Crazy Crop Factors

[lhelmer]

I recently purchased the GH@ guide (it's AWESOME, best $30 I ever spent!!), but I have found one thing to be completely unclear.  What are the crop factors of the 9 recommended lenses?!?!?!

[Axel]

The [i]crop factor[/i] is always relative to full frame. Full frame meaning the old analogue 35mm negative and slide film, which had a size of 36 x 24 mm, aspect ratio 3:2 (3x12:2x12). The Canon 5D's sensor has this size.

If you put a 50mm lens on a 5D, it more or less shows a view you would also have with the naked eye from the same distance. It is therefore called the standard lens. Anything wider is wide angle. Up to 80mm are portrait lenses, and over this you call them tele.

The focal lengths of all the recommended lenses (and of [i]any[/i] lens, because the values are absolute) have to be mulitiplicated by 2 (or 1,86, as Andrew writes, but the wider the AR, the wider the lens should be, so 2 seems in order for 16:9) to give everybody an idea of how wide the angle will be.

BTW.: The 35mm of a film camera once also had the crop factor of 2, because it was 24 x 18 (which is exactly half-frame, but magically changed the aspect ratio to 4:3 - 4x6:3x6) and was transported vertically through the camera. Many of the reasons why things are how they are can be answered by history.

[Andrew Reid]

The sensor size determines the crop factor, not the lens.

Although a lens can be designed to cover only a smaller (crop) sensor like the Nokton 25mm F0.95 rather than full frame.

A lens projects an 'image circle' and this must be large enough to cover the sensor.

I recommend some lenses in the book that work with the 5D Mark III (full frame) as well as crop sensors (the Contax Zeiss stuff is full frame for example).

Glad you enjoyed the book!

[lhelmer]

Thanks so much for responding guys.  I'm so new at all this stuff that I didn't word my question properly. 

I understand that crop factor is relative to sensor size.  What I meant was what size sensor were each of the lenses designed for.  i.e. the Nokton 25m 0.95 is designed for a GH2 sized sensor.  Therefore, on that camera it actually provides a 25mm FOV. 

Some are obvious, but others I am unclear about.  I'm also a little afraid to ask about specific lenses because I don't want to give away the info that Andrew is providing at a price.  I don't want to undercut his business!

[MichalGajdos]

The Nokton 25mm f 0,95 is 50mm equivalent on full frame, like all other lenses.It just covers the micro four thirds sensor so it would be useless on any bigger sensor like CMOS or FullFrame D800, 5D etc and bigger. It suits only the micro4/3 and smaller sensors Nikon J1,V1. However it is possible to  use it on a  bigger sensor via adapters but the lens would vignette (black cornes, circle image= the image from lens would not cover the entire sensor).

Good luck with lens picking, but I feel i can give you a small adivce.At the beging try cheaper lenses this beautiful one costs aroung 900USD, but also great lenses like canon fd 50mm f1,8 or any other FD lenses or Helios m42. All these lenses offer great quality  for small price.