ollypenrice

When using an OAG on Yves' 14 inch I made a strap to stop any movement. (It only rocked in one axis.) I use the old Mesus so have a choice of just two guide speeds. I use slow. Could there be a relationship between the optimal guide speed and the pixel scale of the guide system? I don't know the SiTech system and am just thinking aloud. I would certainly run the guiding assistant as recommended above. My guide RMS in arcsecs was unaffected by moving to ST80 guiders. It's usually in the 0.35" area on a stable night, this on two different mounts. Olly

The 'shuttlecock' stars do indicate that the lens is out of collimation, quite badly so I'd say. Olly

I'll tell you what's wrong with that scope! Nothing. 😁lly

I wouldn't add it on top. In Photoshop I would give it a very hard stretch while keeping the background to the same level as this image. It doesn't contain fine detail so don't be afraid to give it heavy NR. Then I'd add it it to green in blend mode lighten and save that as 'OIII to green.' Next add it to blue in a new iteration, also in Blend Mode Lighten, and save as 'OIII to blue.' If you then paste 'OIII to blue' on top of 'OIII to green' you can use the opacity slider to balance the green-blue contribution of the OIII. There is a significant outer OIII shell around the Owl. Olly

Lovely. If you could add some OIII you'd be delighted by it... This is a really tight capture. Well done. Olly

Very sweetly resolved into to core. Big star control is easy in any program offering layers. Olly

I would never advocate an image scale of 0.33"PP or anything like it. 0.33 is crazy, totally unworkable for long exposure imaging, though not for fast frame work. 0.33"PP would require a guide RMS of about 0.16 arcseconds and uncanny seeing. (Guide error mustn't be more than about half the sampling rate.) Our excellent Mesus run an RMS of around 0.3 arcsecs. I'm not convinced that I was getting any more useful detail out of 0.63"PP than I can get out of my present 0.9"PP so I would make 1"PP the minimum sampling rate. But before you buy anything to give you that rate, what is your guide RMS? A good EQ5 or 6 can give about 0.5 arcsecs under guiding so that will support an image scale of 1"PP when the seeing allows. (If you give PHD2 your guide camera pixel size and guide scope focal length it will give your your guide RMS in arcseconds.) Do you know your guide RMS, by chance? With only 80mm of aperture you are also short of optical resolution so a scope with more aperture and more FL will help on this kind of target. However, many of us would be very happy to work at 2.2"PP on more diffuse targets. On many nights the seeing won't support much more than that. I'd say your M101 was a creditable effort for 80mm/2.2"PP. A lot of the nice resolution you'll have seen in other images will come from good post processing, too. Any kind of sharpening needs lots of signal. You may have enough exposure to give a low noise image unsharpened but when you sharpen you will need twice to four times as much. Only sharpen selected areas of strong signal as well. What I would do with that image is adjust the green-magenta axis in the colour balance. It's very magenta so upping the greens ought to help. Olly

Mrs Gomus suggested I try the lens focus ring and the AF switch. I'm not sure which of these did the trick but one of them did. I gave both a bit of physical exercise and we're now back in business. Many thanks for your helpful suggestions. Olly Edit: Further fiddling has shown the problem to be a slightly sticky focus ring on the stock lens. It still won't shoot, occasionally, but a twist of the ring this way and that frees it up and off it goes again.

The F ratio isn't relevant. For a given camera the sampling rate is determined by the focal length. The key unit for resolution is arcseconds per pixel and this is defined by just two variables, the focal length and the pixel size. F ratio doesn't come into it. (With one minor caveat: it is harder to find and maintain critical focus in fast F ratio scopes because the steep light cone reduces the depth of field. This really only matters much with ultra-fast astrographs.) What image scale are you working at when you say you're under sampled? Our widefield images are taken at a very coarse 3.5"PP so we cannot resolve fine details but there is no reason for the images to look soft or for the stars to look 'blocky' at this scale. It's a matter of choosing the right targets but is this 'soft' at 3.5"PP? To be able to present small, highly detailed subjects like galaxies at large screen sizes you need to be approaching 1"PP. However, the danger of getting a 'soft' result greatly increases at this kind of scale because the seeing has to be good enough to support it and so does the guiding. Coarser pixel scales are far more tolerant of poorer seeing and guiding. It would be helpful to see an example of an image with which you're not happy. I suspect that your sampling rate may not be the culprit and would look at focus and guiding. Beware of the 'round stars' test of guiding. It is a flawed test because equal errors on both axes, even quite large ones, will give you round stars while detail is being blurred out all the same. And, regarding F ratio, remember that more aperture means more object photons. (The 'F ratio myth' is a volatile subject!) There is no reason to fear imaging at F9 if the entire object fits on the chip and you have decent aperture.) Olly

I'm charging a spare battery now so as to try that. It does resemble waiting for a countdown, somewhat, but the restoration to default should have dismissed that, no? Olly

My Canon 1000D has stopped working. Boo Hoo! I only use it for daytime casual pics but I miss it. The screen lights up OK and I can scroll through the menus. I've reset camera settings to default in the appropriate part of the menu but, in any mode, it refuses to take a picture. I get a flashing light on the lower right in the viewfinder and some rather random looking numbers counting down on the main screen. (1/60,1/30, etc.) Any suggestions? Thanks, Olly

How would you time the takeover and how long would it take for the guiding to settle? It sounds like a bit of a nightmare to me. Could you not synchronize the captures by having a reasonably long 'down time' between filter changes? You'd have to use the same sub length on both scopes but that wouldn't be the end of the world, would it? Then you could stick with a single OAG. Olly

About half, I'd say, Steve, though our robotic customers are all from other countries. I don't think a falling pound would discourage our UK regulars, though. It's my poor old pension that's the hardest hit! Of course we're fully shut down for the moment and I'll be taking a very cautious view of when to re-open. That may conceivably be after the Govt. give the official all clear. I do admire your transparent presentation of the situation as it affects you and am sure it's appreciated in the community. Olly

Phew!

Probably somewhat target dependent. I think your camera is colour so you won't be a narrowband specialist? It is easier for more basic optics to give a good image through NB filters because the light is almost monochromatic. In colour imaging you'll see the biggest difference with the upgrade. Images including insistent starfields will give an easily perceptible difference. For all that, the ED80 is no slouch and punches above its weight. Then again, in the Apo world, the Esprits punch above their price. Olly

Much better colour correction, particularly in blue. Smaller, tighter stars. Fascinating black hole in your bank account. What astronomer could resist such temptations? Olly

It actually is recommended that you should clean refractor lenses fairly regularly. Pollen can attack the coatings which are, mechanically, very hard. Baader Wonder fluid is an obvious choice of solvent. The 'don't clean too often' warnings apply more to the very soft aluminized surfaces of optical mirrors. Well done on this job. Olly

I know. It is very, very easy for my wife and me to endorse hard social distancing but we like to think we would say the same if we lived at the top of a tower block. Would we? Well, we hope so. Olly

Just at a time when we need national unity you post this!!! 🤣lly

Good to know people are still confident and enthusiastic. Chins up! I'm afraid we are 100% closed but, in the scheme of things, that's a solution, not a problem. Olly

Very nice indeed and done with modest aperture. Olly

Very good. You have a lot to work with there. This is not a particularly colourful part of the sky but you have the blues showing in the star-forming regions of the 'Eyes' pair galaxies. Also some blues in the edge on spirals. Remember that all digital cameras are mono. An 'OSC' camera is a mono camera with filters and that's exactly what you're using here. Olly

Please note the correction to my earlier post. Olly

Yes! It really conjures up the worst kind of gastric disorder, some mortifying internal malfunction occurring in a public place... 🤣lly

Focal length alone is not relevant to the guiding precision you require. It's the combination of focal length and pixel size which determines your image scale, the area of sky landing on each pixel. The unit is arcseconds per pixel, usually written "PP or similarly. For a rule of thumb, high resolution would be around 1"PP, medium res. would be around 2"PP and low res. around 3"PP. There is no official definition but that's about right. At high or very high resolution an OAG is a safer bet, though I use a guidescope to image at 0.9"PP without difficulty. However, I'm using a refractor. If using a reflector the huge advantage of an OAG is that it is guiding on the same light cone as the imaging camera and, if the mirror moves (as they do) this movement will be guided out. Anyone shooting at high res. and with a reflector should surely choose an OAG. With refractors and at medium or low resolution it will be easier to use a guidescope. (I'm not sure how you'd use an OAG with camera lenses at all.) When setting up a guidescope there is no need to use adjustable rings. They are a source of flexure as Michael has pointed out. The idea has arisen that their purpose is to allow the guidescope to be aligned with the main. In truth the reverse is true. They were designed to allow the imager to search off axis for a guide star for early and insensitive guide cameras. Since modern guide cams always find stars (at least in guidescopes and usually in OAGs) you should just bolt them down hard pointing more or less on axis. I use cheap and cheerful Skywatcher ST80s on both of our imaging rigs and have done so for years. I made sure that everything was mechanically tight on the OTA and focuser and, to extend the tube to reach focus, I fitted and epoxy-bonded a de-lensed Barlow into the focuser. There is no need to search for critical focus in a guide scope. The author of PHD guiding says that a slightly soft focus is best. Have fun, Olly Edit: Thanks to almcl for updating me on the centroid calculations performed by PHD2. Apparently the soft focus preference applied only to PHD1. PHD2 should be in sharp focus. (I haven't touched my guidesope focus in literally years but maybe I should do so!!)