rotatux

On 2/4/2018 at 20:15, alacant said:

Comments -especially on the colour scheme- most welcome

Your colors are lovely, especially the nebula. If I was picky I would say too strongly blue stars and missing gradation in red/orange stars, but the subject is the nebula and it has IMO nice red-orange-grey-blue variations so nothing to complain

Wish I had an occasion to get that one but weather decided otherwise and it's now probably off for me til next year.

M38, the Starfish cluster, and its nice little friend NGC1907.

Which is the full size for image posted in my gallery here:

Hi Nigel

As you tried 1:1 and 1:2 Ha/O3 ratios and I somewhat liked aspects of both but not fully, I wanted to try 1:1.5 ratio by averaging the first two jpegs in Gimp; Unfortunately they are neither aligned nor same scale.

FWIW it would give something like that -- whould be nice too.

17 hours ago, Galen Gilmore said:

Quick question for those of you who use a DSLR for imaging. How many of you use dark frames in your images? I have heard a lot about how dark frames might actually hurt the images more than help them.

I do use darks, which dates back to my old hybrid E-PM1 camera having strong and regular (from shot to shot) thermal noise. YMMV, as the correction brought by darks varies heavily from cam to cam : IIRC most Canon owners here don't do darks. My new E-PL6 has very low thermal and read noise, so I'm in the process of testing the replacement of darks by flats+bias.

13 hours ago, furrysocks2 said:

just a sleep/step/sleep/step loop

Beware that if you use a fixed delay in the sleep, this kind of loop has inherent timeshifting builtin because of various lags in execution.

Unless it's already the case, you should aim for fixed average frequency, by using the builtin clock to compute the next delay each cycle. I mean something like:

avgPeriod = CONSTANT
target = clock() + avgPeriod
while (tracking) :
	step()
	sleep(target - clock())
	target += avgPeriod

NB: BTW, this kind of code works very well even without any interrupt handling, it will absorb and correct minor local variations of time and execution as long as your clock is stable enough.

Nice M1... I personally struggled to frame it (too weak and too small) last year in my H-LP sky and abandonned, so that's some achievement

Oh and question about your HH+Flame: what filter did you use ? your colors look like what I get with my UHC...

You definitively have some valuable data in that sub : Some nebulosity and nice colors.

Your sub is not that much overexposed, I would say it's reasonnable, so that was your stretching. You will do better focus / tracking next time, learning one step after the other (live view focus, exposure settings, stacking, etc.).

I wish I had my first at it that good

Though that's strange all your stars are already burnt at such low ISO, did you use RAW or a cam-produced JPEG ?

While zooming you even get the start of a hint of the Flaming Star Nebula. I like this subject, already had a go at it with an old 135 last year, but being a smaller frame it was more on the center part and only catched the top cluster. Not sure I will have the night to retry it this year :-/

You say 75mm and F4.5... is it a prime or a zoom ?

12 hours ago, furrysocks2 said:

No motors, no finder. Just a laptop, a cheap guide cam

Do you mean you're tracking by hand, following a star in the cam ? I know this can be done in theory, but achieving it... wow

I find the image does not reward your efforts as it should, maybe using shorter subs (and 16bits!) in live stacking could help avoiding trails and enhance final quality. (just a wild guess)

I'm about to flock my tube too, but just a question BTW: is there any risk the flocking material could accumulate water / humidity, and raise condensation, during moisty nights ? or do you combine it with some heating device to avoid it ?

PS: what I actually have for flocking is a somewhat thick felt (I mean maybe equivalent to ±15 sheets of paper)

I don't know your equipment and capture settings (how many subs / overall minutes etc), but it's beautiful. Sadly my FoV is even narrower with the MFT sensor, but I'm planning to take about the same framing (which should just fit in the diagonal) with the help of my now stabilized mount and CC-reducer.

@ neil : in your  first one it was color-less and quite difficult to distinguish fuzzies from stars, so I much prefer your 2nd for its color and easiness to read.

@ nigel : in fact I prefer your first one, which despite less natural (but still good) colors I find more constrasty. You catched nice structure. Still annoyed by that mottling effect (of your processing software?) when zooming in. /Myself must wait for another try at this target with my new cam (since last year) and tightened mount... you lucky, I yet have to find the right cloud-dispersing magic wand

Edit @ neil : strangely your 2nd image shows the same mottling effect on the background than Nigel's... same software ?

Thanks for kind comments.

Yes I quite like the edge-to-edge consistency of this lens (no coma!), as much as I hate its color-diffraction pattern (BTW no tool for this yet under Linux, I tried generic deconvolution as a wild guess but I must still learn how to use it).

For reference, here's the page about tightening this mount: http://nexstarsite.com/Reviews/NexStar102SLT.htm#AltAxis (the last paragraph especially helped IMO).

Here's first output from my session of sept. 22. I got out nearly all night with my Alt-Az mount and a bunch of lenses to test. It's also first light since I tried to fix my mount by tightening hardly the altitude gear as advised by some page on the net; Hopefully on this one it managed 40s exposures with a high keep rate, which it had never achieved yet (whatever the focal).

This one is not really a test any more, as I now know what to get of this lens. I let it uncropped so you can appreciate the FoV given by this setup. Thanks for watching.

M31 - Andromeda Galaxy

Details:
Gear: Olympus E-PL6 with OM-Zuiko 200mm/4 at F/5.4 and TS-Dydimium filter on Celestron NexStar SLT
Capture: 60 lights (/80% keep) x 40s x 3200 ISO, 13 darks
Sky: average (didn't get any SQM, was prb 18-19), 50km from Paris, France
Processing: Regim, Fotoxx

23 hours ago, al-alami said:

I've got sort of an issue, I think with the focuser

You don't tell about capture conditions, so as I wild guess, your star elongation looks approx. perpendicular to the direction of image center. To me this looks more like field rotation, maybe mixed with a bit of coma in angles.

About tilt checking during the day with the cam train on, just a rough idea: maybe focus on a the vertical face of a far building, and check focus along a vertical line on live view ?

3 hours ago, Shaun_Astro said:

Here's 132x19" subs. 

I realise taking 15-20 second subs allows me to keep most of them. 30" was too much for my mount with this 600mm scope on it, and I was chucking out 70% of frames.

Don't be discouraged, I too face a mount that doesn't want to be stable enough more then 20-30s (more often 20). My keep rates vary from 22 to 80%, so you're pretty up the score I think if you would read back this thread it would be somewhat the same for others. You're on your way.

Nice image, you caught much nebula. However I find it's strangely too noisy given the high number of frames you stacked. Maybe you had to stretch very aggressively ? What ISO were your subs ? Did you shoot low on horizon ?

Here's a last-half moon from last month (this one fullsize, contrary to my gallery).

First try at video-like stacking with a proper burst shots sequence. Auto white balance then added some contrast and color saturation. To my surprise some color differenciation appeared, so quite happy with it

This was without Barlow, now I'm just wondering for next try whether I should do 130PDS+barlow or 127MAK ? Optically I prefer the MAK, but the focuser and camera coupling is much better on the 130...

Here's some planetary for a change: 2 sample shots of Saturn taken on 2017-06-11.

Details: ~120s FullHD @ 30p movie crop mode, Olympus E-PL6 with Celestron 127MAK/1500mm and x3/x2 APO Barlows on NexStar SLT, processed with cvastroalign.

(indulgence requested, I'm still learning how to process planetary footage and use cvastroalign)

Edit much later: realized this is not in the thread's subject (not DSO), I should not have posted here. Oops :-/

21 hours ago, Stub Mandrel said:

That's the curse of SGL

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.

22 hours ago, Shaun_Astro said:

Managed to get 65 usable frames out of about 130 with my star discover mount

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)

21 hours ago, Peco4321 said:

polar scope fitted and get Polaris right in the circle

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.

38 minutes ago, scitmon said:

May I submit my first ever real attempt at a DSO with my ED80 Ds-Pro and Az GOTO SynScan

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.

19 hours ago, bobro said:

Here is a comparison of images taken with and without the (DIY) Coma Corrector on my Meade 130EQ scope.

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

On 05/06/2017 at 22:48, bobro said:

Here are the results of using the camera with a 135mm lens at f# from 5.6 to 16, comparing with the camera on the scope at a nominal 5. Same exposure time and ISO for all images.

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.