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<p>I would ignore those smartphone apps as any accurate indication of light. They use the little sensor on the phone that's just designed to keep the display brightness in line with ambient lighting conditions. It was never meant to be an accurate light sensor, and those "lightmeter" apps are no more than toys. Either compare the camera to a proper photographic lightmeter or compare it to the "Sunny 16" rule - which is more like the Sunny 11 rule outside of the tropics.</p>
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<p>For awhile I was using a meter-less Pentax SV until the film advance lever locked up. Sunny 16 served me well then, but I used the iPhone apps because they let me more easily meter with 'aperture priority'. Good tip about Sunny 11, I will definitely try that if I pick up a waist level finder (I <strong>really</strong> like the look of the waist level finder).</p>
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<p>First, I would get the correct batteries as previously mentioned. Second, the Vivitar may not <em>transmit</em> light at fully 2.8, actual T value might be a little slower, so it is possible that the lens is resulting in a lower shutter speed.<br /> To check the meter, I would get a 50mm/f2 or 1.4Nikon lens from somewhere. The good thing is that with the DP-1, pretty much any Nikon manual focus lens will be compatible, as long as it has rabbit ears to couple. You don't have to have AI lenses. Then, compare to a known good meter in reasonably strong daylight, probably in the shade, so that the available light is somewhere in the middle of the meter range. When I used these cameras, I often put a little offset on the ISO setting to tweak, especially for a little underexposure when using slide film.</p>
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<p>I bought two 357s for the Nikon and one for the Olympus XA I am picking up tomorrow. I haven't noticed a difference in metering after the change.<br /> <br /> I am currently half way through a roll of film using the DP-1. I'm confident the meter is working fine as is, but if not, I'll take your suggestion and adjust the ISO.<br /> <br /> I just bought a 50mm 1.4 AI off eBay for $50. Looks like it's in great condition, has a filter/protector and both vintage caps. One of the non-AI versions was sniped away from me at the last second, but I'm glad I picked up the AI type in case I try out other bodies or a dp-12 falls into my lap (you never know?).</p><div></div>