ollypenrice

OK, it's the class Dunce again! Why wouldn't Andrew's ray diagram apply to a reducer? I don't understand why a reducer produces a beam different from the one produced by the objective. Olly

You are quite mistaken Mr Wolf. My husband has the prices absolutely right. Mrs Goldman.

I was meaning no purely physical increase but I have now returned to my original belief that there must be an optical increase. Indeed, most intriguing. I'm glad I don't need an LP filter as well! Olly

In reality there will usually be no physical increase in the distance brought about by inserting a filter because the 'increase' is contained with the thickness allowed for the filterwheel. Yes? No?? Arrrgh. Olly

I agree entirely with Andrew S's ray diagram and this is what made me say that I can't understand the subtraction claims. It's exactly the ray diagram I originally had in my head. It's just that when QSI say the reverse I feel outgunned. Now that Don Goldman agrees with the ray diagram I'm delighted. I've emailed my favourite optical engineer and am awaiting a reply. This is a rum situation! Olly

Steve, if I do the ray diagram I can't see how it can be the opposite but both QSI and Optcorp say that it is. When Optcorp specified my extender for the TEC flattener they subtracted I/3 of the filter's glass thickness from the system FL. This is also what QSI say on the link above. I hate doing things by rote without understanding them but, sheep-like, I now follow the subtraction rule without knowing why. I must say that the Optcorp extender has worked perfectly on the TEC flattener with exacting full frame chip, but this doesn't prove that they were right. I think I need to write to Ralf, the font of optical knowledge... No, it applies to chip distance if we are talking about an add-on flattener that moves with the drawtube. It can be entirely ignored in inherently flat field instruments like Petzvals where all it will do is crop a mm off your backfocus. This shouldn't be tight enough to be affected. Olly

I didn't recognize you by your forum name, almcl! Sorry about that. Steve has it with Alnilam, I suspect. I gave the area a quick eyeball on a widefield and decided it didn't line up as a likely candidate but I hadn't allowed for the orientation of your camera. In doing it properly Steve has fingered the suspect's collar, I'd say. Just in terms of good practice you have no flocking in the tube and you also have a couple of bolt intrusions into what might be the lightpath. SInce the tube also has a raised seam I might be inclined to flock it and trim the finder bolts. I've no idea whether this might be a player. I do have a big visual Newt, as you know, but imaging is far more exacting in terms of things having to be right. Best, Olly Edit, I'd maybe blacken the vanes as well. Matt paints using pigments are best since dye based paints can reflect IR, it seems. Barbecue paints use pigments.

I think it is probably a reflection from the vane. You also need to give the vanes some attention, I think. I'm not well up on Newts but how good is your coillimation and is there a twist in the vane? Olly

As has already been suggested, guiding in only the one necessary direction in Dec (experiment to find which that is) is an excellent cure for oscillation. Being slighty misaligned is a positive advantage in this situation, but not enough to give rotation. Olly

David Lukehust uses them, as indeed do Obsession, so that probably says it's a good idea. Olly

All of the aperture contributes to all of the image so you can't locate the planet between the vanes! The only solution (and a very good one) is to use a curved spider along these lines. http://www.rfroyce.com/spider_cv_8/spider.htm WHat happens here is that each segment of the corve produces a diffraction artifact in a different place. Olly

Hehheh, be fair, I've backed these little Newt images from the start. You don't have any choice, they are excellent. They really are. I'm in a slightly different position in that I'm a provider, sometimes running around like a blue-posteriored fly and even with 'plug and play' I sometimes can't get it all working in time, so adding collimation tasks is not on my to do list. But, hats off, I think that bang for imaging buck I doubt that the 130 can be beaten. Olly

While I've been knocked out by Uranium's images for some time, and said so, I've missed this thread. I don't see anything remotely 'entry level' about the best images posted here. If you want to image at this kind of focal length on a medium to small chip then this telescope clearly has a lot going for it. I think it will take on, quite literally, all comers at any price. It is fast enough to be fast but not so fast as to invite exasperating complications that will rob the imager of many good nights. In refractor terms it has a fair bit of aperture. Apart from the coma corrector it is inherently apochromatic - totally so. What do you get with a car-priced Takahashi FSQ that you don't get with this scope? A vast flatfield circle which you only need with a big chip. Freedom from collimation. No diffraction spikes. These are not nothing, but, yikes, they come at a price... Olly

I have one of these as well, and a Pronto. I prefer the Pronto, personally, but it is heavier. However, I don't find the 66 focuser to be capable of carrying much. It was fine with a small CCD and manual filterwheel but would have no hope of holding my present CCD gear. That said, it couldn't cover a large chip so nobody would ask it to do so. It does give a nice visual image and is incredibly competent as a narrowband imaging scope on chips which it can cover. To be honest it isn't far behind a Baby Q in narrowband and with a small chip. Imaging in broadband does show its limitations, though. Stars are far bigger and less controlled than with the premium stuff, but what do you expect? I think it does well. Since this review it might be worth noting that the little TS Quad has, it seems, had its pinched optics cured. I'm not sure that I'd call my ZS66 a keeper but, then again, I've kept it and have no plans to sell it, so I guess maybe it is! I also started imaging with it so it has some sentimental value. I'll put one of my early attempts below. Atik 16HR, 13Nm Ha filter. Olly

Julian, do you know how Shapely calibrated the Cepheid distance, though? This bit seems to be glossed over in most of the histories. Olly

Yes. (By the way, stars are measured in Watts with a lot of zeros begind the first digit!) Do you know the HR diagram? It Googles. Stars can be placed on the diagram using thier spectra to identify them and then an absolute magnitude (true intrinsic brightness) can be read off on the left hand side. When compared with the distance-affected apparent magnitude this yields an approximate distance. Type 1a supernovae are good bright candles. They should all be similar because they go Pop when the accreting star reaches 1.6 solar masses. Olly

Once beyond parallax we often rely on the idea that there is a difference between how bright something really is and how bright it appears to us at the distance it is from us. If we have a 100 watt lightbulb its hundred watts will be radiated out in all directions (ignoring the brass bit that sticks in the holder!) If we are a metre away we can imagine a spherical shell with a 1 metre radius. That 1 metre shell has, in total, 100 watts worth of light at its imaginary surface. If we move to a distance of 2 metres and imagine a spherical shell around the bulb, the surface of that shell is now 4x larger and the 100 watts are now spread 4x thinner over that surface. So the apparent brightness of the bulb goes down as the inverse square of its distance. Now say we are 100 metes away and we have a photometer with a 1 square metre detector and this measures a certain (small) amount of light flux from the new shell. From this we can calculate the total surface area of the shell and so its radius, which is the distance we were looking for. How do we know the true wattage of a star or a galaxy? Partly from measuremnt of known examples, partly from astrophysics and a knowledge of nuclear energy. Certain types of object are considered 'standard candles.' They should give off a pretty standard wattage so how bright they appear gives an idea of how far away they are. An amateur's answer while waiting for the pros. Olly

This is a great thread. Very interesting. Thanks for the detailed account. Olly

I host one at my place, though it isn't mine. It's a pretty good idea. Olly

I've got two EQ sixes and they work remarkably well. I'm not really knocking them but the fact remains that I would rather have spent another hundred quid on the finer details of finish, like having a properly cleaned interior. Also providing proper instructions regarding maintenance etc would be a simple courtesy to their huge customer base. I don't see myself flinching on either of these points. Olly

If only they would put a hundred quid on the price and make them properly. So near and yet so far. Olly

Excellent! Quite recently I posted a Heads Up pointing to folding garages as a solution to semi permanent setups. I came across them simply because I have a nice little car which I'd like to keep for a long time but with no garage. I have plenty of observatories but I thought, 'Observatory' as soon as I saw them. I'm really pleased you've given them a try. I sent my thoughts to an astro supplier, too. I wouldn't be surprized to see an astro-dedicated version of this idea appear at some point. I really reckon that this has a lot to offer. Olly

Well, I don't necessarily agree. If running unguided then, yes, the best possible alignment is best. But if running guided, a slight misalignment allows you to run the autoguide Dec corrections in one direction only and this can remove the problem of Dec oscillation. I have to do this on one of our mounts routinely. As for balance, like many people I like to run just a little heavy on the east to keep the backlash down. In perfect balalnce the payload can float around in the backlash. Frugal, if your stars are sometimes round then the problem is not PA. That would affect every single sub in the same way. It usually shows as a rotation in the corners. Olly http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/22435624_WLMPTM#!i=2266922474&k=Sc3kgzc

Oh, a lot! Olly

Looks good. We see lots of Rapidos in France and, indeed, I saw one for sale recently. We went for a tiny Eriba Puck pop top instead, in the end, but it has a fraction of the space yours has. Olly