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sockatume

UHC filter vs LED street lights.

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My area has the new white light LED street lights. I get by surprisingly well considering I have them literally directly outside my front and back garden and my eyes scarcely get dark adapted as a result 

I was wondering whether a UHC filter would be effective at cutting down the light pollution from this type of light when viewing nebulae, where I inevitably struggle a bit. I figure that an ordinary light pollution filter is only effective against the narrow emission bands of the old metal vapour lamps, so I can’t do much to improve contrast more generally, right?

Anyone got experience fighting off these lights? Thanks in advance!

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1 hour ago, sockatume said:

My area has the new white light LED street lights. I get by surprisingly well considering I have them literally directly outside my front and back garden and my eyes scarcely get dark adapted as a result 

I was wondering whether a UHC filter would be effective at cutting down the light pollution from this type of light when viewing nebulae, where I inevitably struggle a bit. I figure that an ordinary light pollution filter is only effective against the narrow emission bands of the old metal vapour lamps, so I can’t do much to improve contrast more generally, right?

Anyone got experience fighting off these lights? Thanks in advance!

Yes a UHC will do very well against LED lights. It wont totally block them but it will greatly improve contrast none the less. LEDs are much more problematic for broad band targets like galaxies.

Edited by Adam J
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Mm.. LEDs spread light across the visible spectrum uniformly or so, as far as I am aware, whereas an UHC filter filters (EDIT: what I meant was "passes") one specific area of the spectrum. Therefore, I am not convinced that a UHC filter will be really effective against LEDs.

It is against old street lights as those emitted in the yellow mostly, which is cut off by an UHC filter.

Edited by Piero
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1 hour ago, Piero said:

Mm.. LEDs spread light across the visible spectrum uniformly or so, as far as I am aware, whereas an UHC filter filters one specific area of the spectrum. Therefore, I am not convinced that a UHC filter will be really effective against LEDs.

It is against old street lights as those emitted in the yellow mostly, which is cut off by an UHC filter.

UHC does the opposite - it only lets narrow range of wavelength through.  You still will need a more expensive narrow band filter (like Lumicon) to see any effect, and even then it probably won't be much.  I have Optolong UHC filter, which is relatively wide at about 50nm and I don't see any significant difference from a city.

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Thanks for the extra input.

I’m just starting out so it’s probably not worth the money for me to get a high-end filter, and if a cheap one’s not going to make a big difference under these skies I might just hold off. Maybe spend the money on a Barlow to stretch my eyepieces a bit during planetary observing here, and focus on getting out to darker sites.

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6 minutes ago, sockatume said:

Thanks for the extra input.

I’m just starting out so it’s probably not worth the money for me to get a high-end filter, and if a cheap one’s not going to make a big difference under these skies I might just hold off. Maybe spend the money on a Barlow to stretch my eyepieces a bit during planetary observing here, and focus on getting out to darker sites.

Yes, spending money on observing under dark skies is certainly a better option. On the other hand, dark skies are not required for planetary observations (unless you want to catch Pluto!). Seeing is far more important.

UHC and OIII filters do improve the views under moderate light polluted and dark skies. Unfortunately, under the new LED-based street lights, they are less effective. It is not related to the cost of the filter or whether this is narrow or line-based. LED lights are bad for astronomy because they emit light across the spectrum, EVEN on those bands that are passed through a UHC or OIII filter. Therefore, the filter is not really working because it passes both the nebula light and the light pollution caused by LEDs. 

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I read somewhere that its possible to ask for a shade to be fitted to a streetlight if its causing problems (like it shines into a bedroom window ?  )
I'm just about to ask for one to be fitted to our local searchlight.

 

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I would go with a quality OIII filter.  You want as narrow a passband as possible.  I can't recall ever seeing more detail in a nebula with a UHC than with an OIII (both Lumicon).  Quite the opposite, in fact.  Skip the low cost OIII filters (I have a $16 Zhumell I couldn't resist buying on clearance) since they are little better than a light pollution filter.

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If you haven't done so already, attach an extension, a lightweight shade, to the front end of your telescope, the longer the better, at least a foot long, and to help block out incidental light sources, whether natural(the full Moon), or artificial...

https://stargazerslounge.com/uploads/monthly_11_2012/post-10522-0-87277600-1352846808.jpg

That's for the telescope itself.

Then, for yourself, you can block out the light sources further with something like this, and over the head and shoulders...

old time camera

 

Edited by Alan64
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Good advice, thanks. I'm actually thinking of getting the Heritage 130p next (I have a teeny 76mm reflector right now*), so I would be making a shroud anyway. I can just make an even longer one.

*It's amazing what you can see even with the worst equipment in the worst location.

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13 hours ago, Piero said:

Mm.. LEDs spread light across the visible spectrum uniformly or so, as far as I am aware, whereas an UHC filter filters (EDIT: what I meant was "passes") one specific area of the spectrum. Therefore, I am not convinced that a UHC filter will be really effective against LEDs.

It is against old street lights as those emitted in the yellow mostly, which is cut off by an UHC filter.

Nope it will still increase the contrast of a nebula as a large portion of the LED emission spectrum that is not overlapping with the UHC (and this is most of it) will be blocked leaving only the smaller amount of light that is overlapping.

11 hours ago, pregulla said:

UHC does the opposite - it only lets narrow range of wavelength through.  You still will need a more expensive narrow band filter (like Lumicon) to see any effect, and even then it probably won't be much.  I have Optolong UHC filter, which is relatively wide at about 50nm and I don't see any significant difference from a city.

I would go with a Astronomik UHC as its significantly narrower than the Optolong which is a bit of a budget filter to be honest.

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7 hours ago, Louis D said:

I would go with a quality OIII filter.  You want as narrow a passband as possible.  I can't recall ever seeing more detail in a nebula with a UHC than with an OIII (both Lumicon).  Quite the opposite, in fact.  Skip the low cost OIII filters (I have a $16 Zhumell I couldn't resist buying on clearance) since they are little better than a light pollution filter.

Depends on the nebula, a Hb rich nebula is not going to respond to a OIII filter. So while a OIII filter is much better for targets with OIII it will not help with others at all. But a UHC is useful for all emission nebula targets.

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6 minutes ago, Adam J said:

I would go with a Astronomik UHC as its significantly narrower than the Optolong which is a bit of a budget filter to be honest. 

I do plan on buying higher end 2" filter one day, but they are expensive. I payed $20 for new 1.25" Optolong during 11.11 sale on AliExpress. The idea being that wider filter will still be useful for higher power 1.25" EPs under dark skies even after I buy 2" proper narrow-band UHC. And since I can use 2" filter for both 2" and 1.25" eyepieces buying high end 1.25" filter would be wasteful.

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The low cost UHC's that I've tried recently barely make an impact on nebulae. I was pretty dissapointed in them to be honest with you.

The premium brands (Lumicon, Astronomik and Omega for example) do seem effective but I find myself reaching for my Lumicon O-III filter much more often even with my smaller (100mm - 130mm) aperture scopes. A good O-III really makes a significant difference to a number of nebulae.

They work better still under dark skies of course but sometimes under light pollution such a filter can make the difference between seeing something and seeing nothing at all.

I've yet to find a filter that helps with galaxies whether under LP or dark skies. As someone once posted on another forum when asked what could be purchased for $50-$100 that would improve the views of galaxies, "fuel in the gas tank to get the scope and observer under dark skies" :smiley:

 

 

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38 minutes ago, John said:

I've yet to find a filter that helps with galaxies whether under LP or dark skies

I think an Astronomik CLS works on some. The caveat is that it probably depends on:

  1. The characteristics of the galaxy.
  2. The type and amount of light pollution in the direction the telescope is pointing.

It's not going to be as good as going to a true dark site but it can be the difference between seeing something and not, or making out more than just the core.

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5 hours ago, Adam J said:

Depends on the nebula, a Hb rich nebula is not going to respond to a OIII filter. So while a OIII filter is much better for targets with OIII it will not help with others at all. But a UHC is useful for all emission nebula targets.

An Hβ rich nebula such as the California nebula only reacts well to an expensive, ultra-narrow band Hβ filter under severely light polluted skies.  UHCs do basically nothing to reveal them under such conditions.  So, you end up with a compromised filter trying to do two things (possibly three if they try to include Hα in the deep red) at once and doing neither (none) particularly well.  I basically never reach for my Lumicon UHC anymore.  I do like my Zhumell Moon & Sky Glow for comet hunting along light polluted horizons at sunset.  That's about it for filter preferences for me.  OIII for nebula and M&SG for comet hunting.

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