michael.h.f.wilkinson

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.

A regular D-ERF combined with a solar continuum filter would not work, as the D-ERF doesn't transmit green light. A tri-band ERF does transmit the solar continuum band, so it does help. The tri-band SCT passes O-III rather than solar continuum, so you should use a green or O-III filter instead.

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.

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.

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.

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

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).

I have used various H-alpha scopes for imaging, starting with a second-hand Lunt LS35THa. Despite this not being intended for imaging, I got some pretty neat results (with a planetary camera attached). I then got a Coronado SolarMax-II 60mm, to which I later added a double-stack unit. I still have this one at work for visual purposes, after I got a second-hand Solar Spectrum H-alpha filter with telecentric lens (sort of similar to a Quark) which I use in my APM 80mm triplet refractor. The difference between the three systems in imaging is shown below (click for full resolution) Left to right: Lunt LS35THa, Coronado 60 mm single stack, APM 80mm with Beloptik Tri-Band ERF, Solar Spectrum 0.3 Å H-alpha filter and Baader TZ4 telecentric

I have spotted it quite easily with my C8. At magnitude 12.9 it should just be doable in a 130mm scope

Very nice indeed. If clear outside is right and I get some clear skies I might well go for this target tonight and/or tomorrow night

Very nice first result! Good detail showing

Brilliant idea, might well give that a go!

I have had the Helios Apollo 15x70s and they were excellent, but then the Helios LightQuest 16x80 came along, and it is slightly better and somewhat lighter than the Apollos. The Helios Apollo is a clear step up compared to the generic type, the LightQuest 16x80 is just as easy (or difficult) to hold as the Apollo 15x70, and a marked step up again.

Interesting. The FOV in the Zeiss Victory is pretty good (7.45 deg vs 6.4 for the Trinovid), and clearly better than the cheaper Zeiss Terra 8x25 (6.8 deg). I assume the FOV in the Leica was in part due to restrictions imposed by the narrower optical tubes, given the smaller aperture.

I did consider Swarovski, but like my comparison of 10x42 roof prism binoculars from Zeiss, Leica and Swarovski, I found the Zeiss just a touch more comfortable. Otherwise they are very close in optical performance. The store I went to didn't have similar Leica in stock this time, so I just compared two. Eye placement in binoculars is a very personal thing, so your mileage may vary.

Found some Opticron ones that seem to fit the bill exactly https://www.opticron.co.uk/our-products/accessories/rubber-objective-lens-covers/31027-rubber-objective-lens-covers-25mm-og-l-pair

Yesterday I bit the bullet and got myself an ultra light pair of binoculars (because of course I need more binoculars). The aim is to have a quality pair that I can keep in my coat pocket, so it can travel with me without adding much weight to my luggage. I settled for the Carl Zeiss Victory 8x25 pocket binoculars, given the stellar reviews, and the stellar performance of my other Zeiss Victory binoculars (10x42). These bins have a curious asymmetric design. and fold up to a tiny package. They come with a handy protective case but sadly lack lens caps of any description. I have found 33.7 mm eyepiece caps fit snugly over the eyepieces of these bins, but don't quite fit over the objectives. Optical quality is outstanding, as you would expect, and the eye relief is sufficient for me with my glasses. Hope to bring them to Texas for the eclips, and intend to make some solar filters for them shortly.

Seeing tends to be better at longer wavelengths, hence the trick

I have picked it up once with my Celestron C8, using a red filter to punch through the rather lively seeing. Even then it was difficult to spot, as a more-or-less constant bright dot in the sparkling mess surrounding Sirius A.

Or take up solar astronomy

It helps me select which objects to chase on the night. I live in a Bortle 4-5 (6 on a bad night) suburban setting, with Bortle 2-3 skies fairly close by. I use my biggest scopes (Celestron C8 and Meade SN-6) on planets and moon on bad nights, but gun for fuzzies on good nights. I have visited Bortle 1 and 2 sites on holidays, and everything performs better there. Regarding the usefulness of the Bortle scale for imagers: I can punch through much of the light pollution with narrow-band filters, and capture stuff that is terribly hard to spot visually, so it seems to affect my observing more. Even without narrow-band filters, I can subtract the sky background in ways an observer could never do, so the horsey is an easy target for my 80 mm in imaging. You do need much longer integration times to reduce the photon noise of the sky background, but long exposures can get neat results. 13 h 2 min 30 s total integration time on the Dumbbell Nebula

I sometimes wonder if at this very high magnification range the atmosphere isn't the limiting factor, certainly in the centre of the FOV. You will need near perfect atmospheric conditions for differences in optics to show up. I am not knocking the Svbony EP in any way, it is just that as optics have improved, other limiting factors come into play.

I have friends in Leon, Spain, and they would love to have me over for the 2026 eclipse

The blue ellipse in the paper is due to H-I (neutral hydrogen at 21 cm wavelength). I am not sure how much that region would show up in the optical wavelengths. I would certainly not expect star-forming regions there, but there may be stars, of course.

I do not know about Sirilic, but I have stacked results from different sessions in Astro Pixel Processor without issues. Note that I stacked the non-stretched versions, with background subtracted.