Location, Location, Location.

[Pyrofer]

Ok. So I am relatively new to Astro-photography / Astronomy. I know a little but my main problem is I live in Central London.

I've taken trips out to darker skies but don't get there anywhere near often enough to refine my skills and learn properly. Certainly not often enough to make any investment in equipment worth while.

My question is this. I have seen Light Pollution filters, they apparently "work" but are they good enough to make astro-imaging a real option in Central London?

I've been building a barn door tracker so I can do 30 second+ exposures, am I wasting my time even with a light pollution filter?

I am using a Canon DSLR 500D with a selection of lenses, 24mm F2.8, 50mm F1.8 and a 500mm F8.

I have had reasonable results with the Moon and zoom lenses within London but so far have only managed anything else when out of the city. Is buying a filter (they are like £150 for a good one?) going to be worth while for me?

Here are some images I have taken so far while in dark skies,

Am I going to be able to do this from London, with a pollution filter or am I expecting too much from them?

I want to improve on these images. So far they are all stationary with no tracking and as such are limited to 15s or 6s depending on my lens. I'm stacking them now too as I learn but can't learn quickly when I can't take pictures!

Any advice on Pollution filters and Astronomy from within a city would be great

[ronin]

Problem is that a light pollution filter will filter out the sodium yellow light, sodium produces a narrow set of wavelengths and so this is easy.

Light pollution in London will not be just sodium yellow, and all those other wavelengths will not get removed and so come through on to any image. Consider also that councils are replacing the sodium lights with LED ones that are more polychromatic (white) and the situation for imaging could well get worse not better.

The present LP filters will therefore remove some but for London I suspect not sufficent to be significant.

Using narrow band filters "may" be a solution, however that means imaging at each wavelength seperately and then adding them together. Simple (possibly incorrect) logic says each image will be 3x longer to obtain, one at R, G, B seperately, and I suspect more then 3x.

Source of information and advice may be the BSIA group that meet at Regents Park, this is on the presumption that at least one of them is an imager and so has direct experience.

[rowan46]

From what I understand from others narrowband may be the way to go. It seems counter intuitive but they claim that its quicker than one shot in light polluted sights. The reason being that longer exposures can be used and hence less subs need to be taken. apparently with one shot colour lp shows up much more readily hence shorter subs need to be taken to avoid it showing.

[dph1nm]

A Skywatcher LP filter is perfectly adequate for sodium lights and is only 26 pounds for the 2" version, which can be screwed onto a standard Canon lens with the aid of a step-down ring.

NigelM

[Pyrofer]

Thanks for the advice guys. I hadn't expected the LP filter to be the "Magic Bullet" it is often advertised as.

The one thing that worries me is the wide band light pollution in London instead of Sodium only. Thanks for the tip on the Skywatcher LP filter, I may get one of those and see how it goes.