Crop factor

[ashey]

Excuse me if I am wrong, but after reading some advice on some of the forums on this site I feel the need to clear this up about the crop factor of of your camera and the relation to full frame and what impact a particular lens will have on a crop sensor. As we all know, 50mm on a full frame is exactly that 50mm,now put that lens on a crop sensor body and things change, it will now become 80mm lens on a 1.6x body. Some people have have the notion that you divide the crop factor buy the sensor size, but in fact you multiply it. Here is a guide for those of you that want to know what a given lens will do on a crop body I hope this will be helpful.

http://digital-photography-school.com/wp-content/uploads/2007/03/crop-factor-conversions.gif

[I @ M]

Excuse me if I am wrong,

You are excused.



As we all know, 50mm on a full frame is exactly that 50mm,now put that lens on a crop sensor body and things change, it will now become 80mm lens on a 1.6x body.

A 50mm lens is a 50mm lens whether you fit it to a DSLR with a 35mm sensor size, a 1.3 1.5 1.6 crop factor, micro 4/3 etc etc.
The angle or field of view recorded on the sensor is the only thing that changes. That is all a property of the sensor size and has nothing to do with the lens.

[ameerat42]

...and what about all the guff you read about the "extra reach" of such-and-such a lens on a crop body!

Shiskebab! One thing I reach for is an extra Bex.

"Equivalence", due to subtended angles of the given lens on a given body, is what is at play. But often, that is just taken to mean - and wrongly - "equal".

Oh, alack and alas!

...and so on... and so 4th...

[Ms Monny]

...and what about all the guff you read about the "extra reach" of such-and-such a lens on a crop body!

THAT is what I was trying to say but couldn't think if the terminology or how to put it in here correctly, so I just didn't!!!

It is true though that you LOSE when you put on a wide angle lens, because it crops it....but I have also read that if you put on a 200mm lens on to a crop sensor camera (say x1.6) it then becomes 320mm!! Umm, how does it do that?? I could never get my head around that after reading it...and it was in a well know Photographic Magazine!!

[ashey]

Yes that is true Andrew and you are right that the lens itself dose not change, what I am trying to say is that some people have the misconception that they will get a wider angle of view on a crop sensor with a given lens when in fact they will get a narrower field of view. ie sigma 12/24 which is built for the full frame camera, wont give you 7.5 /15 mm on a crop body it will be 19.2/38.4mm field of view.

[I @ M]

Before any more misconceptions are formed ----

There are a couple of pages in the library that explain ( with pictures :D ) both crop factor (http://www.ausphotography.net.au/forum/showlibrary.php?title=New_To_Photography:Focal_Length_vs_Crop_Factor) and field of view (http://www.ausphotography.net.au/forum/showlibrary.php?title=New_To_Photography:Full_Frame_vs_APS-C_DX_crop_factor_w_example).

[ameerat42]

...it then becomes 320mm!! Umm, how does it do that?? I could never get my head around that after reading it...and it was in a well know Photographic Magazine!!...

MM. Quite easily: it doesn't!!! And therewith is the end of all your worries:D

Instead, it just gives you a field of view that LOOKS AS IF you had used the other lens. BUT-T! The image size STAYS THE SAME.

Those two references in the library that Andrew pointed out explain it quite well.
Am.

[ashey]

Thanks for that info Andrew, I think we can put this to bed.

[Speedway]

Another thing that comes into this is Pixel density. See here (http://www.ausphotography.net.au/forum/showthread.php?20625-Pixel-density-for-bird-photography&highlight=pixel+density). You need to look at all the variables to get the whole picture.
Keith.