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Everything posted by hunterknox

  1. I prefer cotton wool but each to their own. Look for “Cotton wool BP” on the label in the UK. BP = British Pharmacopedia = medical grade Light touch is a given but I also try to rotate the cotton wool as I move it across the surface so the overall effect is lifting rather than polishing. One swipe per cotton wool ball then discard. Imagine you’re a nurse trying not to cross contaminate different parts of the mirror surface. There used to be a great video online of David Sinden cleaning a refractor lens with the proper technique but I’m not sure it’s available anymore. My worry is always dragging whatever’s on the surface over the surface. It’s not exactly analogous but next time there’s a sunny day look at the reflection of the sun on a car bonnet. What you’ll see is scratches in a circle around the reflection of the sun. That’s because there will be scratches in random directions all across the bonnet and it’s the ones in a circle around the solar reflection that bounce back to your eye. Why are there scratches in all directions on car bonnets? Because when cars get washed whatever’s on the bonnet usually gets dragged across it before it gets removed. There’s a huge difference between cars and telescopes but as a general principle if you assume whatever’s on the surface of your mirror and could be abrasive and think about your technique from that starting point you won’t go far wrong.
  2. Think about it like this: how much do you worry about your windows with all that intense sunlight bearing down on their massive surface area? Assuming you’ve got a standard refractor with the lenses at the front then the light and heat that hits the first lens is no more concentrated than it is on a window and on the second (or third) lens it’s slightly more so but not a big deal. As John implies: things aren’t getting too intense until closer to the eyepiece end and the Herschel wedge is designed to deal with the concentrated heat and excess light. The former doesn’t go round corners well and the latter is effectively filtered out using basic darkening (neutral density) filters once the heat’s been sapped away. Refractors with lenses at the back as well as the front (such as Petzval or Steinheil designs) might be more problematic but your Starwave should be just fine. Nice scope, by the way.
  3. Thanks Shimrod - that looks like a backup option. 2kg is not that heavy in normal terms but not ideal on top of my other gear. Should have said I’m carrying everything off the beaten track so the lighter the better but I realise a compromise might be in order somewhere.
  4. I’m looking for an easy way to power my portable setup, which just means powering an Astrotrac and a dew heater, but I can’t seem to find a stock, light-weight battery that will do both. All the astro power tank stuff seems to either have 12v cigar sockets, or a small DC outlet, but not both. Happy to buy a new dew controller if needed but the only ones designed to power a mount as well as dew strips are on the massive side. Any ideas from the Lounge?
  5. Seeing as it’s likely out of warranty it can’t hurt to take a look. The PST uses a 5-sided prism to bounce the light up to the eyepiece. One face should be parallel with the front on the scope, one with the eyepiece. When you’re turning the focuser you’re just screwing the prism holder back and forth within the black box. The holder isn’t a great design. The prism is “pinched”, if you will, at the slides (like a litter picking claw might pinch some rubbish). It’s not a great way of securing something so it’s not unknown for the prism to slip a little which puts the whole optical alignment out of kilter. Have a go at unbolting the hex bolts on the side of the black box and see what you find. They might be a bit stiff - I think mine were loctited. It could just be a case of manually adjusting the the prism so it’s facing the correct way in its cradle. Good luck.
  6. I guess the seeing in York must be fairly stable - flip side of the fog you often get. Anything over 180x is a bonus for me but I don't think you necessarily need the highest magnifications for a reasonable star test. Glad to hear there are no optical horror stories thus far though.
  7. What? Problems appeared as I was typing? Sounds about par for the course. Still got my fingers crossed for you for first light though...
  8. Fortune favours the brave! I'm a sucker for alternative designs of anything. Very interested to see how you get on with this one...
  9. I think the phrase "primarily a visual instrument" comes from the original marketing info. I know a few people who've looked through them, myself included. If you can get excited about seeing a faint, featureless purple circle then it's a visual instrument. If you're a normal person then it's for imaging only. Great scopes, but only for a very small niche. I sold mine when I stopped imaging.
  10. Yep. Never really understood why people do it though, except in very specific circumstances (e.g. using a Daystar filter). If you're struggling to get a perfect circle for your aperture mask there was a guy who used to make Bahrtinov masks who traded on ebay as Morris Engraving. He made me a custom Hartmann mask for a very reasonable price so I'm sure he could do an aperture mask too.
  11. Weirdly my older Solarmax has a red front-end etalon and a red objective, so it might be that the etalons have ERFs up front but that they're not suitable for use without additional energy rejection components.
  12. Here's a solarchat thread on he same topic: http://solarchat.natca.net/viewtopic.php?t=4307&p=43819 In summary, check design specifics with the manufacturer but there doesn't seem to be anything intrinsically bad about using oil-spaced refractors.
  13. I suspect that any glass or oil up front isn't an issue - heat gets concentrated at the back of the scope and if anything the oil im a triplet might help to stabilise any temperature differential betwen lenses. That said I do believe that the earlier TEC 140s aren't recommended for solar viewing - something to do with the collet rings? Later versions had a different design and to say they've been used to impressive effect would be understating it.
  14. I would say no, the 66 is unlikely to be better for solar unless the opticstar's a dog. Aperture still rules for solar refractors and the magnification you can use is more likely to be dictated by seeing than telescope.
  15. Nice one, Stu. you can tell that a mount's a beast when it comes with its own carry handle!
  16. I hate spending money but the Baader wedge is one thing I'd have no hesitation in buying again.
  17. It all comes down to seeing again. You're right that you get the same peering-through-the-atmosphere effect when the sun's very low down but it's usually dominated by ground effects once the sun's heat kicks in and that's worst around mid-day. That's why a lot of land-based solar observatories are up towers and by lakes - it's the best way of ensuring a stable atmosphere. I also find the seeing effects to be wavelength dependent, which would make sense given that red light is refracted to a lesser degree than blue. Back when I was doing imaging I tried to get calcium K done before 9:30, white light before 10:30 and H alpha shortly after. In winter it can be better for observing in some ways due to the lack of a significant temperature differential. One of the best tips I've picked up for white light is that if you switch a continuum filter for a red filter when the atmosphere gets choppy you can get a better view until the seeing breaks up altogether.
  18. Solar's a different kettle of fish when it comes to magnification. I can rarely use magnification over about 60x because the seeing's so affected by the sun's warming effect and I don't think that's uncommon. See how you get on with your existing eyepieces, figure out what your optimal magnification is and if you do feel the need to change try a simple eyepiece like a plossl or an orthoscopic - fewer glass elements is usually better, in my experience.
  19. CA is the last thing that bothers me, as in it does bother me, but it's the last thing on my list of things a scope has to get right. Any kind of perceivable softness (spherical aberration), coma, diffraction spikes usually bug me more. I've tried various ED refractors and have been impressed every time. They do enough of a job on CA that I'd definitely consider them before a Newt or catadiatropic of some kind, but then I'm a refractor guy at heart.
  20. Short refractor + 4-6"l mak or similar on dual alt-az mount. Someone at my astronomy club has a setup like this and I'm convinced it's genius!
  21. As Peter says - the larger the number on the blocking filter the larger the field of view. As a rule of thumb the prime focus image of the sun is the size of the scope's focal length/100. For example, a PST has 400mm focal length, so a BF5, with a 5mm aperture, is sufficient because the prime focus image is ~4mm. If you've got a stage 1 PST mod you'll realise that the field of view is limited - that's the blocking filter limiting it. Coronado BF numbers reflect the clear aperture in millimetres, so BF10 = 10mm, BF15 = 15mm etc. I think the Lunt BF600s are 6mm, 1200s are 12mm etc. Various people have done stage 2 mods with Lunt BFs, which are generally more available. If you need to do some imaging you're better to get the next blocking filter up, so if you're scope's 900mm you'd want a BF10 for visual or BF15 for imaging. The reason for the difference is that for imaging you want your camera at prime focus so your BF goes further up the light cone and therefore needs to be wider in aperture so it doesn't cut off the light cone at the fringes. As for scopes, I've done a stage 1 PST mod and currently have an old "made in the USA" Solarmax, which is lovely. For high resolution you definitely want long focal length. The stand-alone scopes still have a place for full disc and grab & go work though. I wouldn't be without mine. My understanding is that scopes with internal etalons generally have sweet spots but I'd be interested to hear others' experiences on the issue. If I was after a new scope Coronado wouldn't get a look in. I recently got a new BF10 and though it's fine to use I had to cut away some excess glue before using it. Also, the stock Coronado focusers are very poor. Lunts or Quarks (or a Solarscope if you have the means) are definitely where it's at. You can't really go wrong. Keep us posted when you do finally decide!
  22. With longer scopes and a Herschel wedge you can usually get a good fix on the sun by minimising the shadow on the ground, then looking down the objective lens (at a slight angle) to see where the light's catching and then just nudge your scope the right way to centre it on the wedge. I've had no problems with this method on a manual alt-az mount with a scope of similar size.
  23. Ordered a couple of books from Sky & Telescope's online shop. They arrived in the UK quickly enough but I was surprised to receive a customs note with them (since books should be exempt from additional taxes). After 1/2 an hour on the phone to the Post Office and HMRC I was informed that I'd need to pay an additional £19 to receive the items, but could claim this back if they'd been mis-handled. When they were delivered it turned our that, rather than being mis-handled, they'd been mis-labeled as "craft supplies". Contacted S&T requesting a refund of this additional charge, which was entirely a result of their error. Received an answer after over a week, which stated that: "...unless your package was sent to a school or learning institution or you requested that the package be marked as educational we have no way of knowing if it will be used for a personal hobby or craft" This information was not given at the checkout. I responded, pointing out that I had ordered from the S & T shop, which doesn't sell craft supplies, and that I was surprised that they make customs declarations on parcels when they don't know their contents. Received another response to the same effect and stating that: "[sky and Telescope] are under the umbrella of F+W Media a Content and Ecommerce company." So it seems I am to remain out of pocket. It's a shame because I'm certain my future custom would have been worth a lot more.
  24. It's a shame we can't sell organs in this country!
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