ollypenrice

From ODK14 to FSQ106N. Olly

Both systems work. I don't want to get in a fight over this! Just one detail: you don't need guidescope rings. In fact they are a potential menace because they are flexure-prone. All you need to do is bolt the guidescope down hard. It does not need to be precisely aligned with with the imaging scope. In using an OAG with a small refractor you'll be choosing an unusual path but there's no reason for it not to work with a sensitive camera.* Be sure to set it up so that the prism comes in at right angles to the long side of the chip. That way it will get deeper into the light cone without shadowing the image. You can set the prism depth to the deepest possible (in search of more light) in the daytime by shooting flats. (Not flats that you'll use as flats but they'll tell you when the prism is intruding. When it does, just lift it till it doesn't.) Olly * Just one extra thought on this, though. An OAG adds both weight and cable drag to the load carried by the focuser. There are some very bad focusers out there, especially on small refractors where they are quite extended and have short support for the draw tube. The OAG will correct for any deviation this introduces but not for any tilt. Nobody said it was easy! 😁

But what happens in the case of those many telescopes which fail to control the short wavelengths all that well? Won't their performance in delivering a small FWHM be worse than their ability to resolve, say, fine detail in Ha? Olly

That's good. I'm surprised because I didn't find this on the occasion I tried it but maybe that was just a specific case. Olly

How confident are we that FWHM is an accurate indicator of non-stellar resolution? Olly

Yes, that's why I considered the image 'just about OK' at 1:1. Choosing between 1:1 and a downsampled presentation is done subjectively, I'd say. We do occasionally get to FWHM 1.4 on this rig but it varies wildly. Olly

😁 Magic! But the image is now, to my eye, screaming 'empty resolution' where the original was just about OK. Olly

I might have! Olly

The main advantage I was seeing may just have been in final image size rather than in the isolation of new features. Over-sampling does become visually obvious somewhere along the line. The 14 inch data I obtained at about 0.6"PP did not look appealing at full size, ever. On the other hand I regularly post my 0.9"PP images at full size and cropped. Here's an example below at full size and very heavily cropped. I'd rather have it at this screen size than 20% smaller because it's already minute! 🤣 Olly

Difficult in my case because, having decided that the difference was sometimes visible, I took to doing Lum at 0.9 and RGB at 1.1 systematically. (It's a dual rig so this is logical anyway.) I'll try to shoot a comparison shot on a night of good seeing, though. Olly

I like 'agree violently!' 😁 I also like, ' I'm going to argue, by having looked enough at subs, that there is a definite difference in the subs between bin1 and bin2...' If you can see a difference there is a difference! I can sometimes see a difference between 0.9"PP and 1.1"PP on our dual rig, too. Depends on the seeing. Olly

The question is, 'What are the active ingredients in high resolution amateur imaging?' Focal length? Pixel size? Aperture? Seeing? Guiding? We have to put seeing at the top because even quite modest amateur high res setups can offer, on paper, the other four ingredients in a measure which the seeing will always limit. The only way to beat your home seeing is to set up a remote rig in a dedicated location. So what will your seeing support? 0.8 arsecs or 0.9, or whatever? It really isn't likely to be any less. In this case there will be a remarkable number of ways in which to get to that resolution by juxtaposing assorted focal lengths and pixel sizes. The combination I've chosen, small aperture and small pixels, can get very close indeed to what I used to get from a much bigger reflector and bigger pixels, so close that I'm not, personally, chasing more. However, a little more resolution is possible for those who want it. What would really tempt me in a big reflector would be the opportunity to work in bin 2 or even bin 3 while retaining a pixel scale of just under an arcsec per effective pixel. It would be fast. Unfortunately our time with a big reflector was affected by the fact that the camera we had would not bin satisfactorily so we were obliged to over-sample. It was never possible to present an image at full size because it just revealed 'empty resolution.' The price you pay is a drastically reduced FOV in exchange for a very small increase in final resolution. Yer pays yer money... etc. Olly

I think it's time for the imaging snobs to fight back! I'm terrific looking (no really, I just checked) and have a great sense of humour (seriously) and you can't fault me for the fortune I've sunk in imaging gear. I just need a good director and video editor to help me reassert the virtues of intemperate spending. Sponsors, anyone? Roll up, roll up... 😁lly

Payload is not the priority. Accuracy is the priority - and accuracy can be inadequate because the mount is overloaded or because it is simply not able to deliver the tracking accuracy required by the resolution of the system. A mount which will work at low resolution will not necessarily work at high resolution with the same payload. I assume your scope is this one https://www.astroshop.de/fr/telescopes/telescope-orion-optics-uk-n-200-900-ct8-carbon-ota/p,57566 so it has a 900mm focal length. As a rule DSLRs have small pixels (though not all do) but if you use this calculator http://www.12dstring.me.uk/fovcalc.php you'll be able to discover your imaging resolution in arcseconds per pixel. Whatever that resolution is, divide it by two to get an idea of the tracking accuracy you need. If your imaging resolution is 2.0 arcseconds per pixel your mount must deliver an average guiding accuracy of half that, so 1.0 arcsecond. If you are imaging at 1.0 arcsecond per pixel the mount must deliver an accuracy of 0.5 arcseconds. A very good EQ6 with autoguiding, carefully set up, will usually deliver about 0.5 arcseconds. This will support an imaging scale of 1.0 arcseconds. Even then, your local seeing (the stability of the atmosphere, not the clarity of the sky) must play ball. I don't want to bombard you with information overload but there are common errors on the forum about mounts. The main ones are, 1) if the payload is not exceeded the mount will work. No, it must deliver the tracking accuracy the system needs. 2) round stars prove good tracking. No. Equal errors in RA and Dec produce round stars despite bad tracking and lost resolution. Olly

Certainly a better and more ambitious image than my first efforts. Like Knight above, I would look at the black point during processing. I suspect that you've brought it in a tad too far and clipped some of your faintest outlying signal. But, yes, what a great start. Olly

One of my robotic clients wants to run an Avalon Linear Fast Reverse entirely remotely. This is the version which, electronically and electrically, is pure NEQ6. Same motherboard, motors, handset, etc etc. At present he's trying EQ Mod. Plenty of people run this system remotely, as in 'at the bottom of their garden,' but this may involve an initial input at the telescope to start the session, perhaps? Is it actually possible to run the system fully remotely? I'm assuming that doing so would involve retaining a memory of the park position in the software on shut-down and then using a plate solve to refine the pointing at the start of the next evening. I do have a couple of EQ6 mounts and had an Avalon but I never used them remotely so I'm not much help to my client. Any pointers gratefully received. Thanks, Olly

Good on you, Richard. Olly

Any of the proper ones, rear or mid-engined. Not one of those Japanese SUVs with Porsche written on them! 😁 Olly

That's very good. People say Registar is a one trick pony but it's a damned good trick. Olly

Heh heh, I'm not very good at this 3D thinking. Ray's video highlights an important issue very neatly but does it account for a mount pointing at the zenith being in balance with C/W east but not west? Let's say Ray's adjustable weight, CW west, needs to be screwed away from the mount. That's towards the observatory wall, if there is an observatory wall. Now flip it so it's CW east. The adjustable weight is still going to be adjusted towards the observatory wall, so it should still be right. I think the problem is more likely to arise from an increase in cable drag on one side and/or an increase in the amount of cable lifted on one side over the other. We often meet this 3rd axis balancing business when trying to use deliberate imbalance to reduce the effects of backlash. In RA it's easy: you balance the mount east-heavy so the mesh always settles against the drive. You can't just do the same for Dec by being, say, camera end heavy because at the zenith this imbalance reduces to zero when the heavy camera end of the the OTA is directly beneath the light end. 3 axis balancing is not difficult and is vital on dual rigs. As well as the easy adjustment of Dec balance (slide scope forwards-backwards in tube rings) and RA balance (slide CW up-down shaft) you have to set the CW bar horizontal and ensure that the Dec axis will sit still with scope horizontal, vertical or anywhere in between. With the scope(s) vertical this means moving them in horizontal axis. Olly

I think you'd get more interest if you posted good-sized JPEGs of each. Downloading isn't always very fast in some places - like this one!!! Olly

Good stuff. So in terms of imaging choices at higher resolution this trace would support a pixel scale of about twice the error - something like 1.3 arcseconds per pixel. The seeing is still likely to be the limiting factor on most nights. Olly Edit. In all honesty a guide trace of 0.21 arcsecs RMS would be very, very exceptional. My Mesus, which I consider ecemplary, run at a third as much again as that. However, this doesn't mean you're wrong.

Sorry but I'm not up on PHD guide logs so I'm not much use there, and with dual rigs dither is not really possible without inordinate effort so I don't know how it records the trace while dithering. Getting hold of a TEC is a matter of luck. They do come up, though. I was tipped off by a guest about one but couldn't afford it at the time so he bought it himself! I had another chance later and bought mine. The other one on our dual rig was also second hand so they're rare but not impossible. Too big for an HEQ5 though. The flattener is a big chunk of glass and a long way from the centre of gravity. Olly

If you want the best and largest flat field in your approximate budget, with the best controlled stars, buy a used TEC140 with dedicated TEC flattener. You'll also get an FT focuser and the best QC in the business into the bargain. Mine produces tighter stars, especially bright blue ones, than either of the Tak FSQ106 scopes I use here. Indeed much tighter. This is confirmed by a second TEC140 I also use here. Let me be honest: I put the optics last in the imaging priority list. For me it's mount, camera, optics without any doubt whatever. Now you clearly have a supernaturally good HEQ5 if it's pulling an RMS of about 0.2. arcsecs. You cannot bank on that continuing with a heavier scope and and one with a longer moment. Nor can you bank on your outstanding HEQ5 marching on forever, so you might want to leave some budget for a mount upgrade. Be aware that you're leading a charmed life with that mount! 😁 My Mesus run at around 0.3 arcsecs but they've been doing so for years. But what would I buy without pushing your initial parameters? An Esprit 120 from FLO. Olly

Nice. HaOIII? Olly