Stub Mandrel

I'm a convert to a rigid fix. I've never failed to get a guide star with a 2s exposure and a f3.5 scope.

In teh central Atlantic there's an island 27 square miles in area, composed entirely of old telephone handsets and magnifying glass handles.

Cheapest solution? Buy a toy 50mm scope off eBay, fit a 50mm coated doublet from Astromedia, cut down the length of the body to suite (they are 183mm f/l while the originals are usually a fair bit longer) . Use a t-0.965" adaptor with a suitable camera (I use an ASI 120MC). This worked fine for me for a couple of years, but I've now made a nicer body and fitted a helical focuser but kept the lens cell. I have a longer F/.L guide scope for my 150PL which has a 3D printed lens cell, 70mm Astromedia doublet, and a cheap 1.25" focuser of astroboot for about a tenner.

Can you share an example? What you can do is very dependant on what sort of data you can get. If you just want larger with minimal pixelisation, use 'resample' in any good image programme, but this wont add detail. If you get a lot of data you can stack images, this leads to sharper more detailed images that can also be processed to bring out faint details. f you have enough good data you can use 'drizzle' to make the image bigger - typically 1.5, 2 or 3 time larger.

The first two images look good. The last one deosn't seem right. There seems to be a broad dark ring around M27 where the sky background is brown and the rest of the pic has a 'milky' sky background. The other pics aren't like this.

I lost this thread! Managed to get this picture the day after:

Yes, it's disgustingly good 🙂 Perhaps the differences between cooled CCD and CMOS are now largely limited to amp glow (which is apparently really 'support circuitry glow') and if darks can get rid of this the practical advantages of one over the other may now be largely hand waving.

Sorry to but in.. but I always do... why is are CCD subs always so long? is it simply that they have more read noise or this there something more subtle about?

True, worth trying the spreader trick as well - I've had mine too tight to undo with hand pressure until I've put the spreader back on.

Money buys you flatter fields, sharpness to the edge, more contrast, wider fields of view, greater eye relief and better quality construction. But not necessarily more than one or two of these even if you spend a lot of money. Cost goes up a lot faster than the quality. Doing an A/B at our club I could see a very expensive EP being better than one I bought cheaply, but the difference in price was bigger than the difference in the view. That said, I did not have any problems seeing better resulsts with 'affordable' EPs compared to the standard ones thst came with my scope. There are some VERY cheap EPs (look for aspheric eyepiece on eBay). These cost a few quid each(!) have plastic lens elements but are coated and much better than the stock 10/25mm eps that come with most scopes. Worth blowing a tenner on a pair, as they can be treated as 'disposable'. Plossls are always good value general purpose eyepieces, there are ones out there that are very good for little cash in 25mm and 40mm sizes. Avoid short focal length plossls unless you like peering into pinholes. I have a few mid-range EPs that perform very well. A stock Celestron 32mm that came with my C90 Mak (they give you one decent ep rather than two cheap ones). A couple of Skywatcher SWA 'planetary' EPs that work well. Consider second hand. My best quality EP came 'free' with a second hand scope I bought and turned out to be worth s/h about as much as I paid for both (not a fortune). My other more expensive EPs were bought for very fair prices off this forum.

Anything from 400D to 600D is good, getting better as the number gets higher. You can use 400D or lower, but most folks agree the 450D was a big step[ change step towards lower noise & greater sensitivity. The 600D has a fold out screen which is very nice to have. The 700D has some issues with autofocus pixels causing hard to remove yellow lines in stretched pictures that flats don't deal with. I have a 450D, a 1000D (which is the 'economy' version of the 400D) and a 10D which is built like a magnesium battleship but is very poor compared to the others.

Have you loosened off the AZ screws? Alternatively, re-attach the spreader and do it up fairly tight. This can make enough of a difference to lock or unlock the spindle. The peg the az screws bear on will prevent it rotating more than a small amount.

My meteor detecting yagi is held together with black PLA parts, hard to imagine anything more exposed to sun light and weather in this area. Previous weather station parts up on top of the same aluminium pole gradually degaraded so i'm not expecting it to last forever, but after 12 months out I inspected it and couldnt see any signs of degradation, it's been up longer than that now.

? I have PLA parts doing their jobs in the real world. I even found one part that was more reliable printed in PLA than PETG because of the requirements on it and the difficulty of printing consistently in PETG. And yes, I have done experiments such as pull-out tests for things like metric fixings into PLA prints and comparing the strengths of test pieces printed with different orientations. All materials have their limitations, understand these, choose an appropriate material and design well and your parts will cope with the real world.

I've managed to get usable images using 16 second subs in Sharpcap, even with OSC. But it is worth going longer as CMOS does have some read noise! I've found about 30 seconds to be the reliable limit for unguided subs, you can go longer but it's more dependent on mount performance (the odd glitch ruins frames) than PA accuracy (stars slowly become extended with longer runs).

Hmm. Double ended 1/4 whitworth camera adaptor Set of four 50mm castors, two locking. 16A hookup connector. 🙂

I'd agree with whoever it was who pointed out that if you can guide for five minutes, you can guide for 10 minutes or half an hour. CMOS is the obvious option for me because (a) I'm often cloud dodging and (b) my skyglow makes long exposures pointless as it dominates over read noise.

It is, as far as I can tell.

The computer end of a USB3 style cable is backwards compatible - I just bought two 1TB HDDs and they both have USB3 leads but work fine with USB2.

The star K2-18 has appeared as a 'custom object' in Stellarium, but it's virtually on the far side of the sun so a few months before we can get a shot at it! No data on magnitude and it's a dwarf so it may be very faint.The only clue is that the brightest pixel received 1,900 electrons in 103 seconds, this is in IR but it should be detectable with an IR sensitive camera! Weird how the paper talks about the planet K2-18b but doesn't explicitly mention the name of its parent star.

It's that detailed user guide that makes such a difference (not!)

That's interesting. I have one of these, it's... passable but more like 0.8X than the advertised 0.4X

Agreed, I found that LRGB was only worth it if you have really good data, also you need to put everything through WinJupos which can demand massive effort to achieve better results than OSC. If I can get 5000~ frames of OSC the benefits are marginal, at best.

I plan to recruit a mob of mutant henchmen, ostensibly for protection in the case of zombie apocalypse, nuclear war, brexit, asteroid impacts, super volcanoes etc. an to carry my #grabbag. As they won't be busy all the time In between existential planetary crises I thought I could train them to set up and operate my imaging rig, but they seem to be more interested in chewing the legs of my mount and hiding from the cat. Also they won't come out at night, I seem to have mistakenly targeted diurnal, rather than nocturnal mutants with my recruitment literature. 🤪