I was mucking around with exposure times with narrowband over the weekend, was ~75% moon phase and imaging over Melbourne CBD, absolutely blown away by the Astrodome 3nm filters! What I have learned more than anything is that I do need to work on my PEC training when doing hour long exposures. As good as 1 second multistar guiding with MaxIM DL is, without PEC training I don't think I'll ever truly get round stars at that exposure time with an EQ6 Pro.... Although I could be wrong if someone wants to correct me
Thinking about buying PEMPro as I have heard nothing but praise about it
This is a combination of single 1200, 2400 & 3600 exposures in Ha. I was slowly increasing exposure time to not only see whether I would be able to do hour long exposures without warping too much AND to see when I would become read noise limited. In Ha it seems to be near 2 hours! I was surprised from my location to say the least.
They have been bias and flat calibrated but no darks yet, my dark library does not yet extend out that high. Work in progress.
As for processing, did a light MLT, stretched and then a slight unsharp mask followed by a 5 layer HDR. About 5m work in total
wow, thats an impressive image. Whats far more impressive, is 1hr subs on an EQ6, very well done!. Yes, 3nm sure works in urban enviroments, as you have proved, smart purchase. And no darks! sheesh, awesome.
A great result Colin - and congratulations on your 1-hr sub!
As for darks, I would stick to just master bias (ideally super bias), flats and a bad pixel map. Darks will only inject more noise and are IMO unnecessary, unless you have some strong camera-induced signal with longer exposures.
excellent stuff colin, am pretty interested to see the raw frames to ascertain the difference in quality and vs the risk factor (guiding / satellites / clouds etc). 30 mins is as far as i've gone ... but that was with a dslr - haha.
Congratulations on an excellent image. Good composition. Capture seems faultless. Congrats on the 1-hour subs.
You've wrung out the very last drop of nebulosity in the processing - perhaps a tiny bit less pushed might be even better.
Makes us want to rush out and photograph that "Aladin's Cave" star-filled bubble at 8 o'clock and about half way out from the centre.
Very best,
M & T
Thanks M & T, I do agree that it has been pushed a tad too far. I tried going as far as I could without black clipping it. I was just curious to see what could be dragged out of 2 hours of exposure. Planning on getting a fair bit more Ha, thinking I might TRY to stick with the 1 hour subs though. Takes about half an hour with T-Point to get close enough to SCP.
Quote:
Originally Posted by Bassnut
wow, thats an impressive image. Whats far more impressive, is 1hr subs on an EQ6, very well done!. Yes, 3nm sure works in urban enviroments, as you have proved, smart purchase. And no darks! sheesh, awesome.
I was a bit skeptical of what I would be able to achieve with the EQ6. As nice as it is performing I do think I am going to have to be upgrading the mount in the future, still trying to decide what to go with. Thinking the MYT but I am still unsure and it is still a little way off I think.
My RAW subs do look a bit like that before I start any processing or when I look at them through the Low/Medium stretching through MaxIM DL.
Quote:
Originally Posted by Slawomir
A great result Colin - and congratulations on your 1-hr sub!
As for darks, I would stick to just master bias (ideally super bias), flats and a bad pixel map. Darks will only inject more noise and are IMO unnecessary, unless you have some strong camera-induced signal with longer exposures.
I made a master bias from 200 frames, still worth running the Super Bias routine in PI?
I'll have to have a look at creating a bad pixel map, will save near 300 hour in taking darks
Quote:
Originally Posted by gregbradley
A beautiful and deep Ha image Colin. Very impressive.
Thanks Now I just need to get another 80 hours to catch up to a proper deep field!
Quote:
Originally Posted by rustigsmed
excellent stuff colin, am pretty interested to see the raw frames to ascertain the difference in quality and vs the risk factor (guiding / satellites / clouds etc). 30 mins is as far as i've gone ... but that was with a dslr - haha.
looking forward to seeing more!
I did a Linear Fit and then the same processing on all three images. They're full res and ~3mb each.
I think star shapes would be more influenced by PA, focus and tilt rather than PE, so long as your PE is corrected out via guiding. It's always good to experiment and find out what works best with your equipment.
I think star shapes would be more influenced by PA, focus and tilt rather than PE, so long as your PE is corrected out via guiding. It's always good to experiment and find out what works best with your equipment.
That's a good point, could end up being PA. A 23 point model was saying I was within 18" of SCP so I figured that would be close enough for hour long subs... Maybe not!!
I think I'll have to do some shorter subs to be able to check for tilt, hour long is a bit long!
My RAW subs do look a bit like that before I start any processing or when I look at them through the Low/Medium stretching through MaxIM DL.
Hi Colin,
I can see why your picture looks different to mine.
The long subframes even at 1200s have over exposed the center of the Tarantula.
The center is very bright.
I had 1 hour of subframes in Ha binned 1x1 stacked from my 8" f6 Newt. last December.
I made a cropped comparison with mine by rotating & re-sizing mine etc.
I reckon if you did some shorter subframes for the center & blended it in it would be better.
My finished picture was here when I added all the LRGB Ha together https://www.flickr.com/photos/247194...in/photostream
I made a master bias from 200 frames, still worth running the Super Bias routine in PI?
I'll have to have a look at creating a bad pixel map, will save near 300 hour in taking darks
Master Bias will inject some minor noise, while Super Bias will not induce any noise. It only takes one or two mouse clicks to generate a super bias from master bias...
That's a good point, could end up being PA. A 23 point model was saying I was within 18" of SCP so I figured that would be close enough for hour long subs... Maybe not!!
I think I'll have to do some shorter subs to be able to check for tilt, hour long is a bit long!
Hi, Colin,
Rigid camera tilt will show up in a tenth of a second. It is independent of frame length. Camera tilt will show up as stars that are in focus along a line (which may be vertical, horizontal, or diagonal) across the image, but elongated 90 degrees to the line by progressively greater amounts away from that line.
Camera flop is different - the camera can be on square in some parts of the sky but move under gravity in other parts of the sky if the attachment is rickety. You can again test that with very short exposures on a bright star - just check different parts of the sky. The direction of flop can change across the sky.
Incorrect polar alignment can be spotted because the pattern of star enlargement is that of field rotation. Little star trails rotating a tiny bit about your guide star (which might be at the edge of the frame, not necessarily in the middle). I see no evidence of this in your shot.
18 seconds of the SCP is superb. Ten times that is fine, so long as the HOUR ANGLE of the error is roughly 90 degrees (say within 45 degrees) of the hour angle where you are photographing. We (and many others) routinely put our polar axis about 150 sec arc WEST of the pole, and we then photograph between hour angles of about +/- 3 hours of the meridian. It helps with guiding but causes negligible field rotation.
Out of focus stars will of course be blurry but symmetrical on-axis. On very large chips, out-of-focus stars in the corner can look like flying saucers.
Other things that can cause funny stars: wind buffet, momentary loss of guiding due to tiny clouds, and grit causing static friction (grabbing) in bearings and gears. Personally I don't think you have a problem that needs fixing.
Trish and I routinely do 1-hour subs. They give relatively clean noise-free backgrounds at our dark site. Our stars aren't exactly round, but they're not exactly round in a 1 minute shot. It's nothing to do with the long exposure, it's more about hanging 80 Kg of scope and cameras off a not-so-expensive mount. We don't ever get burn-out in nebulosity, but that's because the camera chip (16803) has sufficiently deep quantum wells. 3nM filters have no effect on nebulosity because they let 90% through, but they help prevent star burn-out.
I'm swearing at you, because with the detail in your sub I'm gonna have to opt for 3nm filters when I go NB!
Slawomir, how many bias shots must I take to make a super bias worthwhile?
Quote:
Originally Posted by Slawomir
Master Bias will inject some minor noise, while Super Bias will not induce any noise. It only takes one or two mouse clicks to generate a super bias from master bias...
Thats very cool -loads of depth there. Should be a great shot when finished
I purchased my belt modded and hypertuned EQ6 from Al Sam, because he regularly did 1 hr exposures with it. I'm personally not brave enough to go that long with so many clouds and satellites about, and the likelihood of losing subs, but after seeing yours maybe I can go to 30mins on the next project.
Looking good Colin, quite amazing what can be stretched out of the Tarantula region, huh?
1hr subs hey?...Oooooh scary I haven't ventured past 15min, not because my rig can't handle it but rather I'm just time greedy and perhaps a little paranoid about losing bigger chunks of data.
Slawomir, how many bias shots must I take to make a super bias worthwhile?
I had a master bias made from about 200 bias frames to be on the safe side, but pretty sure it will work fine with perhaps 50 or so. You need to make a master bias first, as SuperBias tool creates super bias from a master bias, not individual bias frames.
That's a good point, could end up being PA. A 23 point model was saying I was within 18" of SCP so I figured that would be close enough for hour long subs... Maybe not!!
I think I'll have to do some shorter subs to be able to check for tilt, hour long is a bit long!
I agree with MnT, that 18" is very good. 1-2 minutes is usually ok.
I haven't ventured past 15min, not because my rig can't handle it but rather I'm just time greedy and perhaps a little paranoid 
about losing bigger chunks of data.
