Why won’t my Nikon D90 go below ISO 200 in bright light, and how can I avoid overexposure at f/1.4?
Asked 3/18/2013
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I’m using a Nikon D90 with an f/1.4 lens in very bright conditions, such as on a beach. With Auto ISO and shutter speed active and the aperture fixed wide open, some shots are overexposed. The camera appears to be hitting its limits at 1/4000 sec and ISO 200. Is 1/4000 the D90’s maximum shutter speed? Why doesn’t Auto ISO go below 200, and what do the manual LO ISO settings mean? If I want to keep the lens at f/1.4, what are my options besides stopping down the aperture?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
5
Since the aperture directly affects image composition, it might not be desirable to stop your lens down when you hit the minimum possible shutter speed and ISO for your camera. The LO ISO option is pointless as well, since this is just an image pulled one stop in software to ISO 100 (in your case), which can be done (and probably better) in your postprocessor of choice.
I'm afraid the only choices in this type of situation are to either use an ND filter of appropriate density to cut the amount of light going through the lens or to use a body with a higher minimum shutter speed.
You might be able to use a circular polariser instead of an ND filter, as these are cheaper and also cut light by 1-2 stops, but can also change the character of the image quite substantially.
Originally by user1293. Source · Licensed CC BY-SA 4.0
user1293
13y ago
0
Generated from our catalog & community — verify before relying on it.
Yes — on the D90, 1/4000 sec is the maximum shutter speed, and ISO 200 is the camera’s normal base ISO. The manual “LO” setting is not a true lower native ISO; it’s essentially a pulled setting (about ISO 100) applied in processing, which is why Auto ISO typically won’t use it.
So if you want to keep shooting at f/1.4 in very bright light, the camera can simply run out of room: it’s already at its fastest shutter speed and lowest standard ISO.
Your practical options are:
- use an ND filter to reduce the light entering the lens
- use a circular polarizer, which also cuts about 1–2 stops, though it can noticeably affect the look of the image
- stop down the aperture
- use a camera body with a faster maximum shutter speed
If maintaining shallow depth of field is the priority, an ND filter is the most straightforward solution.
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