Help - LRGB set for CCD, Astronomik question

[rogerg]

Hi all,

I've always struggled to get nice LRGB images from my CCD (be it ST7 or ST8). To be honest my LRGB images awful. There's just no contrast of colour. I'm currently trying to nail down if it's:
1) filters
2) software processing
3) me

I use Astronomik Type II filters (LRGB). The RGB are labelled as "Astronomik TYP II", they are not labelled with a "c". My "Astronomik TYP II" came with my second hand CFW some 7 years ago. They are all par-focal, 1.25".

Does anyone know the difference between "TYP II" and the currently advertised "Type 2c" ?

After measuring a bunch of stars between exposures I am seeing the following ratios (with example 60s exposure equivalents):
L = 1 (60 seconds)
R = 0.637 (94 seconds equivalent)
G = 0.376 (160 seconds equivalent)
B = 0.170 (353 seconds equivalent)

Does anyone know if these are within the normal range for ratios?

Thanks,
Roger.

[Dennis]

Hi Roger

I believe that the differences may be in sharper wavelength cut-offs, improved transmission, par focal behaviour and IR/UV blocking so a separate IR/UV clear filter is not required.

This is what I understood when I purchased my Astronomic Type 2c LRGB set for my CFW9 a few years ago.

Cheers

Dennis

[rogerg]

Thanks Dennis. That's the sort of thing I'm expecting but just trying to find specifics. I thought mine did have IR blocking but looking at the cases it doesn't say, so perhaps my understanding has been wrong. I've emailed Astronomik to ask for clarification.

[Dennis]

Hi Roger

I vaguely recall that the Type 2c provide a better balance between the RGB set, more like 1:1:1.3 as opposed to something like 1:1.3:1.7, approximate ratios which I have seen associated with other filter types.

It looks like you can purchase (US $45) an on-line calculator (simulator) from Astrodon (http://www.astrodon.com/products/software/rgb_calculator/) which has inventories of the more popular cameras and filters?

Cheers

Dennis

[rogerg]

Interesting.

Shame the software is $45 ... don't think it's worth me buying right now (might be better to put that towards a newer set of filters...) .. but would be very interesting to see what result the Astrodon software gave for ST8-XME + Astronomik Type-II !

Thanks Dennis.

[rogerg]

Dennis,

I received a reply from Astronomik:

"There is a small difference in transmission between these two types. When I recall right the blue filter of the current type is 5nm wider then the first Type II filters. You should be fine with theolder set."

So, based on that my filters may not be a major contributing problem, however it is blue which is weakest for me, compounded by my blue insensitive ST8. This comment above also matches your memory that perhaps the balance was better with the IIc, as I suspect the wider blue spectrum would balance it up more.

Roger.