I have heard back from Wolfi at Teleskop-Express re the carbon tube for the MN190, they don't have one and no plans to make them. He also suggested that they would not do it anyway as they regard it as a closed tube scope and it would trap heat. What he doesn't know is that the MN190 has ventilation through the rear fan. Anyway that is a dead end.
Ken you are right, i never checked that until just now. The MN190 tube seems to be aluminium, it fails to interest a magnet. Boy those two pieces of glass hold some weight. Looks like i don't need to retube it, and any diet will not reduce it further. I would have hated to abandon that beautiful black diamond tube.
I have been reviewing the TS Photoline scopes like the 115mm which is in the ball park focal length and budget wise, so it could go on the short list of refractors.
Mark, all the Mak-Newts have baffle rings ( well at least the Intes ones), and i doubt it's just a styling convention to appeal to refractor fans. I suspect, having built a iStar refractor, that all front mounted glass elements require baffling to manage scatter.
Re pixel size and focal length, there seems to be all sorts of scopes being used with the ASI1600 camera, i have even seen RC images that look fine (to me). I don't know that over sampling is really an issue, under sampling is another matter i think. I still have my cooled Canon 450d DSLR, with its 5.2 micron pixels, which i will be using for OSC when i feel the need for speed. I would not want to go below my target fl range lower limit of 600mm.
I think i need to produce a chart on to track these options and features.
The Borg 107 mm fluorite doublet f/5.6 will be released soon. It's incredibly light and slides down to a very compact size, plus the optics should be great. Hopefully $3k will buy one, but likely just the objective!
Discussed this question with my son last night and it is clear that the family would like to retain some visual capability for the times that they visit, and the grandkids will want to have something to look through soon. So I have modified my criteria slightly to include visual capability to suit.
This creates a no-cost bias towards keeping the MN190 as it is an outstanding visual scope that takes heaps of magnification, as well as an astrograph. However, to be all it can be, I would need to look at sourcing (or making) some rotating rings, or tube slide stopper (without increasing the overall weight, hopefully). Like this: http://i110.photobucket.com/albums/n...d/DSC_0170.jpg
I will shift my attention to 600mm focal length scopes as my wider field imaging tool, and have created a list of refractors mentioned in previous posts here, including the TS Photoline models and others that fit my budget.
Glen,
Just a comment about aging and observing/ telescopes....
Everything seems to get heavier and more awkward to use, then there's the difficulty of justifying large expenses when living on a pension...
IMHO keep it simple.
A quick comment perhaps not entirely relevant - carbon fibre is not an appropriate material for some scopes. For example refractors its a poor match and worse than aluminium alloy which closely matches the change in focus of an APO objective.
I am not sure about a Mak Cass, it does have a corrector plate.
Carbon fibre is certainly the go for mirrored scopes like RCs, CDks, Newts.
Agreed Greg - all the research consensus is that CF is a VERY BAD idea for refractors - hence why many of the manufacturers are going AWAY from using it (not sure if OS is still using it...lord alone knows why!). There are numerous threads on CN about it, including comments from Yuri (TEC) and Roland (AP).
That was pretty much what Wolfi at Tekeskop-Express said, that carbon fibre should not be used on closed tube scopes,, which explains why all their carbon tube offerings are newts or RCs or other open tubes. I noticed looking through their refractors that everything is alumimium tube.
Agreed Greg - all the research consensus is that CF is a VERY BAD idea for refractors - hence why many of the manufacturers are going AWAY from using it (not sure if OS is still using it...lord alone knows why!). There are numerous threads on CN about it, including comments from Yuri (TEC) and Roland (AP).
I was talking to Cris recently and he mentioned that they aren't making their 130mm anymore, not sure whether they are continuing with the 115 but that would be their only refractor if they are.
Glen, you have an MN, which is great for imaging and you have an achro which should be fine for the grandkids to start out with and for your occasional visual use if your eyes are not as good as they used to be. Presumably you don't do visual and imaging at the same time, so maybe you already have appropriate scopes? If you want widefield, the 450D on the MN should do a fair job.
Glen, you have an MN, which is great for imaging and you have an achro which should be fine for the grandkids to start out with and for your occasional visual use if your eyes are not as good as they used to be. Presumably you don't do visual and imaging at the same time, so maybe you already have appropriate scopes? If you want widefield, the 450D on the MN should do a fair job.
Your right Ray, i am more convinced that my solution lies in what i have, but needed to ask the question and get some experienced input.Thanks
That was pretty much what Wolfi at Tekeskop-Express said, that carbon fibre should not be used on closed tube scopes,, which explains why all their carbon tube offerings are newts or RCs or other open tubes. I noticed looking through their refractors that everything is alumimium tube.
The reason that Roland @ Astro-Physics gives for using aluminium tubes for his refractors is that the dimensional changes in an aluminium tube due to temperature change tend to compensate for changes in the focal length of the objective, giving overall better thermal stability.
This isn't going to be a significant factor for closed tube catadioptric designs where I presume the main disadvantage of a CF tube would be a longer cool down time.
Rather than CF, just carefully cut some holes in the tube and add some fans...should keep it equilibrated on warm summer evenings...
The MN190 already has a rear fan port behind the primary, and a ventilated focuser plug, providing a flow through path. I use a filter medium in the focuser to prevent dust getting into the tube or on the mirrors or corrector internal side, fan is oriented to exhaust air from the tube pulling air in through the focuser filter. No issues with equilibrium.
CF was a consideration for weight saving only.
Mark, all the Mak-Newts have baffle rings ( well at least the Intes ones), and i doubt it's just a styling convention to appeal to refractor fans. I suspect, having built a iStar refractor, that all front mounted glass elements require baffling to manage scatter.
I think a mak newt is basically a newtonian with a corrector plate ( albeit just a meniscus). Theres a long technical article by long term AAO telescope operator Steve Lee showing why baffle rings are superfluous in a reflecting telescope and it all made sense . The primary mirror and secondary act as main baffles. Mel Bartels demonstrated how effective the double baffle in double blind study with a flashlight.
GSO RC's also have these baffle rings and again with properly baffled primary and secondary mirror I'd say they are completely superfluous. If it meant you could go thinner aluminium and the rings would increase rigidity the rings may make sense and I suspect that the baffle rings in the MN190 are more for that , plus the perception that they do something extra .
Pretty much all you need in a Newtonian is some black velvet on the tube wall apposite the focusser and behind the secondary . I would imagine that the amount of ambient light hitting the meniscus on a mak newt that wasn't normal to the axis and then scattering inside the corrector would be pretty minimal.
Its an interesting subject and may do well to throw it open on Cloudy Nights for all the experts to mull over !
No diffraction spikes on the MN190 but I do like the simplicity of the straight through focusing position on a refractor or SCT/CDK ect. Makes balancing in all three axis a lot easier
Yes I would agree that straight through focusing is a real plus in so far as balancing and field rotation is concerned. Moonlight's new 'Nitecrawler' worm drive focuser and rotator is a very nice piece of gear that would be great to have.
