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Experience with 3.5nm H-Alpha

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#26 Gavster

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Posted 18 June 2020 - 11:27 PM

Last night I made sure I knew where I was looking and definitely could not see sh2-27 with my 7nm HA on my 10 F3 in my light pollution.  I have ordered the 3.5 maybe it will help.  I'm guessing I have too much LP.

Dale, sh2-27 is huge, about 10 degrees across, so I think the fov of your 10 f3 will be far too small. Looking at the images above I think it’s best to search for it with just your monoculars at 1x and 40 degree fov.



#27 Dale Eason

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Posted 19 June 2020 - 12:48 AM

Dale, sh2-27 is huge, about 10 degrees across, so I think the fov of your 10 f3 will be far too small. Looking at the images above I think it’s best to search for it with just your monoculars at 1x and 40 degree fov.

Yes I did that too with no luck.  



#28 careysub

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Posted 21 June 2020 - 11:17 AM

Just got the Antlia 3.5nm 1.25" filter and tried it out on the bright nebulas in Sagittarius (and Serpens Cauda) around midnight.

 

I am up against the San Bernardino mountains, so my southern exposure looks out across the urbanized valley with my worst light pollution.

 

I was using my camera lens line up with focal lengths from 25mm to 500mm. Of the collection of lenses I have acquired, these are the ones I use for observing:

Tamron 2/3 25mm f/1.4
Canon Nifty Fifty 50mm f/1.8
Computar V5013 CCTV 50mm f/1.3 1" format
Pentax Super Takumar Thorium lens 50mm f/1.4
Canon EF 75-300mm f/4-5.6
Nikon Nikkor 180mm f/2.8 ED
Sigma APO  400mm f/5.6
Kalimar 500mm f/8 mirror lens

 

I ended up with a super-abundance of fast 50mm lenses but they are all good, and light, so I keep them all in use although there is not much difference in their views (minor advantage - I can put different filters on each, and swapping lenses is nicer than fiddling with filters in the dark). Only the Canon and the Pentax Thorium can use 1.25" filters.

 

The most versatile is the Canon 75-300mm which is f/4 at 75mm and f/5.6 at 300mm, excellent mechanically and quite light for a telephoto. It must have plastic aspheric lenses in it to be so light. In this application the weight tradeoff against optical perfection is absolutely worth it. The others provide either a brighter/wider view, or more magnification for close ups. But definitely I started with sweeping and zooming in and out with the Canon telephoto.

 

The nebula pairs M17 and M16 (Swan and Eagle nebulas) and M8 and M20 (Lagoon and Trifid nebulas) showed up very well in all of the lenses with the Antlia filter. Small but detectable in the 25mm. They made a nice quartet at 75mm f/4, and nice bright pairs in the Nikon 180mm. The best close ups were with the Sigma 400mm, which balanced scale and brightness.

 

I tried for NGC 6357, the Lobster Nebula, in Scorpius and it might have been barely detectable, but I am not sure, it was lost in the brightness and haze nearer the horizon.

 

I'll try the same viewing with some of my other filters tonight (I have 5nm, 7nm, 12nm and 35nm also).

 

I'll also try my luck with Sh2-27 using a 50mm lens. For a large dim object like that you need to have surrounding framing to perceive it (I have learned from viewing the Triangulum galaxy). So nothing longer than about 75mm I think.


Edited by careysub, 21 June 2020 - 04:06 PM.

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#29 careysub

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Posted 23 June 2020 - 09:46 AM

Tried again for Sh2-27 last night. I did it just after astronomical twilight, when Ophiuchis was farthest from the light dome of LA (the more stuff trends to the west, the brighter the sky gets). Seeing this large dim, diffuse object even with NV and the best filters still requires a not-too-bright, and more importantly, evenly illuminated sky.

 

For quite awhile I figured that I could not see it, and was afraid that any claim that I had was "averted imagination". But at last I think I was able to identify it. It helps a lot that it is centered on one of the stars defining the constellation, so if you center that star in the FOV you can carefully inspect for the edges. I found it using my F/1.8 50mm with the 3.5nm filter. Even though it fits in the FOV at 75mm, it is not adequate for viewing, you need more dark sky around the edges to perceive it.



#30 AllStarez

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Posted 23 June 2020 - 09:57 AM

Hello Carey

i have started a topic about those big mirror lenses. Since you have a Kalimar 500mm, please could you tell how it performs ? Thanks



#31 Dale Eason

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Posted 24 June 2020 - 12:22 AM

My antila 3.5 arrived yesterday to clouds.  So tonight.  I was out hand held with my Nikon 50 1.18 and Nikor 85 1.18.  I really liked it best on the 85mm.  That field of view was my favorit  After careful study of sh2-27 area I could see it.  But only by sweeping the lens over it and watching the center brighten around the star area.  It would not brighten over other places so I think I was see sh2-27. 

 

Next on Cygnus.  Boy does North America and the Veil pop out much better.  The background is much darker.  I compared it with my HA 7nm.  Nebulae seemed about 20 percent brighter.  There were a few whisp further North and away from Deneb that I had never noticed before.   The large Elephant trunk area was much brighter against the background.  I could see other smaller nebulae scattered further around the Elephant trunk. Perhaps sh2-129 and 1c1396  Several things that  show up on SkiSafari as nameless red blobs when HA Milky Way is turned on.  Pretty sure one was sh2-86 shown in "The Astrophotography Sky Atlas."

 

It is so amazing to see the Veil along with gamma cygni nebula all in the same field of view.  ..  

 b

So I'm verry happy with that filter addition to my kit.  What I don't like about it is the fancy but nearly useless but pretty lexan storage box that it comes in.  It is much larger than my other filter storage boxes and it's magnet lid keeps coming open.and falling off. Letting the filter fall out.  I cut a circle out of the padding so the filter would at least stay down inside the box.  I have to find a smaller one so it can live in my storage case with the others.

 

Dale


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#32 careysub

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Posted 24 June 2020 - 09:23 AM

 What I don't like about it is the fancy but nearly useless but pretty lexan storage box that it comes in. 

 

Dale

 

M procedure is to buy identical storage boxes for the 1.25" and 2" filters, then label them, with white medical tape and ultra-fine Sharpie.

 

That way all of the boxes open in exactly the same way, which is useful for storage in a small case, and important for fiddling with them at night in the dark. I got tired of having to negotiate different case designs in the dark.


Edited by careysub, 24 June 2020 - 01:18 PM.


#33 Mike Lockwood

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Posted 24 June 2020 - 10:32 AM

Agreed, Dale, the storage box is not useful.  Mine doesn't even stay closed on its own, so that makes it a bit dangerous.  It requires a rubber band to keep it closed.

 

I wish it had come in the same type of case as my other filters.



#34 a__l

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Posted 24 June 2020 - 06:25 PM

Dale, What lenses do you have? If it is a Nikon 50mm f/1.8G AF-S Nikkor (or similar), it has a filter diameter of 58 mm.

Specify what size of the 3.5 filter you used and where did you install it? If you move an object across a field, are there any changes in the image (other than vignetting)?



#35 Dale Eason

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Posted 24 June 2020 - 07:01 PM

Dale, What lenses do you have? If it is a Nikon 50mm f/1.8G AF-S Nikkor (or similar), it has a filter diameter of 58 mm.

Specify what size of the 3.5 filter you used and where did you install it? If you move an object across a field, are there any changes in the image (other than vignetting)?

I have a filter adapter from the Nikon lens to the 2 inch filter. I think the lenses take 55mm filter size.  All my filters are 2 inch.  The Nikon lenes are old and none are AF-S lenses. They are all manual focus.  Both the 50 and the 85  are 1.18f. as I stated in the OP.

 

Yes as I said the center brightens more when passing over a nebula than when not over one.  That is how I can see there is something there when the nebula is too dim to see otherwise.



#36 Dale Eason

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Posted 24 June 2020 - 07:03 PM

M procedure is to buy identical storage boxes for the 1.25" and 2" filters, then label them, with white medical tape and ultra-fine Sharpie.

 

That way all of the boxes open in exactly the same way, which is useful for storage in a small case, and important for fiddling with them at night in the dark. I got tired of having to negotiate different case designs in the dark.

That is a great idea.  Where do you get them?   You are right about the fumbling trying to open the various ones.  I have 5 different boxes at present.

 

I have been thinking about 3D printing some but then they will not have a hing.  I would like hinges so you don't have to keep track of he lid.


Edited by Dale Eason, 24 June 2020 - 07:05 PM.


#37 careysub

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Posted 24 June 2020 - 08:49 PM

That is a great idea.  Where do you get them?   You are right about the fumbling trying to open the various ones.  I have 5 different boxes at present.

 

I have been thinking about 3D printing some but then they will not have a hing.  I would like hinges so you don't have to keep track of he lid.

I use these:

https://agenaastro.c...25-filters.html




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