Do these help with "equivalent focal length?

I will answer yor questions individually- Does it even matter? --Yes, having some standard matters, no matter the phrase used. U are only thinking of SLRs, but suppose U wanted to buy a point and shoot camera and wanted to make some real comparisons between the point and shoots and even between the point 'n shoot and an SLR. Using the 35mm standard allows U to make comparisons by looking at the specifications without having to take photos with every camera or camera/lens combination. Equivalent focal length or equivalent angle of view? --Equivalent angle of view is more accurate, but equivalent focal length is easier for comparison purposes, since angles of view are not printed on lenses. Focal length numbers are etched right onto the lenses. So in your opinion which phrase is correct? --Equivalent angle of view or equivalent field of view would be more accurate; equivalent focal length is easier to use in practical terms, just because the focal length numbers are easier to manage. I highly doubt that anyone has memorized the angles of view of their lenses with the various sensors. Thus, the term "equivalent focal length" allows for easier comparisons. U even made focal length comparisons above, when U said that U'd need a 16mm lens on a 1.5x cropped sensor to achieve the same view as a 24mm lens; that's because lenses are named by their focal length and not by their angle of view.

Well EDWIN, lenses with similar focal length have similar magnification, but may cover different angles of view depending on whether or not they are symmetrical, asymmetrical or rectilinear; or square vs rectangular. That being said, you could use any of the terms interchangeably - Equivalent Magnification isn't too helpful (we tend to thing of "magnification" as meaning to make larger); "angle of view" is probably a bit more arcane than "focal length" and doesn't really add anything to the meaning. Does it matter? Probably - I think it is valuable to have a standard against which to compare things, and I like to know what to expect when I buy a lens of a certain length how it will behave on my various cameras. Or should every lens be sold with several focal lengths engraved on the barrel (in fact, many do!)? If there were just 2 sensor sizes that could be used with a given lens, life would be simpler: but Canon has no 1,5x crop cameras in its line-up: there are full frame (1x), APS-C (1.6x) APS-H (1,3x)... Nikon doesn't have a full-frame sensor: their FX is fractionally smaller than a 35mm frame, and their DX has a 1.5x crop factor. How to compare the effect of placing the same lens on a different body? Picking one format and using a multiplier seems sensible enough to me. On the question of consumer cameras ith fixed zoom lenses, and multiple senor sizes, it is even more useful to have a consistent terminology and why not keep the 35mm focal length equivalent as the measure? It isn't hard to understand and offers a simple enough concept for beginners to comprehend.

Hi Edwin. Some of a lenses characteristics are determined by it's focal length, the standard used for comparing lenses is the 35mm format. Does it matter? Well yes, and for reasons you might not expect. Let's take a 100mm lens (35mm format) as an example it will have a specific angle of view. Put that same lens on a camera with a smaller sensor than 35mm and the camera 'crops' the centre out of the projected image, the 'crop' factor, if the crop factor is 1.5 (as on Pentax) then it's angle of view it will have is the same as a 150mm lens (100 X 1.5), and that is not all that changes. It's exactly the same as if you cropped the image from a 35mm format camera in software. Perspective doesn't change, DOF does change! You have altered the SCALE RATIO. The 'crop factor' doesn't matter too much you allow for that when you frame your shot, but sensor size does matter as that alters DOF. The scale ratio is simply the size of your sensor vs the size of the subject expressed as a ratio - something : 1. The 1 is your sensor size the 'something' is how many time your sensor would fit into it. The higher the scale ratio the greater the DOF. An old technique for increasing DOF in Macro photography is to take the picture from further away and then crop the part of the picture you need. This is why it's difficult to get 'selective focus' (with the subject sharp, but the background blurred) shots with cameras that have small sensors, and why they are so good for close up shots with their extended DOF. This may come as a surprise to many but DOF is NOT dependant on focal length. See here for an explanation http://westfield-photo.org/page21.html Chris

A 50mm lens is a 50mm lens on any camera body.If this statement is true, it is only the angle of view which needs consideration. The phrase ' equivalent focal length ' is being used in lieu of 'equivalent field of view'. It might matter to photographers who are regularly working with different format film/sensor.

Well strictly speaking, the correct phrase should be a combination of both, ie. equivalent to the field of view of a x mm focal length lens on a 35mm camera.

Well, in my opinion, it is all pretty much a moot point. I would not necessarily say it does not matter, but as I see it, you have a couple of levels of camera users. You have the total amateurs who know nothing, (and are not the least bit concerned), about all the numbers as relates to a camera. It is put in full auto, and the shutter speed, aperture, ISO, focal length specs, etc are meaningless, abstract, worthless numbers. They might relate to a camera that is advertised as having 6x zoom as not having as much zoom range as one saying 10x zoom. But try to talk to them about sensor size and crop factors and "35mm equivalents" and it is meaningless to them. All they do is look through the viewfinder, (or at the monitor), and what they see is what they know, and how much the scene "gets closer" is what is important when they zoom. Numbers have no relevance what so ever. So in those cases there is no need for technically 100% correct terms to be used, they don't know or care about it anyway. Then there is the other level of photographers who can relate to what a "normal" lens looks like on a 35mm camera, and the equivalent numbers given for the digital cameras has some meaning. It can be called focal length or field of view. The meaning is understood by this group of people, and so trying to use what is technically the "correct" term is not really that big a deal here either. So the "equivalent focal length" specs are just a way to put some kind of standard among various cameras / lenses. The knowledgeable understand it, and the majority of the public that just want a camera in auto for snapshots don't care or relate to the terms and specs anyway. steve