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Questions about C-mount to focuser adapter and filters

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#1 Antares89

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Posted 15 June 2017 - 08:01 PM

I am currently awaiting the arrival of my Mod-3 from ultimate night vision and am still in need of a few things.

I'm going to need a c-mount to focuser adapter to mount the mod-3 on my scope. Should I get the 1.25 inch or 2 inch adapter? According to scopestuff, the 2 inch is threaded for both 2 and 1.25 inch filters.

That brings me to my second question. Which wavelength filters do I need to buy and what size do they need to be? I already have a 2 inch DGM NPB filter. Will that be of any use with night vision? I've been reading that H-alpha filters are a must. Why is that? I was under the impression H-alpha was used when viewing the sun.

Lastly, how do I go about affixing a filter to the mod-3 for filtered 1x views?

Thanks a lot

#2 Eddgie

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Posted 15 June 2017 - 08:31 PM

First, if Richard said you are getting an ENVIS lens, then you attache the filter to the lens using the following part:

 

https://www.rafcamer...s-to-astro-1-25

 

H-a filters are for viewing emission nebula.  If you live under darker skies, you can use something like 12nm but brigher skies, a 7nm or 5nm is going to be useful (depending on the scope).   These can let you see nebula like the Horse Head even from light polluted locations.

 

The other filters people are using are long pass (610nm, 640/650nm, and 685nm). These are for use in areas with light pollution and the more light pollution you have the longer more you get closer to the 685nm but I find 650 to be the best compromise even from my white zone skies.  The 685nm is also useful is you are going to use one of the CCD finder types scopes or fast acrhomats because these will produce very bloated stars if you do not use an pretty strong filter.

 

The reason most people go with 1.25" though is because the 2" filters are very expensive and there really is no need to use a 2" filter on the Mod 3.  

 

If you have a 2" to 1.25" adapter, many of these are threaded on the front for 2" so if you already have one, no need to buy the 2" nose.  You can just use the 1.25" nose.

The other reason for wanting the 1.25" nose is that many people are using CCD finders as low power hand held telescopes.  These are usually about 180mm to 200mm focal lenght and about f/3.9 or f/4.    



#3 Antares89

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Posted 15 June 2017 - 09:45 PM

First, if Richard said you are getting an ENVIS lens, then you attache the filter to the lens using the following part:

https://www.rafcamer...s-to-astro-1-25

H-a filters are for viewing emission nebula. If you live under darker skies, you can use something like 12nm but brigher skies, a 7nm or 5nm is going to be useful (depending on the scope). These can let you see nebula like the Horse Head even from light polluted locations.

The other filters people are using are long pass (610nm, 640/650nm, and 685nm). These are for use in areas with light pollution and the more light pollution you have the longer more you get closer to the 685nm but I find 650 to be the best compromise even from my white zone skies. The 685nm is also useful is you are going to use one of the CCD finder types scopes or fast acrhomats because these will produce very bloated stars if you do not use an pretty strong filter.

The reason most people go with 1.25" though is because the 2" filters are very expensive and there really is no need to use a 2" filter on the Mod 3.

If you have a 2" to 1.25" adapter, many of these are threaded on the front for 2" so if you already have one, no need to buy the 2" nose. You can just use the 1.25" nose.
The other reason for wanting the 1.25" nose is that many people are using CCD finders as low power hand held telescopes. These are usually about 180mm to 200mm focal lenght and about f/3.9 or f/4.

Thanks! This helps a ton!

Could you expand a bit on the use of the long pass filters? H-alpha is used for emission nebula but what are the long pass filters used for?

As a somewhat related question, would my DGM NPB filter be of any use?

Also, any suggestions brand-wise for what filters I should be considering?

Edited by Antares89, 15 June 2017 - 09:49 PM.


#4 pwang99

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Posted 16 June 2017 - 03:09 AM

Thanks! This helps a ton!
Could you expand a bit on the use of the long pass filters? H-alpha is used for emission nebula but what are the long pass filters used for?


I have used 650 and 685 long-pass for general contrast enhancement when looking at 1x or 3x under orange-zone skies. With either of these (Baader 685, cheap ebay $10 650nm), the Milky Way under orange skies is almost as contrasty as naked-eye under really dark skies.
 

As a somewhat related question, would my DGM NPB filter be of any use?


I have a 2" DGM NPB. IIRC, it didn't help as much as a narrowband H-a for cutting in-town light pollution, for nebula. Next time I'm out in the suburbs, I'll have to try it for galaxies and globs.
I *have* tried it on the Andromeda Galaxy, and it didn't do much - but M31 doesn't seem to play well with NV in general.
 

Also, any suggestions brand-wise for what filters I should be considering?


Well, I have an unhelpful comment regarding the Orion 7nm: it is my standard workhorse for nebula, and I have two of them.
So, I love this filter and I do recommend it, but there is this small caveat.

I've had two copies of this filter delaminate on me: one was on loan to a buddy, and another was shortly after a friend got a small amount of beer fizz onto it while we were chilling in the dark. I don't know if the beer is the real culprit in the latter case, but the
de-lamination seemed pretty severe given the small amount of beer that had fizzed onto the filter.

Edited by pwang99, 16 June 2017 - 03:11 AM.


#5 Antares89

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Posted 16 June 2017 - 06:19 AM

Are the narrow band h-alpha filters used exclusively for nebula and the long pass used for everything else?

Still trying to wrap my mind around why both are needed.


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#6 Vondragonnoggin

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Posted 16 June 2017 - 08:44 AM

Are the narrow band h-alpha filters used exclusively for nebula and the long pass used for everything else?

Still trying to wrap my mind around why both are needed.


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Here is a lengthy thread on filtering night vision devices. Filter candidates and why certain filtering is used

 

https://www.cloudyni...ter-candidates/



#7 Eddgie

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Posted 16 June 2017 - 09:35 AM

 

Are the narrow band h-alpha filters used exclusively for nebula and the long pass used for everything else?

Still trying to wrap my mind around why both are needed.


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The narrow band are not only used exclusively for nebula, but are in fact almost essential and not at all optional for this class of target. 

 

The reason is that while the eye has it's peak sensitivity in green, modern Gen 3 night vision device sees its peak sensitivity in near infra-red.  They see in the red band  better than they see green.   The image intensifier though converts the red it sees to green or white which we see easily.

 

The narrow band H-a fitlers then suppress all light pollution and natural sky glow so that only these nebula  that are actually very bright in red light show through to us. 

 

Long pass filters block much of the man made light but not all.  There is a very significant amount of man made light in the red part of the spectrum that most people never think about when thinking about "Light Pollution" and that is car tail lights.  These are generally right in the 600nm to (sadly with LED tail lights) 650nm spectrum.

 

Now we don't see these car tail lights as being super bright, but NV does and I am convinced that in big cities, car taillights, which are not typically as tightly focused as headlights, may be a very large source of light pollution to NV users. 

 

I can actually see my sky get darker even during the winter, starting at about 11:00 PM. When the traffic dies  down for the night, I can almost eliminate my red filters and often by midnight, I am getting my best views unfiltered.  ( would be curious to know if others have seen this, but I see it hugely on the Milky Way at 1x and 3x.  After 11:00 PM, it just seems to really start to come alive). 

 

So, dark skies you don't need long pass unless using acrhomats where they are almost essential for all use except H-a, but how much long pass you need is very dependent on where you live.   You will though almost always want to use narrow band for nebula.  While you can see North American from a dark sky without it, it really pops with a 12nm.   

 

Barnard's Loop is only hinted at without band pass, but at 1x with 12nm, it is glorious (this though is a dark sky target.  You might catch parts of it from the city after  midnight when the traffic has settled, but almost invisible even when high in the sky at 8:00 PM even using a 12nm, but I have never tired with 7nm).


Edited by Eddgie, 16 June 2017 - 12:24 PM.


#8 Jeff Morgan

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Posted 16 June 2017 - 10:03 AM

Get both C-mount adapters. One, because they are inexpensive. Two, because they give you flexibility for different scopes you may come across. Three, because I find the 2" adapter seems to require just a bit more back focus with the Mod 3, and it can get tight in my Newtonians. (IIRC, the 2" adapter will not reach with my 8".)

 

As to filters - conventional ones don't do much for NV because of the spectral range and response of the tubes. (I do wonder if that may be different for the Photonis tubes, who knows?)

 

I find the long-pass filter is a better choice for globulars, open clusters, galaxies, and dark nebula.

 

DN's have to have a lot of opacity to pop with the H-alphas.

 

Jury is still out on planetary nebulas for lack of first-hand experience. M27 and M57 are awesome in NV - but really the only ones I have gone after so far. M57 was cool even at 19x in the Epsilon, long-pass. M27 is great both 12nm H-alpha and long-pass.

 

Last night we had an awesome session on 7500' Mingus Mountain in Arizona. I had the f/2.8 Epsilon out and thought I would be mostly using the 7nm filter. It turns out my observing buddy and I thought the 12nm was a better choice on many (most?) objects. Moral of the story: you want both. There is no right and wrong with the degree of filtration - personal taste dictates which is "best". The tighter the notch on the filter, the more "background" you lose. Also, the degree of light pollution may make the choice different at different observing sites. 

 

A couple of items I noticed last night:

 

1) On the Veil Nebula I seem to recall that with conventional eyepieces, the west arc (associated with 52 Cygni) is the brightest part, with the center wedge difficult. With NV, the western arc is bright, but the eastern arc is noticeably brighter. The central wedge is easily visible and extensive in NV and about as bright the western arc.

 

2) I also had some high hopes for the M11 region and the dark nebula in the area. It was a nice view, but not dramatic like areas of Cygnus or Sagitarius.

 

3) I gotta get on that filter wheel ... 



#9 Antares89

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Posted 16 June 2017 - 10:18 AM

Tons of great info here. Thanks so much.

So it seems the goal of the filters is to filter out light pollution. Since the narrow band filters do the best job, why would you even need a long pass filter?

Is it because the narrow band would filter out the light pollution but also 'filter out' other non-nebula DSOs like galaxies, globulars, etc?


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#10 Antares89

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Posted 16 June 2017 - 10:19 AM

Are the narrow band h-alpha filters used exclusively for nebula and the long pass used for everything else?

Still trying to wrap my mind around why both are needed.


Sent from my iPhone using Tapatalk

Here is a lengthy thread on filtering night vision devices. Filter candidates and why certain filtering is used

https://www.cloudyni...ter-candidates/

Excellent! Thanks!

#11 Jeff Morgan

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Posted 16 June 2017 - 12:07 PM

Is it because the narrow band would filter out the light pollution but also 'filter out' other non-nebula DSOs like galaxies, globulars, etc?
 

 

Reverse your thinking.

 

It is not so much filtering out non-nebula (which are often continuous spectrum emitters). It's filtering things IN.

 

For nebula there is no need to let any (or much) more of the spectrum in. With one exception - sometimes having the context of background is pleasing - a personal taste. Heavy filtering is like the Neutron Bomb - kills the star fields, leaves the nebula standing.

 

There is a reason we all own at least one long-pass ...


Edited by Jeff Morgan, 16 June 2017 - 12:09 PM.


#12 Antares89

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Posted 16 June 2017 - 05:54 PM

Is it because the narrow band would filter out the light pollution but also 'filter out' other non-nebula DSOs like galaxies, globulars, etc?


Reverse your thinking.

It is not so much filtering out non-nebula (which are often continuous spectrum emitters). It's filtering things IN.

For nebula there is no need to let any (or much) more of the spectrum in. With one exception - sometimes having the context of background is pleasing - a personal taste. Heavy filtering is like the Neutron Bomb - kills the star fields, leaves the nebula standing.

There is a reason we all own at least one long-pass ...

So with the long pass you want to filter out just enough light pollution without completely killing the stars, clusters, and galaxies like would be done with a narrow band h-alpha filter?

#13 Jeff Morgan

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Posted 16 June 2017 - 07:06 PM

So with the long pass you want to filter out just enough light pollution without completely killing the stars, clusters, and galaxies like would be done with a narrow band h-alpha filter?

 

 

Thats it.

 

Not too much consequence sacrificing colors shorter than red. And as a happy coincidence the intensifier performance starts tailing off there anyway.

 

I have heard some observing reports from really dark skies (west Texas?) where one can dispense with filters entirely for general viewing, haven't had a chance to try that myself.



#14 pwang99

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Posted 16 June 2017 - 07:29 PM

I have heard some observing reports from really dark skies (west Texas?) where one can dispense with filters entirely for general viewing, haven't had a chance to try that myself.

Yep, under really dark skies, you can have a lot of fun unfiltered.  But even under those conditions, narrowband H-alpha brings out an entirely different contrast profile for nebula.  It's kind of the same result as with M42 under non-dark skies: You can see it with NV without using any filters, but there is a LOT more contrast and a different visual profile under 7nm, 12nm, and 35nm bandwidths.



#15 Antares89

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Posted 17 June 2017 - 10:03 AM

My observing sites range from around 20.5 - 21.6 SQM-L. Would a good starting point be a 12 nm h-alpha and a 610 nm long pass?


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#16 pwang99

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Posted 17 June 2017 - 11:52 AM

I don't think you'd even need the 610 at that point...?

#17 Antares89

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Posted 17 June 2017 - 01:16 PM

I don't think you'd even need the 610 at that point...?


Are you saying the 610 isn't needed with respect to the amount of light pollution?

#18 Eddgie

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Posted 17 June 2017 - 08:45 PM

Yeah, if your sky is that dark, you may not find much benefit in the 610nm.  

 

A lot of times, even in the city, I run unfiltered expect when using ENVIS or 3x.  The slower the scope, the less I think long pass filters help.

 

In fact, I think for galaxies,  at f/4.9 in my 12" dob, I struggle to see any improvement with 610nm and the 680nm actually hurts galaxies I think.

 

But in dark skies, I run pretty much wide open for general observing and 12nm for nebula.  My scopes are pretty fast though.



#19 Antares89

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Posted 18 June 2017 - 09:24 AM

Yeah, if your sky is that dark, you may not find much benefit in the 610nm.

A lot of times, even in the city, I run unfiltered expect when using ENVIS or 3x. The slower the scope, the less I think long pass filters help.

In fact, I think for galaxies, at f/4.9 in my 12" dob, I struggle to see any improvement with 610nm and the 680nm actually hurts galaxies I think.

But in dark skies, I run pretty much wide open for general observing and 12nm for nebula. My scopes are pretty fast though.


Doh! It would probably be helpful if I offered some information about my observing gear/goals. I should have done this at the beginning. I have a Zhumell Z10 dobsonian that I'll be using as well as general unmagnified 1x views. Eventually, I'd like to get set up to enjoy some higher low power views like 3x, 5x etc.

So right now, the plan is to go 12 nm h-alpha for 1x ENVIS and Z10. It sounds like a long pass isn't going to be necessary at least for the Z10. What about for 1x with the ENVIS?

#20 Jeff Morgan

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Posted 18 June 2017 - 09:48 AM

So right now, the plan is to go 12 nm h-alpha for 1x ENVIS and Z10. It sounds like a long pass isn't going to be necessary at least for the Z10. What about for 1x with the ENVIS?

 

 

The Mod 3 travels very well, so having a long pass filter gives you flexibility for other observing locations.

 

The long pass filters are fairly inexpensive. I'd say buy it. 640 is a good all-around choice.


Edited by Jeff Morgan, 18 June 2017 - 09:48 AM.


#21 pwang99

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Posted 18 June 2017 - 10:25 AM

Agree with Jeff. Long pass helps low power views of milky way and everything else. When I was observing at the dam a couple of nights ago, I used it in scopes whenever I wasn't using narrowband, to clean up light pollution and skyglow.

#22 Antares89

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Posted 18 June 2017 - 01:19 PM

So right now, the plan is to go 12 nm h-alpha for 1x ENVIS and Z10. It sounds like a long pass isn't going to be necessary at least for the Z10. What about for 1x with the ENVIS?


The Mod 3 travels very well, so having a long pass filter gives you flexibility for other observing locations.

The long pass filters are fairly inexpensive. I'd say buy it. 640 is a good all-around choice.

So far, I've picked the astronomik 12 nm h-alpha as my h-alpha filter.

I'm looking at the lumicon night sky h-alpha for my 640 nm long pass filter.

Is there another 640 nm long pass I should consider?

#23 Starman81

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Posted 18 June 2017 - 06:30 PM

 

 

So right now, the plan is to go 12 nm h-alpha for 1x ENVIS and Z10. It sounds like a long pass isn't going to be necessary at least for the Z10. What about for 1x with the ENVIS?


The Mod 3 travels very well, so having a long pass filter gives you flexibility for other observing locations.

The long pass filters are fairly inexpensive. I'd say buy it. 640 is a good all-around choice.

So far, I've picked the astronomik 12 nm h-alpha as my h-alpha filter.

I'm looking at the lumicon night sky h-alpha for my 640 nm long pass filter.

Is there another 640 nm long pass I should consider?

 

 

There is another that was being discussed recently, the Astronomik UHC Filter. Along with being a 640nm longpass, it also allows H-beta and OIII, and I have some recollection of reading that it might be good choice for cometary observation (?).

 

But I think the Lumicon one you mentioned will be a fine choice and more economical. 



#24 Antares89

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Posted 18 June 2017 - 08:41 PM

It's official. I have ordered everything I need (I think) to start observing with NV.

I went with the astronomik 12 nm h-alpha and lumicon night sky h-alpha.

Now comes the hard part - waiting for it all to get here :)

I'd like to offer a HUGE thank you to everyone who patiently provided insight, guidance, and direction. I would have been clueless without the help from this forum.

Thanks again!


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#25 AZBenny

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Posted 18 September 2017 - 01:07 PM

Did you ever get your Lumicon night sky H-alpha filter?  I've been trying to buy one, but no one seems to have them in stock and Lumicon isn't promising them until some undisclosed time in 2018.




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