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How did this work out Rob?

Short unexpectedly clear evening gave me a chance to test my 'cut-out-of-thin-card' Tri-Bahtinov mask last evening. Set up using my normal method of conventional Bahtinov and APT's Bahtinov aid, got us down to a very small error, shown in the first image. I then substituted the Tri-bahtinov and got image 2. (not quite right but not too bad) Racked the focusser out about 0.15 mm (approx 10th turn of fine focus knob on the Moonlight focuser) and got image 3. The spikes have shown some movement. Then reacked the focuser a similar distance back past the original position to get image 4. Again the spikes show some change. Lastly I tried returning to the in-focus point - image 5. From these images it appears that collimation isn't too far off, although I would appreciate any comments/observations on this. Two things struck me while doing these tests, one was how much camera tilt we had and how this would affect the result. (APT gave a figure 8% tilt on an image shortly after the mask was removed.) The other was how easy adjusting the collimation screws to correct any perceived mis-collimation would be in the dark. Perhaps a Tri-Bahtinov grabber (think I've readof this somwhere on CN) would help. For the moment I think I'll stick to Concenter and Cheshire in daylight - which doesn't seem to have put collimation too far out?

I think i read that Siril tilt needs a uniform starfield to work. It averages FWHM in center and 4 corners or something, so can be thrown out by irregular star background. The best check by the way is to use your eyes, rather than fussing over numbers. Egg shaped? Star trails? Looks OK full screen? Good to go. Don't pixel peep, especially with junk gear to start with.

I'd suggest some brighter open clusters (the same type of target as the Pleiades). The easiest to find will be the "Beehive" cluster M 44 in the constellation Cancer, in the SW and to spot without optical aids (sailors in ancient Greek took this as a sign for favourable weather conditions). Not far away (8.2° to the SE) is the densely packed cluster M 67. More to the W, the open cluster (oc) M 35 in the western part of Gemini is a brilliant target. When you found it, you may try to spot the smaller and fainter oc NGC 2158 SW. Always beautiful is NGC 7789, "Caroline's Rose" in Cassiopeia, easy to find close to the star Beta Cas (Caph). Hth. Stephan

Specifically - actually purchased an item. Many thanks, Ewan.

Good evening Elp, Many thanks for the detailed reply. I would like to know if anyone has specific purchasing experience with High Point Scientific. Many thanks, in advance. Kind regards, Ewan.

And also Amazon says usually available in 3 to 7 months, feels like ordering a car.

Apart from ASI224MC and ASI678MC with their total sensors surface smaller than a half of the APS-C ( 😁 ) I have also a 2600MM Pro which is permanently attached to a filter wheel and used with bigger scopes. I think I have no choice and have to (reluctantly) disassemble it if I want to perform a proper test.

Good point. I was thinking of post-primary correctors rather than pre-primaries such as Schmidt and Maksutov correctors. Note what I said about a meniscus lens. It describes the important characteristic of a Maksutov corrector. Wikipedia has a good article on this topic, including the existence of sub-aperture correctors.

Mike see the first post and you will see why it’s been written this way, might make you feel a bit of an ass…. I did say ass 😉

Well, people do have good opinions on telescopes like Maksutov Newtonian and Schmidt Newtonian. Granted, those are full aperture correctors and not sub aperture correctors, but can be quite fast systems as well- often F/4-F/5.

I don't doubt it. That's why I mentioned corrective elements. A Newtonian can be, but rarely is, corrected for SA with lenses in the same way as its coma (absent in a spherical mirror) can be and usually is in fast systems. On the same site as my Dilworth is a 0.5m f/3.5 Newtonian astrograph which absolutely requires a coma correcting refractive element.

For newtonian with single curved mirror - it is true that spherical aberration increases rapidly with faster optics. https://www.telescope-optics.net/reflecting.htm For paraboloid - it's equal to 0 but for spherical with K=0, we can see that it is inverse of third power of F/ratio, so telescope has to be really slow, or have small diameter.

Not without corrective elements, they don't. My 0.4m Dilworth contains nothing but spherical surfaces. A train of spherical lenses corrects for spherical aberration. Not sure of the focal ratio of the primary but guessing from the length of the OTA it is probably around f/2.5. Take a look at http://www.astropalma.com/equipment.html to see what I mean. For moderate focal ratios a simple meniscus lens will give most of the correction needed. For photometry it may not matter anyway, as stars are generally defocused to spread the light over a larger number of pixels, thereby reducing the effect of pixel-to-pixel variations in sensitivity. My Beacon Hill 18" Dobsonian worked just fine as a light bucket for my (visual) variable star work, despite having very noticeable spherical aberration. Horses for courses.

Most companies use delivery terms Delivery Duties Unpaid (DDU) so the buyer has to sort out the payment upon importation.

No but you can calculate additional charges quite easily. If importing to the UK the vendor will normally charge 20pc VAT which is remitted to the courier company to pass onto HMRC upon importation. If not then the courier company will ask for this 20pc when the item lands in the country. Note the 20pc applies to item price + shipping. Import duty applies to items higher than 135 which includes shipping cost as part of that 135 limit. The seller should be able to advise you of the export commodity code or Harmonised System (HS) code which you can cross reference with the item description on the gov website to see what pc if any duty will apply based on the item price. Commodity codes are mandatory as part of exporting goods so the seller should be able to advise. If the seller doesn't use a prepayment system and take the additional costs at point of sale (POS) then you'll pay the VAT+Import duty to the courier company handling the importation once the item enters the country and clears customs. You'll have to pay the additional costs before they release the item to you for delivery.

Aurora levels are through the roof

I don't think you can. Why not just stretch it and clone stamp that image. I always do the cleanup after stretching.

I still want to try cloning over some areas in the starless output from starnet. Just to see any effect on how far I can stretch. Just need a way to see un stretched tiff in gimp without stretching it

Has anyone ordered items from this company and their experiences re delivery and any unexpected import duties? Would appreciate any input please. Cheers, Ewan.

Depends on the individual. If someone say buys a full frame sensor camera, they're going to want the full frame looking good. But me personally, I think defects such as lens issues, noise etc just shows that a person took the image via their equipment, completely smooth images look unnatural to me for example, all digital media generally has noise due to how electronics work.

Spherical mirrors at f/8 and slower tend to be very close in figure to a true parabola, so the images can still be quite good if the price is right.

ChatGPT seems skewed toward commercial offerings. It never once mentioned Hubble Optics, Obsession, or any of the European custom Dob makers.

I really like its long eye relief, easy to hold FOV, and seemingly complete lack of SAEP. I will keep an eye out for EOFB in the APM. It is really bad in my 12mm NT4. One night, it was decreasingly hazy edge to center. I swapped it with the 12mm ES-92 and the haziness disappeared. I'm not much of a faint fuzzy hunter under dark skies, so I'm pretty insensitive to EOFB. I'm much more sensitive to SAEP because my pupils rarely dilate very far due to the increasingly severe light pollution around my backyard where I observe from. I'm hoping once the wife and I retire that we can move to a darker site not too close to any major cities.

M51 LRGB taken under the light of a full Moon. Gradient hell! I wouldn't normally bother with a galaxy under such conditions but clear nights are so few and far between this year for me. Edge8HD & 0.7 reducer, ASI294MMPro. A tad under five hours total integration. Pete.