issues close focussing on reflections

[ksporry]

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Here's an interesting one:

 

a couple of weeks ago, I was on an evening workshop shooting reflections.

I found I had a real problem using my M8.2 to focus on reflection sof far away objects in close objects. So if I had a car window in which there was the reflection of a more distant neon sign, i just couldn't get either the window or the subject in focus.

at this close range (one or two feet) I can understand teh range finder no longer works. it indicate s adistorted image that makes it impossible to focus properly. The images simply will not overlap because of the distortion. I can understand this with focussing up close. But all that should do is prevent me from using the range finder from focussing. If I try manual focussing, I just cannot get the focus right for the reflection in the window. I suspect this may be because of the optical effect of shooting reflections, but I couldn't work it out at the time.

I am wondering if I should guess the "illusionary distance" of teh subject (i.e. the perceived distance that the reflection causes. I may not have done this properly.

Any thoughts/ideas how to tacle this issue?

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[jaapv]

Yes - like on RFF, turn the camera 90 degrees. And the closest you can focus the M9 is either 1m or 70 cm, depending on the lens. If you are focussing on a curved surface the virtual distance will vary with the curve, so you will have to focus on one point, not the entire RF patch.

[ksporry]

ok, so now the theory of guestimating the focus range... WIth a 21mm lens I should be able to get a reasonably sharp image stopped down to f8 all the way. I don't... So I think I need to know a bit about focus techniques when focussing on reflections.

[lct]

Is your subject distance closer than 0.7 meter? If so, your lens can focus on it eventually (CV 21/4 for inst.) but not the rangefinder so that you have to guesstimate or measure the subject distance to focus. Otherwise, you just have to focus on the subject that's all.

[Michael Geschlecht]

Hello ksporry,

 

Welcome to the Forum.

 

Don't forget: When you focus on a reflected image you are focussing @ the distance from you to the reflected image + the distance from the reflected image to the subject.

 

1 way people have used to test their rangefinder's accuracy is to set the focus @ 1 distance & look in a mirror. Then move back & forth until the rangefinder patches coincide. Then move slightly sideways to the edge of the mirror. The rangefinder patches should coincide @ 1/2 of the original distance.

 

You should read the distance @ the point where the edge of the mirror meets the frame @ the mirrors surface (there is also the depth thru the mirror's glass cover to consider). Not on the frame itself.

 

Example: Set the rangefinder to 4 meters. Walk back & forth in front of a mirror until the rangefinder images coincide @ the viewfinder window. Move sideways to the edge of the mirror. The line where the edge of the frame @ the mirror's surface (there is that pesky "depth of the glass in front of the mirror" again) should be in focus @ (adjusted for depth of glass) 2 meters.

 

Best Regards,

 

Michael

[giordano]

Depth of field is very often a problem when shooting reflections. As others have said, focusing on the reflection means focusing at (distance from camera to reflecting surface) + (distance from reflecting surface to object),

 

This means that the depth of field you need is (distance from reflecting surface to furthest reflected object that needs to be adequately sharp) + (distance from reflecting surface to closest object to the camera that needs to be adequately sharp). Note that this second distance can be negative: for example if you're photographing a shop window 1m away with a window display behind the window and reflections of the buildings across the street but you're not interested in getting the signwriting on the window itself sharp.

 

The shot below was taken with a Digilux 2 with the lens at 22.5mm, i.e. same field of view as a 90mm lens on 24x36. The DoF is barely adequate. I'm not sure this shot would have worked with a full-frame camera; certainly it would have needed a much smaller aperture, higher ISO and longer exposure.

 

 

 

For this shot (with a M6) I focused first on the signwriting on the glass and then on the reflected buildings across the road, then set the aperture to get the necessary DoF.

 

 

The above applies to flat reflecting surfaces. A convex surface will make the reflected image further away, and a concave one closer.

[Michael Geschlecht]

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Hello John,

 

Nice photos.

 

Somewhat trickier to do w/ a rfdr than w/ an slr.

 

Best Regards,

 

Michael

[ksporry]

just what I wanted to hear, thanks guys! that helps! I thought that this was what I should be doing. indeed, I was focusing within half a meter of the reflective surface, so I guess not only does the range finder struggle with the distance, but the curvature of the surface probably made it worse. I'll keep this discussion in mind next time I shoot reflections

[Hosermage]

how far is the subject from the mirror? If it's far, you could just set it at the hyperfocal distance, frame and shoot (see car image).

 

if it's a bit closer, maybe zone-focus? I took this shot, with the mirror about 1 meter away, and just focused normally (see mirror+son image)

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