Cannot press shutter down on DSLR?

[CWP8]

We recently went on a family holiday with a Nikon D700 with a Tamron 28-300mm f/3.5-6.3 DI VC PZD (we usually shoot with our Nikkor 24-70mm but decided that for family holidays with 2 little kids, something with a longer range and more portability would serve us better). Anyway, to cut to the chase, while we have found that this combination takes decent holiday pics, we had numerous occasions last week when we could not press the shutter down. We have previously experienced this even with the 24-70mm, usually when the subject is too close or light too dark even for that lens, but only very occasionally during around 5 years of use; however, with this Tamron lens, on a one week holiday, we experienced 5 or 6 times when we couldn't make the shot. I've browsed the internet for ideas, and the most plausible explanation seems to be that possibly what we were shooting did not have sufficient contrast or was otherwise a shot where focus could not be properly attained. Reflecting back on when this happened, this could account for maybe a couple of the shots, but, for example, this happened twice when we asked a friend to take a shot of our family from about 2-3 metres, and also when I was trying to shoot the view (sky and buildings) from our hotel balcony, all in good light, situations which have never troubled us before, even with the same Tamron lens (we've been using the lens for a few months now).

Would be very grateful for any ideas on what the problem might be, including whether it might be worth taking the lens back to Tamron to take a look.

Thank you very much in advance for any thoughts!

 

[weepete]

Sounds to me like the autofocus hasn't confirmed and the release priority prevents the shutter from firing if you haven't got autofocus confirmed.

It's probably somewhere in the custom functions to change the release priority if you wish.

I'd check the camera's manual under autofocus subheading.

 

[Dave442]

Yes, i would put the camera in AF-C and Release Priority. That way it will take a picture any time you push the shutter. That way you can eliminate the focus as an issue. Of course if you hand the camera to someone they may take a bunch of Out-Of-Focus shots.
I often set my camera so AF-S is Focus Priority and AF-C is Release Priority.

 

[Peeb72]

Next time it happens, switch to manual focus and see if the problem disappears.

If so, it's an autofocus issue.

 

[CWP8]

Thanks all for these quick replies.

Just to make sure I'm not misunderstanding, if it is indeed an autofocus issue, does that unfortunately mean it's just an inherent unavoidable problem (and we just have to use a workaround whenever it happens) or could it be an issue with my particular lens (or worse camera body) that would benefit from getting it looked at by the manufacturer?

 

[Big Mike]

Welcome to the forum.

Assuming everything is working, the only time your camera won't take a photo when you press the shutter release button, is when it's in still subject focus mode (AF-S) and it can't confirm focus. In AF-S, the camera waits until it has achieved/confirmed focus, before snapping the shot.

There are a few different reasons why your camera/lens may not achieve focus while in AF. The big one is lack of contrast. You can test this out by trying to focus on a blank sheet of paper. The camera will usually 'hunt' (focus in and out) and then it will stop and the AF confirmation light (in the viewfinder) will begin to flash. The most common reason why your scene may not have enough contrast, is when you're in low light. So if you are finding that the camera won't focus in low light situations, that is likely the issue.

This is why most cameras have an AF assist light. It usually comes on when trying to focus in low light (and when in AF-S mode). It's not all that powerful, which is why it's a nice benefit to have an accessory flash. Most flashes (and even the Nikon Off-Shoe cord, I think) have a built-in AF assist light that is better than the one on the camera.

Also, if you can determine that the lack of light is your problem, you can add light another way. I've seen photographers use a handheld flashlight, or a 'video light' attached to the hotshoe.

Another issue is minimum distance. A lens has a minimum focus distance and it won't focus any closer than that. So in that case, you would see the same hunting and it won't take the photo (in AF-S).

As for it being better or worse with different lenses....yeah, that is usually the case.
The biggest issue here is maximum aperture. A lens with a larger maximum aperture will give the camera more light for the AF system to work...and conversely, a lens with a smaller max aperture will be worse. Most cameras need a minimum of F5.6 for the AF system to function properly. So your Tamron 28-300mm f/3.5-6.3 may be causing an issue when zoomed all the way to 300mm.

As mentioned, you can usually get around this by using AF-C (moving subject mode). This mode should take the photo when you press the button, even if it's not in focus yet. So obviously you might get more 'missed focus' shots, but at least it will snap when you press the button. You could also try manual focus mode.

Lastly, the way I teach it to my students, is to learn/remember that focus is basically a distance. You are adjusting the lens to focus at a certain distance. So knowing that....you can use it to your advantage. If you are having trouble focusing on a certain subject, you could figure out how far away they are and focus to that distance. There are a few techniques for how to do that, but the key factor is having the knowledge of how it works and using your head.

 

[table1349]

If all else fails.

Ok, on a serious note. It sounds like the advise already given should solve the problem. BigMike has given a good explanation as to the issue.

 

[CWP8]

Really appreciate the further detailed response. Seems like maybe we have sacrificed a little on the autofocus capabilities to gain more range, and that it's unlikely to be a hardware fault with my lens. Will explore the various suggestions on this thread for ad hoc workarounds. Thanks all.

 

[wfooshee]

When your friend was shooting your group, there may have simply been nothing in view of the focus sensor for it to lock on. As for the view from the balcony, if the picture is mostly sky, it can't focus unless you happen to get a textured cloud or the edge of a cloud under a sensor square.

AF has limits. When shooting AF-S and the default focus release on the shutter, there HAS to be something "focus-able" in the center of the viewfinder. AF-S only uses the center by default. you can set AF-S to use the full field by setting it to auto-select, but then the camera decides what to focus on, and it may not pick the right thing. When on a single sensor, you can move that sensor around the viewfinder with the cursor buttons, but unless sensor selection is AUTO, there's only one active sensor in AF-S.

AF-C can be set to single focus sensor, or any of several group sizes, or auto-select, as well as 3D-tracking. With each of those except 3D tracking, the camera chooses focus according to what it thinks it sees under the active sensors. In 3D tracking, it starts with a single sensor, and whatever is in that sensor when you half-press the shutter, it follows around the viewfinder and keeps in continuous focus. it works great when there's significant contrast between subject and background, not so good when there's not.

There's a shutter setting for both modes, AF-S and AF-C. you can tell the camera focus-priority or release priority. Focus priority means no picture if no focus. Release priority means best quick effort at focus and shoot it anyway. the default is focus priority for AF-S and release priority for AF-C, but you can set either priority with either mode. I actually keep both in focus priority most of the time.

Knowing how the AF works, and understanding the limits each mode presents, will help you understand what's going on when it looks like something doesn't work.