Re: [APML] Tri-Color Filters....Again!

[Chris1011@aol.com]

In a message dated 12/17/2002 5:43:49 PM Central Standard Time, flyboy9990@earthlink.net writes:


> .
>     I put a 72mm step ring inside the optical tube after the secondary to hold 72mm glass filters. Do you think having the filters before the field flattener would make a difference or degrade images in any significant way? At f/3.3 the light will be coming in pretty steep when it hits the filter. 


My knowledge of filters is not so good. If the filter is a dielectric type, then the incident angle is quite important. Look thru the filter and tilt it in front of your eye. Do the colors change? If so, it is dielectric and it will not be quite as good at F3.3 as it would at longer F-ratios. An absorption type filter would be insensitive to angle, but would not have as high a transmission in the passband.

Roland Christen