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About rl

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    Star Forming

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    pershore, worcestershire, uk
  1. One of the hardest things for a newcomer to the hobby is managing expectations! I've owned the ST120 and enjoyed it...it's optimized for wide field low magnification viewing....the image goes a bit soft at magnifications over 100 times. But that's enough to show the rings of Saturn with the Cassini Division and the cloud belts and moons of Jupiter, as will as all the deep sky objects on your list. Virtually all the Messier objects are within its range under the right conditions. The 3.6mm will be too much magnification unless your example is markedly better than the one I had! 5-6mm gives you 100 - 120 times which is a sensible top whack. Try reading the writing on a 5p piece at arm's length....that's the sort of detail image scale you're going to be looking at for the planets at *100. You can see stuff but it's still small. I'd stick with the stock eyepieces for a bit and see how you get on, but a good accessory in the future might be a good quality 20-30mm widefield eyepiece which will make the most of what the scope does best...low power, wide field. This might seem a duplication with the standard 25mm supplied but the improvement in image quality across the whole field can be worthwhile. If you're happy with the standard one, then fine. Most people find themselves getting more critical of image quality as they get more experience, and perfectionism quickly turns into a slippery and expensive slope! Some very expensive wide field eyepieces only serve to show up imperfections like field curvature..if you can try someone else's eyepieces first. Virtually all deep sky objects look like faint bits of cotton wool ..you have to train yourself to pick out the limited detail visible....dark adaption is very important. Going to a dark site helps enormously with any scope. A lot of the fascination is in understanding what you're looking at rather than the immediate visual impact. Having a target list which you've previously researched a bit helps keep up the interest. Sorry for rambling on...stick with it! RL
  2. rl

    Xmas astro presents...

    has she got any sisters?
  3. I'll have a punt on that...pm on the way RL
  4. Like CraigT82 I have the AR90S and echo his comments. It's a great widefield scope. I've used it as a finder on 12" and 14" newts, an application for which it excels. The metalwork is exceptional for the outlay. But as my only scope? It's not brilliant on planets. I would suggest waiting and paying a bit more for a S/H ED80 for maybe £200-£250. This ticks both the planetry and Deep Sky boxes as well as most small scopes can, is just as light and portable and you are less likely to have outgrown it should the interest spark up again. It will generally outperform both the options you are considering. I'd take the extra optical quality over the 10mm aperture increase. Are you really that fixed on a refractor? Secondhand 6" Newts go for under a ton and the short f/5 ones don't weigh a lot. Just my 50p... RL
  5. rl

    Refractor upgrade

    I'm seeing a lot about magnification here.... I guess I date from a similar vintage and, for me, the usual 50* per inch rule does not apply ...the 0.5mm exit pupil shows up too many floaters to be really useful. Not the scope's fault, just ancient eyes. Might something that can provide the same mag but with a bigger exit pupil be worth consideration, like an 8" newt? Of course there are other tradeoffs like bulk and collimation... If this is not an issue then the 120ED has a fantastic reputation. RL
  6. rl

    It does what it says on the tin.

    I bought mine in a fit of pique after having messed up my polar alignment for the umpteenth time because the spirit level in my AZEQ6 was playing up. I expected a lot of buyer's regret but am happy to report being very satisfied. It is undoubtedly a massive wedge to fork out for a posh webcam and some software but it does a brilliant job. The value is all in knowing you can trust the polar alignment and the improved guiding. There are cheaper ways of doing it with platesolving programs and finders but the overall package is hard to beat. RL
  7. From personal experience the ZS61 + flattener + Canon DSLR combo gives good results on the star adventurer mount; it can be made to balance correctly without having the counterweight all the way to the end; I add an extra piece of metal to allow the mounting point to be more towards the camera or it will be a bit bottom-heavy in dec but it's not the end of the world without this refinement. The ZS61 is a very well-made scope with exellent optics but a bit expensive for a 60mm. I believe there are now some ZS61 clones out there which might be a bit cheaper. As already stated, you need the flattener to make use of an APSC-size sensor but also the focal length is reduced (to 245mm from memory?) which helps mask the guiding errors. A very worthwhile addition is a red-dot finder which clips on to the hotshoe on top of the camera. I didn't realise these thinks existed until I got feedback on the review; since the ZS61 has no finder option it's worth it's weight in gold for centering targets quickly. Regards to all, RL
  8. rl

    NGC 891

    Nice work, it's a beautiful galaxy. I always find this one difficult visually in a 12" so I'm not surprised it took so much data. RL
  9. rl

    Astrophotography in Southern Africa

    Some of my most memorable astro nights have been at SAAO at Sutherland in the Karoo, South Africa, which is several thousand feet up. With good dark adaption, you could virtually read a newspaper by the starlight and Venus would throw a visible shadow on white paper. Many Messier objects normally considered binocular targets were naked-eye..there was so much om view it was quite disorientating..it was like learning the sky all over again. Having everything upside-down didn't help. I took a lot of wide field shots with a home-made clockwork drive and a 135mm lens on Ektachrome 100..if I can get them digitized I will put them up here. RL
  10. rl

    Coma Corrector for Visual Use

    I've got the Explore Scientific HR coma corrector in my 8" f/4.5 scope and it works really well. It gives a flat image plane as well as coma correction which means that the overall view is very good indeed with eyepieces also having a matching focal plane, which includes all the more expensive Televue offerings. The view of the moon at *200 with everything in perfect focus all at once is seriously impressive. Downsides; the screw thread adjustment can be a bit of a pain to set in a hurry. The Paracorr tuneable top idea works better in practise. But to be honest it is not that big a deal since there is a compromise setting that works well enough with most of my eyepieces, but it might bug the perfectionists. Also, I find the view through the HR a bit "warm" in the same way as some criticise Nagler eyepieces. But on balance it's a really good bit of kit. If buying secondhand make sure you get the two camera adapters with it. Regards. RL
  11. No-one's said it yet so I'm going to.......the mount is probably the most important part of the deal when starting AP. I'd get at least the HEQ5. By the time you'be added a camera, guidescope, filter wheel, guide camera, focal reducer, flip mirror, dew heaters and any other toys that take your fancy it's very easy to get up to silly weights even with a small scope. You may have to add weight unintentionally in the form of a dovetail/ bracket of some description just to move the scope forward enough to balance with all the accessories attached. A smaller mount can work if there is no wind but you need something that is rock-solid enough to work whenever the sky is clear. The HEQ5 is not without its faults but most of them are well documented by now and have fixes. If you saved a lot of cash buying the Altair scope you might like to invest some of the change in the newer AZ-EQ5 which solves a lot of the original HEQ5 issues The truth is that for most of us lesser mortals the learning curve is steep and painful before getting good results reliably, and guiding issues (along with processing) tend to be a biggie. I'd take advantage of other people's pain and go with the tried and tested route.
  12. rl

    Different Eyes = Different Focus

    If you're short-sighted you will have to rack in the focuser a bit....I believe you also get a little more magnification than the usual simple formula predicts (Fobj/Feyepiece) which assumes the eye is focussed at infinity.
  13. rl

    Guide scope upgrade

    Taking up Olly's suggestion on the maths... Main scope resolution at 600mm f/l = 1 arcsec per pixel for ASI290 with 2.9 micron pixels Guide scope resolution at 200mm f/l = 3.8 arcsec per pixel for ASI120 with 3.75 micronpixels Autoguiders will generally control to 1/10 pixel without too much bother, say 0.4 pixels so if it's all working ok you should be well in. If not, are there other issues like backlash or wind, polar alignment? What does PHD2 report as the guiding error? I have a very similar setup (ASI120MM 60mm guidescope) and generally get better than 0.5 arcsec RMS on a wind-free night. Bear in mind that the Rayleigh limit for an 80mm in green light is only about 1.5 arcsec. If your RMS error were 1 arcsec it would'nt be a disaster.
  14. rl

    Guide scope upgrade

    It sounds like your skies are a lot better than mine...is light pollution really a problem for guiding? Can't you just up the guide cam exposure time? Try 2 or 5 sec..should still be ok if your polar alignment is up to scratch.
  15. rl

    Guide scope upgrade

    If you've already got a filter then it's worth a try. One practical test is worth a lot of posts here, but I would not expect much benefit. It depends heavily on the nature of your light pollution. A star shows a continuous spectrum rather than a line emission spectrum. The filter is going to cut down the star's light along with the light pollution. If your light pollution is old-fashioned sodium light with a line spectrum there might well be an improvement but most modern streetlights are unsportingly white in their output, which will leave the optical SNR little changed but the reduced photon count will only serve to emphasize the read noise on the camera.

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