Advice on Filters' Please

[Taff]

With different type of Nebula in the night sky.How do you know which filter to use on a certain Nebula to capture with a DSLR Camera.I have a CLS clip filter which fits inside the camera,OIII Filter, Light Pollution filter,and a H-Beta filter.But i don't know which filter to use on a certain Nebula.Can anyone help me which filter to use on certain Nebula.Thanks for reading.Mark

[Size9Hex]

Here’s a fairly commonly used reference... https://www.prairieastronomyclub.org/filter-performance-comparisons-for-some-common-nebulae/

Above all though, experiment for yourself! Sometimes you find something useful straying from the established wisdom! My mileage varies according to suburban (Oiii often useful) or dark site (UHC often better) even on the same target, so there’s no single "best" even on the same target.

[vlaiv]

Two general types of nebulae out there:

1. Emission nebula

2. Reflection nebula

Emission nebulae usually are strongest in Ha, OIII and SII - so you would use narrowband filters for such objects. You can use Hbeta filter on it, but all signal that is there in H-Beta is also there in H-alpha. Same gas (hydrogen) emits both wavelengths, and usually H-alpha is stronger (less energetic thus more molecules get excited to this level), so it is preferred for imaging. H-beta is useful for observing since human eye is more sensitive in this wavelength then in red counterpart (Halpha).

UHC filter is good for emission nebulae for both observing and imaging - it is broadband version of OIII + Ha + SII filter - passing light from these three wavelengths (and some more light from continuum because it is not exactly narrowband filter).

CLS filter is similar to UHC but passes more light from continuum, and is considered LPS filter (light pollution suppression). There are better LPS filters out there than CLS as CLS clips too much of wavelength continuum to get proper color balance.

General usage guidelines:

UHC, narrowband filters (H-alpha, H-beta in some cases, OIII, SII) - emission type nebulae (HII region, planetary nebulae, etc)

CLS can be used generally but will be worst of all and will impact color balance.

Good LPS - use in light pollution for any type of target (galaxies, reflection nebulae, and above). Can help or even hurt your images, but that depends on level and type of light pollution you are facing.

[Danjc]

1 hour ago, vlaiv said:

CLS can be used generally but will be worst of all and will impact color balance.

Good LPS - use in light pollution for any type of target (galaxies, reflection nebulae, and above). Can help or even hurt your images, but that depends on level and type of light pollution you are facing.

Apologies to hijack the thread but you touch upon a subject I’m currently interested in. 

Im after a LP filter preferably a clip in for a canon EOS and was initially looking at a Astronomik CLS but you say the CLS are not great and can impact upon colour balance. I appreciate that any LPS filter may impact upon colour balance but what other options do I have. 

My LP consists of LED street lighting at the front but this isn’t a massive issue as I image from round the back where there’s a big field behind my garden. The biggest issue a couple of miles away is a mixture of the orange sodium lights and a big yard that has only what can assume are halogen flood lights. 

Dan. 

[Taff]

Thanks Paul' for your time and for the web page for me to look at.And to Vlaiv' for explaining to me about the filters Thanks.Mark

[Taff]

Not at all Dan' That's what Forums are for to help members' along on subjects.Mark

[vlaiv]

11 minutes ago, Danjc said:

Apologies to hijack the thread but you touch upon a subject I’m currently interested in. 

Im after a LP filter preferably a clip in for a canon EOS and was initially looking at a Astronomik CLS but you say the CLS are not great and can impact upon colour balance. I appreciate that any LPS filter may impact upon colour balance but what other options do I have. 

My LP consists of LED street lighting at the front but this isn’t a massive issue as I image from round the back where there’s a big field behind my garden. The biggest issue a couple of miles away is a mixture of the orange sodium lights and a big yard that has only what can assume are halogen flood lights. 

Dan. 

Let's examine filter curves and LP wavelength distribution to see what would be best and why some LPS filters create trouble with color balancing, while others are sort of OK.

This is Astronomik CLS:

Fairly straight forward response curve - passes 450-540nm range and all above 650nm. It is apparent straight away why color balancing is problem with this filter - it cuts big chunk out of middle of the spectrum where green and red overlap - green and red produce yellow, and most stars out there are yellow, so when you use CLS you end up with images where most stars look either red or blue - no nice white and yellow stars (and galaxies that compose out of the stars).

Here is response curve of one of the best LPS filters (well at least in my view one of the best )

It has very similar curve to one above, except it keeps a bit of blue part of spectrum - 415-430nm, red part is less affected - starting at 640 vs 650 with CLS, it can be used as UV/IR cut filter (or instead of one) because it clips past 700nm and below 400nm, and very important part is two peaks between 540 and 640nm - helps recover some of green / red transition (yellow color).

To select best LPS filter, you must understand your LP. Here are some emission curves of LP sources:

Incandescent light is probably the worst kind - it covers whole spectrum and there is no good filtration against it. It add that distinctive red background to DSLR images (notice amount of red light in graph).

All other sources have certain emission peaks, and it is important for these peaks to fall where there is dip in LPS filter - this way most of the light from LP source will be blocked by filter. CLS will cut almost all LP sources, because most of them have peaks between 540-650 (except maybe MBI), but in doing so it will cut signal from target as well.

IDAS LPS P2 does very similar job, is somewhat less efficient in cutting down HPS and MBI sources, but keeps more target signal and color balance.

There are other versions of LPS filters out there (Hutech has 3 more models D1, D2 and V4), so it's best if you look at their response curves and compare to types of LP that you are dealing with.

https://www.sciencecenter.net/hutech/idas/lps-wideplots.htm

(other hutech LPS versions).

 

 

[Taff]

Thanks Vlaiv' For you to explain and for the graphs to look at.Mark

[Danjc]

Thanks for the very informative post @vlaiv much appreciated. I will look into what will work best for myself and no doubt ask more questions ??