technical help please!

[Baloo]

Am doing this for work and its stretching my job description a bit, as Im by no means a photographer, and I am getting a wee bit confused!

I have taken several photos from a viewpoint in the rural landscape over 180deg using a 50mm lens. I’ve then had the negatives scanned in, and digitally stitched them together to make a photomontage.

I have a wireline model of this view set the same as a 50mm lens with a 45 degree angle of view which fits across the length of A3 paper.

I have to set up the page so that the photomontage is under the wireline and matches exactly.

Technically the wireline should be altered to fit the photo, however I’m doing it the other way round (cos Im blonde!), and to match the photomontage to the wireline I have had to zoom in. Now, this is my question – If the wireline is set at a 50mm zoom and a 45 deg angle of view, if I manipulate the photomontage by zooming and cropping to match exactly the wireline – does this mean that the photo does not truly represent a 50mm view anymore?

Surely it depends on what size you get the photo developed/scanned at? And that the 50mm view would not be altered – it just would be a narrower angle of view?
I am currently being questioned over this and I’ve got confused!

There is also a viewing distance calculation, which is how far you put the paper in front of your eyes to get a representative view, which takes into account the angle of view and length of image on the paper. I can work this out, but of course it is only valid if the image is correct.

If any of that makes sense any advice would be gratefully received!

 

[Rob]

Hi Baloo and welcome to the forum.

Certainly an interesting question and one which is quite tricky to answer. I'm going to pick a sub-set of your question which I'm confident about and answer that!

A 50mm lens on a 35mm SLR camera will closely resemble the level of magnification of the human eye. By creating a panoramic view stitching together pictures, you have a slightly slanted perspective image. If you can stitch the images together successfully, then you have already done very well.

The size of the print does not affect the magnification, unless you are cropping and resizing the image. This, however, assumes that you enlarge all the prints by the same factor - one 6x4 amongst a pile of 10x8 prints will appear smaller for stitching purposes. Scanning resolution will not affect the magnification of the image, only the quality.

In answer to your question: yes, zooming the image (selective cropping) from a 50mm scan or print will alter the magnification, so your 50mm montage is no longer to human eye scale, given your viewing distance is constant.

The viewing distance calculation you refer to is almost entirely theoretical. Yes, you could create a view-port where all the people who look at your wire-model and pictures stand at the same place, but is this likely to happen? I would suspect that a 1/r^2 relationship would work, based on being on top of a print being directly proportional to normal viewing.

Crikey - this probably makes no sense at all!!!!! Give me a shout if I can help (or confuse) further.

Rob

 

[ksmattfish]

Focal length alters magnification. Camera to subject distance alters perspective.

 

[Rob]

Very neatly put! Unlike me!

 

[Baloo]

Thanks – I think I get it now!?

 

[paul rond]

For a erally good explanation, check out this site for an education on lens node and panaramas....

http://www.photo.net/photodb/photo?photo_id=1238134&size=lg