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michael.h.f.wilkinson last won the day on July 23 2022
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The TV Plössl 20mm is no doubt one of the best Plössls you can find, but eye relief alone would make me go for the SLV. I have three of these (5, 9, and 15mm in my travel and outreach set) and their performance is superb. They basically give the same optical quality across their 50° aFOV as the legendary Pentax XWs give across their 70° aFOV. I have several XWs so have been able to verify this. It's almost like having orthos with good eye relief.
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Lovely image of one of my favourite galaxies
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Help with Saxon telescope.
michael.h.f.wilkinson replied to Williamc09's topic in Getting Started Equipment Help and Advice
Indeed a 25mm or even 32 mm would work much better than the 10 mm you have on deep sky objects in general. The wider field makes finding things easier too -
How many telescopes do you own?
michael.h.f.wilkinson replied to Grump Martian's topic in The Astro Lounge
Currently I have the following OTAs Celestron C8 Baader/Celestron 8" Tri-Band SCT Meade SN-6 6" F/5 Schmidt-Newton APM 80 mm F/6 APO triplet Coronado SolarMax II 60 Skywatcher ST80 (guide scope) generic 70mm F/5 achromat (giant finder) 60 mm guide scope If we count binoculars as telescopes that would add Helios LightQuest 16x80 mm Zeiss Victory 10x42 mm Lunt 8x32mm SUNoculars Zeiss Victory Pocket 8x25 mm These scopes may be mounted on the following gear: Vixen Great Polaris Vixen GP-DX iOptron HEM-15 ZWO AM-5 SkyWatcher EQ3-2 Tele-Optic Mini-Giro Home-made P-mount -
Show Us Your Binoculars.
michael.h.f.wilkinson replied to LukeSkywatcher's topic in Discussions - Binoculars
Latest family portrait of my somewhat reduced collection of binoculars. Left are the two Carl Zeiss Victory bins: 10x42 mm in the rear, 8x25 mm (donning Opticron objective caps) in front. On the right we have the Helios LightQuest 16x80 mm in the rear and the Lunt 8x32 mm SUNoculars. I note there has been a shift towards roof prisms, and quality rather than quantity. -
Note that a front-mounted ERF (D-ERF or otherwise) just sits in ordinary daylight. It should not get hotter than any other surface exposed to dirtect sunlight. A D-ERF will actually reflect most of the heat, rather than absorbing much, so will stay comparatively cool. A thicker filter is needed at larger apertures not because it is expected to get hotter, but because it might otherwise deform. A half-aperture ERF, i.e. one halfway down the OTA (which is usually recommended as the smallest one you should consider), receives a 4x larger concentration of light, which is manageable for all sorts of optical glass, especially if it reflects the light and heat, rather than absorbing it.
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Most likely, the view would be a lot better with an ERF of some kind. Apart from being safer, the thermal currents in the tube caused by the heat will be massively reduced. BTW, the thickness of the filter isn't really an issue in a D-ERF. In this case, the coatings do the filtering, the glass is merely there to hold the coatings in place. A smaller aperture requires thinner glass to do the job.
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Just had them out under hazy skies, with some reasonably clear patches. Orion's belt stood out nicely, the stars pin sharp across the field of view. M42 could be spotted, but other DSOs like M65 and M66 were not visible in the haze. The optics seem very sharp, but deserve better skies to work properly. I did find eye placement a bit trickier than in daytime viewing, but a slight twist of the eye cups sorted that out. Normally I would use the bigger binoculars for astronomy, but it is nice to have a portable travel option.
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I should add that using an ERF, which isn't required for a quark or Ca-K module, cuts down tube currents a lot. Imaging in Ca-K without an ERF in place causes considerable reduction in sharpness, I find. With my tri-band ERF (which transmits Ca-K, H-alpha, and the solar continuum band) gives much better results. It may be that the larger aperture scopes suffer from similar issues more than a 60 mm would when using a quark.
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I certainly feel my 80 mm consistently outperforms my 60 mm. I have also use an 8" Tri-Band SCT (a modified C8 with coating on the corrector plate acting as a tri-band ERF), and there the effects of seeing are visible, but under good conditions, it shows a great deal more detail, both in white light and H-alpha. In Ca-K seeing is much more of a problem than in H-alpha, I should add. Both images below were taken with the tri-band SCT
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It is always tricky to compare images with the visual impact in H-alpha. The H-alpha image itself is a uniform shade of red, and it takes a while to get used to that. I very often have people looking through the scope and first just seeing a red disk, and then suddenly gasp as the detail pops out. When imaging, I always use a monochrome camera, as I would be wasting 75% of the pixels otherwise. I then stack about 10-20% of the best shots, sharpen, and apply a colour look-up table which runs from black through red, to orange, then yellow and finally white, to bring out detail. Regarding the image quality, aperture of course plays a big role, but the bandwidth of your etalon has a major role to play as well. The LS35 THa and SolarMax have a bandwidth of 0.7 Å (0.5 Å if double stacked). The Solar Spectrum filter is much narrower, and gives more contrast (at a lower apparent brightness).