[Laser] (OT) Uses for a 35-60 zoom lens

[n5gui at cox.net]

John

I do not follow what you are suggesting.  For communications purposes, there should be no "foreground".  All sources, be they desired signals or "noise" should be far enough away that they can be considered the same as being at infinity.

I am sure there is much that I do not understand about zoom lenses, so you may have a significant point that just highlights my ignorance.  If so, does it really matter if the filter is neutral density?

I am not sure if it is relevant to this discussion, I have noticed that when using a spotting scope with a zoom that changing the zoom setting will require a re-focus of the image.  If I was using such an instrument with a photo sensor, the image of the signal source would probably get fuzzy at one end of the zoom setting compared to the other, but as long as all of the signal energy falls on the sensor, it should not make any difference on the conversion of light energy to electrical current.


Also, not on your topic, but I did have an additional thought on my post that does relate to a specialized filter.  I had suggested that a user can map out the the field of view of the equipment by "swinging" the instrument up, down, left, right, to loss of signal.  Then increase the zoom level and repeat the process.

Suppose instead that you fit the photo sensor with a filter that is clear at the center ( at least as large as the circle of confusion for the worst focus for the instrument ) and gets darker, continuously or perhaps in rings like a target bullseye, as you go out from center.  That way as you "swing" the optics the signal would fade rather than blink out.  Come to think of it, that might be a benefit for centering a fixed magnification ( non zoom ) communications instrument as well.


James
 n5gui


---- John Randall <m0els at yahoo.co.uk> wrote: 
> Hi, Just one though on using a zoom lens. The back focus would need to be set 
> with a neutral density filter, if the background and foreground are to be in 
> focus.
> 
> John
> 
> 
> 
>