The "No EQ" DSO Challenge!

[Nigel G]

My last night imaging session didn't go to well either.

A nice clear night, 12:30 my target was in a good position, so with the LP filter in place I lined up and focused, took a test 60s to see what was visible, a good test, I can see the Flame and Horsehead.

Grab a quick cup of tea and start with a batch of 40s. First sub looks a bit dull, no detail, second worse still, quick look outside to see clouds.  within 10 minutes full cloud cover and temp rise of about 5 degrees.

The star discovery is a good mount with good tracking and yes it can be moved by hand and sent straight back to a target by pressing enter. handy if I move the mount changing camera battery or orientation. It is easy to knock out of line though, just a gentle touch and it moves. Only the altitude has a clutch to tighten.

Nige.

 

[happy-kat]

I got the mount only from astroboot last year which suits me perfectly.

The mount was level and it should be fine on batteries and it was not cold last night. I suspect it was my aligning as I was using the camera image to centre Polaris. 

[Nigel G]

12 minutes ago, happy-kat said:

I got the mount only from astroboot last year which suits me perfectly.

Just had a look at astroboot, never seen it before, some good bargains there.

Thanks,

Nige.

[happy-kat]

The virtuoso has a clutch for both altitude and azimuth. Have it currently tracking I set it up using the red dot finder on a piece of paper inside we'll see what happens. Astroboot appear to offload damaged stock and often split the mount from the telescope very useful for weird connector bits when FLO don't do them.

[Filroden]

Well, I got another clear night last night so added a few more subs to my NGC1333. My focus seemed to wander so it's not as tight as I'd like. I think the dark nebula is starting to show a little clearer but there is still far too little data to really pull it out without really going to town with the noise levels! It's clearer on the high resolution tiff image and seems to be less clear on this jpeg.

30s subs at -20C, 300 gain and 50 offset: 72 x L, 10 x R, 10 x G, 10 x B

45s subs at -20C, 300 gain and 0 offset: 90 x L, 7 x R, 10 x G, 10 x B

Total L of 103.5 mins

For comparison, here's the original:

And here's the annotated version:

[Nigel G]

Ken.

I think I prefer the original image, darker back ground and brighter nebula, although as you said the new image has quite a bit more of the darker nebula visible. The stars are much sharper in the new.

The crop is a bit different so I could be wrong about the brighter nebula 

I am impressed with the CCD images

Cheers

Nige.

 

[Stub Mandrel]

it's really making progress and I think that the dust clouds are starting to emerge in the first one. How much data have you got the patience to accumulate?

This is exactly the sort of multiple short subs on hard target example we need to develop the processing tools for. I hope you don't mind but I've done a rough stretch and you can see there's more detail that will become less noisy with more subs.

I've watched a (very long) video and there's a better way of getting this faint stuff to show with less noise you might want to try  in photoshop:

Create a duplicate layer, run make stars smaller (noel's actions or any other way) several times over. use spot heal tool to get rid of all bright stars (just set it to a circle bigger than a typical big star and click on them - its magic!). Use dust and scratch to eliminate the remaining small stars, setting of about 15 radius? Then blur to remove all noise and use curves to highlight the nebulosity. Correct the black point. Now mix with the original layer using 'screen' mode and it will brighten the nebulosity without overcooking the stars. You can add in extra sharpening and noise removal.

I think this might work on your image.

These are the sorts of things we need to be experimenting with IMHO!

 

[Filroden]

33 minutes ago, Nigel G said:

I think I prefer the original image, darker back ground and brighter nebula, although as you said the new image has quite a bit more of the darker nebula visible.

Yeah. I delierately went too far with the black point on the original image as there wasn't enough data to see much beyond the central emission nebula whereas the dark nebula is just starting to show in the new image so I've left the background much lighter.

3 minutes ago, Stub Mandrel said:

How much data have you got the patience to accumulate?

I think it's worth keeping at this for a lot longer however it already gets above my altitude limits by around 22:00 or 22:30 so I need an early start (astro dark is about 18:30) before I lose it. I think even another couple of hours might do the trick. The slightly longer subs made it a little easier to process (time wise). Though having to calibrate different exposures with different masters plus needing 4 sets of flats for every session, it all becomes quite a tough processing job.

5 minutes ago, Stub Mandrel said:

Create a duplicate layer, run make stars smaller (noel's actions or any other way) several times over. use spot heal tool to get rid of all bright stars (just set it to a circle bigger than a typical big star and click on them - its magic!). Use dust and scratch to eliminate the remaining small stars, setting of about 15 radius? Then blur to remove all noise and use curves to highlight the nebulosity. Correct the black point. Now mix with the original layer using 'screen' mode and it will brighten the nebulosity without overcooking the stars. You can add in extra sharpening and noise removal.

I'm not great with photoshop but I can see what the technique is trying to do so I may be able to do something similar in Pixinsight. I'd normally do this by applying a mask using just the luminance from the image to protect the brighter areas. The brighter the area the more the mask protects it. However, I've not been brave with the bluring of the noise so I'll just have to hit it a little harder!

7 minutes ago, Stub Mandrel said:

These are the sorts of things we need to be experimenting with IMHO!

Indeed, but I only get a month on any given target before it goes our of reach/view for me, so getting more subs will always be a challenge. The good thing is that my main viewing aspect is broadly to the East so I can extend sub lengths a little. 

[Filroden]

Here's my quick attempt at using that Photoshop technique. It was a little scary at the blur stage as it felt like there was nothing left of the image but when it was blended back into the original I think it's made a difference. There's definitely the start of some feint detail in there.

Also, I got my sub counts wrong: this is from 60 x 45s and 102 x 30s L subs. so closer to 90 mins not 103 mins.

[Stub Mandrel]

Definitely getting there!

[Nigel G]

I tried something a little bit different last night, with the LP filter I upped the ISO to 3200 then 6400 and 30s subs just to see how it would turn out.

Correct me if I'm wrong but a 30 second exp at 6400 ISO = 120s at 1600 ISO but with more noise. The subs were pretty good, both Flame and H/H were visible.

There's 50 x 30s at ISO 3200, 45 x 30s at ISO 6400..... PC crashed second time at 01:15 so I packed up. Was hoping for at least 90 minutes.

I didn't mean to take 2 different ISO sets but I wasn't going to bin the 40 or so taken so what the heck do it anyway.

The offsets, 50 @ 3200 ISO bias, 50 @ 6400 ISO bias, 30 ISO 3200 flats, 30 ISO 6400 flats, 30 x darks of each too.

Hmmm all flats darks and bias taken in the morning while still blinking cold in the conservatory observatory.

Next will be normal settings to compare.

Its not brilliant but not bad either. A lot of noise top centre I think due to flats.

 

Cheers

Nige.

 

[Filroden]

I'm not sure digital ISO works like that. You're still only collecting the same number of photons so each 30 sub is exposed to the same signal, it is just amplified the higher the ISO. There is no substitute for longer individual subs.

That said, there are benefits to different ISOs given we're trying to capture low signal noise we want that signal to cover as much dynamic range as possible without it being too noisy. For my Canon I think it hits the sweet spot of low read noise and wider range at about ISO800 or ISO1600. Only experimenting will tell you what's best for your setup.

Is the noise top centre a reflection of the bright star? I know it's so bright it can cause issues. 

Your stars seem to be showing as doughnuts? Is that a processing thing or focus? I get doughnuts in processing from over smoothing masks but I'm not sure what might do that in StarTools.

[Nigel G]

8 hours ago, Filroden said:

I'm not sure digital ISO works like that. You're still only collecting the same number of photons so each 30 sub is exposed to the same signal, it is just amplified the higher the ISO. There is no substitute for longer individual subs.

That said, there are benefits to different ISOs given we're trying to capture low signal noise we want that signal to cover as much dynamic range as possible without it being too noisy. For my Canon I think it hits the sweet spot of low read noise and wider range at about ISO800 or ISO1600. Only experimenting will tell you what's best for your setup.

Is the noise top centre a reflection of the bright star? I know it's so bright it can cause issues. 

Your stars seem to be showing as doughnuts? Is that a processing thing or focus? I get doughnuts in processing from over smoothing masks but I'm not sure what might do that in StarTools.

While I was taking subs Tuesday night I did a quick test, a 40 second at 1600, and a 10 second at 6400, the images looked identical, now I'm sure there's a lot more to it than that but I don't know much about it yet.....

The doughnuts, I recon either a result of 6400 ISO or over developing, to be honest I hadn't noticed, I think I need new reading glasses. Now I see them. StarTools can deal with them easy enough.

The bright spot is quite big in the uncropped image and I think its to do with the flats, I had my telescope balanced on my shoulder like a bazooka aiming at the PC screen while trying to snap shots off, I bet it looked quite funny.

Cheers

Nige.

 

[ecuador]

On 11/2/2016 at 20:57, Nigel G said:

Correct me if I'm wrong but a 30 second exp at 6400 ISO = 120s at 1600 ISO but with more noise.

 

This is completely wrong. It is from the common misconception that ISO has something to do with sensitivity to light (like in the film days). At both ISO 6400 and 1600 the amount of photons detected are the same and depend on the QE of your sensor, which is fixed. ISO is an amplification applied AFTER the detected photons have turned to electrons and we raise the ISO in astrophotography because it is applied before the ADC, so on cameras with noisy ADC we manage to drown that noise with a stronger incoming signal (but we can't do anything about the sensor noise which gets amplified with ISO). In fact, going to ISO 6400 for most cameras is beyond the useful ISO range (since high ISO is applied digitally after the ADC), so it does not give you anything.

If you take a 30 sec at ISO 200 and a 30sec at ISO 3200 both in RAW and assuming the ISO 3200 has not clipped the highlights, and then stretch the histogram equally, you will have the same result and on some cameras (Canon crop DSLRs for example), the ISO 3200 will have just a little less noise because of the reason I mentioned. 30 sec at any ISO is always worse than 120 sec at any ISO (after you stretch them equally) because you have captured 4 times less signal (photons).

[ecuador]

Good explanation: http://dslr-astrophotography.com/iso-dslr-astrophotography/

[Nigel G]

8 hours ago, ecuador said:

Good explanation: http://dslr-astrophotography.com/iso-dslr-astrophotography/

Thanks for the link. 

I guess I Neen to find the best settings for my cameras, 

All knowledge and improvement though 

Nige.

[ecuador]

3 hours ago, Nigel G said:

Thanks for the link. 

I guess I Neen to find the best settings for my cameras, 

All knowledge and improvement though 

Nige.

The rule of the thumb with your 1200D (and most reasonably recent Canon crop) is to use ISO 1600, unless a lower ISO will allow you to go for a longer exposure.

[Stub Mandrel]

I've tried some experiments performing the same linear stretch on 30-second subs at ISO100, 800 and 1600 from my 450D.

The basic assumption is that you need to stretch 800ISO twice as much as 1600, and 100 ISO 16 times as much.

To simulate this I made three 30-second RAWs and converted to 16-bity tiff without any changes.

First I left 100 ISO alone.

I used curves to scale 100 ISO so 16-->256 and 8-->128 (second point needed to get a straight line) and similarly to make 800ISO 128-256

After this the 800 and 1600 darks looked pretty much identical but the 100ISO, as expected was not too good!

I then applied a gamma correction of 3, which approximates to enhancing faint details without overblowing stars. This brings out the noise pretty much to the level you might see in a single sub, processed.

I thinks this 'empirical' test is perhaps more useful than mathematical tests as it shows what will happen if you stretch, then process data at each ISO in exactly the same way after an initial stretch to scale the data identically.

Converted to jpegs,I think you can see that ISO1600 probably just has the edge over ISO800.

These are crops out of the middle of each image. Bear in mind the ISO800 image has been scaled twice as much as ISO 1600.

It's interesting that there is less 'pattern noise' (horizontal lines) at ISO100.

Perhaps the ultimate test would be to do this with, say, 50 darks at each ISO. I'll leave that to Nigel :-)

ISO 1600

ISO 800

ISO 100

 

 

 

[alexbb]

I'll post 2 of my new images taken in AZ mode since I can't set up the mount on EQ mode to point in this area without the balcony window's frame getting in the way. So.. AZ.

I recently acquired a Ha filter and put it on an ASI120MM. New camera acquisition is planned.

You can find more details about the images and their evolution here:

Clear skies,

Alex

[Nigel G]

I restacked the H/H without the 6400 frames and the dodgy flats, the final image is a vast improvement on the original.

The bright ark at the top is much less, it was easer to process too.

I had settled on 800 - 1600 ISO settings as the best outcome generally but with the new LP filter it needed ago, still learnt about ISO now thank guys.

I'll post both to compare, the first is the original image. The second is 46x30s @ 3200 ISO I may have over done the red levels.

 

Cheers

Nige.

[Filroden]

1 hour ago, moise212 said:

I'll post 2 of my new images taken in AZ mode since I can't set up the mount on EQ mode to point in this area without the balcony window's frame getting in the way. So.. AZ.

I recently acquired a Ha filter and put it on an ASI120MM. New camera acquisition is planned.

You can find more details about the images and their evolution here:

Clear skies,

Alex

I like that you've kept the overlaps in the stacks which show the real difference in noise levels. It clearly shows the benefits of stacking more images to reduce noise.

[alexbb]

The outer area was taken through an 135mm lens in a relatively short session compared to the others. The smoother area has more data taken with a 300mm lens and then all manually aligned and combined. You can also see how the stars are much tighter because of the larger lens and longer FL. And Alnitak's companion as well.

[MattJenko]

Reprocessed AltAz M15. 5 mins each RGB channel in 1 sec exposures.

 

[Filroden]

19 minutes ago, MattJenko said:

Reprocessed AltAz M15. 5 mins each RGB channel in 1 sec exposures.

It reminds me of a firework! Lovely colours. You've still got a bit f gradient in the upper right but I think that's an easy fix. 

[Yamez]

Fantastic image, may i ask how you managed 5 minutes in an alt-az?