Filroden

35 minutes ago, Gina said:

I'm beginning to think that my best bet is to take new batches of data rather than try to match up earlier stuff to their biases, darks and flats.  I think I've got myself into a bit of a mess - I think I've probably attacked this from the wrong end.  Should have processed data as I got it but I wasn't ready to do that and there was clear sky just waiting for image capturing.

I know. I'm wrestling with this issue myself. I *could* calibrate and cosmetically correct each sub and only save these for later registration, deleting the original raw subs and their associated flats but I'm nervous I'm discarding the raw data and should my skills improve (mainly around cosmetic correction) then I could never go back and deal with them. I could save the raw files too, but that's doubling my storage requirements. I wonder if I'm being too cautious and should bite the bullet and only store the calibrated files making registration and integration of additional data much easier.

2 minutes ago, MattJenko said:

another advantage of 1 second subs is that it negates the effect of seeing to a certain extent. it is not quite in the realm of fast frame rate high res planetary imaging, but it is getting there. I reckon a bigger aperture than my 10", like a driven 16" dob+, you could do bright targets with 0.5 sec subs and then you could really start pushing towards the actual theoretical limits of the optics, not limited by the seeing.

Also, cameras with very low read noise under dark skies could get you to faster exposure times. I think my ZWO ASI1600 can manage 24fps at max resolution (though I'm not sure my USB connection can handle the data traffic). Though this is now in the realms of video astronomy.

12 minutes ago, parallaxerr said:

The main issue is horrendous light pollution though, such a horrible orange noise to the image. The longer nights may mean I can get out earlier but I'm thinking there's not much point starting until gone midnight when the streetlamps go out and the neighbours go to bed! But, work and the nursery run dictate that I can't be doing that really.

Did I read somewhere recently that someone has had good results with an LP filter? I have a 1.25" Baader Semi-Apo which I found VERY effetive in the ST for visual. As I understand, it "overlays a slightly more aggressive version of the fringe killer coatings onto the neodymium substrate of the Moon & sky-glow filter" so I wonder if the 2" version may suit for AP?

If you can't image late, then try for targets above 30 dec to avoid the worst of it. You can remove much of the gradient in tools like Photoshop (GradientXTerminator), StarTools (wipe) and Pixinsight (ABE and DBE) but it does mean you need your target signal to exceed the light pollution. Again, for bright objects like M33 this should not be a problem, it just adds processing complexity. Only the moon tends to be bright enough to make me not image at all. LP only limits my choice (and time) of targets.

Nige has recently be testing a LP filter and his results so far look very good.

48 minutes ago, parallaxerr said:

I learnt this last night! After imaging M33 I slewed to Pleiades as it's one of my favourite visual targets, however, I left the exposure set at 30s. Result = Big bloaty blue (with the achro) stars!

You shouldn't be getting that much bloat in 30s. For targets with very bright areas you might want to try reducing the ISO as this should give you greater dynamic range but there is a danger that you lose the feinter signal into the read noise (in this case, the nebulosity). My own image of M45 used 30s subs (only 30 in total) and it gave a pleasing enough image of the stars and showed the nebulosity. I'm using a CMOS camera though it is cooled and has a very low read noise. However, I was using a very high gain (equivalent to ISO) so had a limited dynamic range. So a DSLR should be able to cope.

25 minutes ago, parallaxerr said:

Hi everyone,

Good to see the thread's still going strong and getting far too technical for my brain! I've been out of it for a few weeks with illness and a back injury, boo.

Anyway, decided to get back to it tonight, I was planning to add to my M31 data only to find out it's now too high in the sky for my mount.

So...next target is M33. Also having toyed with the idea for a while I've decided to give the ST120 a shot, see if I can't capture a few more photons per sub! I couldn't use the St120 for M33, it wouldn't get it all in but no problem for the smaller targets. Really interested to see how the Baader MPCC works in a different scope - the ST120 is closer to the midpoint of the recommended focal ratio range so should be OK.

My ST already has a Moonlite fitted so the camera is hanging well, but I struggled with focusing a bit, the CA made it a little more tricky so may invest in a bahtinov mask.

Anyway, here it is in all it's glory. Results should be interesting although I'm not getting my hopes too high due to the moon glow and random left over fireworks!

I couldn't manage without the Bahtinov mask. It makes things to much easier and quicker. I once tried the focus aid for the mask in SharpCap but found I was just as accurate and much quicker doing it by eye. I'd find focus, move out of focus and then back into focus (just to make sure). Moon glow shouldn't be too bad for another day or two? It sets in another 2 hours so plenty of targets far enough away! Good luck tonight.

29 minutes ago, Yamez said:

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

It's five minutes of 1 second exposures, so 300 subs being stacked.

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. 

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.

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.

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.

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. 

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:

9 hours ago, happy-kat said:

and I slew by hand.

You had me confused for a second! Just checked the mount specs and it has "A great feature of the Virtuoso is the patented Freedom-Find dual-encoder technology which allows the telescope to be moved manually in either axis without losing alignment or positional information. This gives the user enormous convenience and flexibility during observing sessions."

I'd love that for my mount. It's the noise from my slewing that means I don't like setting up too late.

Does it hold an accurate alignment after a lot of manual slewing?

12 minutes ago, sheeprug said:

Sadly, no. I'm assuming I'll have to do manual tracking, and s/w alignment.

SR

I've not had to manually track but I've seen some cracking images on here of aircraft at 33,000ft taken with a manually tracked dob. I think, with practice, you will be able to achieve longer and longer manually tracked images. As above, even sub-10s exposures can, if enough are taken, show some great detail in brighter objects. Also, a simple wedge might make tracking easier as you're mainly tracking in one direction (dec) with small corrections in RA because of poor polar alignment. I remember building one for an old film pentax camera with 50mm lens from a couple of pieces of plastic, hinges and some nuts and bolts. I had to rotate a handle at the same speed as the second hand on a watch and I was achieving 10 min exposures. Now that's a much wider field which is more forgiving, but the principle is the same!

There is also the option of using just the camera with lens too for some wide-field imaging.

59 minutes ago, sheeprug said:

Hi Everybody.  This is a really really interesting thread, so thanks for all the images and conversation, and as a result I want to play too.

Now regarding kit, I have an 14" OO dob, but as it stands no suitable camera. However, there will be budget for one by Xmas so research is already under way. Normally my inclination would be to go to Canon since (a) I've always used Canon cameras and (b) I gather they have better support/features for astro.  However, in another thread on the 'cameras' part of this site it has been pointed out that the sensors used in Nikon cameras have a better noise performance.  

Now I appreciate that the Nikon vs Canon debate is well documented on this site, but I'm wondering if in the alt/az scenario, where exposures are shorter then than for eq, does the low noise performance become assume a greater importance?

Secondly, regarding the scope, i'm assuming a 14" aperture is good, but a FL of 1600mm may be a little long.  Is that too long in practice? 

SR.       

Welcome also and I hope we can get you started!

You scope is quite fast, f4.5 I think. And it gives a reasonable field of view (i've used my DSLR, a Canon 60D, to illustrate what your scope could image).

One thing to remember with field of view with alt-az imaging is that because of field rotation you will need to crop quite a bit of the edges of any image once integrated, so your target ideally needs to fit within about 70-80% of the frame or you could produce a mosaic.

Your biggest issue will be tracking. Even if motorised, your focal length will reduce what you can reasonably achieve. When I first started I was using an f10 9.24" SCT, i.e. with a 2350mm focal length. I was easily getting 8s exposures and was just started to get confident I could achieve 15s most of the time and 20-30s occasionally. That meant bright DSO like M42 or M57 were within its reach. Since then I've moved to a smaller and much faster scope so 30s is now at my lower end of easy. I suspect, with tracking, you could easily achieve 20s and maybe 30s. That's enough for all the targets we've seen in this thread.

Camera choice should probably be driven by its main purpose. If you want a DSLR for daytime photography, get the one that best suits that need. All DSLR could be used for astrophotography and I doubt the different noise levels will make too much of a difference. That said, if you can get a less noisy camera it will help with the processing! Colour DSLR suffer an inherent reduction in sensitivity due to the way it captures colour, using a RGGB matrix. It means at best you're capturing 25% of the available red and blue data (both important) and 50% of the green (not as important except in a few cases). It also introduces colour noise. Field rotation means you're aligning different pixel positions with each frame, so you could be merging blue data with green, etc. It shows in the noise as colour speckles that seem to 'walk' across the image and needs to attention to reduce in processing without losing signal.

However, a DSLR will work! In the meantime you could always try eyepiece projection and capture images using any camera, even one on a phone, by positioning it where your eye would be. It's not as good but it still feels like progress (and when you do get the DSLR you get that feeling of more improvement again!).

I would say the second image has more detail. I suspect it is the combination of lower background noise and also being easier to remove what little gradient there might be without also removing the galactic disk with it. At first glance I'd say the LP filter is making a big difference! 

1 minute ago, Nigel G said:

Which thread should a discussion on a new topic be posted? There isn't a general discussion topic.

I guess its imaging discussion

Yes, I'd have suggested imaging discussion too. 

Be careful with gradients in Orion as some of it could be dust/nebula! Nonetheless, it's a great composition. I woke up at midnight the other night and saw Orion just coming over the horizon. It was too late to set up (my mount is quite noisy so I prefer to set it up before the neighbours children go to bed) but it's a wonderful sight. 

And you can clearly see the horsehead, something that terrifies me trying to capture in short exposures. 

Is this with the new LP filter?

11 minutes ago, Stub Mandrel said:

Imaging on a Budget  - Imaging using Alt-Az and light EQ mounts using DSLRs, not just for beginners

• Mounts - overcoming the challenges (individual sub-topics created by users can easily address EQ, Alt-AZ, Barn door etc.)
• Scopes - achro refractors to budget reflectors (to cover various entry-level scopes, the 130P-DS thread could go here)
• Accessories - affordable extras to get more out of your imaging time
• Processing - getting the most from short subs and limited total exposure
• Help and advice - Ask anything - the one answer you won't get is spend lots of money!
• Showcase - share your successes

I appreciate the good intentions but this is why I feared suggesting breaking out this thread into multiple threads, even if collected under a sub-forum. By your definition I could no longer post in that entire sub-forum simply because my scope is not considered budget (who's budget do we consider low?) and I've moved from DSLR to a mono-CMOS chip (i.e. the very same technology used by that same DSLR).

Conflating multiple techniques will also confuse. Alt-az suffered from field rotation which limits sub lengths. The solutions to which are very different to the limits placed on EQ mounts. EQ mounts come with their own complications, polar alignment, meridian flips, which do not affect alt-az and their solutions are very different to those used by alt-az mounts even if the effect (limited sub lengths) is the same.

We already have an imaging section where each of these can be discussed. Why should users be partitioned because of budget? You can do guided EQ photography on a lower budget and you can do Alt-Az on a higher budget.

This thread has only a few defining limitations - you image using alt-az and barn door mounts and you image DSOs - there is nothing limiting what scope is used, what camera, what tools to process, what filters are used. It leaves us open to find solutions. As an example, I moved to a mono-camera precisely because it helped me gather more data in 30s that a OSC DSLR. I didn't want to mod my DSLR as it compromises it's main purpose (landscape photography for me) and buying a mono-camera was not too different in price (for me) to buying a second DSLR.

I'd suggest a couple of things:

- create a new thread to discuss this very topic to this thread can stay focused on imaging DSOs with alt-az mounts until a conclusion is reached

- first discuss the objectives and outcomes being sought before reaching to conclusions and solutions

With such a low read noise it's going to be interesting seeing what can be achieved with 1000s of 1s shots. Though I can't imagine how long it would take to stack!

It was supposed to be totally clear here all day and all night. But other than a 30 minute window where I could see Capella/Aldebran/Miflak, it's been 100% cloud cover all day  I guess I won't be adding to my NGC1333 tonight or even this weekend.

I've often wondered if we needed more threads to cover what we discuss here but a few things always stop me from suggesting it:

Not many people are actively involved with posting about alt/az imaging. You'd have to think there are a lot more people on the forum to generate enough posts to make a sub-forum work.

We are probably our own worse nightmares because we mix a few different themes into a single post making it very long - maybe if we broke out this thread into a few posts focused on specific elements and these could be better located in existing sub-fora?

E.g.:

A getting started with alt/az imagery thread for the beginners sub-forum to share how we've used more basic equipment and some of the tips we've learnt that allow us to extend imaging times from when we started (<10s) to now (with Nige achieving 120s)

A processing alt/az imagery and how to use the tools we have to their best

A general alt/az discussion

A members gallery specifically for the best of Alt/Az imagery which could be linked from each of the posts

Version 2 of my recent NGC1333. I realised (seeing it on screen from the forum) that I'd left a bad gradient in the upper left and that the entire image still had a green cast (I missed that step). So I quickly reprocessed it and applied less noise reduction but hopefully improved the sharpening. I also cropped it back a little. Much of the remaining visible noise is actually in the chrominance layer but that's not surprising given how few RGB subs I managed to salvage. 

There is a slight loss of detail but the filter will let you do longer exposures (probably not much of a benefit to us) and should reduce noise when integrating as the noise in the background will be much reduced. I see that as a huge benefit. 

12 minutes ago, Nigel G said:

Last nights results.

4x120s plus 10x60s plus 20x45 plus 60x30s, Matching darks, flat and bias. DSS and new found methods with StarTools. 150p Canon 1300D

I need to re stack without the 120's to see a difference, I think I will do a couple of different stacks to get an idea how effective the longer subs are.

My clip in LP filter arrived today

Cheers

Nige.

 

When you think that's only an hour! It's crystal clear with lots of globular clusters clearly visible. And I love the colour.