Page 1 of 2 12 LastLast
Results 1 to 10 of 11

Thread: Focusing in the dark with a laser

  1. #1

    Join Date
    Apr 2000
    Location
    France
    Posts
    30

    Focusing in the dark with a laser

    I am thinking of buying one of these small and cheap ($20~) laser pointers to use it as a focusing aid in the dark. They produce a fairly small and very bright red dot that can be aimed at the point you want to focus. The range can be up to hundreds of meters, depending on the device.

    I like to take night pictures of monuments, and i believe this could help to get the best focus.

    Has anyone tried such a device in the field ?

    Thanks a lot

  2. #2

    Join Date
    Dec 1999
    Posts
    146

    Focusing in the dark with a laser

    I have no idea with the laser, but I have used a torch projected through the camera and focus until the image of the torches' reflector is sharp. I have yet to ty this out doors but if I use a strong enough torch it should work. However, I am not too clear about the laser idea, only practice should give you an idea of how well it is. BTW, can't you blind people with certain laser pointers?

  3. #3

    Focusing in the dark with a laser

    If I catch your drift correctly, you're thinking of using the laser as a focus illuminator for an AF camera, or for focussing by eye right? In this case I think the spot will be far too small for this purpose, and the diffraction pattern from the laser will probably confuse both your eye and any AF system as well.

    I've used a small Helium-Neon laser to calibrate a split image rangefinder, and this technique works a treat. You point the laser into the eyepiece, and where the spots co-incide is at the focus distance of the rangefinder. I don't see any reason why this method shouldn't work in the field with an already calibrated split-image rangefinder. You might need some sort of clamp to keep the laser and rangefinder together as a unit. My hand aligned Heath-Robinson setup was a bit shaky over a few tens of feet.

  4. #4

    Join Date
    Apr 1999
    Posts
    88

    Focusing in the dark with a laser

    This sure goes slightly off topic, but a well known photographer here in Finland had once a poodle that he used helping view camera focusing in the field. He just commanded the dog further or nearer, and because it was white, it was easy seen on the groundglass. And he even called it for focusing-dog.

  5. #5

    Join Date
    Mar 1998
    Posts
    1,972

    Focusing in the dark with a laser

    Well you have someone to assist you (basically so you don't have to leave the ca mera sitting by its lonesome self) here is a trick I use. take a mini Maglite flashlight, unscrew the reflector so just the naked small bulb is revealed and p lace the flash light on the point you want to focus on. Works like a champ, especially for interiors. the problem with the laser pointers ins the light patt ern is not focused and exhibits a slight scatter when it hits a target from any distance.

  6. #6

    Join Date
    Mar 1998
    Posts
    1,972

    Focusing in the dark with a laser

    Should have read: "

    Well ifyou have someone to assist you (basically so you don 't have to leave the camera sitting by its lonesome self) here is a trick I use. ..

  7. #7

    Join Date
    Apr 2000
    Location
    France
    Posts
    30

    Focusing in the dark with a laser

    Thank you for your comments, I will try this system (at least to see if it really works). Here is the way I think I will make the tests (as soon as I have some time available :-)) :

    1-Find a way to mount the laser on the tripod on a small ball head. I will try to mount it under the platform of the tripod head. The goal here is to be able to aim the beam to a stable point, and to be able to move it in the field to check the focus on different points.

    2- Direct the laser spot to the point to focus. The laser spot is usually smaller that 5 millimeters (or 1/5") up to 100 meters. You can also focus the laser dot if necessary.

    3- Focus the camera by making this red dot the smallest possible. Normally, no diffraction will happen, as this is diffused light. The laser will not go through the camera, but will be directly sent by the pointer optics. This is exactly the same way used in astronomy to focus the telescopes on stars. The stars are point-like sources, and the focus is reached when the star is the smallest. In a way, the laser dot is a kind of artificial star :-).

    I got the idea of this trick because the professional astronomers (I am one of them :-)) use laser artificial stars to correct the star images for all the defects introduced by the turbulent atmosphere (including focus motions, but also further blurs that don't appear on normal photos). This would be more or less the same principle here.

    Also, to have a bright red beam gives it a nicely impressive "high tech" look. I hope people will not think I am a sniper aiming a rifle at someone :-).

    One important point to mention is that the lasers must NOT be aimed into the eye (though this is not so critical for a distance > 20 m normally). This is clearly a point I will check carefully, but when aiming to the ceiling of a cathedral for example, there should be no problem.

    Thank you again for your help: any further comment is of course very welcome :-) !

  8. #8

    Join Date
    Jul 1998
    Location
    Lund, Sweden
    Posts
    2,209

    Focusing in the dark with a laser

    This works, and is better than having nothing to focus on at all, but it suffers from two problems. First, the beam from laser pointers is not very well-collimated, so your spot size on a cathedral roof will be much larger than a few millimeters, and it will have fuzzy edges: in short, it's not an ideal focussing target. Second, even the semiconductor lasers in pointers have enough coherence that you get speckle patterns (the dancing dots you see when the beam is reflected from diffuse surfaces) which can confuse your eye, even when imaged on a ground glass.

    Two improvements on your idea. First, the green laser pointers are easier to see. This is good in itself, but also means they have a lower power rating for a given brightness and are less likely to raise safety issues. Second, the clip-on diffractive elements which cause the beam to look like a cartoon character or a word will provide a target that is easier to focus on.

    Pete's use of a laser through a rangefinder is actually the best way of doing this, although it presupposes that your rangefinder is calibrated to your lens, and that you're not using movements. Graphlex used to sell a lamp for use with their rangefinder-coupled models that was used in just this way.

    The safety issue is not a big deal, but shouldn't be ignored. Many of the cheapie laser pointers are actually more powerful than ones sourced from reputable places. Some of the cheap imports are class III, and would never get approval for this use if the manufacturer ever bothered to try. Even though class III lasers will have a hard time blinding anyone (it can be done, but is unlikely in your proposed use) they can certainly dazzle a car driver at large distances.

  9. #9

    Focusing in the dark with a laser

    The mini-maglite technique mentioned above by Ellis can be easily adapted to a solo working style. Just tape or superclamp the flashlight to a light stand placed at the required distance.

  10. #10

    Focusing in the dark with a laser

    Pierre, I also do not think a small laser dot so far in the distance will provide reliable focus? I do one of two things... if I set up before dark, I mark the focus points on my camera, that way I can come back and simply set up and know focus is perfect with out viewing. But when I am close to my vehicle, I carry a handheld 2 million candle power spot light, that will provide ample light for focussing... assuming your subject is not miles away. They cost less than the laser pointers and are recharged via cigarette lighter. Also, I use this lamp with a color filter so the output color temp is exactly 5500K, then I can use it to light up the subjects at night for some real dramatic effects! Good luck...

Similar Threads

  1. laser prints
    By robc in forum Business
    Replies: 0
    Last Post: 24-Dec-2005, 03:07
  2. Laser printer suggestions
    By Calamity Jane in forum Business
    Replies: 6
    Last Post: 19-Apr-2005, 18:16
  3. Have any of you had laser vision correction?
    By Anne Williams in forum Cameras & Camera Accessories
    Replies: 26
    Last Post: 17-Feb-2005, 13:41
  4. Eyes Laser Surgery
    By dan nguyen in forum Cameras & Camera Accessories
    Replies: 14
    Last Post: 1-Oct-2001, 14:25
  5. Dark focusing screen -- solutions?
    By Howard Slavitt in forum Cameras & Camera Accessories
    Replies: 5
    Last Post: 5-Nov-1998, 00:51

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •