Shooting after reflection on mirror

[Marco Annaratone]

I frankly did not know where to post this...sorry for the poor filing...

I need to shoot at subjects after their image has been reflected by a normal (e.g., bathroom) mirror. That is, I point at the mirror itself to shoot. At the same time I cannot afford to degrade the image significantly. My questions are:

1. Does a normal mirror (cleaned and not marred, of course) degrade the image in such a way that a side-by-side comparison of two prints --- one taken aimed at the subject, the other aimed at the mirror --- will show objectionable differences?
2. If yes, can someone point me to some reference where I can figure out what kind of mirror (flatness, material, etc) I should use not to degrade the image too much?

I could do the experiment myself, but maybe someone knows the answer already and that would save me some time and grief.

If there is a guru of optics out there, please speak out!

Thanks a bunch

[Richard Kelham]

The thickness of the glass in the mirror can lead to refraction causing a double image to form. The only way to do it (AFAIK) is to use a surface silvered mirror. These are delicate and expensive...



Richard

[Ken C]

Just shoot normally and turn the negative over to print.

[Jim Jones]

Like Richard says, you can get a double reflection from an ordinary mirror. This can be particularly noticable if there are small sharp highlights reflected in the mirror, and when the subject is not viewed perpendicular to the plane of the mirror. Some mirrors conspicuously distort the image. To check for this when selecting a mirror, view the image from a position close to the plane of the mirror. This emphasizes the distortion. If the image is little distorted, it will have even less distortion at mormal angles. Most glass mirrors seem flat enough.

[Donald Qualls]

The double reflection is more noticeable the further off the "normal" you shoot. If you shoot directly into the mirror (i.e. a self-portrait of the camera), it's almost undetectable, but if you shoot at a sharp angle (for instance, to avoid a self-portrait when using a wide lens) the distance between the strong and weak reflection will be greater, making the weak reflection more visible.

The cleaner the glass, the less you'll notice this, and eliminating strong light sources or specular reflections from the subject field will also help (a tiny, strong highlight will be easily seen as doubled in the reflection).

One of the best mirrors to use for this is the stainless steel type used in rest stops on the freeway system; it's automatically a front surface, and when new (before it gets scratches, dents, and surface oxidation) is almost as flat as the cheap window glass used for conventional mirrors.

[Struan Gray]

If you can arrange the angles properly, you can almost completely eliminate the reflection from the surface of the glass on a conventional mirror with a polarising filter. Place the subject and the camera roughly 60 off the perpendicular to the plane of the mirror and rotate the polariser until the double image disappears. Use a maglite or table lamp with a bare bulb to optimise the setup. The same polariser orientation will work at other angles too, but not as well.

Then there's the quality of the mirror and its glass. The best thing you can do there is to place the camera as close to the mirror as possible: most of the things a slab of glass or a slightly bent mirror can do to an image get worse as you move away from it.

[Marco Annaratone]

Thank you all for the great advice. I plan to shoot at some angle but not too extreme and I should be quite close to the mirror, which is good.

[David G. Gagnon]

Marco,

Keep in mind that a reflection in the mirror is on a very different plane of focus than the object being reflected. In other words, if you were to stand in 10 feet in front of a mirror and take a picture of yourelf, the focusing distance will be 20 feet. I'm not sure exactly what shot you are trying to compose, but the object and it's relection will be farther away than you think, so you may need to rethink your f stop choice.

DG

[Donald Qualls]

If focusing on ground glass or using a rangefinder, the distances don't really matter. If using a scale, measure from camera to the reflection point in the mirror, then from there to the subject, and add the two measurements.