Ships and Stars

Hi Jetstream, I use a Cheshire eyepiece for the secondary, and a cheapo laser for the primary, seems ok but the endcap with on/off switch has movement affecting the laser. I'll probably get something better, hotech or similar. The scope is F4. Don't have much time on it yet! Waiting for mid-August to start DSO hunting again. Thanks for the information!!

Thank you jetstream! Microblur - that sounds nasty! 😁 Just want to squeeze as much out of my setup, as most of us do. Nice 24" dob by the way!

Loads of varying opinions out there. I've 'heard' that any mirror quality higher than 1/8th PV is not discernible to the average eye, so in my book 1/6 to 1/8 will do. I think most mass production primary mirrors are around 1/4th PV. Strehl ratio is something I'm learning more about slowly. Then there is astigmatism. Also I've heard that simple lack of secondary and primary collimation, along with mirrors not at optimal temperature often rob more viewing quality than any mirror shortcomings. I just posted a question about a boundary layer fan for my dob which blows a steady stream of cooler air across the mirror face, as opposed to cooling the traditional way with rear mounted fans. The boundary layer seems to be more important in the eyes of some. A mirror within 1C of ambient temp is good, within 0.2C is ideal. Then there are the ways that manufacturers measure their mirrors which have caused heated debate. Some come with paperwork stating such and such wavefront and Strehl ratio, then the mirror was tested by an independent lab and returned much, much lower results. Then I've heard the mirror cell which supports the primary must be well-made, or the mirror will slightly deform... I'm sure you will get some more answers soon. Fun eh?😁

Hi all, I picked up my 20" Stargate dob near the end of viewing season here in Scotland around April, so haven't spent a great deal of time with it, but want to get it ship-shape for August onwards. First question if I may - I definitely need to add a dew heater on the secondary mirror - the primary seemed ok the few times I've used it, but the secondary always dewed up in a hurry. How do you reliably power a dew heater, three or four fans and a GOTO Synscan system away from home, especially in the -5 or -10C temps I regularly get at my dark sky spot in Scotland? I'd guess a regular 7Ah power tank is a no! One obvious option I have available is the large 105Ah leisure battery in my campervan. I was thinking I could run a long cable from the van to the scope and have plenty of juice to power everything. At home I'd just use a 12v power supply like the ones from FLO. Ironically, my 105Ah leisure battery is £10 cheaper than the 7Ah Celestron orange power tank. Second question revolves around cooling fans (none at the moment). I'll add three computer cooling fans on the back - there are already mounting spots for those. The bigger issue I see is aiming a good, vibration-free boundary layer fan at the face of the primary on a truss tube dob with the dew cover in place - I was thinking some kind of standalone fan sat near the base with a small plastic duct pointed at the mirror, perhaps through a small window cut into the dew cover and an exhaust port cut opposite. I've read a boundary layer fan can improve mirror-related seeing issues more than rear fans. I've also read a 1C difference between air and mirror temps is acceptable, and less than 0.2C temp difference the target for optimal mirror temps. Thirdly, this begs a related question - if you're using a dew heater on the primary, wouldn't that heat the mirror up and impact views? Obviously not as much as a dewed-up mirror...😀 Any thoughts on any of this welcome - no need to address all of my musings here. References to existing articles welcome - I'm guessing most of these questions are frequently asked, except maybe regarding the boundary layer fan aimed at the business side of the primary... Cheers!

I have a relatively small 20" SW dob I only purchased back in March, so haven't had a great deal of time on it. I haven't used it near zenith yet, most of my targets were around or below 60-70deg. I've used a small step ladder for lunar viewing at home, but my plan is to construct a small elevated platform so I can move around a bit without faffing with a ladder. The platform will need to be easily broken down into flat sheets, so thinking something like dzus fasteners, or some other quick release fasteners so it can lean up against the inside of my van. Before I make something like this, I will look around in more detail for some type of ready-made platform, something besides a ladder, because moving around in the dark, and going up and down a ladder holding expensive eyepieces sounds like a quick way to find trouble! Alternatively I googled 'mobile platform ladder' and came up with a slew of goodies like this: https://www.theworkplacedepot.co.uk/access-mobile-safety-steps?p=33238&vat=1&gclid=EAIaIQobChMIqZexooKH4wIVA53VCh2z2AqOEAkYBSABEgKgRfD_BwE Not the cheapest, but neither is a big dob and a handful of TV eyepieces! However, portability kind of goes out the window if travelling to dark sites.

If it's threaded on, try wrapping an old leather belt for trousers around it by simply running the belt through the buckle until it's drawn down tight around the tube, then wrap the remainder around your fist and unscrew it. This is an old trick to remove stubborn car oil filters when a strap wrench isn't available. It does work. PS look up strap wrench online and basically you are doing the same thing with a belt. Good luck! Cool looking old scope.

Starizona has an excellent online collimation tutorial. I have a 130PDS and I can say I've never been able to see all three primary mirror clips at once, perhaps due to the physical size of the tube in relation to the focuser. Someone else may have more experience with this particular scope, but I just do the secondary first with a Cheshire eyepiece, then adjust the primary with a cheap laser collimator and recheck. It's fairly sharp once that's done, but too much light now for a star test.

Yes the Google Earth views don't indicate much in the way of vegetation, just lots of dirt, sand and rocks! I'll venture down one of these days for a look. Still sounds intriguing and I can brush up on my ten words I know in Portuguese 😀. Thanks very much for the information!

Hello Tubby Bear, Thanks for the information (sorry for my delay in replying!). I thought the desert-like conditions might play a detrimental role in transparency and it seems a fair bit windier than the Canary Islands looking at weather averages. On the light pollution map, Boa Vista outside of Sal Rei is very dark with little light pollution in comparison to Sal. Boa Vista appears to have Bortle 1 skies all along the eastern side (well for now anyway!). Cape Verde sounds chilled out, I don't need a lot of things going on, sleepy is what I prefer most of the time, it sounds nice there. A trip to Santo Antao with a scope is my dream at the moment to check out conditions at the top of a mountain pass at night.

Thanks for the info Paul, yes I was thinking that while Cape Verde may not cut the mustard for world-leading scientific research compared to a handful of other top locations, for us mortals it can't be too bad, especially at the higher altitudes if they are accessible by car or 4x4. I should point out a lot of the higher ground on CV islands seems to be protected by the government, which is great, but may not in turn allows access by anything other than foot or pack animal. A US university set up a weather station on the top of Fogo island I think, and a CV army helicopter was used to lift the equipment up the volcanic cone (still active, by the way!). I will definitely do a write up if I ever make a trip down there with a nice little refractor or some good binos.

Actually it's very, very low precipitation, Cape Verde gets virtually no rain year-round except in those three months, mainly September (notably the inverse of the Canary Islands). Compared to La Palma, it's very much a desert! Actually it is sort of a desert, that's one thing that kind of puts me off the landscape there. The photos I've seen remind me of the Middle East, except a few small areas with some greenery. I think a lot of the drinking water or tap water comes from desalinisation plants or is imported. Good website by the way for averages. I had forgotten about this one. Here's La Palma, Canary Islands for comparison on the rain: https://www.holiday-weather.com/la_palma/averages/

Both places sound wonderful! I've had some exceptionally clear nights in rural Scotland, but it was about -10C and I only seem to get those a few times each winter. My only tropical experience was Koh Tarutao near the Thai mainland, but there was a persistent haze. The best night I've had was SW Ireland in County Kerry. Milky Way was unbelievable. I'm still longing for a more tropical setting however!

Hi Pete, Yes I was thinking that it was 'relatively' cloudier for some reason. 16 nights out of approximately 48 isn't brilliant for observable conditions, but perhaps that was just a seasonable thing or an unusual annual cycle. Having said that, I think the winds converge around Cape Verde, with a southern wind meeting a northerly perhaps causing a local weather front to hang in the area (not 100% on this). Although it didn't make the cut for the world's top telescopes, maybe it just missed the selection? It's a long way to go to find out I suppose, but I'd love to visit sometime. I'll keep a closer eye on the weather there over the next few months, might book an investigatory flight later in the year.

Hi all, Doing a bit (well, a lot) of dreaming recently about truly exceptional quality dark-sky sites. As in the absolute best observing locations on Planet Earth. I know the Rocque de la Muchachos observatory on La Palma in the Canary Islands gets a silver medal, second only to Mauna Kea in Hawaii, for low humidity and cloud cover, stable laminar airflow off the ocean, low-ish light pollution and high elevation generally above the temperature inversion which tends to trap moisture and aerosol pollutants, etc. Some of the western islands of Cape Verde seem like an almost equally brilliant location, but I can't find anything online about Cape Verde star-gazing/astronomy other than a few mentions here and some online adverts for hotel-run trips to darkish spots outside of the tourists areas at low elevations. I am really interested in the more remote, non-touristy islands to the west and south which have several peaks in excess of 1000m, with one in particular reaching almost 3000m and Bortle 1 skies throughout large parts of the islands, probably a good nine hours of true nightly darkness throughout the year, and average temps at lower elevations between 23 and 27C year-round. Sounds terrible, doesn't it? These non-touristy islands seen like very remote places with only a few tiny villages or clusters of small houses up on higher ground, possibly even without any visible 4x4 tracks on satellite imagery, but some of the more established roads (gravel tracks actually, from what I can tell) over the mountain passes must offer simply incredible seeing conditions. Has any intrepid stargazer ventured up on any of the high ground on say Santo Antao or Fogo, with a telescope or even binos? Is Cape Verde hampered by mist and clouds more than the Canary Islands? I seem to get that impression from what reports I've read, but rainfall is virtually zero most of the year. It's a very arid place from what I gather. By the way, I have read the excellent Merle Walker article on high quality astronomical sites, a great resource for any fellow dark-sky dreamers. He mentions Cape Verde in a single sentence or table entry, but seems to discount it for reasons unknown. http://adsabs.harvard.edu/full/1984ESOC...18....3W Cheers all.

Thanks, the tube is on a long list of modifications, so will be a little time before it's up and running, but I have powered it up at night and is working. Worked quite well in fact. I simply held a plossl in front to achieve focus, and it was pretty impressive I reckon. I'll let you know how I get on, but will be a little while.

Hi Peter, thanks very much for the tips, especially on the filters. I didn't pay a huge amount for the NV tube, the XX1332 is fairly old tech these days, but has a large 50mm aperture (again, that might not be of particular use). I am hoping combined with the size of the scope it will reveal a fair bit of detail that would otherwise be difficult to see. I'll try it with some filters once I've adapted it and see how it does, if anything, I'll stick a fast 50mm camera lens on the front and use it for meteor showers, etc. Gen3 seems like a big step up at the moment price-wise, perhaps that will come down a bit as time goes on! Cheers!

Update - I've bought a Mullard XX1332 Gen 2 NV tube from a tank sight, for little more than a really good 2" O-III filter. It apparently has one of the widest FOVs out there with the 50mm sensor. Now I've a bit of a project this summer! Watch this space...

HI all, considering trying out EEVA with a military surplus Gen 2 NV tube on my 20" dob. How crazy would that be! I haven't had much time to research this I'm afraid, thus relying on a bit of help if possible. One tube has a 50mm input and 40mm output window, the other 40mm input/output. There are genuine mil spec tubes. The 50/40mm is supposed to be excellent for astronomy due to resolution. Any thoughts? If not these, what's the best NV tube going for EEVA at the moment under or around £1000? Preferably WAY under £1000 ? but if I'm going to get something, I want to get a really good one rather than keep trading up as I go. Life is too short! Clear skies all.

Yes same here, got to keep the O-III. For laughs, I'll have to try out now and see if it really is as bad as it looks, or if there's some use in it! I'll stick to SGL and ABS - just used to dealing with ebay. I also like FLO of course, can't beat new! ?

Yes I think I will stick to SGL, ABS and think carefully about elsewhere, unless I'm really keen!

I did get a used star atlas in as new condition for the princely sum of £3! ? I'm hooked on bargains, but sometimes buying new is ultimately less hassle of course.

A brief rant and a 'buyer-beware' for other novice astronomers such as myself, or those that generally find a good bargain irresistible. Other than my telescope (thank the gods!), my last three used purchases online lately seem to be total duds or poorly looked-after. The first was barlow that appeared to be stored next to the kitchen hob of a busy chip shop. I did manage to disassemble and clean the grease to an acceptable level of use! Next was the binoviewer. Below is a photo of the internals described as used but 'optically fine'. Maybe the mirror breakage happened in transit (though it was very well wrapped in a protective case) but that doesn't explain the greasy black fingerprints on internal glass...?? Last was a used O-III filter that apparently de-laminated sometime in the Thatcher era, leaving an artistically-attractive off-centre crazed pattern, though probably not very effective as an O-III filter on a scope any longer. Fortunately the binoviewer and filter sellers have instantly accepted a refund, so it's hardly the end of the world, but I seem to spend half my time hanging around the post office queue lately sending stuff back. I think I will be slowly saving up for new items instead, as time is in short supply these days... Mini-rant over and buyer-beware - at least sometimes. Good luck all! ?

Hi John, yes hoping I get many years use out of it and hoping others can have a look as well, especially if they bring nice eyepieces! ? So far it's been fairly simple to assemble and use, and after a few more sessions it should go smoothly. Dew heaters are a must as I've quickly learned, otherwise the night can be cut short in a hurry. The moon was extremely intense through the mirrors - wasn't sure if it could cause permanent damage, but it was borderline painful! Amazing though. My main desire it to observe DSOs, which is why I was lusting after this one. The Veil nebula is on my list if I get another go before summer. I think for a lot less ££, the 18" non-GOTO looks appealing as well. Should you find yourself wandering around NE Scotland with a selection of Ethos eyepieces, do call in! Cheers John!

Wanted to quickly add I wasn't 100% sure this scope would work ok, so just being able to scan the sky in focus was a massive relief. It was purchased sight unseen, second hand (though never used) and apparently not covered under warranty as far as I know. That's why I was particularly nervous (and equally relieved) to quickly test it out. Once I've built up some time with the Stargate later this year, I'll write a more experienced review, though still far from expert, mind! Thanks all.

Hi all, first light and first impressions with the big Stargate 20” dob. This was definitely a milestone event for me with such a big scope, albeit short-lived due to fatigue and cold, and work early the next morning. Disclaimer – I am new to astronomy, this is my first telescope in over 35 years since I had a little Tasco 60mm, which I used twice until the focuser fell apart. For what it's worth, I do have an extensive DSLR background and have done some binocular astronomy which has helped things a little. I love binos, but hankered for something powerful to view DSOs with, without the hassle of imaging complications. I’ve spent the past three months reading about telescopes and gear before settling on this dobsonian when one came up for the right price. Of course, I still have a LOT to learn, both about identifying objects in the night sky, and equipment. The good people here have already helped me out considerably. Thank you! I did my first ever collimation yesterday afternoon using the supplied SW eyepiece. The secondary was rotated about 20deg off, simple fix once I realised why I was staring at the trusses through the pinhole eyepiece, and not the mirror! I didn’t fiddle with the grub screws for the secondary. The primary mirror collimation took a bit of adjusting since it was removed from the rockerbox on arrival. I had to crank down the spring loaded-collimation knobs more than anticipated so the springs were almost fully compressed. Took about ten to fifteen minutes, relatively painless. I reckon I could always fine tune in the field. Last night’s ‘mission’ was to simply check collimation and focus, run through night assembly, and then randomly sweep the sky without GOTO or gizmos and hopefully relax and enjoy the views, and then get a few hours' sleep. After the family was in bed last night after 10pm, I loaded the Stargate into my van and headed to a nearby forestry car park under Bortle 3 skies. Split down into four component parts, base with GOTO drive, rockerbox with mirror, truss rods and top end, it’s quite easy to shift for someone in reasonable health (my back is a bit dodgy, but I was fine). Moving the massive mirror/rockerbox is always a little stressful for me, just make sure the area is clear of trip hazards, check the base is ready to accept it, firm grip, focus and lift away… It was quite clear but COLD last night, much colder than I expected, around -2C onsite. My body was well insulated with wool trousers and down parka, but my hands were going partially numb quite quickly, and heavy frost had started to form within minutes of parking up. Set up of the rockerbox/mirror onto the base and assembly of the trusses was fast, even in the dark with a LED torch set to one lumen firefly mode. The top end with focuser took a little persuasion but clicked right in eventually. The truss clamps were more troublesome in the dark, I’ll be buying glow tape or something to ID the tops and clamp locations on the truss rods. By this time, the frost was growing thick and the plastic flexy mirror cover already had frost/dew on it before I could remove it. I was exhaling clouds of moisture onto everything from the race to assemble. Not a good omen!! I quickly attempted to put the dew shroud around the frame properly, but gave up with numb hands and tossed it over the scope like a blanket and roughly attached the ends so it didn’t obstruct the mirror etc. I wouldn’t be observing at zenith because I didn't bring steps, so no big deal. Job done. I didn't bother with setting up the GOTO alignment and left my finderscope at home, so I just planned on slewing around and taking a casual look. I removed the mirror covers, popped in the 28mm 2” SW eyepiece, took a deep breath, and…couldn’t focus. Brain engaging for a second, I popped the extension tube in place. I tried again with a spin of the focuser wheel. Stars of all magnitudes filled the eyepiece! I had little idea what objects I was looking at, but I saw so many star clusters and double or triple star formations, while a few satellites zipped across the eyepiece. I was delighted to get everything in focus with the 28mm 2" – it seems like a wonderful eyepiece for the money. Yes some coma as expected, but not bothersome to me at all. Just for laughs, I swung towards the crescent moon before it dropped below the horizon and hunted for it until suddenly a huge flash hit my eye. Ouch! I was blown away by the intensity through the 20" mirror – I felt like I needed a welding mask to even quickly look at it. I couldn't look for more than a few seconds due to the intensity (my ND filer arrived this morning). I stepped away from the eyepiece and looked down at my parka – a bright crescent moon was projected across my chest! Not wanting to risk eye damage, I had one last peek with the 28mm and went for the SW 10mm to hopefully dim it a wee bit. I popped the 10mm eyepiece in and got some incredibly close views, but the mirror had not sufficiently cooled for sharp focus. Nevertheless, I can assure you I have never seen the moon in such detail, absolutely breathtaking! Suddenly, nothing seemed to focus well. A quick inspection revealed my secondary mirror was c.60-75% covered in frost, so I fired up the heater in my van about 50m away, whipped the mirror off with a screwdriver (mind the spring underneath!), and warmed the mirror until the frost was cleared, all in the dark, happy days! I reinstalled the secondary at the same index prior to removal, and all seemed fine. After that, the secondary mirror and primary remained crystal clear the rest of the night, but by this time I was cold and growing a little tired. I don't know what magnitude I was seeing down to with the 500p but the light gathering ability is absolutely immense! It is an astonishing scope by my novice standards, and I'm sure I have barely scratched the surface. Although this is a huge scope, you definitely don’t need one like this to have a lot of fun and enjoyment, so don’t sell the jewels just yet. I'm glad I kept my observation binos for times when I can't lug this scope around, and the appeal of a smaller, more portable dob in the future is still there. Last night would have been an equally great night with either of those as well. One thing I can say is you do NOT need a 20" dob to view the moon ?. When I get time to set up before dark for a couple of nights in one spot, get the GOTO aligned, appropriate filters in place, and can target DSOs, etc then the 20" will make more sense and see more of its potential in use. Still, the 500p revealed a ridiculous number of stars with standard eyepieces, no coma corrector and rough collimation. A definite light bucket as they say. So job done, got to quickly see some stars, nothing broken thank the gods, and went to bed just after 3am. It is a lot to take down and pack, but manageable. Must remember finderscope next time! Dew heaters, better eyepieces, coma corrector, barlow & binoviewers, etc are all on the shopping list, but it will take some time to replenish the piggy bank. Not in a rush, summer is almost here! Hoping for a bit more viewing before the nights are too short. Cheers all for your help along the way.