focal length conversion

[Gregory Sheffer]

I am shooting 2k with a 10-100mm lens. If I get a RED 50-150 lens how does that rate with my current lens? Is 100mm in 2k the same as 100mm in 4K? is 50mm the same? etc.

 

[peter roehsler]

A while ago I tried to answer a similar question in this forum. what you will read pretty much applies to the difference between 2 different film formats (2K vs 4K). While RED´s 50-150mm lens is certainly a very good lens, it will only extend your range from 100-150mm, as you have 50-100 covered on your 10-100mm.
hope this helps:
every lens projects a circular image on a surface which is xxx mm away from it. the surface may be a piece of film or an image sensor. the distance from the lens to the surface (when the image on the surface is in focus at infinity) is measured in mm and it is called the flange distance of the lens. now you are free to make use of the sharp image within the circle. some 50mm lenses project a big circle (they are designed for that), so you can easily use them for Hasselblad (6x6 cm image size) as a wide-angle. this way you make most of the available angle with which the lens projects the image on the film. if you choose to take the same lens for 35mm still photography, the part of the circle you use will be smaller, as your image will not be 6x6 cm but only 24x36mm. you use a smaller angle of the available projection and your lens is considered a `normal´ lens for 35mm stills. comes 16mm, even smaller image size, smaller angle - your lens becomes a `portrait´ lens. you are still using the same lens with the same focal length all the way, but you are using different projection angles for different image sizes. when it comes to factors, you compare image sizes and their relations to focal lengths. a 50mm `normal´ lens on a regular 35mm SLR (24x36mm) will behave like a 80mm `telephoto´ on a digital SLR because of it´s smaller image size (sensor), therefore the `factor´ will be 1,6. a digital SLR with a full frame sensor will have no factor.
focal lengths stay fixed, only the angles you use vary.

 

[Birns and Sawyer]

In basic terms, there is no focal lenght conversion, only field of view conversion. So a 25mm 35format lens will behave in 2K exactly as a 25mm 16format lens would behave in 2k, only a 25mm lens in 16format is quite a bit longer than a 25mm lens in 35format.

So the field of view conversion from 4k to 2k (based on 35mm to 16mm) is about 1/2.1 I think.

EX. to match FOV of a 35mm lens from 4k in 2K, you would need a 16mm lens (either format) - 35/2.1 ~ 16.667 ~ 16mm.

Hope that helps.

 

[Dylan Macleod CSC]

http://www.reduser.net/forum/showthread.php?t=1487&page=2

...halfway down the page

 

[MIKE TESTIN]

What is the conversion ratio between still lenses on a Full frame dslr and the Red sensor. How does a Nikon 50mm look on the Red, is it about equal to 75-80mm on the FF dslr in terms of FOV?