At least some Nikon cameras can emulate that TAv function to some extent. Here's how:
1. Switch to manual exposure mode.
2. Turn on Auto ISO.
3. Dial in the aperture and shutter speed that you want.
You'll notice that Auto ISO will adjust your exposure upward or downward, up to as low as the base ISO to as high as the ISO limit that you set in the menus. You'll also notice that the light meter won't move as it usually does, instead showing 0 until you go beyond the minimum or maximum ISO. If you do want to adjust exposure to match your intent, you can use exposure compensation.
Here are test shots. The baseline shot is at ISO 800, f/4, 1/25, taken on manual exposure mode, matrix metering, with the light meter at 0. Let's assume that this is the correct exposure.
In the next shot, I activated Auto ISO, then changed the aperture and shutter to f/5.6, 1/50, with ISO initially at 800. ISO automatically adjusted to 2800, showing that Auto ISO will adjust upward as needed.
In the following shot, I changed the aperture and shutter to f/2.8, 1/13 with ISO initially at 800. ISO automatically adjusted to 220, showing that Auto ISO will also adjust downward as needed.
In this shot, I changed the aperture and shutter to f/2.8, 1/6. ISO could not adjust below the base ISO (ISO 200 for the D300), resulting in overexposure (you do get a warning of sorts because the light meter will show an overexposure).
Michael,
ReplyDeleteThanks for the demo. But I'm seeing two limitations with Auto ISO in M mode:
1. You can't override with any ISO settings outside of the range, until Auto ISO is turned off;
2. In M mode, there's no way to adjust exposure compensation.
I don't know if Pentax has these limitations as I don't have one to play with.
Hi Jenson. Thanks for pointing out both of those issues.
ReplyDeleteAbout the first one, if I understand you correctly, the issue is that you may want to set the Auto ISO limit to let's say 800, but then for specific shots want 1600 or perhaps 100, neither of which are possible with the given Auto ISO range of 200-800. You're right. The problem is further compounded when you want to switch exposure to aperture priority and let's say you don't want Auto ISO active then. What I do to address both issues is to put Auto ISO on 'My Menu' (the short list of items that I change frequently).
Regarding the second one, on my camera (D300), if I use exposure compensation in manual mode with auto ISO set to 'on', I sort of recall it will change the auto ISO setting accordingly. If for example the normal result of a particular aperture and shutter combination is 800 ISO, adjusting exposure comp in manual mode by -0.3 will change the resulting ISO to 640 instead, resulting in an image that is -0.3 stops darker. I'll confirm this later. Please let me know if I misunderstood.
Thanks again.
Best regards,
Mic
Michael, with regard to the 2nd one, you are right about the it. I didn't notice before.
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