First Light with Astrodon 3nm Ha Filter - NGC 6888

[steppenwolf]

Typically, my first light image with my new 3nm Astrodon Ha filter took place under almost full Moon conditions but in some ways, this was quite a useful test in its own right as clear skies and full Moons seem to attract one another!  There isn't much in the way of available nebulae around this time of the year so an early riser like the Crescent Nebula seemed as good a choice as any but I had to wait until 00:20 before I could get started. Nice to see the Soap Bubble Nebula in there as well.

Mount: Mesu 200
Telescope: William Optics FLT98
CCD Camera: QSI 683 WSG-8
Guiding: OAG/LodeStar
Filter: Astrodon 3nm Ha
Exposure: 13 x 1200 sec
Date: 09/05/17 + 10/05/17
Calibration: Bias, Darks & Flats

I think I'm going to like this filter .....

[kirkster501]

Wow Steve, that's superb!

Steve

[swag72]

Great Crescent Steve  I'm so pleased that everything is sorted and clearly working so well together. There's going to be some great images from you this summer

[toxic]

wow nice first light and image  

[tooth_dr]

Hi Steve. So much texture going on there. It looks amazing. With it having such a narrow waveband is it hard to see stars to get it framed and focused etc. Compared to e.g. 12nm what are the main differences ?

 

 Thanks 

Adam

[steppenwolf]

15 minutes ago, tooth_dr said:

With it having such a narrow waveband is it hard to see stars to get it framed and focused etc. Compared to e.g. 12nm what are the main differences ?

Hi Adam,

Somewhat to my surprise, autofocus worked seamlessly using exactly the same settings as for my 7nm Ha filter (10 second exposure on a magnitude +6.0 star) so focus, despite the smaller stars, does not seem to be an issue at all. Framing is done by overlaying a facsimile of the sensor over a Cartes du Ciel sky view, adjusting its position and orientation to frame the object as required and then slewing to the correct position. To be sure that the image is accurately positioned, the slew is followed by a platesolve and fine tuning correction. However, although the stars are dimmer, the all important Ha is still 'full strength', there is just much less out of band data so a short exposure and a check on screen for the framing will still work fine.

[swag72]

8 hours ago, tooth_dr said:

Hi Steve. So much texture going on there. It looks amazing. With it having such a narrow waveband is it hard to see stars to get it framed and focused etc. Compared to e.g. 12nm what are the main differences ?

It is worth noting here that the time taken to auto focus depends a lot on the software used. I know that Steve uses Maxim and this involves slewing to a bright star, focusing and then slewing back to the target. SGP focuses without moving from the target frame and so there's little chance of a nice bright star in the frame. To that end, my auto focus exposures are 45s for each step and there's at least 7 steps to focus.

[gnomus]

Congrats on the new filter.

In the past, I used 25 second exposures for my SGP 3nm autofocus.  However, I spent a couple of hours one evening calculating average filter offsets.  A tedious task, but now I autofocus using 5 second Lum exposures then apply the offset.  Since I use a 9 step focus routine (plus one on the calculated focus position), this saves 200s per focus run.  It probably adds up to an extra sub or two over the course of an evening.  Other than the tedium of working them out, is there a downside to using offsets?

[tony210]

Great image! - attractive idea if you can master it as you have done -makes imaging with the moon an option!-Tony.

[ollypenrice]

Super result with tremendous dynamic range. I love this filter. (For some reason I thought you already had the 5nm, Steve. Is this not so?)

9 hours ago, tooth_dr said:

Hi Steve. So much texture going on there. It looks amazing. With it having such a narrow waveband is it hard to see stars to get it framed and focused etc. Compared to e.g. 12nm what are the main differences ?

 

 Thanks 

Adam

Adam, all replies so far have been by auto focus users. If, like me, you are in the stone age of finger-twiddling, then here's my experience...  Framing is not difficult because, for reasons covered by Steve, you get a very visible and structured image of the nebulosity in quite short exposures. However, I focus using B-mask then FWHM and it is sometimes the case that I don't get a workable star in the image. I therefore make sure that I've got a good focus on a bright star nearby. Initially this will be the alignment star I need to set the mount up for the evening. After that a slew out and back is needed. If all this is a bit of a pest, the results are worth it. The Astrodon 3 produces what is almost a ready-processed image, in that it is already packed with contrast and tiny stars once given your favourite stretch. Most of the effort in Ha processing, for me, was in managing the local contrasts, especially the faint ones, and the stars. The filter takes care of both.

The high contrasts of this filter also play really well when adding Ha to LRGB. The small stars don't affect the LRGB stars and the high contrasts add more structure to the red channel.

Olly

[Filroden]

13 hours ago, steppenwolf said:

I think I'm going to like this filter .....

I think so to. That's a lovely image. It makes me feel like I'm looking down through water on a stingray or jellyfish, all illuminated by starlight. It's also answered any question I had about its ability to handle moonlight!

2 hours ago, swag72 said:

my auto focus exposures are 45s for each step

 

1 hour ago, gnomus said:

I used 25 second exposures for my SGP 3nm autofocus

Are you both using binning for the autofocus routine? I also use SGPro and started autofocus at 10s but have since reduced this to only 5s using bin4. I usually run my camera at its unity gain. With 9 steps and processing time it takes about minute to reach focus. I've never had it fail though I did have to shorten the step size when I introduced the Ha filter into the wheel.

[gnomus]

10 minutes ago, Filroden said:

....

Are you both using binning for the autofocus routine? I also use SGPro and started autofocus at 10s but have since reduced this to only 5s using bin4. I usually run my camera at its unity gain. With 9 steps and processing time it takes about minute to reach focus. I've never had it fail though I did have to shorten the step size when I introduced the Ha filter into the wheel.

I use binx2 for all autofocus routines.

[swag72]

1 hour ago, gnomus said:

I use binx2 for all autofocus routines.

Like Steve, I use 2x2 bin. I'd like to use 3x3 for narrowband, but in SGP there's no facility to specify different binning for different filters..... and I found that 3x3 bin on luminance and broadband filters gave me some odd results.

[Filroden]

22 minutes ago, swag72 said:

but in SGP there's no facility to specify different binning for different filters

Having searched their request list I couldn't see this being asked for. So I've created a new request to add this functionality  

[steppenwolf]

I do indeed slew to a focus star (hence the mag. +6.0) so I 'pair' my imaging objects with a suitable focus star and mag. +6.0 works with all the filters I have which range from LRGB, IDAS LP, 3nm and 7nm Ha, 3n and 8.5nm OIII, 8nm SII and 8nm Hb.

I have also tried focusing using the Luminance filter and relying on offsets for each of the other filters and this too worked but I didn't like the idea as much as focusing with the actual filter that I was going to use!

For both focusing and plate solving, I bin 2 x 2

For what it's worth, this is the full un-cropped version but as it was just a test image, the framing wasn't optimal, I just centred the Crescent!

[DaveS]

Do you know, I like that better than the cropped version, it shows the Crescent in context with the filaments to the left looking like they're reaching out to engulf it.

Now you've got the 3nm HII, time to add the 3nm [NII]? .

[tooth_dr]

Thanks for all the info. You are all on a totally different level to me but I'm glad that I understood most of what is being explained!

[steppenwolf]

2 hours ago, DaveS said:

Do you know, I like that better than the cropped version, it shows the Crescent in context with the filaments to the left looking like they're reaching out to engulf it.

Now you've got the 3nm HII, time to add the 3nm [NII]? .

I agree, set in its wider context is nice but as I was just testing, it was centred in the frame and I try no to do that with smaller objects these days!

The Ha and OIII cost more than a half decent telescope so I think I'll pass on the NII (for now )

[Barry-Wilson]

Congratulations Steve - super tight Ha mono.  Roll on the summer and I hope you get the weather for lots of imaging time.

I too like the context of the uncropped image.

[Allinthehead]

Very nice. Anyone want to buy an astrodon 5nm?

[gnomus]

Possibly.  What size is it?

[Allinthehead]

5 minutes ago, gnomus said:

Possibly.  What size is it?

Sorry Steve. That was tongue in cheek seeing how good the 3nm is.

[gnomus]

41 minutes ago, Allinthehead said:

Sorry Steve. That was tongue in cheek seeing how good the 3nm is.

You can't blame me for trying though... 

[steppenwolf]

On 11/05/2017 at 08:27, ollypenrice said:

Super result with tremendous dynamic range. I love this filter. (For some reason I thought you already had the 5nm, Steve. Is this not so?)

@ollypenriceuntil now, I have been using a Baader narrowband set so the Ha bandwidth has hitherto been 7nm. I did consider the ramifications of NII being excluded by the 3nm but still captured with the 5nm and decided that for the objects that interest me most, 3nm would be fine. For planetary nebulae, I still have the option using the 7nm filter as it remains in my carousel and has been a good filter in the past.

[ollypenrice]

12 minutes ago, steppenwolf said:

@ollypenriceuntil now, I have been using a Baader narrowband set so the Ha bandwidth has hitherto been 7nm. I did consider the ramifications of NII being excluded by the 3nm but still captured with the 5nm and decided that for the objects that interest me most, 3nm would be fine. For planetary nebulae, I still have the option using the 7nm filter as it remains in my carousel and has been a good filter in the past.

I must be remembering your pointing out the inclusion/exclusion of the NII line then. I'm dead certain you'll love the 3.

Olly