Crop factor revisited... at DVinfo.net

Piotr Wozniacki · September 29th, 2012, 07:01 AM

I know it's a dumb question, but I really got confused... It's about the "crop factor" again, so please bear it with me

Below are 2 screengrabs straight from the FS100; one is with the pancake 16mm lens, the other - with the Tokina 17mm F3.5.

Shouldn't they both be more similar as far as the angle of view is concerned? I mean, it's just 1mm focal length difference... Does it account for the difference seen, or do the 2 lens have different crop factors?

Please note - I did put "crop factor" in quotation marks :)

I understand the NEX is an APS-C lens, while the Tokina 17mm is a FF lens - but their focal lengths are supposed to be expressed in FF terms... So, again: can the 1 mm difference make such a big difference?

Chris Medico · September 29th, 2012, 02:18 PM

Based on a straight angle of view calculation the difference between a 16 and 17mm on a 1.5x crop imager should be 3-4 degrees (~70 vs ~74deg).

What you are demonstrating is the focal length stated on one or both of the lenses are approximations only.

Shaun Roemich · September 29th, 2012, 07:54 PM

Quote:

Originally Posted by Piotr Wozniacki

but their focal lengths are supposed to be expressed in FF terms...

Focal lengths are ABSOLUTE. They aren't expressed in "terms".

The 16mm is almost 6% wider than the 17mm, BTW.

Bill Pryor · October 1st, 2012, 03:18 PM

The photo on the right side looks like it has cropped in a lot more on the right side than on the left side.

Jean-Philippe Archibald · October 2nd, 2012, 06:33 AM

From your screen grabs, the camera seem to have been panned to the left and tilted down a bit between the two shots, so it's harder to spot the differences.

Off topic, the tokina is a lot sharper!!! ;-)

Piotr Wozniacki · October 3rd, 2012, 01:41 AM

Yeah - the camera wasn't at the same exact position, as those pics were not even taken on the same day.

Which doesn't change the fact the lenses' angle of view is considerably more different than one would expect basing on the 1mm difference in their respective focal lengths...

As to the sharpness - well, the Tokina is actually very soft when wide open (at F3.5).

Marcus Marchesseault · October 4th, 2012, 02:23 AM

Think about it. The shorter the focal length, the greater a difference per millimeter. What would be the difference between a 1mm and a 2mm lens that is twice the focal length? What would be the difference between a 399mm and 400mm lens? Anything below 24mm is really wide and has serious perspective distortion so it doesn't surprise me that two lenses with slightly different focal length from different manufacturers might have a different framing.

Kevin Dooley · October 14th, 2012, 10:34 AM

To echo some things above - there are no "terms" on focal length - just like there really is no "crop factor". 16mm is always 16mm.

I use to have a Canon 16-35L for my 5DII. I almost never ran it at 16mm because I didn't like the look. I would usually bump it in to about 17 or 18mm - so there should be a difference.

There will be a very noticeable difference on wider lenses, however the really key factor is the change in camera location. Try the same setup again and this time swap lenses without moving the camera. The pictures are pretty useless as an example unless the only thing different is the lens. In fact, 17mm shot looks like the camera may actually be closer than the 16mm shot, in addiction to be higher (and tilted down to compensate) and then panned left a hair.

September 29th, 2012, 07:01 AM	#1
Piotr Wozniacki Inner Circle Join Date: Aug 2006 Location: Poland Posts: 4,086	Crop factor revisited... I know it's a dumb question, but I really got confused... It's about the "crop factor" again, so please bear it with me Below are 2 screengrabs straight from the FS100; one is with the pancake 16mm lens, the other - with the Tokina 17mm F3.5. Shouldn't they both be more similar as far as the angle of view is concerned? I mean, it's just 1mm focal length difference... Does it account for the difference seen, or do the 2 lens have different crop factors? Please note - I did put "crop factor" in quotation marks :) I understand the NEX is an APS-C lens, while the Tokina 17mm is a FF lens - but their focal lengths are supposed to be expressed in FF terms... So, again: can the 1 mm difference make such a big difference? Attached Thumbnails __________________ Sony PXW-FS7 \| DaVinci Resolve Studio; Magix Vegas Pro; i7-5960X CPU; 64 GB RAM; 2x GTX 1080 8GB GPU; Decklink 4K Extreme 12G; 4x 3TB WD Black in RAID 0; 1TB M.2 NVMe cache drive Last edited by Piotr Wozniacki; September 29th, 2012 at 07:32 AM.

September 29th, 2012, 02:18 PM	#2
Chris Medico Inner Circle Join Date: Aug 2006 Location: Efland NC, USA Posts: 2,322	Re: Crop factor revisited... Based on a straight angle of view calculation the difference between a 16 and 17mm on a 1.5x crop imager should be 3-4 degrees (~70 vs ~74deg). What you are demonstrating is the focal length stated on one or both of the lenses are approximations only. __________________ http://www.LandYachtMedia.com

October 1st, 2012, 03:18 PM	#4
Bill Pryor Contributor Join Date: Jan 2003 Location: Kansas City, MO Posts: 4,449	Re: Crop factor revisited... The photo on the right side looks like it has cropped in a lot more on the right side than on the left side.

October 2nd, 2012, 06:33 AM	#5
Jean-Philippe Archibald Trustee Join Date: Sep 2003 Location: Saguenay, Québec, Canada Posts: 1,051	Re: Crop factor revisited... From your screen grabs, the camera seem to have been panned to the left and tilted down a bit between the two shots, so it's harder to spot the differences. Off topic, the tokina is a lot sharper!!! ;-) __________________ Jean-Philippe Archibald http://www.jparchibald.com - http://www.vimeo.com/jparchib

October 3rd, 2012, 01:41 AM	#6
Piotr Wozniacki Inner Circle Join Date: Aug 2006 Location: Poland Posts: 4,086	Re: Crop factor revisited... Yeah - the camera wasn't at the same exact position, as those pics were not even taken on the same day. Which doesn't change the fact the lenses' angle of view is considerably more different than one would expect basing on the 1mm difference in their respective focal lengths... As to the sharpness - well, the Tokina is actually very soft when wide open (at F3.5). __________________ Sony PXW-FS7 \| DaVinci Resolve Studio; Magix Vegas Pro; i7-5960X CPU; 64 GB RAM; 2x GTX 1080 8GB GPU; Decklink 4K Extreme 12G; 4x 3TB WD Black in RAID 0; 1TB M.2 NVMe cache drive

October 4th, 2012, 02:23 AM	#7
Marcus Marchesseault Trustee Join Date: Nov 2005 Location: Honolulu, HI Posts: 1,961	Re: Crop factor revisited... Think about it. The shorter the focal length, the greater a difference per millimeter. What would be the difference between a 1mm and a 2mm lens that is twice the focal length? What would be the difference between a 399mm and 400mm lens? Anything below 24mm is really wide and has serious perspective distortion so it doesn't surprise me that two lenses with slightly different focal length from different manufacturers might have a different framing.

October 14th, 2012, 10:34 AM	#8
Kevin Dooley Major Player Join Date: Dec 2003 Location: Fort Worth, TX Posts: 414	Re: Crop factor revisited... To echo some things above - there are no "terms" on focal length - just like there really is no "crop factor". 16mm is always 16mm. I use to have a Canon 16-35L for my 5DII. I almost never ran it at 16mm because I didn't like the look. I would usually bump it in to about 17 or 18mm - so there should be a difference. There will be a very noticeable difference on wider lenses, however the really key factor is the change in camera location. Try the same setup again and this time swap lenses without moving the camera. The pictures are pretty useless as an example unless the only thing different is the lens. In fact, 17mm shot looks like the camera may actually be closer than the 16mm shot, in addiction to be higher (and tilted down to compensate) and then panned left a hair. __________________ Kevin Dooley Media Director, Pantego Bible Church