The Astro-Imaging Thread

[Green Baron]

I'm so jealous. Every night when the sun goes down clouds condensate over the western slopes of the island. I mean, i moved here (partly) because of the sky ... unfortunately i am not independent from electricity with the telescope and can't easily flee from the cover.

This is probably a stupid hint, but Newtons need a slight offset of the secondary

, towards the main and away from the focuser. It is not much and if there is no problem with uneven illumination i think it can be ignored.

Btw., i find the first picture really nice, besides of the coma !

 

@munlander1: Always raws. Jpegs are just piles of artefacts and information loss, for internet presentation only. You can make a few darks and biases with the iso setting you used and stack them into a master dark and a master bias. Inspect them. You need a stretching tool like a histogram tool because the stacked images have a high dynamic range, depending on the picture format of your stacking tool (usually fits or tiffs, the latter mostly deprecated).

 

[munlander1]

3 hours ago, kurja said:

I would expect that to be caused by a problem in calibration, not alignment or integration, did you check that the lights were ok before stacking?

When the darks were stacked like lights, they had the vertical lines.

[_Augustus_]

 

Meade 2080, Quickcam, 1.5x Barlow.

[munlander1]

@_Augustus_ in the lower one, what craters are those?

[Epox75]

24 minutes ago, Green Baron said:

I'm so jealous. Every night when the sun goes down clouds condensate over the western slopes of the island. I mean, i moved here (partly) because of the sky ... unfortunately i am not independent from electricity with the telescope and can't easily flee from the cover.

This is probably a stupid hint, but Newtons need a slight offset of the secondary

, towards the main and away from the focuser. It is not much and if there is no problem with uneven illumination i think it can be ignored.

Btw., i find the first picture really nice, besides of the coma !

 

Thank you... lol I was so close to the corrector that I wonder how will it be tonight, I hope to do at least 3 hours integration on a single filter.  And don't be Jealous I don't know where you live but it can't be much worse than here in the Netherlands. I mean I spent whole months in the winter without seeing nothing but a compact cover of clouds, very depressing and I thank KSP for making these months less painful. Spring and summers are usually nice thou. Soon it will be a good day to make some picture, I love the feeling of being with my scope again after a long forced hiatus. 

Considering the build of the scope I definitely doubt that the secondary offset was wanted. Anyway it's just perfect, If I leave the secondary as it is, it will probably offset by itself overtime

@munlander1 I am no expert of DSLR but have you tried to take the darks again? Sometimes a little distraction may lead to catastrophic results

 

[munlander1]

Just now, Epox75 said:

@munlander1 I am no expert of DSLR but have you tried to take the darks again? Sometimes a little distraction may lead to catastrophic results

 

No, might go downstairs to take them again.

[_Augustus_]

16 minutes ago, munlander1 said:

@_Augustus_ in the lower one, what craters are those?

Theophilus, Cyrillus, and Catharina.

Also, here's a shot of the Moon's south pole:

http://www.astrobin.com/297955/?nc=user

[kurja]

2 hours ago, munlander1 said:

When the darks were stacked like lights, they had the vertical lines.

There you have it then. You can't really calibrate jpegs, it just doesn't work period. Always use raw - which strictly speaking isn't all that raw either... that's why people use custom firmware, or a dedicated ccd.

[munlander1]

1 minute ago, kurja said:

There you have it then. You can't really calibrate jpegs, it just doesn't work period. Always use raw - which strictly speaking isn't all that raw either... that's why people use custom firmware, or a dedicated ccd.

https://m.imgur.com/rPNCqww

[kurja]

What we are trying to achieve with calibration, is to record expected error sources (calibration frames) so we could remove thus quantized error from our signal (light frames). Once your data has been interpolated into a viewable image, that signal no longer exists. Lossy image file format like .jpeg being a worst case scenario really. To make matters worse, dslr cameras apply "proprietary techniques" to "enhance" the data before it is recorded to a .raw file; in many cases, bias frames can just as well be substituted with generated files of uniform values and usefulness of darks is questionable too (ymmv, case by case, matter of debate). You'll just have to try and see what works for you, and what's not worth the effort.

Edited June 1, 2017 by kurja

[_Augustus_]

I figured out flats! Yay!

http://www.astrobin.com/298082/

Composite of 40 images taken with my Meade 2080 and Quickcam.

[munlander1]

There is a spot about 5mm on my primary mirror formed from what I think was a dew drop from this winter. Should I clean it off or keep it? It's also on the very edge of it too.

Edited June 2, 2017 by munlander1

[Epox75]

8 hours ago, munlander1 said:

There is a spot about 5mm on my primary mirror formed from what I think was a dew drop from this winter. Should I clean it off or keep it? It's also on the very edge of it too.

Keep it, you want more of those drops before do the cleaning!

 

So... the good thing about the monorail focuser is that is big, sturdy, precise and the bad thing is that I never used it, so.... guess what I did? I did focus on a star, forgot to lock it, slew to IC 1396 and left it like this for 3 hours and a half. I really need to make a checklist, too many things to remember each session. 

Anyway 95x120sec exposures with Lumicon Deepsky filter. The distance from the Corrector was 56mm this time, much better. But still i'd beat myself for that focus thing

Reprocessed with pixinsight:

 

Edited June 3, 2017 by Epox75

[munlander1]

M81 fell into the trees  but I am getting color on m8 and shooting in raw format.

[Green Baron]

Very impressive @Epox75 ! And, yes, it is sub-millimeter work to get the right distances. But it should be in an epsilon distance around the calculated distance from scope focal length, backfocus of camera and the corrector's datasheet. And a newton might need recalibration during a session from what i heard.

All my elements in the queue between camera and telescope/corrector are 2" (m48) thread and t2 adapters at the end. In between is a filter drawer for 2" filters. And i got this element for fine adjustments.

[munlander1]

When I looked at the images in file explorer, I had all this nebulousity. Once I loaded the images into dss it disappeared except for a small fraction of it. Is dss just not showing it? 

[Epox75]

4 hours ago, Green Baron said:

Very impressive @Epox75 ! And, yes, it is sub-millimeter work to get the right distances. But it should be in an epsilon distance around the calculated distance from scope focal length, backfocus of camera and the corrector's datasheet. And a newton might need recalibration during a session from what i heard.

All my elements in the queue between camera and telescope/corrector are 2" (m48) thread and t2 adapters at the end. In between is a filter drawer for 2" filters. And i got this element for fine adjustments.

Thank you! The extensions I ordered are on their way and as well a Schmidt Cassegrain  2'' visual back with t2 male thread, that means goodbye to all the 1.25'' pieces  I don't think collimation went off during last session, if you look at the single exposures, the smallest and fainter starts look like little donuts and the hole is right in the center from the first to the last exposure. I am quite sure about what happened, I focused on Polaris, forgot to lock the focuser and slew to IC 1396 and that's when the focuser must have moved a bit, my imaging payload weights 1,250 kg (camera, EFW, coma corrector).

 I also have that element and a shorter one, residues of my old filter wheel. Anyway I think I am calling the summer break now nights are way too short and bright, should last until mid July. The next session I'll do, I'll "weight" all my filters. I came up with this idea yesterday when I was reading information about the Hubble Ultra Deep Field and reading the numbers about the exposures. The "lighter" filter I have is the Lumicon Deep Sky, if I do a 30sec exposure with that filter and the median ADU is for instance 3000 and then I use for instance the IR-pass filter same exposure, same target, same conditions and the median adu is 1000 then I know that filter needs 3 times the exposure time of my luminance. 

[kurja]

12 hours ago, munlander1 said:

When I looked at the images in file explorer, I had all this nebulousity. Once I loaded the images into dss it disappeared except for a small fraction of it. Is dss just not showing it? 

How any raw file looks like on your screen very much depends on what software and what presets are being used to render the image. Not sure about DSS but I'd presume it's showing you the raw as linear (which would explain the lower contrast). Looking at images in file explorer? As in, just thumbnails or you opened the pics into some viewer program? Either way, you're likely to see the embedded preview jpeg (with camera presets).

Edited June 3, 2017 by kurja

[munlander1]

Well, the first one is stacked with histogram adjustment, other in individual light frame.

 

[kurja]

You mean that one seems to have more color?

[Green Baron]

5 hours ago, munlander1 said:

Well, the first one is stacked with histogram adjustment, other in individual light frame.

I am not sure if i understand what your question is. I have difficulties comparing the pictures because they show different clipping. What comes to my mind is that you haven't found the focus yet and suffer from severe coma, as one would expect with a newton f/4 and an aps-c size chip. Both problems can be overcome.

Combining steps makes it much more difficult to find difficulties and sort out problems, address one problem after the other. With a series of exposures do the stacking as described in all the tutorials and save the stacked image. When stacking you can play with the stacking parameters but nothing more.

DSS shows a stretched image after the process, you can save it as a suggestion by DSS, but always keep the unprocessed stacked fits or tiff image. That image, though it looks less impressive than the suggestion, includes many magnitudes more of information and is the working base for you post processing in another program(s).

 

To sum up: find the right focus on a star in the center of the image, if that is solved then try the stacking. Afterwards address the coma problem (because that is going to cost a little something), then you can do successful post processing.

 

Edited June 4, 2017 by Green Baron

[_Augustus_]

Jupiter two days ago:

http://www.astrobin.com/298433/

[Green Baron]

22 minutes ago, _Augustus_ said:

Jupiter two days ago:

http://www.astrobin.com/298433/

I could just barely hold me back, it looks so ... sweet :-)

 

[munlander1]

So what do you guys do once you start imaging?

Since I take darks every night, and plan to continue this till I have more exposure time (at 1.5 hours rn) could I have too many darks?

Edited June 7, 2017 by munlander1

[Green Baron]

3 hours ago, munlander1 said:

... could I have too many darks?

In principle and following theory: no. With a dslr you should take darks for every series of light frames so they where made at the same temperature as the corresponding lights. You shouldn't use darks taken at 10°C to raise the snr of light frames taken at 15°C.

Otoh, photography in general can be a very personal hobby. If you are content with the outcome of mixing "warm lights" and "cold darks" (or vice versa) then why not ... just try it.

Even with ccd that can be set to a temperature i would take a new set of darks every few months. A chip changes over time, it doesn't get better, because entropy and so on ... :-)