Cosmic Geoff

The choice of eyepieces you could buy is very wide. The 10mm often supplied in scope kits is not great. The 25mm may be more acceptable, likewise the Barlow lens. I'd suggest you try using the scope for a few nights before shopping for accessories.

Focus the image. And maybe reduce the exposure time.

Today I tried another experiment I had been wanting to try but had been prevented by clouds. At around 8pm I exposed the ASI462 camera to some blue evening sky, via the filter wheel but without a telescope, to measure the relative response through various filters., using Sharpcap Histogram. Taking the exposure time with the UV/IR cut filter as 1, the exposures with the UV filter was x72 and with the IR-pass filter x2.9. So what can one conclude from this? It seems that the long exposure with UV is caused by the low relative response of the camera and/or there not being much UV in the first place. There is probably some UV cut in the Mak and SCT previously used but it is not clear how much.

If you already have a 130mm reflector, and have a limit of £500, that rather limits the possibilities. For viewing planets you want maximum aperture, so £500 worth of Dobsonian would give the greatest aperture for your money. Any sort of scope other than a short focal ratio achromat will serve for planetary viewing, but a Newtonian gives the greatest performance per £. If you want to see lots of planetary detail, try imaging. It often shows far more than a novice observer can see. Not cheap or instant, but satisfying.

As a retired electronics engineer, I am wondering how a mount could be powered by 12v AC (clearly indicated in the photo above by 12v ~) and by +12v DC? With AC, the speed could be locked to the mains 50 HZ, but with DC, some sort of intermediate circuitry to control the motor speed should be present. However, the second 12v connection, with two small round holes, is clearly not keyed for polarity. Isn't there a user manual anywhere? A step-down transformer will be required to supply 12v AC from the mains.

The choice of eyepieces is very wide. Any of the 1.25" barrel size should be usable. What is your budget? A typical price for a decent but non-exotic eyepiece is £50, and you might want a set of 3, plus a Barlow lens if you don't have one. Plossl eyepieces will work in your scope and may be cheaper.

Today I finally was able to make the trial on Venus I wanted to do a while ago, but was frustrated by clouds. I took some images with Venus at its greatest height in the afternoon, with a SCT. CPC800, filter wheel, Astromania UV filter, ZWO IR-cut, ZWO IR pass filter, ASI462MC UV exposure 5.8ms, visible exposure 0.032ms, IR exposure 0.112 ms. Note that the UV exposure is 180x the visible-band exposure. While an exposure of 5.8 ms wouldn't be so bad for imaging Saturn at night, the result here was dismal. The IR image turned out the best. The SCT apparently does not perform better than my Mak in UV.

You need a clear view to the North (for planets and northerly objects) Other directions are less important. Why $800? Can't you use building blocks which are pretty cheap, if ugly? Maybe build a viewing platform high enough to deter the animals?

Be aware of overall dimensions if you are thinking of buying an 8" Newtonian. The Dob version will require you to stand for viewing objects near the zenith, and crouch to view near the horizon. If you put it on a tripod, and fully extend the legs, you should be able to stand for observing objects near the horizon, but if you aim it at the zenith the eyepiece will be about 7 feet off the ground, and maybe in an awkward position as well - really not good. But if you don't have board fences around, you don't need to extend the tripod legs. SCTs with their short tube and eyepiece at the back are more user-friendly in practice (but more expensive). The 5" scopes will not show you as much as a 6" or 8", but at a dark skies site will still show you lots of stuff. I second the comments about mounts. A lot of the entry level scopes come with what I call a 'wobblemount', while what you actually want is a tripod that looks as if it was made with scaffolding poles. Another option is to buy a small Newtonian, either as an OTA or as a mini-Dob, and put it of a solid tripod like the AZ4-2. A small Newt would be more expendable than a 6" SCT should the livestock kick it over. 🙄 I suggest you regard your first scope as something to test the waters with, rather than a lifetime purchase. Keen amateur astronomers often trade up, or acquire a collection of scopes.

Without referring to the instruction manual, I think that when these messages appear (which are essentially for information) you have to escape out of the setup routine to a choice of objects or utilities, otherwise it takes you back to the alignment routine.

The pictured Omni looks like mine. I found I could screw the nosepiece onto ZWO cameras.

I suggest that the Celestron Powerseeker 127 is not worth much investment for upgrades. See this review: Celestron Powerseeker 127 EQ review | Space one of many critical reviews. I had hands-on of a similar instrument at the local astronomical society and found it almost unusable.

My laptop chargers deliver 19 volts. There are many sensible options - either a rechargeable battery or a mains powered regulated PSU. Whatever you use, it must deliver at least +12v to 13.8v and be capable of delivering several amps. I mostly use a multifunction car engine starter, or a Celestron LiFePo battery pack. The car starter can inflate my car tyres as well as running my GoTo scopes. The Celestron power pack also acts as a useful work light and has USB power sockets.

The two ends should look the same as regards wire order. I guess that without a good cable to compare with, you can't tell how it should be reassembled.

Maks rarely if ever require collimation. I have not had to touch mine even after several years of ownership. The design has been used for gunsights on tanks, which suggests a certain robustness. 🙂 Even quality refractors can be collimated, if you are determined to tinker. Maks DO require a dew shield. Refractors also require a dew shield, but they mostly have one built-in and less conspicuous. If FLO are offering you a customer return Mak, buy it quick before it goes out of stock. I'm sure it will perform exactly the same as a new one. A no-brainer unless you have a fetish about pristine packaging or clamp marks on the dovetail.

Depends on the retailer. FLO only sell new, and sometimes sell customer returns which are fully refurbished, checked and as-new, AFAIK. Other retailers selling second-hand astro equipment may provide gear that they have not checked and tested. I bought a used SCT from a certain company for an attractive price. The seller pointed out that it had superficial scuffs and dents. I found that it was well out of collimation, and the power plug was making poor contact, causing erratic failure of the GoTo. Rather than launch a complaints procedure, it seemed less bother to set-to and fix the problems. Since then, the scope has performed as well as a new one. But if I had been a clueless newbie, I would probably have ended up trying to return the scope. for a refund. In conclusion, if you don't have a clue how to fix or adjust a telescope, don't buy one that might require attention. Also be aware that there is not much that can go wrong with a telescope in the way of in-service failure, other than the electronics. The chances of the electronics failing at some time are the same whether the scope is new or used, but if it is under warranty at least you have a come-back. I had issues with one mount which required re-loading of the mount firmware to restore it to operation. This required a certain familiarity with adapters and computer operation on my part, otherwise it would have meant an expensive encounter with a specialist repairer. Lesson 2: don't buy a GoTo model unless you are confident with computer operations.

Another trial effort with my 127mm Mak, ASI462MC, and Astromania UV filter and other filters. I got a UV image in mid-afternoon with an exposure of around 7ms and a satisfactory frame rate. These are all from a 5000 frame video, cropped and centered in PIPP. Visual exposure time ~0.06ms, IR exposure time ~0.15ms, so the UV exposure is 100 or 50 times longer. While I got an UV image, it isn't very good. The sky background was much brighter on the laptop screen than it appears here. Interesting discussion here: https://www.cloudynights.com/topic/849249-are-newts-better-uvch4-planetary-imagers/ Among other things, a Classic Cassegrain should work well, and blue filters might show something if your scope has glass. Bad news on this topic for SCT owners: https://www.researchgate.net/figure/Transmission-for-an-8-Celestron-SCT-Schmidt-corrector-plate-coated-with-Celestrons_fig3_241553344#:~:text=In-house transmissivity tests on a modern Celestron 8",H and J-bands was about 74% on average. Steep dropoff below 400nm.

People used to make their own Newtonian telescopes when I was a boy, but nobody, except hobbyists who want a Project, does this anymore. In most markets it is cheaper to buy a used telescope than to buy parts to make your own. Beware of reviews written by people (e.g. shoppers on Amazon) who know little about telescopes.

Image above captured on 15th at 20:58 to 21:13 UT, exposure 425ms. (127mm Mak) A test with the same kit the next afternoon, with Venus near the meridian, gave an exposure of ~35ms, and without the diagonal and ADC more like 9.4ms (times so much shorter that I thought something had gone wrong somewhere). A test the same evening, with a 203mm SCT at around 21:30 UT and thin cloud about, gave an exposure time of ~900 ms, without diagonal or ADC, so clearly not worth trying to take an image video. I would like to try again with Venus near the meridian, but conditions have not been suitable, and I also need a means of aligning the SCT in daylight.

My experiments indicate that eliminating the prism diagonal and the ADC has some beneficial effect on the UV exposure rate. I also found indications that the time of day (altitude) had a significant effect. To support the latter, charts indicate some attenuation of UVA at zenith, and if one looks up "air mass coefficient" it can be seen that the path through the air increases with increasing zenith distance. At least one Venus imager reported improved results with daytime imaging.

Kon - your series of images looks great. It seems that my Astromania filter is not the problem. I will try eliminating glass (eg prism diagonal & ADC) from the optical path of my Mak and 8" SCT and see if that helps at all.

Some digging reveals that the ASI462MC could have a relative response of 0.1 to 0.2 in the near UV, the other (more expensive) UV pass filters have a relative response of 80% at around 320-380nm, and as for optical glass, it varies. Some pass near UV while others act as an effective UV-cut filter. Seeing the curves, one wonders why anybody would want to spend money on a UV-cut filter for any gear with glass elements...

I received the Astromania budget 3-filter set today and this evening tried it out with my 127mm Mak. Full setup: 127mm Celestron Mak, Circle T prism diagonal, filter wheel, ADC, ASI462MC. Video of 2000 frames. I found that the exposure time with the UV filter was astoundingly long at around 460ms (2.4 frames/sec. Compare with visual band: 0.2ms, IR 0.4ms, and just for comparison, not imaged: OIII 7.8ms, methane 7.8ms. I wonder if it is the UV filter or the sundry other components that causes the low sensitivity. The ASI462MC camera is probably not ideal for this role but I expected better.

The ASI183MC appears to have a significant IR response (though the spec does not show the response beyond 700nm) I would recommend using an UV/IR filter. ZWO offer one for around £25 which I have used successfully with other of their cameras. Other ZWO cameras come with a fisheye lens, which I have found mainly useful for demonstrating the funny colours you get if you don't fit an IR-cut filter. You could experiment with aiming your outfit at treetops in daylight.

I had a look through the front of my 127mm Mak (now several years old) under a strong light this morning, and could see white specks of dust apparently on the large (main) mirror. These clearly do not affect the operation and I do not intend to do anything about it. I am reminded of some previous threads in which newbies are advised not to shine a strong light into their telescope lest it reveal anxiety-inducing dust that does not affect the telescope operation. The secondary mirror surface consists of an aluminised area in the middle of the corrector lens and cannot be seen by the user. Be careful what you ask for when requesting a refund or exchange. As noted above, there may be a limited period for a no-fault return, and if you claim there is a fault, the seller may dispute this or let you wait a few months while it is sent back to China for examination. Do you want an exchange Mak with the same focus mechanism that you clearly don't like? BTW, some owners fit refractor-style focus assemblies to the back of their SCTs or IIRC, their Maks.