Triffid in HaRGB

[DJScotty]

Hi there all...

Been a looooooooong time since I have done any imaging.
Anyway, the camera is all fixed, I have a moonlite focuser on the 10 inch newt and my guiding is sorted. Only a slight adjustment to the secondary is now required to have everything as good as I am willing to tolerate.

The Triffid. (Nowhere near as good as Mr Peter Ward)

Ha - 5 minute subs, 9 hours
RGB - 2 minute subs, 5 hours per channel

HaR blended 50/50

Full calibration. CLS filter

Atik 11000 on AZEQ6.

Thanks for looking, and as always, C&C welcomed (encouraged, as critique builds improvement)

Cheers,

DJ Scotty :D

[RickS]

Good to see you imaging again, Scott. Quite a decent M20. You've managed to keep the reflection neb looking good which is tricky when adding Ha.

Cheers,
Rick.

[DJScotty]

Thanks Rick. Great to be back in the saddle again.
I am thinking about doing something with a star mask. Do you think it will add or subtract from the image. Never done a star mask before

[Peter Ward]

I guess my recent M20 made an impression :thumbsup: but it's great to see anyone getting back into imaging after such a long hiatus

I would suggest you try *much* longer subs. Mine are typically 15 minutes...and have been extending toward 30 minutes of late with narrow band filters ;)

A good effort just the same!

[DJScotty]

It made a mighty impression Mr Ward.
In the past i have done 30 minute subs with narrow band but I am currently struggling with my oag as it is a m42 thread which seems to be interfering with the performance of the m48 mpcc. Add to that i can't get the guide camera to come to focus with the oag due to its position in the imaging train. So I am stuck with a separate guide setup which of course brings flexure into the equation hence the shorter subs. Going to test out 10 minute subs tonight on the lagoon and see how bad the flexure is.

Thanks for your feedback peter. Appreciated
Scott

[glend]

Nice image but i can not grasp the need for super long subs in narrowband. Cameras like the ultra low noise, high sensitivity ASI1600MM-Cool are getting very nice results in narrowband with 300" (5 min) subs, sure you need a number of them, minimum 20 probably, but it makes mount, guiding, much less probkematic. I don't want to take anything away from the image posted here, but talk of 30 min narrowband subs is rapidly becoming 'old school' with the new camera developments.

[DJScotty]

Thanks Glenn.
You raise an excellent point. The other reason for the shorter subs is an experiment. In theory 150 x 2 minute subs should give the same results as 10 x 30 minute subs should it not? And you are absolutely right. Short subs are certainly easier to guide etc. The only issue is storage of additional data and longer processing times.
I am very tempted to off load the atik11000 to buy one of the zwo cameras you mentioned

[strongmanmike]

Welcome home Scott :hi:...a nice start back on the..?..often frustrating hobby road that we have somehow managed to become a little addicted too :thumbsup:

Mike

[Peter Ward]

Ah..this old chestnut. :)

Let's say you have a noiseless 95% QE camera ( I wish :) )......then one might be tempted to say you could stack hundreds of 2 second exposures and expect to get a great result.

Sadly the physical reality is the photons are simply not raining down fast enough for that to work well with very dim objects/structures. Shot noise will dominate the image.

Guess I'll have to go back to my "old school" KAF16803 sensor... chilled to 65C below ambient... and calibrate out the noise...a good deal of which is from cosmic rays. ;)

Anyway...the point is to explore what your gear can do and to have fun in the process :thumbsup:

[RickS]

It will depend a lot on what you do with it :) I use star masks for a bunch of things but probably most commonly for reducing star size and boosting star colour.



I think it's a little too early to read an obituary for "old school" imaging yet. It still seems to work ;)

The new CMOS technology is promising but it has a way to go before it's a solution to every astro imaging need. The ASI1600 sensor does not suit long focal lengths and it's only a tiny chip, 1/4 the size of the one that Scott is using and 1/6 the size of mine.

I'll be happy to switch cameras when I can get something better than a KAF-16803 sensor for the sort of imaging I want to do, but I don't think it will happen for a while yet. In the meantime I'm very pleased that there's a low cost alternative to DSLRs at the entry level.

Cheers,
Rick.

[DJScotty]

Thanks Peter. That has cleared that up in my head to some degree. I guess it comes down to being "lucky" enough to have the sensor collecting particular photons at that particular time. Add to that the download time and the dithering delay, you are missing a few photons there I guess. Having longer exposures increases the likelihood of collecting those elusive photons and getting the signal above the noise. But on that train of thought, similar to the whole monkey randomly typing the complete works of Shakespeare, if you have enough short exposures you will get a decent result - EVENTUALLY... But, how long will that take!?

once again, thanks Peter, that has helped

[DJScotty]

I really want to try to make the stars have that separate/ "3D' appearance rather than having them be a "part" of the black(ish) background, if you get what I mean.

[DJScotty]

Thanks Mike. Good to be home

[Atmos]

You've done a nice job there Scott, the KAF-11002 sensor is notoriously noisy (read noise) and not a friendly narrowband sensor due to also having quite a low QE compared to many newer sensors. It is a fantastic sensor for LRGB where read noise isn't so much of an issue, even better when coupled with a 50mm for wide field! Sadly, for narrowband you do need to be pushing 1 hour subs for that fainter stuff.

With the ASI-1600 comparison though, yes it has a really low read noise but as Rick has mentioned, it is not suited to longer focal lengths due to the tiny pixels. At gain 0 the 1600 is at par with the 16803 (they become sky limited at the same time[difference in read noise approximately equals different in pixel size]) but the 16803 has 5x the well capacity. At unity, the 1600 reaches sky limited 3.75 times faster but saturation 40x faster!

When you get that OAG back on Scotty you'll be able to push that Ha a lot harder that's for sure :) The Atik 11000 sensors is a great one, just isn't overly narrowband friendly without long exposures :)

[DJScotty]

Thanks Colin. That certainly is some food for thought. I think after long thought over the past few months that the 11000 will stay unless it breaks down again.
Tried 10 minute subs tonight. Shocking flexure. So 5 minutes it is until the oag is sorted.

Anyone know of a celestron oag for sale :lol:

[Placidus]

The reflection nebulosity came out really well using your method. Well done!

I understand your need to use short subs to get round differential flexure. Short subs work fine with really bright targets and fast F-ratios. Eventually, you'll want to photograph fainter things and off-axis guiding (or an instrument with no differential flexure) will be the way to go.

Regarding exotic CMOS sensors and electronics, I agree wholeheartedly with Peter, Colin, and Rick.

Consider an extremely faint target, say the outermost super-faint and rarely imaged chevrons in the Helix, or the ultra-faint OIII bubble near NGC 602. I've imaged parts of these where there may not be even one single photon per five minute sub per pixel at 3.5 metres focal length. You need literally tens of hours of exposure with a 20 inch scope. Readout noise is overwhelming. A very quiet chip will help. But even with fancy electronics, you will always do far better with one hour subs than with 5 minute subs.

For more routine objects, not blindingly bright, you can get away with shorter subs, but you will still always do better with a few longer subs than with squillions of short ones.

[DJScotty]

Thanks m&t for your comments and thoughts. I take them with high esteem. I have manged to fix all the problems with the oag and am pulling some lovely 10 minute subs. So i will see in the morning once I get some flats applied to my shots.
Once again thanks for your time and thoughts

Scott :thumbsup: