OIII Filter Confusion

[Rickvanman]

Hi there, I 've got some pretty bad light pollution issues from my garden, so decided to take the plunge and get a filter to help tackle it.  Someone recommended the Astronomik OIII 12nm CCD EOS Clip In Filter, so I took the plunge and went for it.

The filter makes everything really green.  I know this might sound like a daft question, but is there a way to coax out the natural colours of the DSO's from these green images, or will I just have to just settle for them being monochrome?   

Appreciate any insight - Thanks :o)

[Adam J]

51 minutes ago, Rickvanman said:

Hi, I 've got some pretty bad light pollution issues from my garden, so decided to take the plunge and get a filter to help tackle it.  Someone recommended the Astronomik OIII 12nm CCD EOS Clip In Filter, so I took the plunge and went for it.

The filter makes everything really green.  Is there a way to coax out the natural colours of the DSO's from these green images, or will I just have to just settle for them being monochrome?   

Layman's terms please :o) 

TIA

Ok where to start.

The Astronomik OIII filter you purchased belongs to a class of filter know as a narrow band filter.

These filters are specifically designed to filter out the very narrow emission wavelength associated with transitional modes (emission lines) within the electron shells of certain elements.

So that was the technical version...

The Layman version is that the filter you bought only lets through emissions from Oxygen 3 (OIII) so the Oxygen atoms within nebula. The wavelength of that light is green so when you take a picture only green light gets to the sensor and hence the image is green.

The bad news is that there is no full color data to retrieve only the green OIII light was let through.

I am sorry to say that you have been poorly advised, if you want to take one shot color images with your DSLR. An OIII filter will block light pollution yes but it wont let you take a color image.

In moderate light pollution I would have advised a CLS CCD Clip filter. In medium light pollution I would have recommended a UHC Clip filter.

In very bad light pollution I would then recommend narrow band filters, H-a would have been a better choice as your first one.

Also of note is that narrow band filters only work with nebula really, the UHC too mostly. The only one i would recommend for galaxies at all is the CLS filter.

OIII can work with DSLR's  for nebula depending on the exact one you have and the ambient temperature which needs to be low to allow very long exposures. However, depending on the rest of your setup you may not be able to get the OIII to work.

Here is an example of what you can get with an OIII filter with a DSLR (once stacked converted to mono, originally was green). But this is a cooled DSLR with long (10min) exposures.

You will get decent images of brighter nebular but I dont want to oversell it, you are unlikely to get that kind of result with a un-cooled DSLR and short exposures.

You can combine several separate images taken with several separate narrow band filters to get color but I am not sure you really want to go down that path.

Most likely what you actually want it a mild UHC filter. But I would need to know more about your setup and what you want to image before I would make a definitive recommendation to you.

For example to make best use of any filter your DSLR needs to be modified.

I can only think that the chap who advised you was thinking about visual filters not imaging with a DSLR.

[Rickvanman]

Many thanks for the insight Adam. Much appreciated. 

It's unfortunate about my initial LP filter purchase, I'll have to sack my advisor and put the oiii filter on eBay :o)  

Ideally, I'm looking for a LP filter that will allow me to take colour shots, but won't reduce the light levels too much so I can still work with shorter exposure times and not have to get involved with star tracking just yet.

my current setup is below: 

EQ mount:  Skywatcher HEQ5 pro GOTO with SkyScan hand controller.
Telescope:  Explore Scientific AR 152mm (8") f/6.5 Air Spaced Double Refractor OTA with 8x50mm straight through finderscope
Camera:      Canon EOS 1100D DSLR  (unmodded)

Appreciate any recommendations - Thanks  :o)

 

[Dave In Vermont]

For light pollution (or LP for short), it helps to be specific about the type of lighting you're being bombarded with. The newer LED's are virtually impossible to filter out and/or block - aside from setting-up a physical 'block,' such as stringing curtains from trees or such (being inventive helps). But for other types, such as Sodium-Vapor (those bright orange ones), or Mercury Lights (blue-purple commonly used in streetlighting) - a good Broadband-Filter can help. But only a trip to a dedicated 'Dark-Sky' site will truly alleviate the problem.

To try to prevent your city or town from putting in the 1/10th the cost to operate full-spectrum LED's, without proper baffling to aim the light emitted down to the ground/street only (which many places do these days - especially if you approach the city-council during the planning-stage and show them this will be the best option and will save on health-problems in developing childrens' brains (for one thing)). For help and information, contact the International Dark Sky Association:

http://darksky.org/

So let us know what you're dealing with, and we'll let you know about what options/filters/approaches would work best for you.

Starry & Dark Skies,

Dave

[Rickvanman]

Thanks for the info Dave, I'm not sure of the exact type of street lights I'm dealing with,  only that they are a pale salmon pink-ish kind of white. I don't think they're LED though.  There is a dark-sky campsite an hour's drive from here, maybe I'll have to make it my plan B :o)

[Dave In Vermont]

Perhaps these images will help. This 1st. one shows the effects & colour of a Sodium-Vapor streetlight:

 

 

And this shows the effect & colour of a baffled LED:

 

 

Good to hear you have the "Plan B Option" relatively close-by! For your at-home situation, I'm sure it can be somewhat alleviated. It's pretty amazing what people like us can see even from a swamp of streetlights and neon, et al, like central London or New York City.

A 'tip-of-the-keys' to sharkmelley of SGL for the excellent images aka teaching-aids!

Dave

[Geoff_L]

Unfortunately, I suspect that Swindon has gone the same way as Cornwall and fitted LED lighting pretty much throughout. Here's an article from the Swindon Advertiser from July 2013 that describes LED as the "way forward". It's impossible to filter out these lights in the way you can with sodium vapour lighting. FWIW, I bought a Baader CLS "Nebula" filter that was meant to give "City Light Suppression", but it's useless against LED street lighting. Thankfully I have a dark sky site about fifteen minutes drive away.

[DaveS]

Pale salmon-pink sounds like high-pressure sodium. An Astronomik CLS filter will work against these. Unless you're going to mod your DSLR you won't need the CLS-CCD filter as these are designed for sensors without IR filters.

[spillage]

2 hours ago, DaveS said:

Pale salmon-pink sounds like high-pressure sodium. An Astronomik CLS filter will work against these. Unless you're going to mod your DSLR you won't need the CLS-CCD filter as these are designed for sensors without IR filters.

I am sure that a modded dslr will benefit from a ccd filter as it only stops a certain wavelength of ir coming through that is not wanted and allow the good ir to pass. Sorry I do not have the scientific reason.

 

[DaveS]

A full spectrum mod will pass all the IR so will need a CLS-CCD filter. and un-modded DSLR has a strong IR-Red filter already in place so will naturally cut the IR. I'm not sure about eg Baader replacement filter modded DSLRs as I went straight from basic DSLR to cooled CCD, and never looked back.

[Dave In Vermont]

7 hours ago, Geoff_L said:

Unfortunately, I suspect that Swindon has gone the same way as Cornwall and fitted LED lighting pretty much throughout. Here's an article from the Swindon Advertiser from July 2013 that describes LED as the "way forward". It's impossible to filter out these lights in the way you can with sodium vapour lighting. FWIW, I bought a Baader CLS "Nebula" filter that was meant to give "City Light Suppression", but it's useless against LED street lighting. Thankfully I have a dark sky site about fifteen minutes drive away.

Yes - IF the LED is allowed to shine, without a directional baffle - everywhere. Then you are royally skewered. But with proper baffling, they are effectively neutered.

While it's quite possible to retrofit baffles post-installation of the LED's, it's also much more expensive to a city/town/municipality to do so - as opposed to installing such at the onset. And £££ is why they are installed in the first-place. This is why approaching your town before-hand is a vital step.

The literature from the IDSA can show the many dangers of NOT doing this. Not just for us weirdos with tubes & glass - for childrens' development, longevity of all people, and prevention of the extinction of entire species of life. To mention some, but hardly all.

http://darksky.org/

https://www.lightpollutionmap.info/#zoom=1&lat=1660314&lon=0&layers=B0TFFFFF

Had enough yet? I hope so!

Get active,

Dave