ollypenrice

The two images show quite different errors. The first one has doubled stellar images, one 'star' larger than the other. This tells us that the mount spends most of its time in one place but sometimes jumps quickly to another, for a shorter period of time, where it produces a smaller displaced image. This is consistent with backlash, the mount spending more time at one side of the backlash in the gears than on the other, and very little time in between. The second image shows the mount spending most of its time in one place but sometimes being driven away from for a short time and returning to the first point. That would certainly be consistent with wind. Olly

Thanks. I don't know Jones 1 so will look it up right away. (There's something marvelous in the sound of 'Jones Emberson One' to my ear. It's the presence of the letters on in each word: they resemble each other while not being identical. (Consonance to the poetry enthusiast. ) Olly

Once again, imaged with Paul Kummer using RASA 8, ASI2600MC Pro and Avalon Linear. This is a small planetary for 400mm of FL and the image is simple one shot colour with no added narrowband. 3 hours. This is a very tight crop. A lovely object which I've never imaged before. Edit: Please scroll down for a six hour version. It's better. Olly

Dob for me. Stable, simple, elegant. Few things in life work as well as this. Olly

It's your Doctors and Nurses game that we really want to hear about... Olly

0.56"PP is flatly impossible to achieve with any mount or guider simply because the seeing won't allow it. The seeing will blur our any detail below a certain value in arcsecs. What that value is depends on your site's seeing but it will not be less than 1" and almost certainly won't be less than 1.5." You mount will support 1.5 or so as well. If I were you I'd forget these long FL scopes and go for something shorter, with as much aperture as possible. If you go for an over-sampled system (long FL) you will starve each pixel of light, as Wim said, and you will also restrict your FOV for absolutely no gain whatever in fine detail resolution. To my mind, the modern camera works with FLs up to a metre or so, after which they are pretty pointless except in places with very exceptional seeing. Our RASA 8 is working at about 1.9"PP and can - just - be out resolved by a TEC140 working at 1.4. Given the RASA has a FL of just 400mm it shows how the long FL is a thing of the past - in my view. Olly

Could you post the whole frame? I'm just wondering about the OAG. Olly

You have to be careful with the phrase 'expanding faster/slower than the speed of light.' The expansion of the universe, outside gravitationally bound systems, must be measured on a cubic unit by cubic unit basis. Small cubic units of universe don't expand by much at all. It is only when you have an enormous number of cubic units, each expanding by a small amount, that you end up with distant objects moving away from each other at huge speeds. Olly

I'm completely relaxed about 'cropping' and never give it a thought. Digital astro-imaging began on tiny chips. Now they're much bigger, which is nice if you want what's captured. If you don't, crop. Of course, there is no hiding place if you are working at full size: you have to have enough data to look clean at 100% but, if you do, all is good. Olly

Agreed. This is a WIP but three hours on Jones Emberson 1 in one shot colour, no filters. Olly

I do my own prints on an Epson 15000 ink tank printer. It's cheap to run, does up to extended A3 and, although it's only a 4 ink system, I'm very happy with the quality. Olly

Have you considered the 'sentry box' design? With this system a sentry-box like shed covers the scope snugly and rolls off fully for use. They are very easy to make since all you need is a plywood floor with a cut-out to let it roll half way past the pier. This is on wheels and rails. Onto it you can bolt a bog standard shed or make your own. I have a 2.2 metre square rolling roof observatory which I'm currently using for visual with an German equatorial 14 inch SCT. I find it 'possible' but too small. Olly

A reducer would help because, as it is, you are still heavily oversampled even when binning 2x2. The fundametal problem is that modern amateur cameras are easily oversampled by more than a metre of FL. or even less than that. Binning and resizing will work, though. Olly

The key thing is to set weight aside for a moment and think in terms of what matters, which is resolution. Inevitably, with modern amateur cameras, you will be imaging at a very high level of resolution in arcseconds per pixel. What camera do you intend to use and do you aim to use a reducer? Run it through this calculator: https://www.12dstring.me.uk/fovcalc.php What you need to know is the resolution of the proposed system in arcseconds per pixel. Once you know that, consider the following: - your autoguided mount must deliver a tracking accuracy of no more than half the final image scale. A very good HEQ5 or HEQ6 can deliver about 0.5" RMS so it will support an image scale of about 1 arcsec per pixel. Your mount might not be as good as that and you might have to accept twice that error, meaning a best image scale of 2"P.P. - then again, the seeing might limit you to a best possible resolution of 1.5"PP anyway (or worse) so that means a tracking accuracy of 0.75 arcsecs is all you need. - in reality, with the Edge HD, you are quite likely to be imaging at a completely unrealistic image scale and will need to bin your data or resize it, which isn't a problem, really. If we are going to think this through properly, we must start with 'What camera?' and 'what image scale does this give you?' Olly

Sorted, I'd say. Olly

I'd pack the RASA 8. The Arp catalogue is all about the faint stuff. I'm beginning to think that, with a RASA 11, I could do every kind of target in the book. A bit more resolution on the small stuff and no great loss of FOV on the wide. But beware of anything I say because I'm on fire with the zeal of the convert! Olly

If you hold an Ha filter up to the light you can certainly see through it and most solar scopes pass Ha only. However, the sun is rather bright! Personally, I've always found visual OIII filters and UHC to give very similar results, though my OIII gives a green tinge which the UHC doesn't. The fact that DSLR cameras pass very little Ha indicates that it is not a major component to the spectrum we perceive. Olly

Great resolution. With more integration the faint stuff will come and come. OPlly

Super! Nice to see you in colour again, Pieter. Olly

Two great targets. I've never done the Headphones but they are on our list. Both images seem well worth pursuing. Olly

Nice! The background looks a bit warm to me, rather on the brown side, but you've managed to flatten it. After DBE I tend to use Curves to attack residual background irregularities. I put a fixing point on the Curve at the value of the brightest background pixels and fix the curve above that with plenty of fixing points. I then lift the bottom end of the curve, beneath these points, to lift them up part way towards the brightest ones. Unlike noise removal, this introduces no pixel-to-pixel communication and looks pretty natural. Olly

When we started using the RASA 8 I did not expect it to be all that good on fine detail in galaxies but did expect it to be a great hoover of the faint stuff. In fact it does both. It doesn't give great star shapes straight from camera but this is not indicative of poor resolution of non-stellar detail. With modern post-processing tools the stars can be made to behave! Olly

I think it's certainly true that there will be no going back from the star removal procedures now available. Processing is transformed. This is by far the biggest advance in any aspect of astrophotography that I've seen in the fifteen years I've been doing it. You can get so much more out of the nebulosity once you are not trying to control the stars at the same time. The data are clearly very good. Olly

The first step in post-processing an asttrophoto is the adjustment of colour balance and the correction of colour and brightness gradients. The first requirement is to get your eye in on what's right and what's wrong with the image's colour. In the stack, the image is very green. In the single sub it's blue. In Photoshop you can also measure the background sky (the darkest parts) by putting the colour sampler tool onto them and reading off the values in red, green and blue. They should be equal. I'm sure you can do this in other graphics programs as well. Olly

You'll enjoy it. It's a great target, pointed out to me by a guest. My ideal choice would be a RASA 11, I think, with the 2600 chip. Olly