Help with focusing for reflections

[christakis]

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This is more of a technical question really than a practical one. I just need to put my engineering mind to rest because it's bugging me.

 

I never shoot reflections but thought I'd give it a try during a rare, but pleasant, spell of sunshine in Manchester. The reflection was on a bench. I focused on the bench and took the shot.

 

The reflection seems to be miss-focused although the surface of the bench looks to be perfectly focused. Should I've focused to infinity to have correct focus for the reflection?

 

Say I was facing a mirror that was 1m away and wanted to take a shot of me. Do I focus at 1m or 2m?

 

Thanks for your input,

Christakis

 

PS: Here's the image troubling my mind

[Doug A]

Say I was facing a mirror that was 1m away and wanted to take a shot of me. Do I focus at 1m or 2m?

 

If you want the mirror frame to appear in focus and don't care about your reflection, then focus at 1m. If you want your reflection to appear in focus and don't care about the mirror frame, then focus at 2m. If you want both the mirror frame and your reflection to appear in focus then stop down and focus so that the depth of focus marks on the lens indicate that it will be sharp at 1m _and_ at 2m.

[christakis]

If you want the mirror frame to appear in focus and don't care about your reflection, then focus at 1m. If you want your reflection to appear in focus and don't care about the mirror frame, then focus at 2m. If you want both the mirror frame and your reflection to appear in focus then stop down and focus so that the depth of focus marks on the lens indicate that it will be sharp at 1m _and_ at 2m.

 

Thanks curmudgeon,

 

That's what I thought. Your answer couldn't be any clearer. Appreciate it.

 

Chris

[farnz]

Chris,

 

Perhaps a stupid question, but was the reflected image on the bench in focus in your viewfinder when you took the shot?

 

Pete.

[christakis]

Chris,

 

Perhaps a stupid question, but was the reflected image on the bench in focus in your viewfinder when you took the shot?

 

Pete.

 

Well that's where it gets complicated and the reason why I got confused... Initially I tried focusing on the reflection itself. Since the background was dark it was difficult to do that in the middle of the reflection so I opted to focus on the tips of the purple towers. When I tried focusing there, I could not achieve proper focus: Even with my lens set to infinity, the tips of the two planes wouldn't align. That's what caused me to say ah, focus on the surface of the bench.

 

Perhaps, I forgot something important which cracks the case open. I will go back and try it again at some point. Being at an angle to the bench made things even more complicated since I was "multiple distances" away from it.

 

One thing is for sure. It's not a focus calibration issue...

[Nicoleica]

One other factor may apply here. The surface of the benches do not appear to be perfectly smooth, and would seem to be diffusing the image a bit. This would probably result in less than perfect sharpness of the reflection however you focussed.

[SJP]

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The reflected image is/remains at a large distance w.r.t. the lens regardless of how close the bench/puddle is situated. Focus on the bench then the bench is sharp and the reflection is not, focus on the reflected image then the bench will not be sharp.

 

If you want both to be sharp then you need to stop down f/8 - f/16 ballpark should work.

 

Still it is a picture that works for me.

[christakis]

Nicole, you are right the surface wasn't "mirror smooth" but was shiny and smooth enough to get a reflection off it. Looking at it again, I think the "diffusion" adds to the effect.

 

Stephen, perhaps stepping down would make this look better but shooting wide open and getting so sharp results is addictive! I've only had my M for a few weeks now you see; shooting wide open is still exciting :-) I know it's no excuse but... do you blame me?

 

Chris

[SJP]

Stepping down would be different, but not neccesarily better.

[tobey bilek]

Focus on the reflection and it will be near infinity. You may have trouble if the bench is not mirror smooth as the reflection will never be sharp. Use the line thru the patch technique to get it as close as possible.

 

Maybe you will bring some cleaning material for the bench next time. Pick the same time of day.

[pop]

The "optical" distance of something seen in a mirror is (the distance between you and the mirror) + (the distance between the mirror and the thing seen in the mirror).

 

In your original scene, you set the distance to infinity if you want the tower to be in focus. Set the distance to 2m or so if you want the bench in focus. If you want both to be sharp, pick an aperture and distance setting which covers the range from 2m up to infinity.

[menos I M6]

This bugged me a long time as well, shooting mirror reflections - thanks for clearing things up - same engineering brain here, refusing to think, what seems not obvious ;-)