Talk:Crop factor

From Wikipedia, the free encyclopedia

[edit] Incorrect info removed from article

I removed the following sentences from the article:

---

1 New lenses designed for specific use on DSLRs are subject to the same crop factor, depsite projecting a smaller image.

2 The standard focal length measurements are dependent on the camera sensor size, not the lenses.

3 This causes confusion because a 18-70mm digital or regular lens will never be 18-70 mm by conventional film camera standards.

4 The entire range is multiplied by the crop factor when a digital camera is used.

5 As cameras transition from film to digital so does the conventional understanding of the focal length numbers when used on the two different formats.

---

I understand what the original editor means, but it's phrased incorrectly and could cause confusion for users unfamiliar with the concept.

Sentence 1 is false: Lenses which cast an image circle designed for the sensor size are not subject to a crop factor, because the image isn't being cropped. I know what was meant -- that for folks used to equating certain focal lengths with certain FOVs, the smaller sensor makes such correlations inaccurate. However this has always been true, even before digital sensors came into being. A photographer who was used to large-format cameras having 120mm wide-angle lenses couldn't assume a 120mm lens on a Nikon SLR was wide-angle. Nor could a medium-format user who thought a 100mm lens was a normal lens. It all depends on your frame of reference.

Sentence 2 is also technically false. Focal length is dependent on nothing other than the actual focal length of the lens, measured in millimeters. As before, the editor is equating focal length with FOV. They are not the same. FOV varies according to sensor size, focal length of the lens and image circle size. Focal length does not vary due to sensor size.

Sentence 3 is also false. An 18mm lens is an 18mm lens no matter what camera it is attached to. A 70mm lens is a 70mm lens no matter what camera it is attached to. What varies is the FOV captured by the sensor.

Sentence 4 is correct w/r/t FOV vs. focal length.

Sentence 5 would be correct if reworded to address how FOV varies with sensor size.

Moondigger, I agree with most of your changes, but not really number 1. You also inserted the last clause of this sentence, which I have removed: "Crop factor is the ratio of linear photographic area lost in a DSLR camera compared to a standard 35 mm film frame, when used with lenses designed for that frame."

I know what you're getting at here, but if you look at how crop factor is used, it's as a characterization of a camera format, independent of any lens, irrespective of any imaging circle size, etc. It doesn't matter that the designed-for-digital lenses have their image circles cropped less; the camera still has the crop factor that it has. The term has caused great confusion by focusing on cropping. The FLM term isn't much better in the confusion that it causes, but I put that in, too, since it's also widely used. Dicklyon 20:00, 8 September 2006 (UTC)

Dicklyon, the article was written the way it was to address a term that has indeed arisen due to the existence of smaller-than-35mm frame DSLRs that take lenses designed for the full 24x36mm film frame. I realize that the term "crop factor" can be generically applied to any sensor smaller than the reference frame, but that generalization did not exist (and the term did not exist!) until the advent of DSLRs that took lenses designed for a larger format. Photographers with boatloads of lenses designed for the 35mm format were adopting new DSLR camera bodies that worked with their existing lenses -- yet the images produced were (are) radically different than the images they'd get with the same lenses on their old film bodies. The term arose specifically because of that situation. And, I should point out that photographers without a good understanding of the term are most likely to look it up here specifically because of its use in discussions/advertising/etc of lenses designed for use with the 35mm frame on their digital cameras.

So I disagree with the way you've generalized the article and removed references to the very origin of the term. I am not opposed to the incorporation of the information you have incorporated, but I am opposed to the wholesale removal of all references to the format the lens was designed for. It is not immaterial to the discussion, as you claim in your edit notes on the history page. In fact it is the very genesis of the term as applied. The fact that it can be generically applied to any sensor smaller than the reference frame can and should be in the article, but not as the primary definition.

That said, I do not wish to get into a revert war, and don't have time to re-write the article tonight to incorporate both sets of information. If you would like to edit it to include the information you excised, please do. Otherwise I'll re-incorporate it at a later time. -- Moondigger 01:56, 9 September 2006 (UTC)

I'm not sure what you want back in that I took out, so feel free to state it more explicitly here. In the mean time, I'll see if I can improve toward the needs of those DSLR shooters. I agree that's where it's mainly used (and misused), but I think the more general definitions will help people understand it better. Dicklyon 02:20, 9 September 2006 (UTC)

OK, I added various bits of info and clarification. Feel free to have the next crack at it. Dicklyon 03:25, 9 September 2006 (UTC)

I apologize if my comments came across the wrong way. I wasn't trying to exert any proprietary claim on the article, and I was in a bit of a crabby mood when I first responded. I just skimmed through the article and it looks good -- certainly better than it was prior to your edits. I'll give it a thorough once-over for copyediting purposes, but it looks really good. Thanks... -- Moondigger 03:14, 10 September 2006 (UTC)

Thanks. And if anyone knows about feeling crabby over wiki edits, it's me. Dicklyon 06:29, 10 September 2006 (UTC)