vlaiv

No wonder they feel the need for security lights - someone is constantly taking pictures of their house

I think that this chart holds for Fraunhofer doublet with F2/BK7 glass combination. There are scopes out there that are marketed as achromatic refractors - yet employ different glass types, for example this scope: https://www.teleskop-express.de/shop/product_info.php/info/p2229_TS-Optics-6--f-5-9-Refractor---2-5--R-P-Focuser---Ohara--Japan--Objective.html It uses K9 and F4 glasses (according to TS) and has better CA correction than "standard" 6" F/8 achromat (to quote TS: " The Ohara objective has a better color correcture than a standard 150mm f8 achromatic refractor"). I've read reports of that telescope being rather good performer for fast achromat. There has also been one instance where someone measured 127mm ES scope and concluded that objective is stopped down - which helps with level of SA and CA (not saying that above 152 is stopped - but that is something that should be checked).

Use higher power EP and center planet in the field of view. Longer FL eyepieces and wide field eyepieces have large field stop - larger than sensor and you can easily miss sensor if you don't get centering exact. Use short FL ortho to center the planet - that will be much better match to sensor size. Another trick that you can use - is to defocus planet. When you start defocusing planet - it gets bigger and at some point it will start appearing on chip - then center it and refocus again.

There could be several things happening that would explain this. First off - not all of us are equally sensitive in violet part of spectrum. We don't notice it as much as other types of color blindness - but it can be there. Second - not all of us are equally bothered by sight of purple. Similar to pain, discomfort threshold - there are different thresholds when people start saying it is annoying. Some get annoyed at slight hint of CA - others can tolerate quite a bit. Third - give just 152mm and F/6.5 stats - there is really no way of knowing how good/bad CA will be. We don't know design of the lens nor type of glass used. We don't know how good spherochromatism was controlled.

Is that refractor? If you have that - then use it instead of ST80. 130p / 130pds are basic newtonian scopes - with parabolic mirror (thus suffer coma, and spherical mirror at that speed would be very poor performer). Avoid any Bird Jones designs - you'll recognize those by short tube and very long focal length - while focuser / eyepiece is on the side of the tube - like this: that scope has 1440mm of FL - no way 1.4m of FL can fit inside such short tube (and it is not Mak or SCT or other variant of Cassegrain - these have eyepiece at the back of the tube). If you have above 102 F/6.5 and you can get CG-4 with motors - use that combination. You'll need wratten #8 to use with achromat scope to tame chromatic aberration and you'll need to stop down aperture a bit - make it F/8 scope so use say 80mm aperture mask. In similar combination, I was able to get rather decent images - like this one: That was done with 4" F/5 refractor (bigger brother of ST80) - but with very light weight camera with small sensor (planetary / guider cam) and stopped down to 66mm and with use of wratten #8 filter. It was on Heq5 mount without guiding. Can't remember exposure time.

In that case look for DC/DC converter. Something like this: https://www.hycopower.com/product/12V-to-72V.html for example or similar - just make sure it can output at least 0.5A

That scope can be used as very good planetary and lunar scope - but "in a second role" - not as it's primary role. Primary role would be DSO and wide field. Since it is F/6.5 - it has FL of 988mm. It can be easily turned into 120mm F/7.5 achromat (equivalent to SW evostar 120/1000) or 100mm F/10 (equivalent to SW evostar 102mm F/10) with simple aperture mask. It can even be "apochromatic" 3" - with 76mm aperture mask, it will be F/13 scope. Yes that is 3" F/13 - color index of 4.33 - that is color free for most intents and purposes. Drawback of course is that it needs Heq5/Eq6 class mount to hold it steady as it is very heavy scope (probably 11-12kg with accessories and possibly even more).

All that was on F/4 or F/5 scope (and is there any difference?)

Hi and welcome to SGL. $400 for AP setup? That is not going to happen. Even simple star tracker is going to decimate your budget quite quickly: https://www.ioptron.com/product-p/3322.htm In fact - if you can, do that - get star tracker, kit lens, and that DSLR that you have and start doing AP with that kit. (Just keep in mind that above star tracker does not include tripod). If you have any DIY skills - save money for later and start with simple barn door tracker: https://nightskypix.com/how-to-build-a-barn-door-tracker/ (although - do google search, you'll find many different designs). If you have access to 3d printer - maybe you can print your EQ mount. That will save you quite a bit of budget. Rest of the budget is best spent on good lens. https://www.instructables.com/Equatorial-Mount-for-DSLR/ https://www.thingiverse.com/thing:3327081 Any scope that you might want to use for AP is going to cost at least as whole budget you have now. Scopes like ST80 - are going to be awful to do AP with - for many reasons. They have strong chromatic aberration as well as often strong spherical aberration. They have field curvature and their focuser will have trouble holding DSLR straight so you'll have tilt as well. As far as scopes go - you want either something like SkyWatcher 130PDS with coma corrector or small ED doublet with field flattener - either way, it will eat up $400 or a bit more. If you want to try with ST80 - at least consider upgrading focuser to something better - like GSO crayford for refractors. And we did not even touch the most important bit - the mount. Mount should really consume most of your budget as it is most important part of AP setup. Astrophotography is expensive.

Read this review: https://www.scopereviews.com/page1y.html

Moon plays a part but also sky conditions. LP levels fluctuate during the night as people turn lights on/off and traffic changes (car headlights). Local haze / fog even very small will amplify glow from surrounding lights as light is scattered by water molecules. Visibility of targets will also be impacted by high altitude transparency. Dust, fire, pollution - all contribute to decline of transparency. If you want fairly accurate assessment of current LP levels - get SQM - sky quality meter: http://www.unihedron.com/projects/darksky/ If you have iPhone - look up app that should do the same https://apps.apple.com/us/app/dark-sky-meter/id602989060 As for high level transparency forecast, I use Copernicus service: https://atmosphere.copernicus.eu/charts/cams/aerosol-forecasts?facets=undefined&time=2021102100,3,2021102103&projection=classical_global&layer_name=composition_aod550 Zoom in on area of interest, set wanted time and look what level of transparency is expected. Up to 0.3 is ok - other is going to start to impact things severely. For overview of how these two fit together (atmospheric extinction and AOD) - see this article: https://skyandtelescope.org/astronomy-resources/transparency-and-atmospheric-extinction/

You don't look at histogram nor ADU value for that. You simply repeat whatever settings you used for Flats - just with your scope covered. Say you needed 1.2s exposure for your flats. You cover the scope and using same settings - gain, offset, temperature and exposure length of 1.2s - you take your flat darks. When doing flats - use assistant to tell you exposure length needed (although you really don't need assistant to do that - take flat exposure - if too bright, dial it down, if to faint - prolong it until you get it right) and remember that exposure. Take all your flats at the same exposure time and take your flat darks at the same exposure length. Btw, APT flat assistant has been known to mess up flats, so I recommend taking them manually. ADU of 30000 and histogram are just guidelines. You want your histogram not to be clipped - no over exposed bits and you want your flats to be strong in signal not weak. You want histogram peaks to be to the right - but not as far right so that it clips in highlights - there should be room to the right. This is if you set histogram to whole range 0-65535.

Dark flats are to flats the same as darks are to lights. Flat exposures although short tend to also accumulate some of dark current and bias signal (especially narrow band flats which tend to be longer than broadband and give more time for dark current to accumulate). You want to remove these and for that reason you want to take dark flats. They are taken at exact same settings as flats - but with scope cover on. For proper calibration of your subs - you need just darks, flats and flat darks. You don't need bias, and actually in this simple sort of calibration - bias is redundant. Bias is useful when you want to do dark scaling (ok for CCD - not as much for CMOS) or you want to do approximate calibration and you substitute say flat darks with bias because flats have short exposure.

You should probably recompose image - moons without derotation (just RGB align) and Jupiter with channels derotated.

Do look into that, but I always prefer to bin later in software - gives a bit more options and with CMOS sensors - makes no difference.

Yes, that would make it 71.5mm or x0.72 reduction factor - which is "ideal" for 4/3 size chip (about 21-22mm diagonal). 22mm / 0.72 = 30.55mm - you can just about squeeze 30.55 onto 22mm using 0.72 reduction. I'd probably opt for that version. That + x3 software binning to get you at ~1.6"/px. That would be a good place to be with DSLR. Just keep in mind that you'll benefit from longer exposures since you are natively at only 0.55"/px (which means read noise will dominate as sky flux will be low), so keep exposures as long as feasible. When you get your images - stack them as you normally would and then before you start processing - bin result x3. It changes nothing with respect to focal reducer - but you might want to loose it when using focal reducer (or at least use 25mm version). This is because focal reducer moves focus point inward / shortens back focus, but its really best checked - if you can reach focus with extension - leave it, if not - remove it. Simple as that. Without reductor - you'll probably need extension to comfortably reach focus.

That 12" is massive!

@tooth_dr Sorry, I did not mention that I don't use APP - but as pointed out - there should be way to do it. If not - other software could be possibly used to do it. I would easily do that in ImageJ for example.

->

It will hurt a bit. Further away you move sensor - larger reduction factor. You are already trying to illuminate and correct APS-C sensor. There is formula for reduction that goes something like this reduction_factor = 1 - distance / focal_length Focal length of x0.67 reductor is 303mm. This means that you need to place sensor at 101mm (from the center of the lens) to get x0.67 reduction as 1 - 101 / 303 = 0.66666 = ~0.67 You actually get 101mm away from center of the lens when you use 85mm of extensions. Which means that center of the lens is roughly 16mm away from the thread (this is important to know) Say you want 0.72 reduction - what distance do you need? 0.72 = 1 - x/303 x = 303 * (1-0.72) = 84.84mm This is from center of the lens, but since lens to thread distance is 16mm - actual spacing is 84.84 - 16mm = ~ 68.84mm = ~69mm RC8 will illuminate at max 30mm without too much distortion - but if you add x0.67 reducer - it will "shrink" that field to 30 * 0.67 = 21mm. That means that beyond central ~21mm you can expect some rather poor star shapes on your 28mm sensor. I'd use APS-C sensor without reductor on RC8 - only with flattener if you have too much curvature at the edges.

I just now realized what was original question. Don't do it - image with green being in focus. You can always blur green channel a bit if you decide to "equalize" star FWHM. That + split bin would be my choice. Alternative would be to use Green as luminance (works only on some targets), or to process stars separately and use Green as luminance for stars only. Later would be good on say Ha regions - since Ha is red signal mostly - it will be a bit blurry anyway so no point in correcting that but tight good looking stars can be had if you starnet++ image and extract stars only and then blur green to match R and B for color but use Green that is sharp for luminance.

It should be fairly easy to debayer each sub after calibration and then split them to have R, G and B mono subs - and they would act as normal R, G and B subs produced with mono camera and filters.

Don't you have an option in APP to stack multiple stack registered to same reference frame? That should be option since you can shoot HaLRGB data - which would mean 5 different stacks - all need to be aligned. As for combining the data - I have very good method, but it's rather complicated, so better stick to simpler techniques (unless you really want to give it a go - then I'll explain).

I'm slightly baffled by scale of Jupiter in the final image. You say that you drizzled x1.5 and then scaled up x2. Final image should thus be x3 the size of capture - yet it seems to be only x2?

Not sure about that ... vs