Filroden

4 minutes ago, JohnSadlerAstro said:

On a serious note, (not wanting my humour to get me banned)!

What would you suggest as the best method for taking white frames? I've been having trouble with vignette, but as my sensor is large, its more one-sided. (I'm ok with dust as my DSLR auto cleans the sensor every time it turns on or off).

John

I fold about half a dozen sheets of white paper so they hand from the end of the scope and act as a diffuser then I put up a completely white image on my TV screen. So long as you expose for long enough to not capture the screen refresh then it seems to work well.

4 minutes ago, The Admiral said:

That certainly is a design flaw. It would have been good if ASI had offered to replace/upgrade earlier models.

I'm pleased to say that I don't seem to have a great deal of problem with my camera; I think the sensor 'cleaning' cycle it invokes each time I switch off is doing a fair job.

I'm surprised at the amount of vignetting you are getting Ken. Is that because the filters are only just large enough, or did you get that with your 'scope prior to use of the ASI?

It's a complete redesign of the body so they can't offer an upgrade kit. They have offered $200 off a new camera if you owned the previous version. Given the camera's popularity, resale value of the older versions should be high, so it wouldn't be too much of a loss. I just need to be more careful.

My flats above have been stretched to highlight the variations. The "flat" flats look more like yours (example of the L filter below). I've always had about that much vignetting but the flats seem to fully correct it, so I've not been too bothered by it.

Would you believe it...the only filter with any discernible difference is the Ha filter which has two nice blobs in the centre. There's quite a bit of dust on the sensor. It's a design flaw with the first two versions of the ZWO ASI1600 camera. ZWO included 4 desiccant tablets inside the camera next to the sensor window so any time you unscrew the camera body there is a risk it grinds the tables, spreading dust everywhere. The third version removes this flaw. Looks like I need to open it again.

11 minutes ago, The Admiral said:

It wouldn't surprise me if the dust is emphasised because of the narrowness of the passband

When I did some quick integrations of my M81/82 images last night the dust was clear in the L channel but was invisible in the Ha. I think it's because there is so little background in the Ha and the signal is weaker that it's just harder to spot. Now I have time to properly calibrate all the files it will be interesting to see the difference.

I will also see if I can balance the flats and subtract the Ha from the L to see if there is any real difference. Given it's a new filter, I would hope it is clean so the flat should mainly be dealing with dust near the sensor and the vignetting of the optics. If so, I could possibly be lazy in the future and correct Ha using the L flat.

That, or I have to figure out how to get my light box working so I can increase the intensity when doing Ha flats and reduce the exposure time. 32s exposures means I also need to correct for darks. With 1s exposures I could get away with using the bias as a dark.

1 hour ago, The Admiral said:

Nice. I'm envious of your FoV! Ha does seem to give a 3-dimensional effect.

Does Ha present particular problems in this regard? I'm thinking in terms of the emission spectrum of the source used. I use an led light, others laptop screens etc. and I wonder what they emit at 654nm.

Ian

Thank you. It is such a richer image than the original luminance that I used. I'm going to have to study the tutorials about blending it into L and into R. I may try three versions:

1. Mono Ha with stars removed and tinted red

2. LHaRGB

3. HaRGB

The latter to see if it retains more detail without the L channel.

I've just taken flats using a white image on my LED TV. The Ha flat took 32s compared to between 1s and 2s for the LRGB. I can't see much difference between the results yet but I've somehow managed to put more dust onto the camera having (I though) given the whole system a good going over with the blower when I fitted the Ha filter.

Well, here's early sight of my integration of the Ha images. I only managed 34 x 30s and 22 x 60s, all taken at 300 gain, 50 offset and -20C. I haven't inspected them, rejected any images, or applied any calibration. This is uncropped and only stretched with levels and curves. I have to say, Ha data is so much cleaner to work with than LRGB! I'll be taking flats tomorrow and doing a proper integration of this, and my LRGB data (not that I got much before it went behind the steam vent). I also took a quick peek at M81 and it's a breath taking galaxy (but that one really does need calibrating!).

Just now, The Admiral said:

That's looking very promising Ken, plenty of detail in just a single sub., and you have the benefit of a FoV which gives good coverage. Looking forward to see the finished image.

By the way, what version of Skysafari are you using, and does it use the iCloud to provide proper operation? There doesn't seem to be a decent comparison of versions.

Ian

The developer website shows the comparison, mainly differences in object databases. http://skysafariastronomy.com/

I went with the Pro but bought it when they do there 50% discounts, which are quite frequent (maybe once every month or two). You can sync your settings across iDevices but otherwise there is no need to use the cloud.

How is the fog? I'm seeing lots of bad reports for the whole south of England including high pollution alerts. 

Well, that didn't last long. The target is already too close to my neighbour's heating vent and there is no other easy target to its east. So I've moved to M81/82 to see what I can get. Just doing LRGB as the targets are small in my fov and any Ha data will be lost.

Just took my first Ha sub. What a nightmare finding focus. I had to reduce the step range on my autofocus as the stars quickly went too far out of focus to be measured.

Here's a single 60s sub of NGC2239 at 300 gain, 50 offset and -20c.

Edit: looks like I still might have tilt/spacing issues. The stars in the upper right are looking elongated in every sub so far (though an improvement over my previous settings which had all four corners looking elongated).

My first Ha sub. A single sub of 60s at 300 gain, 50 offset and -20C. No calibration, just a quick levels and curves stretch and no noise reduction. Going to go lie down now...

Actually, I've set my first sequence to be 30 x 60s Ha, 10 x 30s RGB and 30 x 30s L. Hopefully I can repeat that sequence a few times to add to my original data.

13 minutes ago, Gina said:

Am I wasting my time or should I give it one more try?  One more would all it would be - it's getting decidedly cold out there

If the reboot worked it's worth one last try, though why it stops working I have no clue. I can't imagine the cold would have such a quick effect.

I've just taken everything outside. It's looking like my first clear night in about three weeks. I've just recalibrate the auto-focused and need to do the same for my StarSense to get accurate gotos. And then I'm hoping to get my first Ha images of the Rosette.

I remember calibrating my Mac and laptop but I hadn't calibrated the new TV. However, having run it now, it calibrates and now has an overly warm hue, making whites appears a pale red. When I bring up a colour chart, I have to say the uncalibrated looks much better than the calibrated.

1 hour ago, The Admiral said:

Yeah, well!! Is it colour calibrated?

Err...maybe...quickly finding my Spyder after the house move and setting it running!

22 minutes ago, Gina said:

wrong size gear teeth

Hopefully no damage done?

11 minutes ago, The Admiral said:

I can just about make something out in the original now that I know what I'm looking for.

It helps that my main monitor is a 40" 4k TV though sometimes I think images have more contrast and richer colours on the iPad.

3 minutes ago, The Admiral said:

But I think that most of my stars are saturated though.

In Photoshop, if you have Noel's actions, I think it can bring the colour from the star's halo (which shouldn't be saturated) into the centre. It's pretty neat and I think I found a way to do it in PI but I've not been able to replicate it again!

5 minutes ago, Filroden said:

It just looks too straight and suggests a stacking artifact rather than the edge of the nebula.

The more I look at it the more I think you could be right. It's not quite straight (at 1:1 scale it looks very straight but zoomed in it does show some variation). I think its position in the corner has thrown me.

3 minutes ago, The Admiral said:

I was thinking something along those lines too as I was replying, but not in such a clear way! I don't think that there is any way of precisely colour balancing, it's not as though one can introduce a grey card! There would have to be some assumption made about what constitutes a neutral reference.

Ian

I think it's a reasonable assumption to make in general. We know the total distribution of stars in the galaxy (and in others), so the total integration of this distribution should define the correct colour given enough stars. However, at large scale, there are uneven distribution of stars (clusters spring to mind or whether you are imaging towards the core or an arm of the galaxy or into the halo) where one colour may dominate. So applied with caution it's my preferred method of balancing the colour (after background removal) but I wouldn't hold it up as being accurate. If the image was plate solved and each star's colour positively identified from a database taken from spectroscopic measuresments and this value was used to balance the colour, then I'd think it's closer to a true colour.

4 minutes ago, The Admiral said:

Just to be clear, when you say "..in your first image" are you referring to the one I posted yesterday, or to the first of the two images I posted today?

The one you posted yesterday, though of the two today, I prefer the first of those too.

It was this area (I've cropped and boosted the contrast/brightness). It just looks too straight and suggests a stacking artifact rather than the edge of the nebula.

13 minutes ago, rotatux said:

I'd like to see what Regim B-V color calibration can give on that one. Also, Isn't there a similar feature in Pixinsight ?

Yes, the ColourCalibration module balances the background (a user defined area) based on the star colours (either the whole image or another user defined area if there is a lot of nebulosity). I think there is an assumption over the total integrated star colour and it balances to that. However, given stars are not always randomly distributed, I don't find this any more a valid calibration than balancing the histrogram in Photoshop, using the colour temperature slider in Lightroom or any other method.

Sounds ideal for a snooze...I mean working on the focusing

It's a tough call. I've waited until now to comment as I wanted to see the colour on different screens. I really love the graduation between the lighter core and the darker edges, and this shows really well in your first image. The Rosette does have a lot of OIII, so it should not be just red, so I think the shading is valid (the green/blue of the OIII would soften the strong Ha into being more pink/magenta). After that, it's really just to taste.

It's a good composition, nicely cropped though I think you've missed a stacking artifact in the lower right corner which probably just needs a gradient adding in Lightroom to balance it (rather than crop it out). It's a sharp image without looking sharpened  Your stars are nice too. 

Given how much data you've already collected, a night off, even if clear, is deserved!

I'm not yet convinced the idea of subtracting the two images works to isolate N. When I zoom into the full resolution image, there is so much overlap that data from the Ha must still be in the subtracted image, as there probably shouldn't be so much N visible (I think it should be much lower than OIII and probably more on a par with SII for visibility).

Still, I've now seen the Seagull in a wideangle shot and it looks a wonderful target. I think it's just a little too big to fit into a single frame for me, and probably too low given my horizon, but it's a target I will be adding to my wish list.