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Advice on filters for observing wanted

filters observing
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#1 FredOz

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Posted 22 January 2021 - 02:37 PM

Hi All,

 

I have difficulty seeing nebulae such as the Blinking Planetary, NGC 6826 or the N. American Nebula, NGC 7000 (neither of which I've successively observed) and I do not see others well, such as the Clown Face, NCG 2392 even from a nearby dark-sky site (~Bortle 2.5) near Granite Mtn. outside of Prescott, AZ.

 

I have a cheap filter, Svbony UHC, O-III but notice little to no improvement, just a little coloring.  Would it be worthwhile to buy a more expensive filter such as the Lumicon UHC-filter or at least the Optolong UHC Nebula Filter?

 

And speaking of filters, what about one or a couple planetary filters to increase contrast, such as a light blue #82A or others?

 

--- Fred



#2 jeffreym

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Posted 22 January 2021 - 02:51 PM

Check out this thread.

https://www.cloudyni...al-observation/

Jeff


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#3 spereira

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Posted 22 January 2021 - 03:07 PM

Moving to Deep Sky Observing.

 

smp



#4 sevenofnine

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Posted 22 January 2021 - 07:24 PM

There are many threads as suggested on this topic. From what I've gathered the general consensus is that filters are becoming less effective because of the changing light sources. The move to LED has changed the pollution and there is no filter to help with that. Also you will have to manage your expectations as well. A small scope's aperture will only allow so many objects to be seen clearly. If you don't have it yet the best guide I've found is "Turn Left at Orion" by Guy Consolmagno and Dan Davis. Instead a pretty photographs, it's illustrated with drawings which are much more like what you really see in a small telescope. Good luck and enjoy the hunting!


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#5 Frugal Astronomer

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Posted 23 January 2021 - 04:02 PM

I'm using an 8inch dob, but in my experience, you may indeed find that a better filter helps.  Some of the things you mentioned are just hard to see (like the North American nebula).  But others are very doable (Clown Face, Blinking, etc.) especially from a dark site.  I started with a generic UHC filter and found that it did very little to nothing for me.  Then I got a DGM optics NPB filter and saw a big difference.  It turned a faint whisp into a Swan and almost nothing at all into visible East and West Veils.  I have no problem seeing Blinking, Clown Face, and other planetaries without a filter from Bortle 5 where I view, but the NPB filter helps make some of them more defined. 

 

I'm currently considering adding a Lumicon OIII to my kit, but that's probably all I'll get.  I've read a lot about planet filters and decided they weren't worth it for me, but certainly other like them or they wouldn't be for sale.



#6 sg6

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Posted 23 January 2021 - 04:52 PM

For filters you need to know the nature and so the spectrum of the target and you need to know what the filter does. Also some attributes of the eye.

 

A UHC and OIII are going to be somewhat similar visually.

Both will pass the OIII and I expect the Hb to the eye.

The UHC may well pass the Ha to the eye.

However the eye at night vision mode - dark adapted - will not pick up the Ha readily, it will be a dim grey, if anything.

 

That is if the target emits in those wavelengths. An OIII filter on an Ha target basically means nothing at the eye in regards the target.

 

Aim at a "white" target and unless the UHC is being used in place of a light pollution filter all you do is block a lot of the light from the target.

 

Often a filter is chosen to increase the contrast.

 

The classic statement is that "No filter adds anything, they all remove something."

To increase contrast you have to choose the filter to pass the relevant wavelengths from the target, but block the unwanted wavelengths in the sky/view around the target.

 

There are lots of posts saying they want to increase the brightness of A, so which filter should they use?

 

The first thing you need to determine is the relevant wavelengths from the targets you are having little/no success with. If they are predominently Ha the the UHC and certainly the OIII are not a great deal of use.

 

The other overlooked bit is that an OIII filter will pass say 10% of the spectrum to your eye, OR, 90% of the incoming light is blocked. You will need that 150mm mirror.



#7 havasman

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Posted 23 January 2021 - 04:59 PM

Would it be worthwhile to buy a more expensive filter such as the Lumicon UHC-filter?

 

 

In a word, yes. It is a reliable, consistently manufactured narrowband nebula filter. Those characteristics set it apart from the ones you reference. Add a Lumicon O-III filter and you've got coverage for 95% of the objects that will benefit from a nebula filter. From sites available to you, they should be very effective. Larger exit pupils can be helpful, particularly with larger nebulae.

 

Read these articles  -  https://www.prairiea...ep-sky-objects/

https://www.prairiea...common-nebulae/

They are standard reference manuals for nebula filter use. Their specific gear advice is a bit dated but the general filter advice remains valuable.

It is flatly false that narrowband nebula filters require larger apertures to be effective. Good nebula filters pass selected bandwidths of energy and block the rest. Matching the passband of the filter to the emission band of a nebula results in increased apparent contrast between the object and the field because the field is darkened. This remains true in small aperture scopes. Lumicon filters are as effective in my 4" refractor as they are in the 16" Dob. The image is different obviously but equivalent to how they differ w/o filter on any object.

 

The Lumicon filters are at the top of the performance range. Televue filters are also very good.


Edited by havasman, 23 January 2021 - 05:06 PM.

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#8 Starman1

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Posted 23 January 2021 - 05:01 PM

Hi All,

 

I have difficulty seeing nebulae such as the Blinking Planetary, NGC 6826 or the N. American Nebula, NGC 7000 (neither of which I've successively observed) and I do not see others well, such as the Clown Face, NCG 2392 even from a nearby dark-sky site (~Bortle 2.5) near Granite Mtn. outside of Prescott, AZ.

 

I have a cheap filter, Svbony UHC, O-III but notice little to no improvement, just a little coloring.  Would it be worthwhile to buy a more expensive filter such as the Lumicon UHC-filter or at least the Optolong UHC Nebula Filter?

 

And speaking of filters, what about one or a couple planetary filters to increase contrast, such as a light blue #82A or others?

 

--- Fred

Emission nebulae emit light in the spectral lines of Hydrogen and oxygen.  The lines that are relevant for our night vision's sensitivity are H-ß and O-III

Unless you know the spectrum of the nebula, a filter that passes both H-ß and O-III will be more "universal" than one that passes only H-ß or only O-III.

 

In general, a narrower bandwidth to the filter rejects more sky light and enhances contrast more between the nebula and sky than a filter with a wider bandwidth.

 

The ones with nice narrowband bandwidths that pick up those 3 spectral lines but enhance well are TeleVue Nebustar, Astronomik UHC, DGM NPB, Lumicon UHC, ICS UHC

Many less expensive filters have wide bandwidths and enhance a lot less.

 

Tricks for use to achieve maximum results with a filter:

--use low power, under 10x/inch of aperture.  Higher powers don't work as well with the filters because contrast is significantly reduced.

--you must be well dark-adapted.  That means at least 30-45 minutes outside away from all lights.  If you are not dark adapted, the filters will be worthless to you.

--try to observe the nebulae above a 30° altitude in the sky, preferably when the nebula crosses the N-S meridian in the sky.  The higher the nebula, the easier it is to see.

--make sure the nebula is one that can be seen in a scope, not just one that is typically photographed.  Don't even bother with the Heart and Soul Nebulae, the California, etc. unless you are viewing from a pristine sky with no light pollution.

--be aware the overall field will be darker because the light of the stars is suppressed along with sky light.  The nebula filters are for looking at nebulae, not stars.


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#9 NYJohn S

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Posted 23 January 2021 - 06:48 PM

I think if you’re not seeing bright compact planetary nebula like the blinking & clown face its probably a magnification issue. At low power they can look like stars. If you increase the magnification it will become obvious they’re something different. Filters will help with the others.
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#10 Sheol

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Posted 23 January 2021 - 08:12 PM

                          Get an OIII filter also, often very useful for PNs. Otherwise, as John just said, crank up the magnification. Their high magnitudes allow for this, & the small size practically begs for it.

                           As for the North American Nebula? Use your finder or a pair of binoculars. This thing is so big & spread out, that in your average medium 'scope it vanishes. But its often pretty obvious in finders.

 

                        Clear Skies,

                             Matt.



#11 MarMax

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Posted 23 January 2021 - 10:23 PM

I have limited experience with filters but have always followed Don's (Starman1) advice. It's a bit expensive to outfit yourself with UHC (narrow), OIII and H-β but I've found that using a manual filter wheel is a great way to easily use filters. And yes, the better filters definitely work better.

 

I can never remember which nebula are best with which filter so I have my wheel set up with all of them and just cycle through and see what looks best. Most of the time a filter will provide a bit more nebulosity, but sometimes it's best without. And the averted vision trick can be key to really seeing things.

 

My wife and I love to look at M42 and cycle from no filter through all of the flavors just to see the differences. The other thing I've noticed is you need to adjust your focus for each filter. And at the light polluted home base I've never seen any hint of nebulosity from the CA or No. American, either with or without filters.


Edited by MarMax, 23 January 2021 - 10:23 PM.



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