Random Question on Focus Distance

[Derrel]

Good lord, the inaccurate "information" just continues! Just took the D2x into the bathroom with the 36-72mm Series E zoom on there. Focused on the MIRROR corner at 5', as marked on the lens focusing distance scale. My refelction in the mirror>? OUT OF FOCUS. Could not even tell what brand of camera I had in my hands when I looked at myself reflected in the mirror.

Next, I positioned the focus scale at precisely 10 feet. Guess what? The NIKON on the pentaprism was READABLE. Huh...science!!!

Oh....I first did this test in 1977. See my profile photo? Know how I know where to set the focus point, manually?

If you are fairly near-sighted, you can likely see the hair-cutting tools on the barber's shelf in front of tyou, some 5 feet or so from the barber's chair.....BUT you will NOT be able to see yourself clearly reflected in the mirror. OMG!!! human eyes and camera lenses work the same way!

This has jack-squat to do with "Depth of Field".

 

[480sparky]

But wouldn't you want the focus to be on the reflective surface, where the image now originates?

Edit: and no im not taking selfies haha. Thought this would be an interesting discussion

Your image originates with YOU. You're not shooting a painting of yourself.

 

[480sparky]

If your image 'originates' from the mirror, that means all light falling on the mirror MUST be focused on it.

How, pray tell, does that happen? Do photons magically know they're approaching a mirror and alter their course? Is there some Captain Wavelength commanding, "Reflective surface, dead ahead. Hard over to port!!!" while at the same time Admiral Kirk, approaching from the other side of the room, yells, "Sulu.... evasive maneuvers!!!"?

Go back to basic physics. Angle of incidence = angle of reflectance.

 

[Dave442]

If the camera is focused on an object reflected in the mirror then the distance is the sum of distance from the object to the mirror plus distance from the mirror to the sensor.

I well remember using my 500mm mirror lens, the camera did not focus on one of the internal mirrors of the lens, it focused on the object that was reflected by those mirrors.

 

[greybeard]

If you shoot something in a mirror, and I do it from time to time with my car side mirror, the subject will be infocus but the mirror frame will be out of focus. And if you focus on the mirror frame, the subject will be out of focus. So, the answer is 10'

 

[smoke665]

Imagine if I gave you five dollars on your way to the liquor store, plus I gave you five more dollars upon your return home from the lower store.

How many dollars would you have once home from the liquor store? 10 dollars

We'll duh, I'd be $10 in the hole. You can't buy anything decent at our stores for $5.

 

[greybeard]

 

[JonA_CT]

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I was wondering why this took so long, hahaha...note that I didn't put any effort in myself, however.

 

[SoulfulRecover]

I was wondering how long it would take for someone to try it out