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I made another attempt with above tif that you posted. First split channels, then did x2 binning to see if I can recover some SNR, then did some weird background removal algorithm of mine and did basic processing in Gimp - stretch + denoise. This is looking better now - there is a "green" zone in center which might be due to missing flat darks, and strange gradients were mix of LP and issue with framing - bottom right are outer parts of Heart.

That is a good point - XCels have very good price at FLO and one of those would cost me about the same as TS HR eyepiece. They have two focal lengths in my range of interest. I did read sometimes that they had QC issues - like dirt inside, but I guess that is now sorted out. On the other hand I do wonder about sharpness compared to those I listed as potential purchase.

I'm suspecting it might be something with stacking - not 100% sure, but something tells me it could be a problem with stacking. I just checked out values in red channel (nebula is mostly Ha - so red), and background is at 0.042-0.043 while nebulosity is about 0.045 (in 0-1 range). For some reason it is very low in signal and it's just above background noise - this is why it is so difficult to process. That and fairly strange gradients, which might be quite legitimate LP are causing trouble. I suspect that there might be something wrong with stacking because signal is so low and maybe background equalization went wrong or selection of stacking method was wrong ... Maybe I'm wrong with thinking this way

While BSTs are an option in my budget range, Meade offering here costs as much as Vixen SLV so over budget. Since ER is not such an issue for me, I would rather choose ES62 5.5mm over Meade. Going by what I've read, they should at least be equal in performance or ES62 might be even ahead, and in my case getting ES62 would be about $50 cheaper then Meade!

Guess offset of 30 should be ok and even if it did cause trouble - it would be different kind of trouble, so that is fine. Flats are fine too, regardless of method. Try adding flat darks - it should take only a minute to run 50 subs at 5ms or so, and it might help with calibration. If you want, maybe upload all subs somewhere (like google drive or what ever) and I can try calibration and stacking in ImageJ to compare results?

That is actually excellent capture given 90mm of aperture!

Everything seems to be in order with these (you've got a strong flat panel - very short flat exposure, but that is fine, on my setup I also have flats of a few milliseconds). Only thing that I would "change" is maybe getting additional 50 or so flat darks to see if that will help (it might). Same settings as flats, just cover scope (read off exposure length from flat file name and use unity gain settings like you already did for flats). Oh, btw - what was your offset (it is set in ASCOM driver together with gain)?

You mention APP for stacking, but Autosave shows DSS as software used to create it. What sort of stacking did you use? This Autosave.tif when stretched in Gimp can provide image like this: For some reason it feels that something was not done properly in stacking phase, there is too much noise and gradients are very strange - it might be due to improper darks or maybe due to flats calibration - don't know, but like I said, I suspect that something might be optimal in calibration and stacking ...

I did consider SLVs but at that price - it's close to ES 82 line, and you see where that leads ... Unfortunately, second hand EP market here where I am is almost non existent and getting them from abroad puts additional strain on both seller - shipping internationally and also on me as I might have problems with customs (no original invoice so they are free to "judge" value of item themselves which involves quick lookup online and I would probably end up paying import fees calculated based on price of new item). I've also read that they are closer to 45 degrees AFOV then 50 - and that would be a bit too narrow for me as both scopes are manually tracked, probably not an issue if one is using motorized mount. This is quite reassuring, what scope did you use it with?

Due to situation I'm somewhat constrained in astro spending lately. B-day is coming up soon, so that is perfect excuse to get some new astro gear I'm struggling to make a choice between two contenders, and I'll give my "pros" and "cons" so far, but would like help of collective wisdom I want EP around 5mm. Don't need to be very wide field, I'm perfectly happy with about 60 degrees of AFOV. Does not need to be really long eye relief - 12-13mm and upwards is fine. Would like it to be sharp - as sharp as can be for my intended budget, and over much of the field. It's going to be high power eyepiece, so attention to light scatter / ghosting / easy eye positioning and all those nice things is a bonus. Intended scopes will be 8" F/6 dob and F/10 4" achromat. I prefer EP only vs EP + barlow. My contenders are ES 5.5mm 62deg and 5mm TS HR planetary at the moment - so this gives you idea of what sort of budget is allocated for this - sub $100. My main concern with ES offering is that it is probably best in that line and there are no other FLs that would be interesting to me in this line - next is 9mm and that is FL that I would not consider. In fact in the long run I would be interested in range between 3mm and 7mm for high power viewing. This is why TS HR line is interesting - it sort of ticks the right boxes. It is 58 degrees, good ER, scopes are not very demanding in terms of edge performance, it has my range of interest covered with focal lengths (3.2, 4, 5, 6, 7) ... but there is a problem - past experience. Although TS HR line is said to be the best of TMB planetary like EPs I do own one such EP, I believe by SkyWatcher and it is not performing to my liking. It's got a bit of ghosting, there is quite a bit of scatter and sharpness is lower than I would like. I guess I'm spoiled by ES 11mm 82 in terms of sharpness - that is level of sharpness I would like in high power EP. Another option that I might consider, but that one is based on trying something novel rather than going for known things - TS HR zoom 7.2 - 21.5mm that I would pair with GSO x2 barlow nose piece (at approx x1.5) to give me something like 4.8mm-15mm. Problem of course is narrower field of view. Both scopes are ALT-AZ without tracking. What is your take on all of that?

I'm 1m83 but when thinking about 16" dobs - my primary concern is eyepiece height and observing comfort. Eye level is lower than persons height, and sometimes I like to share a view with friends - some of them have smaller height, so my guess is that max EP height should not go over 1.5m for comfortable viewing of most grownups. 16" can be be F/4.5 - 1800mm FL and F/4 - so 1600mm. You need to account for dob base, distance of secondary to focal point (it will be something like 400mm), but I reckon that F/4.5 is proper FL for 16" scope. I don't like the idea of step ladder in the dark for observing near zenith. With F/4.5 you need coma corrector and possibly the best way to go about it is to look for integrated CC - one that is pre adjusted to focal position, so you don't have to fiddle around with spacing for different eyepieces.

LP has no impact on attainable resolution. There are couple of things that impact system's ability to resolve detail, I'll name major three: - seeing conditions (very variable and in general very unpredictable, but you can get a sense for average conditions on your location, as well as "best" - few times a year events) - scope aperture - mount performance (tracking / guiding) There are other aspects as well, but are not easily quantified (like Ha narrow band imaging - lower intrinsic resolution due to longer wavelength but less susceptible to seeing, telescope Strehl in particular wavelength - some scopes like ED doublets are not completely color free so some parts of the spectrum loose resolution because of this, ....) Best way to asses if you need higher resolution is to examine your average FWHM that you get in your subs. You can safely use following formula to assume close to optimum sampling rate for your system / conditions on a given night (I know that is going in "reverse" - finding out optimum resolution after you've done imaging - but it is good for future reference to help you decide if it is feasible to switch to different resolution) - FWHM / 1.6 = sampling rate. Aperture has impact on resolved detail, and some general guidelines about that can be as follows: below 80mm - around 2"/px 80mm - 100mm - somewhere between 1.5"/px and 2"/px 100mm - 150mm - in range of 1.5"/px - 1.2"/px If you want to try to approach 1"/px you will need 200+mm aperture. In reality, for most mounts, most seeing conditions and most amateur scopes you should not go below 1"/px. Having said all of that, if you plan for example to change to CMOS style camera, you can use one with smaller pixels but it requires certain changes in workflow. You will be sampling below 1"/px in some cases, but there are ways to "adjust" your data to particular resolution after the capture - software binning - which is feasible with low read noise cameras like CMOS. Currently you can do integer binning in software, but there is also way to do fractional binning - although not implemented in software that I'm aware of. This would let you "dial in" sampling rate of your subs prior to stacking and processing to be as close match to captured detail as possible. This is "advanced topic" but we can discuss it in detail if you are interested.

IR guiding has advantage over regular guiding in that IR part of the spectrum is less sensitive to atmospheric seeing. That is why I mentioned IR pass filter and IR sensitive camera for OAG. It should provide more "stable" guiding with respect to seeing (less chasing the seeing).

What are you downloading? Maybe complete VisualStudio? VSCode is completely separate product - open source editor. When I start installer download for Windows platform it is only 50Mb. https://code.visualstudio.com/

It "supports binning" pretty much in the way every camera supports binning - it is in fact software binning. Rather hardware bin in CMOS sensors is not true hardware binning it is software binning done in sensor that has some disadvantages over regular binning (reduced "dynamic range"). Pretty much all CMOS sensors don't support true hardware binning because of the way they are built and the way true hardware binning works. But manual is right - if you need to bin for any other reason than faster transfer speeds (that you can get also by using ROI) - do it in software with this camera. On pixel size vs F/ratio - there is well know relationship (although many don't know how to calculate it properly) between pixel size and maximum F/ratio that will produce critical sampling - optimal sampling to get max possible detail that telescope can provide (or rather aperture of that telescope). Larger the pixel size - slower the F/ratio needs to be, regardless of focal length or aperture of telescope on their own - it is combination of the two that counts. ASI178 has 2.4um pixels and optimum F/ratio for sampling image with such pixel size is around F/9 (depending on wavelength, usually green light is given). For Ha this value is F/7.2. If you plan on using slower scope - you need to use larger pixel camera (or do some tricks with binning or sparse sampling). ASI290 has 2.9um pixels and has critical sampling for Ha of ~F/8.7 so it is a good match at F/15.5 if you do sparse sampling for example or binning x2 in software (it's better to do sparse sampling than regular binning due to pixel blur).

Do you think it has any advantage over OAG + regular ASI camera sensitive in IR + IR pass filter, apart from obvious - larger FOV to choose stars from?

This is actually great tool. Many people struggle to combine NB images for example, ending up with very colorful stars. Above program allows one to do the stretch on each wavelength, remove stars, combine nebula and adjust palette and then paste in stars in pure white (or maybe do RGB star color if data is available). It also lets us choose which wavelength stars to add to final image - for example Ha only stars if Ha has the least FWHM - stars will be tight in final image, that increases perception of sharpness.

There is difference, both in optical layout and how they perform. Barlow is negative lens, here is diagram: Powermate is telecentric lens Both work as focal extenders, but there are differences: Barlow: - magnification changes with barlow element to eyepiece distance (or sensor distance - further away greater magnification) - will impact eye relief of eyepieces (increase it) - some eyepieces will vignette with barlow - in some applications it is less suitable than telecentric - like Ha filters for solar observation - usually fewer glass elements (most often 2 elements) Telecentric: - magnification stays relatively the same regardless of the distance (there can be very small shift depending on telecentric design) - will not change eye relief of eyepiece - usually no problem with eyepiece vignetting (where barlow produces problems) - it is more suitable for some applications like Ha filters for solar. This is due to fact that emerging light from telecentric is parallel - look at diagram, so total angles remain the same - important with Ha etalon where exact wavelength depends on angle of incidence of light ray, barlows on the other hand have principal ray at the angle when further of axis, so beam that is spread over principal ray will have one side less angled but other even more angled - and that is bad for Ha etalons - more glass elements (4 I believe is most often)

I can't think of anything radically new - all things were here already in one form or another and most recent items, be that software or hardware are evolution rather than revolution. There might be something new, that is in principle again evolution of existing items, but made me think of the use for it that could be labeled as new (at least I did not find any reference to the idea so far): Multiband narrow band filters, like tri and quad NB filters. In principle it is evolution of NB filters and UHC filters to combine properties of both - UHC giving idea of multiple lines and NB giving idea of narrow band pass - so it is in fact evolution of filter, but novel idea is to use it as L layer for NB in the same way we use L in LRGB. It has couple of advantages - for example capture of Hb - improving Ha/Hb signal strength (in comparison to pure Ha) - better SNR. Capturing all bands at the same time - improves SNR again even if lines are completely spatially separated in the image. Pretty much advantage that LRGB has over RGB with added Hb component in quad band example. It has also use as extreme UHC nebular filter for both mono and OSC capture, but to me above application is probably the best use of such filter (and a novel idea as far as I can tell).

I would say that there is a bit of connection between that image and usage of binning in astrophotograpy. One way binning is used on CCD sensors is to capture R, G and B information at lower resolution, for similar reason as is presented on above image - brain is more sensitive to variations in brightness than it is in color. This image shows more than just that, it shows that brain sees "in context" - in the same way it "reads" in context - Fqr exgmole, yiu shgud be abqe to rkad thws sedtjnce, although it is total rubbish - Brain sees start and end of every word and its length and based on context is able to reconstruct what's it is saying. In similar way in above B&W image with superimposed grid - grid is providing hint of color, and our brain just fills in the blanks (but it relies heavily on context - we know what sort of color ones skin should be and possible clothes colors and such). On the other hand, binning in AP has also different usage, and I don't think above image could be used to explain that.

Brilliant! Please do include as much info as you can on mount mechanics / behavior.

I guessed it was something like that - that is why I asked about drizzling. You say you feel it is better when you drizzle, can you tell me why? I'm interested because you should have better SNR without drizzle and there is nothing to be gained from drizzling (no detail) - according to theory.

I'm just wondering, since drizzle can lower SNR. With ASI1600 and Esprit 100 you will be sampling at 1.43"/px, and that is sort of optimum resolution for ~ 2.3" FWHM stars. What is your average FWHM in subs, have you measured it?

Just a quick question, why did you drizzle M16?

This makes sense. I don't know exact numbers, but we could do some math to arrive to approximate figure. For 150P and F/5 scope, FL is 750mm. Focal point of such scope will be about 150mm away from outside tube walls - sw has about 60mm high focuser, it needs to be racked out a bit to reach focus and there is at least 50mm 2" to 1.25" adapter. There is additional 75mm distance between secondary and tube wall, so total distance between mirrors is about 525mm. Beginning of the tube to optical axis of focuser I would say is about 120mm, main mirror is about 15mm thick and there is another 20mm of main mirror cell and back of the tube. If we add all these together - 120+525+15+20 = 680. That agrees with said 673mm very well. Similar calculation can be done with 150PL and I think we will get close to it's quoted length of 1156mm. It's got 1.25" focuser so focus position will be closer, and distance to the top of the tube probably a bit less.