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I’m taking night pictures with Canon EFS 18-135mm STM lens and EOS 450D body. I’ve noticed that when I’m trying to shoot distant objects and there is enough light for the AF to work the pictures come out nice and sharp. But sometimes AF is unable to lock on the right focus (too dark?) so I try manual focus. But even though I turn the focus ring all the way to „infinity” the pictures are very out of focus. Essentially using MF I can’t find the focus setting to make the picure sharp. But in the same distance to object but a bit brighter circumstances AF successfully finds the right focus.

Is this normal? Shouldn’t MF set all the way to infinity result in a sharp picture of distant objects? I’m trying to take a picture of an urban landscape at night. And yes, i’m using a tripod.

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    Most lenses go past infinity; did you check pulling it back a tad wasn't what you needed, or does it not even pass through infinity before it hits the stop? – Tetsujin Jun 7 '18 at 12:59
  • Thing is that there is no stop on the focus ring. I can rotate it infinitly in the same direction. But focus changes only on some subset of the angle. After that point (not marked in anyway on the lens itself) rotating more just does nothing. – user196530 Jun 7 '18 at 13:12
  • I don't know that particular lens, but on the ones of mine with 'infinite spin' you can just very slightly feel a change in resistance as it reaches the end of the travel. It sometimes takes me a couple of tries before I feel it. – Tetsujin Jun 7 '18 at 13:33
  • Actually, better: How can I find infinity focus on a kit lens with no markers? – mattdm Jun 7 '18 at 13:47
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The problem is that on the modern lenses there is no clear point marking the infinite (it is marked as L___, so it is somewhere theeeeere). Never the less you have a few possibilities:

  • use a laser pointer or a torch and autofocus with that,

  • use the lcd screen and magnify the view 5x or 10x, then focus manually (if it is super dark, set ISO to 6400 or 12800, focus and go back to the desired ISO value),

  • prefocus during the day (the best from the tripod) and mark on the lens with a marker or a piece of a duct tape where the focus point is on the lens, and come back later to exactly the same spot and focus manually to the marker.

  • There are no indicators on the focus ring on the lens. And there is no stop point when I rotate it in any of the directions. Though it’s visible that the focus changes obly up to some angle. I can you elaborate on method 2? Which lcd screen, camera’s? Or an external one like a smartphone? Solution 1 sounds promising tho – user196530 Jun 7 '18 at 13:17
  • It’s this specific one cyfrowe.pl/aparaty/… – user196530 Jun 7 '18 at 13:22
  • Ok, it may be hard to mark anything on this particular lens. I meant using the live view on the lcd screen on the back of the camera, but as this model can go up to ISO 1600 only, that can be not enough in the darkness. I would recommend the 1st option as the best: use a laser pointer, AF on the beam dot, switch to manual (MF) and you are ready to go as long as you stay in the same place. – Piotr Kepka Jun 7 '18 at 13:37
  • I always go with option nr 2, results are better that any autofocus system, even during the day. There is always some light in the distance, go to live-view, zoom in on it all the way, focus manually, and take the picture. – Orbit Jun 9 '18 at 12:01
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All Canon STM lenses are 'focus-by-wire'. This means that there is no direct mechanical connection between the focusing ring and the lens' focusing elements. When one turns the ring to manually focus the lens, a position sensor sends a message to the camera telling it how far you moved the ring. The camera then sends instruction to the lens to move by a corresponding amount.

Most STM lenses reset to a specific focus distance each time the camera is powered on.

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Since the focusing ring does not move when the focusing distance is reset, marking the focusing ring will not work if the camera is powered off and back on, or goes into 'standby' mode and is then reactivated. The relationship between the respective positions of the ring and the focus elements also changes if the ring is turned past the limits of focus travel in either direction. In short, there is non 1:1 correspondence between the position of the focusing ring and the focusing elements themselves.

This makes focusing on infinity using the position of the ring impossible with STM lenses.

For how to manually focus in the dark please see:

How can I focus quickly outdoors in the dark?
How does one focus for landscape photos in very dark conditions?

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