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rl

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Everything posted by rl

  1. To be honest I'm not sure where you go from here. The FSQ85 would be the dream widefield astrograph for most people. I thought being a quad Petzval design the flattening was built-in? If you add an extra flattener the curvature will simply go the other way. I've seen some good reviews of the 5-element Askar and they're all checked in the UK before sale.
  2. I did a whole bunch of astrophotography with Ektachrome over a 12-year period from 1985 - 1997. By chance I came across the original edition of Michael Covington's book "Astrophotography for the Amateur " in a bookshop in Muscat, Oman which got me hooked on the AP side of things. I used to do my own E6 processing in the bath ..used to love the excitement as the wet film came out of the tank...it would be milky for about an hour until it dried hard...revealing the results of the night's labours. Manual guiding was a real chore...keeping the crosshairs on the star for a 20-minute exposure was a real test of endurance on a cold night. My job took me to several of the world's best observatories at the time. I made a clock drive that would work in either hemisphere so I could take shots with a 50mm lens in Chile and South Africa. I'm inspired to sort through the detritus of my astronomy life and find a few of those slides...
  3. The idea of maximum magnification is to extract all the detail in the image without over-magnifying which makes it dimmer and fuzzy. The image at the prime focus contains a finite amount of detail. the bigger the aperture, the more detail. It's like a mosaic...the bigger the aperture, the smaller the pieces in the mosaic. The resolution (mosaic piece size) depends on the wavelength of the light and the scope aperture. Resolution in arcseconds = 138mm divided by the scope aperture in millimetres, so a 60mm scope will resolve just over 2 arcseconds of angle. A 6" will resolve to about 0.9 arcseconds which is finer detail The maximum magnification will match the scope's resolution to that of the eye. Now, people's eyes are all a bit different so there is no cast-in-stone rule for this, but on average most people's eyes can resolve between 1 and 4 arcminutes of angle depending on the brightness of the object and its contrast. This is between 60 and 240 arcseconds. Thus, for your 60mm scope resolving 2 arcseconds, you need to multiply by 60/2 to 240/2 or 30 to 120 times. For a 6" scope, you get 60/0.9 to 240/0.9 or 66 to 267 times. The 50 times per inch figure is just a generalisation of this principle assumimg your eye resolves just over 4 arcminutes. A lot of caveats apply. Astigmatism in your eye favours higher magnification. Floaters favour dropping the magnification down a bit since the very narrow exit pupil is more easily scattered.
  4. Lovely shot. Illustrates the real power of simple kit in good hands. Where was it taken from? Was it London as per your signature? If so, the filter is proving its worth.
  5. I can't speak about this exact scope but I had one of the clones for about 9 months. It was great optically on widefield viewing and acceptable on planets with the usual caveats on CA, altogether a good performer for a short achromat. It was quite compact with the dewcap folded down, and the front lens cap screwed on which I liked. I'm sure I read somewhere that some of the clones offer a 3" focuser which would suit the ES 30mm 100 degree eyepiece which very few scopes do. It's a big step in bulk from the ST120 which I've also owned in the past. However it was no match optically for my OO 8" f4.5 which was also 2 kg lighter. I also have a 6" f/10 triplet which was much better on the high resolution stuff.
  6. Is this an observatory setup with a once-in-a-blue-moon lift on to the mount or will it be a regular thing? I would suggest the C11 would be a LOT more convenient for visual use given the eyepiece positioning. The Newt may well prove optically the more versatile setup (but SCT aficionados may beg to differ). If your main interest is deep sky photography then personally I'd go with the Newt just on speed. You can do planets and spectroscopy well on either. My OO CT12 f/4 was wonderful on an EQ8. It did very well indeed visually on planets ..don't let the fast f-ratio put you off. Providing your scope has a decent mirror the sky will be the limiting factor most of the time. The only down side was rotating it in the cradles to access the eyepiece, and you could need steps when it pointed towards the zenith. The CT12 sat very high in the cradles to get a balance. Convenience counts for a lot with big scopes....made that mistake myself more than once!
  7. I bought my AZEQ6 6 years ago and it's been a wonderful mount. I've never used the AZ feature. If I were buying again I'd look carefully at the EQ6R which can handle a couple of kilogrammes more. The extra saddle on the AZEQ6 gives you the option of hanging a short (ish) focal length camera as part of the counterweights for guided widefield shots while your main instrument is doing the business. Works well up to 3-400 mm focal length guiding on the main instrument.
  8. What is your first scope? Short focus achromatic doublets are not considered the best for lunar / planetary due to residual chromatic aberration and possibly spherical aberration as well. They are very good for contrasty low magnification widefield viewing on deep sky if you accept the aperture limitations. It will need a decent mount. I've owned a similar scope and it was ok for casual viewing on planets but not exceptional. I'm now lucky enough to have a 6" f/10 triplet and there is no contest which is the best.. You might do better with a 4" f/10 (TAL or Skywatcher) or save up for an apochromatic scope. Sometimes 4" apos come up for £500 secondhand, but the s/h market has gone a bit crazy at the moment. A 6" f/8 Newtonian makes a good planetary instrument....
  9. Fair comment . It seems (and is) a fortune for a bit of metal. But the sad fact is that the cost of getting a piece of precision metalwork done on a one-off basis in the UK tends to incur this sort of cost by the time the engineering drawing, setting up time, materials, anodising, labour and reasonable profit are all factored in. If you can find a mate with a lathe and mill I'm sure he can knock one out from a bit of scrap for 50 quid and a couple of beers as a favour and it will be just as good...but factories can't work that way. I work in an industry where laying out a grand for a one-off prototype bit of metal is the norm. A reasonable question would be why they are not fitted as standard, made from cheaper aluminium rather than stainless steel. In that case, you would get a batch of 20 made at once, all for a much lower unit cost. The answer is that the tube is just about good enough not to need it. They've been selling these things for over 10 years now successfully without reinforcement which I suppose makes that aspect of the design fit for purpose. They do seem to change parts every now and then presumably in response to customer feedback or supply shortages. I have to admit, I always treat mine with kid gloves when moving it around.. A similar thing exists with their AG range where you can order some reinforcing rings for the focuser if you're intending using very heavy cameras. The cost of the rings is of the same order as your radius block, but are rather more complex to machine since there are multiple parts involved. But because they are using the same part for the tube rings, the unit cost is comparatively reasonable for the number of machining operations through economies of scale (but still expensive!). Similarly with the AG, you have to specify the adapter dimensions you need to match the coma corrector to your particular camera assembly for the back focus. These are made individually to customer's requirements and are subsequently expensive. I bought mine off their scrap stall at Astrofest for 20 quid and modded them myself..looks like some customers got their dimensions wrong! In a way it's best to be grateful we have a choice. If you want decent quality at minimum cost then go the Skywatcher route, but they won't stop the factory in China for a different paint job. If you want something a bit bespoke with slightly better quality optics then OO can often oblige..at a cost and often a wait.
  10. I have the exact same scope and it's absolutely fine with a Paracorr and an Ethos 21. It'a as much about distance as weight..cascading lots of accessories puts up the bending moment quite quickly. I will admit, I've had exactly the same thought process in the past and have considered reinforcing the tube with a couple of 1/4 inch square bars on the inside using the focusser screws for fixing, thus spreading the bending moment over a longer section of the tube. . However it's never been really necessary. I'm sure by now OO would have addressed the problem if enough people were seeing it. But....given your plans you will need a Barlow before the binocular assembly to "pull" the focal plane out of the tube, followed by the Denkmeier or whatever,..and then a couple of eyepieces on top. I'd do a few sums and add up the bending moments and see if you can simulate the load first before you drop that sort of wedge.. What is true is that the tube dents quite easily if you happen to knock it at 3am while putting it away....but that's the price for a lighter tube compared to steel of similar thickness.
  11. As an advert for a 3" refractor that takes some beating...I struggle to get anywhere near that quality with a 6"
  12. Very nice indeed. We will of course be expecting comparisons.... Looks like the age-old debate is about to real its ugly head again...!
  13. You may not even be able to install Windows 11....Microsoft in their wisdom have made it a requirement to have a "Trust" module present....only machines made in the last 3-4 years with the latest Intel / Amd processors have this facility. There are probably 10 PCs/ Laptops in my house...not one will handle Windows 11. There is an online facility somewhere to check if your PC is suitable. Intel / AMD must be laughing all the way to the bank.....and I would'nt be surprised to see the secondhand prices of machines without this facility drop through the floor.
  14. Interesting comparison. To my eyes both are good shots but the C11 wins...the stars look a bit tighter and the nebula has better detail.
  15. Thanks for the heads-up. I'm pretty sure I've just about spotted it with an Altair 60mm triplet at *105. I would not have recognised it for what it was without your post...Ganymede looks like a small stain just off the equatorial line. Going back to check while the seeing is playing ball..
  16. I don't suppose you've entered the focal length in centimetres rather than millimetres? (Just part of my envy management strategy...)
  17. Nice report, well written. Glad to see you're getting to grips with the star hopping! The seeing in Pershore was excellent last night. Using the 14" with the APM 13mm 100 degree the focus was really snappy (*140). I watched the Io transit early in the evening. I was amazed how sharp and how black the shadow was compared to the view in smaller scopes...and how much smaller the shadow appeared compared to Io itself. I managed to pick up Io while it was still on the disk and follow it off over a period of about 30 mins. Moved on to Saturn..spotted all 5 moons on the S+T predictor, plus one field star which caused some confusion. Hints-no more- of the crepe ring. Moved on to M71 in Sagitta. One of my favourites...never sure whether it's a large compact open cluster or a small loose globular. I could see a lot of stars with direct vision, but averted vision really opened it up right into the core. One thing that really struck me last night was that looking at an object centered in a 100 degree eyepiece means that all the outer field is effectively been seen with averted vision and is thus enhanced..this was particularly noticeable trolling through the Cygnus star field. I only used one eyepiece last night..the 13mm would be a good contender for a "do-it-all" eyepiece in this scope. RL
  18. Nice scopes... The focal lengths are both quite long. Thus the Barlow lens in the kit won't see much use. neither will the 6mm in the SCT. The 32mm will be a decent low power eyepiece for the SCT. The same kit is available under different brand names (Revelation) at lower cost....I keep one permanently in the car with a 60mm refractor for quick viewing sessions while out and about. If the car gets broken into and the whole lot nicked it's an inconvenience but not a disaster. They work just fine in this context. But for home use I'd not be too happy for long. The BST Starguider range seems to get universal praise if you're on a limited budget. They have more field of view and are probably better corrected. The problem about going top-end is that one fixed focal length eyepiece won't cover all situations. Peter's comment about getting a zoom has a lot of merit.
  19. The answer depends a lot on the scope. If it's a fast Newtonian (say f/5 or faster) the Plossls in the Celestron set might be a disappointment. If you have a long refractor they will work well. Something like the TV Delite (at £240!) will work well in all scopes. You don't have to pay TV money for a good eyepiece nowadays. There are loads of others nearly as good for a fraction of the cost. Baader Morpheus, ES, APM spring to mind. What is your scope? What are your preferred targets?
  20. This question depends a lot on the quality of the eyepieces you buy. When I got my first 14" Newt...it was a f/5.7 scope, pretty long by modern standards, so relatively easy on off-axis eyepiece aberrations, or so I thought. I bought a set of GSO 2" eyepieces being sold as a set by Telescope House...they included a 42mm, 30mm and 26mm 5-element jobbies. The view was awful in all of them...anything further than 50% of the way to the edge was just a seagull/ cross/ chromatic mess of mushy astigmatism with coma. I thought a Paracorr would sort it all out and so bought one..which was disappointment number two. The Paracorr only takes out coma...the view was slightly better but still awful. Certainly not worth spending 200 quid on (2007 prices..). My biggest problems by far were with off-axis astigmatism in the cheap eyepieces. . So in the end I bit the bullet and splashed out on a 13 Ethos, and the 28mm UWAN, and the view was indeed virtually perfect in both. The Paracorr is only really effective once all the other nasties are taken out of the equation. I appreciate the Ethos series is stupid money especially post-brexit, but some of the clones do come pretty close. Wide field is really useful in this sort of Dob because it will allow you lots more time to look rather than spending all night nudging the thing. Maybe not 100 degrees..there are some really good 82 options out there. Personally I'd get one good low-power eyepiece to start. This will have the worst coma. See if you can live with it first...if you can't then get the Paracorr. I would expect a 20mm eyepiece to see a lot of use so you might as well have it in focus. True. It's too high for the vast majority of nights. I find that *200 is a good top whack for a lot of scopes 4" and upwards in average UK conditions just because seeing limits the optical system's performance. You will occasionally need more when the seeing co-operates but an 8mm eyepiece will see a lot of use in the high-power role. I occasionally use 4.7mm (without a paracorr!) Good collimation is pretty important. Lasers are very convenient but far from the total answer. I use one for rough alignment and follow up with a Cheshire eyepiece. We all have our pet methods on this one. There is a whole encyclopaedia of threads about collimation on this site! The good news is that the OO cells hold collimation pretty well. The biggest risk to collimation is knocking the scope as you carry it about. Truth is my OO VX14 in only perfectly balanced for a 21 Ethos plus paracorr. I rely on the friction brake a lot. At least it tips up rather than down... I have a couple of weights with strings and cuphooks that can be clipped to the front if I feel like using a 6mm ortho...
  21. I have what I suspect is the exact type of scope you are purchasing...and it's a stonking piece of kit. If you're planning on moving it often, some form of scope buggy might be in order. I don't see any mention of a coma corrector....I find a Paracorr makes a very useful improvement at focal lengths 13mm and above. It is of course a personal thing how much coma you can cope with, but once you've dropped a massive wedge (not literally..)on a 1/10 mirror and a bunch of top-notch eyepieces to match, you find yourself looking out for distortions so it seems a shame to compromise the overall magnificence of the view! As the cliche goes..Other coma correctors are available...but the Paracorr is hard to beat for operational convenience. But try without first and see how you get on. Once you're up above *150 magnification the coma gets small enough to ignore, and I've had the occasional suspicion it detracts from the detail on planets even though it's supposed not to. Taking it out leads to balance issues assuming you balanced the scope in the first place for a Paracorr plus a Nirvana 28.. If you do go for the Paracorr then you might want to re-run your sums to account for the 15% extra magnification. I've several examples of non-Televue 100 degree eyepieces..including the ES 9mm and the APM 13mm, 3.5mm Myriad. My overall totally non-scientific impression is that APM comes closest to matching the real TV deal for levels of contrast. I prefer the 10mm Ethos to the 9mm ES. I actually spent a long time waiting for a secondhand E13 to turn up at under 400 quid and gave up when a APM 13mm came up for less than half that price. I've not been disappointed. I'm using a UWAN 28mm as my lowest-power finding eyepiece. Lots of field, but the sky is a bit bright in average UK skies to utilise a 7mm exit pupil effectively. The Ethos 21 is more useful to study objects with. The APM 20mm might well be worth a punt given the stratospheric price of the E21.
  22. Absolutely massive H alpha peak last night; raw data. This is raw data where the instrument is less sensitive at the alpha line compared to the beta.. I expect the Purkunjie effect will be a serious issue now doing visual magnitude estimates.
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