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IC 1396, MN190, DSLR... but noise and not good timing


AndyUK

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Wonderful start, we have the same kit btw.. as does Deneb (Nadeem)

I have the USB filter wheel and 314 + power lead all bunched with a coily cable tidy and so far have had no issues, I have tried a 10 minute sub with bunched and not with no change in detail... maybe I'm lucky :)

Looking forward to the summer,

Maybe we should all get together take a filter choice and share the data :eek:

.

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LDN1105 is the Elephants Trunk nebula which is a HA emission nebula and Vdb 142 is actually a small blue reflection nebula at the head of the elephant
Thanks for clearing that up Kevin...!

Uranium - I've just tried all 3 astro shops in my neighbourhood, and none of them have any extension tubes, let alone a 50mm one :(. One did have a 1.25" (which I know would have done), but, call me fussy, I want a compression-type, not a cheapy screw-only (which is what a butchered SW barlow would have been). The same shop also had an empty box where a 2"/50mm used to be, but the owner was ill today and the assistant had no idea where to start looking for it - I just wanted destined to buy anything today... or use the Atik tonight :(.

I know I should be listening more carefully when people start talking about chip to thread distances / inward / back focus and also trying to understand it better, but for some reason my eyes start to glaze over at the very mention of it :BangHead: - I know it's important though so I'll have a search on the web...

(Coco - we have the same kit btw.. as does Deneb (Nadeem)
Yay... :eek:! I'd like to say great minds think alike, but I think it's more luck in my case... I'm not sure I have much of a clue at the moment - All I know is I need to get something reasonable out of it within a few weeks, other my budget holder may start asking questions about my "benefits projection"... :)

Maybe we should all get together take a filter choice and share the data :icon_salut:

I'd certainly be up for that! However, at the moment I'd be limited to Ha - I'm hoping to get the filter wheel and LRGB set towards the end of the summer...
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Actually thats a damn good idea, get a few peeps together to work on one target - each using their chosen filter (L,R,G or :eek:. Though you would have to account for the varying focal lengths of each others telescopes, types (need all fraccys), filter brands (would all need to be using Baader), and whether that particular target is available from each persons location. It'l get done four times quicker :) but needs a bit of co-ordination.

Andy, it looks like youre going to have to order your extension rings online then. Why is it that its always a bank holiday when you really need something?

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Cheers again Uranium...

Why is it that its always a bank holiday when you really need something?
Exactly what I was thinking... :icon_salut: Ho hum... (First light will have to wait - I've seen one on FLO and they were very quick delivering the Atik, so I think I'll go with them...

Coco's idea is indeed excellent, especially as the 3 of us have MN190's and Atik 314L+ :). Target availability might be an issue though - I'm a bit limited from the back garden, but I reckon it could well be worth the effort :eek:.

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ahh... I dont have the MN190 :) Id love to, but its looking like next year when I get that. Im allowed one major purchase per year, and first I have to get the EQ6 before can entertain the thought of an MN190 (drool....).

We'd all be better off if we used our 80mm APOs, which are similar in focal legnth. Hmmm... not much about for 80mm fracs at the moment though, Leo triplet maybe?

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I seem to be "stuck" on imaging with the MN190 at the moment, even though I do also have an Equinox 80. I think I may have used the 80 once in the last 3 months... which is a shame as it's a fine scope! However, I'm fully expecting that the narrow FOV afforded by the 314 may well see me reaching for the 80 on some subjects... That's the reason why I originally bought it :icon_salut:.

It's certainly a very intriguing and interesting idea if groups of people with similar scopes / cameras etc could co-operate in pooling subs / callibration frames to put an image together though... :eek:. Sadly the Leo triplet has headed off into my streetlight zone now... and by the time it gets out of it, it will have either set or be hiding behind the Horse Chestnut :BangHead:

(I really must raise the idea of moving house sometime... :))

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Cheers Olly...

I'd be tempted to steer right a bit and mosaic in the Trunk
I hadn't thought about a mosaic - I thought I was going to have to start all over again... Thanks for the idea Olly! With any luck I can get another 25+ subs tonight and if I can shift the trunk on the right to the left of the frame, I'll see if I can give it a go...

(I have a sneaking suspicion that this might prove that I really do also need to buy Registar though :))

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Well over the coming months were going to be getting the veil, and NGC7023 (always a toughie) will be coming into view a bit earlier. They're both pretty big and a mix of the equinox and ed80's (with focal reducers) would work out quite well i think. The focal lengths would differ by about 25mm, but Maxim or registar will fix that in a jiffy.

Let us know when youre ready for some sort of collaboration. It would be an interesting test of processing skills, we could each produce our own version. And maybe if im good for the rest of the year, santa will bring me a MN190... then its hammer time for every dso out there :)

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I've actually already started on NGC 7023 with the DSLR/MN190, although it is a little low (and yes, it certainly is a tricky one (NGC 7023). I'm struggling with noise (surprise surprise)).

However, it would be fun to see what we can get by trying to combine data, but I don't have a focal reducer and (as I noted) I'm a bit restricted with regards to filters at the moment as I only have Ha, but hopefully later in the year I'll have the wheel and LRGB, so I'll get in touch with you then... :)

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Okay, I had another go at this last night and shifted the framing - The noise was still very evident (banding and general noise) and for last night's I had to use darks (as only using bias and flats was horrendous).

Now this doesn't hold up to too much scrutiny as although I tried to match contrast, colour etc etc, try as I might, it's been a nightmare, and to be frank, with all this noise, I think (hope!) I can do a better job with the 314 when I can get it up and running (severely reduced noise!)

I also found that as I'd had to crop the original image to remove some slight misframing over the 2 sessions, getting the two panes to scale accurately wasn't really that possible either and you can very easily see the join (Eric & Ernie joke there somewhere?).

I know I could have played about a lot more with this before posting but again, due to the noise, I'm just treating this as an exercise now - My first attempt at a DSO Mosaic!

I can now begin to understand why this is recommended (and, as I suspected, I think I'm going to need to buy Registar for use with the 314 at sometime probably pretty soon :)), but is there an easy way to colour/contrast match the panes or is this "simply" down to processing skills? Also, when putting the panes together in Photoshop, is there any specific technique...?

post-18819-133877568256_thumb.jpg

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Hi Mike - I started another thread on Mosaics with photoshop - Three options came up:

1. DSS in Mosaic mode (restack from scratch - Although it did create the mosaic, there was still a nasty straight line across it on the DSS output, so I stopped at that point

2. Photoshop - File/Automate/Photomerge (Lukebl suggestion) - Process the separate frames as close as possible and then put the two panes through this. Appeared to work excellently!

3. MS ICE - Same as Photoshop. Seemed to be very quick too...

Here's the final result (produced through PS)

post-18819-133877568689_thumb.jpg

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It doesnt seem to work that way for me, the numbers seem to jump around too much for me to get accurate focus. I prefer the "visual" method that the B or Y mask offers. Why take one minute when you can do it in 30 seconds :eek:

Andy, im not sure whether its worth getting a barlow just to take it apart as its normally the "free" options available becuase SW always throw so much stuff in with their OTAs. You might be better served by getting a set of t extension rings and a couple of rubber O rings (can be found at a hardware shop) to act as variable spacers or to prevent over-tightening. I think my t extension set was 15,10 & 6mm, it was less than 20 quid anyways :)

Not sure if youre aware, when calculating corrector/flattener distances to the CCD - on the 314L+ the distance from the top of the t thread to the ccd chip is 12mm. Also, you will find that the t thread is quite shallow on the camera, so any t thread rings I use (apart from the male/male one I got with filter wheel) doesnt sit quite flush against the camera (threads still showing), so you will gain about 2 or 3mm there too.

I use a B mask to get close but then check in FWHM. I'm certain it is more accurate. To stop the rapid jumping select your star and run it on longer loops, 3, 4 or 5 seconds. These allow the seeing to average out. I reckon on at least five minutes to get perfect focus. It is hugely, monumentally, important and gets harder as f ratio diminshes.

Mosaics: before giving yout two files to ICE pick the one you like best in Ps. Give it a big canvas to fit the other one on and paste it there. Slide it till is roughly aligned. If you have a co registering programme use it but if not a rough alignment will do. Now measure the RGB values in the same spot on the overlapping part of each image and adjust them in curves, each channel separately, on the second best image till they are as close as poss. to the first.

If you have a gradient on one image that isn't on the other you will have to put a well feathered lasso round it and adjust accordingly. You may also need to adjust saturation (or there is a better one in CS3, is it colour intensity?). Check Levels on both as well. Now ICE should do a much better job.

Using Registar co-registered images you can paste one over the other, say right over left, and feather the edge. Then you can do another in which you feather left over right and combine them. You can even do a new version with the panels cropped in different places and combine them in layers. In fact the 'two versions with different crops' trick might work in ICE if you feed it the files in the same order. You could end up with ttwo versions, each with a slightly visible joint, which largely disappear when layered together. Can't promise it would work!

You have a great project here.

Olly

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cheers olly, I'll give it another go. The exposure time was 0.5s for my previous attempts, so I'll try 3 or 4 seconds and see how I get on. Not sure when thats going to be though, even though we've had all this time off but not getting much done due to all this high cloud.

Cant wait til my little one is old enough so we can go to somewhere thats got nailed-on clear sky at times like these.

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cheers olly, I'll give it another go. The exposure time was 0.5s for my previous attempts, so I'll try 3 or 4 seconds and see how I get on. Not sure when thats going to be though, even though we've had all this time off but not getting much done due to all this high cloud.

Cant wait til my little one is old enough so we can go to somewhere thats got nailed-on clear sky at times like these.

Ah, yes, FWHM will give a lively ride in half second subs. If I get, say 1.8 on the B mask I reckon on getting down to about 1.6 with FWHM. But the mask is so fast.

Olly

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Thanks for that Olly - Much appreciated... It all seems very logical, and I really should have thought of some of that myself. I got as far as the big canvas and then using layers, but that's about as far as I got - After that I squinted at the screen whilst applying yet another adjustment to one of the layers which was never quite right...

One other thing I note... Prior to imaging with the DSLR, I line up on a bright star and then use a B Mask to focus (viewing it 10x zoomed on liveview). I then shoot a check frame (10s) and play it back with zoom to check the cross-section point... Yet when I put the raw frames through DSS, I think the lowest FWHM I've ever had is about 4.5 (:)), yet you're noting a value at 1.8 (:eek:) - Would I be right in my feeling that my focusing process is way out?

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remember that focus FWHM values will not be the same for different exposures. You may get 1.0 with a one second exposure and that could rise to, say, 4 after a five minute exposure. It is not the focus that is changing but the seeing. A longer exposure puts you at more risk of the seeing making the focus look worse.

Dennis

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(Phew!) Thanks for that explanation, Dennis...! I was starting to think I might need to go to an optician or get laser eye surgery or something. However, it would be useful to see the FWHM value BEFORE getting to the frame registration stage, so this info from Olly (longer loop for FWHM check) will be very useful when I'm able to start using the 314L.

(I'm still amazed at it being possible to get a value of 1.8 though - There must be some most truly excellent seeing at Olly's place!)

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Using my standard 3 second focus routine and with the Atik 4000s measured in Artemis Capture I get below a value of one ocassionally. Say one night in ten. If I am not below two I change my plans - eg shoot colour rather than luminance, or very long luminance subs that will be used mainly for noise reduction on faint background stuff, with tighter luminance layered on for the detail at a later stage. Remember though, that we have good glass to play with and are at three thousand feet.

Olly

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Hi Mike - Yes, I really must get around to trying APT sometime... even if it's just to test out the FWHM

Olly - I don't think the word "envy" really captures the whole feeling somehow... If I had to wait to get an FWHM below 2... I don't think I'd have started :)!

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