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About rfdesigner

  • Rank
    Sub Dwarf

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  • Interests
    Astronomy... really!
  • Location
    somewhere in the uncharted backwaters of the galaxy's unfashionable Western Spiral Arm
  1. FCM coating

    For reference, Multi-coated means the anti-reflectance works well over a range of wavelengths. single coated means it will work nearly perfectly at one wavelength then deteriorate away from that i.e. green is excellent, deep red and deep blue rather less so.
  2. First try on astrophotography: Hourglass nebula

    Getting anything on a scope of that focal length with just a webcam is an achievement, well done. I'm sure you appreciate you're a touch out of focus, and some kind of autoguiding would help.. do you have access to a DSLR?, in which case your SPC900 would make a very nice guide camera. Derek
  3. Triangulum Galaxy (M33)

    Nice capture, M33 is hard. I always fractionally unbalance and misalign the polar so as to maintain a very slight drift and keep the gears meshed. There appears to be a little colour speckle noise when viewed at full resolution, is this hot pixels or just the top of the background noise?.. though even printed A4 you're not going to see this, only if you wanted to print bigger than that... which if fully polished I'm sure this could do. well done Derek
  4. £150 to spend

    what do you expect to do? Travel / only use from home Planets / Deep sky or both Image / View (Imaging is going to cost much more than £150) I would normally advise a basic lightweight newt.. generally you get best bang for buck with them, don't bother with putting much cash into the mount, you'll end up throwing away any mount at that price level (usable deep sky imaging mounts start near £1000) A nice portable scope will get used and used, even if you end up with £10k worth of imaging rig. Derek
  5. Abell 56 not see often on the website

    oh, another Abell pn.. this one looks very hard to capture at all, well done. I'm wondering with these very faint nebula if a scaled red sequence could be subtracted to take out the foreground stars leaving the nebula more visible.
  6. Abell 39 in colour

    Not an easy object.. just showing the background galaxies through the nebula. very nice
  7. How many hot pixels?

    looks like it might not be a myth http://www.bluehoursite.com/articles/how-get-rid-stuckdead-pixels-canon-dslr-camera
  8. How many hot pixels?

    Here's a stretched master dark frame from my KAF8300 based camera, as you can see it's a touch snowy.. but that's OK, it doesn't really matter if you have just one hot pixel or hundreds, you should be running some kind of hot pixel mitigation, either a hot pixel repair algorithm on each sub prior to stacking or a statistical stack or both.
  9. Mirror Cells

    Harvey Thanks.. in fact I have played with PLOP.. and with my mirror, due to the thickness I can just about get away with just a 3 point cell (which is just as well as that's what it has at the moment).. but I'll go for a 9 point if I'm making... the key as I see it is to use enough material to avoid excessive flexure and to make it sufficiently accurately to get the pressure even. I'm guessing half a dozen pixels of image shift from a meridian flip would be about the right level of stiffness to aim for. Very good news on the worm and crown.. I will look forward to seeing your post. Derek
  10. Mirror Cells

    I want to keep weight down. The primary mirror is 50mm thick and the window is 18mm thick.. being a 12" scope that's a lot of glass. I'll have to do some stress analysis and find out how much I can get away with before I see noticeable image shift as the scope flips. HFD.. ah.. is it based on the Focusmax software? The focuser I have is a JMI crayford with the motofocus option.. swapping out the motor for a stepper is as much work as adding some kind of a rotary encoder (for me the mechanics is the hard bit, I find the electronics is relatively easy) JMI do offer some kind of a position sensor setup, but again I can see the bank account suffering........... thinking about it though, it'll still be cheaper than a Carbon Fibre tube. hmmmm.
  11. Mirror Cells

    I could do an ally one, I was concerned about the weight though.. especially if I have a bottom plate that is solid except for the fan holes, I suppose I could use a thin frame then bolt on a thin sheet to seal it. I'm auto guiding but the worm's a bit rough and my focus is drifting, so where I should be getting 2 arc sec FWHM round stars, I can get nearer 4"x3", which is about 3" of defocus and about 2" of drive "thrashing" (I have had 2"x2" but only at very high declinations, near the equator it's pretty bad. I've tried programming in a PEC algorithum, but I only have a 4 minute main frequency, no faster ones as my steppers drive the worms directly, all the rest of the thrashing is worm/wheel roughness. I've had a quick look at Sequence Generator Pro.. does it require a position sensor on the focuser?.. it seems to do pretty much everything else, nice program. Derek
  12. Aluminium vs steel

    Deleted by RFdesigner
  13. Aluminium vs steel

    There is an excellent article on the cloudynights site, but it seems their server is down at the moment. I believe this link will work when it's back up http://www.cloudynights.com/item.php?item_id=1275
  14. Mirror Cells

    No takers? hmm.. an update on my own efforts Q1: Materials: I've looked at nylon and carbon fibre, both have drawbacks... nylon is much easier to work with but will end up heavier and the last thing I need is extra weight, CF is a pain to fabricate.. I'm after lightweight but workable, any other ideas? Q2: Venting: I've realised I have another option, keep it sealed, but install a fan to keep the air in the tube well mixed.. thus I accept the air could be somewhat hotter than ambient, but at least it's all the same. (within 1C) Q3: Autofocus: the more look into this the more I realise I need a position sensor, a rotational encoder on the focusser knob looks like the way to go.. does no one do autofocus? Derek
  15. Glass spider

    Can I suggest starting by just trying the proposed window and leaving your spider in place, just cap the tube..no centre hole, KISS. Cutting the hole could release a strain, and give you a false negative. As an engineer I like to take single steps, especially on "research" projects, which arguably this is. One unknown at a time.. Just take the piece of glass, hold it over the top and see if you still have a telescope or a light scattering tool, also means you can do a with/without test under identical conditions. If it succeeds, cut the hole, and test it.. if that succeeds, mount the secondary in the hole, and so on.. One step at a time.. In my case David Sindon ground mine.. I knew it would work, this is cheaper but you're taking a risk, if it doesn't go right it's worth knowing exactly what caused the failure in case you want a second go. Good luck