Giles_B

Thanks, that's a great article https://www.baader-planetarium.com/en/downloads/dl/file/id/160/product/2871/testreview_mirror_vs_dielectric_vs_prism_diagonal_comparison_w_paolini.pdf - interestingly the light paths of the prism diagonals are all clustered in a 63-67mm range, whereas the mirror diagonals are anywhere from 73-112mm I'm hoping that Lacerta might have some definitive data on their Herschel prism.

A bit more info - from the 365 astronomy page on the Lacerta wedge: "The Herschel-LAC2s version takes up about 110mm of back focus." Can't for the life of me find data on the Takahashi 1.25" wedge that Steve is using.

Having persuaded @bomberbaz to part with his Scopetech f12.5 refractor, I'm looking for some advice to make sure I don't run into compatibility problems when using a Herschel wedge. I've read elsewhere that Japanese refractors can have problems with diagonals as they are often set up to be used straight through. I'm hoping to use this scope mainly for solar with a Lacerta Herschel wedge. Steve reports he has used the scope with a prism diagonal with no problems, but it seems prudent to check whether I can expect similar performance from a solar wedge - in other words is the effect of a herschel prism similar to a normal prism diagonal - and do all prism diagonals (and all herchel wedges) have a similar effect on the focal train?

I've not had any problems with dew with the soft cases. I'm not sure if this is just because my observing sessions are usually no more than four hours, and finish before the worst dew points, or if dew precipitates less on the soft fibres of the case covers.

I have an Explore Scientific soft case - https://www.harrisontelescopes.co.uk/acatalog/explore-case.html A bit pricey for what it is, but can hold a surprising number of 1.25" eyepieces and other assorted junk and it is deep enough to store the Naglers vertically. It's a bit challenged with 2" eyepieces so, with economy in mind, I also use a ebay sourced soft camera lens bag - https://www.ebay.co.uk/itm/373763645966?var=642804111044 - cheaper than anything aimed at astronomy, and does the job for the big stuff, although the chaotic approach won't suit everyone.

I have a year less experience with telescopes than you, and there are limits to what can be seen in a picture taken down the focuser barrel, but the collimation looks okay to me - in the second picture all three mirror clips aren't visible, but I think this is due to the angle the photo is taken at. I'd expect the image of to be offset in an f5 scope. Hopefully wiser heads will also weigh in here. When you say "everything" gets blurry at 150-200x do you mean planets? or stars and DSOs as well? - I have a 10" Dob under city skies and about 11m above sea level - and 200x is the limit on planetary magnification on average - exceptionally I'll get a clear image up to 400x, but that is unusual. My personal experience, after a lot of fussing about my own collimation, is that the seeing usually the limiting factor, not poor collimation.

Thanks for the tip!

Thanks to you both - I think a dome might be a bit beyond me, but I'll continue to ponder. A hood seems to me the best way of reducing peripheral distractions, but I also thibk i won't like the mild claustrophobia of a hood, so quite like the freedom of a shield. I suppose I'll just get one option and either love it or hate it....!

+1 for dust in the wedge - I noticed my wedge smoking during a session a month ago, que big panic, but the wedge turned out to mildly warm on the outer surface of the heatsink - so I assumed there had just been a piece of debris - perhaps a seed or even an unfortunate insect, that had wafted into the wedge. I guess if something more substantial had entered the wedge it may have produced heat such as the OP describes.

I'm thinking of ditching the "coat over the head" method of solar observing and buying (or crafting) some specific equipment to keep myself in shade. There seem to be two options, either a cover that goes over me and the telescope like this: https://www.rothervalleyoptics.co.uk/telegizmos-solar-observing-hood.html, or a shield that attaches to the telescope, or eyepiece as in this example: https://astrospares.co.uk/products/baader-solarprotection-shield Of course, these things are all pretty simple, so I'd consider a DIY option, but it would need to be more sophisticated than hiding under my coat! NB I have both white light and Ha working in parallel (on a Sky-Tee), so I'll probably need any "shield" option to be x 2. Has anyone got experience of either or both designs, and if so, which do you think is the better option?

I agree an 8" Dob is a good choice. If your only worry is that Dobs can be bulky then all you need to do is shop around as this is not always the case. Most dobs come with a laminated MDF base, and so the material is intrinsically heavy. That said, I've owned a 10" Orion Intelliscope it was not unmanageable, so I'd imagine you wouldn't have a big problem with an 8". There are some, like my current Orion Optics (UK) Dobs, with a base that is a tad lighter and much portable (although the base, made of steel in this case, always needs to be heavy enough to stop the telescope from tipping) - but admittedly this is probably beyond the budget you suggest. There are others, though, where the MDF base design is a bit more thoughtful - like the Bresser Dobsonians - and these may hit the sweet spot for you. Rather than go on my rather patchy knowledge of what is available, just make sure you have a good conversation with the telescope retailer making clear you want a big aperture but one of your main criteria is that the base is lighter and more portable.

If only I hadn't had work - I managed three hours then stopped at midnight. The sky was absolutely crystal clear over Bristol - ranks with some of the best seeing I've experienced in the city. Most of my time spent on the Saturn, with a huge amount of detail visible in the rings. Just amazing. Came out again at 6am to walk the dog, and still crystal clear. If only it hadn't been a work night!

"If you have a finder scope, remove it, or make a similar filter for the finder's objective as well." Thanks to @Gfamily for reminding me of this important point in his answer to a another post about solar filters in the beginners forum today.

Solar film over the aperture is what you need, in order to filter all the light before it hits your primary mirror - a sheet of film will fit within your budget. You can buy premade aperture filters, but this is probably a bit beyond your budget. Using some solar film and crafting your own filter is possible without too much effort - just make sure the film is well secured to the aperture. The film is extremely safe, but obviously if the film is poorly secured and slips ... your telescope, eyepiece and probably your eyesight (if you are at the eyepiece at the time) is at stake - so make sure you double check before each session, and you will overcome any risk. And DO make sure you point the aperture down at the end of the session - I almost smoked (literally) my 130mm reflector while packing up by carelessly removing the aperture filter while it was still taking some of the glare of the sun - luckily the smell of the cheap plastic focuser singeing was enough to alert me - but the lesson was well learned: the sun is a powerful energy source and needs to be treated with respect! There is nothing you can safely do at the eyepiece end. You will find "solar filters" for screwing to eyepieces but these are NOT safe - this is especially true of a large newtonian like yours, as pointing it at the sun without an aperture filter will certainly crack the glass in the eyepiece filter, crack the eyepiece - assuming it hasn't fried your primary and secondary first. You may also want to rig up a solar finder, or buy one - it can be surprisingly tricky to find the sun. You will probably find that a 200mm reflector won't give the best views - the seeing during the day is poorer and the optimum is about 100mm of aperture or less. Ultimately a refractor is the way to go if you get more serious. However, solar film will give you a good taster of the joys of solar observation, so I'd really encourage giving it a spin!

Great idea - I never cease to be amazed at the adaptability of Lego - Lego seems particularly likely to be useful for testing the Baader LaserColli mk2, which is a really awkward shape. Now as for the uses for a bottle or two of wine....

@Astro_Dad thanks, really I should have contacted Celestron myself. I think I'll give it a try with some cotton wool and detergent, I agree that alcohol based cleaners feel a bit dangerous. I guess if I can't get the mirror cleaned with detergent I'll think about something stronger.

+1 for the Baader from me (mine has held collimation well even after a drop to the floor) however I have two caveats: 1) any 1.25" collimating device in a 2" focuser will suffer from the imprecise alignment of the 2"->1.25" reducer. I found my collimation got a lot more precise with a Howie Glatter Parallizer https://www.firstlightoptics.com/adapters/howie-glatter-t-adapter-parallizer.html - but given these now cost almost £90, you may want to get a collimator with 2" capability in the first place. 2) I'd recommend at least having a collimating cap, and more usefully a Cheshire as backup. That way you can routinely check the laser has led to spot on collimation, check the secondary is correctly positioned and so forth. Often when I've asked for advice on forums about this or that issue, the first advice is to check collimation - having two (or more!) tools gives me greater confidence that the collimation is okay.

Thank you for that really comprehensive answer!

Thank-you both, for all of these answers. @vlaiv - I particularly appreciate your identifying and linking to the relevant calculators. Certainly the ball-park figures suggest I would have the room to use the artificial star, but I appreciate the help with the maths! One thing both of your answers have made me realise is that there is a difference between using the artificial star for star testing and collimation. My understanding is that star testing is used as a final 'acid' test of collimation - that an out of focus star will show a pattern in the airy disk that indicates optical aberrations associated with miscollimation as well as other optical defects. What I don't fully understand in your answers is how I would use an artificial star to check collimation without doing a star test - could anyone explain?

I'm considering buying an artificial star to further assist collimation of my f4,8 10" Dob - I find tracking a real star a bit tricky with a Dobsonian. However, although I travel to more open locations from time to time, a lot of my observing is done in my garden, and I am not sure if I have the necessary distance in my garden to focus on an artificial star - does anyone have any practical experience? I realise not all artificial stars created equally, so really want a rough indication of the distance needed for a 20-50 micron unit.

I'm guessing this thread gets the attention of many Dobsonian owners who are using a modded starsense explorer unit, as well as straight up users of the celestron dob, so with that in mind I have a more general query. I had a mildly frustrating night last night because the star sense adaptor (I.e. the phone plus holder and mirror) was slow or sometimes unable to plate solve. This tended to be in brighter areas of the sky, but I emphasise it was a dark night at a Bortle 4 location - it has plate solved in brighter conditions in the past. Obviously this needs to be replicated to show if there is a genuine issue, but I did have a good look at the mirror on the adaptor this morning - it is pretty filthy, with plenty of stuck dots of pollen and dust. I haven't cleaned it in the 2+ years since I bought it. Has anyone cleaned the mirror? I ask because the technicalities of cleaning a small, glued mirror on the star sense are clearly a bit different to cleaning a primary mirror. I'm guessing the mirror on the star sense adaptor has no protective coatings that I could damage, plus i don't want to soak the mirror in water and end up rusting the fixings or softening the glue, so I'm wondering if Baader cleaning fluid might be okay?

Apologies if this is a bit off the wall, but is there any dust in the usb port? This is the most common reason I've had usb devices fail to detect on my PC. Usually a small amount of dust gets compacted inside the port, that needs a dig around with the wire from a paperclip to remove it.

Okay - here's the full report. Actually I didn't prepare and use the off-axis mask until Sunday, but it is interesting to compare the two days I was out on both Saturday 2-4am and Sunday 2-4am (on Sunday I'd planned to observe sooner when Saturn was higher but I overslept *sigh*) Saturday, Saturn was somewhat low. I could get good magnification down to about 6mm, but lower than that there was too much wobble. Saturn was pretty unvarigated white disk and ring, perhaps a hint of banding but very faint. Once again I found it impossible to make out the Cassini division, which has been one of my main gripes with my observations. I tried a neutral density filter, which made things darker, but didn't help much. Then, reminded of something I thought I had read about, I tried a UV/IR blocking filter. This was a revelation, cleaning up the wobble, allowing me to advance the zoom eyepiece a stop down to 5mm (but no further) and for my first time giving me a clear difference in the banding of the inner and outer ring - although I couldn't make out a clear black line between the two. Anyway I was happy that I had seen the Cassini division at long last 😃 - I eventually stopped observing when I lost sight of Saturn behind a tree. I turned to Jupiter - much higher in the sky than Saturn - and was amazed I could take the magnification down to a full 3mm and still see a well defined disk with clear banding and - to my delight - the shadow of Europa in transit. In all I spent about 30 minutes looking at Jupiter, and 90 on Saturn, before calling it a night. All in all very successful, so I was full of enthusiasm to try again with a stopped down scope. I fashioned a mask with a 3.5" aperture - maybe a little small in retrospect - and once again got Saturn in my sights. The seeing was, if anything, a bit poorer than the night before, and the UV/IR filter produced a less dramatic effect, although again I could make out faint banding and differentiate the inner and outer sections of the ring. Trying the off-axis filter - I was presented with a slightly dimmer (although nevertheless quite visible) image, and no real discernable effect, except perhaps slightly fainter details. Switching to Jupiter, the effect was more pronounced dimmness and fainter details. So my feeling is that Steve was right here - essentially I got the same viewing experience, probably slightly worse, because I'd stopped down to a 3.5" not a 4". And yes, for one night of the two the view was really good, and I went to bed tired but excited having at last seen some detail in the rings and viewed some of that wonderful transit! Anyway, Thank-you all for the help and advice (and sorry to sneak an observation report into Scopes and whole setups!). As far as new scopes go, @rl is very, very kindly gifting me an unwanted 90mm f/8.8 Meade refractor, so I am very excited about getting a 'first frac' and trying this with some white light solar 😁

Personally I start with looking at the levels of light pollution using https://www.lightpollutionmap.info/ Then I either visit the place in the day or use google street view to work out likely sites - it should give you a good sense of the level of the horizon.

Okay, thanks - I got a bit worried for a moment! Yes, I suppose there is still some pent up expectation as I've not long moved to a 10" reflector, and even more recently used it on planets for the first time. I think you have answered my question really, which was whether I could get a frac that would "do it all" - looks like it's a firm "no" and I should just concentrate on what is needed for solar - which is probably quite a bit cheaper (in the first instance) anyway. By the way @globular the tip on stopping down is really appreciated - I'll try it next time I'm out (this weekend looks likely to be clear 😀)