From: "Duane" <macastronomer@mac.com>

Date: October 25, 2005 10:03:45 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: Color Filters :(

I bet they don't IR and I'll bet that's my problem. I was wondering about that (which is why 

I mentioned the lack of IR in my post).

At first I was thinking, why would I need IR, I'm only letting through the blue light? But now 

that I think rationally about it—light is subtractive and it's not letting through blue light, 

it's letting through all light and blocking yellow. As the green blocks magenta and the red 

blocks cyan. All of them letting through the rest of the spectrum including IR.

That is also why I had so much trouble getting a decent focus. Oh well. Hopefully I'll get 

another clear sky before the end of the week. Here's hoping for a clear Friday. I'm heading 

to Eagle Bluff, my favorite dark sky site (about 50 minutes drive from home).

I will say this about the Imaging Source camera. It is a LOT more light sensitive. Without 

barlowing, its so bright that its completely washed out, even with the fastest shutter speed 

and everything cranked down. I was amazed at the visibility at 30fps with the 5x 

powermate.

Although this mornings results were disapointing, I can't wait to go out and do it again—

correctly. All is not lost though. Now I have a few more images for my "Oops, don't to this" 

section of my website :)

Duane

--- In Astro_IIDC@yahoogroups.com, Alan Friedman <alan@g...> wrote:

Hi Duane -

Do your RGB filters block IR? The camera is very sensitive to IR - 

including this wavelength in the R,G and B streams will skew the colors 

significantly. If the filters are not coated to block IR you will need 

to add a UV/IR cut filter in front of the wheel.

The focus will vary in the different colors of light. The amount will 

depend on the type of scope and the various refractive elements 

(barlows, etc) you have in the equation. It doesn't vary that much 

between R and B, but enough to make it important to refocus if the 

seeing is good. You might try to focus in green light and see if this 

is OK for R and B too. If you image with an IR pass filter you will 

need to refocus at this wavelength.

Alan

On Oct 25, 2005, at 1:40 PM, Duane wrote:

OK, I tried the new B&W Firewire camera this morning. First light (yay)

I need some more time using it. This morning was pretty quick and 

dirty.

However, my question today is, why are my colors not turning out 

right? I did RGB through

the Apogee filter wheel and the image comes out like this:

http://groups.yahoo.com/group/Astro_IIDC/files/Planetary/Mars1.jpg

All the images were shot one after the other, the only change being 

the flip of the wheel.

In a new photoshop image I placed each one in their corresponding 

channel. Not until

after doing this did I sharpen.

What's up with this color?

Also, is it normal that each of these colors have a little different 

focus? This particular

image I didn't adjust anything (just took the shots). But I noticed 

on subsequent images

that the filters had a different focus.

A big peeve I have of this filter wheel is the threading. It does not 

match the standard filter

thread. I have an IR filter I wanted to put in the fourth slot and it 

won't go. I looked at the

threads on the included filters and compared to my IR filter and they 

are not the same. I

didn't use IR on any of these.

Any ideas on what I'd doing wrong? I took several shots and even have 

a very sick looking

Saturn to do with my ill Mars.

Thanks for the help.

Duane

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