vlaiv

As you get above say 10" or so - most telescope come with 3" or larger focusers - that is because of field illumination. SCT is really not very good DSO imaging scope. If you want to compare - compare it with EdgeHD, or maybe RC type scopes.

Could be worth asking @FLO if above outlined data is correct. Would C11 XLT suit your needs?

You probably stacked with DSS and you have slight rotation between first and last frame. This is artifact of bilinear interpolation and the way it impacts SNR depending on ratio of adjacent pixels used. Easiest fix would be to use latest version of Siril and register images using some other interpolation method - like Lanczos 4 in Siril. If you are using other software for stacking than DSS - change interpolation method used for aligning images.

Yes, except maybe avoid use of lower focal ratio in context of speed. It is regularly used that way - but that only holds true if you use fixed resolution - like comparing impact with same camera without introduction of binning. As soon as you introduce resolution in the story - things change. Think of it this way: larger aperture often means larger focal length. Larger focal length means higher resolution with same pixel size. Binning reduces resolution and brings it back to starting one - in the end of this process we have larger aperture at same resolution - which is faster system. It is aperture at resolution that is important bit.

There is some increase in resolution for DSO imaging - but not as much as for planetary imaging. For planetary / lucky type imaging, resolution grows linearly with aperture diameter. For DSO / long exposure things are not quite so straight forward. Aperture combines with seeing and mount performance to produce final FWHM. This is for diffraction limited optics. Once you start adding reducers / flatteners / coma correctors and examine FWHM over larger field - things get even worse, as scopes tend not be diffraction limited in those cases. As far as speed is concerned - that really depends. I would put it like this - larger aperture scope has potential to be part of faster setup. We can define speed of setup by simple metric of "aperture at resolution". Resolution is determined by focal length and pixel size. Speed grows with aperture size, and falls with increase in resolution - 200mm at 2"/px is faster than 100mm at 2"/px, and 100mm at 2"/px is faster than 100mm at 1"/px. If you change both parameters - aperture and resolution - then you have to take their squares in order to compare them - so something like aperture^2 * sampling rate ^2. Comparing 200mm at 1"/px vs 100mm at 2"/px would then give you 200^2 * 1^2 = 40000 versus 100^2 * 2^2 = 40000 So 200mm aperture at 1"/px is as fast as 100mm at 2"/px. There is another very important aspect of speed - that favors big scopes. Big scopes tend to illuminate big sensors - and that is advantage. Say you compare 8" F/8 scope and ASI1600 to 16" F/8 scope and ASI6200. They will produce same FOV, can be binned to the same resolution and at same resolution 16" will clearly win as it has x4 aperture surface. Thing is - you can't illuminate ASI6200 with 8" F/8 RC - at least not natively without flattener. And even with flattener - it is really question of how good corner stars will be at such large sensor.

Hi and welcome to SGL. There is much simpler method for doing that - that does not require binary stars. You start exposure and slew bright start in RA or DEC while exposing. You don't need to expose for long - like 5 seconds is enough. Star will make a trail in your image. Make trail horizontal or vertical (for landscape or portrait orientation of FOV) by rotating camera and checking line again (you might need 2-3 rounds).

Yes, there seems to be somewhat of a gap between lighter mounts supporting ~6Kg payload and ones supporting 12-15Kg (and having slow mo and all - and not costing arm and a leg). I was also looking at ScopeTech zero mount as replacement for Az-4, but don't think it will work well with long tubes like that.

Ok, that is a problem. You really want SkyTee II for such a long scope. I fear that Az5 simply won't be able to cope with size / length of the scope - and Az4 will make it less than comfortable. I have 4" F/10 on Az4 - and I can't wait to replace mount with something better. Here is small 4" shootout on planets this summer. You can see that 4" F/10 is starting to make Az4 a bit small already. Maybe go with Eq5 instead? Refractors work well on EQ type mounts as you can easily rotate diagonal without the need to rotate the whole scope?

Duo/Tri band filters and in general UHC type filters are beneficial on emission type nebulae - like Ha regions, Planetary nebulae, stellar nurseries and so on. They will perform very poorly against galaxies, reflection nebulae, clusters .... You won't benefit from any other type of filter give your sky.

I don't think you can sensibly measure SNR in a single image. Simplest criteria and one that I believe DSS is using is background brightness. In fact - you have that data in file list. If LP is stronger - more unwanted signal will get in the image (higher background value) - and as that signal is removed associated noise remains. If you want very good measure - you would do "linear fit" against reference image in form of A*image + B. A is multiplicative constant that means sky transparency versus reference B is additive constant that means LP levels versus reference image. Higher A and lower B means better image in terms of SNR.

Well, you did say dream setup You can scale that down to fit your budget. I'm looking to replace my mount as well and so far my goal has been Mesu, but there seems to be new mount that is equally good in performance but lighter. Take a look at E.Fric by Gemini Telescope Design. It is replacement for their G53f. 18Kg mount with 30Kg payload. Add to that 10-12" RC and ASI2600 camera - either mono or color, your choice. That is APS-C sized chip.

I think it has more to do with the fact that it would take seriously complex process to make 10-20 dielectric layers on pixel that is couple of microns by couple of microns. You simply can't make effective interference filter on top of such small electron - so you need to settle for absorption filter.

Another explanation can be astronomical refraction. As you track the star - it changes Alt coordinate - gets higher in the sky and its apparent position changes from the true position. https://en.wikipedia.org/wiki/Atmospheric_refraction (see section astronomical refraction) Since you are tracking at an "angle" - if you are not tracking due south - some of motion goes into RA component and some goes into DEC.

While we are talking off topic - here is quick question (some what related to what you have written) - how do you find your CEM70 (and is it stock model without iThis and iThat)? How well does it guide? (you mentioned that you purchased all of that together and I took a look at your equipment list and there it was - cem70 ).

@Staring You seem to be hung up on small pixels thing. Yes, it is very nice to see modern CMOS sensors having 3.7µm or even smaller - down to 2.4µm pixel size, but that is just consequence of marketing - quest for higher megapixel cameras, and hurts more than it helps with Astrophotography. If you want flight portable scope - it's going to be short and small aperture - like 60-90mm range. With these scopes - best working resolutions are around 3-4"/px range. Maybe down to 2"/px - but that would be pushing it (depends on seeing and guiding). 80mm has airy disk of 3.21" in diameter - and that is diffraction limited optics on axis without influence of seeing or guiding. With 400mm of FL - you need 6µm pixel size to get ~3"/px. So that is almost twice the size of small pixels (and sometimes even more - for very small pixels). If you want to work with APS-C sized sensor - and you want your stars to be perfect - maybe look into doing things differently. Use scope at native focal length, get good flattener that will make good stars to the edge of the sensor and bin your data x2 to increase pixel size. For example - 80mm F/6 will have 480mm of FL. With sensor that has 3.76µm pixel size (IMX571) and bin x2 you'll get very good resolution 3.23"/px, and I think that you'll be much happier with corner stars. Remember - if you have 28mm diagonal sensor and you use x0.8 reducer for example - you want that scope to have pin point stars up to 35mm without reducer - just flattener. That is tall order for faster scopes with small aperture. If you want to go higher resolution - at 2"/px or below - then you need to start thinking aperture - at least 5"-6" of it for those resolutions (2"-1.5" - and higher than that at least 8").

That's settled then - never ever going to learn to speak French (not that I was going to anyway, but this way it's official ).

"Saint Mary's Church in a hollow of white hazel near the rapid whirlpool of the church of Saint Tysilio with a red cave"? Or perhaps this: Taumatawhakatangi­hangakoauauotamatea­turipukakapikimaunga­horonukupokaiwhen­uakitanatahu Which would be translated from Maori like: "The summit where Tamatea, the man with the big knees, the climber of mountains, the land-swallower who travelled about, played his nose flute to his loved one" source: https://en.wikipedia.org/wiki/List_of_long_place_names

2" vs 2.5" focuser and simply large margin of TS. I was looking for pier adapter for my Heq5. Altair Astro makes one for £66.63 (VAT & shipping excluded). Same item at TS is sold for 110,84 EUR (again VAT and shipping excluded). £66 is about 80e, so that is 30e margin right there (and they might have some sort of discount when getting the item from AA). Unfortunately for me - AA does not ship items to my country so I'll be forced to order from TS if/when I decide to purchase that adapter.

I've heard that some people dealt with the issue with hacksaw - so that is an option too.

Sony, Bony or Bonny - this is very good deal: It is probably FPL-51, but for visual, I think that price is more than fair.

I actually like the way it sounds pronounced like that.

I've read on several occasions that GPU CC pushes focal point further out so you need to rack out tube more - and it solves issues with protruding focuser tube. You'll also want to mask off mirror clips for perfect stars. https://www.teleskop-express.de/shop/product_info.php/info/p6706_TS-Optics-NEWTON-Coma-Corrector-1-0x-TSGPU-Superflat---4-element---2--connection.html

That is a real thing? Reminds me of wysiwyg

You can always donate those if you don't see much use for them

Indeed - changing profile of any single curve would be to alter spherical aberration at that wavelength. But changing of their position also changes "properties" of their spherical aberration at point of best focus which is tied to green. Imagine that you have single wavelength of light and it has some curve like in the graph. Straight vertical curve is easy - no aberration and there is single point of best focus - one that puts vertical line at horizontal 0. But if line is curved - you need to find place of best focus - where point is smallest at focus plane / most concentrated light. We tend to do that for green light as our eyes are most sensitive to green. If we keep green fixed - and prism changes position of blue and red - it changes shape of their spots - they can get more focused or less focused, or rather their spot diagram changes. I know that this sounds like focus shift - but it's a bit different: Top would be pure focus shift without spherical aberration. There is point of perfect focus and as you move away from it - spot grows linearly in size. But what happens is at bottom image - spot diagram changes and morphs as you move its focus position (and there is no perfect focus point).