I just bought the last one Amazon had in stock. I'll try it out as soon as it arrives. Could you guide me on how to test for field curvature? Focus at center, check edge sharpness, focus at edge, check center sharpness; then compare to without a filter?
p.2 #2 · Sigma 14-24mm f/2.8 DG DN first impressions
timerickson wrote:
I just bought the last one Amazon had in stock. I'll try it out as soon as it arrives. Could you guide me on how to test for field curvature? Focus at center, check edge sharpness, focus at edge, check center sharpness; then compare to without a filter?
Find a flat field infinity distance scene. Set the camera on a sturdy tripod and change the lens to MF.
1) Without the gel: MF focus on center and take a picture.
2) Remove the lens and apply the ND gel: Without changing focus (or focus again on center) and take another picture.
Compare both images for mid-field and corner areas for differences in field curvature. Usually it's more of an issue at the wider range but you could test for 14mm and 24mm.
p.2 #4 · Sigma 14-24mm f/2.8 DG DN first impressions
Sean Goebel wrote:
Was this focused in the center? If so, it looks quite good.
I am seriously considering replacing my Sigma 14 1.8 with this lens for backpacking astrophotography... the 1.8 weighs approximately two bricks and has an annoying amount of coma.
It was corner focused, but here is a center vs corner star sharpness comparison from a single shot. Crops at 100% again, 14mm, F2.8, minimal sharpening.
The lack of CA is indeed very impressive. It is noticeably better than both the Loxia 25 and Nokton 21 even when just when looking through the viewfinder.
p.2 #6 · Sigma 14-24mm f/2.8 DG DN first impressions
rvh23 wrote:
It was corner focused, but here is a center vs corner star sharpness comparison from a single shot. Crops at 100% again, 14mm, F2.8, minimal sharpening.
p.2 #7 · Sigma 14-24mm f/2.8 DG DN first impressions
rvh23 wrote:
Here is an illustration of the lens' field curvature (at infinity) for 14mm at F2.8. Top is corner sharpness resulting from center-focusing, and bottom the improved result when focusing for the corner. A7rII / minimal CR default sharpening.
** edit ** actually this was at 14.6mm rather than 14mm according to the exif, but close enough
I'm confused by this comparison for center focus and corner focus, both supposedly wide open.
If focus was moved for the corner focus sample, the object focused upon in the corner would be sharper, and closer objects might be sharper as well (or less sharp), and farther objects might be less sharp (or more sharp), depending on whether the field curved toward or away from the camera. But EVERYTHING in the corner focused sample is sharper, implying not (just) a change of focus point, but a change in depth of field.
Are you sure you did not accidentally swap in a shot at a smaller aperture?
p.2 #8 · Sigma 14-24mm f/2.8 DG DN first impressions
rvh23 wrote:
The lack of CA is indeed very impressive. It is noticeably better than both the Loxia 25 and Nokton 21 even when just when looking through the viewfinder.
How is the Sigma 14-24/2.8's performance at center and mid-field against primes like the CV 21/1.4 or FE 24/1.4?
The Tamron 17-28/2.8 pretty much matches them at center + mid-field but it's not quite as sharp at the extreme corners. The Tamron performs very similarly to the CV 15/4.5 III everywhere in the frame. (only loses by a small margin at center)
p.2 #9 · Sigma 14-24mm f/2.8 DG DN first impressions
2ndviolinman wrote:
I'm confused by this comparison for center focus and corner focus, both supposedly wide open.
If focus was moved for the corner focus sample, the object focused upon in the corner would be sharper, and closer objects might be sharper as well (or less sharp), and farther objects might be less sharp (or more sharp), depending on whether the field curved toward or away from the camera. But EVERYTHING in the corner focused sample is sharper, implying not (just) a change of focus point, but a change in depth of field.
Are you sure you did not accidentally swap in a shot at a smaller aperture?...Show more →
No, only focus was changed. Best center focus at infinity is further away (at 14mm focal length it's about 10m on my lens) than for the corners (where it's about 6m). So when you center-focus for infinity, nearby objects in the corners will be more out of focus than those same objects are at best corner-focus for infinity.
p.2 #10 · Sigma 14-24mm f/2.8 DG DN first impressions
Some sunshine this morning so I had a chance to look at flare, which looks very well controlled for such a wide lens. You can induce partial-ring flare in the far corner closest to the sun when the sun is just off center, but it disappears quickly as you move the sun further away from center. Mostly flare is confined to moderate ghosting. Contrast usually remains at a high level. Here are some blue sky 14mm shots at F6.3 with the sun moving gradually from center to a far corner.
p.2 #12 · Sigma 14-24mm f/2.8 DG DN first impressions
Fred Miranda wrote:
How is the Sigma 14-24/2.8's performance at center and mid-field against primes like the CV 21/1.4 or FE 24/1.4?
The Tamron 17-28/2.8 pretty much matches them at center + mid-field but it's not quite as sharp at the extreme corners. The Tamron performs very similarly to the CV 15/4.5 III everywhere in the frame. (only loses by a small margin at center)
I'll try to get some CV21/1.4 comparisons for center and mid-frame shortly. But certainly in the corners this zoom is much sharper than the CV15. I don't have my Sigma 14/1.8 anymore to do a direct comparison, but I think it is in fact as sharp (or maybe even better) as that in the corners. But in the center of the frame the 14/1.8 is phenomenal, as you can also see from Roger's MTFs at lensrentals. I don't think the zoom can match it there.
p.2 #14 · Sigma 14-24mm f/2.8 DG DN first impressions
Center, mid-frame (halfway between center and far corner), and far corner comparisons between the Sigma 14-24 at 21mm/F2.8 and the Nokton 21 also at F2.8. As before 100% crops, A7rII, minimal CR default sharpening, focused for best sharpness in each region to eliminate any FC.
The Sigma is turning out to be a killer lens, exceeding my expectations on all measures.
p.2 #15 · Sigma 14-24mm f/2.8 DG DN first impressions
rvh23 wrote:
I'll try to get some CV21/1.4 comparisons for center and mid-frame shortly. But certainly in the corners this zoom is much sharper than the CV15. I don't have my Sigma 14/1.8 anymore to do a direct comparison, but I think it is in fact as sharp (or maybe even better) as that in the corners. But in the center of the frame the 14/1.8 is phenomenal, as you can also see from Roger's MTFs at lensrentals. I don't think the zoom can match it there.
With 18 elements, the Sigma 14-24/2.8 better be very sharp at 14mm! I don't think the tiny CV 15/4.5 has a chance but it did match the Tamron 17-28. (15mm vs 17mm at f/5.6)
p.2 #16 · Sigma 14-24mm f/2.8 DG DN first impressions
The amazing thing about this zoom is that it's sharp wide open at 2.8 across the whole zoom range. No matter how many elements they used to achieve that, it's an astounding feat. I wouldn't be surprised if it's actually sharper wide open (at 15mm) than the CV15 or Laowa 15 are at any aperture.
p.2 #17 · Sigma 14-24mm f/2.8 DG DN first impressions
More good news for me at least, is that the lens exhibits absolutely minimal focus breathing, which is great for focus stacking. Here is a comparison of two 14mm F6.3 shots of a large tile without moving the camera. One focused at 6m (where infinity is sharp on this particular lens at 14mm) and the other at 0.5m corresponding to a typical close object in near-far composition. You can see there is minimal difference in FOV between the two shots.
The lower image is a combination of the two shots, both 'thresholded', one with black lines and the other with grey lines (using overlay with partial transparency).
Also evident is the simple barrel distortion this lens produces at 14mm (uncorrected) which will presumably be easily corrected once a lens profile becomes available.
p.2 #18 · Sigma 14-24mm f/2.8 DG DN first impressions
rvh23 wrote:
More good news for me at least, is that the lens exhibits absolutely minimal focus breathing, which is great for focus stacking. Here is a comparison of two 14mm F6.3 shots of a large tile without moving the camera. One focused at 6m (where infinity is sharp on this particular lens at 14mm) and the other at 0.5m corresponding to a typical close object in near-far composition. You can see there is minimal difference in FOV between the two shots.
The lower image is a combination of the two shots, both 'thresholded', one with black lines and the other with grey lines (using overlay with partial transparency).
Also evident is the simple barrel distortion this lens produces at 14mm (uncorrected) which will presumably be easily corrected once a lens profile becomes available.
p.2 #20 · Sigma 14-24mm f/2.8 DG DN first impressions
Thanks for sharing.
WRT the samples in the previous page,
(1) which corners are these? UL/LL/UR/LR etc.
(2) would you mind showing the full images, so we can get an idea of what proportion of the frame these crops represent?
(3) do you have any crops of the center?
