FX vs DX Lens

[Dao]

And this is why I wish the 'crop factor conversion' idea would disappear from the face of the earth. Erase it. Delete it. Send it to the Trash Bin. Eradicate it. As if it never existed.

Back in my film days, there was no such thing as a 'conversion factor' to compare lenses between 135, 120 and 4x5 formats. I never heard of a number to multiply (or divide by) when changing from 35mm to 6x4.5 format, or to 6x7 format, or to 4x5 format. I never had to 'convert' the 80mm lens of my Mamiya 645 to 'the equivelant of __mm on my 35mm camera". Nor convert the 150mm on my 4x5 to 'the equivelant of __mm on my RB67 camera". A 50mm was standard on my 35mm bodies, 80 was standard on my 645, 105 standard on my RB67 and 150mm standard on a 4x5.

I understand why the manufacturers created the 'conversion' factor. It was a marketing tool to help sell fledgling digital SLRs to an uneducated populace. The bulk of that populace that had grown up with one format: 35mm. Everyone and their uncle owned a 35mm film camera. Most carried a 50mm 'standard' lens. Many purchased 28mm wide-angles and 135mm telephotos. So that was 'the gold standard' back then.

Then along came digital. But the sensors were smaller than a 35mm frame. So the manufacturers needed an easy way for those transitioning to digital to 'relearn' how focal length related to FOV. "Conversion factor' seemed like the perfect choice. And it was. At least back then.

But today, we have an entire generation that has never even SEEN a 35mm film camera, let alone understand focal length, sensor/film plane size and how the two relate to FOV. So today, the 'conversion factor' has royally muddied the waters. Not to mention the internet, and it's ability to spread incorrect information that will be accepted as gospel.

And next, the assumption (and even firm belief with some) that the 'conversion factor' applies to other properties of the lens, such as aperture and minimum focus.

I say it's time to deposit 'the conversion factor' concept into the dustbin of history. Let it reside the Hall of Useless Technology, next to ice picks, buggy whips and 8-track tapes.

I agree. For most people who only use a crop sensor body, crop factor really do not mean much. It is like me saying "This thing taste like SxxT!" It only valid if I really taste SxxT before which I of course did not LOL. I agree it is more or less a marketing thing. Like those 10X zoom or 30x zoom in point and shoot. The zoom factor do not mean much unless you know what is the starting point.

 

[JBPhotog]

I too go way back to the film days. In my experience people who were knowledgeable knew how to find the focal length for a ‘native’ focal length lens. It’s simple really, it’s the diagonal of the exposed film/sensor dimensions. So for a 35mm camera the actual ‘normal lens’ focal length is 43 mm, or (24)2 + (36)2 = (the square of 1872) 43.26mm.

There have always been equivalent focal length conversations as far back as I can recall. I would agree the whole “crap factor” argument has gotten out of hand, I guess math skills have also gone the way of buggy whips. It is just simpler to do the math to find out if the lens meets the requirements for the shot.