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chiltonstar

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About chiltonstar

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    Brown Dwarf

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    Wildlife photography + astronomy of course
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    Wessex/N. Berkshire Downs
  1. Yes, eg a prism image (uncorrected) using my prism of Vega. H alpha is nicely shown, although not much further into the red. Chris
  2. But resolution in the red and NIR is presumably fairly poor because of the non-linear dispersion of a prism which compresses the spectrum at the red end? Chris
  3. Many thanks for these very useful replies. The camera (Nikon D750) is un-modded so does have a UV/IR cut off unfortunately, but my AS1224 (colour) doesn't seem to go much lower in wavelength even without one. The reason I need to go down a bit more (apart from the interesting spectral lines below 400 nm!) is because I'm using an objective prism and need the 410 nm H line if possible as one of the three lines I've been using to linearize the spectrum from the prism using the BASS software. The prism is mounted in front of an ED80 (fl 600 mm) which is close to the fl of the original lens in the Hilger 0.5 m spectrograph that the prism came from. That went down to about 320 nm or so, but using film rather than a sensor of course. In the blue part of the spectrum, the objective prism is giving me a resolution of about 3 - 4 times better than I get with the SA100 I have. Chris
  4. This is a very useful thread which I have been following avidly as part of attempting to reboot my astro spectrometry interest! A question for the experts, in keeping with the title of the thread, are any of the commonly-available cameras able to go further into the UV and IR than the AS1224 I have, or the DSLR I normally use which runs out of steam below 420 nm or above 680 nm? Chris
  5. ....but not in a 127 Mak though, which is the OP's question. Chris
  6. I used cable ties (or black insulating tape which works as well) to keep the profile down a bit. I've got a twin finder bracket as John above mentions but it places the finders too far out from the scope and is a bit oversized for the relatively small scope. You can see what I mean in this image which is on my much bigger 180 Mak - it's too awkward for that even and I've dispensed with it in favour of an rdf (Rigel) on the finder as well. Re the base: it was an old SW RDF - I partly dismantled it to leave the flat plastic bit on it which would fit against the curve of the RACI barrel. On my other Mak and using a Rigel which is far better, I've filed a spare base down a bit to make a smooth curve which fits against the barrel. Chris
  7. Some of the most memorable:- - first sight of Saturn through a real telescope! - a horizon to horizon fireball complete with sound effects (hiss-whoosh) - M31, naked eye, huge from near the summit of Monte Rosa Chris
  8. Looks a very pretty scope, and it's clearly you we've got to blame for the hideous weather at the mo! Certainly a bit of coma and astigmatism in the 6" then? Does the 33% obstruction include the baffles, or is it just based on the secondary mirror diameter? That first light is eagerly awaited by many of us I think! Chris
  9. But aren't the deficiencies of a classical cassegrain design addressed with evolved designs like the Rumak (eg 180 Mak)? Maybe modern optical materials have improved classical cassegrains? Chris
  10. How significant are coma and astigmatism with the Omegon in practice - any good practical assessments from "discerning users"? As it is a classical cassegrain design, presumably there are diffraction spikes as well? Chris
  11. Some have been updated including the 180 and 150 I believe - it must have been carried out some months before I got my 180 in 2015; the rear of the scope was modified as well with a 2" focuser. Some models have not been modified (eg 127 Mak), although this is such a good scope that whether it's 127mm or 119mm aperture is not that critical for most of us. I am not sure that the Orion models (also Synta of course) were modified at the same time as those branded SW here - Skywatcher could maybe help on this point. Again, there are several threads on CN that go into the apparent and true apertures of the various Mak models made by Synta. I've taken this from another post (from Skywatcher/Synta originally) and it gives some idea of the true optical arrangement:- Per the OP's question the SW rep listed the 180's as:•True Aperture: 182mm•Primary Aperture: 199mm•Baffle Opening: 31.9mm•Rear Cell Opening: 31mm•Secondary Diameter: 41mm•Obstruction by Diameter: 23%•Obstruction by Area: 5%" The obstruction figure quoted is for the front mirror though and does not include the baffles apparently. Chris
  12. The 180 is a true 180 John (I've tested mine and found 179mm when it is in focus and the rear focus position is normal (ie no long focusers to extend fl). There are a number of threads on cool-down time and cladding on CN; my own experience is that post-cladding (insulation), cool down is not a problem for me provided the air temperature is not dropping too fast. It has not been an issue in Summer, but last Winter cool-down was slightly more noticeable on days with bright sunshine and warmish, but with clear frosty nights. To be fair, on these occasions the seeing was poor anyway. Chris
  13. Nothing clever. I filed the base of the Rigel to fit the barrel of the RACI and attached it with a couple of cable ties. Chris
  14. I used a roll of the stuff that B&Q sell for insulating behind radiators; Al on one side and polystyrene on the other. Makes the scope look a bit hubble'ish, but this is what it looks like:- Chris
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