(Before you start reading this, extend the screen to the right; I prepared it separately in word processing and pasted here, so it does not wrap like when created here.)
I had the good fortune to be invited by Joelin to observe with he and Moshen in Mariposa, CA, on the 18th. He had rented an AirB&B for a few days at a nice dark location in the Sierra foothills, east of the central valley, only 90 minutes from where I live. We started observing about 7 p.m. In short order heavy dew had formed on all of our equipment… by 11, the dew had turned to ice. We weren’t cold though… Moshen brought some great hand warmers!
Joelin is an astrophotographer who is waiting for his ordered Mod 3C NVD to arrive. Moshen and I brought our Mod 3Cs and I brought a second NVD that I just assembled last Saturday. The “new” one is an AB Micro, using a 1x C-mount Envis lens (from my Mod 3C), with a 12 yr. old F9800, thin film, green phosphor tube that had been originally part of a Collins I Cubed. The specs on the tube are pretty average, well below most of what appears for astro use in this forum. For comparison, here are the specs for my L3 white phosphor, the green Micro/F9800, and Moshen’s Mod 3C/L3 tubes:
Ray’s Mod 3C/L3 Micro/F9800 Moshen’s Mod 3/L3
PCR 2680 2274 2574
EBI 1.1 .9 .5
Gain 61433 57663 62647
S/N 33.8 28.5 33
Halo .7 1.1 .7
RES 72 LP/MM 64 LP/MM 72 LP/MM
Mfg. 2016 2008 2017
Joelin used the Micro for some AP experiments during the evening, but later, we did some comparisons between the WP tube and the thin film green tube. I have to say, I missed gain control on the Micro… but only for the first few minutes. My eyes adapted to the bright image pretty quickly. Skies were pretty dark; Joelin's SQM read 21.4
First, we sat down and passed around Moshen’s Mod 3C, and my Mod 3C for a comparison between them. Try as we may, we could not detect a difference in the images presented by our two L3 tubes. We wondered if threshold subjects might reveal some distinguishing difference between them, but we saw none at 1x. You can see that our specs are pretty close on these L3 tubes. The biggest difference between these two WP tubes is the EBI… but the temp was hovering near freezing, so it is likely that no visible difference in the EBI would have shown anyway.
Then we held both Mod 3C devices at the same time, merging the image into a bino view. Whoa! That was amazing! We both had an Astronomik 12nm H-a filter, so we put those on and tried the hand held BV mode again. This was really eye-opening… literally. Now I know what Eddgie and Gavster mean about the effect of NV binoculars being more than the sum of the parts! Three differences make it pretty great: first, the image is wider so I was seeing a larger FoV, second, there is a perceived overall brightness increase, and third, it’s just more relaxed viewing than with a monocular… perhaps the most important factor of the three.
Then we compared Moshen’s Mod 3C and my Micro, holding the white phosphor or the green phosphor for quick, same-eye, comparisons. I found that the Mod 3C with its WP tube, showed a very tiny bit more contrast when aiming at dark terrestrial spaces where trees provided a very dark background. Just guessing, my thought was that the difference in gain and photo cathode response was presenting the slightly brighter image in the L3 tube. However, turning both NVDs to the sky at 1x, where there was more light, there was almost no detectible difference in the image… equal brightness (Mod 3C using full gain), equal sharpness and about the same halo around bright stars. And, no bothersome scintillation in either device.
We added the H-a 12nm filters, and here I saw a bit more difference in brightness, but it was quite subtle. The Micro/F9800 presented a tiny bit more perceived scintillation, so the tube was probably working a bit harder with less available light because of filtration. Pointing the Micro at the stars (where more light was available), I could see no difference in contrast between the Mod 3C and the Micro, except for the color difference. Stars were just as bright and sharp in the Micro as the Mod 3C, and there was only a slight bit of scintillation; it was far from being distracting.
THEN, I held both the Micro and Mod 3C up (both at 1x with gain turned all the way up on the Mod 3C) and merged the image like a pair of binoculars again. WOW! The really strange aspect of this “experiment” was the way my eyes/brain merged the color of the two NVDs. With one green and one white phosphor tube, the merged image appeared as a slightly greenish-blue tint for both of my eyes. This seems like a game changer to me. If a lower spec tube (read that as less expensive tube) can show the night sky this well when used with a higher spec tube, then NV BVing is within the realm of possibility for a larger number users.
Cost? I purchased a brand new Micro housing kit from NVD with ocular for $525. The 12 yr. old F9800 thin film tube was $900. Now, I have ordered two Computar V5013 C-mount objective lenses $100 each to use with my Micro and Mod 3C, along with two $5 step rings so I can use my 2” filters as first surface objective filtration… for 2x BV observing. I’ll report back on this continuing “experiment” in a few weeks.
Thanks to Joelin for getting us together. Thanks to both Joelin and Moshen for such a great evening… and to Moshen for sharing his NVD for the comparisons. We had lots of NV discussions during the evening. The next morning, we had a late breakfast and chatted for 2 hrs. before heading home. Although Moshen and I have known each other on-line for 2.5 years, this was our first in-person greeting, and it was a great pleasure.