rotatux

Are you talking of this one ? Yes it's made for us :-D or at least we are about equal with EQ mounts... Just have to get out all night for good DSO views. Still somewhat manageable, it's currently dark here by 22:00 to 22h30 (on holidays in my deep country site). Weather says 2 or 3 hours clear of clouds tonight, I hope it's right...

Splendid, nice colors and I can guess more "hidden" data. With more subs and some processing (push more, strip some background, ...) a very nice image will come Your T5i camera seems to be a modern one, maybe you could push up the ISO a bit (e.g. 800-1600) to reduce sub duration and get more frames per session, while keeping the best dynamic range possible ?

Well if you can regularly achieve 60s subs like on this M51, your setup is very good and you're quickly going to obtain much better (depth, color), images

Hello mAnKiNd, welcome to SGL and wish you lucky weather with your new gear Just like Neil, I have this CC and never saw any CA with whatever stars, apart from diffraction spikes of course :-P I don't have it but have seen how it's made and what others tell on it, and I'm pretty sure it does NOT have the protrusion problem of the SW. The SW has it because it's collar prevents it from going deeper into the focuser. But the Baader can thread in as a M48 filter, allowing it to go I think at least 20mm deeper into the focuser, if you have the right 2"/T2 or EOS adapter.

Nice moon sharpness, but the green tint on highlights give it much of... an alien look In Jupiter it was just in time to catch the shadow on the disk's edge, congratulations.

That's weird... and quite surprising given you did AP with it. If so, the focus plane must be well outside the tube, and the focuser should rack out to get focus with eyepiece. What kind of adaptation do you use as 1.25" holder from the focuser ? Err, do you mean you already moved up the primary to avoid the focuser tube going into the light cone ? Then your focus is even more outside the tube, and so I would understand the origin of the problem especially since IIRC your focal is ~20mm longer than mine. For other uses I recently ordered a shorter 2">1.25" adapter (one with annular holder, like that) which I incidentally tried with EP but it proved too short for my focuser range (could not rack out enough). Maybe that kind of model would suit you. I just measured it to be 27mm±0.5 shorter than the stock adapter which came in my scope's package (the one with 2 parts which you unscrew to use for T2).

I didn't explicitly read about it, just 0/ having a relatively strong mathematical and physics background (just as many people here ;-)), 1/ implicitly understood the thing after several months studying articles about "how to grind your mirror yourself" with rotation-based grinding machines and 2/ watching photos of how the pro-equivalent machines are made (basically the same principles as amateurs, just less rudimentary). You will note in those setups the mirror chocks / holders position can have some liberty in their blocking position depending on small mirror plate irregularities on the edge, which is the source of the shift discussed. For a factory it's not as difficult as you may think, they don't HAVE to optical-test the mirrors, just know its center of rotation, which is easy for them because THEY grind the mirror. Of course it needs a bit of organisation and QA, so depending on brands and periods YMMV and I admit there must be exceptions For the 2 serious newtons I had in my life (130PDS and Lightbridge 12") both spot's position were perfect (i.e. could be used for collimation).

Yes for a sphere the perpendicular to any point on the surface is a symmetry axis. For a paraboloid only the perpendicular to the optical center is such a symmetry axis. Difference comes from making / grinding imperfections. That's an approximation, but think of the optical center as the mirror's center of rotation during grinding. If the mirror plate is not perfectly centered on the rotation center from the start, you end up after grinding with an optical center that could be a few mm off from the geometrical (disk) center. However I don't know of a simple way to find the optical center. Since you completely lost it during cleaning, better to have the geometric center approximation rather than nothing !

My 2¢: Having gone the laser way and get lost, I would rather advise you to get a "Cheshire"... does not need batteries, much easier to use, good enough to very good results. I've got a long version, but wonder if a short version may be better and easier when framing the primary edges (bigger view) to align the secondary. Beware not to touch it unconsciously : the spot doesn't mark the geometrical center of the mirror, but it's optical center. The two are identical for a spherical shape but can be distinct for a parabolic shape such as the 130PDS'. It's supposed to be setup correctly at factory, so be sure to test your mirror on optical bench before thinking about moving it.

Nice one for a first. With your barlow it somewhat looks like my first shots with a Mak127, your progress will be fast and easy once you start using longer stacks. 10-15s per sub seems fine given your setup, though you will want longer ones at some point About your 130 not focusing enough out of the tube... maybe try a lower power barlow such as 1.25X; I don't think ocular projection would gain you anything as with a DSLR the projection distance would be too long and induce a focal multiplier bigger than your current barlow. Or try one of the primary-mirror-raising mods :-P

Makes sense, but if I had to design such a filter as an engineer I would make it such that it only lowers undesirable signals to unnoticeable levels at the sensor's output. Which makes me think the sensor cells are already not very sensitive to IR (and H-alpha), when I see the slope of all the curves on the IR side. For ref, my filter should be at about 35% at 656 which is nearly comparable to yours. All things being relative, as he compares to "full frame" sensors. One should actually look at pixel size rather than whole-sensor size, to get a hint of capture range. Of course FF are ahead of the race, but latest APS DSLR models with 24mpx and more have equal or smaller pixels than the E-M5. My darks were fine, so the problem didn't come from them. But I think I've pinpointed the "problem". I did a few camera flats, with just the camera, T2 and M48 adapter, and various or no filters, against daylight (or rather, what clouds transmit :-/). Then did stats on the resulting images, all taken at same exposure (ISO and duration). As Ken hinted, the filters eat on red and green, and let a growing part of blue pass (as show by the relative "B-V" shift). One could object this is on visible light, not H-alpha or O3, but it probably just has the same effect on them, as these are supposed to be wide-band filters. IMO this explains the severe blueish shift I have with the UHC, not only there is much less total light -- though I wouldn't bet on bad transmission as those stats are with indirect sunlight so much of the spectrum is impacted, not just star/nebula light -- but there is 3x less red transmitted. So my 20s of Rosette, given it essentially comes in the reds, are equivalent to 6.7s without filter or 10s with Didymium. I would bet that's why I don't get enough absolute signal. I have yet to find a combination of exposure that gets more signal, but that UHC filter may not be part of the solution, as strangely as it sounds.

With all that new gear for many people, no wonder why it's been rainy or cloudy for several weeks ;-) Congratulations both, all nice buys.

Yes your setup with APS-size sensor and no flattener/corrector has nearly exactly the same FoV as me with M4/3 and ComaCorr. The Rosette framing of both images indeed look the same. Nice picture Ian BTW ;-) Looked at kolarivision site. I found a cam with same sensor as me, the E-P1. However it's only the characteristic of the filter, not the sensor. I know from sensorgen.info that my sensor has 38% quantum efficiency (though I don't know how to mesaure and check it myself), but I suspect that value also varies with wavelength, so I can't get any conclusion (the net light sensitivity should account for both the filter and the sensor). About noise: The first generation sensor (12.3mpx) is from Olympus and indeed quite noisy, though manageable. But the 16mpx sensor found in E-PM2/PL5/6/7, E-M5/10 is from Sony and much better (3x less noisy, and 1.6x more sensitive at 60% QE) -- that's what I'm willing to get, maybe second hand. Your 2nd link conforts me in this opinion. Interesting... makes sense given my technique, I need to double check my "NG darks": as the target was rapidly climbing in the sky, I may have captured the wrong gradient and mismatched a bit with the lights background. Oh damn, I have yet to write a blog entry on that "NG dark" technique of mine :-P Thank you Nige. I don't think separate bias would help as I already use traditionnal (not scaled) darks dedicated to each session or even subject. I hope it's LP and it can be sorted out, the filter was here to help. I would like lower ISO if I could achieve longer subs, but the mount is so erratic I'm afraid I wouldn't capture any signal as lower ISO + 20s. Will retry on occasion though.

I found he brilliantly explains how stacking can get you additional bit depth (though there seems to be a off-by-one error in bit gains for each of his stacks). (reading links from your last post, will follow up later ;-) )

Two new pics finished (actually one has to stop somewhere), one half-success and another failed. First is my #2 try at nebulas around Alnitak. Much better than my try #1, still progress to be done. I guess I can't catch more unless going to a darker site (was taken from Paris suburbs). Capture: 101 good of 123 lights x 25s x 2500iso, 30 NG darks, Olympus E-PM1 with Skywatcher 130PDS on Celestron Nexstar SLT, Skywatcher ComaCorr and TS-UHC filter. Processing: Regim, Fotoxx. Second is Rosette on which I failed to capture enough SNR (sorry for your eyes ;-)). I had to stretch so much I had to process the noise, even then the result isn't satisfying. Surely I was too ambitious when reducing the sub length to 20s, I suspect the UHC filter dims the overall image and requires at least 25-30s; Stars were burnt in my previous 30s try, so I decided to reduce it, but I might need HDR on it (or stop trying to image from Paris suburbs from which I can only barely see Orion's belt). Capture: 50 good + 42 average lights (of 122) x 20s x 2500iso, 56 NG darks, Olympus E-PM1 with Skywatcher 130PDS on Celestron SLT mount, Skywatcher ComaCorr and TS UHC filter. Processing: Regim, Fotoxx. A few days ago Ken gave me the idea to try to calibrate the color levels coming on the sensor through my filters, so I'm in the process of making some kind of flat in different filter configurations. Hoping to understand my filters characteristics and those bad star colors.