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Popping the Myth of the Focal Length Multiplier I
- Thread starter Chato
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Joe0Bloggs
Veteran Member
Actually no, then it would become purely a crop factor. The term 'focal length multiplier' can be used with some merit exactly BECAUSE the pixels on crop cameras are denser and hence extract more detail out of the smaller area.
KEITH-C
Forum Pro
Like others I have grown tired of this thrashing of an old subject. I have yet to hear of anyone who moves yards backwards in order to get the same FOV that any lens would give on a FF camera when they are using a cropped sensor - I wonder why ?
Keith-C
Keith-C
John Bean (UK)
Forum Pro
Well, he is a writer after all ;-)
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Tim the Grey
Veteran Member
You confirmed WHICH 'Full frame' you keep referring to.
I have 4 different size 'Full Frame' SLRs in my house, which one are you talking about?
If you are going to sound off as though you want to be taken seriously, then DEFINE your terms, sir!
8^)
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I have 4 different size 'Full Frame' SLRs in my house, which one are you talking about?
If you are going to sound off as though you want to be taken seriously, then DEFINE your terms, sir!
8^)
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Henrik Andersson
Senior Member
I don't agree with you here. At 45mm and F5.6 you are definitely diffraction limited on small sensor systems. Even on 35mmFF you start to become diffraction limited.
And remember that the 450mm lens only have to be a F56 to have the same resolving power and diffraction limitations if the format is 10x bigger then used with the 45mm lens.
The diffractions will of course be 10x bigger on the F56 system but detail will also be 10x bigger.
Aperture have everything to do with resolving power/detail if you are diffraction limited. I hope you agree on that sentence ?
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Henrik
In another thread I am arguing with people who TELL me that thier little digicam with it's 450mm EQUIVALENT, and 10x cropping factor can match the resolving power of a 450mm telephoto lens.
Now, I'm not referring to the quibling argument that the sensor is inferior, etc, etc,
NB. A sensor, no matter HOW large, or How many MP's cannot resolve detail that the light striking it does not possess. The larger lens, in the scientific meaning of the word "magnification," resolves more detail. The MUCH smaller lens, due to the crtopping factor gives us "empty magnification." The illusion of magnirifaction because we are presented with the larger BUT cropped image.
They are arguing, that the resolving power of the system allows the 45mm lens to match the real telephoto - in other words, the cropping factor is REALLY a focal lenght multiplier The FLM - which is is not - That is BOTH a marketing term, and/or a term to give you the angle of view.
Here is the scientific definition of "empty magnification."
************
Magnification and Resolution
A microscopy demonstration by Donald Cronkite and Jewel Reuter
NSTA demos at the Swift Instruments booth. March 23 and 24, 2001
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."
http://www.classtech2000.com/nsta01/magres/magres.htm
Dave
nickleback
Forum Pro
Small-sensor cameras typically have around f/3 or f/3.5 max aperture at this focal length. The G7 is an exception (i.e. not typical) at f/4.8 and is bumping up against diffraction at the pixel level.
For 35mm systems diffraction limits are typically around f/22, but it all depends on the situation. If you are shooting very fine grain film and want maximum detail you should use a smaller CoC and therefore choose a larger aperture. But then you are very limited in what lenses you can use to get that detail through the glass.
I agree with everything here.
But typically, camera lenses at max aperture are not diffraction limited. I hope you agree with that.
Even on the G7, max detail is not wide open. Max detail on this camera is achieved at a diffraction-limited (by pixel size) aperture, presumably because the lens can't resolve more than that wide open. The review on this site used 22mm f/5, even though f/3.6 was the max aperture available at that focal length.
(warning: huge image)
http://www.dpreview.com/reviews/canong7/Samples/resolution/canonG7-F5.jpg
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To quote from the scientific definition of "Empty Magnification,"
"A clear blur is still a blur."
http://www.classtech2000.com/nsta01/magres/magres.htm
And that in fact is what you get when you multiply the number of pixels on the sensor. You get NO additional resolving power - merely the ability to clarify what is resolved BY THE LENS.
Now obviously if you have sensor of two pixels its ability to resolve detail will be, shall I say, reduced...
Nontheless the sensor cannot resolve detail that is not being presented to it. There is no Magic to the science of optics. You cannot turn a 45mm lens into a 450mm lens by reciting the formula or more pixels...
Dave
nickleback
Forum Pro
It can.
http://www.dpreview.com/reviews/panasonicfz50/page18.asp
http://www.dpreview.com/reviews/canoneos400d/page28.asp
Panasonic FZ50: 1850/1800 LPH
Canon 400D: 2200/1800 LPH
Both seem to resolve detail quite well. The 400D did a bit better, but it's shooting through a prime lens. If I believed your story, the Pany numbers should be about 1/3 the Canon numbers.
Absolutely correct. What you fail to notice is that the detail is there for the sensor to see.
You should read this link. NA is the angle of light. It is directly related to f number, not aperture diameter. In other words, NA for an f/2.8 lens is the same whether the lens is 45mm f/28 or 450mm f/2.8.
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tko wrote:
(snip)
And there is the practical aspects of why this question comes up. People who do photography who need telephoto - i.e. wildlife, astronomy, sports, etc, are sometimes under the impression that their $400 digicam can match real telephoto lenses and equipment.
Absolutely, the high resolution (not to be confused with resolving power) of these sensors can create some pretty pictures - but they have the resolving power of their little lens, not the resolving power of the actually focal length.
If a birders shot cannot resolve feathers with their 45mm lens, then equally so they cannot resolve feathers with the 450 equivalent -
Dave
(snip)
The above is completlely false. And that's why this question comes up. You are argueing against the science of optics and physics.
And there is the practical aspects of why this question comes up. People who do photography who need telephoto - i.e. wildlife, astronomy, sports, etc, are sometimes under the impression that their $400 digicam can match real telephoto lenses and equipment.
Absolutely, the high resolution (not to be confused with resolving power) of these sensors can create some pretty pictures - but they have the resolving power of their little lens, not the resolving power of the actually focal length.
If a birders shot cannot resolve feathers with their 45mm lens, then equally so they cannot resolve feathers with the 450 equivalent -
Dave
Jim F.
Veteran Member
Come on Tim, you know what he's talking about. FF here is not a MF or LF or anything else; 99.99999999% of the time it means a 24x36 35mm format as sold by all previous film body mfgs and now only by Canon.
I did not see in the test of the digicams what focal length was chosen. While the sSLR's were shot with primes.
Clearly comparing a prime with a prime will yield similar results in resolving power.
Dave
Jim F.
Veteran Member
Dave,
This is bad, bad bad...
Don't annoy the villagers. I've fought this argument for many years here and the only thing you do it get them (the 1.5x, 1.6x crowds) lathered up and reaching for their pitchforks.
The more enlightened know that pixel density is not the same thing as magnification or lens extension, but for your own good stay away from the "knoin" camp if you want to keep your head. Many over there still howl at the moon when someone brings up the dreaded "larger sensor".
You'll be pilloried while they're preparing your stake......
This is bad, bad bad...
Don't annoy the villagers. I've fought this argument for many years here and the only thing you do it get them (the 1.5x, 1.6x crowds) lathered up and reaching for their pitchforks.
The more enlightened know that pixel density is not the same thing as magnification or lens extension, but for your own good stay away from the "knoin" camp if you want to keep your head. Many over there still howl at the moon when someone brings up the dreaded "larger sensor".
You'll be pilloried while they're preparing your stake......
I suspect the error is that the above formula is for calculating the image resolution which doesn't tell us about overall detail unless the format size is taken into account. One could have a very high image resolution while at the same time having a poor resolution of the object being photographed or vice versa. This explains the high resolutions achievable with large format systems despite the low (image) resolution lenses used.
Perhaps the better formula would be something like 250,000λ d where λ is the wavelength in metres and d is the aperture, also in meters. This formula gives the resolving power of the lens in seconds of arc so clearly, larger physical apertures can achieve higher resolutions, irrespective of focal ratio.
Focal length is (theoretically) unimportant when calculating the resolving power of a lens but in the real world, it's far easier to construct diffraction limited optics with relatively slower focal ratios which implies large focal lengths if one desires to use large apertures.
nickleback
Forum Pro
Click on the image and check the EXIF data, it is about 20mm IIRC. The Canon was shot with a 50mm lens. The distance is about the same. Yet, somehow, both resolve the same detail. According to you, this is not possible. Perhaps you should rethink your theories.
The comparison is a prime on the DSLR and a zoom on a digicam with a sensor 1/3 the size. The digicam is handicapped. Regardless, both end up with quite similar resolution at similar "35mm effective" focal lengths (i.e. around 80mm).
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Gerard M Foley
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keithallenlaw
Veteran Member
Exactly what I said, thank you. What do you get when you give
the 5D the same pixel density as a 30D? Basically a MKIIDs
Its all about the resolution and you basically quoted me but
from a different angle...
Logic is superior to emotion
BUT
Emotion is much more fun!
Watch out for the exposure police.
They will tell you that its wrong even
though they weren't there to witness it.
Come visit me at:
http://www.pbase.com/keithallenlaw
See my profile for what i shoot with.
the 5D the same pixel density as a 30D? Basically a MKIIDs
Its all about the resolution and you basically quoted me but
from a different angle...
--
Logic is superior to emotion
BUT
Emotion is much more fun!
Watch out for the exposure police.
They will tell you that its wrong even
though they weren't there to witness it.
Come visit me at:
http://www.pbase.com/keithallenlaw
See my profile for what i shoot with.
(I do not recommend reading this old subthread):
http://forums.dpreview.com/forums/read.asp?forum=1018&message=21847767
Boris
http://forums.dpreview.com/forums/read.asp?forum=1018&message=21847767
Would you please, please, stop quoting microscope-related articles? We're talking about digital cameras here. Not about microscopes. Things that you read about microscopes do not necessarily apply to digital cameras. Even though, as you point out, they are written by (gasp) scientists.
Resolving power is not a digital-camera related notion. Digital cameras deal with resolution , and resolution can - and does - grow with the number of pixels.
But, do you notice that the notion resolving power can't account for this reduction?Now obviously if you have sensor of two pixels its ability to
resolve detail will be, shall I say, reduced...
So, how do you explain the small-sensor digicams?
Boris
nickleback
Forum Pro
Yep.
"can" achieve is different from "does" achieve.
It's a nice theoretical argument, but it doesn't pan out for the cameras in question. Undoubtably if you had a very fine 450mm f/2.8 in front of a 35mm sensor with 2 micron pixels, and a very fine 90mm f/2.8 in front a 1/1.8" sensor also with 2 micron pixels, the 35mm sensor will absolutely smoke the 1/1.8" sensor for detail.
But that would be a 216mp 35mm sensor and 10mp 1/1.8". The 1/1.8" sensor with that pixel count exists today, the 35mm with that pixel count doesn't.
In the real world we are comparing cameras of similar pixel count. 6mp, 8mp, 10mp, 12mp, whatever, but not 216mp. At similar pixel counts, they test out about the same for resolution.
If you were to stuff 216mp into a 1/1.8" sensor and compare it to 216mp on a 35mm sensor, the 35mm sensor cam would win unless the 1/1.8" sensor cam has a very fine f/0.5 lens (and f/0.5 is the most you can do in air). Good luck!
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