Re: Photographing a mirror

Jürgen Exner wrote:
carp <yeeehi@xxxxxxxxx> wrote:
I would like to photograph a reflection in a mirror. The camera is
pointed head on at the reflection, lets say 40cm away from the mirror.

1) From which point of my lens should I measure the distance to the
mirror?

From the focal point of the lens, which depending on the design of the
lens is often but not always in the last third or quarter of the lens.
J - ? Just nitpicking, but aren't lens focus distance scales supposed to use the sensor (or film) plane as the origin point?


But why are you interested in the distance to the mirror? I though you
wanted to get a picture of the relection, not the mirror?

2) When trying to accurately measure the distance to the image (the
reflection) what range should I manually enter into the camera, if I
don't use auto-focus?
C - if you are focusing on the subject not the mirror, it is the total distance. So camera-to-mirror *plus* mirror-to-subject.


3) Would auto-focus work? (I want to get an un-blurred image of the
reflection.)
Yes, as long as mirror is clean, and not so small that the AF tries to focus on the frame..


Ultrasound measurement will not because if will measure the distance to
the mirror. Infrared, and any optical system should work without a
problem.
J - Apart from those old Polaroids, are there any mainstream cameras that use ultrasound?


4) If I am aiming at 30 degrees to the mirror, rather than straight at
it, will that effect the calculation?
C - Nope, as long as you use the method referred to in 2)

As they said, just use AF or manual focus - why do you need the distance?
.

Relevant Pages

  • Re: Einsteins lopsided caricature of space and time
    ... >> dimensional velocity vectors), are the next step. ... in order for the distance (as measured ... Where is the mirror and is it co-moving with the ... flight times of the signal before and after the reflection ...
    (sci.physics.relativity)
  • Re: Einsteins lopsided caricature of space and time
    ... If the object and mirror would be moving ... the distance x' between them would not be the ... >> What matters is the single event of reflection, ... >> yourself, sitting in that chair. ...
    (sci.physics.relativity)
  • Re: Einsteins lopsided caricature of space and time
    ... but we have been working with speeds. ... Where is the mirror and is it co-moving with the ... > flight times of the signal before and after the reflection ... > object and that it always has a distance x' (as measured ...
    (sci.physics.relativity)
  • Re: Prism Light Speed
    ... So the least distance is a stationary ... meter on the other side of the center of curvature of the mirror. ... >a ray of light might take going from A to B via a reflection off a flat ... That means that the total path lengths ADB ...
    (sci.optics)
  • Re: Prism Light Speed
    ... So the least distance is a stationary ... meter on the other side of the center of curvature of the mirror. ... >a ray of light might take going from A to B via a reflection off a flat ... That means that the total path lengths ADB ...
    (sci.astro.amateur)