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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…
I have observed many objects of different types during this time outside. So, I am going to divide up this report into object type sections so you can scroll to objects of your favorite kind…
First up planetary nebula, this is an object type that I rarely write about but having bumped into a few of these while out nebula hunting with my 5nm narrowband Ha filter combined with my PVS-14 night vision, I decided to build a Sky Safari observing list based on “The Brightest Planetary Nebulae Observing Atlas” by Massimo Zecchin and get out and observe them with a plan. The eyepiece attached to the PVS-14 for these observations was a 27mm Panoptic yielding x77 magnification.
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”.
NGC7008 (Fetus) – small dim, almost square shaped patch. Black circle at centre then dominated by thick bright outer layer (does not go all around the outside).
NGC6905 (Blue Flash) – tiny, dim patch made of moving lines. Looks brighter on one side.
NGC6543 (Cat’s Eye) – small bright patch. Tiny dark spot in the centre. Seems to have a thin layer of lighter dancing lines all around the outside.
NGC7662 (Blue Snowball) – tiny. Very bright solid ball. There is a faint detached outer circle.
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.
M76 (Little Dumbbell) – Looks like a “box kite”. Brighter patches at either end, connected by fainter central oblong section.
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. 😀
Another object that I has not been on my radar for several months! Well, I managed to find three over the last few nights.
C/2017 T2 (PANSTARRS) – With the 55mm Plossl (x38) it was small but easily seen.
C/2018 N2 (ASASSN) – With the 27mm Panoptic I found a decent sized fuzzy blob to the side of a star. It was easily seen and the best of the three. 😀
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!
Now the great square is in the south, there are some of the brightest night sky galaxies available for observing. I have observed the following NGC6946, 6643, 6503, 6140, 6015, Stephans Quintet, 7331, 185, 147, 278, M110, M32/32, M33, NGC404, IC10, NGC669, 684, 672, 972, 925, 949, 1023, 891, 1160, 1161, 7814, M74.
It’s a decent list, but the outcome has been disappointment. The only galaxies that I observed the spiral arms were M33, 31, 74, NGC891, 6643, 7331. Here are a few descriptions from my notes:
NGC6946 (Fireworks) – With the 55mm Plossl and no filters, I could see the twin fingered arms coming out from the core around the back. I got hints of a third fainter arm coming out underneath.
NGC6643 – A small galaxy. You can easily see the core and surrounding halo. There were some faint anti-clockwise arms beyond the halo but they were tough to see in direct vision.
NGC6503 – small and bright. Slightly edge-on. Tiny bright core with large halo surrounding. Hints of black lanes within the outer halo.
Stephans Quintet – All 5 galaxies easily seen with the 55mm Plossl (x38). There was even a sixth galaxy in the fov (NGC7320C)!
NGC7331 – bright core, slightly dimmer halo surrounding. Swirly fainter disc beyond that. Hints of a lane top-side and a black patch (usually signifies that arms are there) behind core on outer edge. I could see the four “flea” galaxies that sit to the LHS.
NGC891 – Wonderful. Large edge-on galaxy with swollen core section and thick black lane running its full length in direct vision.
NGC751 – A strange one, with the appearance of a double-core. Sky Safari says its two galaxies NGC750 & 751).
M74 – At first I see a mid-sized fuzzy patch but I keep looking. I see a circle around the core appear first, then an arm seems to leave at 3o’clock and curve up and left. Then I see another arm at 9o’clock going out and down anti-clockwise. I note a four star rectangle and add it to my reference sketch. I can see images that confirm the arms on the internet.
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.
I have written about my experiences with M31 and M33 many times before, so I won’t be repeating myself today. Instead, I want to talk about an H-alpha experiment that I carried out over a couple of hours with M31 & M33 as my targets.
I loaded my Chroma 5nm Ha filter into the Paracorr2, then added the 55mm Plossl for maximum image brightness and pointed at M33. To my surprise there was a very large galaxy sitting in the fov with many fuzzy shapes abounding. It took a few minutes to take it all in and start to recognize NGC604 and work back from there…
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.
Regular observers of M31 will know that it’s a dead loss below the core to see very much at all! Well, in Ha the lower section can match the upper section and in fact I saw a greater number of Ha patches in the lower section including a couple of really big ones.
Here are my sketches of the two halves of M31:
I spent many hours looking at the many large and small nebulae in the Milky Way from Cygnus to Orion. I have written about them many times before and will not do so today.
I was also able to spend some time scanning the “empty spaces” in Sky Safari looking for objects that I could find with the night vision and marking them for the "AG1-" night vision object catalog that I am continuing to work on...
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!
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.
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.
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!
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.
Last year I viewed 17 supernovae, down to a magnitude of 16.8
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.
Night Vision works well on comets, in a side-by-side test with traditional eyepieces, I saw better results with the night vision device.
Night Vision gives great results with open clusters. The smallest ones just jump out at the eyepiece as you nudge around.
Failure – night vision is no good for planets. They are too bright.
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,