ollypenrice

Care needed, here. You can't just eyeball a guide graph and learn anything. Using an off axis guider in a large reflector our guide graph looked like the Himalayan skyline but the true guide performance was stunning, around 0.3 arcseconds. You say you have an RMS of 0.7 but have you fed your guide camera pixel size and and guidescope focal length into PHD? If you have, then 0.7 is quite good and will support a sampling rate of twice that, so 1.4 arcsecs per pixel. But (this is very important) if you haven't fed that info into PHD then the 0.7 will mean an RMS of 0.7 of a pixel at the autoguider. Given the short FL of most guiders, that will translate into a much larger error than 0.7 of a pixel at the imaging camera. So are you dead sure your RMS is being recorded in arcseconds rather than pixels? Olly

Here are a couple of images scandalously undersampled at 3.5 "PP. https://www.astrobin.com/383965/ https://www.astrobin.com/301531/?nc=&nce= On widefield targets like these you can be undersampled and still get results which I think are nice. On small targets, though, the only way to capture fine detail is to use a finer pixel scale, somewhere around 1.0 "PP. You can go for less but will the seeing not blur out the extra detail? It probably will. I wouldn't get hung up over the difference between 1.8 and 2.7"PP. Nor would I get hung up on the HEQ5/NEQ6 business. There is no evidence that I'm aware of to suggest that one is more accurate than the other. The six just has a bigger payload. Individual examples vary considerably so either could be more or less accurate than the other. Before making the fatal mistake of fixing something that ain't broke, check your guide stats. If PHD knows your guide cam pixel size and guidescope FL it will give you the RMS in arcseconds. The RMS in arcseconds should be no more than half your sampling rate in arcsecs per pixel. So if you are getting an RMS of 1 arcsecond while imaging at 2"PP you are fine. A good HEQ5 can often manage 0.5". Olly

One simple trick is to use a spirit level. Set your counterweight bar to horizontal using a normal one. Then, if using a DSLR, hold it against the bottom of the camera and set that to horizontal as well (or vertical if in portrait mode.) If using a dedicated astro camera you can use double sided tape to stick a mini spirit level to the back of the camera. To find horizontal just take a sub of a few seconds while slewing slowly in RA. The star trails show the present camera angle. Adjust till the trails are perfectly horizontal and then stick on the mini spirit level. That will let you get a repeatable orientation very quickly. This is a minefield! The really important aspect of light grasp is not how much light the scope grasps but how much light each pixel grasps. Unfortunately there is no ready made popular unit to describe this. It is determined by sampling rate in arcseconds of sky per pixel, and also by aperture. Sampling rate is determined by focal length and pixel size. Aperture, of course, is decided by the size of the objective. Depending on the specifics, a move from 80mm to 100mm might increase or decrease the amount of light arriving on each pixel. I think the sanest way to look at telescopes is to start with the focal length because that will decide the framing of your picture. Short FL means wide field, long FL means tight framing of small objects. A move from 80mm to 100mm will, in all probability, bring a small increase in FL. Do you want that? It probably won't be enough to give great results on small galaxies and planetaries but it may be enough to crop a larger object which you don't want to crop! Once you have chosen your focal length, consider the aperture. Provided you don't compare F ratios of different focal lengths, F ratio and aperture are effectively synonymous as they are in the camera lens world. At your chosen FL a fast F ratio is to be preferred. Rather than agonize over the small print of a scope's spec I would look for its results on here, on Astrobin and on other sites to see what you think of them. £1800 would put you within bargaining range for a Takahashi FSQ106N. This is the old, fluorite version of the FSQ which I use myself and generally prefer over the latest one because it holds focus better during cooldown. It has a 530mm FL, can cover a full frame chip and operates at a speedy F5. A bit heavy for the HEQ5 though. I'd also consider a TeleVue TV85 with dedicated flattener-reducer. Very well made and seriously under-rated for AP, so prices are attractive. Check out Frans Kroon who has one of these in his arsenal: http://www.franskroon.nl/ngc2237.htm You will not have any mechanical issues with one of these. Olly

Ah, right, so you have a half-round router tool? I don't have one but that makes sense. Olly

Lovely. How did you make the half-round cutouts on the reverse side of the seat back? Were they holes drilled in a plank which was originally twice as thick and then split? I'm most intrigued! Olly

I agree. I have two, have had them for years, and have spent precisely no time whatever tinkering with them. Olly

I can't believe your mount is so old! I remember talking to you on the phone while you were considering this purchase. It was the first time we spoke. That means that the mount which Yves brought here, and which I subsequently bought from him for my own use, must be significantly older than that. It is still working perfectly, as it always does. Since it was installed it has never been moved, adjusted or anything else. I just use it. It has to be the best astro-purchase I ever made. If it has any rivals they would be a second Mesu I bought second hand, just as good, and my second hand TEC 140. I do have a few other favourites but, in the name of progress, I may be selling some of them so I won't mention them here because I don't want to use this thread for promotional purposes. I really think it is dead simple. The Mesu 200 is a work of genius. Olly

It is hard to know how to do justice to the privilege of sharing your most excellent company on here. All I can say is that I do, and most deeply, appreciate it. And I repeat that, twice at the very least! lly

If you have focus you can shoot flats in the evening twilight. It doesn't have to be perfect focus. A known point on the drawtube would do. Olly

Flats do correct for dust motes but also for vignetting. I think that, if you take a set, you'll be very lucky indeed if they look like a featureless, entirely even surface when stretched. Even the cleanest and most evenly illuminated optics produce flats which are far from flat - which is why we need them. The image below shows a flat to which a flat has been applied. If, when you take a flat, it does not look just like this (and it won't!) you need flats. Olly

Upper right and lower left corners show some strange, hard-edged artifacts. I can only guess but they might be the result of vignetting aggressively over-processed. Did you take flats? I don't think your focus is nailed and I would back off by a very long way on noise reduction. This has the 'vaseline on the lens look,' which NR produces. I'm not pulling any punches but giving you my honest 'quick assessment.' Olly

I use both and wouldn't bother with an OAG on an instrument that didn't need it. Olly

Agreed, but you don't need a 3D printer. These only became essential when somebody invented them. Prior to that there was a sensible solution costing nothing and working every time... I think that Samyang lens knocks out some great stuff. I had a brief adventure with their 85mm... Olly

Have you tried twilight natural sky flats? I would switch the drive off and leave a few seconds between exposures. (I've never done this myself but people do make it work.) Olly

No, as Alan says, a poorly aligned mount will show rotation around the guide star. That's possible, certainly, but I think it more likely to be too much distance from the reducer as per Newbie Alert's second diagram. Olly

Again, that's an F5 refractor, meaning it has a very fast F ratio. The faster the F ratio, the harder it is for the lens to bring all the colours to the same focal plane. The larger the objective, the more this becomes difficult. This is quite a large refractor for F5 so it will never have the kind of colour correction needed for imaging. It describes itself as an achromat, not an apochromat, meaning it has limited colour correction. Even the best apochromats are not perfect so I wouldn't consider an achromat for imaging. The camera is more demanding on colour correction than the eye. Although it's an old design, this one https://www.firstlightoptics.com/pro-series/skywatcher-evostar-80ed-ds-pro-ota.html is widely regarded as hitting the sweet spot between price and performance, visually and with a camera. For imaging you'd need the dedicated field flattener. It does not try to reach an unrealistic F ratio. (I have an F5 refractor but the price new would be about 12x this. Fast photographic optics are extremely expensive.) You do not have much aperture with 80mm for visual observing but, under clear Oz skies, you would get stunning wider views. In a nutshell the visual and photographic requisites are fundamentally contradictory, especially without a big budget. Olly

It was triggered by a Dragonfly control unit since the system is robotic. Basically the motor was fixed and the chain ran from one end of the roof to the other. The same unit now triggers the gate openers. You need magnetic sensors at each end to instruct the motor to stop but this control facility is built into both garage door and driveway gate systems. Trust me only to have a picture taken before the anti-lift was fitted to this one! But I've marked it in red. You can see that the roof sides come down below the level of the rail carriers. We then fit a full length baton along the bottom of the roof sides, on the inside, so that it runs along below the rail carriers. If it tries to lift this baton hits the rail carriers. This means that the anti-lift operates along the full movement of the roof. Olly

It's common for pinched optics to be worse in cold weather when the metal parts of the cell contract. Does this ring any bells for you? Olly

I'll have to see if I can find the original data but it was taken a long time ago. However, David's post above gives a very good impression of the 'look' I disliked in my image and why I gave the stars a slight blur. Olly

I should have mentioned it earlier but do you know the Photoshop plug-in Hasta La Vista Green? It is very similar to Pixinsight's SCNR green and is excellent for precisely the kind of green cast we see in your first image. It's available (voluntary contribution) from Rogelio Bernal Andreo's website Deep Sky Colors. On a very sad note, we might spare a thought for Rogelio who lost his wife, recently, to a sudden cerebral accident. His website is a source of high quality information as well as remarkable images. Olly

I say it because in the image below, Tak Baby Q with reducer and Atik 4000 CCD, I had to blur the stars. The reducer took the system beyond 3.5"PP and the stars were certainly blocky. The image was undersampled and did not meet my house standard, if you like. It depends on other factors, too. You may get some natural blurring from the seeing, small stars may be worse affected than large, and so on. I like to be able to present images at 100% (ie full size) and beyond 3.5"PP I cannot do that to my own satisfaction. This is based on many years of imaging. Larger stars sort themselves out, as you demonstrate. I find that smaller ones don't. Olly

The Clarkvision website, when I last visited it, struck me as being full of nonsense. I would not advise using it. I'm not going to pick a favourite because I think you went in the right direction from the first one but went too far. Most experienced imagers would jump on the green cast left of the Milky Way in the first one. It needs a slight correction but not as far as the second one takes it. Other than that I don't see the images (either of them) as over-processed. Olly

It would be well worth stepping right back from the fine details and camera specifics to understand a small number of underlying concepts. Get these clear in your mind first, then get into the specifics. That's the only way to avoid buying the wrong kit. Long focal length means small field of view and potentially higher resolution of detail. Planets are small, lots of deep sky objects are vast. Fast focal ratio means shorter exposure time but only compare focal ratios when the focal lengths are the same or very similar. Rough guide to pixel sizes: small pixels, 3 micron or less. Large pixels 7 micron or more. They are getting smaller, especially with CMOS cameras. Sampling rate: how much sky area lands on each pixel. More sky per pixel means more light/faster exposure but less resolution of detail. Unit is arcseconds (of sky) per pixel. For deep sky imaging, below about 1 arcsecond per pixel the seeing (atmospheric blurring) will kill finer detail. Above about 3.5"PP stars risk looking blocky and pixelated. High resolution (arising from long focal length and/or small pixels) requires more accurate guiding and more accurate focus and better seeing, so is more difficult. So imaging at 1 arcsec per pixel is much more demanding than imaging at 3.5 arcsecs per pixel. Olly

In your position I'd be more inclined to travel with a smallish refractor than an SCT, especially if bouncing along in the outback! There are lots on the market, from Takahashi downwards. They take more rattling and shaking without going out of collimation and they reach ambient temperature more quickly, which might also be a big deal. Vast, wide open dark skies are also perfect for wide fields of view and these are less demanding on guiding, which might mean more time collecting light and less time tuning the kit each night. Olly

I think it just stops driving for corrections in that direction, but I'm not certain. Backlash is never a good thing but, arguably, it cannot be fully eliminated from a worm and wheel since a few microns of grease will always be needed between the gears. The more persistent problem is eccentricity, meaning the clearance in the mesh will be inconsistent during a cycle. A fairly common solution involves spring-loading the worm side into mesh with the wheel, allowing eccentricity to be compensated for. Without this there will be a tight spot in the cycle which will experience binding before the rest, so the best you can do is get that part to have as little backlash as possible without binding. This will mean there's a potential for backlash at other points in the cycle. So find the tight spot, adjust the mesh there and that's about it. The standard way to minimize the effects of RA backlash is to run the mount east-heavy so that it tends to rest against the driven side. The motor is always pushing against the wheel. In perfect balance it will tend to oscillate across the backlash. (In Dec you can try running the guide corrections in just one direction after trial and error to see which direction should be disabled. Again, this lets the payload settle against one side of mesh.) Olly