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Filter advice please

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#1 alexvh

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Posted 02 August 2021 - 03:21 PM

Hey guys,

My OVNI -B is coming soon....

 

The dealer has suggested two filters :

1.  h-alpha filter 7nm

2. Astronomik 642nm

 

I really enjoy galaxies. I have a 16'' f 4.5 dob and a 9.25'' SCT....

 

What do you guys think? Also - 2'' filter or 1.25''???

 

Many thanks

Alex



#2 PEterW

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Posted 02 August 2021 - 03:49 PM

Depends how you’re going to plug it all together, can you get away with only 1.25 or 2”. I’d pop a 685nm long pass in as they’re cheap and really help stars under light pollution.

Peter

#3 Mazerski

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Posted 02 August 2021 - 05:32 PM

The 610, 642 and 685nm IR filters block out excess light so the view you get has good contrast between sky and star stuff (open clusters, globulars and galaxies).

 

In high light pollution the 610 is not useful as it lets too much light in and all contrast is lost.

The Astronomik 642 allows some nebulosity and the Baader 685 knocks out most nebulosity with the darker background.

 

Example: the 642nm IR on M42 looks great - you see more stars than with the Ha filter and you still get a lot of nebulosity. In handheld mode with say a 135mm f/2.8 lens, the Milky Way clouds in the area of the Eagle down thru Lagoon look great (still with 642). The 685 and 642 IR are required for me.

 

It depends on how much light pollution you have.

 

Ha - I have light pollution and find the Astronomik 6nm is the one I use the most.



#4 ButterFly

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Posted 02 August 2021 - 07:03 PM

It really does depend on you skies.  Let us know more.

 

My yard is about Bortle 5 and my dark sites are fairly close by.  The Astronomik 642 and 6nm are great together.  Filters from the same company tend to be parfocal, so there isn't much focus shift when sliding back and forth.



#5 alexvh

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Posted 03 August 2021 - 06:02 AM

Thanks guys. I have moderate light pollution at home . But I travel to very dark skies often…

#6 alexvh

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Posted 03 August 2021 - 06:02 AM

What is the 7nm used for?

#7 AllStarez

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Posted 03 August 2021 - 06:08 AM

It is essential for nebulosity :)

with my Ovni M i really enjoy the 7, but also the 3/3.5nm for even more contrast (but less stars). I also have a 685 but barely use it at home, i prefer a 12nm astronomik


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#8 AllStarez

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Posted 03 August 2021 - 06:09 AM

Check this thread, you got it all :

https://www.cloudyni...s-used-with-nv/



#9 slavicek

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Posted 03 August 2021 - 10:33 PM

What is the 7nm used for?

Nebulas, nebulas, nebulas! I'd recommend you 5nm Ha filter. 3.5nm is too narrow and faint, 7nm is wider and not as sharp. 5nm gives me brightest and sharpest nebula views.



#10 M44

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Posted 04 August 2021 - 01:23 AM

Hey guys,

My OVNI -B is coming soon....

 

The dealer has suggested two filters :

1.  h-alpha filter 7nm

2. Astronomik 642nm

 

I really enjoy galaxies. I have a 16'' f 4.5 dob and a 9.25'' SCT....

 

What do you guys think? Also - 2'' filter or 1.25''???

 

Many thanks

Alex

The first filter should be Astrinomik 642nm. So you can start viewing Milkyway right away. 

The second one I suggest Astronomik 6nm h-alpha. 

 

I do have both 2" and 1.25" filters of the above two. 1.25" I use with PVS-14 at 1x and I use 2" filters with Televue 67mm plossl with any scope. 



#11 Gustoresto

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Posted 22 September 2021 - 05:34 PM

I can't seem to find how guys R attaching 1.25 filters to a pvs 14(?)     Is it a slip /friction fit in the objective housing??  Thx Gus



#12 Mazerski

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Posted 22 September 2021 - 06:47 PM

Gus,

 

Someone else can verify that the PVS14 objective has the same inside thread size as the c-mount ENVIS... if so, you need the thin ring adapter from RAF Camera:

 

https://rafcamera.co...s-to-astro-1-25

 

See photo

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#13 stnagy

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Posted 22 September 2021 - 07:52 PM

Yes, it's the same inside thread size for the PVS-14 objective and ENVIS lens. 



#14 a__l

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Posted 22 September 2021 - 10:22 PM

This is not USA or even EU smile.gif


Edited by a__l, 22 September 2021 - 10:24 PM.


#15 GOLGO13

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Posted 22 September 2021 - 10:28 PM

This is not USA or even EU smile.gif


They do a good job. I had no trouble ordering from them.

#16 Gustoresto

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Posted 23 September 2021 - 06:27 AM

They do a good job. I had no trouble ordering from them.

The "add to cart" button was greyed out. I'll try later.   THX 4 tip on adapter. Was hoping it could B this simple!     Gus



#17 Mort H

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Posted 23 September 2021 - 06:21 PM

Hi Alex,

 

I'm a recent OVNI-B owner, and I've already observed under both dark sky and light polluted conditions.  Not a ton of experience yet but I can relate a few things so far:

 

1)  I use a 2" filter wheel in all four OVNI-B modes (prime focus, afocal, camera lens, 1x hand-held), therefore with my OVNI-B setups I have not found a need for 1.25" filters.  I DO want the 2" filters, those are a must-have for me.  (I actually do have a couple 1.25" filters, but only because the 2" ones were out of stock and I was impatient to try them, I CAN use 1.25" filters in all but my afocal mode.)

 

2)  For nebulae you want a narrowband H-alpha filter.  I have 12nm, 8nm, 6.5nm, 5nm, 3.5nm.  Total overkill, but it's my money, I'm free to waste it however I please, haha!  I was interested to compare them, at least I've had that opportunity.  They are all good, phenomenal even!

In dark skies I like something around 6.5nm/8nm (if I was forced to pick a favorite...they are all good, it can be like splitting hairs at a dark sky site).

In light polluted skies, the 3.5nm is clearly my favorite (the others are still good).

Bottom line, one narrowband H-alpha filter is an absolute must-have.  And I would want two, to cover the bases (3.5nm and 6.5nm would be my choice).

 

3)  The 3.5nm I like for light-polluted skies is the Baader f/2 version.  I don't own the non-f/2 version, so I can't directly compare.  I can tell you I like the f/2 version, it's working well for me.

 

4)  For galaxies and such I have 610nm, 642nm, 685nm IR (long-pass) filters.

For dark sky I don't use any filter when galaxy-hunting.  But the filter wheel makes it easy to rotate in a filter any time I would want.  If I did, it would be the 610nm, but since I don't feel like I need any filter at all, I consider the 610nm to be the least useful filter really.

For light pollution, the 685nm will be most effective, at the cost of killing any nebulosity you encounter.  The 642nm can be a nice compromise when you want to include some nebulosity in your view.

Bottom line, for IR filters I would want both 642nm and 685nm, the 610nm is optional in my view.

 

So there's my two cents'...though I guess it doesn't really add much of anything to what the others have already said in their good comments...


Edited by Mort H, 24 September 2021 - 05:40 AM.

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#18 Mort H

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Posted 23 September 2021 - 06:35 PM

I will also say that some folks prefer 5nm to 3.5nm.  Though I'm far from the world's expert, I suspect there are many factors in play here:

 

- amount of light pollution.

- scope or NV mode (prime focus, afocal, camera lens, 1x).

- power.

- is the 3.5nm the f/2 version or non-f/2 version.

- your NV device (especially does it have a continuous manual gain control).

 

Certainly the amount of light pollution is a big factor.  I would prefer the 5nm myself with less light pollution, and I prefer the 3.5nm with more light pollution.

 

So it can depend on things that for you are not going to be the same as for me or somebody else.


Edited by Mort H, 24 September 2021 - 06:37 AM.

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#19 GeezerGazer

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Posted 25 September 2021 - 06:24 PM

I very much agree with Mort H.  There are many variables involved in filter selection... combined with personal preferences and tolerance levels.  

 

Selection of 1.25" or 2" is based on how you intend to use them.  In prime focus, you might be able to get away with 1.25", at least for a while.  But in afocal, you will find 2" a necessity.  I started with 1.25" filters, then started buying 2" filters and sold all of my 1.25".  I have used NV in prime and afocal, and definitely have a strong preference for prime focus.  But many NV users are limited to afocal, while some use both prime and afocal for the advantages each can provide.  After 5 yrs of using my Mod 3C, I have found no explicit need for afocal, so now I only use prime focus.  It's a journey and our paths are different because of equipment we choose, our sky conditions, our selection of NV targets, even our eyes and vision.  And you will find that there is a variety of ways to adapt your NVD for expanded use.

 

The recommendations your vendor has given are probably a good starting point based on his knowledge of the products.  I went through something similar to Mort H. who currently has a plethora of H-a filters.  At one time I had 3.5, 5, 6, 7, 8 & 12nm filters.  My experience was that one nm of difference was nearly impossible to distinguish.  And even 2nm of difference are quite subtle.  If you observe under fairly dark skies, buy a 7nm.  If you live in a light polluted suburb, buy the 6nm.  If you buy both of them, you will likely not see a difference between them.  Currently I own just two filters, a 7nm which I often use, and a 3.5 which I use occasionally, mainly to see very dim H-a.  But if I were observing in a white zone, the 3.5nm would get a lot more use.  

 

Your OVNI-B is different than my Mod 3C or the OVNI-M, in that it splits the signal for two eyed viewing.  Because of this difference, you will probably be quite happy with a 6.5nm as Mort H recommends, 7nm as your vendor recommends, or even an 8nm filter.  The 6-7nm is a sweet spot for most H-a use under a variety of conditions.  Re-read what Mort H wrote because he is using your OVNI-B.  waytogo.gif

 

For additional information concerning filters used with NV, you should click on the Filters section in the BEST of NV thread, found here:  https://www.cloudyni...842-best-of-nv/

 

Good luck and have lots of fun with your OVNI-B.  smile.gif


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#20 GeezerGazer

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Posted 25 September 2021 - 06:39 PM

This old thread is packed with information about filters, specifically used with PVS-7 goggles which are similar to your OVNI-B.  This thread is in the BEST of NV, and you might find it of particular interest:  

https://www.cloudyni...tes/?hl= filter


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