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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? :)

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My first thought when reading your original question was autofocus, b/c I had similar situation with my Canon once and only after the fact I understood what went wrong. However, you said that on Auto mode you can take a picture, so it ruled out this option. From your edit it seems like it was this problem after all, so I wonder why Auto mode is able to lock focus while Manual mode is not??? –  ysap Jul 29 '11 at 7:38
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I often ask myself why I can't take a photo - but the answers are less technical. ;) –  AJ Finch Jul 29 '11 at 11:04
    
I suspect that you're trying to focus on something that is closer than the lens's minimum focusing distance. This might not be easily visible when using manual focus, but the image will not be in sharp focus. Try moving the camera back a couple of inches. –  Chinmay Kanchi Jan 7 '13 at 16:44

4 Answers 4

up vote 15 down vote accepted

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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ElendilTheTall - Please read my comment to the question. Can you explain why the focus supposedly locks when the camera is in Auto mode (are things different with Nikon)? –  ysap Jul 29 '11 at 7:41
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Possibly because Auto mode turns on the AF illuminator, which obviously allows the AF to work. –  ElendilTheTall Jul 29 '11 at 7:58
    
Good point. [... filler so I can press Enter ...] –  ysap Jul 29 '11 at 8:11

It's the auto-focus mode:

  • When in AF-A or AF-S, the camera will not shoot until it has achieved a focus-lock. Therefore, when you are in the dark, where the AF cannot work, it never locks, and therefore never takes the exposure.
  • When in AF-C, the camera takes an exposure immediately upon full shutter depression, independently of focus state.
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Aren't you in a mirror lockup mode? At this mode the first press will lock the mirror in the up-position, and the second press will take the picture. Is it possible that you actually have a very short (frustrated?) second press, so your image is completely dark?

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Not really sure what this mirror lockup mode is. From what I gather here: photo.net/nikon-camera-forum/00Nes5 it has something to do when you want to clean the lens. I was having a hard time taking a picture, but when I did, the picture was not completely dark. –  O_O Jul 29 '11 at 7:19
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Mirror lockup just puts the mirror in the up position, exposing the sensor when you take the picture (as opposed to half-press, where the mirror is down, allowing you to see the scene through the viewfinder. It is actually necessary if you want to clean the sensor, not the lens (and you do this when the lens is removed from the body). However, this is the secondary use. The first reason is to eliminate camera shake when doing long (relatively) exposures. [... cont] –  ysap Jul 29 '11 at 7:34
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[cont...] When the reflex mechanism lifts the mirror, it is done extremely fast and stops violently when the mirror hits the stopper. This causes shake, which can reduce your image sharpness. If you pre-lock your mirror, then the actual exposure is smoother and the image is sharper. –  ysap Jul 29 '11 at 7:35

Because its too dark to auto-focus.

Because to auto-focus, the camera sensor needs to sense light. Since you are shooting in the dark, there is no light, and it can't achieve focus-lock.

You don't really want or need to adjust the focus, whatever is causing the light trails is going to be far away, so you can set the manual focus to infinity or just a tad short of infinity, and you'll be fine. Technically, you want the lens at the hyperfocal point. See http://www.dofmaster.com/hyperfocal.html

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