dark sky exposure times

[blink138 (Pat)]

hello members i want to ask everyone realistically how much longer a dslr exposure can be got from being in a dark sky?
i reside 4km from perth cbd and well.... we could classify that as fairly severe light pollution i guess
going an hour or two outside of the big smoke could we turn a 2min to a 4min with same iso etc.? anyones experience please let me know.... and also would you still use a light pollution filter in a relatively dark sky?

[loki78 (Jon)]

I'm also curious about at which point in the skies people would stop using their light pollution filters. Good question.

[blink138 (Pat)]

if only someone would help us jon ha ha!
come on members somebody here has done urban and dark sky AP surely!
pat

[alocky (Andrew lockwood)]

I've started using an astronomik CLS filter at my semi-dark sky out near York (70km from Perth CBD). It seems to work fairly well on the airglow as well as the light pollution. I've been playing with my new light box, it's interesting to compare the effect of the CLS on the led light, it certainly knocks the reds down, and appears to boost the blue- not sure how that works.
Cheers,
Andrew

[batema (Mark)]

I have done 10 minute subs in dark sky locations and maybe even 15 minutes but I would always take darks at the same length to reduce the noise problem.

Mark

[ZeroID (Brent)]

A CLS is cheap enough and good value IMHO. I'd be getting one regardless and experimenting for myself. It has made a big difference in my suburban location. In a dark sky site ? Don't know but worth trying to see and if it allows you to do better at your LP'd site then saves you petrol and time and gives more opportunities locally.
(I have an Astronomik CLS btw)

[naskies (Dave)]

At home (intersection of three freeways in Brisbane), it takes only 45 seconds for my DSLR pointed high in the sky to get a middle histogram peak using f/4 and ISO 800.

The best skies I've ever experienced were in Roma QLD, where the same exposure settings didn't reach middle histogram even after 20 mins... a "modest" difference

Furthermore, since the signal is so much stronger and there's no light pollution gradient to deal with, processing is MUCH easier.

[pluto (Hugh)]

I don't have first hand experience but, as I understand it, light pollution filters like the Astronomik CLS are designed to improve contrast on emission nebulae. So even under dark skies you should see a difference when imaging, or viewing, emission nebulae.

[niko]

yes, most definitely you could turn 2 min into 4. I image in both Melbourne inner suburbs and 1.5hrs from Melb at a dark sky site - the difference is astronomical! I don't bother with the CLS filter out there vecause, well there ain't no light pollution!

[blink138 (Pat)]

thanks very much members that has answered a lot of questions for me
it appears that you may be able to at least double the exposure time even when only an hour or so from the city........ and very dark skies even longer
LPS filters sounds like at least some experimentation, i have the IDAS LPS2 i think and it works very well for me
pat

[Marcus]

So you all find LP filters pretty useful I assume? I was told not to bother with them when I started. Which filter would be suitable for the lights in Melbourne (inner suburbs)?

[alocky (Andrew lockwood)]

I've attached a couple of histograms from a series of flats (same iso and exposure) with and without the 2" CLS filter in my FSQ106ED, using the excellent lightbox I bought from Peter Miller.
You can see the CLS filter drops the intensity (lower histogram) to at least 50% of the unfiltered example, so doubling the exposure will only get you back to where you were, but hopefully with less light pollution or airglow.
cheers,
Andrew.