The "No EQ" DSO Challenge!

[Filroden]

Here's my latest rendition of the Rosette using Ha as Luminance and some very poor RGB data to add colour (there is now no Ha in the colour data). 

There is a definite graduation of red shades. Looking at bi-colour narrowband images using Ha and OIII, you can definitely see a lot more OIII in the same areas as the lighter areas in my image, suggesting that it is the OIII signal shifting the colour from 656nm towards the lighter reds. There just isn't enough OIII to completely move the colour from red into a more green shade (which does occur in small parts of M42). I've never captured blue stars - mine all range from white through to red/orange, but when I check the yellow and orange stars they do match the expected spectral class (and the white stars match the hotter OBA stars).

[Herzy]

I took this on Saturday with the clubs SE mount and an AT72ED from a dark site. I can't get the core to look right. The nebula was so bright even in 45s subs that it appeared all white. I layered some old pictures I had over it to make it more visible, but it still is blown out. I also don't like the blurred feeling to the image. Seems like the detail is all blurred.

[Nigel G]

Very nice Ken.

Your Rosette is the best Alt-AZ image I have seen. Its every bit as good as an EQ mounted scope. 10/10.

We have reached the 100 pages with this thread now, its almost impossible to find previous information now without spending an hour or 2 looking through it all.

Cheers

Nige.

[Nigel G]

Herzy, that's a great image, loads of dust visible, more than I have seen before.

Have you tried reducing highlights and increasing shadows, the brightness could be the reason for loss of fine detail.

Well done.

Nige.

[The Admiral]

 

2 hours ago, Filroden said:

Here's my latest rendition of the Rosette using Ha as Luminance and some very poor RGB data to add colour (there is now no Ha in the colour data).

A super image Ken, this colour one is a hundred times better than the your earlier one! It's nice to see some variation in colour, coupled with a feeling of solidity about the object, yet at the same time retaining that certain nebulous-ness. That is something that Ha seems to bring to the table. Mind you, seeing your other posts, Ha seems to also bring some processing challenges!

And yay! 100 pages

Ian

[Nigel G]

24 minutes ago, Herzy said:

I took this on Saturday with the clubs SE mount and an AT72ED from a dark site. I can't get the core to look right. The nebula was so bright even in 45s subs that it appeared all white. I layered some old pictures I had over it to make it more visible, but it still is blown out. I also don't like the blurred feeling to the image. Seems like the detail is all blurred.

I just had a quick go at reducing the highlights and boosting the shadows, ( hope you  don't mind ) I think it would work better during initial processing,  there's a lot of nebula and dust in there ?

I have done this on my tablet so can't see if I have over done it until I get to my pc. 

It's a great image, I would love to have a go from a fits file.

Nige.

 

Edited January 30, 2017 by Nigel G

[SteveNickolls]

19 minutes ago, Nigel G said:

We have reached the 100 pages with this thread now, its almost impossible to find previous information now without spending an hour or 2 looking through it all.

And still not a further word from Admin/Mods, do you think they have fallen asleep? Such a shame not wanting to help us advance Alt-Az imaging when it is so popular a thread.

Not to end on a sour note-100 pages is grand going!

Cheers,
Steve

 

[The Admiral]

17 hours ago, mxgallagher said:

Having been inspired by what I've seen here, and eventually getting a clear night. I dusted off the t-ring adapter for the 250 goto dob and had a stab at m31

Just over 7mins worth of 10s subs at 3200iso on an eos 70d

Not edited much, just had a quick play with the levels in gimp

That's a great start, and you've got 7 mins worth of subs with a 250, which means 6x more photons that my 102mm frac  would get in the same time. So I can't help feeling that there is a lot more data in your image still to be teased out. It's all down to the processing now. I know many use Photoshop and Gimp, successfully, to do the initial stretching, but I'm not one, but it might be worth trying some astro specific software instead. Most can be had on free trial so you might want to investigate further, though do bear in mind not to expect them to give you what you want straight out of the box. They all have a significant learning curve, but are well worth the effort in the long run.

Also, if you rotate the camera you can fit more of M31 in across the diagonal!

Interesting to see a GoTo dob being used for deep sky imaging. I wonder if we'll see more of that in these pages; no reason why not.

Ian

 

[SteveNickolls]

Hey Nigel,

Way to go-you got a the mention on the Astro Imaging Channel for your mosaic-great going! Light under a bushel :-)

Cheers,
Steve

 

[rotatux]

3 hours ago, Filroden said:

UHC filters remove most of the green/yellow wavelengths (see the image below for an example). This probably affects calibration, particularly of the yellow stars. You may first have to manually rebalance the image and then run a more automated calibration.

You must be right, though I could not find the specific response curve for my filter. When I look through it during day, I see all seems red and blue, something like a mix between 2 eyes of a red-blue 3D glasses. At first I thought it would remove essentially yellow and a bit of red, but it's narrower actually and removes green as well (confirmed by looking at trees folliage and grass, which turn brown or dark red).

So Regim's calibration must be trying to compensate for the lack of green in stars, and the image ends with too much green. Sounds correct.

Now, what's the best and more practical way to get back a correct green channel ? If I play with balance to raise green level, I may end with the same green cast as auto-calibration since there's not enough green from the start (but will try). Capture green from another session, like you do with L+R+G+B(+Ha) ? Apart from the inconveniences of multi-session and number of subs, I would have to do it with a narrow green filter to be efficient -- if it exists   and that would somewhere negate the use of a UHC filter. Or synthetize a fictive green channel from the two others ? Would be wrong as the red+green/blue ratio is precisely what changes from star and star and enters the definition of the B-V index. Back to home to think and try :-P

[Filroden]

51 minutes ago, Herzy said:

I took this on Saturday with the clubs SE mount and an AT72ED from a dark site. I can't get the core to look right. The nebula was so bright even in 45s subs that it appeared all white. I layered some old pictures I had over it to make it more visible, but it still is blown out. I also don't like the blurred feeling to the image. Seems like the detail is all blurred.

I suspect the layering has added noise and given you the impression of it now being blurred. I think there is some fine detail in the nebula but you probably need to mask the fainter details and potentially deliberately blur it more while leaving the brighter areas in their full detail. Not only will this draw attention into the detail but it will hide some of that noise

You have a strange colour cast that almost looks like it's a vignette. Have your flats introduced something?

[Filroden]

1 minute ago, rotatux said:

Now, what's the best and more practical way to get back a correct green channel ? If I play with balance to raise green level, I may end with the same green cast as auto-calibration since there's not enough green from the start (but will try). Capture green from another session, like you do with L+R+G+B(+Ha) ? Apart from the inconveniences of multi-session and number of subs, I would have to do it with a narrow green filter to be efficient -- if it exists   and that would somewhere negate the use of a UHC filter. Or synthetize a fictive green channel from the two others ? Would be wrong as the red+green/blue ratio is precisely what changes from star and star and enters the definition of the B-V index. Back to home to think and try :-P

All I could suggest is taking a test image of a colour card using the filter and find out what setting you need to bring the colours back to how they should look. I'd try with white balance/colour temperature first, as it's a single setting. If this works, then it becomes an easy step in the process.

As soon as you start to rebalance the RGB histograms or try to synthesis a green channel you are back where you started I think (though obviously missing the light pollution which can dominate in that green/yellow region). Not necessarily a bad thing, but there must be a way to do this easily.

[Filroden]

58 minutes ago, Nigel G said:

Your Rosette is the best Alt-AZ image I have seen. Its every bit as good as an EQ mounted scope. 10/10.

 

49 minutes ago, The Admiral said:

A super image Ken, this colour one is a hundred times better than the your earlier one! It's nice to see some variation in colour, coupled with a feeling of solidity about the object, yet at the same time retaining that certain nebulous-ness. That is something that Ha seems to bring to the table. Mind you, seeing your other posts, Ha seems to also bring some processing challenges!

Thank you both. I have to admit that the Ha data almost processes itself. It requires no background wipe, needs very little noise reduction and so long as I'm careful doing the stretching you get a really good image in quick order. I can only image how much easier it becomes with even more data! The trouble comes when trying to blend very clean, strong data with much weaker data. My initial attempt used the Ha also in the red channel, but this totally dominated the image - so while there was some pale natural star colours, the nebula looked like a tinted mono image. With a little more work on my very poor RGB data I was at least able to achieve something. I have halos that I would like to eliminate but there is not much more I can do with the RGB data. It has some nasty gradients, is very noisy and the three channels are very badly balanced. Once I get another clear night my intention is to collect 60s exposures for RGB and discard all previous data.

[The Admiral]

3 hours ago, rotatux said:

That's a matter of camera. Actually I've tested 800, 1000, 1250, and 1600. With only 12-bits depth and 30% quantum efficiency (taken from sensorgen), most if not all deep sky (not clusters) subjects' data just happens to be below the minimum first value above zero with short exposures. Said otherwise, lower ISOs just don't give me enough data to stretch within my exposure limits. So I need to amplify more than all of you 14-bits sensors owners, and 2500 is my camera's maximum of analog amplification (3200 and above is digital). Would be different if my mount accepted to do 40-50s subs

Good news is my read noise is about the same at every iso, so I prefer to always use the same ISO level and vary the length and number of subs. Bad news is my noise is quite high so I need about 80-100 subs to tame it.

BTW don't be fooled by the DR such as indicated at sensorgen.info, it's for a single shot: If you consider stacking removes the noise, you get full DR for any analog-scaled ISO from a sensor-only point of view; What matters then is to avoid saturation of your subject wanted parts (you may saturate some subs for HDR to get faint parts), and hence match the subject brightness range to your camera by adapting the exposure. It's good if you have the choice to adapt the exposure, to lower ISO in addition to varying sub length, I don't think I have that choice.

I suppose that I tend to work the other way and expose for a convenient maximum of 30s irrespective, on the basis that the longer I image the more photons I'll collect, which must be a good thing as it improves the photon statistics and gives more signal from the sensor. The big problem of course is saturation of stars/particularly bright parts of the target. Where I want to retain as much information about the stars I've tended to drop down to ISO400 in order to give more headroom before the DAC. With M42 though, I used both ISO400 and reduced the exposure down to 2s for a proportion of the subs in order to blend later. With my camera, ISO1600 is the max analogue gain.

The other thing, as I understand it, is that it is not strictly necessary to have sufficient gain to get from 0 to 1 out of the DAC. First, sky background will take you above the 'floor', and averaging the signal from all the subs will, provided you are not doing integer arithmetic, allow interpolation between DAC units. The reason is that the photon and other statistics will sometimes give a zero, and other times 1, and perhaps occasionally 2, and the average will be somewhere between. So may be it might be possible to use a lower ISO to advantage.

Ian

[The Admiral]

56 minutes ago, SteveNickolls said:

Hey Nigel,

Way to go-you got a the mention on the Astro Imaging Channel for your mosaic-great going! Light under a bushel :-)

Cheers,
Steve

 

Congrats Nige!

Ian

[Filroden]

4 minutes ago, The Admiral said:

Congrats Nige!

Ian

Indeed! /bow

It is an amazing image and well worth being showcased. 

[The Admiral]

1 hour ago, Herzy said:

I took this on Saturday with the clubs SE mount and an AT72ED from a dark site. I can't get the core to look right. The nebula was so bright even in 45s subs that it appeared all white. I layered some old pictures I had over it to make it more visible, but it still is blown out. I also don't like the blurred feeling to the image. Seems like the detail is all blurred.

Nice shot Herzy, bags of detail of surrounding dust clouds. I agree with Nige, you could probably afford to bring that out a bit more.

As to the blown core, if  there is some more detail available in the core with a much less stretch, you may be able to blend the low stretch image with the full stretch image. Otherwise, I think that 45s is likely to have over-cooked it, and perhaps if you have another opportunity you could try a much shorter exposure, say a few seconds, to blend with it.

Ian

[Filroden]

You can always copy the raw image, process one fully and leave the other only slightly stretched. You can then blend them so you can pull out more of the core. 

[Nigel G]

Wow, I never thought I'd get a mention there. cool.

Thanks guy's.

That's made my day  

Thanks Steve, I might of missed that if you hadn't posted it.

Edited January 30, 2017 by Nigel G

[Samibotss]

100 pages and counting

[Stub Mandrel]

Keeping it all in one thread makes it easier to delete everything when the images get too good 

[rotatux]

1 hour ago, The Admiral said:

The other thing, as I understand it, is that it is not strictly necessary to have sufficient gain to get from 0 to 1 out of the DAC. First, sky background will take you above the 'floor', and averaging the signal from all the subs will, provided you are not doing integer arithmetic, allow interpolation between DAC units. The reason is that the photon and other statistics will sometimes give a zero, and other times 1, and perhaps occasionally 2, and the average will be somewhere between. So may be it might be possible to use a lower ISO to advantage.

Thanks for pointing that Ian. It was already discussed in the thread (which I have read once entirely) so I was aware of it, and is actually one of the triggers which made me come back at Alt-az imaging

But it's also a matter of precision: if you get one bit (literally) of signal out of each sub, it would take 256 subs to gain 8 bits of precision (not taking noise into account) and have something to stretch -- maybe less bits would do, I take 8 as a known reference. Also, depending on sub exposure, you could also get less than a full bit of signal (lol! I like quantum physics ), needing even more subs. There's also the matter of image depth through imaging software chain: if I get subs with 1-bit of signal each it means they are at position 12, so to get 8 bits of precision requires software to process at least up to 20 bits.

That's where I may be hitting Regim's 16-bit depth limit (of images). On M42 all was fine but on Rosette and Horsehead I feel I'm at the stretching limit. With the number of subs I take, the remaining noise should be near level 0 or 1. I stop stretching steps when noise becomes significant, but at the same time I understand there's no more signal to come because I've used all the bits within available depth. Feels like a dead end -- though I'm in the process of trying to "pre-scale" the images, which *will* saturate more stars but I hope allow stacking to expose more bits of signal.

[rotatux]

6 hours ago, Filroden said:

Here's my latest rendition of the Rosette using Ha as Luminance and some very poor RGB data to add colour (there is now no Ha in the colour data).

Not so poor ! That RGB did much good to your image, with nice star colors (even if it lacks a bit of blue) and delightful and delicate color change between red, pink and orange in the nebula. Eventually it's not all red ;-)

 

4 hours ago, Herzy said:

I took this on Saturday with the clubs SE mount and an AT72ED from a dark site. I can't get the core to look right. The nebula was so bright even in 45s subs that it appeared all white. I layered some old pictures I had over it to make it more visible, but it still is blown out. I also don't like the blurred feeling to the image. Seems like the detail is all blurred.

Thanks for that superb image. I knew all this region is dust and feature rich, but seing it all revealed like this blows me off. Don't mind blurring too much, some images (including this one) are better appreciated as a whole rather going into the details.

[mxgallagher]

Thanks for all the tips and support. I'll have a go at processing again in GIMP 2.9 using curves rather than levels and see what I can get. Hopefully I'll get another clear night soon - I think I can probably push the mount to 15s subs if I get the tracking spot on, that plus more data should help.

Might also try some other targets - only really went for m31 as it was easy to get in frame using my finder

Thanks again 

[Herzy]

5 hours ago, Nigel G said:

I just had a quick go at reducing the highlights and boosting the shadows, ( hope you  don't mind ) I think it would work better during initial processing,  there's a lot of nebula and dust in there ?

I have done this on my tablet so can't see if I have over done it until I get to my pc. 

It's a great image, I would love to have a go from a fits file.

Nige.

 

Don't mind at all! You made the faint dust really pop! It is a little oversaturated, but that's an easy fix. When I get home from school I'll link the full stacked file so you can give it a go. You'll see that the core is way overexposed. The layering helped a lot.