Rangefinders and SLRs: A Technical Question on Focusing

[stanley_rogouski]

<p>I use a Nikon n80 and I trashed my ancient Canonnet 28, so I

cannot experiment with this question myself. </p>

 

<p>I know the basics. An SLR focuses through the lens itself and a

rangefinder uses a device that syncs with the lens and estimates the

distance of the object you're focusing on. </p>

 

<p>Anyway, note this photograph <a

href=http://rogouski.net/mirror/objects-closer.jpg>CLICK HERE</a>.

</p>

 

<p>Note how the text on the mirror is in focus, but the objects in

the mirror are not. Now note this one </P>

 

<p><a href=http://rogouski.net/mirror/mirror-angel.jpg>CLICK

HERE</a>.

</p>

 

Note that the objects in the mirror *are* in focus but the text on

the mirror is not. </p>

 

<p> have to admit this surprised me. I had assumed that I would focus

on both the text and the objects in the mirror but no, the glass of

the mirror seems to take into account the distance between the mirror

and the objects in the distance.</p>

 

<p>In order to get both the text on the mirror and the objects in the

mirror in focus, I would have to use a very small aperture and step

back slightly. Since the only film I had was Velvia 50 and since I

didn't have a tripod with me, I didn't try it.</p>

 

<p>Anyway, once again, I wish I had not trashed my old Canonnet 28

since I could have played around with the idea myself, but I was

wondering how a rangefinder would handle this. After all, it

estimates distance, right? Would it only measure the distance of the

mirror or would it, like my Nikon, measure the distance of the

objects from the mirror?</P>

[wind.dk]

For the reflected scene, the mirror is just a part of the optical path the light goes through from the objects to the film, so optically the focus distance to the objects seen through the mirror is the distance from the film to the mirror plus the distance from the mirror to the reflected objects.

 

The text on the mirror is at the distance of the mirror only.

 

This is the same wether you use a rangefinder or an SLR, though with a rangefinder you might be fooled by the apparently in focus image of the text in the viewfinder if you were focusing on the reflected scene or vice versa.

[tito sobrinho]

Remember, a camera lens does not respond like our eyes+brain. The object on the mirror is at infinity and for this reason you have to use the near+far relationship i.e. "sharp" on the mirror frame and "sharp" at the mirror surface, using a WA lens and or a small aperture or better a view camera with movements. Like Ivar wrote, a rangefinder camera would not improve it.

[al_kaplan1]

A rangefinder does not "estimate" distance, any more that the optical system in an SLR "estimates" distance. It measures the distance, based on some rather simple math.

[tito sobrinho]

...and, If your SLR camera has a DOF preview lever or button, use it to estimate the near+far relationship.

[harry_soletsky1]

This is where the DOF marks on the M2 and M3 would be useful. There is nothing inherently better using an SLR to estimate DOF as the image is so small in stoping down and it's also so dark it's less useful then you would think. I used a Nikon F3 with ground glass screen and didn't find stopping down to check DOF very helpful. The View camera folks use a magnifier on the ground glass image to check DOF. Up to about 50mm rangefinders are better, above 90mm SLRs are better for focusing and 90mm is about the same but that is a separate question.

[stanley_rogouski]

Sorry about that. I thought I had changed "estimates" to "measures" in the post. My bad.

[ray .]

I'm not sure why it surprises you- the printing on the mirror is a foot or so away and the reflection is at or near infinity. You have to choose which to focus on regardless of what camera you're using, or if you want both in focus, step back and use depth of field.

 

If you really miss your Canonet, they can be gotten pretty cheaply on ebay

[stanley_rogouski]

I don't really miss the Canonet since the lightmeter wasn't working and I really like the "on demand gridlines" the n80 has:)

 

Now that I've asked the question, it actually makes sense. The light travels a certain distance even though it's reflected off the mirror.

 

Thanks for helping me clarify it.

[kelly_flanigan1]

Rangefinder focus is on Truck/car at the center; with at F1.0 Aperture. Note reflection in mirror is in focus; but not the text "objects in mirror are closer than they appear".<BR><BR><IMG SRC=http://www.ezshots.com/members/tripods/images/tripods-322.jpg><BR><BR><A HREF=http://www.ezshots.com/members/tripods/images/tripods-323.jpg target = "_blank">

<IMG SRC=http://www.ezshots.com/members/tripods/thumbs/tripods-323-thumb.jpg BORDER=0></A><BR><bR><BR><IMG SRC=http://www.ezshots.com/members/tripods/images/tripods-324.jpg>

[charles_stobbs2]

There shouldn't be any text on a driver's side mirror

[myke_1977]

right charles! the drivers side mirror is a .85 mag while the passenger sid is actually a .58!

[tom_burke3]

I'm sure I remember something about this in basic physics when I was at school -

something about the "the image in a mirror is as far 'behind' the mirror as the object

that is being reflected is in fromt of it"? So if you focus on the mirror itself you're

focusing in front of the image; if you focus on the image you're focusing behind the

mirror.

[stanley_rogouski]

I was using a 50mm lens for those two photos and I thought of taking the shot in the mirror because I didn't have a 24mm lens and I wanted to capture the sweep of the cemetary's tombstones.

 

Do mirror's have focal lengths, ranges of vision. I think a 50mm lens let's you view 52% of the scene and a 28mm lens 72% of the scene.

 

The rear view mirror of a car seems to be panaromic, but is it?

 

And is there a difference with what focal length I use to photograph the mirror. For example, what if I use a 24mm lens instead of a 50 or a 105? If I use a 105 on a mirro that provides 50% of the scene, do I get 50% of the scene using a lens that would normally give me 40% or something?

[kelly_flanigan1]

The "door" rear view mirrors on todays cars are slightly spherical; this increases the field of view in the mirror; and makes the images/objects appear slightly smaller.....

[tito sobrinho]

Harry, I never liked those 2 little lines on my M3 and M2. They were always quite useless to me and eventually were discontinued. They are not part of my M4 and M5. I still like the DOF button on my Leicaflex SL and also on my Nikon F. On the latter, I use an eyecup or the waist level finder with the magnification loupe. Since, I follow LF discipline, I use the DOF all the time.