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alanjgreen

28-29 Nov-Borg 107FL & 20" Dob team up to tease out & map more faint nebula (Night Vision)

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Dates: 28th & 29th November 2019.
Scopes: 20” f3.6 Lukehurst Dob & Borg 107FL f5.6 (focal length 600mm).
Night Vision: PVS-14 with Photonis 4g INTENS.
Eyepieces: Plossl 55mm (Dob f2 x38, Borg f2.6 x11). Filters: Chroma 5nm Ha filter.

 

Introduction.
Last time outside was the 8th November and I had a great night with the Borg 107FL and Night Vision identifying many new “areas of interest”.
See my report and sketches here: 

 


But then we have had three weeks of clouds!


Anyway, last weekend we got three clear(ish) nights outside so I decided to use the Borg 107FL as a spotting scope to identify further areas to then check out with the Big Dob. It seems that it is easy to look straight through faint nebula and not see the bigger picture with the greater magnification proving a disadvantage with the dobsonian.


This report will cover a mix of two sessions (Night one – Borg 107FL) and (Night Two – 20” dobsonian). I will detail my wide field observations and sketch and then follow up with the detailed greater magnification/aperture view of the exact same area accompanied by a photo from Sky Safari with locations marked.

 

Area of interest 1 – Heart & Soul nebula region.
Starting with my wide field observations, here is a sketch I made of this area of the sky.

heart.jpg.966079ee1ff3c7b36069799b70d3ccb9.jpg

The big thing I found was a rectangular structure that is attached to the side of the Heart nebula. It had some brighter areas within it and a smaller parallel line inside it. There was an obvious “loop” coming from the “mole head” part of the Heart and beyond the loop I saw a small patch and a longer snake patch too. I have marked some of the smaller Sharpless (sh) that I saw on the sketch as well.
After quite a long time examining the Heart, I slewed to the Soul (foetus) next door, where some nice intricate interior detail and brighter mouth and chin areas were observed together with a couple of small Sharpless just of the sides were also noted.


Now, onto the Dob observations from the following night. Here is a Sky Safari view…

 heart1.jpg.fd8de11b4b910365019031546ab7df43.jpg

GSC 4051-1604 – large faintish patch fills fov. Stars have cleared black areas inside. Double star in a black patch stands out.
TYC 4054-1657-1 - marks the right angled corner of faint box extension to heart nebula.
HD 15022 – Triangular shaped patch fills fov. Some small black areas inside.
GSC 4046-0016 – a “line” section. Two brighter patches stand-out.
TYC 4050-2042-1 – return section of “loop”. Exiting & returning to the “mole head”.
TYC 4056-1055-1 – Long curving corner section of faint nebula lane coming from the Heart.
TYC 4051-2885-1 – Junction of two curved loops (curved X shape), brighter central area with black patch & stars inside.
TYC 4059-0328-1 – very faint large section of reflection neb. Plenty of black helps the nebula to stand out.
GSC 4058-0834 – “house” shaped star cluster set in a large nebula patch.
TYC 4052-1055-1 – small nebula patch (part of a long thick curvy lane that winds along here).
SAO 012401 – very tiny, bright nebula patch.
HD 20798 – small circular patch next to a star (the last in a line of stars). Black circular area too.
TYC 4049-0064-1 – double lane of nebula. One side brighter with some brighter patches too.

 

Area of interest 2 – Flaming Star region.
It was time to revisit the Flaming star region. I familiarized myself with a look at my sketch from last time out then started to note and sketch further nebula details seen at the eyepiece. I could see a sketch what looked like loops of nebula coming from the main bright blobs (sketched as dashed lines). There was a clear right angled corner piece above IC417. I then hit the multi-patched area of sh2-233/235 which looked great. On the other side there was a sweeping curved section that ended in a double patch (maybe sh2-227). I could see a small bright blob below that (guessed as NGC1778 but may be something else sh2-228?). Finally, I noted a small patch hanging off the side of the Flaming star itself. Here is my sketch from 28th November.
fs.jpg.dedf1d957d721af00c54f5692e6aee46.jpg


Now, onto my 20” dob observations from the following night…


TYC 2393-1581-1 – oblong patch to LHS of tail of Flaming star.
HD 243596 – patch between IC410 & Spider.
HD 36834 – thick lane of nebula brighter section connects to HD35345.
TYC2415-0413-1 – large patch connected to HD35345.
HD 36212 – large nebula patch with many stars.
SAO 058274 – large nebula patch under the pinwheel cluster.

More work needed here...
fs1.jpg.3a6962f09b1066a677b19c6da64d2384.jpg

 

 

Area of interest 3 – Fox Fur & Rosette region.
Next, the Fox Fur & Rosette, which is proving to be a great area to explore with a small wide field scope. The Fox Fur is rising rapidly up the list of “great nebulas of the night sky”! Once again, I started by checking my sketch from last time out and then worked to see and sketch further details… Here is what I ended with…


fox.jpg.836865225ec9773c6dacb7a64faa5ecf.jpg


It’s really hard to find a decent image of this area wide field. Everyone seems obsessed capturing the tiny Cone and misses out on the vast lush areas greatness! Search for “Fox Fur Nebula Rosette” and you can find some – it’s well worth it. 

This time I noted some of the black detail inside the thick “comma” shape and also a smaller detached patch above.

I cannot reach this region from my shed so there is no dob confirmation text.

 

Area of interest 4 – IC434 & Horsehead region.
Onto the expansive region that contains IC434 and the horsehead. Last time out I noted a long extension to the left hand side and down parallel to IC434. This time I was lucky enough to see even more. IC434 was a complete rectangle of nebula surrounding Sigma Orionis in its centre. With more time I began to notice a separate nebula lane running up the left side of this. It was fainter and ended with a curvy section around Alnilam at the top. The bottom end was right angled as shown below in my sketch…

 434.jpg.a6c39e6c8a6f044767e7fd8505d9c52e.jpg

I cannot reach this region from my shed so there is no dob confirmation text.

 orion.jpg.5fd012b7b055b67bde9c2d97a8dbbf71.jpg

 

Finish with the search for some Comets.
I was out again on the 30th November where I managed a couple of hours observing before fog descended. The highlight was that I bagged four comets as follows:
Equipment: 20” dob, 27mm Panoptic (x77 magnification), PVS-14 Night Vision.


C/260P McNaught – A small fuzzy blob next to a star. No core to speak of.
C/114P Wiseman-Skiff – (found WEST of where Sky Safari says it is so beware!) It appeared brighter than C/260P. A small fuzzy patch with wide brighter core (but not a bright “dot” core).
C/2018 N2 (ASSASN) – Easy. Bright dot core and halo surrounds. Next to 2 stars LHS.
C/2017 T2 (PANSTARRS) – Very Easy. Bright dot core and dust halo. Small tail heads NW.

 

 

Epilogue

The above approach proved a success, identifying potential areas for detailed searching with the dob in advance really helped me to focus where I looked with the dob and helped me to linger longer at a location waiting for nebula to pop out at me.

I will be relocating the dob to the back of the shed for the next new moon so Orion and the Rosette can be reached. Then I can firm up some more exact locations thanks to the push-to connection to Sky Safari that the dob has (via a Nexus wifi unit).

 

Clear Skies,

Alan

Edited by alanjgreen

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Alan, wonderful work. I am enjoying the fact that you are exploring the area of interest, teasing out details, checking against images, comparing scopes - what I call observation astronomy. It really enables one to learn, see more.......I have just been doing the same with my interest in lunar sketching. 

Am I right in thinking that NV is particularly suited to nebulae observing rather than small faint galaxies which I do with my C11/ultrastar set up?

A great read, capturing the excitement of observing such fascinating objects.

Mike

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51 minutes ago, Mike JW said:

Alan, wonderful work. I am enjoying the fact that you are exploring the area of interest, teasing out details, checking against images, comparing scopes - what I call observation astronomy. It really enables one to learn, see more.......I have just been doing the same with my interest in lunar sketching. 

Am I right in thinking that NV is particularly suited to nebulae observing rather than small faint galaxies which I do with my C11/ultrastar set up?

A great read, capturing the excitement of observing such fascinating objects.

Mike

NV is made for infra red part of the spectrum and Ha (hydrogen alpha) is red. Therefore any source in the night sky that is strong in Ha will appear easily with night vision.

The narrowband Ha filter allows me to filter everything else away and then nebula just pop out into view. What I really like is seeing the jet black hydrogen sections which really stand out much better than with no NV.

I did an experiment to observe M33 reported here, where you can see my sketch showing how the areas on new star birth really pop out with the filter.

For general galaxy viewing, no filter or a UHC filter works well (to get rid of the moon light for example). It is the tiny galaxies where all the light from the galaxy is concentrated in a small location that are easiest to see! Hickson groups are easy for instance.

The larger galaxies where the red Ha light is less concentrated are not so good but with the right magnification (and fast focal ratio) arms can be readily observed in many galaxies ( I have seen arms in 68 galaxies so far). Leo and Virgo are superb with NV, tiny galaxy patches everywhere.

With the 20”, I can now observe PGC and UGC galaxies easily.

Supernovas to mag 17 are now achievable too.

Night Vision is not a one trick pony but you need a scope with long focal length, Dob or SCT to get decent magnification from a 55mm plossl.

You need the 55mm plossl to get the effective focal ratio of your system doubled and get more light (exit pupil) into the NV unit.

Alan

Edited by alanjgreen

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    • By alanjgreen
      Date: Friday 8th November 2019. 0300-0600am
      Scope: Borg 107FL f5.6 (focal length 600mm).
      Night Vision: PVS-14 with Photonis 4g INTENS.
      Eyepieces: Plossl 55mm (f2.6 x11).
      Filters: Chroma 5nm Ha filter.
      Moon: 0%
       
      Introduction.
      It’s now been over a week since the “never ending” clear skies went away. With the full moon approaching I saw an opportunity to maybe get out for a few early morning hours after the moon had set.
      The skies were clearing when I went to bed and the Devils Orb was already giving the appearance of daylight outside.
      I had a short restless sleep with the occasional peek to see if the moon was still lighting the edges of my bedroom curtains. Once I was satisfied that it had gone and having taken a few minutes to “motivate myself”, I slipped out from the warm bed and headed downstairs to get dressed.
      It was pretty windy outside which meant the roll-off shed would not be used tonight so I prepared the Borg107 for a trip outside onto the patio. It took me 20 minutes to get ready before I relayed my kit outside.
      I quickly performed a 2-star alignment for the Skywatcher AZGTi mount and headed to M45 to test it out…  The Pleiades were all bright and sparkly in my fov set against a lovely black background (“looks good” I thought to myself).
      I had no real plan for the session, so I decided to look at the brightest areas of Orion plus some of the larger Sharpless from my “Best of Sharpless”.
      I added the Night Vision PVS-14 to the TeleVue 55mm Plossl and added the Chroma 5nm Ha narrowband filter to the front of my 2” diagonal.
       
      NGC2244/Rosette.
      Where else to start but my favourite nebula – The Rosette! It appeared bright and mid-sized (at x11 magnification). Thin bright lanes seemed to trace out the “petals of a flower”. Multi-toned fainter nebula filled in the gaps, then with the dark black central hole and cluster to complete the view. I lingered a while before slewing down and into three spread-out nebula patches (sh2-280, 282 & 284). They are all different which makes them more appealing. The first is a circular patch with two small dark circular shapes inside (sh2-280), then we have an oblong shaped patch (sh2-282), finally on the other side of a bright star we arrive at the circular patch sh2-284.

       
      NGC2264/Cone/Fox-Fur nebula.
      Now for the first “surprise bonus” of the night. I centred on NGC2264 and when I looked in the eyepiece I found the fov filled with faint multi-textured nebula. I located the MINUTE Cone nebula, it was very tiny but a clear black triangle nevertheless! I traced the parent Fox Fur into what looked like a “comma” shape. This comma shape was sitting above a right angled long thick lane. Below this I found a mid-sized curved lane and followed this down and left to arrive back at the Rosette.
      I decided to make a sketch of the large area just covered as the individual segments were so clear to see (and you do the daftest things when only half awake!)
       

      I found the Xmas tree in the tail (of the comma) slightly brighter. I noted a dark lane running through the comma tail section.
       
      IC405 Flaming star/IC410/sh2-230
      I have had recent success with the sh2-230 undefined area around IC410/405 with the big dob. So it was time to see what the 4” aperture of the Borg could tease out of this region. This is a beautiful detailed large section that really comes out well under low x11 magnification. IC405 and IC410 are immediately obvious. The magnificence (intricate detail) of the upper head section is not so striking at this low magnification but you then notice that the Flame is larger than expected and in fact has an extra patch that seems to extend the tail section further out. IC410 sits by the side and has the appearance of “a mask”, I see two black eyes cutting into the small bright shape. Above IC410 there are two tiny patches (Spider and Fly) then above them I see a large faint circular patch (unknown). To the left of this and above the Flame is a double curved lane which has several brighter sections visible within it (sh2-230) which I have seen before. But my eye is drawn further left and up where there appears to be a huge circular edge (unknown).

       
      NGC1499 California.
      While looking at Sky Safari, I decide to see NGC1499 (another nebula where the big dob has been working hard recently). Wow, this area is great at low magnification. The “traditional” section of the California is the brightest and easily seen in its entirety but it’s the large extension section to the right (that must be at least the same length again!). Then while examining the tail and crown sections at the left end, I begin to notice a huge structure that seems to sit behind the California nebula. I sketch out what I can see. This background section is vertical where the California appears horizontal. It is faint and has curves under the California where it seems to meet a large faint patch (that has 6 bright stars inside), I add these to the sketch…

       
      IC2177 Seagull nebula.
      Looking for big and bright nebula, I choose to see the Seagull next… The traditional “head and shoulders” fills the fov. I slew around and trace out a large additional structure leaving the “top shoulder” and travelling right and then down to finish at an extended “foot” patch just above the Duck nebula. I sketch out the Seagull and then hunt around for any patches (I know there are plenty to small Sharpless around here). I find two small patches at the end of an extended “leg” section (I thought that one of these was Thor’s Helmet but after slewing to that later then I think I am wrong so I need to revisit and sort out what they are?)

       
      Sh2-240 Spagetti.
      I pick a large nebula from the best of Sharpless, sh2-240 next. It appears as a large circular faint shape. There is a central vertical zig-zag section and I see several hortizontal-ish black lanes travelling through the patch (as I get my eye in). There is definitely lots to see here and its deserving of its place in the “best of Sharpless”.
       
      M42/M43/NGC1973, Orion and the Running Man.
      Okay, I’ve waited long enough! I slew to NGC1973. The only thing you see at the eyepiece initially is M42 of course! It’s so bright and wonderfully detailed. At this low magnification it reminds me of a “bird in flight” with bended wings. The “fish head” is the brightest section but I am fond of the blackness that spews from the fish head and seems to spread out and around M43 next door, it is black as black can be. M43 has an intricate shape inside its almost complete circular patch, but I speed by to seek out the Running man. Tonight the bright patch is clear as day and as I look on a black shape within the bright patch comes and goes, it’s not a “pair of legs” but it’s a black patch within nevertheless.
       
      Flame/IC434/Horsehead.
      I slew directly up from M42 and a bright patch comes into view, over to the right a bit and there is IC434 bright and thick. The horsehead is tiny but clearly visible and having a decent shape tonight. However, I am completely drawn to the long nebula bend section to the left which runs down from the Flame too. I do not remember noticing this section before but it’s been a year since Orion was here and I cannot remember everything that I see!

      I now manually slew up from the Flame to find a thick horizontal nebula lane running across the full fov. I follow it right and then down and back under until I find myself back at the Orion nebula (M42). I guess this is Barnards Loop. I had earlier searched for it to the left of Alnitak (as that’s where it is with the dob but this “star diagonal” used in refractors regularly sends me the wrong way when I try to retrace the big dob steps!
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      NGC2174/Monkey’s head.
      Instead, I move onto the Monkeys Head. It appears small and bright but as usual I see “Mickey Mouse” with the refractor and star diagonal turning things around. I slew around and pick out two patches above, one is sh2-247 the other is unknown. I slew below and find the wonderful tiny triple nebula sh2-254,255 & 257 (another Best of Sharpless member).

       
      NGC2395 Medusa – A small shimmering crescent moon shape is observed.
      M1 Crab – A small shimmering patch. With time at the eyepiece I see a bright circle around the outside and the occasional jumping line details within but cannot hold the interior in my view.
      NGC2359 Thor – A small faintish semi-circle.
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      Sh2-265 – Picking another large Sharpless object, I headed for SAO 112667. I found a small bright patch (sh2-263) then above that a huge bright nebula that after slewing around, reminded me of a “walkie-talkie”. It had a pointed section at the upper LHS. And an interesting double lane at the lower sections.

       
      Sh2-260 – Next I picked sh2-260 (which I have only ever seen with the big dob). I slewed to SAO 112142 where I discovered a very large faint nebula shape. It was larger than the fov and seemed to appear as a “thin teardrop” shape. I cannot find any images of this so at the moment it is unknown to me.
       
      Epilogue.
      I noticed the sky brightening from around 0550hrs so I headed for a last look at the Rosette and Flaming Star regions before deciding to pack up at 0600hrs.
      I am glad that I made the effort to get up as I felt like I got “more than I imagined” from my session (which sent me back to bed happy, if a little cold – at least I had my hot water bottle to bring my feet back to life).
      I think that I have concluded that I need to get the widefield Borg 107FL out more frequently, when it’s cold then the dob in the shed is a much more appealing thought.
      -          I have added an unexpected 7 entries to the “Ag1-xx” nebula catalog for the unknown/extra patches that I will need to come back and confirm… (up to 97 entries now).
      I also now have some lingering memories to help me through the barren spell of the full moon (out here in the dark countryside, the full moon is a real killer!).
       
      Hope you enjoyed the read and my sketches!
      Alan
    • By alanjgreen
      Dates: 26th thru 30th Oct 2019. (Over twenty hours of observing time!!!)
      Scope: 20” f3.6 Lukehurst Dob with Paracorr (fl = 2089mm & f4.1).
      Night Vision: PVS-14 with Photonis 4g INTENS.
      Eyepieces: Plossl 55mm (f2 x38), Panoptic 27mm (f4 x77).
      Filters: Chroma 5nm Ha filter.
       
      It’s a Miracle!
      I have been out observing on each of the last five nights racking up a combined time outside of over twenty hours – It’s a long time since I have had such a good run. I have written 17 pages of notes during my sessions too…
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      Planetary Nebula.
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      NGC6826 (Blinking Planetary) – Very bright solid ball with a thin halo of lighter shade.
      NGC7027 (Magic Carpet) – small bright ball, there is either a fine line running through it or it is two-toned. Has a detached faint circle around it.
      NGC7048 (Disk Ghost) – small dim circular patch made up of “dancing lines”. Looks alive.
      NGC7026 (Cheeseburger) – Tiny and bright. Made of two patches with a haze on either side. Reminds me of an “overhead shot of a rowing boat with oars out either side in the water”.
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      NGC6905 (Blue Flash) – tiny, dim patch made of moving lines. Looks brighter on one side.
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      NGC40 (Bow Tie) – Excellent. Very bright with two curved sides. The inside is filled with fuzzy stuff that is leaking out from both ends. There is a small circle at the centre.
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      NGC1501 (Oyster) – Tiny and bright. Looks alive. Reminds me of a bright “woolen ball”.
      IC2149 (Red Sword) – very tiny but bright. Has a small circle around it.
      NGC1514 (Crystal Ball) – star inside a black circle with multi-toned nebula shell encircling that. Nebula is multi-lined and shimmering. Looks alive.
      NGC7139 – Small mesmerizing ball. Shimmering jumping lines within. Alive.
      The "alive" planetary nebulae are great to look at, they are literally moving and dancing around in the fov. 😀
       
       
      Comets.
      Another object that I has not been on my radar for several months! Well, I managed to find three over the last few nights.
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      C/114P Wiseman-Skiff – Even with the 27mm Panoptic, this was a tough object to find. I needed to turn the gain up to the max but I found it exactly where Sky Safari said it should be!
       
      Galaxies.
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      NGC751 – A strange one, with the appearance of a double-core. Sky Safari says its two galaxies NGC750 & 751).
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      IC10 - I had already observed this underwhelming galaxy earlier in the session when I happened upon it again by chance (whilst I had the 5nm Ha filter fitted and was just sky scanning) and found it as a pleasing patch, it was only when checking Sky Safari that I found out it was the IC10 galaxy that I was looking at. It appeared so much clearer with the Ha filter that I wondered what the bigger galaxies on offer would look like in Ha?
       
      Lets try Andromeda & Triangulum in H-alpha.
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      With no Ha filter then the big reverse S of the main arms is clear in direct vision, now the arms are not clear but if I look carefully then I can trace tiny Ha patches that are marking out the arms in the fov. I decided to start sketching these patches and add the occasional curve where I was seeing “implied” arm structure.
      It was quite a surprise just how far out from the core some of these Ha patches are located, signifying that actual physical size of M33 is larger that we may think when visually observing our neighbour.
      Here is my sketch:

       
      Onto M31, where the results were less impressive but I was able to see the galaxy and some Ha components within so it was not a waste of time at all.
      I noted three Ha patches in the upper sections of M31 but it was the lower sections that were a bit of a revelation.
       
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      Here are my sketches of the two halves of M31:

       
      Nebulae.
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      I am now up to 82 objects having added a further 38 objects during October. I have also managed to revisit 52 of the objects to confirm their existence and descriptions.  
      Time to catch up on my sleep.
      The weather forecast seems to say wet weather until full moon, so it looks like I will be stuck inside for the next couple of weeks, guess there is no pleasure without pain!
       
      Clear Skies,
      Alan
    • By alanjgreen
      Time does not stand still...
      It has been 17 months since I wrote the original version of the above named article and there have been a few changes in the intervening time period…
      1.       I now have 17 months more a-focal experience of using a telescope with a night vision device attached directly to the eyepiece.
      2.       A new forum has been created for the discussion of such “Electronic Assisted” observing equipment on this website.
      So I decided to revise my article and post it in this new “most applicable” forum.
      Let us start with the basics…
       
      What is a-focal observing?
      “a-focal observing” simply means that the night vision device is attached directly to an eyepiece (after the focal point of the telescope). You are placing the night vision device’s objective at the exit pupil point in the light path.
      The easiest way to achieve this is the use the “TNV-14 Eyepiece Adapter” (available from Tele Vue). This adapter has threads on either side to connect (1) any Dioptrx accepting Tele Vue eyepiece to (2) a PVS-14 Night Vision device.
      http://www.televue.com/engine/TV3b_page.asp?id=36

      Here is a picture of a Tele Vue 55mm Plossl connected to a PVS-14 using the TNV-14 adapter.

      To perform “a-focal” observing we need to simply insert this “stack” into any telescope focuser. If the attached eyepiece can achieve focus then there will be a focused image available to view in the PVS-14.
       
      Here we see the stack attached to my 20” dobsonian and my 107mm Borg refractor…


       
      What are the advantages of a-focal?
      The biggest advantage is that you WILL be able to reach focus in any scope. Unlike other options you are simply placing the night vision at the point of the exit pupil. For Newtonians, this is a big point.
       
      Fundamentals of a-focal observing.
      Now we are past the basics, we have some slight more complicated “fundamentals” to get our heads around…
      1. The PVS-14 night vision device is designed to work at a focal ratio of f1.2 (which is very fast). To get the most from the device then we need to aim to send light from the eyepiece as fast as possible to take maximum advantage of the night vision device. A faster focal ratio results in a brighter image, a slower focal ratio results in a dimmer image.
      - Here we have been given a “lucky break”. Because the PVS-14 has an effective focal length of around 26mm, if we use any eyepiece with a focal length greater than 26mm then the “effective” focal ratio of our system gets “magically” increased.
      [I will show how we calculate this effective focal ratio shortly but think of this on a par with adding a focal reducer into the light train].
      Unfortunately, any eyepiece with a focal length less than 26mm will decrease this “effective” focal ratio of our system.
       
      2. The PVS-14 has a fixed forty (40) degree field of view. It does not matter how wide field our eyepiece is, the night vision device will only ever show the centre forty degrees. This means that you don’t need 100 degree Ethos or 82 degree Nagler eyepieces, narrower field of view Plossl, Panoptics & DeLite’s will be fine.
      - Again, don’t panic! There will be so much to see in the forty degrees that it will feel like 100 degrees. I have come from 100 degree eyepieces and I have never once wondered where my huge FOV went
       3. Eyepiece eye relief is important. You need eyepieces with enough eye relief to match the distance from the top lens surface of the eyepiece to the position of the night vision objective lens. Too much or too little eye relief will result in loss or distortion to the outer edges.
       
      What is the minimum set of eyepieces that I need?
      I use a total of four (4) Tele Vue eyepieces with my Night Vision device:
      1.       Tele Vue 55mm Plossl. This is my main work horse eyepiece. I use this eyepiece for >90% of my observing time. The reason it is my most used eyepiece is that it gives my telescopes the fastest possible “effective focal ratio” (which results in the brightest possible image at the eyepiece). In simple terms think of this eyepiece as being able to double the speed of your telescope (like a 0.5x reducer). I use this eyepiece for nebulae, galaxies & open clusters.
      2.       Tele Vue 35mm Panoptic. I use this eyepiece occasionally when I want more magnification but still want a bright accelerated image (it acts like a 0.7x reducer for the effective focal ratio). An alternative to this eyepiece would be the Panoptic 41mm - I use the 35mm because it’s half the weight of the 41mm! I use this eyepiece for nebulas, galaxies, comets, large open clusters.
      3.       Tele Vue Panoptic 27mm. I use this eyepiece again for greater magnification, usually for supernovae, globulars, comets & open clusters. I do not use this for nebulas and galaxies as the effective focal ratio is now too low and details are becoming lost at the eyepiece.
      4.       Tele Vue DeLite 18.2mm. This is my least used eyepiece (as its focal length is smaller than the 26mm of the night vision device). In use, it has the effect of slowing my effective focal ratio and producing a dimmer image. It does however produce about the maximum useable magnification with my night vision a-focal setup and I have been successful using it for faint tiny supernovae and bright globular clusters.

       
      What about the huge exit pupils?
      [Exit pupil is the width of the light beam being emitted from the top of the eyepiece and traditionally astronomers baulk at anything wider that the width of the astronomers own eye pupil as it is not possible for our eye to consume the whole of the light beam]
      [Exit pupil is calculated as the eyepiece focal length divided by the telescope focal ratio so a 55mm Plossl in an f4 scope will produce a light beam 13.75mm wide]
      As the night vision objective lens is 20mm wide then it can take all that light in and process it with room to spare! Whilst your eye pupil would be flooded and loads of light wasted, no light is wasted in this case.
      But as the eyepiece focal lengths get shorter (and the exit pupils get smaller too), the night vision device soon starts to become starved of light.
       
      How do I calculate this “eyepiece focal ratio” exactly?
      Now seems the right time to show the maths to calculate the “effective” focal ratio of your telescope/night vision setup:
      Effective focal ratio = NVD / (EPFL / TFR) where
              NVD = night vision device focal length = 26mm
              EPFL = eyepiece focal length
              TFR = telescope focal ratio
       
      As an example, if we have a telescope with a focal ratio of f4, the 55mm Plossl will produce an “effective” focal ratio of f1.9.
      [Effective focal ratio = 26/ (55/4)  =1.9] 
       
      Does the focal ratio of my scope actually change?
      The answer is NO. These changes in “effective” focal ratio that I mention only happen inside the night vision device. If your scope is f4 then it will remain f4.
       
      Is a-focal observing, low magnification observing?
      Simple answer = Yes it is. You need to get as much light as possible into the night vision device as fast as you can get it to go. All of the photons that you can get into the device will be amplified by the night vision device enabling you to see views containing previously unseen detail. In some cases, the amount of new detail on offer will be overwhelming!
      At first, you will want to change eyepieces to achieve greater magnification but you soon discover that you actually see less detail (due to loss of effective focal ratio and exit pupil) so you soon return to the longer focal length eyepieces.
       
      How do I calculate the magnification that each eyepiece will give me?
      There is no change here. Take your telescope focal length and divide by eyepiece focal length.
      If your scope has a focal length of 1800mm then you would get the following magnifications from my eyepiece set:
      -          55mm Plossl (1800/55 = x33)
      -          35mm Panoptic (1800/35 = x52)
      -          27mm Panoptic (1800/27 = x67)
      -          18.2mm DeLite (1800/18.2 = x99)
       
      How do I calculate the TFOV?
      I used Sky Safari for this. I setup my eyepieces in the “equipment” section using a setting of 40 degrees for the fov and it did the rest…
       
      Can I use a coma corrector with night vision?
      If your telescope has a fast focal ratio and you find that you need a coma corrector now then you will still need it for use with night vision. I used a Tele Vue Paracorr2 with my 20” dobsonian before I had night vision and I am still using it with Night Vision. In a big reflector, the best place for filters in the light path remains on the bottom of the Paracorr.
       
      What about filters?
      This brings us nicely onto every astronomers “favourite” topic – filters!

      When combined with filters, night vision devices can allow us to not only see what was not visible before but also to steal back some darkness by blocking out our old enemy, the moon!
      In the Cumbrian countryside, the night sky has an SQL of around 21.6, class 4 Bortle. Please take this into account when reading my experiences as your SQM may not be the same as mine.
      1.     General observing – For general observing, I do not use any filters as the best results are achieved by letting all the light into the night vision device. The PVS-14 has manual GAIN which means there is a knob that can be turned to decrease the gain and darken the image at the eyepiece – this is the only filter that I use in general observing.
              Moon – If the moon is up then I add a Baader 610nm Red filter into the light path. This is a good filter for reducing the effects of the moon on the sky background. It can also be effective if viewing low to the horizon where light pollution can be an issue.
      2.     Filters for observing Nebulae
      For nebulae viewing, a narrowband Ha filter in mandatory. I have tried 12nm, 6nm and 5nm and my preferred choice of bandwidth is the 5nm. As this filter is the “key” to seeing nebula then please do not scrimp of a “cheapie”. If you want to get the maximum from your expensive night vision device then only consider top brands such as Chroma, Astrodon, Astronomik or Baader.  I am currently using a Chroma 5nm Ha narrowband filter.
      Your choice of Ha narrowband filter will directly affect whether you see some of the fainter nebulae objects or you do not see them!
      3.      Filters for observing Galaxies
      For galaxy viewing, there is no filter that can improve the unfiltered view. 
      However, if the moon is up then I use either the Baader 610nm red filter or an Astronomik UHC Visual filter. If you are viewing tiny smudges then either are okay, if you are viewing larger galaxies with spiral arms, then I find that the Astronomik UHC Visual filter gives slightly more spiral arms than the 610nm red. Both beat unfiltered viewing if the moon is up.
      @GavStar is using a “Baader IR pass” (685nm) filter from his city location for all non-Nebula targets to cut out the light pollution.
       
      Which night vision units can I connect to my telescope for “a-focal” observing?
      As a UK based astronomer there are very few options for us to purchase a Night Vision Device with the latest military specifications. The Tele Vue adapter works with the PVS-14 night vision device so this led me in that direction. 
      I purchased my PVS-14 from www.actinblack.com based in Luxembourg.
      Please do read my article on “Understanding Night Vision Tube Specs a little better” and do be prepared to wait a month or two for actinblack to get a new batch of tubes into stock (from which you can then pick the best one for astronomy use). I had to wait two months for a new batch of Photonis tubes to come into stock before I was sent three tube specification sheets to choose from via email.
      Having selected my tube then it was delivered to me in under a week from placing the order.

       
      Which telescope do I need for Night Vision?
      This is a good question and one that will be debated long into the future. My opinion is that the best telescopes for a-focal night vision use are telescopes with fast focal ratio.
      I am using an f3.6 dobsonian and an f5.6 refractor.
      Our goal is to achieve the brightest possible image at the eyepiece and focal ratio is the key to achieve that.
      As we can see from above, there is a rather restricted set of eyepieces needed for night vision astronomy but if we pair these eyepieces with telescopes of varying focal lengths then we can get a wide range of actual field of views and magnifications. This drove my minimal set to two telescopes, one long focal length dobsonian with good aperture and largest possible magnifications (with long focal length eyepieces) and one short focal length refractor for wide field with decent apperture (> 4") and light enough for travel.
       
      What can I see using Night Vision a-focally?
      At this point, I want to point you to some of the many posts from @GavStar  available on this website. His images do reflect what I can see visually with my two setups.
      Let me go on to summarize what I have been seeing in the last 17 months since the initial article.
      Nebulae
      I have now almost completed the full Sharpless catalog (303 of 313 objects). The only ones that I have not seen are the ones that are too low to my horizon!
      Galaxies
      I am working through the 200 brightest galaxies available in the skies above us. This project is more than half way complete and so far I have observed the spiral arms of 68 galaxies with direct vision.
      Supernovae
      Last year I viewed 17 supernovae, down to a magnitude of 16.8
      Globular Clusters
      I have so far failed to give sufficient time to Globulars, but their brightness means that I have been able to see some of the smallest and faintest on offer above us. I will get to these once my Galaxy project is completed.
      Comets
      Night Vision works well on comets, in a side-by-side test with traditional eyepieces, I saw better results with the night vision device.
      Open Clusters
      Night Vision gives great results with open clusters. The smallest ones just jump out at the eyepiece as you nudge around.
      Planets
      Failure – night vision is no good for planets. They are too bright.
      Moon
      Failure – night vision is no good for the moon. It is too bright.
      Here are a few links to some of my reports (there are many more if you use the search facility)...
      Do you still use eyepieces for observing?
      My eyepiece case has been mostly sold off now. I have a set of short focal length DeLite eyepieces for planetary and I have some eyepiece pairs for solar observing with my Lunt LS60.
      I use eyepieces to complete the 2-star alignments of my telescopes then it’s become automatic to just switch straight to the Tele Vue Plossl and my night vision to get into my nights observing. With the GAIN turned down it really is no different to using an eyepiece and you just see so much more…
       
      Hope this helps somebody,
      Alan
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