OK so silly Question ---- OR is it???

BRASH said:
I don't have a 1.8 lens so can't try that but at f/8 it looks fine (apart from me being the subject:)). Like I said just a quick try, handheld, no exact measurements or scientific set up. Just did it out of interest because I was intrigued by the question, never thought about it before. Obviously never read the right books. I must learn to read!!
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AT f8 DOF is coming into play, and you're not far from the hyperfocal distance. Shoot wide open and you'll see a difference.
 
Have to agree, this is probably one of the best silly question threads I have seen in a long time too :D

I would also have gone with 12ft before it was confirmed, mainly because I often shoot mirror reflections and if the lens is wide open, you can't get reflection and mirror in focus at same time, ergo my assumption has always been the focal distance is double the mirror distance.
 
Yv said:
Have to agree, this is probably one of the best silly question threads I have seen in a long time too :D

I would also have gone with 12ft before it was confirmed, mainly because I often shoot mirror reflections and if the lens is wide open, you can't get reflection and mirror in focus at same time, ergo my assumption has always been the focal distance is double the mirror distance.
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This^

I asked the Mrs the question (she's not what you'd call 'technical'), I reminded her she often shoots a bridal prep shot in a mirror, the answer to her was then obvious. Because you can't shoot a reflection shot by focussing on the mirror frame.
 
Steve Smith said:
There is no image on the mirror. It's the reflection of an image 6' away.

Steve.
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There is an image on the mirror. Its just that it is not in focus. If you were to put a sensor, or film, where the mirror is you would record an image, albeit of a lot of interfering light waves :)
 
Suvv said:
There is an image on the mirror. Its just that it is not in focus. If you were to put a sensor, or film, where the mirror is you would record an image, albeit of a lot of interfering light waves :)
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I wouldn't call it an image. And what you are referring to as an image is available at any position.


Steve.
 
Well that certainly created some interest, and past the Morning nicely.
thanks for all you replies,some I agree, with others not.

Did I know the answer??

Yes cos` I went and tried it in a Mirror but it makes you think don`t it.
 
Another thing with mirrors, when you see an image of a bride or whatever brushing her hair or finishing her make-up, what she's actually doing is looking at a reflection of the camera.
 
(using a full length mirror) Does it make a difference if you have a mahoosive beer belly? :D
 
Make the experiment more extreme. Hold a mirror at 45 degrees, a few inches away from your lens and position yourself so you can see through a window (or go outside) and focus on a distant object.

Now see if you have set your focus near infinity or if you had to use a macro setting to focus on the mirror a few inches away.

I think it's a lot more obvious now - even without actually doing the experiment.


Steve.
 
ghoti said:
If you only had to focus as far as the mirror to render everything in the reflection sharp, landscape photographers would simply shoot into mirrors all of the time.
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Or flipped on it's head, if there's a mirror in the image path, and a mirror makes everything at the mirror distance 'in focus' (as some believe), how come when we look through the viewfinder of an SLR everything's not in focus?
 
Indeed basic physics, there is a virtual image 6' behind the mirror. Just go look at yourself in a mirror and see if you can see your own reflection and the background (assuming it is some distance behind you) sharp at the same time.
 
Phil V said:
Or flipped on it's head, if there's a mirror in the image path, and a mirror makes everything at the mirror distance 'in focus' (as some believe), how come when we look through the viewfinder of an SLR everything's not in focus?
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I was going to post a similar response. However, you don't look into the mirror, you look at the ground glass (or plastic) screen.


Steve.
 
Steve Smith said:
I was going to post a similar response. However, you don't look into the mirror, you look at the ground glass (or plastic) screen.


Steve.
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But the light is reflecting off a mirror on it's way to your eye.
 
Phil V said:
But the light is reflecting off a mirror on it's way to your eye.
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HUH!! Didn`t you come up with the correct answer 57 posts ago Phil, but don`t stop now I`m enjoying the explanations that are coming forth!!
 
If you are holding your camera six feet from a mirror, the light reflected from your camera (and anything in the same plane) has travelled twelve feet when it returns to your camera from the mirror. Hence, as far as the physics is concerned, the object you are focussing on is twelve feet away.
If you hold your camera in front of a mirror that is six feet away and are interested in capturing an object that is three hundred feet behind you, reflected in the mirror, then, as far as the physics is concerned, that object is three hundred and six feet away.
It's as simple as that.
 
Draw a moustache on a mirror.

Photograph yourself or somebody adjacent to you 'wearing' the moustache in the reflection.

Use a large aperture / shallow dof and check your focus ;)
 
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For more fun with mirrors and how they challenge our intution have a watch of these:


 
Why is this still being debated. It's 12ft. Stop arguing with Physics. LOL
 
This used to be basic O-level physics, covered in experiments about parallax where we lined up pins behind mirrors. One pin was in front of the mirror, the other was placed behind the mirror so it lined up with the image. The second pin was the same distance behind the mirror as the first one was in front. So the answer to the OP's question is 12ft.
 
stryvya said:
HUH!! Didn`t you come up with the correct answer 57 posts ago Phil, but don`t stop now I`m enjoying the explanations that are coming forth!!
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Yes. But it seems other people still need convincing :p

Like Richard said 'classic TP thread' the correct answer in the first response, but people are still debating it 2 pages later :D
 
BRASH said:
Yeh, 6ft. Well worked for me 24-105 lens @ f/8 the image was in focus.
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What was your focal length though?

I mean if you shoot at f8, with a subject distance of 12 feet as you suggest, then at 24mm the depth of field goes from 6'1" to 344', so would be in focus.
At 6' subject distance you've a depth of field of 4'1" to 11' 7". F8 isn't a good test.
 
Jonathan has summed up it up with the experiment. In a plane mirror the image is as far behind the mirror as the object is in front.

Dave
 
If you mooch around the charity shops long enough you're virtually guaranteed to come across a photography book printed in the 70/80s illustrating this, normally in chapter one. During this time the scientific photographic principles were valued and topics like this and the inverse square law were explained explained in detail.
 
Blank_Canvas said:
If you mooch around the charity shops long enough you're virtually guaranteed to come across a photography book printed in the 70/80s illustrating this, normally in chapter one. During this time the scientific photographic principles were valued and topics like this and the inverse square law were explained explained in detail.
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Let's be honest, you shouldn't need a 70s/80s photography book because this is Year 8 science.
 
ghoti said:
Let's be honest, you shouldn't need a 70s/80s photography book because this is Year 8 science.
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Well I sort of alluded to that in post 20 but since the the dumbing down and demise of education in this country they do offer some hope and salvation !
 
Blank_Canvas said:
Well I sort of alluded to that in post 20 but since the the dumbing down and demise of education in this country they do offer some hope and salvation !
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This hasn't been dumbed down at school. It's already about as basic as you can get. It's fundamental optics and is covered adequately in early high school when kids play around with ray boxes, mirrors and lenses. Any 13 year old who pays attention in science class could answer this question in about a second.
The image is, for all intents and purposes, 12' away. You focus at 12'. The end.
 
ghoti said:
This hasn't been dumbed down at school. It's already about as basic as you can get. It's fundamental optics and is covered adequately in early high school when kids play around with ray boxes, mirrors and lenses. Any 13 year old who pays attention in science class could answer this question in about a second.
The image is, for all intents and purposes, 12' away. You focus at 12'. The end.
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Judging by some of the replies on here it would appear not !

I'm not referring to the 12" that's a given !
 
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no such thing as a stupid question........ only stupid answers :) my tag line lol
 
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