5DSR (24-70 F2.8 II vs Sigma 18-35 F1.8) center sharpness test

I have been slowly Dot tuning all my lens to the 5DSR and I decided to put my crop Sigma 18-35 F1.8 on the 5DSR to see what it looked like, get it dialled in, and then decided to test out what focal lengths would create a clean picture using the 1.3 crop mode and also what apertures would clean up the heavy vignetting that this lens can have (plus the new Sigma 24-35 F2 is getting a lot of attention so it got me interested again in trying the F1.8 crop version on a full frame)

I tested the 18-35 at 1.8 and 2.8 at 18mm, 24mm and 35mm - this equates at an available 1.3 crop on the 5DSR of 'pretty close' to 24mm, 35mm and 50mm - which makes it a very interesting wedding lens possibility for a low light F1.8 Prime combo on the 5DSR when shooting in 1.3x crop mode which would basically create 38 megapixel pictures - and since the 70-200 F2.8 IS II is better at 70mm than the 24-70 II (plus it comes with IS) it becomes potentially a very useful lens if low light is an issue at a particular wedding. I also tested the 24-70 F2.8 II at 24,35 and 50mm@ F2.8 for comparison.

The setup was:
- RRS tripod
- lens was dot tuned just prior
- 10 second delay shot in live view
- picture was heavily cropped to show tuning printout
- SOOC with LR standard 25 sharpness and lens correction
- distance was 12 feet (very similar to a common shooting range for the 24-70)
- to put into perspective what 13 feet / 4 meters is for the 24-50mm range, the Dot Tune method recommends 50 x the focal length for tuning the lens - so for 24,35,50mm equates to 1.25meters, 1.75meters, 2.5 meters - so 4 meters is significantly outside this range from a zoom perspective and should highlight the lens' resolving power


So here is the setup
- this is what it looked like at 35mm at 1.3x crop @ F2.8 (approx 46m in FF)

IMAGE LINK: https://flic.kr/p/vYdW​6M

IMAGE LINK: https://flic.kr/p/wUjo​Cu

IMAGE LINK: https://flic.kr/p/wVzH​ng

IMAGE LINK: https://flic.kr/p/wCyJ​JX

IMAGE LINK: https://flic.kr/p/wUjo​A5

IMAGE LINK: https://flic.kr/p/vYbC​gn

IMAGE LINK: https://flic.kr/p/wSJE​bS

and now the Canon 24-70 F2.8 almost similar focal lengths

5DSR was returned to full frame mode


@24mm F2.8

IMAGE LINK: https://flic.kr/p/vY37​od

IMAGE LINK: https://flic.kr/p/wUjs​Cy

IMAGE LINK: https://flic.kr/p/vY37​sG

Observations
1) there is no question when you look at the results side by side that if you try and compare the Sigma at (18,24,35) cropped at 1.3x against the Canon Full-framed at (24,35,50) then the Canon is sharper at every 'almost' equivalent FL - i.e 18 vs 24, 24 vs 35 and 35 vs 50
2) if you compare the same FL's of the Sigma vs the Canon, (24 vs 24 and 35 vs 35) then they appear very similar at F2.8
3) what I also found very interesting is that at F1.8 on the Sigma, if you compare 24 F1.8 Sigma to 24F2.8 Canon (sized the same) and 35 F1.8 Sigma to 35 F2.8 Canon, the Sigma shows good sharpness
4) In terms of whether the Sigma can be shot on the 5DSR cleanly at 1.3x crop - yes it can at all the focal lengths except that at 18mm, even with the Profile correction, the corners are dark so at 18mm, a 4x5 cropping is required to create a clean picture - even then there is the tiniest bit still remaining.
5) on full frame mode, using profile correction and some additional vignetting control, you can shoot the Sigma at 25-35mm using a 4x5 crop but at F1.8 at 25mm the lens still has some slight vignetting but it is perfectly fine at F2.8.

Hadn't considered using the 18-35 Sigma on the 5DSR but this test has me now thinking about it.

here is a picture taken at 25mm F1.8 with a 4x5 crop on full frame mode with Profile correction and additional vignetting control done with a radial filter to lighten up the corners

so you are able to use the lens on a fullframe - not optimal but many people crop to 4x5 so it is very doable - and 1 1/3rd stops faster than the $2000 Canon 24x70 II (which is just a very, very good lens) - but the Sigma is very sharp

IMAGE LINK: https://flic.kr/p/wVPh​uH

- out of interest, decided to shoot the 35F2 at F2-F2.8 just for comparison
- the 35F2 looks slightly sharper up until F2.8 where I like the Sigma image better
- the canon seems to have a magenta cast / CA to all apertures from F2 to F2.8 (which is interesting as I hadn't noticed it before) - it can easily be removed in LR which I checked after posting the images

Sigma 18-35 at on full frame mode @ F2

IMAGE LINK: https://flic.kr/p/wT5c​DU

IMAGE LINK: https://flic.kr/p/vYwa​Cx

IMAGE LINK: https://flic.kr/p/vYwa​QB

IMAGE LINK: https://flic.kr/p/vYnz​hf

IMAGE LINK: https://flic.kr/p/vYwa​Ba

IMAGE LINK: https://flic.kr/p/wCUe​sv

IMAGE LINK: https://flic.kr/p/wCUe​wi

IMAGE LINK: https://flic.kr/p/wCM6​yE

very interesting thanks

now what I's like to see to help me decide between the 2.8 and the f4 with IS is whether you can get good results forte canon 2.8 HANDHELD

ye see eye s I know its supposed to be used on a tripod cemented and bolted down and used with a remote and five year timer but the fact is I will use it handheld sometimes!


and when not shooting landscapes I may want to wander round the countryside wander round the town, sometimes with his trousers up sometimes with them down, when they were up they were up, when they were down....he was arrested. (to quote Spike Milligan). ho ho ho

anyway yes I wanna lens for going walks round town.. and the 2.8 is noticeably sharper than the f4 BUT will it be so handheld?...only you can help me answer tis question....
:p

I Simonius wrote in post #17902490
very interesting thanks

now what I's like to see to help me decide between the 2.8 and the f4 with IS is whether you can get good results forte canon 2.8 HANDHELD

ye see eye s I know its supposed to be used on a tripod cemented and bolted down and used with a remote and five year timer but the fact is I will use it handheld sometimes!


and when not shooting landscapes I may want to wander round the countryside wander round the town, sometimes with his trousers up sometimes with them down, when they were up they were up, when they were down....he was arrested. (to quote Spike Milligan). ho ho ho

anyway yes I wanna lens for going walks round town.. and the 2.8 is noticeably sharper than the f4 BUT will it be so handheld?...only you can help me answer tis question....
:p

I don't know! Do you think you could do it with a 7DII with a matching focal length lens? If the answer is yes then remember that for equal sized output you had to enlarge the image from the 7DII 1.6× as much.

I had a similar argument with a Canon rep at my local camera store (WEX), who suggested that trying to shoot aviation subjects using a 600mm lens handheld at 1/160s on a 5DS was stupidity, yet thought it would be perfectly fine to try the same using a 7DII. It was only once I had pointed out that if I crop the image from both cameras to cover the same 15×10mm area of sensor that I would end up with the same number of pixels from both cameras that he started to actually think about what he was saying. Rather than just spewing the Canon mantra of how hard the camera was to get good clean shots out of.

Alan