ollypenrice

I hear you, but I bought two second hand mounts which both turned out to be the most reliable items I ever bought. They were Mesus, however. Olly

I don't think it's for any of us to say what the advice ought to be. What we should do is state our own view and give reasons. That's how forums work. Looking back, my own advice has sometimes been mainstream, as in start with the mount - sometimes middle of the road, as in putting camera before optics - and sometimes minority, as in start with mono and filters, autoguide from the start and don't feel obliged to start with a DSLR. I also try not to post outside my competence. 'I'm not a planetary imager, but...' I certainly hope I've never said that and, if I have, I apologize now! Olly

OK but, even if this is entirely correct, what does it say, in your view, about the HEQ5 being the minimum mount? Olly

It's not intended to be bleak but to point out the nature of the problem. The (nice) photo above is of the brightest deep sky object in the sky, the Trapezium region of Orion. It's the only DS object I've ever imaged which required a maximum exposure time of around ten seconds. Its nearest rival is the large blob in the middle of M31, which isn't worth imaging anyway! Olly

But that is, consistently, the advice usually given. It's certainly what I always recommend along with a priority order of mount-camera-optics. I won't budge on putting the mount first. It's also cheaper to image at a coarse pixel scale than a fine one, so it might be more accurate to say, 'Avoid spending your money by choosing a short focal length.' For once cheaper is better because it would be silly to start imaging at the hard end of the focal length scale. Why won't I budge on the mount coming first? Partly because the 'round stars test' is oft-repeated but wrong. It tells you only that your tracking errors are about equal in RA and Dec yet it tells you nothing whatever about how large they are. It doesn't matter what your camera and lens are: if they're moving relative to your target the image will be blurred. 3.5 arcsecs per pixel meets your low res imaging requirement. The periodic error of an unguided HEQ5 could easily be 10x that. We must come back to the simple rule that guide RMS in arcseconds must be half or less of that of the imaging scale. Olly

Work out your image scale in arcseconds per pixel. Record your guide RMS in arcseconds. If your guide RMS is less than half your image scale you do not need a different mount. That's about it if you want a rule of thumb. Olly

Remote data come in two flavours, either from your own gear controlled remotely at a dark site or from time bought on a remote observatory. In this discussion I think only the latter is relevant. Setting up your own gear remotely is more expensive than keeping it at home because you have the cost of the installation and the rental to add on and you also need better equipment. The last time I looked, time bought from commercial observatories was very expensive indeed. I remember calculating that renting time on a 14 inch scope/premium mount/premium CCD with filters would equal the cost of buying that equipment after about five photos. Yes, we weren't messing about with the photos we were taking, most having between 10 and 20 hours' exposure, but I don't think renting scope time is any kind of budget solution unless the situation has changed. Back on the 'HEQ5 as minimum,' question, I've just looked at the first twenty images on the deep sky imaging board. The HEQ5 would have been the minimum mount for every single one of those images. Olly

Because I do this for a living I have a premium Mesu 200 mount but what would I lose if, with a small refractor and camera imaging at 2.5 arcsecs per pixel, I went for an HEQ5 instead? I can answer that. Nothing. The HEQ5 is an élite mount at a budget price. Respect, say I. Olly

This forum has a deep sky imaging section (among others.) If the kind of deep sky imaging the beginner is asking about is based on what they generally see on that part of the forum, then an HEQ5 is the minimum if they want a high probablity of success and an enjoyable time not fighting their mount. With a modest scope and slightly less modest camera you can become a player in high grade deep sky imaging. In this context, in this context, the advice that an HEQ5 is the minimum is perfectly sound. If this is not the context then other advice comes into play and the HEQ5 is certainly not the minimum mount. There are other kinds of astrophotography for which an HEQ5 is not needed or even well adapted. There is no point in arguing about the mount before we have a coherent agreement as to what is meant by deep sky imaging. Olly

Not sure about this. Some objects won't show at all in anything but one NB filter. I don't find that it's easier to make out objects in my 7nm Ha than my 3nm. Nor is the broader bandpass faster. Rather the opposite, in fact. Personally I'm wary of iOptron. We had a new one arrive here recently, dead on arrival with a circuit board fault. No new boards available. Later, one was supplied but the wrong one. The right one was still not available. The owner went for a full refund. My feeling is that they knock out too many new products, using the customers as beta testers. Compare this with the long production runs and minor improvements in the Skywatcher business model. What will the iOptron spares situation be in five years? This is just my personal feeling and I'm sure there are plenty of happy iOptron customers. Olly

I remember that, Ron. They were overhead today, in fact. We had a squadron of them last year after a wolf-kill of some sheep... I now have a better telephoto so will try harder! Olly

It might be worth checking your source for this particular Ishihara test. I've just done a 12-sample Ishihara test online and, as usual, saw every figure. I'm certainly not colour blind but, in this, I can't see a letter or number so I think it tests for something else. There are control tests with nothing in them and also tests in which only a colour blind person will distinguish a figure. A good while ago I took UCLAN's Introduction to Astronomy distance learning course. One of the tasks was to rank ten naked eye stars from red to blue. I was surprised to find I got the order right (ie in accordance with spectral class) apart from inverting one adjacent pair near the middle. This makes me think that your vision may have a limitation but, to be sure, I'd go to a dark site with a few other people who know the sky well enough to be sure you were all talking about the same star! Very big apertures are not the best for star colour in my experience. A reflector is the most reliable on colour and being out of focus slightly helps to spread the colour and diminish the brightness. Olly Edit: Sorry, I missed the later posts and the test problem has already been resolved.

Good stuff. Wigan, land of my birth, triumphs again! 🤣 Do you have a built-in, failsafe, anti-lift system? You need one. In fact you need two because one isn't enough! Looking at your early photo of the outside it looks as if you could have something coming down from the sides of the roof and extending beneath the rail carriers. The is what I've done on a number of our sheds. In the picture below you can see the unfinished anti-lift system: the roof sides extend below the level of the rail carriers and are awaiting a baton running horizontally along the bottom of the roof sides under the wooden rail carriers. Once in place it is impossible to lift off the roof. SGL has seen flying roofs on several occasions. Do not join this club!!! Olly

You need to be clear on what your objectives are or you risk landing yourself in an accidental downgrade. I take it your scope is the 102 F7, meaning it has a focal length of 714mm. This is giving you a resolution of 1.08 arcseconds per pixel with your camera. It's a near-certainty that this will be over-sampled already. Your guide RMS would need to be no worse than half the 1.08 value, which is possible with a good EQ6 but it's probably right on the upper limit. Your sky would also have to have exceptionally good seeing to deliver real resolution at this scale. What this means is that increasing your focal length would give you no more real detail but would reduce your field of view. That could only be described as a downgrade. Why do it? By going up to 5" you could, in principle, go for a larger scope with a similar focal length to the present one, meaning you'd be upgrading your aperture to put more light onto each pixel. That would be fine if you could find such a telescope, but can you? And at £1000? It's an unfortunate optical fact that colour correction becomes more difficult (read more expensive) as aperture increases, which is why even the best larger refractors have fairly slow F ratios. My TEC140 is, like your 102, F7 and it didn't cost £1000, alas. You already have a high resolution setup with an image scale suitable for galaxies. It's very similar to the scale at which I image galaxies. What you might find more productive in terms of giving you more choice would be a short focal length setup such as a small refractor or the remarkable Samyang 135 lens. Olly

I've never used Curves in PI, Rodd. In Ps you can just place the cursor on a part of the image, Alt Click and that brightness point appears on the curve and will pin it if not touched. (Or you can raise or lower it, as you wish.) Olly

Where in France are you? I'm in the South East (05) with an excellent sky. There are lots of amateur and professional observatories around here. Welcome to this excellent forum. Olly

I'll second that! Olly

Yes, you describe the problem very precisely here. Whether or not the technique could help in your case I don't know, but one way I like to reduce noise in the background sky is to do so using Curves. The idea is to lift the darkest background pixels to values very similar (but not identical to) those of the brightest background pixels. So I just pin the curve at and above the brightest pixels and lift it below that point. This compresses the range of background brightnesses, reducing noise but, critically, doing so without any of the pixel to pixel communication which causes the oily, noise-reduced look. I'd be inclined to try this shortly before the final, hard stretch so this stretch could be done with a less varied background sky. Once I have the background sky at the level I want and with the look I want, I now do the reverse of what I did in Curves earlier: pin at and below the background level and stretch only above it. This is great for dragging up the faintest nebulosity from out of the background. Olly

I wouldn't hesitate to crop it, Rodd, and bring it in closer as you did later. It holds up really well. I do wonder if it's not a tiny bit black clipped? The sky is dark and smooth and the faint nebulosity looks slightly clipped on the upper side of the galaxy but this is only based on what we're seeing here. The coloour is gorgeous, deep, rich and varied from blue to red. Olly

Watch your black point. You have discarded a huge amount of your data. If we look at your histogram we see the peak, containing all the nebulosity, crammed up against the left hand side. Much of that nebulosity would have been to the left of what is no longer there. There should always be a small amount of flat line to the left of the histogram peak, like this: There is a big temptation to move the black point slider (bottom left) to the right in order to get rid of gradients. Never, ever, do that. Fix gradients using a gradient tool like DBE in Pixinsight or Gradient Xterminator or equivalents in AstroArt, APP, etc etc. You need to preserve that little flat line to the left of the peak or you are 'black clipping' your image and when the data are gone, they're gone. Olly

It would make a great print and we hope to have the technology by today or tomorrow... Olly

Damn, that's good! Transition from beach to sky is divine. Olly

It can, yes, but beware of the 'round stars' test which gets more publicity than it deserves. Round stars don't tell you that your tracking is good, they tell that it might be good or might just be equally bad in both RA and Dec. I think you'll be surprised what that Samyang lens can do on an accurate mount. The other thing to spend a lot of time on is focus. What you really need with that lens is a fine focus device. Telescope Service make them or you can make your own, as I did for a manual ultra-fine focus on a Tak 106. Telescope Service: Home made tangent arm gadget: It's the same principle in both cases: a bolt pushes an arm attached to the moving part of the lens or focuser. Olly

Exposure depends on your light source but, if the histogram peaks about half way, the flats ought to work. What makes you doubt them? Olly

Although this may be counter intuitive, an imaging rig must be built from the mount up. Once you have a sufficiently accurate and stable mount, autoguided, you have a platform which can take deep sky photos. I would advise you to forget working unguided, it is not the way forward. If you got a guided HEQ5 going you could really see what your Samyang 135 can do. It is a superb lens. At some point you could consider a telescope as well. The humble 130PDS gives great results provided you sort out the collimation. If this worries you, a refractor is easier. Reality check: galaxies, apart from M31, M33, M101 and the tricky IC342, are small targets needing longer focal lengths, meaning a bigger scope and, probably, an EQ6 rather than an EQ5. However, there are galaxy groups which look good in shorter focal lengths. Olly