billyharris72

Thinking about it, the new cooled CMOS cameras could make a great pairing with an EQ3. Rarely need subs over about 30 seconds; even narrowband won't need more than about a minute.

No! You can't do deep sky imaging with an EQ3. You just cant. So stop it ... right now!

A bit of Googling on this suggests bins from about 20 x 80 should do the trick. Seem to remember doing it in my Heritage 130P with a 25mm e.p. (which would be x26) though much easier around x40. As others have said it's not the distance (which is pretty wide) but the relative faintness of te companion that can make Polaris a bit tricky.

Billy.

There is an interesting article by Simon White in Decembers BAA Journal that covers just this issue. He argues that, where the errors in polar alignment are relatively small, the declination of the target is of little practical importance (note that he's assuming PAE of the order of 1 arcminute or so). His little thought experiment is roughly as follows (it's based on the small angle of error meaning we can treat the sky as a flat rotating disk):

Imagine a perfectly polar aligned mount, with the scope focused dead centre on a star (any star will do). Now move the scope out of alignment by a small amount (say 1 arcmin). The star will move exactly this much in the field of view, so it is now offset from the centre by 1 arcminute. If we leave the mount to track for 1 sidereal day (and imagine we could watch the star the whole time) we would see the star describe a circle in the eyepiece, around the centre of the field of view, and return exactly to the point where it started. A distance of 2 x Pi x PAE, or 0.262 arcsecs per minute for a 1 minute error. We know that pixel scale in arcseconds is given by 206 x pixel size / focal length. That means the time to drift 1 pixel (in minutes) is given by:

206 x pixel size  x 24 x 60 / (2Pi x focal length x PAE(arcmin))

He uses this to work out a little table of time (in the article for a Nikon D90) for a one second drift with various lenses and focal length scopes (with an 805mm scope there is 1 pixel of drift every 322 seconds; while a 200mm lens will take 21 minutes for the same drift). The figure from that table can then be divided by the actual alignment error (assuming this is known) to calculate the approximate achievable exposure time. The figure is easy to adjust of you are happy to accommodate more than 1 pixel of drift.

Not mathematically exact, but a straightforward rule of thumb that (according to White) gives results that are very close to the original Hook formulae.

I recently picked up the Versascope (intending to use it for autoguiding) and was quite impressed. It has a bit more aperture, is flexible in terms of accepting a range of eps and has a standard Synta finder shoe. At a push I reckon it could double as an ultra portable refractor (albeit with significant CA and sub-optimal focuser) and should make an excellent, versatile finder.

One thing I will say with regard to RACI finders is that, optically, you will lose relative to classical straight through finders. For me, comparing the Skywatcher 9x50 RACI and 9x50 straight through is night and day, with much more detail visible in the latter. That said I still prefer RACI - what you lose oprtically you get back in ergonomics and intuitve navigation.

Got a (brief, between the clouds) chance to point this at the Moon about 20 mins ago. Thoughts as follows:

• CA noticeable, but not enough to cause an obvious problem, even at x60 on the Moon. Clear views of mountains and the Mare.
• Slight loss of sharpness at x60 vs x40, but the higher magnification still usable.
• Decent view of Theophilis, Cyrillus and Catharina. Central peaks of first 2 and flat floor of the last clearly resolved as is the apparent defile (or is it just shadow) between Cyrillus and Catharina.
• Heading across the Mare Nectaris, Madler, Isodorus and Capella all clear.
• Hopping over to Mare Crisium same is true of Proclus.

Last night managed to catch the rings of Saturn (equally briefly), with views that were acceptable, though using it in darker conditions showed control of stray light is poor (the tube is well baffled, but made of plastic, so slighlty shiny). Also noticed what appears to be a tiny speck that may be inside the zoom eyepiece (though it's right at the edge and not at all intrusive).

Compared with budget binos (I see this scope as occupying a similar niche) I'd say that optically is compares okay to the Strathspey 15x60 and Visionary HD 12 x 60 when it's operating in the x20-x30 range, and the additional range of magnification gives that bit more flexibility.

Of course, I imagine quality control on these is non-existent - I may have lucked out and got a decent unit.

My dad picked one of these up for £20 a couple of weeks ago when it was on offer - I'd toyed with getting one myself but thought better of it. I've had a play with it today (daylight only) and have to say I was pleasantly surprised. To be clear this is not a great piece of optical equipment, but it is also far from the unusable junk I was fully expecting it to be. Basic specifications and thoughts below.

• 50mm objective, with 20-60 zoom eyepiece
• 2.2-1 degree FOV from the instructions, looks bang on from my test. Narrow, but not unusable.
• Weighs about 1kg. Cheap and plastic feeling; not water resistant.
• Focuser knob on top of scope body. No difficulty getting a sharp image at any zoom setting
• Targets (roosting birds, church clock, household aerials) all very clean and well corrected at 20x, and good at 30x. Starts to struggle a bit at higher magnifications.
• Chromatic aberration negligible on targets I was viewing at x20. By x30 it becomes more noticeable, with a distinct yellowish cast to the image background above about x40. Even at x40 it was still possible to get detail on target. Above this CA becomes pretty bad and compromises fine detail. But even so, I was still able to see detail in the eyes of blackbirds roosting perhaps 200m away.
• Comes with a tripod that's so bad it's actually funny.

Overall then, not an objectively great piece of kit, but usable, and for £20 actually very good value. If I paid £50 for bins and got an image as sharp as the image in this spotter at x20 I would not feel ripped off. It's the kind of thing it might make sense to leave in the car as a grab and go option, and at that price it's not something you'd need to worry about breaking.

Could all change under the stars of course - if I get the chance I'll give it a try an post what I find.

Billy.

Another piece of software I've started messing about with is GCX (it's in the Ubuntu repos and I'm sure Debian also). Manages (among other things), image processing, reduction and stacking, fitting field stars to catalogue files / WCS, aperture photometry, telescope control and camera control. Just started with it but seems very smooth and the documentation is excellent.

Good little scopes these. I went for the 80mm as I wanted something really portable and have been pleased with it. It's poor on planets, but with the Baader semi apo filter the lunar views are actually quite good. 

21 minutes ago, Vox45 said:

Note that I was talking about Linux being 'astro ready' for Windows user who want to make the switch in the most transparent way possible. Just the fact that ASCOM and EQMOD are not cross-platform can be quite a turn off for some.

I think the other turn off is lack of documentation. A lot of the best Linux astronomy software is aimed at academic astronomers and observatories; it's not always the most user friendly.

The following list is useful and highlights some of the main software available.

https://help.ubuntu.com/community/UbuntuScience/Astronomy

Also:

Iris

Siril (a simplified Linux native version of IRIS)

Virtual Moon Atlas

Distro Astro seems to have a tonne of bundled software.