Nikon 24-70mm f/2.8 off by 1 stop

Correlli

I have never heard that the position of the aperture does have an impact on dof at all. I know that there are some rules about where the aperture should be but not that it influences dof. If anyone does know some sources about this subject I would really be interested.

simba

Thanks for all of your great comments. I will provide some more details and post my test pictures if I can when I get back home tonight. However, I don't see an option to add pictures to this forum. Any ideas?

spraynpray

Read the thread on how to post pictures on the main forum page simba.

Symphotic

I just checked my lenses against each other. The sigma meters a half stop more transmission. I want to play around with the quantification of depth of field. Part of the problem is that the field of view is not exactly the same at 35 mm, so the actual focal lengths are not the same. Even though the EXIF data read the same focal length, the Sigma is visibly a wider field of view. (This is not unusual: when we measure the FOV for our industrial cameras it never back calculates to the stated focal length of the lens.)

UPDATE:

To get exactly the same field of view for the 24-70 as the Sigma 35 I have to zoom to where the EXIF data on my 24-70 reads 32 when I focus at a distance of 670 mm. That doesn't surprise me. I'll take a look at what it does at infinity focus.

Anyway, I think comparing a prime with a zoom, especially at close focus, is like comparing the moon with a snapping turtle. (they're both round, but there are significant other differences.)

Msmoto

@simba

http://forum.nikonrumors.com/discussion/46/how-to-post-a-photo-on-photo-a-day#Item_97

JJ_SO

JJ_SO, thanks for the testing. Can't see the images though.

There are no more images than this screenshot.

ChromiumPrime

This topic truly got me intrigued especially about the DoF. I have the 24-70 as well as 35 1.8G and 50 1.8G so I'll try and run my own testing tomorrow and see what I come up with. I do have a few speculations as to what's causing the differences but I want to run my own tests first. I'll post the results here tomorrow.

simba

Thanks again for your comments. I just created an account on flickr and uploaded my test pictures as follows:
http://www.flickr.com/photos/94482349@N04/

The pictures were taken in my living room a few days ago. I intended to test the sharpness, color and bokeh of my new toy Sigma. Nothing fancy. Anyway, my setup was as follows:

Camera: Nikon D800
Format: raw, converted to jpg and removed personal and copyright info for upload
Lens hood: no
ISO: 100
Active D-Lighting: off
Tripod: yes
Focus point: center
Aperture priority, MUP and remote shutter

Results:
DS8_2601: shutter speed 1/25s
DS8_2611: shutter speed 1/50s
DS8_2612: shutter speed 1/25s
Bokeh: make your judgment

Note that Sigma is a little wider for the same 35mm focal length, so its depth of field is supposed to be deeper.

@Symphotic, I did try the depth of field preview button for the Nikon 24-70 @f/2.8 and it was certainly wide open. That is, the image did not get any darker. Thanks for your suggestion.

I am happy with the results. I gain 3 stops instead of 2 that I expected with the new toy. However, it will be good to know why.

spraynpray

Well I just almost hypnotised myself by flicking back and forth and yes, those pics do seem to support your claim that the performance of the 24-70 at f2.8 looks like the 35 at f4. The FoV seems to be a little different (focus breathing?) - what would happen to the exposure if you adjusted the FoV to be the same as the 35?

Golf007sd

@simba: First) I do not see anything that would suggest your 24-70 2.8 is off my 1-stop. 2) Did you crop the photos you shared with us?

Ironheart

This is a very interesting thread. I was just wondering, one of those dumb questions, do any of the lenses in question here have filters (clear or othwise) as even a clear filter will soak up some light? Perhaps a cheaper one may darken more than a higher quality one? Just trying to eliminate variables.

Also, since the aperture adjustment is a mechanical linkage (except for the new 800mm) there could be variances lens to lens as you stop down. Just how accurate is that little metal tab anyway?

simba

@spraynpray: If I zoom out the Nikon 24-70 to match Sigma, the focal length will be shorter, and DOF should be deeper. That is, the gap between Nikon and Sigma will even be bigger.
@Golf007sd:
1) If you compare the aperture and shutter speed of the Nikon and Sigma pictures, you should know the exposure of Nikon one is 1 stop longer.
2) I didn't crop the photos, which were posted in 4912 x 7360. However, flickr seems to limit the resolution. If you right click on the photos, you will see the largest view size is 2048.

Msmoto

@simba

Flickr may limit size on a regular member. For full size it may require a "Pro" subscription.

paulr

Flickr do limit the size to none pro members including the amount of images you can put on