Questions for HW specialist - DPChallenge Forums

Pentax DA 18-55mm f/3.5-5.6 AF

11/28/2005 09:32:34 PM · #1

I shot these 2 photography the same day from the same place, with an interval of a few minutes. With the canon lens the sun was above my head, slightly in my back and qith the sigma the sun was above my head slightly in front of me. Both were shot in RAW, converted with ACR3.3 everything auto and without ANY sharpness for none of them. Could differences in quality alone justify for this or is the sigma broken?

Canon 50mm f/1.8 at f/5.6

Sigma 18-50mm f3.5-5.6 DC at f/8.0

faidoi

Pentax K10D

11/28/2005 09:34:08 PM · #2

Are these 100% crop?

Pentax DA 18-55mm f/3.5-5.6 AF

11/28/2005 09:35:06 PM · #3

Originally posted by faidoi:

Are these 100% crop?

Yes

petrakka

11/28/2005 09:39:37 PM · #4

sigma's not broken, it's just sigma.

faidoi

Pentax K10D

11/28/2005 10:06:22 PM · #5

Shutter speed too slow? What is the EXIF on the Sigma shot? @ F8.0 = use tripod possibly.

Canon RF 24-70mm f/2.8 L IS

11/28/2005 10:09:35 PM · #6

Originally posted by faidoi:

Shutter speed too slow? What is the EXIF on the Sigma shot? @ F8.0 = use tripod possibly.

The EXIF says
focal lenght: 34mm
Aperture: f/8.0
Shutter speed: 1/200s
ISO: 100

This was shot with a tripod and the timer on the camera.

kirbic

Canon EOS R5

11/28/2005 10:59:26 PM · #7

Your're comparing an average zoom against a very good prime. The zoom is performing about as I'd expect, maybe a bit worse. It might improve a bit at f/11.
The Sigma looks like it is suffering from a combination of internal reflection (causing lack of contrast) and coma (causing the "glow" around highlights). The contrast might be helped by shielding it from the sun. Were you using a filter on this lens? That might be another source of issues.

downtherabbithole

Canon EOS-30D

Canon EF 28-135mm f/3.5-5.6 IS USM

11/28/2005 11:06:35 PM · #8

Originally posted by petrakka:

sigma's not broken, it's just sigma.

agreed, that is what it looks like for me.

srdanz

Canon EOS-5D Mark IV

Canon EF-S 10-22mm f/3.5-4.5 USM

11/28/2005 11:18:43 PM · #9

I have the same two lenses, and I use sigma for 18mm or thereabout only. Whenever I need 50mm I switch to the prime lens. If I need 40mm, I take a few steps back...

It is normal - the difference in sharpness is always going to be there. I use that little lens hood that came with the sigma to try to reduce flares/that and the polarizer filter helps some.