rotatux

I rather suspect our browsers to be the culprit... Some of them try to be smart and alter color profiles (for the sake of cohesion I presume). To check, you could try to open your local image in a browser tab, rather than going through SGL submission, and compare with external viewer of even PS. BTW nice image, I like star colors too (a bit too cyan?). Interestingly the version I prefer is your last one without darks (less contrasty mottles), but it's maybe just a matter of black point.

At your current keep rate, you may also improve it dramatically by dropping your sub exposure time a little, say from 30s to 25s or 20s. BTW you don't tell how long your subs are. Nice pic however, it has depth and colors; Details and your processing skill will improve with time and practice (and yet more subs as always :-P)

Not enough: you have to rotate the polar scope to either 1/ match your local longitude + date + hour, or 2/ match other constellations around NCP (such as Ursa Minor/Major and Cassiopeia). Otherwise you may be up to 2x40' (1.33°) offset from NCP, and that might explain your trouble.

No need to ask and welcome to altaz imagers. That's a very nice image, with crips stars and beautiful colors (stars and nebula). The blue background is nice too, after all. Did you have any experience with astro imaging before ? if that's your first it's a very good one.

It appears your CC introduces more vignetting as there was initially. Meaning you will *need* flats to correct your images taken with it The global level is also very different : 202 vs 217 (on the full-width bottom area below the label) which is about 7%. This is difficult to see (and hereforth quantify) with the eye+screen, so I used Gimp to measure (though I wanted the median, it only offered the mean, but that's another story). I think that result is not bad per itself (90-95% Tx factor is usual with good glass assemblies), but if you're comparing brightness variations between apertures, you should remember to apply that value as transmission factor of the CC. Such an interesting subject that I'm now planning myself to check exposure levels from all my lenses/scopes x apertures, just to try to clarify whether focal+transmission ratio play a role alone, or must be combined with focal (have seen both theories defendable). Just need to build a DIY light lab to keep things constant :-P

Very interesting. Though, for the sake of comparison, I'd like to see the scope's result without CC, to account for just the mirrors' transmission, and starting the lens at f/4.0. Given that I've heard pixel individual illumination should be proportional to F ratio (all other conditions being equal), it's quite strange to observe your scope's F:5 result to be between the lens F:8 and F:11. That's a kind of flat images you made, but was your light source for them constant in intensity and distance ? BTW I don't believe in the T-stop explanation, as that would make the result even worse, i.e. the lens results around the scope's would not be F:8 and F:11 but more something like F:9 and F:12 (assuming 80% transmission). Don't forget that your 2 newton's mirrors each have typically 95% reflectivity so overall ~90% transmission.

Interesting: so DSS does multiple iterations, while Regim does only one. Hence the very different "kappa" values. It might just as well fall back on my values range if using iterations=1. While I'm highly confident at the mathematical / statistical meaning of doing only one iteration, I'm more in unknown territory about doing many, especially as it will progressively shift the average value used as criteria. I still have to think about it as it seems to "just work" for many people. Is there some kind of synthetic report in DSS, where it would indicate the net proportion of kept pixels, so we can get an idea of the final selectivity of this algorithm ?

BTW this algorithm has a parameter, let's call it the "sigma factor". What values are you using ? /me depends on subs quality: poor => 0.5 or less, average => 1.0, good => 1.25 to 1.5, very good => 1.6 and above. I also noticed how the pixel keep rate seems related to the sigma factor, e.g. 0.5 gives around 25%, 1.0 => 50%, 1.5 => 75 to 90%. So that may also be a selection criteria if you want to keep a given pixel percentage of your subs.

For me it's another story as I am on holidays... I made a session for the whole night on 2017-05-24 from 10pm to 4:30am, had to stop after daylight had become too strong. Unfortunately some strong wind came after 11:30pm (black night starting around 11:00pm) and ruined most of my subs... the Nexstar SLT is so brittle that any wind will make my tubes shake , how are yours ? (especially the Synscan) And the show must go on, here's one which came out not so bad from what I could save. The Leo Triplet. Gear: Olympus E-PL6 with Skywatcher 130PDS 632mm/4.86 and SWCC at f/4.55 on Celestron Nexstar SLT Capture: 22 lights (/ 18% keep) x 30s x 3200iso, 23 darks Process: Regim 3.4, Fotoxx 12.01+

No, never astro-modded either the PM1 or the PL6. Currently I don't intend to, as IMO I'm unable to do it and would just detroy the sensor if trying. What would you think of the red sensitivity of the stock PL6, based on my image of America ? Intuitively I find it's much better than PM1, when I compare with e.g. that previous try.

Thanks Neil. I don't have Photoshop (no Windows, no Mac). If you know of a Gimp plugin then I could try something else... Actually if you look carefully there's both blue and red rings around bright edges (check that moon image where the red ring is obvious), but with different size and intensity. That's a type of CA (I think "color dispersion") which I have no plugin to handle; That's neither Directional CA nor Lateral CA, which I already have a plugin for. I'm ready to accept it as the price to pay for using the lens at full-aperture. Though I *can* reduce or get rid of it by using a DIY mask to reduce aperture to F/5 or F/5.6, but I'm just reluctant to use them because that fault is very uniform up to the edges (kind of artistic, one would say) and makes star colors more obvious.

Let me share two more processed images from 2017-05-16' ~night~ with the OM-Zuiko 200/4. First is Bode's galaxies, code M81 and M82. Two more NGC galaxies in the scene. Shows somewhat unexpected structure for that FL. Details in my gallery. Second is America Nebula (NGC7000) and Pelican Nebula. The 200 FL fits almost perfectly that targets. Details in my gallery. I tried some HDR to detach the brightest stars and give some 3D look, but that masked the faintest parts under the Pelican, so I stayed with the traditional version.

Hi Steve, thanks for comments. Absolutely no filter, as most of the time they remove too much wanted photons Setup details are in my gallery page: follow the rabbit link just under the first image ;-) . I was trying a new way to not clutter posts too much, would you prefer / should I rather copy the settings in each post ?

2 nights ago I managed to have another go at Markarian's chain, and tried different settings (mainly, higher ISO: 3200 instead of 2000). I find it's much better than previous try, maybe except blobby stars typical of refractors and strange star colors (though I see it also in SDSS images on astrometry.net). Was also much easier to process, as I didn't have to go at the limit of stretching to get decent details. Of course still more frames wanted, but I had other targets within that available 2 hours window. Details in my gallery. And annotated with astrometry.net job: Discovered Siamese Twins (left half-height) and strange NGC4299 (lower right border), going to read about them.

As requested, plate solve of my previous image through astrometry.net: (job)