Astronomik Filter Experiences

[groberts]

Just purchased a second hand (nearly new) Astronomik CLS filter for use with my unmodified Canon 700D and took some basic shots (with a telephoto lens on a tripod i.e. no tracking) of the sky last night to see how it performed.  As expected it darkens the sky (no surprise there)  but I am wondering what / if from experience any compensations should be made when using this for longer exposure / tracked astronomy exposures e.g. DSO etc?

I am thinking - longer exposure certainly plus maybe higher ISO possibly, to put the 'quantity of light back into the image that the filter takes out.  Whilst the filter clearly works on selective wavelengths, is there an impact on the overall 'quantity' of light that therefore requires the aforementioned adjustments, compared to without a filter?     

On another point, I found the filer to be quite loose at first and, following some guidance found elsewhere here on SGL, noticed that the metal 'clip' sections that hold the filer in should be slightly prised out slightly from time-to-time using a blade to maintain their holding ability - I did this and it's OK.  (i) is this correct (ii) in time does this not weaken the clip through metal fatigue and perhaps lead to failure? Seems like a crude set-up either way.

Would also be interested to know how other Astronomik filters perform, or are they only really useful with a modded camera? 

 

Without filter, 8 secs @ ISO 800

With filter, 8 secs @ ISO 800

[wxsatuser]

I don't make any compensation as such, just expose for an in camera histogram of 25>40%.

I normally use ISO 1600 with my 60Da and with a 200mm lens at f4 ish I get around 5minute subs.

With an ED80 the subs easily go to 10 or 15minutes depending on sky conditions.