Padraic M

Super pictures! Lovely part of the world by day or night.

I haven't thought much about this, but the normal way to control brightness of a LED or a LED string is using a PWM signal on a MCU. Does anyone know what limitations are there in terms of PWM frequency vs exposure time? For example, it seems obvious that a PWM frequency of 1kHz would limit the minimum exposure to at least 1/1000sec, but is it as simple as that? Does the duty cycle matter, or is frequency the only factor? If PWM isn't suitable, does that leave a series resistor as the only option? (not good for adjustable brightness!)

On this point: I haven't used ASIStudio for stacking so can't say anything about its capabilities. I've used DSS a lot in the past, and currently use Astro Pixel Processor. You can stack multiple sessions with either of these packages, using different sets of calibration frames for each session. With APP, you can even stack different sessions taken with different scopes and cameras! A standard technique that imagers on this forum use, is to revisit a target, possibly even years later, and capture more data. If using the same camera, you can probably reuse your dark (or bias) frames, but you will almost certainly need new flats and dark flats. Each stacking session consists of a set of light frames with matching darks/bias and flats/darkflats. The stacking software will apply the correct calibration frames to the correct lights while stacking. If you are using the same calibration frames for everything, you can just add all of the lights to the same session. As a crude example, take a look at this experiment below. I had a wide-field capture of the Bubble nebula region, taken with a 400mm refractor from last year. This is a mono Hydrogen-alpha 1.5-hour integration. I then set up a Celestron C8 SCT at 2032mm with the same camera, and centred the Bubble nebula and captured an additional 5.5 hours. APP registered and stacked the widefield lights and the long FL lights with no issue. You can see that I didn't apply flats as there is vignetting (and some light pollution) but what you can also see is a huge reduction in noise in the central area because of the extra total integration time. Now with a little crop, rotation and simple curves adjustment in Gimp, I can get a passable Bubble close-up!

+1 for this. Was about to post when I saw bobro had beaten me to it. You don't need to discard your satellite subs unless they're really interfering with the final image. You MAY decide to discard cloudy subs as they are probably not contributing anything to the end image. But depending on your stacking settings, they may be automatically discarded anyway. I will generally use all or at least 95% of my subs unless something disastrous happened during the night like a cable snag or full cloud. Re flats; if I'm imaging on multiple nights with the same rig, one set of flats will do. Dust generally won't redistribute to any great extent. Just make sure that you don't make any non-trivial changes to the imaging train; leave the camera, focuser, filter wheel etc. attached and in the same position. Don't rotate the camera wrt to any of the components. Don't make big changes to the focuser (e.g. racking completely inwards for storage). Refocusing for a different filter or a temperature change is fine as it's likely to be a tiny movement. ideally you shouldn't move the scope before taking flats, but I regularly do that and it usually works fine (e.g. weather doesn't look good and I need to bring the scope inside in a hurry; or I have to go away and don't have time to do flats first; or I take the rig inside then realise the old flats aren't working. I use Nina for capture control, so first thing in the morning after a night of imaging I use the Nina Flats Wizard and a cheap flat panel (an artist's LED tracing panel €10 from ebay wrapped in a t-shirt) to take flats for each filter. Usually done in 5-10 minutes. 30 flats and 30 dark flats for each filter. After the first stacking, you will have created a Masterflat and Masterdarkflat so you can delete or archive the source flats/darkflats. You will be able to tell when you need new flats as you'll see the circles and vignettes appearing. I take it you didn't use flats for your M31 above? When you see those circles it tells you that either you need new flats, or if you have new flats, that your process for capturing flats isn't working.

Nice shot Stuart!

Interesting - that's a distance I haven't tried. It's close to the 100mm above, which looks almost reasonable.

Hi all, I'm having trouble finding the right configuration for my Celestron classic C8 (non-EdgeHD) with the Celestron 0.63x FF/FR and the OVL OAG, and I'd love to get some opinions on what the correct set-up is. Also, if I'm asking too much of a non-EdgeHD SCT then please let me know so I can stop wasting clear skies! It's very difficult to find a definitive answer in Celestron documentation or online, defining the back-focus distance required between the FR and the camera sensor, and from where to measure that distance. The most common answers are either 105mm or 85mm, measured from the male threading on the reducer. No mention of whether it's at the camera end of the male thread (also the back edge of the last glass element) which incidentally is hidden when all connections are in situ, or whether it's from the scope end of the thread. There's 10mm difference between these two planes. I've taken some test images at varying distances as shown below; the distance is measured from the scope end of the reducer male thread as shown in the picture. I'm not happy with any of the results; it's very hard even to pick a favourite, or to match the images with the OVL diagram. I have collimated with Bob's knobs and I believe it's reasonably well adjusted. The components, from scope to camera are: Celestron 0.63x reducer/flattener; WO SCT-M48 adapter; various M48 extensions if needed; OVL OAG (16mm depth); various M42 extensions if needed; ZWO EFW (20mm); filter adjustment .67mm; ZWO ASI1600MM Pro (12.5mm). Also fyi, guide camera is ZWO ASI290MM Mini. I can get good focus on imaging camera and guide camera. Sample images and associated distances: 85mm - 1420mm focal length; f/7.1 100mm - 1409mm focal length; f/7 115mm - 1344mm focal length; f/6.72 128mm – 1224mm focal length; f/6.12 Finally, a helpful image from OPT Corp giving guidance for back focus:

Fully agree with what the guys have already said - flats are an essential part of processing astro images, and aren't hard to do once you understand the process. All of the stacking software packages support applying flat frames. You have a really impressive setup there! But, be really careful with all of that cleaning! You really don't need to clean optics or cameras AT ALL and are much more likely to do damage than to fix the problem. I've never cleaned mine. We all get spots and circles just like those on our images. Flat frames are the solution to dirt, dust and shadows that can come from all sorts of sources, including dust, internal reflections, vignetting, etc.

Well done! But it is an amazing image.

Well done Carole, that's amazing!

Well done again @malc-c. That soldering was quite sloppy.

Now that is sooo much better! You're getting value for your 20 hours exposure time and there's a load of detail visible that was hidden in the first version. However, to me it's just crying out for more contrast, and I think the data has it in it. It's just a little flat to my eyes. I took a look at the TIFF in Gimp and you can see in the histogram, that space to the left is wasted dynamic range. One tiny adjustment to the black point makes a huge difference; just make sure you leave a little space to the left of the curve, otherwise you're losing some of the dark detail. There may be more that you can pull out with a bit more time. There are a bunch of youtube videos explaining levels and curves adjustment, including @carastro's excellent tutorials on how to do this in Photoshop.

To be honest, I'm not the best person to ask as I'm struggling to fix a similar problem myself with a long focal-length SCT. I think I have it sorted if only I could get a clear night to test it out.

This should be an unfair comparison and very hard on your poor 450D! The 2600 is a superb camera. I've seen lots of really good images from it on here in the last few months. That star distortion isn't bad, but could possibly be improved a little alright. You may need to move the sensor very slightly outwards, according to this helpful chart:

Agreed! And the same views from every back garden in this part of the northern hemisphere! It's mind-boggling, if only more people looked up. btw I love your avatar, it looks vaguely familiar....

Welcome Malcolm, enjoy that Tak!

That's a lovely image Carole. I've seen a few close-detail images this week of the Wall and of the interior of the Heart nebula and they're fascinating. Is this a crop or is that the full FOV? Focal length with the reducer is 480mm right?

I use Nina for autofocus, and it works really well. I use a Primalucelab Sesto Senso on a 80mm refractor, and also a Celestron SCT focuser on a C8. The process is the same for both. A couple of points to keep in mind. As Wim said, it works by identifying stars in the imaging loop, and calculates their 'sharpness' (FWHM or HFD). This process won't really work with anything else, although you can buy test stars (small point light sources) that could work. Autofocus routines generally rely on the scope being close to focus to begin with, so you will still need to focus manually get into the rough focus zone. This can be done during the day (preferably, as it's easier to find a treetop than a star!) but I have good success finding a bright star at night (Vega at the moment) with a very-well-aligned finder scope, and getting it focused by eye. I sometimes use Sharpcap to help with this, but can do it in Nina either. Start looping in Sharpcap or Nina, and use the Celestron or ZWO focus manager until you see those out-of-focus star donuts. The closer you get with this initial focus, the better autofocus will work. I know this sounds counter-intuitive, but once autofocus has found its focus point, it can repeat this process automatically until you do something to change the focus configuration like manually changing the focuser, or removing/replacing it. Autofocus may need to be done routinely during the night as you change filters, or if the temperature changes. With experience of your own set-up, you will be able to decide when you need to rerun the autofocus routine. In Nina, you can programme the refocusing into your imaging sequence so everything is done automatically during the night.

I got one of these recently, and it works a lot better than my laptop screen! Easier to use too for lengthy editing sessions. It's full sRGB. I haven't calibrated it but I don't see that as a necessity for me just yet - when my processing skills are better I may need to look at that. Oh and they sent me back €34 too so at under €200 it was very good value.

I just tried it here and it loads two sensors, which is correct. SharpCap 3.2.6480 NINA 1.10 HF3 Default folder is C:\Users\<username>\AppData\Roaming\SharpCap\SensorCharacteristics There are two json files there for my 1600MM - one for 8 bit and one for 16 bit. Exposure calculator can reference the two files: If you haven't done sensor analysis yourself, there are pre-installed sensor files for a variety of cameras in: C:\Program Files (x86)\SharpCap 3.2\SensorLibrary

I have one of those - I tried the motor drive but never figured it out. Whenever I take it out now I just go manual. The mount is very shaky, and there are certain positions where the ra/dec knobs get caught against the setting circles.

Following this thread with interest as I haven't cracked this problem yet. I've just velcroed it to the vixen plate below the scope, where it hangs very precariously. And yes I have the mounting bracket but that doesn't mate with the dovetail rail. Bolting it to the top dovetail bar is a good solution, I've seen others do that. But that's where my guidescope is and there's no room for the PPB without going double-decker, and I'd be a little concerned about balance. I've looked into mounting it in the guidescope shoe - there's a 3d print design on Thingverse for the PPBAdv; you could do similar for the UPB with some small mods. https://www.thingiverse.com/thing:4861744

+1 for what Stuart said - he types faster than I do! It depends on what type of astrophotography you intend to do. Traditionally, Sharpcap is good for planetary, lunar or solar imaging (very bright and sometimes very small objects) which uses very different techniques to Deep Sky imaging (relatively large but very faint objects such as galaxies and nebulas etc.). Sharpcap uses cameras in video mode to capture sequences of short-exposure images of the target object, which can be stacked to give one sharp, detailed image using a selection of the best frames from the video sequence. Detailed pictures of Saturn and Jupiter will generally have been captured using Sharpcap or one of a number of other packages that do similar. There are also other packages to use for post-processing such as Autostakkert, Registax etc. that are specifically designed to process these video image sequences. APT is specifically designed for DSO imaging which takes long-exposure still images of objects that are often so faint that they can't be seen with the naked eye. APT also provides a range of tools that help you plan an imaging session, locate your object (GOTO and plate solving), cool your camera, execute hours-long capture sequences with regular automated refocusing etc., and even park your mount and shut down your equipment automatically when the sequence ends. The differences here are obvious - a Sharpcap planetary imaging session might last 9 minutes comprising 3x3 minute video segments with red, green and blue filters. An APT session could be 6 hours a night for three nights capturing 18 hours of data on a faint nebula through red, green, blue, hydrogen-alpha, Sii, Oiii filters while (hopefully) you are tucked up asleep in bed. All so far so good. However, this all gets complicated because with the latest version of Sharpcap, you can now also programme up lengthy sequences for DSO imaging. I haven't tried any of this, and I don't know of anyone who has, but I'm sure as it starts to get traction in the community, we will start to hear how well Sharpcap does this job. Like Stuart, most DSO imagers will use Sharpcap only for polar alignment, as its PA tool is superb. I sometimes also use it to help with initial focusing of my imaging and guide cameras (autofocus routines normally expect the camera to be very close to focus already). So if you intend to capture planetary, lunar or solar images, then Sharpcap, Firecapture or ASICap would be the tools of choice. For DSO imaging, NINA and APT are very popular choices, and people who also want observatory controls may go for Sequence Generator Pro or MaximDL. BackyardEOS is an easy option for Canon or Nikon DSLR users.

2600 OSC and capture images that you can't get at home.... leave the narrowband for London. Don't forget to look up and take it all in yourself too!

I power both from the Nevada, through a cigarette splitter. I intend to remove the splitter, power the PPB from Nevada, and power everything else from there (as @Sp@ce_d said above). Also would agree that if money is not an issue, why not go for the Ultimate but that's always the case in this game! While I'm very happy with the PPBAdv, there are plenty of features on the Ultimate that are very nice to have - each of the power outputs is individually switchable, and can be set on/off at boot. 6 USB rather than 4. Better NINA support. Your choice!