light pollution filter vs. no filter

[psy1280]

I'm planning on doing some f/6 EAA with my SCT 8" using a ZWO294 MC Pro. Whether to use a light pollution filter or not has me very confused. Some say the filter is a hinderence (I believe with IR light) when it comes to galaxies (not sure about clusters). I'm in a Bortle 7 (probably a 7+) with a New York City dome about 8 miles to my south. Since I only have an Eastern exposure (i.e., trees), I'm looking right into that dome.

Do I go for something like the Optolong L-pro or not? All opinions welcome

Joe

[admin]

Hi,

it rather depends on the type of light pollution that you have to deal with – older streetlights were often low pressure sodium which has a very narrow spectrum and a characteristic orange light. Light pollution filters worked really well on these. High pressure sodium lights still produce a yellowish light but with a whiter tinge to it – still some help from LPF's, but less as you need a wider band to cut out the pollution and that affects your imaging more. More modern lights – like LED street lighting – have wideband spectrums and filters really don't help.

Overall, just look at the colour of the sky glow – if it strongly orange then try a filter. If it's more white then the filter probably won't help.

Cheers, Robin

[BlackWikkett]

Heya

I've been using 294 for a while now in Bortle 5-6 skies and wouldn't go without the LPS filter. I've had good results with the IDAS D1. Without the LPS light gradients are very evident. You can check out some of my images in the gallery forum.

-Chris

[Menno555]

I am in Bortle 8 and can confirm what Robin is writing about non-orange sky glow. With my setup (8" SCT f/10) a filter does enhance contrast, so especially the background is "blacker". But only to around 50 to 60 seconds exposures. Beyond that, glow is starting to show: one half will get brighter then the other half. But it also depend on how much captures you are stacking: the more captures you stack, the more any sky glow will become visible.
For my setup and skies the best results on shorter exposures like 30 seconds were with a Baader Neodymium filter. It is not a light pollution filter as such but will filter enough of the artificial lights, enhance contrast, is also a IR/UV block filter and almost no loss of image brightness. And is way cheaper then a Optolong
About the IR block: that is something what you want with deep sky. All cameras like the 294 don't have that and when capturing, the IR light will form little blurred halo's. But you only need that if you are capturing without any filter. The Optolong L-Pro is blocking IR, so no extra filter needed then.

One final tip: look at the horizon. Somebody told me this (obvious) thing: sometime the skies look clear, you see a lot of stars above you. But in heavily light polluted areas, that is not saying much: when you see a haze on the horizon, even a thin one, it will effect everything. So best changes are when the horizon is also clear.

Menno

[umasscrew39]

I've tried every LP filter invented.....I think. And have read just about every review/opinion on their use. The messaging out there is a mess- mass confusion, debating, etc. The variables are just too many to give a simple direct answer. The type of light as Robin mention is the big one but also the type of sensor, how you use it (EAA vs. AP), scope type, PP methods if even used, DSO type, blah, blah, blah. At times, I have said the heck with it and just stopped using a filter to see how things looked. To my surprise, more often than not, the DSO was ok looking. I think the biggest breaking has been the recently developed duo NB filters for OSC cameras such as the Optolong L-eNhance and similar filters for emission nebulae although for a few years I used the IDAS filters which are also very helpful. For galaxies, LP filters are just about worthless in my opinion. I may use the Optolong L-Pro which is ok, nothing special.

[turfpit]

have read just about every review/opinion on their use. The messaging out there is a mess- mass confusion, debating, etc. The variables are just too many to give a simple direct answer.

Completely agree with that statement.

Dave

[psy1280]

Thank you all for the valued advice. I found Robin's note very helpful as I stare into an orange LP sky! Looks like I'll be selecting a LP filter.

Thanks again,
Joe