Light Pollution help please

[Kluson]

 

Hi all ,

 

I think I posted this in the wrong place first off so I'll repost here, Hope you guys can offer some advice and point us in the right direction.

If I look at the light pollution map it shows our location as Bortle 4, however we have a haulage company not so far away who has its flood lights on all night! As well as our Neighbours recent garden lighting acquisition 😞

In reality we are probably more like a 5 In order to avoid the Haulage lamp glow we face more towards our local town which then gives us a white sky glow. We can  have a kindly word with our neighbours so we can probably discount the polution caused by them. We are using a modified DSLR with the IR cut filter removed. I am thinking about perhaps a Filter to improve things a little. Given our circumstances and camera what filter do you guys think would be best suited for us?. We photograph mainly Nebulae ( all types) Globular clusters and Galaxies. Occasionally planets and the Moon. We are using a Celestron Nexstar 6SE with the 6.3 Focal reducer giving us F6.3  945mm  along with a F6  360mm ED doublet refractor with a field flattener. Is there an all round  filter which would help, without breaking the bank. We are thinking along the lines of a 1.25 or 2 inch filter rather than a clip in , as at some stage we will upgrade the DSLR  to an Astro camera still probably OSC. I know we are asking a lot but I am sure there are others in a similar situation who have managed to overcome this problem.

Hope you can help - Many thanks in advance.

[Dan_Paris]

  Hi,

based on my experience (under Bortle 7/8 skies)

 

5 hours ago, Kluson said:

Given our circumstances and camera what filter do you guys think would be best suited for us?. We photograph mainly Nebulae ( all types) Globular clusters and Galaxies. Occasionally planets and the Moon.

Light pollution filters are useful for emission nebulæ (some others will advise you better about which filter model to choose for this application) but not really  useful (I would even say counterproductive) for galaxies, globular clusters or reflection nebulæ. In those cases the proper way to fight against light pollution is to shoot rather short subs without any light pollution filter  (in my case, 60sec at f/4) and to stack many of them (in my case, at least 200, often 300 or more).

 

5 hours ago, Kluson said:

as at some stage we will upgrade the DSLR  to an Astro camera still probably OSC.

 

Light pollution implies a big penalty in terms of signal/noise ratio. To fight against it you'd like to accumulate as much signal as possible, a goal that you could accomplish in much less time with a mono camera than with a color camera. Color cameras work well under very dark skies, under light-polluted ones not so much.

 

Edited August 22, 2023 by Dan_Paris

[RT65CB-SWL]

I am in a Bortle 5/6 area and surrounded by LED streetlights.

A Neodymium or UHC filter may help, especially for visual. That said, I am not into astro-imaging at the time of writing/posting.

 

[windjammer]

I am in central/north London Bortle 10 or worse.  I don't think filters will do the trick.  I think a mono astro cam with RGB and narrow band filters is the way to go.  I shelter my scope in a hide during ops, so direct light is cut off - my terraced house neighbours are light pollution shockers. I tend to choose the objects for imaging at higher elevations and choose the time of year to go for them - above 60 degrees; so things like the classic nebs down south are not really feasible.  Getting hold of good gradient removal tools is a must if you don't have them already - GradXpert is v good and free.  

Narrowband will punch through anything - my cam (atik 460) and astronomik n/b filters will manage 600s+ exposure times before you see the LP step in the histogram (that is with about 60 arcsec square fov with my scope) .  RGBs, 300s.

Simon

[windjammer]

A follow up thought: the bit depth of your cam is also important.  Your astro data is a thin layer of useful signal above a fixed lump of LP - which you subtract.  The more bit depth you have in the surviving narrow data layer the better.  Is your DSLR 12 or 14 bit ?  A 16 bit astro cam will give you 4x or 8x more detail than 14/12bit DSLR.

Simon

 

[Elp]

For OSC and emission nebulae rich in hydrogen alpha and o3 an Optolong Lenhance/Extreme/Ultimate will go a long way in blocking unwanted light pollution, you won't believe how well they work until you've used them, I haven't got experience of the latter, as you go up the range the narrower their bandpass so become even tighter around the emission they do allow through.

Other brand equivalents which come highly regarded but I haven't used as I get my milage with my lextreme is the IDAS NBZ and the Antlia ALPT.

Note, many if not all will give you star halos around the very bright stars, it bothers a lot of people but not me.

For broadband targets like galaxies you dont really have much of an option as the usual filters block the signal you're trying to capture such as a CLS filter or Optolong Lpro, it's better to image them with just a standard UV/IR block or luminence filter (you use these to prevent IR bloat from stars) and try to saturate your pixels as much as possible from the signal you're trying to capture before LP becomes evident in each image. If you're not doing it already, use a pre process software like Siril (it's free, no excuse) and integrate Background Extraction into your workflow (among other things), you'll be amazed what it does to your images for removing LP gradients.

Edited August 28, 2023 by Elp

[tomato]

For inspiration take a look at @Lee_P’s images on here. He images from Bristol city centre (Bortle 8 ) and gets phenomenal results, although he does have quite a high end setup.

And +1 for LP removal software. Sometimes my raw stacks can be completely washed out but after applying the LP removal tool, the nebulosity and contrast are all there.

[Dan_Paris]

11 hours ago, windjammer said:

A follow up thought: the bit depth of your cam is also important.  Your astro data is a thin layer of useful signal above a fixed lump of LP - which you subtract.  The more bit depth you have in the surviving narrow data layer the better.  Is your DSLR 12 or 14 bit ?  A 16 bit astro cam will give you 4x or 8x more detail than 14/12bit DSLR.

It really depends on the type of imaging. For broadband imaging with a relatively fast telescope, especially with high levels of light pollution, you typically stack a large number of short exposures (for me, typically 300x60 sec for the luminance). In those conditions even a 12bit camera will give you far more than 16 bits of dynamic range at the end.

For narrowband imaging, the number of frames is usually much less so the bit depth of the camera is more important.

[carastro]

I agree with Simon.  I live in SE London Bortle 8 and can only do NB from here. 
 

Can you try speaking to the Haulage company.  
 

 

 

 

[Lee_P]

4 hours ago, tomato said:

For inspiration take a look at @Lee_P’s images on here. He images from Bristol city centre (Bortle 8 ) and gets phenomenal results, although he does have quite a high end setup.

And +1 for LP removal software. Sometimes my raw stacks can be completely washed out but after applying the LP removal tool, the nebulosity and contrast are all there.

My astrophotography ambition is to be thought of as someone who's good at imaging through light pollution, so @tomato's comment here has made my day 😂

For the OP @Kluson, I think Bortle 4/5 is actually a pretty low light pollution level (I'd happily swap with you!) but there might be some content on my website Urban Astrophotography that's useful to you.

[tomato]

Yes, Bortle 4/5 is pretty good for a home location, I estimate my back garden is Bortle 5/6 with a pesky LED street light right opposite, but it doesn't bother me one bit. I just keep on taking subs if I am near it and let the LP removal software do it's thing.

[Kluson]

Thanks so much for all the replies @carastro Yes we did have a word with them but it’s health and safety.  I guess I am lucky compared to some. @Lee_P Wow is all I can say. You really are a true inspiration. Thanks so much for your link. I am sure I will find help there.  Our set up is pretty easily transportable and it’s not so far to darker skies. I can imagine some of the people on here thinking “ This chap doesn’t know when he is well off “. Well you are probably right 😀.  Such is the way of beginners.  I will follow @Lee_P with interest. Thanks so much for the inspiration. 
thanks all

D

[tomato]

Single intrusive lit areas in an otherwise dark site can be a pain, especially for visual observers. I once went on an astro themed holiday to a dark location, it was a superb dark site but there was a floodlit farm yard about a quarter of a mile away which killed your night vision, I was very glad when they were switched off around 23:30.

[Fegato]

16 hours ago, windjammer said:

A follow up thought: the bit depth of your cam is also important.  Your astro data is a thin layer of useful signal above a fixed lump of LP - which you subtract.  The more bit depth you have in the surviving narrow data layer the better.  Is your DSLR 12 or 14 bit ?  A 16 bit astro cam will give you 4x or 8x more detail than 14/12bit DSLR.

Simon

 

I don’t believe that’s true about bit depth in terms of anything a human can perceive once stacking has taken place. See e.g

 

[Kluson]

4 hours ago, tomato said:

Single intrusive lit areas in an otherwise dark site can be a pain, especially for visual observers. I once went on an astro themed holiday to a dark location, it was a superb dark site but there was a floodlit farm yard about a quarter of a mile away which killed your night vision, I was very glad when they were switched off around 23:30

 

Yes, this is the biggest issue for us when we are observing.  Especially as we have older eyes which take a little longer to adjust  

 

Edited August 28, 2023 by Kluson