Re: arc headlights and dynamos - A bit more research

Posted by John Greenly on Jan 30, 2020; 3:56pm
URL: http://c-sng-discussion-forum.254.s1.nabble.com/arc-headlights-and-dynamos-tp15165p15215.html

Hi Skip,

thank you for your contributions to the discussion!  I look forward to seeing your model.

I apologize if I was not clear in my post, but the position I gave for the tank was indeed measured from the #12 photo, not the B3B's.  It is true though that the photo of #21 gave me very nearly the same result.  

One very nice thing you can do before fastening your tank permanently is to take a photo of your model from the same viewpoint as the prototype photo and compare directly.  You can do this with no mathematics at all.  Use your camera to photograph the prototype photo- lay it flat and photograph straight on.   Then  just by trial and error you can take pictures of the model, moving the camera until you get the image to exactly correspond to the prototype image at four widely separated points, say for instance the top and bottom corners of the cab, the top of the stack and the pilot beam end.  That'll get you the same perspective on the model, and then you can compare the tank position directly.  When I do one of these measurements I always try to check my work this way.   I stick pieces of tape onto the screen and make pencil marks for the reference points.  It's important to match them exactly.  I use an iPad camera for this because the screen is big enough to use directly without having to download onto a computer to look at.  

iPad or cell phone cameras are generally excellent for model photos because their tiny optics give great depth of field in closeup use.    It's interesting-  the lens aperture and focal length of a phone camera is in fact a miniature scale model of a full-size camera. If you had one with aperture and focal length scaled down by 1:87, it would act optically on HO scale scenes exactly like a big camera would on the prototype.   If that were true it would mean that the depth of field in scale feet would be the same as the depth of field in real feet for the full-size camera at the same numerical aperture (f-number).   Just looking at the size of the lens, I think phone cameras might be roughly in the neighborhood of O scale.

Cheers,
John