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Don Pensack

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About Don Pensack

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    Audio, films, traveling, and astronomy of course.
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  1. all large Hydrogen emission nebulae, like M42/43 emit most of their energy at H-α and H-ß But, all of them also emit light from the excitation of other ions, like O-III, S-II, N-II and various Helium wavelengths. So looking at M42, say, with an O-III filter will reveal different details than you might see in a narrowband UHC-type filter simply because the contrast on the O-III features will be boosted. But, that will be at the sacrifice of the H-ß features. The combination of the H emission and O emission will probably yield the largest view of the nebula. M42 is so bright, it is a special case. I've verified several times that it damages your night vision because of its brightness, which is why it is one of a very small handful of nebulae in which color is seen. I usually see the most color and the largest extent of nebula in that one with a broadband filter (example Baader UHC-S) or a UHC filter with unrestrained red (examples: Astronomik UHC or DGM NPB), but, so far, nothing has beaten the view of the nebula in my 12.5" at a high altitude site (2550m) under skies of mag.21.95 mpsas (essentially pristine--no light pollution at all) without a filter. That night, not only were greens and reddish hues visible, but also beige-yellow and dusty rose, and bluish hues. And nebulosity was seen all the way to NGC1977, which appeared distinctly blue.
  2. Since I've used narrow bandwidth filters with 50mm finders and even with the naked eye, I'll try to explain: The narrower the bandwidth, the greater the suppression of non-nebular light and the greater the contrast between the nebula and sky. Some people with smaller scopes have remarked that this makes the overall field image too dim for the small scope because it dims the stars and the sky, leaving mostly the nebula, and the nebula is fairly faint in the first place in their scopes. I think at least part of that, and the reason some have said the narrower filters are better in larger apertures is that they are not using the filters correctly. There are some "parameters" of use that have to be followed for them to work well: 1. You must be completely dark adapted--at least 30-45 minutes outside away from all lights--for the sensitivity of the eye to increase to its maximum. 2. You should use low powers: a maximum of 10x/inch of aperture, or an exit pupil of 2.5mm and larger. 3. the filters don't work well in a hazy, cloudy, or otherwise not clear sky, and I KNOW a lot of observers tend to observe in those conditions, despite the poor results. 4. the nebula in question should be higher than 30° from the horizon or extinction due to the atmosphere will reduce its visibility 5. nebula filters work better if the background sky is not so bright that the improvement isn't sufficient to enable you to see the nebula. Nothing can make a faint nebula visible in bright city lights. 6. Use the right filter on the right nebula. An O-III filter isn't the right filter to use on a large hydrogen emission gas cloud like M42, M8, M20, M17, M16 because it suppresses the light from hydrogen emission. The nebula filters work by dimming the background by 2.5 to 3 magnitudes while only dimming the nebula by about 0.05-0.1 magnitude. A wider filter dims the background less so doesn't improve contrast to as great a degree, Hence, the visibility of the nebula will also be less. Yes, there will be some contrast enhancement, but the extra brightness of the background will only reduce the size of the nebula seen and reduce the details seen in the nebula. When I have used an O-III filter to see the Veil Nebula with a 50mm finder scope, the field did darken, but the nebula became visible. That's the purpose for the filters, right? To make the nebulae more visible to the eye when looking through a telescope. In a really big scope, where the nebula is easily visible without a filter, paradoxically a wider filter can be used and still see a good view of the nebula. Less contrast enhancement still works when there is aperture to waste. Still, even there the narrower filters improve visibility more and create greater contrast. And contrast enhancement even works at very dark sites by suppressing sky glow. So, other than price (the main motivator for the purchase of a lesser-performing filter), might there be a reason to prefer a filter with less contrast enhancement? Maybe, if the overall field + nebula is what the observer is viewing. NGC2359 is in a rich Milky Way field and seems to sit suspended in front of a background haze of faint stars. The best contrast for the nebula suppresses the starlight and reduces that impression of the field of the nebula. If studying the nebula only, the narrowest O-III filter is best. But if looking for an overall aesthetic experience, a wider filter might be the choice. But I can say that because I view with 32cm in a dark sky, dark enough to see the Veil Nebula with an O-III filter held up to the eye, and Barnard's Loop in Orion with an H-ß filter held up to the eye. With a little more light pollution, the nebula would disappear, and ONLY the narrowest of filters would make it visible at all. So, back to the small scope: if the small scope has any chance at all to see the nebula, it is by yielding the best contrast enhancement possible, and that is with a narrower filter. But it is a matter of using the filter correctly, as I outlined.
  3. To be fair, ANY contrast enhancement will still be.....contrast enhancement. But some economical filters with better bandwidths include DGM, Orion (US), Omegon, SkyWatcher, Zhumell
  4. The eye relief on the 9mm is 2mm longer than the eye relief on the 5.5mm. You might also look at the 9mm APM XWA, which has 0.5mm more eye relief than the ES9. The half-way point in magnification between your 5.5mm and a 13mm is a 7.7mm, not a 9mm. 8mm would be closest. APM's 7mm 100° is about a month away.
  5. The Delos' upper barrel, like all TeleVue eyepieces, is aluminum. I forgot about the two-part adjustable eyecup on the Delos. Add the weight of that plus the chromed brass lower barrel, and that pretty much accounts for the weight difference with the Morpheus.
  6. I assume you mean later in the year when Jupiter and Saturn are higher in the sky. Right now, they're down in the muck and even low power sees a bad image. The planet "season" is over. With a 130mm reflector, you'll be lucky to break 200x and get a clear image even when they are high in the sky. As a general rule, magnifications over 30x/inch (154x in your scope) get questionable and require pretty darned good seeing conditions, rare when the planets are high in the sky, but impossible below 20°, where they are now. I would suggest you make sure your lower powers are filled in. For example, a good collection of eyepieces for you might be 28mm, 20mm, 14mm, 10mm, 7mm You have a good way of looking at it--achieve ultra-high powers with a Barlow--but the number of nights you'll be able to use any magnification over 200x will be few and the Barlow will receive very little use. I'd get the 7mm--it'll receive a lot more use. But also look to filling in your lower powers if you don't already have them.
  7. A great comment! It points to the enhancement of different details with different filters. That's especially true of M42/43. Even a broadband filter like the UHC-S is wonderful on that object.
  8. Excellent on planetary nebulae, supernova remnants, and Wolf-Rayet excitation nebulae. However, removing the H-ß line in the spectrum hurts the large H-III regions like M42/43, M8, M17, M20, M16 and the large gas clouds like NGC1499, NGC7000, the nebulosity around Gamma Cygni, , the Horsehead, and most of the Sharpless nebula. So it's worthwhile having both a narrowband UHC type AND an O-III filter. But if you had just one, it should be a narrowband so that all emission nebulae get enhanced.
  9. 1) Yes, because a good UHC filter will pass the hydrogen emission from the nebula and reveal a larger size to most nebulae. If you only view planetary nebulae, or the Veil, stick to O-III. Pass on the Explore Scientific filter--it is too wide a bandwidth to be useful. Literally twice as wide a bandwidth as the good UHC filters. Stick to Astronomik, TeleVue Nebustar , Lumicon, DGM NPB and ICS for a UHC filter.
  10. No plastic in the Morpheus--it's aluminum. Per Baader: " Hard aluminium alloy with industrial quality UV-stabilized anodizing surrounds a set of 8 lenses with one ED- and two Lanthanum elements. However, the 17.3mm Delos has a chromed brass lower barrel, and is a bit longer, and might possibly have more elements internally. Nope. I stand corrected--the element count is the same. The 100g difference must be in the outer barrels mostly and perhaps the thickness of internal elements somewhat.
  11. Just be aware, an O-III filter does not work well on the large H-II region gas clouds. A UHC works better on M42/43, M8, M20, M17, M16, hydrogen clouds in Cygnus. An O-III filter will work better on planetary nebulae, WolfRayet excitation nebulae, supernova remnants (except M1, where a UHC works better)
  12. 1. It requires 2.5mm of in-travel compared to other 1.25" eyepieces that have their focal planes at the shoulder of the eyepiece. I doubt that little amount of travel will cause a problem. 2. I can actually get too close to the eyepiece while wearing glasses and experience blackouts. I would guess it might even be a little more than 20mm of effective eye relief. I have a lot of eyepieces that are compatible with glasses, but none has more than the 17.5mm. If you wear glasses, you needn't worry. There is only one category of glasses that might not work: if the lens of your glasses is so large it presses against your eyebrow and you have deepset eyes, then the distance from your pupil to the outside of the eyeglasses lens might be quite large. You'll still see the field, but it could possibly be reduced. But if the SLV works for you, the 17.5mm Morpheus will be just fine.
  13. Nebulae emit light in discrete wavelengths and any other light passing the filter is extraneous to seeing the nebula. The more of the extraneous light suppressed, the darker the background behind the nebula and the more contrast there is between nebula and sky. To achieve that, a bandwidth in the filter that just passes the light of the nebula is ideal. But there are always slight irregularities in the production of filters, so the bandwidth needs to be about 8nm wider than the minimum possible bandwidth of 14.6nm. So a 23nm bandwidth UHC filter would be the ideal. It would be a universal nebula filter and work on all the emission nebulae. Most of today's higher-quality UHC type narrowband filters are in the 22-27nm bandwidth range, like Astronomik, TeleVue, DGM, Lumicon, ICS. A lot of the inexpensive Chinese-made nebula filters are in the 45-50nm bandwidth range, and are not effective at increasing contrast in light-polluted skies. So since only 22-23nm of bandwidth is necessary for maximum contrast, any extra bandwidth just lets a bit too much light pollution through. There is a little contrast enhancement, just not enough to make a large difference. So, what can you do to maximize the experience? 1. Use only low powers with the filter. On an 10" scope, a maximum of 100x. 2. Make sure you are as dark-adapted as possible. That means 30-45 minutes outside, away from all lights, i.e. at least 30 minutes after turning off all lights. 3. Make sure the object you're looking at is at least 30° above the horizon. Your nebula target would lose ~0.2-0.3 magnitudes of brightness at the zenith, and double that at 30°. It could lose a whopping 2.0-3.0 magnitudes at the horizon!! So try to view the nebula when it is near or crossing the imaginary N-S meridian. 4. Make sure the nebula is an emission-type nebula. The nebula filters won't help reflection nebulae like those in the Pleaides or M78 in Orion. 5. Buy the size that fits your lowest power eyepieces, star diagonal, or bottom of the 2" to 1.25" adapter.
  14. Mark The glass is only inset about 1mm from the threaded side of the filter. When pressed into foam, the glass will make contact with the foam as the aluminum around the glass is compressed into the foam. On the other side of the filter, the glass is recessed 3-4mm into the aluminum and when that side of the filter housing is pressed into the foam, only aluminum contacts the foam and the glass is still above the foam.
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