12.8MP on the 5D.

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Old Mar 10, 2006, 11:24 AM   #97
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Quote:
You guys are THICK!


oh man, I had to pick myself up off the floor twice, and I still cant stop laughing! Stop clinging to that silly and irrelevant example and respond to some of the posts made in the last two pages. Particularly (this one was for you):

Quote:
Very specific example then, Canon Rebel XT wtih a 35mm f/1.4L lens. What is the sensor resolution? What is the lens resolution?
Feel free to guess and aproximate, to suit your hypothesis.

I can just see you over there at your keyboard chanting "I know this makes sense, I know it makes sense, I know it makes sense". Well, I believe that you believe....
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Old Mar 10, 2006, 11:52 AM   #98
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JimC wrote:
Quote:

What difference does it make in real world use with these cameras?

Who cares how they resolve the detail if the results you can get are the same using a shorter focal length on a smaller sensor, versus a longer focal length lens on a model with a larger sensor?

As long as the lens is capable of resolving the detail a sensor is capable of capturing, it doesn't make any difference which solution you use for detail purposes.

Now, if you look at other differences (for example, depth of field), then one solution may be preferrable versus another, for what you are trying to accomplish.

Heck, Steve shoots with a Nikon DSLR most of the time. But, do you know what camera he uses to take the closeups you see in the reviews? A Nikon Coolpix 4500. Before that, he used a Nikon Coolpix 995. Before that, he used a Nikon Coolpix 990...

Why? Dramatically greater depth of field for any given aperture and angle of view, with virtually no distortion because the "sweet spot" for macro use with these cameras is at around half zoom. That's a benefit of using a much shorter focal length lens with a smaller sensor if you want more versus less depth of field.

You use the best tool for what you're shooting. But, for detail purposes, it really doesn't make any difference if you're using a solution with an APS-C size sensor with a shorter focal length lens, or a solution with a 35mm size sensor using a longer focal length to get the same framing, provided the sensors and image processing are equivalent for resolution they are capable of capturing.

Absolutely! A truly valid point! Noise, useable ISO are far more practacle things to discuss when talking about photography.

But after all, this started as a discussion on the scientific meaning of the terms, "Focal lenght multiplier," and "Cropping Factor."

And I do believe that I have made my case.

Morever this touches on my personal use and my own photographic equipment. What is an academic discussion when you are using a 200mm vs 300mm lens suddenly become a real aspect to photography when you are shooting an 1100mm, or as I occasionally do, a 2200mm lens.

But we've beaten this to death. I will allow Mr. T. Moreau to enjoy my "ignorance" of basic science, and simply say that laughter is good for your health. If I've given him some good laughs with my posts - I can enjoy my good deeds...:lol:

Full frame from 200 feet off. D1x, 5 MP sensor



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Old Mar 10, 2006, 12:27 PM   #99
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I almost hate to comment here, as this thread seems to have turned into a type that I hate (and one you almost never see on this from.) I haven't read it all, but it seem like people are basically restating their position, not really listening to each other and just going back and forth without going anywhere. Most here seem to be ignoring what JimC has recently said. Maybe this is not true, but it certainly looks like it. I have to agree with it, so I wanted to re-inforce it.

So, could someone please tell me why the following situation would not produce the results I believe they will produce:

With these assumptions:
- both the 200mm and 300mm lenses are idential except for the focal length. Down to the screws used to hold them together... I mean IDENTIAL.
- I have one camera with a full frame 8MP sensor (4000x2000 pixels)
- I have one camera with a 1.5x "crop" factor 2MP sensor (2000x1000 pixels)
- We will assume the photosites are of similar size, density and "quality". Truly imaging if you just took a knife and cut 1/4 off each side of the 8MP sesor - you'd be left with the middle 1/2 of the sensor and we put that in the other camera.
- The cameras are idential. Same image processing... everything. Imagine that smaller sensor was swapped into the same camera body (not possible in reality, I know.)

In this situation:
- Lets assume a reasonable target distance of 100 feet away. (Ignore the solar system distances like photographing mars. To many issues creep in which we can safely ignore at more reasonable distances.)
- Assume that the two camera bodies are put one above the other on the same tripod.
- Assume the 8MP camera as a 300mm lens. Assume the 2MP camera has a 200mm lens.
- Both take pictures at the same time.
- I go back to my computer and crop the full frame camera's image to the middle 2000x1000 pixels. (we all know that a 1.5x crop factor camera actually as 1/4 the resolution, right?)

Then I believe it is exactly correct to say this (and my personal experience bares this out, DAMN IT):
the images produced, when examined on the computer, will be almost exactly the same (except a slight difference in depth of field & the slight difference in location because the images were not capture from exactly the same point.) Everything will be the same size in the image and will have the same amount of detail.

If this is not true, I'd like to hear why.

In my experience, when I switched from the 20D (8MP 1.6x crop factor) to the 1D MkII N (8MP 1.3x crop factor) it was as if all my lenses were shorter. My subjects were smaller in the frame (I'm ignoring depth of field issues.) They didn't have a noticable abount of detail loss (although they should have, the photosites are more densly packed in the 20D and therefor should resolve more detail. The reality so far is that I have been unable to notice this difference.) So I had to start using the 2x TC instead of my 1.4x TC because I needed to make up that extra "reach" I "lost" on my 600mm. I gained a lot (faster AF, deeper faster RAW buffer, and more) but I also lost some thing.

And I wanted to add that DBB's comments about resolving power and magnification should almost be moved into a separate thread. They are interesting and should be discussed outside of this thread (and its current tone.)

Eric

ps. I hope I don't regret posting into this tread. The way Mark47 and tmoreau have been going at each other is very un-"stevesforums" like. I notice that neither of you have posted a lot here and this thread has gone in a way which we generally don't like here. If you two perfer this type of heated back-and-forth (which usually resolve with no resolution) I would suggest joining www.dpreview.com instead. From what I've seen over there, the... "tone"(right word?) of this thread would fit in much better there.
pps. I'm not trying to encourage either of you to leave, I'm just staying the above from years of experience posting here. Personally, I'd rather see this thread evolve or die... and not continue as it is. But I don't control that... if it does continue, I'll just ignore it. I'm a firm believer of "if it hurts, don't do that" and taking personal responsibility.
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Old Mar 10, 2006, 12:56 PM   #100
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Okey-dokey, lets dive right into the numerical aperture value that you hold so dear yet haven't explained in your own words. First, some reference material that doesn't come from a "hiigh" school. That link shows there is some relation to photography, in fact using the aperture specification that is included in all marketing specs for all lenses. Good. This page is the next step on our journey, and contains a wealth of good information. There is another page that goes into greater detail about the f-stop designation and how to better understand it, A Tedious Explanation of the f/stop.

"Picture quality also varies with f-stop. The optimal f-stop varies with the lens characteristics. For modern standard lenses having 6 or 7 elements, the sharpest image is obtained around f/5.6–f/8, while for older standard lenses having only 4 elements (Tessar formula) stopping to f/11 will give the sharpest image. The reason the sharpness is best at medium f-numbers is that the sharpness at high f-number is constrained by diffraction, whereas at low f-numbers limitations of the lens design known as aberrations will dominate."

Remember the gigapixel lens? 215mm f/22, that means the aperture is Ø9.77mm, four billion pixels. A 100mm f/2.8 SLR lens has an aperture diameter of 35.7mm! Well not really, the aperture values I just listed would be accurate only if the apertue was right behind the front element. Its not, so its actually smaller, but the ratios still work out the same.

"The size of the finest detail that can be resolved is proportional to λ/NA, where λ is the wavelength of the light. A lens with a larger numerical aperture will be able to visualize finer details than a lens with a smaller numerical aperture."

Blah blah blah, anybody want to crunch the numbers and tell us what the smallest theoretical detail a 100mm f/8 lens can resolve at 100 yards? Do the same for a 150mm f/8 lens, while your at it. This is easy, and it answers my previous question twice posed scientifically (remember, the one you refused to answer even with a general guesswork of a response?). Its limitation of course, is that this is the best a lens could perform, and its actual performance will likely be less.

Now that were done with that sludge, what does it all mean? Simply, that the lens can resolve more than the sensors we put behind them, with current sensor technology. Gee, where have I heard that before. Bottom line, the "crop factor" does indeed make a 100mm lens the practical equivilent of a 150mm lens, and the mysterious "magnification" factor... well its not a factor.
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