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10-01-2006, 12:31 AM   #1
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crop factor, quality, digital to analog comparison

I posted this question before but am unsatisifed with the answers I received. There's something missing. This is the basic premise;

(I understand the fov aspect; that the 135mm is equivalent in terms of fov relative to the 200mm being used on film cameras; it is the quality with respect to reach and image size captured proceeding then to quality captured, that I'm questioning. )


1.The size of the capture of a bird is X mm using a 200mm lens and an analog camera.

2.The size of the bird is Ymm using a 135mm lens on a digital camera.

X will not equal Y UNLESS I up-res the digital negative, correct?. Doing this, don’t I lose quality relative to the analog print? (I had heard that the APS-C and film were equivalent in terms of resolution; I'm assuming this means at the same size--but is that printed image or onscreen sizes?)

So, is the quality of a digital 135mm focal length capture on APS-C, printed at 8x10 the same as that of an 8x10 print, captured on analog film and taken with a 200mm lens?


I guess the way I see it, if you are used to taking pictures at the long end (say, 200mm and above but I'm sure this theory is across the board), that using anything less than the same focal length will give you less quality given the object captured is the exact same size, upon printing.

To tell someone then that a 50-135mm on digital medium is equivalent to using a 70-200 on analog, will give the wrong perception. The fov will be equivalent due to the crop factor but the size of the object on the picture (captured with the 135mm on digital) will be smaller unless up-resed digitally and doing so, degrades the image relative to the analog capture at 200mm. Is this a fair statement?

And yes, I'm assuming exact same lens qualities. That is, that the quality of the 135 is equal to that of the 200 (if used on the same medium), just to take out individual lens characteristics.


Sorry, but the logic is escaping me then as to how anyone could advise someone coming into digital that they will be just as well off with the shorter (than they are used to) focal length lens (135 from 200).

Maybe I just need the logic spelled out to me, but unless the resolution of digital is greater than film, using the same lens FL, any up-resing will lower the capture's quality.


Help?


Michael


Last edited by MichaelRD; 10-01-2006 at 12:36 AM.
10-01-2006, 06:17 AM   #2
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To tell someone then that a 50-135mm on digital medium is equivalent to using a 70-200 on analog, will give the wrong perception. The fov will be equivalent due to the crop factor but the size of the object on the picture (captured with the 135mm on digital) will be smaller unless up-resed digitally and doing so, degrades the image relative to the analog capture at 200mm. Is this a fair statement?

Yes and no. Yes there is a difference between the 2 captures, the fov will be the same, the print of the images will not. It's the old battle of film vs. digital. If I shoot with a 28mm on my D and then shoot the same shot with a film body with a 50mm and print both on an 8x10 sheet. The film printed in a dark room. I will see the difference with a loup and at times with my eyes. I believe it has more to do with dynamic range than anything else.

The NO part, your dealing with 2 different media. There's no equal comparison. If you scan the neg and compare the 2 on screen, your comparing the ccd image vs.the image generated by the scanner.

I shoot 30% film and 70% digi. I find an advantage with the digi using long lens and high iso settings. The grain of the print of the digi is less. ISO 800-1600 film is like rocks :-) The FOV with the digi has helped at times also.

Don't know if this helps, just my take on the situation.

Dana
10-01-2006, 07:45 AM   #3
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An APS-C sized sensor is no match for film

QuoteOriginally posted by MichaelRD Quote
1.The size of the capture of a bird is X mm using a 200mm lens and an analog camera.

2.The size of the bird is Ymm using a 135mm lens on a digital camera.

X will not equal Y UNLESS I up-res the digital negative, correct?. Doing this, donít I lose quality relative to the analog print? (I had heard that the APS-C and film were equivalent in terms of resolution; I'm assuming this means at the same size--but is that printed image or onscreen sizes?)

So, is the quality of a digital 135mm focal length capture on APS-C, printed at 8x10 the same as that of an 8x10 print, captured on analog film and taken with a 200mm lens? ...
Michael
Correct, X is not equal to Y.
Yes, you lose quality by upsampling.
No, current APS-C sensors and film are NOT equivalent in terms of resolution.

Film outperforms digital by far, so your premise for the discussion is false.

A 35 mm negative from a slow film professionally scanned can yield upwards of 40 MP. You can get up to 24MP from a below $1,000 scanner.

If you need the best possible resolution, use film. If you need convenience, fun and fast turn around use digital.
10-01-2006, 10:45 AM   #4
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QuoteOriginally posted by Ole Quote
Correct, X is not equal to Y.
Film outperforms digital by far, so your premise for the discussion is false.

A 35 mm negative from a slow film professionally scanned can yield upwards of 40 MP. You can get up to 24MP from a below $1,000 scanner.

If you need the best possible resolution, use film. If you need convenience, fun and fast turn around use digital.
And you need to win a lottery in order to buy lenses that can actually render 40 or 24mp on film.

10-01-2006, 11:09 AM   #5
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more confusion...

Please set me straight if I've got this totally wrong...

A 50mm lens on a digital camera will produce the fov of a 75mm lens on film, but that is essentially a crop - the image that is projected on the ccd by the 50mm lens is exactly the same size as the same lens would produce on a film camera. The optics are identical, it's just that the ccd is smaller and only can register a portion of the projected image.

The way I see it, if you're going to compare apples with apples, you should compare the quality of the digital image with the corresponding portion of the film image. Then it "simply" comes down to digital resolution vs film resolution, which I realise is a whole other can of worms. I read something about grain size, lines per inch, pixels per inch, and so forth, glazed over and decided I didn't care so long as I was getting pictures that made me happy!

By extension, because the 50mm on digital is optically the same as the 50mm on film, although it produces the fov equivalent to 75mm on film, the other optical qualities are not the same, e.g. depth of field, foreshortening, etc.

So how wrong am I?

Julie
10-01-2006, 12:01 PM   #6
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Please set me straight if I've got this totally wrong...


Everything you said is true .

There maybe a very slight change in DOF because of the smaller sensor, this shows up more in the small digicams rather than the dslr.
10-01-2006, 12:30 PM   #7
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thanks everyone

Thank you everyone for chiming in and pretty much verifying what I've been thinking. It wasn't my opinion that film and digital were similar--I was just repeating what was mentioned in the other thread. So because the opposite is true, that the digital medium is not as resolute as film, then in no way would one be able to take the same quality picture of the same object, with distance in mind, when using a shorter focal length lens that fov-wise, matches up to a longer focal length lens on film. When someone suggests then that the new 50-135 from Pentax is like using a 70-200 on film, this is in error, except for the fov considerations, yes?

This all started because when I crossed over from analog to digital, the opinions and perceptions I got while reading poster responses all seemed to convince me that my 60-300 ancient off brand Pentax-fit lens was now like using a 90-450. Even once I found out that the object I was trying to capture, a bird in this case, would NOT be magnified (as if I really was using a 450mm lens), the advice rang hollow. I'd still need the real 450 to get the effect of bringing the object closer. THAT is what bothers me when such statements are thrown around because I think we all want to believe we now have greater reach as well as the narrower field of view. If I want a similar picture as I used to get using the 60-300, I'll STILL need a lens with 300mm of reach at the long end AND I'll probably STILL get less quality because you've all now educated me that the resolution of film is still superior, yes?


Ok, guess my lil quest can end if that's all cleared up...


Michael
10-01-2006, 06:01 PM   #8
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QuoteOriginally posted by MichaelRD Quote
This all started because when I crossed over from analog to digital, the opinions and perceptions I got while reading poster responses all seemed to convince me that my 60-300 ancient off brand Pentax-fit lens was now like using a 90-450. Even once I found out that the object I was trying to capture, a bird in this case, would NOT be magnified (as if I really was using a 450mm lens), the advice rang hollow. I'd still need the real 450 to get the effect of bringing the object closer. THAT is what bothers me when such statements are thrown around because I think we all want to believe we now have greater reach as well as the narrower field of view. If I want a similar picture as I used to get using the 60-300, I'll STILL need a lens with 300mm of reach at the long end AND I'll probably STILL get less quality because you've all now educated me that the resolution of film is still superior, yes?
Michael
You're not quite right here.

Let's say that you print to a 4in by 6in (10cm x 15cm) piece of paper, and you do not crop. That is, the full 35mm negative is printed, and the full digital file is printed.

If the bird filled all of the sensor with a 300mm lens, then you would need a 450 mm lens for the bird to fill all of the negative.

In other words (resolution set aside), if you want identical results (a given bird filling the frame), the the APS-C sixed sensor does give more reach; you need only a 300mm, not a 450mm in this example.

10-01-2006, 07:44 PM   #9
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hmmm

QuoteOriginally posted by Ole Quote
You're not quite right here.

Let's say that you print to a 4in by 6in (10cm x 15cm) piece of paper, and you do not crop. That is, the full 35mm negative is printed, and the full digital file is printed.

If the bird filled all of the sensor with a 300mm lens, then you would need a 450 mm lens for the bird to fill all of the negative.

In other words (resolution set aside), if you want identical results (a given bird filling the frame), the the APS-C sixed sensor does give more reach; you need only a 300mm, not a 450mm in this example.
Ole;

In simplest terms because this still stymies me, if I stand in the same spot, take a picture of the bird with 135mm on a digital camera then do the same using the 200mm on a film camera, then we print both at 4x6, the following is going to be true?

1.image size of the object (bird) will be identical
2.fov captured will be identical
3.level of detail will be???? (quality=??)

I would assume the level of detail seen in the 200mm to be the same quantum difference as if I'd taken the same pic using the 135mm on the film camera. That is, the 200 will show more, be better at depicting detail than the 135. Especially if the resolution of digital does not equal film, how could someone get parity comparing the capture of 135 on digital to the capture of 200 on film?

I guess I could state it this way, too; I take a pic using the 200 on film, print the pic at 4x6, physically crop the pic by a factor of 1.5x and the result should look better than if I'd taken the pic using a 135 on digital and printing that out at 4x6. Would that be a fair assertion?
10-01-2006, 08:10 PM   #10
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QuoteOriginally posted by MichaelRD Quote
Thank you everyone for chiming in and pretty much verifying what I've been thinking. It wasn't my opinion that film and digital were similar--I was just repeating what was mentioned in the other thread. So because the opposite is true, that the digital medium is not as resolute as film, then in no way would one be able to take the same quality picture of the same object, with distance in mind, when using a shorter focal length lens that fov-wise, matches up to a longer focal length lens on film. When someone suggests then that the new 50-135 from Pentax is like using a 70-200 on film, this is in error, except for the fov considerations, yes?
Perhaps it would be helpful to separate the two variables that are getting confused here - film/sensor size and film/sensor resolution.

The way a lens functions is relative to the size of the sensor. Imagine taking a picture of tree with a full frame sensor and a 100mm lens, a picture where the bottom of the tree is at the bottom of the frame and the tip is at the top.

To get that same coverage while standing the same distance from the tree while using a "1.5x APS" sensor you would need only a 67mm lens.

My Oly C2100z would capture the same scene with the zoom set at ~18.5mm due to its quite small sensor.



--

Resolution is something different, and has no relation to lens. 35mm color film can range from about 14 megs (very slow, very fine grained film - shot, processed, and scanned carefully) to only a couple of megs for fast (ISO 1600/3200) film.

For what most people shoot, ISOs in the 100-400 range one gets about 5-7 megs worth of information.

http://www.clarkvision.com/imagedetail/film.vs.digital.1.html

You could use a four meg 1.5x APS camera and a 12 meg 1.5x APS camera and the image captured would be the same with a 67mm lens. The tree would still stretch from the top to the bottom of the print.

The difference would be the amount of resolution in the image. You could make better large prints with the 12 meg camera. If you printed each file 12"x16" the 12 meg image would be "crisper", you would be better able to see the details.
10-01-2006, 08:11 PM   #11
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A while back we compared film to digital, maybe this will help illustrate the issue:

http://themotec.com/Ole/WEB_Gallery34/index.htm#8

Compare the 50mm digital shot with the 70mm film shot: they are basically identical regarding "reach" and FOV.

We did not discuss resolution in the test.
10-01-2006, 09:05 PM   #12
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How about putting the 50mm (1.5x) digital and the 70mm (35mm film) frames together in a single frame?

That should make it easier for people to see.
10-01-2006, 09:46 PM   #13
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QuoteOriginally posted by Bob Wallace Quote
How about putting the 50mm (1.5x) digital and the 70mm (35mm film) frames together in a single frame?

That should make it easier for people to see.
Here you go:

Note, the 70mm focal length picture is shot with a zoom, so the focal length is probably not exactly 70mm.
Attached Images
 
10-01-2006, 10:11 PM   #14
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Nice. That should make it easier for people to see how the 1.5x crop factor works.

You might want to add a note that the two images were taken at the same distance from the scene.
10-02-2006, 08:47 AM   #15
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again, thanks

Thanks Ole and Bob for continuing this discussion. I guess I'm convinced. Not having my old ME Super anymore, this wasn't an experiment I could easily do anymore, so I'm glad there's an example. Must be the Doubting Thomas in me that has to see the actual evidence. So though it still seems like some sort of magnification magic is going on, I can see that the two images are pretty darn close in quality. I actually downloaded the two separates and did what you did, Ole, in PS so I could see them side by side. Thanks again. To verify, the digital version at 50mm wasn't cropped or up-resed(nor the 70mm film version), correct?


Michael
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