michael.h.f.wilkinson

Creating a mosaic in MS-ICE is a piece of cake. Once you have stacked each of the panels, and sharpened them, just put the results into MS-ICE and away you go. The main thing is to ensure enough overlap between adjacent panes of the mosaic (20-25% is generally enough), and it does help to keep the exposure times roughly constant. MS-ICE can also handle very big images. This is a 155 Mpixel mosaic taken with my C8 and ASI183MC.

That sounds about right. You can always do a mosaic to capture the whole moon. MS-ICE (Image Compositing Editor) is perfect for this (and free). Stellarium also has a handy tool to visualise the FOV, if you enter the right scope and camera specs

Well, if you like seeing lots of little luminous seagulls filling 50% + of the field of view, it would be great

For imaging there are various solutions, but for visual, an ultra-fast scope really doesn't add anything, except nightmares for eyepiece designers. In theory, a fast scope gives a wider field of view, but that has its limits. Suppose I have an F/2 scope. The very longest EP I might try is a 14mm to reach a 7 mm exit pupil. Anything significantly longer is going to effectively reduce that precious speed and aperture. This F/2 14 mm combination is going to give me the exact same view as a 28mm EP in an F/4 scope, assuming the EPs have the same apparent FOV. This is simply because the same amount of light is spread out over the same apparent field of view, the same solid angle, assuming the transmission through the optics is the same. However, the F/4 scope is likely to be better corrected, needs fewer elements to get the correction right, probably has a smaller secondary obstruction, and the eyepiece can be considerably simpler at F/4, so again, less glass, fewer glass-air interfaces are needed. That all adds up to the F/4 scope with a 28mm transmitting more light, being better corrected, lighter and cheaper than an F/2 scope. Note that for imaging speed is of importance, because the same amount of light is concentrated on a smaller surface area (in square mm). So for a given sensor or pixel size, more light is gathered per unit of time

Very nice indeed. Don't think my mount would take that, however.

F/10 or F/12 makes very little difference, especially if quality EPs are used. The views of planets through my C8 with e.g. a Pentax XW 10 or XW 7 are excellent. Even F/6 or F/8 should not be a problem for quality EPs. The above image of Jupiter was taken with a Meade TeleXtender, which works fine, but I cannot see the difference between the image obtained by a 14mm Delos with 2x TeleXtender and XW7 without. The great advantage of shorter focal length is the wider field of view you get. My C8 at F/10 gives me a maximum field of view of 1.34 deg in a 2" EP, whereas the classical Cassegrain would give 1.17. By contrats, going to F/15 as with certain Mak-Cas designs gives only 0.89 deg FOV.

My C8 has been my all-round visual scope for several decades (over 25 years of service), very easy to lift (5.3 kg, 11.6 lbs), collimation is rock solid. I have a 6" F/5 Schmidt-Newton for wider views, and an APM 80 mm F/6 APO triplet for even wider stuff, and solar observing. I have used a Questar 90 mak-cass (not mine). Excellent little scope, which can't touch the amount of detail my C8 can bring out in good seeing (neither can my APO triplet, aperture is king on planets). Note that the Questar has 31% central obstruction, the C8 33% Not a big difference. I have thought about getting larger aperture scopes (and might still do so), but I do not think the C8 is going anywhere soon, especially when it can produce these kind of planetary images.

Try M13. It shows up distinctly as a fuzzy ball (no stars resolved) easily found in the trapezium forming the body of Hercules. Note that you should not expect to see anything like the photos, stars are only really easily resolved with an 8" scope

I actually have a student working on a very different, very fast approach to star removal. It would be interesting to see how that fares on reflector data. Ideally we should have a prototype running by the end of next month, but to date he only has data from my 80mm refractor and 6" Schmidt Newton available, so no diffraction spikes

I have found the majority of the Messier objects with similar bins, so it is definitely possible. Which ones were you trying to find?

I don't think I want my scope outside in the kind of weather we have had here recently. I do store them in a comparatively cold (but dry) garage (now mainly bike shed), so cooling time is limited.

I built my own. I don't really have a plan, but I am pleased with the result. I use a Dobson-like approach of Teflon disks to ensure smooth motion The parallelogram itself is held in a kind of fork mount. The arms of the parallelogram are made of thin strips of hardwood glued together to counter warping. It holds my Helios LightQuest 16x80 bins very nicely indeed

I actually managed a glimpse with the Coronado 60mm. Big AR indeed, quite a bit of plage visible. Didn't note any flaring at the moment. Nice prom fairly close by

Looks very interesting. Thanks for the heads up. Cloudy here, alas

Very interesting discussion. I am getting a Starizona Night Owl 0.4x reducer for my C8, and whilst no RASA, it is a big improvement over what I can currently achieve. Its image circle also fits the ASI183MM I have neatly. I will certainly see whether I can image this region, preferably from the Lauwersoog Dark Sky Park. The RASA is still definitely on the wish list, of course. I might also give this region a wide-field shot with the Sigma 50-100 mm F/1.8 zoom, just to see what happens

Nice one John. I remember picking it up some years back (consulting my log, it was August 22, 2012), and being pleased at picking up this distant globular (quite easy with the C8), and adding yet another Herschel-400 object to the bag. The three planetaries on that list are also well worth a visit

By default APP saves results linearly, so only the brightest stars are visible. You can save the stretched version, by using the save button below the histogram, and not forgetting to have the box "stretch" ticked. If you can post the linear fits file you have, I can give it a go if you like

Good M101 given the amount of exposure time. I tend to use APP not just for stacking, but also its gradient removal and background and star calibration tools. Even pretty nasty gradients are dealt with well in the "remove light pollution" tool of APP

I got these shots of NEOWISE last year with a Sigma 50-100 F/1.8 at 100 mm and full aperture. I also used it with my ASI183MM-Pro on some wide targets (at 100 mm and full aperture) Stars are not perfect, but I am quite happy with the results

I would happily go for either as a first, all-round visual and planetary and lunar imaging scope. I got my C8 over 25 years ago, and never regretted buying it. It is compact, has nice aperture, travels well, holds collimation as a rock. For DSO imaging, and wide-field views, the APM 80 mm F/6 triplet with reducer/flattener is way better. Then there are Mak-Newts. These can provide aperture enough for lunar and planetary, and are fast enough for DSO imaging. Heavier than the corresponding SCT. If I didn't already have a 6" Schmidt-Newton, I would certainly be considering a Mak-Newt.

But personally I would not start with an 8" F/10 scope for DSOs. Not easy to guide, and long exposures are required. The reducers (typically 0.7x) for the EdgeHD scopes are far more expensive than the 0.63x reducer/corrector of the SCTs, and even the Starizona 0.4x reducer is cheaper. The 0.63x give pretty decent correction over an APS-C sensor, and the 0.4x appears to be well corrected for an ASI183-size sensor.

For imaging, the eyepieces don't really play a role. In that image, as I recall, I used a 2x TeleXtender and ASI224MC camera. Right now I would probably go for the ASI183MC without additional optics. Visually, eyepieces can certainly make a difference, but at F/10 the SCT or EdgeHD scopes aren't picky. Simple Plossl designs will work well (I used them for a long time, before switching to something more expensive). I think these scopes come with something like a 25mm Plossl, which is a pretty decent EP to start with. For planets, a few EPs around the 10mm mark would be useful. If you can take the short eye relief, Plossls and orthoscopics are fine at the shorter focal lengths for planets. I cannot stand the short eye relief, so would opt for something like the Vixen SLVs, the Pentax XFs (not that expensive, but only available in 12mm and 8.5mm). If you want to splash out, Pentax XWs and Tele-Vue Delos EPs are great, and offer a much wider FOV. Be sure to read this post before spending:

For imaging, I think the CGEM has a clear advantage, especially with the heavier OTA of the C9.25 (considerably heavier than the C8). Note that you can always put others scopes on the mount. Planetary and lunar imaging are a lot easier to master than DSO, and are a lot quicker in practice, because you don't need hours of exposure time. I have been using my C8 on its Vixen Great Polaris mount for planetary imaging for a long time before getting a smaller scope (80mm F/6 triplet) to start doing DSOs. You can always first get the C9.25, which is outstanding for planets, both photographically and visuall, and great for DSOs visually, and add a DSO imaging scope (or two ) later. To get an idea of what a C8 can do on planets, here is one of my best planetary shots (when Jupiter was a lot higher in the sky, I should add):

A, the good old 4077. Now why don't they do reruns of that show

BTW, the 8" EdgeHD is no slouch on planets and the moon either. I have the classic C8, and it gives great results on the planets, moon and sun, but in terms of guiding, even with a focal reducer (0.63x) it is quite a handful. Most of my DSO imaging is with either a 80 mm F/6 triplet with 0.8x focal reducer, or my Meade 6" F/5 Schmidt Newton. I am getting a Starizona Night Owl 0.4x reducer (for regular SCTs, not the EdgeHDs), and that brings the scope down to a more manageable 800 mm focal length at F/4. The image circle is only 16 mm however, but that fits my ASI183MM camera precisely. That reducer is not suitable for DSLRs. If planets are your passion, however, the C9.25 has the edge