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Night Vision with 90 mm Refractor, Bortle 4 SE Sky


Maxim Usatov
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Got a chance to take 90 mm refractor out with PVS-14 under Bortle 4 skies in South-East England. Initially planned for a bigger telescope, but literally didn't fit into my car with all the family belongings and whatnot, so had to change last minute to a grab-and-go rich field setup. Had clear sky four nights, high humidity though, and dew overcoming my heating, settling on the lens on a few occasions. It was quite cold, so had to limit myself to 2-3 hour sessions. This is in no chronological order, as brighter, spectacular objects were mixed with faint fuzzies description of which would be unremarkable.

Leo Triplet – all three galaxies, considerably bright and small, fit nicely in the 3-degree field of view of a 40 mm Plossl at 13X magnification. M66 and M65 exhibited bright stellar cores, with a 12.3 magnitude star seen on the eastern side of M65. No dark lane visible in the fainter of NGC 3628 “Hamburger” due to poor image contrast, as transparency was only 4 out of 7, and the sky was bright, but the galaxy’s rectangular side-on shape was obvious. Albeit lacking much detail, the triplet at 35 Mly was a magnificent unforgettable sight.

M51 and NGC 5195 pair was beautiful, considerably bright (cB) and small (S), with hints of spiral structure appearing as a concentric circle. Was happy to see this pair live, especially spending much time processing deep view of it and learning how to combine data from different telescopes - more than 10 years ago. I couldn’t see the bridge between the two galaxies at 13X with certainty, albeit returning to this location on two different nights, although on one night I thought I could see it.

M81 and M82 were simply stunning, both bright (B), fitting in the same field of view at 13X. M82 showed knotting and asymmetric irregular brightness distribution and two, occasionally three, dust lanes running perpendicular to its body, popping in and out of view. The details were more prominent with a 2X barlow providing 26X magnification. I think I could see irregularities in M81 gradient, signifying hints of structure, but this could have been an illusion.

M106 (cB, S) extended almost edge-on, had a bright core and a faint disk. In my log I have put ~ 30-degree inclination to the line of sight, which corresponds nicely to 27 degrees in the literature (Ann & Yu 1981). A hint of the dust lane on the south-eastern side. I should have probably used higher magnification to confirm this, but the cold weather and lakes of water forming on the atlas have dented my enthusiasm.

Other galaxies demanded a darker background, warmer weather and more aperture to enjoy, so I just made a few brief remarks in my log and went on. I visited a number of galaxies from NGC, M105 (F), M63 (cB, ~ 30 degrees edge-on disk), M96 and M95 (cF), M108 (F, bM), M109 (vF, S, bM, stellar core). I couldn’t detect Leo I at all. The “Black Eye” M64 had unusually bright center in contrast to its faint disk, similar to M106, due to all the dust excess in it, I suppose. M101 appeared as faint, round, featureless glow (bM), with scintillating stellar core.

From NGC, remarkable was the 2903 in Leo (cB, S, R, gbM, stellar core). I thought I could see the dust lane in 4631 “the Whale” (cF, S, edge-on), but was uncertain. 4565, “the Needle” (F, E, bM) showed no dust lane that night. Dark sky is very important even with NV. If the details are sunken in sky glow, there’s little that could be done to get them out, I guess. The AGC 1656 Coma Galaxy Cluster clearly demanded a bigger aperture.


 

Absolutely spectacular Milky Way objects were those within about 30 kly – the right niche for a 90 mm f/5.6 refractor:

M35 is one of my favorite small telescope objects, very bright and rich open cluster, brilliant even without NV. In my log I’ve recorded it as Trumpler class III3r. The much more distant NGC 2158 nearby appeared virtually as an irregular globular - a small roundish haze, unresolved at 13X, and completely unseen without NV that night. The Interstellarum Deep Sky Atlas lists both M35 and NGC 2158 as visible in 4-inch aperture, but the latter is actually a difficult object being 6 times further away. NGC 2158 partially resolved into stars with 685 nm IR-pass filter, which provided the best contrast on open clusters.

M37 is another spectacular open cluster, detached with strong concentration, recorded it as class I2r. Without NV, a reddish 9-magnitude F8 star HD 39183 was prominent in its center at 29X magnification. M35 and M37 are objects that, I think, can deliver equal amounts of excitement with and without NV.

M36 “the Frog” is quite a curiosity nearby, recorded as class II2r. I could see its irregular shape resembling T. rex footprint rather than a frog. I suggest it should be renamed the T. rex cluster!

M38, bright open cluster, appeared as a four-petal shape with an underdensity of stars in the middle, recorded as class IV2r, as it wasn’t much detached from the field in the NV view.

M3 globular cluster was splendid, very bright – literally photographic view. Amazing! Only the core region remained unresolved at 13X, however, when I switched to 26X, I could immediately resolve stars right in its center as well. It appeared even better at 38X, producing more resolved stars as I pumped up the mag.

M13 appeared partially resolved, very bright, many individual stars seen - with curved “arms” emanating from the center. Just out of curiosity I’ve tried looking without NV and got a fuzzy ball with some individual brighter stars resolved – a very much different view. NV works wonders on star clusters. It was fairly low on the horizon for me, so M3 took the throne of being the most spectacular object this trip.

M67 – one of my small telescope favorites as well – appeared bright, rich, fully resolved, class II2r.


 

Other objects:

M53 (cB, S, vmBM), a more distant globular cluster at ~58 kly, appeared significantly more concentrated than M3, with few stars resolved on the periphery. I couldn’t find NGC 5053 nearby.

IC443, “the Jellyfish” supernova remnant (F, S) appeared as a cometary shape, well-defined edge on one side. 7 nm H-alpha filter provided the best view. Faint with 12 nm H-alpha filter, and not seen at all with IR-pass, DGM NPB filter or unfiltered.

M97 “the Owl” planetary was more of a technical exercise. Not seen at all unfiltered in NV to my surprise, but considerably bright with 7 nm H-alpha filter, albeit still a featureless round blob in a sea of noise – no eyes seen. 12 nm H-alpha filter produced an image with less noise, but less contrast. With 642 nm IR-pass filter it was very, very faint, irregular glow. I remember seeing a much better image with C11 on a darker sky in Ukraine about 15 years ago, without NV, of course. The problem this trip was the lack of transparency.

On galaxies unfiltered views were definitely the best. 685 nm was the winner for star clusters, and 7 nm H-alpha for HII emission nebulae.

Whew, anybody still reading this?

Max

 

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Edited by Maxim Usatov
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2 hours ago, Maxim Usatov said:

Thanks, Marv. I am actually much slower - this was 2-3 hours per night, 4 nights. 🙂

Sorry, didn’t pick up on the ‘clear four nights’ bit. Even more thumbs up from me going four nights on the trot to a darker site. You deserve that entry in your diary and thank you for sharing.

M

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Great report Max. Nice to see a night vision report given there are only a few UK astro nvers.

Currently, the skies are not that conducive to night vision with a small scope as a) night vision is more impressive on emission nebulae, and b) due to need to use long focal length eyepieces (to get brighter views), the image scale is too small for many of the objects as you stated. I think a minimum of 10 inches aperture is really needed with nv to get the best of these smaller objects.

August/September will be a great time for your nv plus 90mm refractor as Cygnus will be high in the sky and Sagittarius is also nicely visible. A few days ago I got up at 3am to catch these with my nv and 103mm Binoscope. Absolutely fantastic views even from light polluted London of the North American, pelican, gamma cygni, crescent, eagle (dark pillars of creation visible at 10x mag), and swan.

As an experienced observer, I’d be very interested in your initial thoughts regarding standard glass observing vs night vision observing? Which objects do you prefer with each one etc?

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Thinking out loud, "standard glass" would be needed to perceive colors - carbon stars, double stars, open clusters and PNs, and some very bright emission nebulae. Also, NV tends to flatten the dynamic range, so estimating concentration class of globulars, or brightness range and even the degree of detachment of open clusters could be confusing. During this trip I had NV most of the time and used standard glass to complement the view. What other situations could be there - wide fields of view, perhaps? The 40-deg AFOV of PVS-14 doesn't bother me much, but going back to 76-deg Baader Morpheus produces wow effect, especially with Technicolor back on.

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Enjoyed reading your report Max. Good to see someone else enjoying night vision in the UK. By way of comparison I observe from central London - the very worst skies for deep sky. But tonight I had great results on M3, M5 and especially M81/82. I was using Takahashi FC-100DC and Delite 18.2mm with Baader 685nm to bump up the scale (my main NV nebula scope is F/3.3 Epsilon 130d, but it’s difficult to get sufficient magnification for small targets like globs), and tonight’s set up really paid dividends at around 40x, despite the near full moon.

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Galaxies from central London? Really puzzled. I could barely see NGC 2903 in Leo which is quite bright, but transparency was not very good that night. I would be very curious to compare views through different telescopes/NV devices. Probably need to try pump up the magnification. Bright globular clusters are looking extremely good in NV indeed!

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1 hour ago, Maxim Usatov said:

Galaxies from central London? Really puzzled. I could barely see NGC 2903 in Leo which is quite bright, but transparency was not very good that night. I would be very curious to compare views through different telescopes/NV devices. Probably need to try pump up the magnification. Bright globular clusters are looking extremely good in NV indeed!

Transparency is key, for sure. But I was surprised just how good views were yesterday, considering brightness of the Moon. First time I’ve tried this combination on M81/82, but am now going to explore further with Delite 18.2 and 100mm frac on star targets, where the speed of the system is less critical than with nebulae.
Night vision continues to surprise. I’ve had some evenings where an ‘easy’ target like the Nth America nebula is only just visible, even with a 3nm Ha filter. Never quite know what you’re going to get.

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