yves_colombe

Sorry, I didn't read your message carefully enough. You say you have the same results without filter. This seems very strange. What are exactly the parameters for this photograph (body, lens, filter)?

As Jesper said, this effect is typical for the use of a filter. This is explained in great detail on the following pages by Paul van Walree :

 

http://www.vanwalree.com/optics/filterflare.html

 

http://www.vanwalree.com/optics/flare.html#filter

 

Simply remove the filter! :)

Roberto, the light-sensitive elements in usual interline-transfer CCDs (mostly used in compact digital cameras) are photodiodes. So the Fuji Super CCD... doesn't need to be a CMOS! ;)

Just a remark : the point you need to find is not the rear nodal point, nor the front nodal point, but the center of the entrance pupil. It can be found as suggested on the web page given by Leonard. Why this point is the center of the entrance pupil and not one of the nodal points has been explained in this forum some months ago, see http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=003bju . (note : I made a mistake in point 1 of my first message in this thread, corrected by Arne Croell).

The magnification depends one the use you consider. The "academic" use is the following : you put the document in the front focal plane of the loupe and you look at its image (located at infinity). When compared to the reference situation (that is : document viewed with naked eye at 250mm), this leads to the magnification 250 / f (called "commercial magnification" in French), where f is the focal length of the loupe (in mm).

 

A different use is often considered : you put the document at the distance for which its image is viewed at 250mm (as you guessed, I think). If you assume for simplification that your eye is located close to the rear nodal point, simple geometrical optics yields the magnification 1 + 250 / f.

I've seen your drawings. Well, maybe I was wrong about your French... ;) - kidding. They just show the mistake almost everybody makes (including me before being interested in this issue). You should draw (even grossly) the positions of the two image points. Only one will be on the film (because the other corresponds to a subject that is out-of-focus). Then you draw the rays that * actually * go through the lens (and the aperture stop) and hit the film. These rays are not only determined by the positions of the image points - these positions can be found with the nodal points alone, so the entrance pupil would play no role. To draw these rays, you will have to consider the entrance pupil... then you will get it.

 

[i will be away for some days]

Yves

Hi Struan (nice STM pictures!)

 

first - yes, that's it exactly. In a more common discussion - but Emmanuel wanted to see and explain exactly what happens - one could forget about the fact that only one plane of the object space is imaged sharply, and simply state that the relative positions of objects from the foreground to the background, as recorded on film, remain unaltered during this rotation.

 

second - your French is perfect! Kingslake and Ray merely state that the entrance pupil is the center of perspective of the picture (regarding the object space; the center of perspective for the image space is the center of the exit pupil), without thrusting into a more detailed study.

Yes you are right Arne, my mistake. What I had somewhere in my mind was that in a symmetrical lens the front nodal point coincides with the center of the entrance pupil, and the rear nodal point coincides with the center of the exit pupil... (easily seen with a ray going physically through the center of the lens)

 

Yves

My two euro-cents about nodal points :

 

* in (fully-) symmetrical lenses (such as Schneider G-Claron or Schneider Makro-Symmar) the front and rear nodal points share the same location, at the center of the lens

 

* with a conventional camera (ie not a rotary panoramic camera), when you shoot multiple pictures that will be stitched into a panoramic view, you have to rotate around an axis crossing the entrance pupil center, not the front nodal point [of course when there are only distant objects in the frame, this is quite needless]. See for example the "Lens FAQ" by David Jacobson. This topic has also been discussed at great length with Emmanuel Bigler on the French site www.galerie-photo.org (search "Point nodal" in the upper frame when it is loaded). Remark : in symmetrical lenses the entrance pupil won't be at the center of the lens, because the aperture stop is at the center of the lens and the entrance pupil is the (virtual) image of the stop made by the front lenses.

 

* In a rotary panoramic camera, the lens rotates around its rear nodal point because this makes the image almost stationary (so there is no blur when the "light slit", which has a finite width, goes across the film). In return for which, the "point of view" will change across the image, because the center of the entrance pupil will move (unless it coincides with the rear nodal point). This is not a problem because no stitching is needed.

 

Yves