Sigma USB dock

**HanSch** · 02-03-2022, 05:48 AM

Originally posted by stevebrot

When you find out if it is worth it, let me know.

I am very fond of my 17-70/2.8-4.0 (C), but have often wondered if it might benefit from a session with the USB Dock.

Steve

I gave it a try, with the 17-70 on my K3 Mk.iii.
First I made an adjustment with the Dot-tune method, mentioned more often in this forum. This worked pretty well over the zoom range, except for the 70mm zoom setting. With a correction of +2 in the camera, the whole range was covered except 70mm.
Than I put the lens in the dock and made corrections for 70mm only, and they varied considerably with the focus distance (+5 to -4). A lengthy process, even for only one focal length. Mind, that the + correction in-camera corresponds with a - correction in the lens. For 70mm the Dot-tune method resulted in a +8 correction in the K3. Because I selected +2 over the whole range, an extra lens correction at infinity of -4 was needed. For very close focussing this changed to +5.
I didn't check if the +2 correction for 17-50mm was correct for very short focus distances, considering that if you need to focus at say 1 foot with 20mm, you will probably use a small aperture to get both your subject and the surroundings more or less sharp.

Didn't make any shots in practical situations yet, so the result has to be confirmed.

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02-03-2022, 05:48 AM	#16
HanSch Site Supporter Join Date: Sep 2010 Location: Venlo Photos: Gallery Posts: 163 Original Poster	Originally posted by stevebrot When you find out if it is worth it, let me know. I am very fond of my 17-70/2.8-4.0 (C), but have often wondered if it might benefit from a session with the USB Dock. Steve I gave it a try, with the 17-70 on my K3 Mk.iii. First I made an adjustment with the Dot-tune method, mentioned more often in this forum. This worked pretty well over the zoom range, except for the 70mm zoom setting. With a correction of +2 in the camera, the whole range was covered except 70mm. Than I put the lens in the dock and made corrections for 70mm only, and they varied considerably with the focus distance (+5 to -4). A lengthy process, even for only one focal length. Mind, that the + correction in-camera corresponds with a - correction in the lens. For 70mm the Dot-tune method resulted in a +8 correction in the K3. Because I selected +2 over the whole range, an extra lens correction at infinity of -4 was needed. For very close focussing this changed to +5. I didn't check if the +2 correction for 17-50mm was correct for very short focus distances, considering that if you need to focus at say 1 foot with 20mm, you will probably use a small aperture to get both your subject and the surroundings more or less sharp. Didn't make any shots in practical situations yet, so the result has to be confirmed.