vlaiv

If we consider "capability vs budget" sweet spot for APO refractor, then I'd say this one is in pretty sweet spot: https://www.teleskop-express.de/shop/product_info.php/info/p3041_TS-Optics-PHOTOLINE-115-mm-f-7-Triplet-Apo---2-5--RAP-focuser.html add in this flattener / reducer: https://www.teleskop-express.de/shop/product_info.php/info/p11122_Riccardi-0-75x-APO-Reducer-and-Flattener-with-M63x1-Thread.html You'll be hard pressed to find such aperture, color correction and field flatness at that price point.

178mc is good, so is 224mc and 385mc You really can't miss with any of them for planetary. It's just about sensor size if you decide to use them on lunar for example. If you go with 178mc, then you won't need barlow. With 224mc and 385mc you'll need x1.5 barlow to get the max resolution (with C8).

This is very good for first DSO image. I'd say that first thing to do is to check collimation of the scope. Stars are not round and they change shape across the image and my first guess would be that scope is not quite collimated properly. Second thing of course is to plan for flats in the future

Best you can hope to get is just two dots much like regular star in the image. Neptune has about 2.2-2.4" of angular diameter - so even with very large scope - it will be only a few pixels across. Triton is about x20 smaller by diameter (24700km vs 1350km) so it will be less than half a pixel with even large telescope. No way to resolve it. Neptune has magnitude of about 8 while Triton has mag 13.5. Both are well within reach of long exposure astrophotography - ideally you want to expose for tens of seconds and stack multiple such exposures to accumulate at least 10-15 minutes of imaging in order to record both of these.

See if you can get longer exposures as well. That camera has ~8e of read noise. Ideally for NB you want something like 20-30 minutes of exposure if your gear is up for it.

This was with taken with narrowband filters and QHY 9 camera? What sort of exposure length did you use?

Sigma reject is good algorithm that for most part should behave like average. There are two important things to understand with sigma reject: 1. Meaning of sigma If we have normal distribution of data, then 68.27% of all data samples falls in one sigma interval around mean value. 95.45% falls into 2s interval and 99.73% falls into 3s interval. If you for example put 1 sigma as your parameter and have perfect data without any satellite trails or whatever - it will only stack about 70% of your subs. For regular data you want to have sigma between 2 and 3 because you want to stack between 95% and 99% of your subs. 2. For above to work properly - you need to have normalized data. Way you normalize your subs is very important As target moves across the sky - it changes amount of atmosphere lights get thru and hence brightness of the target. If one frame is taken in zenith and another frame is taken when target is at 45° altitude, then second one will be just 70% signal strength compared to first one Transparency changes during the night and so does light pollution (target moves and people turn lights on/off). This thing with light pollution changes background value. This makes data incompatible for sigma reject, and in order to make it compatible - well you need to normalize it. I'm afraid that I never had much faith in DSS frame normalization process - primarily because I don't understand how DSS does it. I know how it should be done - and options present in DSS don't really fit into my understanding of it: In any case - you should fiddle with these settings - probably use Rational instead of linear and use middle for calibration method or something like that. Don't use median methods (like in image above) - use regular average methods (simple Kappa Sigma, and keep number of iterations to say 3, so 3 and 3 is good value for Kappa-Sigma clipping).

Indeed it looks a bit better. Same region as before - but I did apply a bit of noise reduction this time. I think it is mix of both - faint target and some setting in DSS.

Yes, I'd like to rule out any strange setting in DSS that might cause problems (like setting rejection too high so you end up with just one or few stacked subs and similar) - but Veil is really faint and delicate structure. Not much signal there and signal that is there is rather faint - or rather "in strands / filaments" not in bulk so you can clearly display it in image.

If you are concerned with stacking parameters - try setting everything to simple average (no rejection, don't use median - put everything on average) - and see how much improvement there is. In the end - it could be that nebulosity is faint and you need more integration time - but I'd check with above average approach, just to make sure.

Same region as opened in ImageJ without any stretching: Same region in Gimp after light stretch: Btw, data is looking rather noisy if you push it a bit more, how many subs did you stack and what stacking parameters did you use?

Not sure if I understand. Can you post linear data in 32bit FITS format for inspection? Don't apply any curve changes from DSS to it.

What exactly is bothering you about that image? I can see few things that I consider bad in image: 1. Image is over sampled, stars are not pin points, but rather "balls" of light 2. There is black point clipping evident - there is no smooth transition between faint regions and background but rather steep one. Data has been pushed more than it can handle and histogram has been clipped 3. Noise grain is too large - that is just consequence of DSS and the way it aligns subs - it uses bilinear interpolation. If you want to get better looking background noise (finer grain) - use Siril and Lanczos interpolation for frame alignment

Yes, best solution to periodic error is to guide. Alternative that will lessen elongation in RA is to do PEC - periodic error correction. Belt mod usually also lessens the periodic error. Neither of the two eliminate it completely and are worth doing even if you plan on guiding as they help the guider by reducing the amount of corrections it needs to do.

Periodic error.

I'm afraid it's not that simple. UHC is going to boost emission parts of the target and improve SNR there but it will irreversibly loose true color information in stars. In principle, you can recover star color if you have additional information about each star in the image - but that requires special processing. If you want to keep star color and still have boost in emission part of nebulae - it is best to shoot both - stars without filter and nebula with filter and combine data in special way.

No, listed weight means just scope and other bits - no counter weights. CWs are not counted towards total. You can put approximately 15Kg and get decent results from HEQ5 - but you'll need 3 x 5Kg counter weights. For example - 8" F/6 ota from Skywatcher DOB + 60mm guide scope from TS balanced by x2 white and one black 5Kg counter weight :D: Or, in another words, yes Heq5 is capable of carrying 100mm class refractor and 8" guide scope weighing at about 8.5Kg balanced with only 2x5Kg:

Yes, I believe it would work. That is probably cheapest option. SCT reducer would thread onto SC thread of that adapter and then it can simply be inserted in existing Click Lock Baader adapter like regular 2" accessory.

I'm no expert on SCTs, but I think you need something like this: https://agenaastro.com/meade-3-25-2-sct-reducing-adapter.html SC thread comes in two sizes - 3.25" and 2" versions. Your reducer seems to be made for 2" SC thread while scope features 3.25" SC thread on rear port (all Meade and Celestron models 10" or larger have this version at the back apparently). You need adapter like above one to connect focal reducer to read port of the scope - you'll also need to change click lock to different version. https://www.firstlightoptics.com/adapters/baader-click-lock-2-for-celestron-meade-sct.html You now seem to have 3.25" version or this one: https://www.firstlightoptics.com/adapters/baader-planetarium-2-clicklock-adapter-for-large-325-sct-thread.html Or maybe consider getting diagonal with SC thread because there is 105mm working distance for that reducer: https://www.teleskop-express.de/shop/product_info.php/info/p87_TS-SC-star-diagonal---99--reflection---quartz---1-12-lambda.html

I think it will be more than fine. I'm happily using Heq5 for imaging with ~12Kg on it and it performs very well (it is belt modded and tuned mount though).

Even if this was the case - it would not change performance of the mount in any way. You can clamp telescope "sideways" - and it will still work. This is because DEC axis with Heq5 is not absolute axis (nor is it RA for that matter) - and "home" is where you tell it. Take for example this case; Puck and clamp are at 90° to optical axis of the scopes and mount will still be happy with that.

Do OO give mirror surface or wavefront figures?

I'm not sure that you'll read off anything meaningful from that. Is this scope reflector? This should be the most important bit: Which says that wavefront aberration is about 1/13.5th PV wave or 1/66.66th RMS wave Both are exceptionally good results. 1/4th wave is diffraction limited optics, 1/6th is considered good, 1/8th very good and 1/10th excellent. Problem is - that we don't know anything about how these numbers were derived. Is this system performance? What wavelength? Is it just main mirror in case of Newtonian. How was it measured? What wavefront components were removed? I honestly doubt accuracy of this report as is.

https://www.timeanddate.com/sun/serbia/novi-sad (just enter your location)

As far as ISO goes, there is really no "magic" involved - one can calculate the best ISO setting for their situation - it just involves a bit of measurement. ISO setting should be related to exposure length used. When one changes ISO - they also change read noise and read noise should be ideally swamped by another noise source - usually LP noise, but since DSLRs are not cooled - maybe even thermal noise. Lower ISO usually means higher read noise and need for longer exposure, higher ISO usually means lower read noise and shorter exposure are sufficient. Process of measuring read noise and LP/thermal noise in given exposure is a bit involved and one can do it if they wish - other than that, just use ISO in 400-1600 range and there is no need to change it depending on target type - there is no preferred ISO for nebulae or for galaxies and such.