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Old Mar 9, 2006, 1:13 PM   #61
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I think this one does an even better job of explaing this:

http://www.popphoto.com/article.asp?...p;print_page=y

it says this:

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That's actually in-camera cropping and not focal-length magnification.
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Old Mar 9, 2006, 1:33 PM   #62
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It's not cropping if you use a lens designed specifically for a given sensor or film size (and you can get lenses with a smaller image circle designed for DSLR models).

You'll still have more apparent magnification (narrower angle of view) for any given focal length, using the same focal length lens on a smaller sensor or film size compared to using that focal length on a 35mm model.

The opposite is also true.

If you use a camera with film (or sensor) that's larger than 35mm film (for example 645 format), you get less apparent magnification (wider angle of view) for any given actual focal length.

Is the 35mm camera using a "cropped view" compared to the 645 format camera, since the 35mm camera has a narrower angle of view for a given focal length lens (more apparent magnification)?

No, because the lenses for both were designed specifically for that format, and the angle of view you have for a given focal length lens is related to the size of the sensor or film.

The confusion stems from the fact that DSLR manufacturers designed cameras that can also take lenses designed for 35mm film models.

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Old Mar 9, 2006, 2:06 PM   #63
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Everyone would do well for forget about magnification. You've chosen a camera that has X megapixels and can produce X amount of detail on an enlarged print. You have decided this is enough resolving power for you, ie, you can print full frame at your desired size and have all the detail you need.

Now, choose a lens that fills the frame with your subject, and your done. Feel confident that the lens you chose can out-resolve your sensor, because chances are it can (with very few exceptions in the current market).

Did you choose a 50mm lens? 200mm? 10mm? Does it matter? It does not.

If the attached chart is incorrect, I'm sure somebody will let me know. Otherwise, it should explain the whole equivalency mess fairly clearly.

Jim's link from the first page is great because it tells you the FOV in degrees for the common 35mm focal lengths. You can use this and the conversion factors to back figure the FOV of any camera with 35mm equivilent focal lengths published.

http://consumer.usa.canon.com/app/ht...al_length.html
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Old Mar 9, 2006, 2:07 PM   #64
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JimC wrote:
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It's not cropping if you use a lens designed specifically for a given sensor or film size (and you can get lenses with a smaller image circle designed for DSLR models).
Do you mean lenses like the Canon EF-S range? But I'll be using my existing lenses (canon & Tamron EF) that I've had for many years. So I'll get cropping as described on the sites I posted above. How about the frame you see in the view finder? The article here

http://www.the-digital-picture.com/C...op-Factor.aspx

says I will be seeing 95% of the frame on a 20D (which I expect is the same on a 30D). I am guessing this means 95% of the frame that the resultant image will show right?
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Old Mar 9, 2006, 2:15 PM   #65
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Yes, you'll have the stated percentage of the view seen by the sensor, not of the entire image circle being projected by the lens, if the lens is not designed specfically for the smaller format sensor.

That's where the confusion comes in (because manufacturers decided to use bodies that take the same lenses a 35mm camera can use).

Models like the Olympus E series don't have this problem, since the lenses are designed specifically for the smaller sensor. But, because the sensor is smaller, you get more apparent magnifcation (narrower angle of view) for any given actual focal length.

These Olympus DSLR models are not cropping anything. But, you still need to multiply the actual focal length of a lens by 2x to see how it compares from an angle of view perspective to the same focal length lens used on a 35mm camera.

With prosumer models using tiny sensors, with very short focal length lenses to get the same angle of view as you'd need a much longer focal length lens for on a 35mm model, you don't have as much confusion.

For one thing, they usually publish the 35mm equivalent focal lengths for these models (even though the actual focal lengths are usually marked on the lenses).

That's what the so called "crop factors" and "focal length multipliers" are good for (helping users understand how the angle of view/apparent magnifcation compares to a 35mm model, since 35mm cameras are very popular).


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Old Mar 9, 2006, 2:43 PM   #66
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OK, thanks for the explanation Jim. I think I get it now. I was wondering if I should be getting an FF D-SLR. Now I have made up my mind, I am definetely getting an EOS 30D :-)
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Old Mar 9, 2006, 4:47 PM   #67
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JimC wrote:
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DBB wrote:
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Actaully the Nikon D2x puts MORE pixels on the target than the Mark II 1Ds...:G

Does it not?

If you can't SEE tjhe details, no sensor will be able to resolve them.

Dave
Actually, no. The D2x is 12 Megapixels versus the 16MP sensor in the Canon.

But, if you used the same lens on both cameras, you'd get more apparent magnification with the D2x (but the Canon would have a higher resolution sensor to help make up the difference). Can you reach a point where sensor can resolve more than a lens? Sure.

I applaud Canon for keeping the new EOS-30D at 8 Megapixels. That helps to keep noise down, and helps insure that you don't have a problem with the sensor outresolving the lens.

But, if you test a model like the D2x, it still outresolves an 8MP model like the EOS-20D on resolution chart tests (so with better quality lenses, we haven't reached that point yet).
The D2x BECAUSE of it's crop factor puts more pixels on the target. Remember, it's a crop. The two, shooting from the same distance, the Mark II would have to be 18 MP to match the D2x.

With the Mark 11 I used the Swarovski Scope, with the Nikon I used the Sigma 50 to 500....

I must say I find the arguments about light gathering pendantic. I have an 8x magnifying glass with a diameter of 1/3 of an inch. I have a 2x magnifying glass, 6 inches in diameter.

The argument seems to be, that any low mm lens (assuming a very high quality) can resolve the same amount of detail as the most powerful of telephoto's given that the sensor has enough MP's to clarify the result.

If this is true then it's easily tested. There are a number of P&S camera's with small sensors and large crop factors. They can certainly match (at low ISO's) any DSLR. Such being the case, one could simply shoot the moon, and test the results.

You WILL lose.
***********************

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

For a crystal clear demonstration take a look at this link
http://homepages.gac.edu/~cellab/chp...figure1-1.html

Dave
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Old Mar 9, 2006, 5:03 PM   #68
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You're showing resolution limitations of the objectives used in those examples.

In the case of most current DSLR models using good quality lenses, the sensors are capable of outresolving the lenses.

If you want samples, just look at our review samples. You'll see cases where a model with a smaller sensor using a shorter actual focal length lens can outresolve a model with a larger sensor using a longer focal length lens. We have some of the same subjects in each review. That's not always the case, since we are starting to see some pretty absurd pixel counts in very small cameras.

Phil Askey over at dpreview.com performs resolution chart tests, too. Even an 8MP prosumer model like the Olympus C-8080Z can outresolve a 6MP Canon EOS-10D, and come very close to the EOS-20D.

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Old Mar 9, 2006, 5:05 PM   #69
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This is a nice thread, but it got a little more technical than what my feeble little mind can handle...:?:?:?!!!!

JimC, nice take on the "crop issue" especially in using the 4/3 as an example. I'm gonna be reading this thread until I understand what everybody means.

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Old Mar 9, 2006, 5:08 PM   #70
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Bottom line (as I mentioned before), you have to take each sensor/lens combination on a case by case basis to see what the combination is capable of resolving.

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