Last night was my first chance to really compare the PVS-7 and Mod3 WP filmless side-by-side.
My aims last night were to test:
- Qualitative differences between the PVS-7 and the Mod3
- Make a final determination on a few Baader filters I had purchased, to see if they were worth keeping
- See how well an 80mm f/6 APO serves as a night vision grab & go scope. This includes optical performance (image scale, brightness) as well as overall ergonomics.
- Understand the logistics of using *both* the PVS-7 and the Mod3 for an observing session under light-polluted skies
- Finally see the Andromeda Galaxy with magnification and amplification. I only got into NV back in May, and actually haven't managed to look at M31 yet with NV in a scope!
Additionally, I wanted to gauge the pure, un-amplified visual performance of the Stellarvue 80mm APO. It's my first APO and it's also been 20 years since I really observed with an 80mm, so I wanted to get a feel again for instruments of this size.
I don't get very many nights of observing nowadays, so when I do, I try to get a lot done!
- PVS-7 pseudo-binocular with a good Gen3 (D) tube
- Mod3 monocular with L3 filmless White Phosphor. Detailed specs: PC=2167, EBI=0.3, SNR=31.1, Resolution=64 lp/mm, Halo=0.7, FOM=1990.4
- Scope: Stellarvue SV80ST 80mm f/6 triplet APO
- Mount: Stellarvue M2 alt-az
I also have a variety of accessories for the night vision stuff, which are mostly detailed in my Night Vision "purchasing guide" post here.
My location is my in-laws' house in Liberty Hill, TX, halfway between downtown Austin and Canyon of the Eagles (the location of the Austin Astronomy Club's observatory and primary dark-sky site). It's a solid yellow on the dark sky map, but the dark sky map does not account for a Texas-sized high school football stadium and parking lot adjacent to our property, just a few hundred yards away towards the south. The bright-white parking lot floodlights are on all the time, because... I guess they don't want anyone stealing the football stadium? In any case, on muggy nights like last night, the glow is much worse all around, and the skies are closer to orange/red-zone.
So, this is why we have night vision! :-)
PVS-7 vs. Mod 3
My first comparison tests were at 1x, with no filters. The view through the Mod3 is undoubtedly clearer, and although the "greenness" of the PVS-7 has never bothered me, the White Phosphor color is definitely more "natural". Looking up at the sky, both revealed a tremendous number of stars. The Milky Way was already somewhat visible with the naked eye, and with night vision, it was even more apparent, but still very ghostly because of the lack of filters.
One major difference is that with the PVS-7, the level of scintillation is just what it is. But with the Mod3, I can turn down the gain, until the scintillation is just barely visible. This is a much, much more pleasant viewing experience. One thing that I noticed is that the perceptual effect is highly non-linear. That is, there is a threshold level of gain beyond which I perceive no visual benefit, just slightly more scintillation. In the viscinity of this threshold, I can dramatically change the amount of background amplification and contrast, with very small tweaks of the gain knob. This is not too surprising to me, since I am very well aware of the logarithmic response of the human visual system, but it's neat to see the effect first-hand. Throughout the night, I found myself turning down the gain to find an optimal spot on the brightness/scintillation tradeoff curve.
Red/IR Longpass Filter
I have two filters: a 55mm 680nm IR Filter ("Ebay $10 Chinese Special"), and the Baader Red 610nm Longpass.
I bought the 55mm IR filter when I first got the PVS-7, and it's a champ. I hand-hold it in front of the PVS-7, or I can also hand-hold it inside the front of the 3x Afocal lens. Even from red-zone downtown Austin, it never fails to bring the Milky Way into sharp contrast. The only downside is that it has to be hand-held. I had hoped that the Baader 610nm would be an equivalent longpass that I can mount in the NV device.
Comparing the two filters side by side, from what I could tell, they were similar in performance. The larger 680nm filter displayed somewhat more contrast, but not by too much. Although the convenience of the 610nm outweighed the increased contrast, I think that the right thing for me to do is to sell the 610nm filter, and get the Baader 685nm IR Longpass.
The views through the PVS-7 and Mod3 were different, but in ways that are hard to describe. I am fortunate that the tube in my PVS-7 is pretty darn good. There are no blemishes, and the IR-filtered view of the Milky Way definitely rivals that of the Mod3. However, the white phosphor is visually more pleasant, and it's a little bit sharper and clearer. At 1x, looking at the beautiful river of light of the Milky Way, the manual gain control of the Mod3 is not really needed, because there is enough light coming in, to where the scintillation in the PVS-7 is not a problem.
However, I did experiment with turning the gain down to lower levels in the Mod3, and this yielded a very, very lovely view with almost no scintillation.
It's worth reiterating, yet again, just how amazing this setup is. I'm standing next to a (Texan!) high school football stadium, in Bortle 4.5 skies, and the view through the Mod3 is easily Bortle 1, with zero scintillation or other artifacts. A Mod-3 monocular, with a $10 IR filter, instantly puts all of the sky within reach. With the IR filter, so much texture is visible in Sagittarius, and the stars in the Lagoon glow as a bright fuzz-patch. The nebulosity in the dark lanes in Sagitarrius are visible, but not in great contrast. The river of the Milky Way sweeps up through Cygnus and over into Cassiopeia, where M31 hangs nearby.
The visceral experience of this is what I have dreamt of in astronomy, since I was a child!
H-alpha: 7nm Narrowband vs 35nm
Next up, after sweeping the Milky Way and taking it all in, I switch to narrowband H-alpha to survey larger nebula.
The Orion 7nm H-Alpha Extra Narrowband filter has been my workhorse since I started with night vision 4 months ago. In my opinion, a narrowband filter like this is a must have accessory for night vision. In fact, if you have a Night Vision device and you don't have a narrowband filter, the most apt analogy would be like having a car and no road to drive it on. I am eager to try an even narrower at some point, but those filters are much, much more expensive.
I also have a Baader 35nm interline CCD filter, and just wanted to see how it would perform. The result for night vision was basically "meh". It lacked the contrast and punch of the 7nm, and wasn't particularly useful for viewing the sky at 1x.
With the narrowband filter, the background of the Milky Way fades somewhat, and the overall view gains contrast, because there is much less light coming through. However, this means that there is also more scintillation. The PVS-7 automatically cranks up the gain (to the maximum, as far as I can tell), so the result is a high-contrast view of the night sky, with the nebulae glowing like little clouds, but with sparkly scintillation speckling the view, as an artifact of night vision. As others have noted, and I can confirm, the scintillation is not a really big issue, and you quickly learn to get over it.
However, that's not to say that the view wouldn't be improved if there wasn't scintillation. Once again, the gain knob on the Mod3 provides the ability to manually set this trade-off. While sweeping the sky at 1x, the PVS-7s provided their standard amazing views. But in the Mod3, I was able to turn down the gain so that while the absolutely brightness of the nebulae was lower, there was also dramatically less scintillation.
In the last several months, I have absolutely gotten spoiled with the narrowband H-alpha view through my PVS-7. Seeing the Lagoon and Trifid nebulas, looking up at the North American, Pelican, and Gamma Cygni region... these are now my new "normal". But they've always had sparkly scintillation, which I'm mostly able to ignore.
Last night, I experienced the next level with the Mod3. I turned down the gain just a hair, so most of the scintillation was gone, and I was left with a "pure", brightened view of all of these glorious sights...
Snapping the 3x afocal on, I craned my neck to look directly up at various targets in Cygnus. It was spectacular. Gamma Cygnus and the dark lanes running through the subtle nebulosity there was stunning. The fragments of the Veil were beautiful... I had to stop multiple times just to rest my neck, until finally I just bit the bullet and laid down on the concrete driveway. Then I just drank it all in. At one point I couldn't find my bearings because there were just SO MANY STARS, so I ended up looking for the Veil Nebula, and sighting from there. It's really something else to be nebula-hopping instead of star-hopping!
Night Vision in the 80mm f/6 APO
As I've mentioned in other posts, my main telescope is a Celestron 11" EdgeHD forkmount. This is a beast of a scope but it's optically amazing. I've used my PVS-7 through it several times, and been blown away each time. The photos I posted from last month's star party were taken with this C11, using Eddgie's L3 WP (I think an NVD Micro) with a 0.5x focal reducer.
However, it is heavy and bulky, and entails dragging along a bunch of other gear. I wanted a lightweight grab-and-go setup. I've been on the fence for a while trying to figure out whether to go for a fast dob, a handheld zoomable front-end for night vision (something in the 50mm-200mm focal length range), or a small APO refractor. I saw this Stellarvue come up on Astromart and decided to go for it. My reasoning was that it would be potentially useful for astrophotography or "live video" EAA, and it would also be much more portable for plain unamplified visual astronomy. Additionally, a Dob would perhaps incur more domestic political cost b/c of its perceived footprint and space requirements in our already-cramped home office. :-)
A big part of the appeal of night vision for me is the same reason I got turned on to EAA in general (although I don't have much experience yet with my Atik Infinity): I live in town, and I have a very busy life including young children, so I can't do 2 hour drives out to dark sites. In the same vein of the photographers' mantra about the "best camera" being the one that you have with you, the "best optics" for me are the ones that I can actually go and use on a regular basis. So, the portability of the telescope is a big component of my overall hobby investment.
So, I set up the refractor, dropped in the Mod3 with my ScopeStuff C-mount to 2" adapter, and immediately noticed a small inconvenience: when screwed in all the way, the adapter presses against the gain control knob. It's not a problem, but it does mean that I will probably use the 1.25" adapter more often in the future.
With the scope, I primarily wanted to check out the major nebula highlights. The first thing I looked at was the Lagoon and Trifid nebulas. Since I wasn't "digiscoping", my field of view was dictated by just the Mod3 itself, and the image scale was a good one to sweep this part of the Milky Way. The attached photo, taken with my iPhone, shows the composition. The default views in the PVS-7 and the Mod3 are not too dissimilar, although as always, the Mod3 is just somewhat sharper, and I find the bluish-white tint visually more pleasing, because it's closer to the grayscale I'm used to observing.
I use the term "default views", because, once again, the manual gain control is a game-changer. I can turn down the scintillation until it falls well below the threshold of distraction, and I can still see a very amplified image. The effect is actually really cool going the other way: turning gain down to almost zero, so that I can just see the stars and only faintly make out the nebulosity. Then, I just turn up the gain knob to boost the brightness, until I get to what I need, in order to observe subtle structure. It might as well be called the "Add Aperture" knob. :-)
I looked at the Lagoon, the Trifid, the Swan, the Eagle, the North American, the Pelican, the Pacman, the Veil, the Garnet Star nebulas. Just visually sighting down the tube, then looking through the Mod3 and sweeping through the stars until I find the nebula. This is deep-sky observing as it should be!
One unexpected result, however, was that since I have gotten spoiled with the Goto features of my CPC1100, I had to actually work a bit to find particular objects. This is where having the PVS-7 out, in conjunction with the Mod3 in the telescope, was a nice combination. Unfortunately I had to keep swapping the narrowband filter out between the two, but that's a very minor complaint. I'm just going to have to order another one!
I wanted to see the Andromeda Galaxy with night vision, but I didn't need the H-alpha for that. I wanted some kind filter, however, to cut out the skyglow and light pollution. I decided to use a 2" Lumicon UHC. In retrospect, I probably should have used the Lumicon Deep Sky filter for general viewing.
One thing that popped out at me after switching from the H-alpha to the UHC was just how much brighter everything was. The wide field of view of the little 80mm refractor was just awash in stars. When I was a kid I loved sweeping my Newtonian across the rich starfields in Cassiopeia, and I was doing the same thing last night...
The Andromeda Galaxy itself was very nice. I couldn't see much structure, but after turning down the gain to reduce scintillation, I could use averted vision and see M32. In the past, I've been able to do some averted vision with the PVS-7, but the scintillation makes it somewhat more challenging.
I also looked at some open clusters and just kind of tooled around. There are so, so many stars out there. If you like stars and star fields, Night Vision is a great enhancement for that. I would say that the Mod3 again outshines the PVS-7 for this, but not by too much, because of the manual gain. Stars don't need too much amplification, but the PVS-7 will automatically crank the gain no matter what, so you end up with unnecessarily high scintillation.
Photographing night vision
I really wish I could figure out a better way to capture the in-person experience of night vision for people. As anyone can tell see, the photos that we tend to share, hastily taken with hand-held smartphones, are grainy and are compounded by bad JPEG artifacts and digital camera noise. They are terrible compared to even the worst CCD or DSLR photos, and really don't do the NV devices justice. Now, part of the issue is that when I've got my NV tube in the eyepiece, I don't give a rip what the photos look like, because I'm too busy oggling the view! But I think that as advocates of this technology, we could do a better job if only we could figure out better ways to photograph (and therefore convey) our experience.
As a final task for the night, I decided to go to a regular eyepiece. I dropped in my 14mm Delos, and looked at Albireo, one of the loveliest summer stars. The optical quality of the Stellarvue refractor was very satisfactory. The field was rich with pinpoint stars, and the orange and blue Albireo shone beautifully. I also looked back at the Sagittarius region and the Lagoon Nebula with the Delos. The view was lovely, and it was what I expected; it was as nice as can be expected for passive glass. It also starkly reminded me of how spoiled I've become now with the night vision. A thought occurred to me: 99.99% of my fellow astronomers cannot just turn a knob and pump up the brightness. This is the view they get, and will have to be content with, unless they buy a huge light bucket dob, or drive hours away from civilization.. and even then, it's not clear to me that the view will be comparable to what I'm seeing in the Mod3.
Of course, if I were to drop the Mod3 into a huge light bucket several hours away from civilization, I'm sure the views would be more amazing still!
One of the things that got me excited last night, standing next to a scope that's barely larger than my very first Criterion refractor (75mm), was that night vision has really unlocked the stars for me. There is just so much to look at in the night sky, when every night can be turned into a dark sky with just the flip of a switch. The star maps no longer feel like a "catalogue of things you could be looking at", just taunting me, and are now instead a catalogue of things I'd like to see and can actually see.
The Mod3 is an amazing device. Having now done an initial comparison with the PVS-7, I would say that I am definitely keeping both. First, the value of (pseudo-)binocular viewing with both eyes cannot be overstated. I hadn't realized that monocular viewing would feel as restrictive as it did, since up until I got my binoviewer last summer, I've always only ever looked through a telescope with a single eyepiece. (And honestly, the binoviewer is very nice on planets and clusters, but was underwhelming on nebula because of the light starvation.) Of course, some people's solution to this problem is to buy a SECOND Mod3, but I'm not quite there yet. Maybe if my sales guys knock it out of the park this year, that can come out of my Christmas bonus. ;-)
Secondly, although the Mod3 outperforms the PVS-7 in many respects, and the manual gain control is a crucial feature, the PVS-7 is a fabulous device. (I'm especially lucky in that I got a good tube, and I can confirm that now that I can put it side-by-side against my much more expensive L3 filmless.) I would be happy with just it alone for a long time. However, now that I've experienced the additional dimension of viewing experience available with manual gain control, I think that I will just use the PVS-7 for high-brightness situations (1x, 3x with IR filters, and clusters with Deep Sky filter). For low-brightness H-alpha viewing, that will clearly be the domain of the Mod3.
So, several things in terms of gear:
- Get two 1.25" 685nm IR longpass filters, sell the 610nm Red filter
- Get a second narrowband H-alpha filter... either a 7nm just like I currently have, or sell some other gear so I can get a 5nm or 3nm one
- Start investigating portable Goto mount options to replace the M2 mount
- Get one of the 50mm-ish finderscopes and adapt it to C-mount or 1.25" mount
In terms of things to do (maybe tonight!):
- Hold up the NV to eyepieces, to zoom in more on some kinds of objects. The 480mm focal length is definitely too short for some things I'd like to get better looks at, including galaxies and whatnot.
- Try using my DSLR and futz with manual photo settings to take better shots through the NV
- Get a more effective workflow going in terms of observing session planning, now that I can actually see lots of stuff!
Edited by pwang99, 04 September 2016 - 08:58 PM.