Xiga

This is going to be fascinating to watch@ollypenrice! Can't wait to see your results with this once you've ironed out all the kinks.

ps - TAIC recently did a presentation on the RASA, specifically the 8" version. Could be worth a skim in case it contains a few nuggets of information. 

I've also ordered one of these 2" CMOS 3.5nm filters, but just the Ha one. Looking forward to using it but am pretty relaxed about delivery time, as we've no astro dark up here in N.I for another month or so anyway. 

Ps - I was watching one of The Astro Imaging Channel's YouTube videos recently, the one on the RASA 8, and the presenter said that Fast filters (I.e ones that work down to F2) are only needed if you are using filters of around 3nm. He said even 5nm filters work just fine on fast optics. Just thought I'd pass it on in case it proves useful to some (assuming it's true of course!). 

Thanks all ☺️

On 30/06/2021 at 18:56, Allinthehead said:

My image below made the shortlist😀

 

Congratulations Richard! A real badge of honour even to just make the shortlist. Well done! 👏

I used 1s Flats when doing Broadband imaging. For Narrowband it was longer, I think they were in the region of 7s to 10s. 

Try not to use super fast exposures for your flats if you can avoid it. For mine, I just plonk my iPad onto the dew shield with a piece of opal plastic in between as a diffuser. I then lower the screen brightness until a roughly 1s exposure gives a histogram somewhere in the middle. 

Seeing as i haven't imaged anything since October of last year (don't ask!) i've been forced to get creative and dig through some old data to see what i could come up with. As it turns out, i had some Ha data of the Crescent Nebula taken with my Ha-modified Nikon D5300 and SW 80ED from way back in Nov 2018 that never made it into a final image. Last October I did a mosaic of the entire Cygnus region in SHO for which i used an ancient 50mm Zuiko lens to shoot the Sii and Oiii (i did the Ha at 135mm) and so i had the crazy idea to try and use the 50mm Sii and Oiii data together with the SW 80ED Ha data to see if i could make something even remotely resembling a passable SHO version of NGC 6888. 

Try as i might, i simply couldn't get the Sii and Oiii data to register to the 80ED data. Hardly surprising i suppose! So in the end i just used PS to rotate and scale them to get them as close as i could. I was actually surprised at what came out colour-wise, even though the Sii and Oiii channels are obviously nowhere near nuanced enough to provide any small-scale structure to the colours they imparted. I was also expecting to just have to resort to using white stars in the final image, so I was even more surprised when i was able to generate useable SHO star colours for the majority of the stars as well. All in all, quite an enjoyable endeavour being able to turn old unfinished data into something half-decent (i hope!). 

Full details:

13 x 1200s (4.33 hrs) of Ha; Nikon D5300 at ISO 200; SW 80ED

21 x 1200s (7 hrs) of Oiii; Atik383l+  Zuiko 50mm lens @ F4

11 x 1200s (3.67 hrs) of Sii; Atik383l+  Zuiko 50mm lens @ F4

Stacked in APP, processed in PS. Downscaled in post to 65% of the Ha-80ED res. 

CS folks!

Good luck with your D5300 Michael, you will do very well to find a better AP camera for the money. I got mine back in 2016 and sent it off to JTW Astronomy (who luckily for you are based in Amsterdam) for Ha modification and it's been a pleasure to use ever since. I'm lucky to now have a cooled mono astro camera, but i still have my D5300 and nothing will ever make me part with it, it's that good. 

FWIW, i've never encountered the concentric rings problem in any of my images. I used ISO 200 exclusively, but then i never imaged at a fast F-ratio, i was always at F6.3 so maybe that was the reason. In any case, it's good that there is now a fix for those who were affected by it. Mark is a true genius it has to be said. 

The picture above is just a low res version from the Irish Times' website. I've attached a full res one below for completeness:

6 hours ago, tooth_dr said:

A massive well done to Ciarán @Xiga who was runner up in the Dublin Institute for Advanced Studies astrophotography competition, Reach for the Stars! 
 

https://www.irishtimes.com/culture/art-and-design/reach-for-the-stars-the-best-of-irish-astrophotography-1.4575756?mode=amp

 

Thanks Adam. Very kind if you to post this so cheers mate. 

It came as a bit of a shock I admit. I wasn't expecting it at all so it totally made my day when i found out ☺️ 

Alas, I don't get to take too many photos these days. This was my most recent one, and it was from last October! 😕 I really need to get my mount back so I can get back in the game. It's been over 6 months months now...☹

Reading this (and being Irish) i couldn't help myself 😅

ps - The overly-large moons do bother me a bit i must say. 

That's sumptuous Tom. Striking, yet somehow subtle at the same time. And always nice to see something a bit different too. 

10 hours ago, Allinthehead said:

Yes the mount is outside all year round and is protected by one of these.

https://www.firstlightoptics.com/telegizmos-telescope-covers/telegizmos-365-scope-cover-for-8-9-fork-mounted-scts.html

It's a great cover but there can be a little moisture on the mount at times. No worse than what you might expect on a humid night.

Dew shield works very well, no need for anything else.

Thanks Richard. Good to know, as I've no room for an obsy, but maybe something like your setup could be within my reach. Cheers!

Richard, I didn't know you used a pier. So do you leave your mount outside permanently? I see you don't have a Dome or RoR, so how do you protect the mount from the elements, in particular moisture? 

Also, do you need to use any other form of dew control other than the dew shield?

Well done Spongey and Happy-Kat! 🥳 

It really was a cracking data set. It's so nice to actually get to play with data, rather than fight against it (as is usually the case with my own, lol). 

1 hour ago, PadrePeace said:

Shot this over three sessions for 8.5hrs of integration. 1000 x 30s subs, 1x1 binned, gain 200 on my uncooled ASI234MC strapped onto my APM107/700. 
First time I’ve done the Needle and quite pleased though it needs a few more hours, but that will have to wait until next year as the UK dark window is closing fast now. 
Hope you enjoy this. 
Clear skies

 

That's an incredible image for what is essentially a Planetary camera. Your perseverance (1000 subs!) has certainly paid off. Touché! 

ps - If you want to see an absolutely insane Lucky imaging DSO image, then check out the one below. He took over 40k of Lights, ranging from 0.5s to 7s. I can only assume he has access to a SuperComputer 😂

https://www.cloudynights.com/topic/568316-m82-full-power-with-short-exposure-t300-qhy5iii-290-m-qhy5iii-178-c/

23 minutes ago, vlaiv said:

There are several things I would like to answer here.

First - about amount of data in channel.

If you do proper color calibration - then although you spend say 1/4 of the time on blue - you will have "proper" amount of blue. Only difference will be in noise. For any given SNR you can boost your signal to needed level - but since you have fixed SNR with set number of subs stacked - you'll also amplify noise to match (SNR does not change when multiplying by a number).

However - above has nothing to do with saturation. Don't mix the two.

Color in astronomical images has been topic of much controversy and I'll offer my view on it.

You want to preserve RGB ratio in order to preserve physical property of recorded light. This is best we can do as far as color goes. This also means that we need to do color calibration properly if we want to be able to do that - and that means that we will end up with RGB ratio for each pixel that represents color of the light in that pixel.

If you only shot 1/4 of the time for blue channel - it will be multiplied with certain number to get accurate RGB ratio (color calibration) - that will also multiply the noise. You will end up with proper RGB ratio for your image after color calibration - but channel that lacks exposure will be noisy.

In fact - I would say that if you are going to sacrifice a channel for imaging time - let that be red channel.

Blue channel is attenuated the most by atmosphere. Sensors also tend to be the least sensitive in this part of spectrum. Even if you dedicate same time to each of channels - blue is going do get worst SNR because of that. There is also photon energy. Blue part of spectrum has shortest wavelengths. For same energy in R, G and B - given that shortest wavelength photons have highest energy - there will be the least photons in blue part of spectrum. That means the least signal as signal with photo detectors represents photon counts.

If you can - expose the blue channel the longest.

By the way PCC in PI will not produce accurate color.

In the end - you need to think how you ended up with less data.

There are multiple ways to end up with less data.

Say you only shot 1/4 of subs in blue in comparison to red and green channel - but you used average stacking method, and you used same sub duration.

Then you "don't need to do anything". One sub will contain the same amount of signal as stack of 20 or more subs using average method. It is only the noise that will be different (average of 20,20,20,20 is the same as single 20)

If you used 1/4 exposure time for blue channel than others - then you need to multiply value of blue subs with 4 to "equalize" them ( if you have 5,5,5,5 and you add average them you get 5, while others will be average of 20, 20, 20, 20 = 20 - so you need to multiply 5 with 4 to get 20).

If you used same duration subs - but used additive stacking - you again need to multiply blue channel with 4 to "equalize" things (again 5+5+5+5 is 20 - so is 4x20).

 

Thanks Vlaiv 🤙 I only picked Blue at random really, not because i would intentionally choose to shoot less of it, but it's good to know that Red is the channel one could potentially get away with less of. My query was really just one born out of curiosity, because i can definitely see me encountering this situation at some point (1 weak channel) and no opportunity to add to it for a long time (perhaps the following year) so i was just curious what would happen, and you've answered it perfectly so thanks! It makes total sense too. I just wasn't sure if i would need to multiply the weak channel myself or whether the colour calibration routine would effectively do that for me, and it sounds like it would. 

2 hours ago, ollypenrice said:

 

2 hours ago, ollypenrice said:

 

Multiple (phone!) post. Mods please delete. 

2 hours ago, ollypenrice said:

 

Multiple (phone!) post. Mods please delete. 

2 hours ago, ollypenrice said:

 

Multiple (phone!) post. Mods please delete. 

2 hours ago, ollypenrice said:

It's a good question and, since I wouldn't start to construct an image with a significant inequality between colour channels, I have no experience on which to draw. (Sorry if that answer sounds a bit 'holier than thou' but it's the truth. I don't recall trying this. I'll work on an image with, say, one sub short or maybe even two in a stack of twelve per channel but I don't think I've tried to fix a greater imbalance than that. )

I think, technically, that you can stretch the short channel to the same point as the others and will find that it's all there but will have far more noise. You could then noise reduce it and hope for the best. I'd be interested to see if @vlaiv agreed and suspect that he would, but I don't want to speak for him.

There's also a bit more to it, sometimes, viz, 1) using your RGB-only as you would use short subs for controlling a very bright part of the image, overexposed in your luminance. Yes, you could shoot short luminance but you may already have what you need in the RGB itself. Apart from something with the dynamic range of M42 I often find this works very sweetly, but it does require full quality RGB and precludes binning the RGB in most cases. 2) Stars are often much better in RGB than LRGB. They are both smaller and more colourful but, again, they need to be from a full quality RGB layer rather than a 'fixed' one.

Olly

Thanks Olly. It would certainly make for an interesting comparison I think. 

I don't get much opportunity to image these days (I completed all of 5 images in 2020, and none so far this year) so I guess I'll find out myself what the precise downsides to this are soon enough! 

@ollypenrice can i ask a technical question of you please? I'm about to get into LRGB imaging myself for the first time, and i was wondering, what happens if you have significantly less exposure in one of the colour channels? I know the answer is of course just to shoot more of it, lol, but for the sake of argument, let's say you wanted to make an image with what you had, but you only had 25% of Blue vs the other channels. When you do colour calibration (e.g PCC in P.I) will this account for things, to the extent that the image will have the 'correct' colour, but will just need the Blues saturated more, or will the colour balance be way out of whack? Or alternatively, would the Blue data need boosting at all? I know APP has the option to add a multiplication factor to any channel when combining the RGB together.

ps - Like Adam, i too bought a 268M but i haven't had a chance to use it yet. I'm already starting to wonder if i should have gone for the Colour version instead (not for quality reasons, just mainly so i can get some sleep while imaging! I don't have a permanent setup, so have to resort to using a filter drawer). 

7 hours ago, Adreneline said:

Thank you Ciarán.

I imaged the 'whole thing' last December with the Samyang ....

... but the RedCat can't capture the same fov hence the focus on NGC7822 itself.

Cosmic Question Mark fits the bill very nicely although to be fair just about everything we image is a bit of a question mark  

I might have to try a mosaic with the RedCat and get a bit more detail than the Samyang offers. Another project to add to the list!

Thanks again.

Adrian

 

Very nice Cosmic Question Mark Adrian with the Samyang 135! Looking forward to the Redcat version now. Should make for an even more awesome Cosmic Question Mark.

Ok, ok, i'll get my coat....😁 

Very nice Adrian.

How does the 'Cosmic Question Mark' sound? 😋

There is a small circular patch of Ha below the main object, which doesn't usually make it into most images of NGC 7822, but when you see the whole thing, I think it looks like a question mark. 

https://images.app.goo.gl/GQiJ1oHrfVTQaYUJ7

Oh, what data! I tried shooting this myself a couple of years back, but i was so disappointed with the quality of the data, i didn't even bother to process it fully. This data set, however, was an absolute joy to process!

For this, i used APP to create a Super Lum using both the Lum and RGB. APP also used to remove any gradients, combine the RGB, and do star colour calibration. Then into PS for the rest. 

The RGB was stretched manually in PS using Shadows/Highlights (to preserve the colour, although Arcsinh stretching also worked well). Some use of the Dehaze filter in PS, then Topaz Denoise AI used for NR and sharpening (core only). 

These days i always try and incorporate Sternet into my workflow, but on this occasion i had to admit defeat and resort to good old star reduction instead. I used a host of options, Noel's and Annie's actions, some use of the minimum filter, and also Images Plus too. 

Cheers!

19 hours ago, Spongey said:

The only two useful gains imo (for DSO imaging) for the ASI2600 are gain 0 and gain 100. Everything else you just sacrifice dynamic range for minor gains elsewhere.

Gain 0 for ZWO = Gain 0, mode 1 (High gain mode) on QHY.

Gain 50 for ZWO = Gain 56, mode 1 (High gain mode) on QHY.

Thanks for the spreadsheet, very kind of you to share that with us 🙏

Can i just check something please - should the 2nd line above actually read: Gain 100 for ZWO = Gain 56, mode 1 (High gain mode) on QHY ?