The Admiral

Provided that the panel is close and the lens is at infinity, I shouldn't think the moire is a result of interference between pixel pitches. You'd be much more likely to see that if the lens was focused on the screen. As such, adding diffusing media won't help. I think it's more likely due to a "collision" between the screen refresh cycle and the moving shutter slit. The way around that would be to ensure that the exposure is sufficiently long as to encompass many refresh cycles. In other words, you'll need to turn the screen brightness down (or display a grey rather than white screen), or lower the ISO, or both. Adding diffusing media would of course also have the effect of reducing screen brightness. I used a laptop screen close up to the scope to do my flats, and I did need to make sure that the exposure time was reasonably long in order to avoid patterning. I'm not sure why the ISO needs to be the same as for the lights. After all, all ISO does is change the gain for the whole sensor output, and I can't see that it would affect the uniformity of response across the sensor. I have seen the view extolled though, and I must admit I prefer to keep settings identical so far as possible, so I'd prefer to try dimming the screen in the first instance. Not exactly practising what one preaches though . Ian Edit. Just been having a quick read (https://www.cloudynights.com/topic/483388-flats-and-iso/) about ISO for flats. First impression is there's more to this than meets the eye (or should that be camera)! As always .

A couple of lovely images there Steve. The modded Canon, filter and Samyang seems to be working out well. I too look forward to seeing some other panels in this region. Ian

I was reading in Astronomy Now about Kepler disovering a new kind of supernova called a FELT, a fast evolving luminous transient. Apparently these transients last several days, but it made me wonder whether any more had been heard about your finding? Interesting thread! Ian

If you are happy pressing the button of a remote release, that's up to you, but an intervalometer of some kind makes life easy. I would not recommend just pressing the camera button though as that is likely to induce shake and give you star trails. Incidentally, you can't guide properly on an Alt-Az mount. Ian

OK, using your image from the post, never a good thing for quality but it can illustrate the point, here is what I get when I 'stretch' the histogram. You will note that there are many more stars, and the two trails are clearly seen. For this example I've added a bit of brightness and then applied a steep tone curve to stretch the histogram, whilst at the same time tried to retain some minimal brightness in the sky. I've had a go at setting the colour balance with the dropper, but it is very dependent on just where you place it. But we have some other issues too. First I think is the problem with light pollution, which is turning the top, and particularly the left, orangey. You most likely also have vignetting, i.e. where the exposure isn't even across the frame, making the centre brighter than the periphery. This is not your fault; it's something we all have to deal with. This is where there is an advantage to specialist astro processing applications in dealing with these situations. Some people use Photoshop with useful astro plug-ins, some of us use StarTools, not a free application but very reasonably priced. There are others around too. Additionally, a closer inspection shows a lot of noise in the background. This is by no means a masterclass , but I hope it illustrates the point. Astro imaging is fraught with difficulties owing to the low brightness of the subjects and our very light polluted skies. But, they are eminently soluble and I'd encourage you to keep at it, and read up on it too. There's a lot of fascinating stuff to learn! Ian

Hi Leonid, So far no one has asked how you processed your image, but that is fairly critical in the production of astro images. First of all, what most folk do is take a series of images and overlay them all in a process called 'stacking'. There are free programs around that you can use for this, such as Deep Sky Stacker (DSS). See http://deepskystacker.free.fr/english/index.html. It's not difficult to use. Following that, the stacked image has its contrast considerably enhanced, something we call 'stretching'. A single image such as yours will also need stretching. In order to get the image looking decently bright, you'll find that all the noise in the image will also be revealed, and it might not look so good. This is a constant battle for astro imagers, and it's the reason why they stack many images together, as in doing so the noise is reduced as the square root of the number of images stacked. I see that you are using Lightroom. To stretch your single image sufficiently I doubt that the 'contrast' slider will give you enough, so probably you will have to resort to using curves and applying a steep transformation (i.e. the 'Tone Curve' on the RH panel). You can also play around with the colour balance to get the background sky neutral, and do a bit (lot!) of noise reduction. The stretching essentially pushes the top end of the histogram all the way to the right; the bottom end is adjusted so that it is just above black clipping.These images are not processed in the same way as conventional images, but much more aggressively. Hope this helps. Ian

Ambitious! I have a sneaking feeling that stacking the stacked batches doesn't gain you the same noise reduction as stacking all at once. Bit early in the morning for proofs . I used to stack a couple of hundred frames with DSS, though with a moderately fast computer, but only 32-bit. If you've got a decent amount of RAM then the new 64-bit version of DSS would be worth a try. Ian

Some years ago a heating engineer was checking out a fault with our boiler, and checked whether the live and neutral had been swapped, as apparently that might have manifested itself as a fault. It was OK, but he related a tale that they had installed all the boilers on a new housing development, and it transpired that the live and neutral to the estate had been swapped! It might be apochryphal, but I like to think it is true. Ian

Similarly, I bought an OEM 32v power supply intended for a range HP printers. I cut off the proprietary plug and replaced it with a 'barrel' plug, assuming the brown wire was positive. It wasn't! Fortunately, no damage was done. But the moral is always to check the polarity before connecting to something expensive. Ian

I second that! Alt-Az imaging still requires a significant integrated exposure time as with other methods of imaging, except you have to take many, many more of short exposure subs. Have a look at the looonnng thread "No EQ Challenge" and get a feel for what others are using. Ian

Thanks for posting, I agree that is brilliant. Takes a bit of 'mouse action' to keep the two in view when well zoomed in, but fun though. Well worth exploring a bit more. The multi-sling shot trajectories are impressive. Ian

I find that the default simple theme (white background) doesn't have it, never has. Ian

Well, I know we share the same sentiments Steve, and your interjection comes as no surprise . But alas I guess you are preaching to the converted in this thread. Ian

You might not say that if you were in the UK living with the incessant poor weather Ian

Pleased to hear it and that you've decided to go for one, I'm sure you won't regret it. I bought mine not for any theoretical gains but purely because I wanted to be able to better image some of the larger DSOs. There's the added advantage of also flattening the field so I get stars reasonably sharp across the whole FoV. Without it, I'd have felt the need for a field flattener anyway. I've always used it for deep sky imaging, even for smaller objects. Ian