Stub Mandrel

I would say that, in the UK at least, perhaps not on top of a volcano in Tenerife, seeing is the limiting factor. Imaging planets or the moon with live video shows how much things get spread, even on apparently 'perfect' evenings!

Just seen adam's comment - I think his point about ASI1600 (with 3.8um pixels) and a Canon 450D with 5.7um pixels making focus more critical is valid.

A 1-degree change in temperature will change the length of a steel 600mm f/l scope by about 0.004mm. For a f4.5 scope like the 130P-DS the 'critical focus zone' where the focused image of a star is smaller than its airy disc is 50 microns or 0.05mm http://www.wilmslowastro.com/software/formulae.htm#CFZ So assuming you focus perfectly in the middle of that zone, a temperature change of just over 6 degrees will put you out (just) of focus. The 130P-DS when used with a DSLR pretty much matches the pixel size to the size of the airy disc of a perfectly focused star. I suspect the extent to which any out of focus caused by thermal expansion will be detectable given the added effects of seeing on star sizes (I have never got stars smaller than about 2 pixels across).

Not sure if this will be clear, I've trimmed the nylon button with a scalpel to tidy it up.

If I have learnt anything from my dabbling in engineering, it is that if the best engineering solution is the one that maximises performance and reliability and minimises cost and complexity, it rarely satisfies the wants of upgraders. The performance of the 130P-DS, like any newtonian, is down to the quality and design of its optics, the ability to collimate and focus it accurately and its stability (i.e. how well it keeps collimated and focused in use). For me, the main improvements would be: Making the collimation smoother by using a spring loaded arrangement. A better focus lock screw (I plan to chop the end of the nylon button shorter as it seems to have bent slightly and can put focus out when tightened.

Cheap white PLA... Still waiting for 8" ducting pipe so I can make a Newt! First two orders off ebay got cancelled, presumably the stock level was a fantasy... ?

Looks like it passed ?

I miss disposable plastic bags, for all sorts of uses, from rubbish bags to removing silicone from my hands. At least 'bags for life' are more robust and you only need one, not two double-bagged for safely gathering in the dog-doo Joe Walsh style.

I once got sent an AVR by Farnell, about 12mm square. It was between two anti-static 'Waffles' for holding, say, 256 ICs, and about 30cm long. In a plastic bag. Inside a cardboard box. Surrounded by bags of air. Inside a box big enough to hold a PC and accessories. I have no idea if this was rank stupidity or some witty employee taking the proverbial ?

I saw Slade in 1984. A good mate of mine who had dropped out of uni but stayed in town promoted them in Aberystwyth. I got to be local crew and see the band close up, and we watched from the best Private Box in the building (it would have been more fun at ground level) ? I'd seen lots of bands like Sabbath, Motorhead, Jethro Tull, Rush, Stranglers etc. etc. etc. but for some reason, I'd assumed that all the 'Top of the Pops' bands of my teenage years like Mud, Sweet etc. weren't 'proper' rock bands. Slade put me right on that...

Took this one with my phone last night ? Hand held, steadied against a scope.

So near but so far last night... I left my SD card at home which wasted half an hour fetching it. I also forgot my dewshield. My shots of M81 and M82 were washed out by light pollution and moonlight, while my attempt at a faint nebula in Auriga lost to the moonlight and condensation A final run on M42 as the moon was going down showed how close I was to decent data. This is just a screeen grab of a stack, crudely processed, you can see the promise ruined by the blur caused by condensation...

Nice one. Astra Image would do a good job of controlling that sort of noise.

Show us your neck-strap...

I had the green plug/sockets melt - now direct soldered. I also had a heater cartridge fall out and reduce a print to a molten mess. I now use a hot end with a clamp rather than relying on a screw against the cartridge.

That would work. For now just block it with a towel or similar and see the difference.

I think I've had more success with cooling reducing noise. Here are two-minute master darks from DSS, both from a similar number of frames, one cooled, one not. It's fairly easy to see the difference by the histograms. Even if you moved the lower point on the uncooled one so they were equally black, you can see there is much more noise

I typed this before seeing your photo: You need a BIG heatsink. That's at least 140 watts to dump, so to keep the heatsink no more than 10 degrees above ambient you need a 1/14 = 0.07 degree per watt heatsink. The temperature of the finger is cooling below the HOT side of the peltier, not ambient, this means you need to dump the relatively tiny amount of heat in the camera and all that power you are putting through the peltier. You need forced cooling to keep the hot side as close to ambient as possible. If the heatsink is inadequate you will actually heat the cold finger! It can be better to use a less powerful peltier if your heatsink is too small. I use a 40W peltier, with a big heatsink and an 80mm fan. Having seen your picture - what insulation do you have on the back of the cold finger? it doesn't look like much. I have a 3D printed box, filled with foam, and all exposed copper is foam covered.

Don't use the camera sensor, miles from the imaging area. I just put an NTC sensor on my cold finger where it enters the case. After five minutes the temperature was pathetic, about 11C, peeled back the foam to take a look and there's ice forming on the cold finger.... I seems the sensor needs to be intimately fixed to the cold finger to be accurate. Also... a BIG heatsink and a decent fan are essential.

Good luck, let us know how you get on.

From an engineering perspective the payloads of mounts are questionable without actually knowing what the limiting factors are. It's very difficult to believe that the mounts are actually modelled or tested to define a limit in a strictly scientific manner. I would imagine they are just tested by piling on dead weight until they cease to operate properly, then benchmark load that is rather lower is assumed and a lower one again taken for imaging. The 50% rule for imaging can be no more than a rule of thumb, a very long visual scope puts more demands on a mount's accuracy and mechanical robustness than a short focal length imaging scope of similar weight. Also, the manufactuer's specifications will probably be grounded in assuming the average user will not be setting up with great skill. Their concern will be that it happily handles the scopes they sell if for even if the user hasn't balanced them properly, for example. Also they need to show that each mount can handle more then the next smallest - without making the smallest ones seem totally inadequate. The bearings used are capable of supporting heavier weights by a factor of at least ten. A properly balance load is unlikely to be difficult to drive, but balancing in all tree dimensions is impractical; we have to accept some out of balance (indeed some is useful as it counteracts backlash) but this needs to be kept low enough not to overload the drive. This means the net out of balance of a large scope needs to be kept as low as with a small scope. The heavier load will have greater inertia/momentum and this may make it slower to respond to guiding and more liable to overshoot. A heavier load will probably have a lower resonant frequency and this may make it steadier. With an overweight but balanced load, I feel greatest risk of damage would be stripping gears by trying to accelerate or decelerate an overweight load too fast. My intuitive feeling is that if fast slewing of long, heavy scopes is avoided and care taken with balancing the mount is unlikely to be damaged. In terms of performance, overweight may degrade the absolute performance, but I am sure this would be a gentle falling away rather than a sudden 'cliff edge' (as would happen if the mount was unbalanced and stalled a motor). My experience is that an EQ3 will quite happily handle a 150PL (quite a big scope, 1200mm newtonian) for astrophotography, and that to do this successfully what was needed was an EQ5-style tripod. In other words, the wobbly standard tripod was the limiting factor, not the mount. That said, I now use an HEQ5, my main conclusion is that teh bigger mount makes setting things up a bit easier, but not as much as I expected.

I got a thick layer of hoar frost on the front glass of the sensor. I took this as a good sign - the sensor itself must be well below zero to do this, backed up by a minute level noise (other than a few hot pixels) in my darks. Recently the wiring for one of my three paralleled dropper resistors fell off and even with 2/3rds the normal heating thr sensor gradually misted over. I had to experiment a fair bit, I wanted the lowest possible heating current that kept the sensor clear on a damp night. I suspect CCD's are better sealed than DSLRs. Neil

I have a suspicion that they are always made to require at least a small spacer to allow for variations in camera sensor distances. Coma correctors don't seem to need similar adjustment so I'm guessing they are less critical as they work in a different way.