andrew s

I may have misunderstood but if the laser in on the spacecraft as is the light sail how does it overcome Newtons 3rd law, action and reaction are equal and opposite? Regards Andrew

Exactly, that's the Physicists moto. Regards Andrew

Well there are certainly ups and downs with my new mount. On the up I added a SW 8" extension pillar to raise the scope as the walls of the observatory were too high and the existing pillar two low having been designed for a larger mount and telescope. Clearly the SW engineering quality is a bit off compared to Rowan. I am not sure who tapped the holes but it was good they were cap head screw as it needs a "crowbar" to undo them and do them up again. Good job it's a one off exercise. On the down side the Nexus DSC is broken. Rather than cut off the cigarette lighter plug (my normal response) I ordered a socket that arrived yesterday. I even read the manual (most unusual) then plugged it all in and ran some test. Worked as It said on the tin. Went back some time later to see if the GPS had locked in and noticed the battery was nearly flat rather than the expected 100%. Out with the multi-meter check power supply voltage etc. Out with the bench power supply, volts ok but no current. Ok unplugged the DC plug and re-plugged it into the DSC. The DC socked fell off the PCB and into the guts of the DSC. Powered it down and took it off the mount. Shacking the unit gently returned the socket to its hole but it is too big to come out. However, giggling it around all the pins look pristine as does the PCB, in fact too pristine, my hunch is it was never soldered in. I am so glad I got this from FLO. I have messaged them the good news and I am sure they will sort it out with their normal excellent service. Regards Andrew PS for those with children or grandchildren of a certain age "Chase is on the case" or at least Grant is🙂

I fully agree, but there are many forks visual/imaging, photometry and spectroscopy/art imaging, variable stars magnitude estimates/sketching etc. each to is own as long as it's enjoyable. We live in an age where we have far more options at a reasonable cost than in the past. Regards Andrew

@Stu I included the150P and 100ED on the very old rule of thumb that the minimum for serious astronomy was a 4" refractor or 6" reflector often repeated by Sir PM. If I was going to have just one telescope for general use it would be the best quality 8" Newtonian I could lay my hands on. You could then go almost any where. Wynne corrector for imaging, powermate for planets etc. If truth be told my wow moment was an 8" Hinds A mirror in a homemade Newt, after two indifferent refractors and a disastrous Cosmotron SCT. It snapped into focus and the diffraction spikes were to die for. Loved them ever since. Enjoy your (whatever the collective noun is for telescopes is) of telescopes. Regards Andrew

Just a thought. If you use it with a manual mount don't leave it pointing at the Sun and go away. The Sun will quickly go off axis and melt all the plastic inside your Takahashi! Seriously I nearly set my observatory on fire with a 16" mirror which was nowhere near pointing at the Sun. It could vaporise the black coating etc. Regards Andrew

Safety, and to keep out wavelength you can't see reducing heating. It's common to do this on h alpha solar scopes. Regards Andrew

The title did have me worried for a while though. Regards Andrew

If it were me I would use it with a full aperture UV IR cut filter. Regards Andrew

In the old days the fine focus on Schmidt cameras was done with micrometer heads at the mirror. You could try 3 at the base of one at the top with steeper motors for movement. Regards Andrew

I am happy to accept that if you can have two or more telescopes then a small apo refractor for bright wide field observing and a large reflector for dimmer smaller objects is ideal. However, that is not the point I have been trying to counter. I have just been looking at the intrinsic comparison of reflectors and refractors. Say you are looking for your first telescope and you go to the FLO website what might you chose for visual work. 6mm max pupil as per @Alien 13. Sky_watcher for price performance. You might consider: Heritage 150 P 150 mm diameter f/5 750 mm fl £199 Heritage 130P 130 mm diameter f/5 650 mm fl £142 Evostar 80ED 80 mm diameter f/7.5 600 mm fl £379 without mount Evostar 100ED 100 mm diameter f/9 900 mm fl £757 without mount. I would submit that there are eyepieces available to allow the maximum possible field stop for all these in a 2" and that for all of them the magnification can be such that the exit pupil is 6mm or less. The reflectors can be equipped with a coma corrector for the cost of the refractor mounts / field flateners. I conclude that at the two ends of the spectrum the small refractor and large Dobsonian are givens but there is an overlap where things are not so clear cut. On @Stu f/1 Dob it might be worth considering that the ESO VLT 8m mirrors are f1.8 and while it might not do for visual that f/1 Schmidt Cameras were made. Indeed as a teenager I visited the Cambridge astronomy department where the were trying out an all mirror telescope design which is only now being build as the LSST (3.5 degree field). The main mirror was just 200mm in diameter. So extremes are possible for specific use just like the Scopetech 80mm f/12.5 or LSST. Regards Andrew PS In the end I don't think the technology matters that much. Some of the best telescopes are hybrids.

Ok thanks, but that's not what I thought was being proposed. I was being too absolutist thinking what could be done rather than what is commonly is done. Regards Andrew

I am struggling with this. Can you give some examples? Are you thinking visual and or imaging? Regards Andrew

You have to wonder why professional astronomers seek larger and larger telescopes given how unimportant aperture seems to be. Maybe it's because amateur astronomers focus largely on relatively large and relatively bright objects and when they don't they seek (let me speculate) aperture. Regards Andrew

Had a quick look and it seems to be fairly standard FLWR cosmology as applied to our Universe. The data current points to our Universe beging spatially flat so the curved options are not very likely. Regards Andrew

@Tommohawk what do you mean by "light grasp" as 60mm has much less light gathering capability (photons per second) than a 300mm. Regards Andrew Sorry just noticed others had made the same point.

Don't forget the refractor is just that. It will need a mount and tripod. Plus with the eyepiece is at the lower end you need a taller mount/tripod. All in all will it be more portable that the Heritage 150? Regards Andrew

Yes indeed. There are always lots of hidden assumptions in these discussions. Visual v imaging, sky quality, telescope quality and or cost, deep sky or solar system, portable or permanent. Amazing any ever agrees. Regards Andrew

How about the 130? Half the price! Half the weight! 😋 Regards Andrew

Maybe for visual but for imaging you can use much shorter exposures with the larger aperture and more effectively stop the seeing. Getting lucky scales as aperture squared. No need for a desert just excellent collimation. 😉😄 Regards Andrew

No, yes. Regards Andrew

However, you could get a reflector with an aperture that would put its Airy disk and first ring completely inside the Airy disk of a refractor for less money. Regards Andrew

For some applications a mixture is ideal as in planetary Maksutov or at the other extreem a fast astrograph like the Takahashi Epsilons. Regards Andrew

I think you have a choice. Built in flattener and rely on the manufacturer to get it right or separate FF and have to fiddle with it. You pays your money and takes your choice. Regards Andrew

Red will be less distorted by atmospheric variations both absolutely and differentially across the field (same reason the sky is blue) may e that's why it works best? Regards Andrew