SD1 focus and Program exposure

Started May 27, 2012 | Discussions thread
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Tom Schum
Senior MemberPosts: 2,997Gear list
SD1 focus and Program exposure
May 27, 2012

I was out yesterday doing landscapes with my SD1 + 85mm.

I noticed that in program exposure mode (P) the bias was to make the shutter speeds very high, and to open the lens F-stop wide.

I think this is due to the fact that the 85mm F1.4 EX DG HSM does not have OS. I am guessing any lens without OS will suffer the same fate. I haven't tried other non-OS lenses yet, nor have I tried program mode with OS switched off using lenses such as the 17-50.

Normally this sort of thing is not a bad idea. Camera shake is a big problem, all the more since the sensor resolution is very high and will show all traces of camera movement while the exposure is being made.

However, this is accompanied by opening up the lens, making focus very critical even at a range of hundreds of meters in full sunlight. I was trying to manually focus yesterday, but not having much luck because there was a little haze in the air (hot and muggy, without rain). So, I couldn't see the slight shimmering that appears in the focus screen when a lens is perfectly focused.

I changed to Aperture Priority (A) mode, set my F-stop to F5.6, and did some focus bracketing. Because of the focus bracketing, I got the shot.

While struggling with this, I tried autofocus several times and noticed that there is a small error band when using autofocus. So you can autofocus twice and get different results. These effects are very subtle and hard to see, except in post processing. This post is merely cautionary information for other SD1 and SD1M users who are going after pixel-level sharpness. The problems are much less apparent in my SD15.

I am gradually getting to a point that I need a ground-glass (or better) focus screen in the camera. The existing screen is virtually transparent, so while manually focusing I basically have to compare the focus against the black squares and circles etched into the factory-supplied focus screen. This is difficult.

Also, the 85mm F1.4 EX DG HSM uses a clutch-type focus ring (it does not rotate while autofocusing) so there is no way to use a "mark the focus ring" approach. The focus scale is internal, behind a window, so it does not make practical sense to try to mark it directly either.

Because of these experiences with my SD1, I look forward to a future version or hopefully a firmware revision that will support live-view sensor-based autofocus.
Tom Schum

 Tom Schum's gear list:Tom Schum's gear list
Sigma DP3 Merrill Fujifilm X-E1 Sigma 50mm F2.8 EX DG Macro Samyang 8mm F2.8 UMC Fisheye Sigma 18-250mm F3.5-6.3 DC Macro OS HSM +3 more
Panasonic Lumix DMC-F5 Sigma SD1 Sigma SD15
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