I just bought a second hand Sigma 135/1.8 DG HSM Art. It arrived this afternoon and I made some testshots before it was getting too dark. At first sight, the sharpness looked very good on the camera display (S1Rii), when I zoomed in. But when I look with DXO at the RAW images on my 4K PC screen, it seems that either I used a too slow shutter speed or the lens has a problem when using AFC with higher fps. I used face/eye detect.
First, I used shutter speed of 1/250s at F1.8 (ISO Auto), AFC. Some images were tack sharp in the series, some not. Pictures of my son sitting on a couch. With the great IBIS of Panasonic these should be sharp even at 200% enlargement, right?
Then I tried the same with 1/400s. Same problem.
It seems that at closer focusing distances (head only or head & shoulder), the images (the eyes) are at 200% sharper than at longer distances (full body portraits). Always relative of course.
If I use my Sigma 70-200/2.8 Sport with the same camera, I do not have these problems. But I only use that zoom with 1/1000s-1/1500s shutterspeed. I upgraded now the FW of the 135/1.8 lens from 1.1. to 1.2. The FW of S1Rii is already the newest one (1.2)
Any idea, what could be the reason for this?
I will try new shots with different settings and comparison shots with other lenses during daylight tomorrow.
First, I used shutter speed of 1/250s at F1.8 (ISO Auto), AFC. Some images were tack sharp in the series, some not. Pictures of my son sitting on a couch. With the great IBIS of Panasonic these should be sharp even at 200% enlargement, right?
Then I tried the same with 1/400s. Same problem.
It seems that at closer focusing distances (head only or head & shoulder), the images (the eyes) are at 200% sharper than at longer distances (full body portraits). Always relative of course.
If I use my Sigma 70-200/2.8 Sport with the same camera, I do not have these problems. But I only use that zoom with 1/1000s-1/1500s shutterspeed. I upgraded now the FW of the 135/1.8 lens from 1.1. to 1.2. The FW of S1Rii is already the newest one (1.2)
Any idea, what could be the reason for this?
I will try new shots with different settings and comparison shots with other lenses during daylight tomorrow.