Samsung 45mm f/1.8 Review (2d)

Started Apr 26, 2013 | Discussions thread
viking79
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Re: 45's low light AF?
In reply to Tjalpics, May 17, 2013

Tjalpics wrote:

Thanks a lot, Eric! Appreciate that.

Strange that it failed to focus completely. Probably 'cause you kept it at ISO100, because my 30mm performs quite well with the latest NX11 lens & body firmwares - on the NX10 sensor. Nevertheless, the 45mm is still a contender.

I had the camera set at 1/20, f/1.8, ISO 3200, but set it to ISO 100 just to get the standardized EV rating, EV = log ( N^2/t) / log 2, where N is f stop number (1.8), and t is shutter speed (1.6" at ISO 100).  I was in A mode at +1 EV since I was photographing a largely white chart.

And even with the 50 watt bulb the high contrast edge on my chart was very easy for the camera to focus on at EV 1 (this is pretty dim), because the sensor gains up the image and it looks about like it would normally.  I would say refocus speed at EV 1 felt the same as EV 7 so I didn't spend the time measuring it right now, something like 1/4 second.

When it failed to focus was when I turned off the 50 watt bulb and the chart was pretty dark with little contrast, just the light from the neighboring room.  I need to find my variable AC transformer or a dimmable light that I can use to see where the focus fails.

So at some EV level the camera stops being able to focus.  I don't know what level that is since I don't have that variable light source yet.

I will say that you need a high contrast edge, and as long as you have that it can focus in very low light at relatively high speed.

What you need to remember when using contrast detect focus is to make sure you have contrast on a vertical edge in the image where you want to focus.  Even if you have only a candle light the camera will be able to focus as long as you give it contrast.

I think too often people try to focus on a shadowed front side of a person, just turn them towards a light source and get some contrast.  Focus on a collar or any other higher contrast part, sometimes the whites of an eye or a catchlight reflecting off the eye are adequate.

Eric

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