rotatux

2 hours ago, The Admiral said:

Also use Kappa-Sigma clipping

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.

2 hours ago, Stub Mandrel said:

blue/violet haloes which are caused by blue/UV overspill and achromatic lenses

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)

About read noise: yes for my cam it is about constant (and low) when varying ISO, just like sensorgen says.

I've also done my own tests and can confirm this, as those graphs show. I believe they would look the same on any modern CMOS sensor, apart from the data range (my sensor is 12-bits so 0-4095 only). What's more interesting for us is that the saturation capacity is not the same at all for each color (I don't speak of mono sensors of course), and it appears sensorsen only covered green capacity.

BTW intermediate isos are real steps in the amplification stage, so worth investigating, contrary to what many sites say about staying to "round" values.

You can also see that the E-PL6 has about max range at 800 iso in the reds where it's the weakest. So IMO there would be no point going to 400 or 200 iso, let apart to expose correctly for the chosen duration.

Additionally I generally prefer to raise ISO because 1/ IMO half to quarter of the data range is acceptable (sacrifices only 1 or 2 bits that will be gained back with stacking), and 2/ I want higher numeric values ("ADU") to average out to higher precision numbers (this is debatable and depends highly on my 16-bit limited software processing chain).

This is been debated here many times ;-) so I would prefer not to expand too much and come back with more actual results... i.e. DSO images

2 hours ago, Uranium235 said:

You mean this one? (give it a few moments to load, its very big!) But, it wasnt with the 130pds, it was from the Star 71.

Yes exactly thanks for pointing to it

Didn't exactly remember where I saw it, so cited from memory -- wrong of course.

2 hours ago, The Admiral said:

I'm not sure that you would achieve much by increasing the ISO would you? The image would require less stretching but you will be starting with a noisier image.

I should explain more precisely: The background was limiting exposure because of the nearby moon and dust. I wanted to use 30s because that was the (theoretical) max in that zone to avoid FoV rotation, then had to severely limit ISO to get an acceptable bg level. But at such iso level I have quite high saturation capacity (I would say too much!), and the sensor could be used IMO more efficiently at higher ISO. Thinking back, higher ISO and shorter subs would have lead to more frames (and less noise) within given time.

2 hours ago, The Admiral said:

It would be interesting to plate-solve and get idents for them all!

nova.astrometry.net is down with 503 just now, but @Uranium235 already posted a even wider FoV of this region in a giant annotated image, in the "imaging with 130PDS" topic.
 Next try I shoot at this (and post a better version), I shall remember to add a plate solve version.

2 hours ago, The Admiral said:

And that's with only 7 minutes of exposure, with a lot more frames

In fact the result could have been even better if I pushed the ISO (which my new cam would easily allow) but the odds -- fov rotation, dust and nearby 68% moon -- were against me. Next try in a few days (weather and moon permitting).

After several months without getting outside because of bad weather, can't resist to post some results trying new gear (camera body and lens).

Markarian's Chain and neighbours: Exposure's not right and result is missing depth, but as this is my first at this subject. Stunned by the number of catchable galaxies sitting there.

Pleased with the result and the new lens, but not yet good enough to post to the 30sDSO challenge.

See here for details.

1 hour ago, The Admiral said:

I suddenly got interested in the latest challenge, until I realised that it was time limited and there would likely be no chance of imaging this side of summer. Pity, it's made for us Alt-Az imagers!

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...

5 hours ago, Atreta said:

m8 - lagoon nebula 1x300s iso 400

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

19 hours ago, mAnKiNd said:

1)    Skywatcher 0.9x CC, 2-element [...] Cons: [...] Chromatic aberrations on mid-sized stars. [...]

Just like Neil, I have this CC and never saw any CA with whatever stars, apart from diffraction spikes of course :-P

19 hours ago, mAnKiNd said:

2)    Baader MPCC MKIII, 2- element [...] Cons: [...] Same protrusion in drawtube as above.

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.

1 hour ago, Stub Mandrel said:

I can't rack the focuser in enough to get focus!

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 ?

1 hour ago, Stub Mandrel said:

I'm not going to move the mirror - I don't want the focuser tube to give me funny stars again.

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).

20 hours ago, gazza said:

I wonder where you heard this? I've never heard or seen any evidence of this factory testing for optical centre? On the contrary I've seen many scopes that were impossible to critically collimate accurately using a factory placed spot, which became easy once a centre spot was accurately placed - indicating that the optical centre was the mechanical centre......Could you please provide a reference, I'd love to know how they determine the optical centre.....

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 !

1 hour ago, Adam J said:

Anyone got a suggestion for a quality collimator....preferably still costing less than the scope?

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.

1 hour ago, Adam J said:

I am starting to wonder if my centre spot is actually central..

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.

9 hours ago, The-MathMog said:

Here is the result of one of my only semi-successful sessions with imaging. [...]

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

On 11/2/2017 at 15:10, The Admiral said:

I've taken the simplistic view that the QE for an unfiltered sensor to Hα will be similar to the QE at other wavelengths, on the basis that if the sensitivity fell off quickly with increasing wavelength there'd be no need for the IR filter in the first place.

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.

On 11/2/2017 at 15:10, The Admiral said:

as Wrotniak states "The E-M5 and E-M1 are not cameras designed to perform well in long-exposure astrophotography." [...]

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.

On 11/2/2017 at 14:38, rotatux said:

I need to double check my "NG darks"

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.

17 hours ago, Nigel G said:

I cashed in my scrap copper I have been saving ( 2 years worth ) and treated myself to a refractor  The Equinox 80ED Pro.

A big problem being I haven't seen any stars for over a week now, I'm itching to use it, first try will be on the Alt-AZ mount but how long will I have to wait.

30 minutes ago, Tangoringo said:

the other day Ive managed to grab an HEQ5 Pro with a William Optics Megrev 90 for 600GBP. Can't wait now to get my hands on it to have a play. Needless to say, expect a load of help requests over the coming months.

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.