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H-alpha Filter Recommendation for SLR and scope use

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#1 bobo99

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Posted 01 September 2021 - 12:39 PM

I just recently picked up a 2600 FOM OVNI-M. In addition to this I've got a pvs14 with a FOM of ~1900.

I currently have:

1.25" - 7nm Baader H-alpha
1.25" 12 nm Astronomik - H-alpha.
1.25" 685 longpass
2" 685 long pass

Using this with an 8" f/5 scope, and a 80mm f5 scope. Also have a Cosmicar 72mm lens. Have the 55mm televue, and am trying to find the 67mm converter.

1) I am looking for recommendations on an adapter that will let me use the 1.25" filters with c-mount lenses (hopefully without having to unmount the filters from their housing)

2) Also have been eyeing the 2" 3.5nm Baader h-alpha filters.If I were to get the baader, do I need to version designed for fast scopes down to f1.8 (given the focal reducation of afocal), or do I just consider teh f/5 nature of the scope?

3)Understand the Chroma filters are highly sought after, but a bit steep in price. Which 2, 2" halpha filters would you recommend for halpha? 3.5nm and 5nm?

Thanks!

Edited by bobo99, 01 September 2021 - 11:24 PM.


#2 GeezerGazer

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Posted 01 September 2021 - 09:56 PM

Bobo,

You have a fine collection of gear, but you will find there are limitations to all systems.  To answer your questions: 

 

1.  1.25" filters are typically used on the front of small objectives like the Envis lens; adapters are made for that purpose for Envis lenses.  If you have a small 1x objective, you need to determine the filter thread size at the front of the objective.  Then search for standard camera adapters that can be used to connect the filter to the objective lens.  This can involve more than one adapter.   It would help to know what 1x lens you are using.

 

 For objectives having a larger lens like the Cosmicar 75mm, typically 2" filters are applied to the front of the lens.  Attaching a 1.25" filter to the front of a larger objective lens will result in severe vignetting.  There is no adapter that allows a 1.25" filter to be used behind a C-mount lens.  The only way to use a filter behind a C-mount lens is to use an unmounted filter of 24mm diameter inside the C-mount opening on your Ovni-M.

 

Since your Ovni-M can be used in prime focus, you can use a 1.25" nose attached to the Ovni-M housing (in place of the 1x lens) and attach filters to that nose for use in your telescopes.  

 

2.  In afocal, since you have a TV 55, a 2" filter screws onto the bottom of the eyepiece.  This means that the light cone is coming to it from your f:5 system.  The focal reduction between the telescope eyepiece and the 1x lens occurs after the filter, thus the filter is working in an f:5 system.  You do not need filters made for a very fast optical system.  

 

3.  Yes, Chroma is very expensive.  I have owned many H-a filters made by each of the filter makers and did comparisons between them when used in prime focus with my Mod 3C.  I found no difference between results using an 8nm Chroma compared to my 7nm Optolong.  I can see no difference between H-a filters separated by 1nm.  Even when comparing differences between a 5nm and 7nm filter (2nm of difference) the visual impact is very subtle.   If you are primarily a visual observer, a 6-7nm H-a filter is very useful.  A 3nm or 3.5nm may be a better choice for use with an afocal system.  But there are tradeoffs with more scintillation and fewer stars seen.  A narrower 3-3.5nm also suffers more band shift than wider pass band filters.  

 

I currently use a 7nm Optolong and a 3.5nm Antlia filter.  I am satisfied with their performance.  But I use my NVD in prime focus and most of my filter use is for NV Phonetography, using my iPhone.  You should get opinions from others if you intend to use the 55/67mm eyepiece in afocal.  I have tried many afocal eyepieces and consider the TV 55/67 the best, but I have sold them all because I prefer using my NVD in prime focus.  This is a matter of personal preference.  

 

If you are using a Single Lens Reflex camera to take photos with NV, you will probably want to use your NVD in a prime focus system.  The following is one page from the BEST of NV thread found near the top of the forum:

https://www.cloudyni...nv-photography/

 

Within the BEST of NV, there is more information concerning filters, and differences. between prime focus as compared to afocal use of your NVD.  The BEST of NV is an index.  Click on any of the topics to find a list of threads with information about the selected topic.  Wishing you all the best.

Ray


Edited by GeezerGazer, 01 September 2021 - 10:24 PM.


#3 a__l

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Posted 02 September 2021 - 05:00 AM

Bobo,

I have significantly more telescopes and lenses. On all telescopes I can use afocal TV 67 (several lenses, including those from the PVS-14) or prime focus (with various coma correctors).
In fact, for all these devices, I use one 2" 7 nm H-Alfa. In my opinion, this is quite sufficient.
I have a 685 nm Baader, but I don't see any advantage of using it NV without a filter in my environment. Therefore, it is in the box without moving.


Edited by a__l, 02 September 2021 - 05:07 AM.

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#4 bobo99

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Posted 02 September 2021 - 11:58 AM

Bobo,

You have a fine collection of gear, but you will find there are limitations to all systems.  To answer your questions: 

 

1.  1.25" filters are typically used on the front of small objectives like the Envis lens; adapters are made for that purpose for Envis lenses.  If you have a small 1x objective, you need to determine the filter thread size at the front of the objective.  Then search for standard camera adapters that can be used to connect the filter to the objective lens.  This can involve more than one adapter.   It would help to know what 1x lens you are using.

 

 For objectives having a larger lens like the Cosmicar 75mm, typically 2" filters are applied to the front of the lens.  Attaching a 1.25" filter to the front of a larger objective lens will result in severe vignetting.  There is no adapter that allows a 1.25" filter to be used behind a C-mount lens.  The only way to use a filter behind a C-mount lens is to use an unmounted filter of 24mm diameter inside the C-mount opening on your Ovni-M.

 

Since your Ovni-M can be used in prime focus, you can use a 1.25" nose attached to the Ovni-M housing (in place of the 1x lens) and attach filters to that nose for use in your telescopes.  

 

2.  In afocal, since you have a TV 55, a 2" filter screws onto the bottom of the eyepiece.  This means that the light cone is coming to it from your f:5 system.  The focal reduction between the telescope eyepiece and the 1x lens occurs after the filter, thus the filter is working in an f:5 system.  You do not need filters made for a very fast optical system.  

 

3.  Yes, Chroma is very expensive.  I have owned many H-a filters made by each of the filter makers and did comparisons between them when used in prime focus with my Mod 3C.  I found no difference between results using an 8nm Chroma compared to my 7nm Optolong.  I can see no difference between H-a filters separated by 1nm.  Even when comparing differences between a 5nm and 7nm filter (2nm of difference) the visual impact is very subtle.   If you are primarily a visual observer, a 6-7nm H-a filter is very useful.  A 3nm or 3.5nm may be a better choice for use with an afocal system.  But there are tradeoffs with more scintillation and fewer stars seen.  A narrower 3-3.5nm also suffers more band shift than wider pass band filters.  

 

I currently use a 7nm Optolong and a 3.5nm Antlia filter.  I am satisfied with their performance.  But I use my NVD in prime focus and most of my filter use is for NV Phonetography, using my iPhone.  You should get opinions from others if you intend to use the 55/67mm eyepiece in afocal.  I have tried many afocal eyepieces and consider the TV 55/67 the best, but I have sold them all because I prefer using my NVD in prime focus.  This is a matter of personal preference.  

 

If you are using a Single Lens Reflex camera to take photos with NV, you will probably want to use your NVD in a prime focus system.  The following is one page from the BEST of NV thread found near the top of the forum:

https://www.cloudyni...nv-photography/

 

Within the BEST of NV, there is more information concerning filters, and differences. between prime focus as compared to afocal use of your NVD.  The BEST of NV is an index.  Click on any of the topics to find a list of threads with information about the selected topic.  Wishing you all the best.

Ray

Thanks for the recommendations and links! The 1x lens I am using is the one that came with the OVNI.

It looks like the easiest way is to umount the 1.25" filter from the housing and slip it between the c-mount lens and the OVNI. Not idea, but it's a solution.

 

https://www.cloudyni...lenses-filters/

 

Bobo,

I have significantly more telescopes and lenses. On all telescopes I can use afocal TV 67 (several lenses, including those from the PVS-14) or prime focus (with various coma correctors).
In fact, for all these devices, I use one 2" 7 nm H-Alfa. In my opinion, this is quite sufficient.
I have a 685 nm Baader, but I don't see any advantage of using it NV without a filter in my environment. Therefore, it is in the box without moving.

@a__l, depending on which tube specs you have, you've never considered trying a more narrow bandpass filter ? 5nm? 3nm?
 



#5 GeezerGazer

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Posted 02 September 2021 - 12:52 PM

Bobo,

Your title here indicates that you intend to use your SLR camera with NV.  You will find that the stack of lenses in afocal, with the TV 55/67, the NVD and then the SLR with its own lens, is probably too long and heavy for most focusers, not to mention the balance issues that will arise, whether or not you use a diagonal.

 

I recommend you try it in prime focus, using a 2" nose adapter with 2" filter attached to your NVD and your camera with lens attached to the NVD ocular/eyepiece.  This reduces both the weight and length of the stack in your focuser.  In addition, without a special relay lens between the camera and NVD, distortions may occur in your images, because the camera lens will be looking through the NVD eyepiece.  Using a special relay lens eliminates both the NVD eyepiece and the camera lens from the stack and improves the images as seen in photos by jdbastro.  

 

Finally, if your camera uses an auto-focus lens, focus might be inhibited by the weight of the camera.  This was true for me when I attempted using a Fujifilm X-T30 and X-T4 with any auto-focus lens.  The filter threads at the front of the auto-focus lens were designed to hold the minimal weight of a filter, not the significant weight of the camera, so the auto focus motors were strained beyond their limits and would not focus.  If you have a manual focus camera lens, that would be a better choice.  

Clear Skies.



#6 Kstevens

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Posted 02 September 2021 - 04:17 PM


Finally, if your camera uses an auto-focus lens, focus might be inhibited by the weight of the camera.  This was true for me when I attempted using a Fujifilm X-T30 and X-T4 with any auto-focus lens.  The filter threads at the front of the auto-focus lens were designed to hold the minimal weight of a filter, not the significant weight of the camera, so the auto focus motors were strained beyond their limits and would not focus.  If you have a manual focus camera lens, that would be a better choice.  

Clear Skies.

I just recently picked up a Fuji x-e4 mirrorless that doesn't have the weight and overhead of IBIS in the X-T30/T4.  I have been using a Viltrox 23mm 1.4 autofocus lens with 52mm step-down rings and don't seem to be having any problems as of yet with the internal lens focusing servos bogging down when supporting the weight of the camera when using the filter rings.  However, I am still on a learning curve with this new camera.


Edited by Kstevens, 02 September 2021 - 04:18 PM.

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#7 a__l

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Posted 02 September 2021 - 08:41 PM

@a__l, depending on which tube specs you have, you've never considered trying a more narrow bandpass filter ? 5nm? 3nm?

 

I've seen a lot of photos on CN with different filters. I have observed at almost all the h-alfa that Stellarium shows for the times of the year in which I looked. Main telescope 18" f/4. Only a dark site (or close, I don't have a background meter). I don't think the price of 2" 3 nm is justified for those minor changes that will be due to the replacement of a narrower filter. In addition, the stellar environment is additionally suppressed and additional noise appears, which I do not like.


Edited by a__l, 02 September 2021 - 08:50 PM.


#8 GOLGO13

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Posted 02 September 2021 - 09:19 PM

Bobo,

I have significantly more telescopes and lenses. On all telescopes I can use afocal TV 67 (several lenses, including those from the PVS-14) or prime focus (with various coma correctors).
In fact, for all these devices, I use one 2" 7 nm H-Alfa. In my opinion, this is quite sufficient.
I have a 685 nm Baader, but I don't see any advantage of using it NV without a filter in my environment. Therefore, it is in the box without moving.

I think this is because you are in a dark sky. We need to remember we have people in very different situations. In my bortle 6 sky the 685 helps quite a bit. It greatly darkens the background sky compared to unfiltered.

 

I remember Edggie saying you would use different filters in different light pollution situations. In heavy light pollution the 685nm. In moderate the 642. In dark skies 610 or unfiltered.

 

I find the 685nm helps the most at low powers but also in the telescope. Just was testing it in the 10 inch dob with the 67mm setup. It was quite helpful. I wouldn't say it's 100 percent necessary but it's a more pleasing view. Maybe a 30-40 percent improvement.


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