Re: [APML] Optical coatings/alignment - IC410

[Chris1011@aol.com]

In a message dated 1/22/2002 7:37:33 PM Pacific Standard Time, ccjd@ix.netcom.com writes:


> My thought is that it's the
> coating on the FF. I'm 99.9% sure the elements are multi-coated but maybe
> the internal surfaces are not?


It is not the field flattener. This lens is fully multi-coated with less than .25% reflection per surface. As I said earlier, I'm betting that the deep sky filter reflects a large portion of the light back up the tube, where it then bounces off the rear element of the FF. This surface then reflects 1/4% of the light back down, defocused by the increased optical path, to form a halo around the star. If you remove the filter element, I bet you get no such halo. Using the filter by itself also will result in no halo because there is no other surface to reflect the light back down.

Roland Christen