Rallemikken

I'm slowly accepting that focal lenght ain't king, done some testing myself lately. The one that started this topic had a HEQ5. Maybe an 8" f/5 or the shorter 8" f/4 (if wind is an issue) would be the better choice. Most bang for the bucks. Don't think a triplet was on the table. Costly. And I wouldn't go under 800mm for a dedicated galaxy rig, regardless. 800-1000mm would suit the slightly older Canon cameras like the 450D, 600D and 5D MkII. I see that 1200mm might be a little long for those.

Well explained. Not easy to grasp, though.... Most other things makes sense, but in this case it's harder to see. I'll do some reading-up and considering taking better care of the photons I capture. Bigger aperture is not on the table, means new mount, not budget for that. Some sort of calculator or guide on this issue would be great. Scope here, camera here, bortle value here, general conditions; good, average or poor. Then an answer, and a few picture samples of what can be expected. Let me play around with sensor and pixel size, find the limitations of my setup. Maybe a dedicated astro camera instead of a new scope? Things to wrap my brain around during summer.

Don't know the maths behind this so well, but I'm aiming at targets smaller than 15 arcminutes. Mostly below 10. When I do that with the 200PDS, it's extremely difficult to pull out much detail in post-procesing. I'd hope a longer scope could help.

I'd like some advice regarding 8" cassegrains vs. Ritchey-Chrétien at same aperture. Nearing seasons end for the third time since I sunk down in this hole, and I'm already planning for next winter. My rig is a HEQ5 and a SW 200PDS, 8" newt. Works fine, have an obsy. Wind no problem. Bortle 4, almost 3. I've decided to stick to my old trustied Canon cameras (five in total). Have found out that these DSLR's are better suited for well defined targets than thin clouds of dust and gas. Anyway, I'd like a new and shiny scope, and I'm considering some more focal lenght for all those tiny galaxies that more or less are out of reach today. My first thougt was the 8" Ritchey-Chrétien. I have an 6" f/4 newt for nebulas and such, and a focal lenght of 1600 would be a natural progression in my current setup (600mm and 1000mm). My question is: Will a 8" cassegrain be useful at all for me? Not world champion in guiding, but not that bad either. I'm aiming at things smaller than Bode's, but don't want to be stuck with a scope to long. Not that interrested in planets and the moon, my new scope will be for DSO's. I've done some attempts with a 2,5X barlow on my 200PDS with mixed results. I assume a native focal lenght will be better, but it will be a trade-off regarding number of frames on any given night. I don't like to expose longer than 2-3 minutes, I've found out that the number of useable frames in the stack is vital. Do anyone have any experience on this usecase? Havn't seen many use their casses for galaxies and other faint, small targets, mostly planetary.

Loosen the clutches and give it a swing. Make the shed big enough for you to walk around the scope, belly first, no mather how it points. And a few inces on that again. When the sh*t hits the fan in the wee hours, maybe a meridian flip gone horrible wrong, you don't want to stumble and fall all over the rig.....

Maybe there will not be a next time. This has happened to me once, during 100+ sessions the last three years. Never found out what was happening, and it scared me, but it never repeated. I run Ekos/INDI, belive that your rig does the same. I was nearby and just turned everything off, and rebooted the system. All OK.

Don't use the images in Stellarium for framing, they are not always sized correct. http://astronomy.tools/calculators/field_of_view/?fov[]=40||37||1|1|0&fov[]=53||37||1|1|0&messier=82 Pure maths. This camera is 5184 pixels wide. With the shortest scope M82 will cover only 570 pixels in width. That is not much room for details. One may argue that the shorter scope is faster, but in this case it will be fast in only gathering black emtyness. If you plan to spend some time on this, you will very fast run out of reasonably big galaxies. They are small. And don't even consider a barlow. Been there, done that. The whole point of the reflectrors is to avoid any glass between the target and the sensor. The long 6" will give good perfomance without any correctors, anyway, with galaxies we always put them in center, don't we??

The Sky-Watcher Explorer 150PDS (750mm) will be short for galaxies. I have a 200 PDS (1000mm) and I would like to have an additional 200-500mm. If you have decided on 6" I'd go for the Sky-Watcher Explorer 150PL with 1200mm focal lenght. Especially if you image with DSLR, as I do. Only a handful of galaxies are bigger than 25 arcminutes, most are smaller than 15. The 150PDS and a Canon 600D is 102 minutes wide. M82, the Cigar Galaxy, is 11 minutes wide. And that's midsize.

You don't say which camera. If it's an old Canon, they have two removeable films or layers in front of the sensor. When we astromod these cameras we remove one or both. The sensor may be undamaged.

Some time ago I bought this - https://shop.4tronix.co.uk/products/secondary-mirror-heater for my SW 200PDS. The provided doublesided tape was fiddly, difficult to use and a generally a mess. I reached for the tubes with epoxy glue and did it properly. Everything all well, untill recently when the weather got really cold. and my stars suddenly looked like fish-hooks. On the positive side; I'v be become an expert in collimation, and I had another scope to play with in the meantime. PS: The element was an execellent piece of hardware, but be aware, it doesn't fit on all secondaries. Not on my StellaLyra dob, which has just donated it's spider and secondary to my imaging scope... Just as well, lession learned. Btw, this spider prevents the user to rotate the mirror freely. Good or bad??

Absolutely. There are many apps and programs geared against astrophotography, each with it's own strenghts and weaknesses. Many of them claimes to take you all the way, from a folder of subs to finished image. That may be so, but the result will improve dramatically if you master a pure image manipilation program for the finishing touches. One example: Gradients. Untill now I've used Siril's 'Background Extraction' with mixed results. The tool has improved, but it steals details and it adds noise, no mather how I tweak and turn. This week I've spent some cloudy nights on old data, and learned to do a super-smooth gradient removal in Gimp. In short, it uses the gradient tool on an overlayed layer. I finetune the effect with the transparency slider, and merge down once it's perfect. In this way I can deal with different gradients one after another, without altering a single pixel, other than the luminence value. I consider Gimp a more mature and pro application than it's competitors, the menus and dialog boxes are designed in such a way that you as a user gets insight in what's going on on the technical (and mathematical) level. Maybe overwhelming for the novice, but be persistent! Gimp is a castle with many hidden rooms; you just have to learn to recognize the frames and handles......

Most likely better, only one way to find out. I shoot with DSLR, but have a few rules I stand by: I operate within a certain range of ISO (gain); 400 - 1600. The fainter target, the higher ISO. The more dominamt stars, the less ISO. When I've decided on a certain ISO I take test exposures. Finally I set on an exposure time where the histogram peak is within one-fourth and one-third from the left egde. Then I start gathering, and continue over several sessions untill I have at least 100. Experience so far has tought me that much of the result lies in the number of frames, and the skill to drop frames before stacking. Cycle trough the subs before stacking, and watch the histogram peak wander back and fourth as you go up and down on the list. On closer inspection you will see that the most details lies in the darkest frames.

Very nice! This is why I'm considering a dedicated astrocamera myself. I'm nearing the end of my third season with a DSLR, and has to admit I've never catched details like this. The span and variations in colors are incredible. And they are genuine; this is shot with a color camera. No 'creative' editing in postprocessing, other than getting the most out of what already is there. The noise (if there was some) is evened out. Image is clean. Maybe I'd put a feathered mask over the most detailed sections, and give them a careful high-pass filter. Makes wonders, without adding noise if done correct. Other than that, perfect!

Naah; it's red! Seriously, on entrylevel equipment, data isn't always like as good as the hotshots on youtube. We'll have to live with it, and make the best out of it. On the way, we usually lear a lot. First, I'd say 300 seconds is a bit to long. The stars float out of shape, and in my experience, the bigger the number of subs, the less noise in the final image (as long as the signal isn't to low). This is processed using two free and open-source apps : The .tif is opened in Siril, and given a manual color corrction and a 'remove green filter', and finally a autostretch-bomb. Then it's opened in Gimp, and processed in this order: 1 - Ian's Noise Reduction; the G'Mic plugin. Play with the options. Gamma all the way to the right. Best to do as early as possible. 2 - A wee furter stretch with levels (the bomb didn't detonate as it should). Take the left arrow all the way. 3 - A careful 'Value Propegate' on the stars, in order to supress them a bit. Select based on color, increase two pixels and feather three. 4 and finally - color adjustment and two rounds of a modest 'High Pass'. My best tip: Reduce exposure time, and gather more subs. And lean a little heavier on Siril and Gimp.

If you are able to flash an image onto a card, my way should be achieveable. And if you can't cope with that, well, no pi or berries for you. You boot the image, answer the questions on startup, let it update (if it's online) and reboot. Now you have the regular Pi desktop, on my try it picked up the wireless at once. You edit two - 2- config files, you do two - 2 - commands in the terminal, and the rest is done in the graphical interface, mainly Synaptic. The default Chromium webrowser refused to start on my Pi, so I installed Firefox instead. For remote access I suggest X2go. Check out https://packages.debian.org/search?keywords=indi&searchon=names&suite=testing&section=all This is the Debian Testing repo as of now. Up untill now imuch of this has been removed when testing goes to stable. That's why we must enable the testing repo. There is also some precompiled AstroPi images: https://downloads.raspberrypi.org/AstroPi/images/AstroPi-2022-11-07/ No idea what this is, size indicates a full install. Debian, Ubuntu? No risk in trying. maybe everything is catered for!

Got it running on a Pi3 B+ in a breeze. Flashed the image, tuned the repo's and installed KStars and a handfull of INDI drivers. No 'dist-upgrade' yet, but a number of files had to be upgraded in order to accept the latest KStars. Seems stable, but slow, as expected. No problems, other than the usual ones. That is, I run Canon DSLR's, and it's a well known secret that you have to remove the memory card in order to get them connected...... My own 'Astroberry', so to speak.

Correct me if I'm wrong, but isn't Raspberry Pi OS (64-bit) an arm64 build of Debian Bullseye? https://downloads.raspberrypi.org/raspios_arm64/images/ Debian testing (Bookworm) has the latest KStars, and almost every INDI-driver compiled for this architecture. On a cloudy night, why not flash a card with the latest raspios, boot it, enable testing in /etc/apt/sources.list. Do an 'apt update' and' apt dist-upgrade', and install KStars and INDI from there? Try it, and give a report! https://packages.debian.org/bookworm/arm64/kstars/download (Not for download, version info only. In Debian you install with 'apt' on command line or 'Synaptic' on the desktop)

You don't say which camera you use. I assume it's a stock DSLR or a dedicated astro color camera. They present the images as is, that means they show you what you would see if your own eyes was super-sensitive. Or as close to that as possible. Trust that color rendition, and use it as a baseline. Make subtle changes in hue and chroma, but dont be tempted to make them anything else than what they are. Use the background as a dipstick when you finetune the colors. Different things gives different color deviations: Light pollution often gives an overall white/yellow tint, while moonshine most often gives a blue tint. Have you astromodded your DSLR camera you will have a red tint. Learn to deal with it in post processing before you start adding filters in your light train. Many of the images you see around are shot in mono, and blended and composed with false colors in post-processing. Some are true to the original colors, and try to get their composed images as near the original colors as possible, while others process their images in a more "artistic" way, to get dramatic effects or conform to a specific palette. I.e. the Hubble palette - almost a standard today, not even close to the real colors.

https://www.indilib.org/forum/index.html As always, it's a good idea to have an alternative. Make a complete KStars/Ekos/INDI install on anoher laptop/RPi4, test if it works there. Maybe you can get things going just by replacing the memorycard with the OS in the Pi with a backup? Trouble with platesolving indicates a config error someplace, while cameras randomly crashing is a sign of bad connections or conflicting USB-ports.