Thursday 29 January 2015

autofocus - Why can't I take a photo in dark with auto focus, manual mode?


I'm dorking around with a Nikon D80 and I am a total beginner. I am trying to shoot some light trails but the darn thing doesn't even take a picture. I am in manual mode with the bulb setting. For some reason, when I hold down the button, it does not take a picture. I can hold the button half way for the lens to auto focus (is that what it is doing when it is moving?), but when I press down all the way, the camera refuses to take a picture. When I go back to automatic mode, it happily takes a photo. What am I doing wrong? Thanks!!


Edited post: I am thinking it has something to do with how far/close the subject is. If there is something close, the camera doesn't want to take a picture, but if there is nothing right in front of it, it will take a pic in manual mode... (Generally hypothesizing right now.)


Answer: I think I found out what is wrong. The lens was on auto focus. I guess I had to change it to manual to use manual mode..... It works now (taking a pic of something close up that is..) Could anyone give a more detailed explanation as to what happened here? :)




Answer



Re. your answer - you don't have to have the focus set to Manual just because you're in Manual mode, but autofocus systems generally don't work in the dark. Therefore the camera will fail to focus and refuse to take a picture. By switching to manual you remove that problem.


Switching to Auto mode may allow autofocus because it turns the AF illuminator on. Autofocus works by splitting the image coming through the lens and then calculating the focus needed to recombine it. If the image is too dark, the camera can't 'see' what it's splitting and recombining, and so it will fail to focus. The AF illuminator lights up the scene so the camera can make its decision, but it's usually turned off when in the priority or manual modes.


When light painting, it's best to pre-focus manually with the lights on, then leave it on manual and turn the lights off.


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