Final word: crop factor

[jaypie77]

I'd like to put forward a question about crop factor and, specifically, my 300D.

First, though, I have read every link in the world about this so I don't need a link. I just want opinions and confirmation that I "get it."

Next, the facts that I think I know: The 300D has a 1.6x crop factor. This is because the sensor is smaller than a 35mm negative and so you are getting a smaller sized 35mm negative. However, at 6.3 MP, the 300D sensor has a higher resolution than 35mm film and thus, despite being a smaller size sensor and picking up a smaller picture, the image that is recorded by the sensor is much better than 35mm film.

Some people make the mistake of thinking that a 100mm lens on a 300D magically becomes a 160mm lens. This is not the case. Instead, you see a similar image to the image that a 160mm lens on a 35mm film camera would see.

So, my question is, if you compare a 160mm film shot and a 100mm 300D shot, would the higher resolution of the 300D make the 300D shot actually as good as the 160mm film shot? Would it be better or worse? (I think maybe worse). If it is worse, where would that 100mm film shot be equivalent to film in terms of resolution of an image?

I hope I didn't screw that up somewhere.

[PacAce]

Yup, you've got most if it all right except for the part about the digital image being much better in terms of resolution than film, which is simply not true at all. :)

[CyberDyneSystems]

Well it depends.... (the resolution part)

Many claim the 1Ds allready has more resolution than 35mm?

The 10D has higher density than even the 1Ds

Thus if you were to maintain the "crop" on the print side.. than would the 10D/Rebel have more detail than the associted 1.6x crop straight from a 35mm negative?

I'm not sure what the consensu is on what res = 35mm but I seem to recall 9MP being used an awefull lot in the past. If it is 9MP then both the 1Ds at 11MP and the Rebel at 6.3 in a smaller area have more res per square mm than 35mm

[Jon]

The only cavil I'd have with your understanding is the assumption that the 300D has "better" resolution than film. It has better resolution than some films, but there are some extremely fine-grained films out there, capable of making unenhanced enlargements substantially better than out-of-the-camera 300D shots can produce.

Assuming the 300d and a 35 mm camera/film combo with identical sensor resolution (in lp/mm), and lenses with equal resolving power, with enlargements to the same size the film camera would have the edge, as the digital image would have to be magnified 1.6x more to get the same size enlargement. Say, 200 lp/mm from each. 15 mm on the 300D gives you 3000 line pairs. 24 mm on the film camera gives you 4800 line pairs. Enlarge the 15 mm to 6" (15 cm, 10x), 500 line pairs/in. Enlarge 24 mm to 6" (6. x), 800 line pairs/inch.

[Jesper]

Some people make the mistake of thinking that a 100mm lens on a 300D magically becomes a 160mm lens. This is not the case. Instead, you see a similar image to the image that a 160mm lens on a 35mm film camera would see.

With the risk of confusing you totally again.... :roll:

The image you get with a 300D and a 100mm lens is NOT the same as what you get with a 160mm lens on a 35mm film camera.

The image you get with a 300D and 100mm lens is exactly the same as what you get with the same 100mm lens on a 35mm camera, and you cut off a border of your 36 x 24 mm negative, so that you end up with a negative the size of the sensor (22.7 x 15.1 mm) - provided you are taking the photo from exactly the same point of view.

With a 160mm lens on a 35mm camera, the field of view will be the same as with a 100mm lens on a 300D, but the perspective and depth-of-field will be different (longer focal length, depth of field will be shallower).

The question of resolution is something entirely different and doesn't really have anything to do with the crop factor. You can't compare digital pixels and film so easily, because they work very differently. With film, the resolution depends on the grains in the film itself. There are high-resolution (with fine grain) and low-resolution (with coarse grain) films available.

[DAMphyne]

And the grains are molecule sized blobs of varied shape and sizes
Pixels are Square. :idea:
How do you compare that difference?

[evilenglishman]

I don't think you can compare the quality of digital being the same as film.

slide and negative film create a continuous tone image which is devoid of any resolution - of course grain comes into it, but this is comparable to noise in digital, not pixels.

You can easily blow up a 35mm slide to A2 and see no grain or noise when its printed, you cannot do that with digital (yet) and get anywhere near the same quality.

[toddb]

I always thought it was like 22MP for film or something (if you could give it a number). The other thing other then resolutions is tonal density. We think 12bits per channel on our cameras where film is much greater (on some film). The questions is can you tell. Maybe is certain situations. Makes me want to pick up a Elan 7 film body just to see now that I have allot of digital practice, lol. The way I shoot now I wouldn't be able to aford film let alone the processing of it.

I found a couple links with a google search:
http://pws.prserv.net/varney/iso/digflmres.htm
http://medfmt.8k.com/mf/lenslpm.html

As always, I love this forum because I pick up useful info. I had a misconception before this post that I was calculating DOF with the crop factor...so my 50mm as an 80mm lens....but after reading this post, the DOF should still be calculated as 50mm...right?

[hmhm]

The 100mm lens projects the same image onto the film/sensor plane regardless of whether you put it on a 35mm film camera or a 300d. The 35mm film camera will "capture" a 24mm x 36mm rectangle of that (circular) image. The 300d sensor is smaller, and thus will capture a smaller rectangle (about 16mm x 22mm).

Nothing about the 300d changes the focal length of the lens. But since the sensor is smaller (we call this a "smaller format"), a lens of a given focal length will yield a smaller angle of view when used with a 300d then if it was used on a 35mm film camera. Since the sensor is 1/1.6 the size of a 35mm film frame (in each dimension, 1/1.6 the width and 1/1.6 the height), a 100mm lens on the 300d yields an angle of view comparable to a 160mm lens on a 35mm film camera.

So to relate angle of view to 35mm film camera equivalence, you multiply the focal length by 1.6 .

But we care about focal length for other things, besides angle view, how does the crop affect them?

Well, to relate depth of field to 35mm film, you have to assume that the 300d user is either using a shorter focal length to get the same angle of view, or "backing up". The net effect will be that the 300d will have deeper depth of field at the same aperture as the 35mm film camera, or it will have comparable depth of field if you use an f-stop that's 1/1.6 the f-stop used on the 35mm film camera (e.g. f/10 on the 300d and f/16 on the 35mm film camera).

How about perspective? Well some people erroneously associate perspective with focal length, they want to say that a 24mm lens has a "wide-angle" perspective. Well, perspective depends entirely on the distance between the camera and the subject, and if you're using a shorter focal length on the 300d, then you'll stand the same distance from your subject (as with 35mm film), and thus you'll get the same perspective. If, instead, you use the same focal length on the 300d but "back up" to squeeze your subject into the 300d's crop, then you'll be standing further away, and your subject will have "flatter" perspective than 35mm film.

I don't think anybody claims that a 6MP sensor yields more resolution than film. But some people like the "smoother" image quality of digital vs film grain, and will declare the 6MP image to be superior, despite lower resolution. And if you print no larger than 8x12 or so, then greater resolution isn't really necessary. But if you want bigger prints, film will yield more detail.

So resolution isn't the "end-all" of image quality.
-harry

[hmhm]

slide and negative film create a continuous tone image which is devoid of any resolution...

Long before digital marketeers stole the term "resolution" and defined it to mean "the number of megapixels printed on the shiny yellow label on the front of the camera", film geeks were using test charts and microscopes to measure the resolution of lenses and films. Resolution is generally expressed in "line-pairs per millimeter", and is measured by seeing how close together a pair of lines can be and still be "captured" with sufficient contrast in-between (i.e. the space in-between the black lines needs to be sufficiently "light" for them to be considered "resolved").
-harry

[hmhm]

I had a misconception before this post that I was calculating DOF with the crop factor...so my 50mm as an 80mm lens....but after reading this post, the DOF should still be calculated as 50mm...right?

You should calculate depth of field using the real focal length, the number printed on the barrel of the lens (assuming it's not a point 'n' shoot that prints "35mm equivalents" on the lens), but you need to adjust the "circle of confusion" to be smaller, about 1/1.6 what you'd use on a 35mm film camera, to compensate for the greater enlargement (the ratio of film/sensor size to print size).
-harry

[CyberDyneSystems]

Final Word?

Hahahahahaha

There IS no final word where the "X-Factor" is concerned..

It seems we are doomed to debate this particular topic till doomsday! :lol: 8)

[Rayz]

I agree with Harry on this issue. Full frame 35mm is 1.6x the size of the 300D in both dimensions (2.6x the area, 1.6 squared). For equivalent DoF with full frame 35mm, for any shot taken from the same position, the focal length of the lens must be multiplied by 1.6 and the f stop # must also be multiplied by 1.6.

Thus, an 80mm lens on full frame 35mm at f5.6 produces the same Field of View and DoF as a 50mm lens on the 300D at f3.5.

This is basic optics and iron clad. Only the 'flat earthers' would disagree.

However, resolution is another matter. Depth of Field is, in part, a subjective phenomenon. We're talking about 'acceptable' sharpness of out-of-focus areas in relation to in-focus areas. There's only ever one point in one plane that's truly in focus. The higher resolution sensor, coupled with the higher resolving lens, will upset the apple cart.

Unfortunately, the 300D sensor does not resolve higher than 35mm film, nor even the upcoming 20D (although it must be getting pretty close).