Icesheet

This is a reprocess of a previous image I posted here in a pseudo SHO palette. I couldn't get a satisfactory result in HOO previously but with some help from scripts in PixInsight I am able to produce something more pleasing to my eye at least. However, I'm not sure if the balance (Ha/ OIII) is right and wondering if anyone can comment. Most images I see in this are are more dominated by the Ha signal and don't seem to have as much OIII as I have (just to clarify it’s not a lot of OIII, basically the light shades of blue/green around the crescent nebula). Is this right or is there something happening at the colour calibration stage or elsewhere? 

Tak FS60 CB with ASI2600MC

30x300s with L-extreme

20x180s RGB

45 minutes ago, Laurin Dave said:

Very nice..    Having recently discovered and been impressed by the Foraxx palette script for narrowband in PI  I'd suggest you run your data through it, it'll produce an SHO type image from either SHO or just HO data.

Dave

Thanks Dave, I will definitely give that a try. Is it native to PixInsight or a 3rd party script?

Edit: Just googled, I see it’s a third party plugin.

36 minutes ago, simmo39 said:

Brilliant result, knocks my effort on WR 134 out of the field!

Thanks! Just seen your effort and it’s fantastic too. Much prefer the red in Ha that you have. I couldn’t bring out the O3 in WR134 without getting more pink hues in Ha. 

First light for my Askar 400. Had been looking for something at this FL and couldn’t pass up an open box offer. It seems very well corrected for my 2600MC on first outing and love the simplicity of not fussing with spacing etc.

This is just over 3.5hrs on an area of Cygnus covering the Tulip Nebula and WR134. Had to throw away about 30% of subs due to dew I hadn’t noticed. Still, pretty happy with what I pulled out. May look to add more in the future. 
 

Askar FRA400 & ZWO ASI2600MC

44*300s with L-extreme 

Processed in PixInsight. 
 

14 hours ago, powerlord said:

I stopped watching his videos as he kept deleting my comments. I'll wait for another reviewer, much as I'd like to view.

He’s always came across as one of the more open and honest YouTuber’s out there (unless it’s something that competes with NINA). Curious as to what kind of comments he deleted if you’re willing to share. 

Cuiv has just given a first look. Looks impressive! Can’t wait to get mine now. 
 

Thanks again @vlaiv. Thinking of it as standard deviation helps me visualise it and understand it better (even if it’s not exactly the case).  

4 hours ago, vlaiv said:

I think that they are given for all wavelengths unless otherwise stated.

This is also useful as the scope I’m looking at looks particularly bloated in blue. Someone before mentioned it, but using one of these fringe killer filters might really help tighten things up. 
 

Interesting stuff!
 

Sorry to keep banging the spot diagram drum here but looking at these is confusing me further! To keep it consistent (if that’s possible) here’s the diagram for the 0.6x and 0.8x reducers. First of all, the wavelengths are the opposite way round. I’ll assume that’s a printing error somehow. I’ll also assume the colour key does not relate to the wavelength since the green spot isn’t actually in the green wavelength. Then, actually looking at the spot diagram itself. The centre spot for the 0.6x has a size of ~20um, according to the scale. However the RMS radius for the centre shows 6um which would be 12um spot size presumably. Or am I interpreting this wrong? Is it the spot from the GEO radius they are representing on the diagram? Then finally, the RMS and GEO radius. Are they representative of all wavelengths or just one?

Btw, the error in my initial post was I thought the box size was 20um so miscalculated spot size.  

14 hours ago, vlaiv said:

I just use simple formulae that are available for different things.

For example - airy disk radius in radians is 1.22 x lambda / aperture diameter, where lambda and aperture diameter are expressed in meters (or micrometers - it does not matter as long as they are the same). Lambda is usually taken to be 550nm (or 0.55um) as that sits in the middle of 400-700nm visible range.

Find more information here:

https://en.wikipedia.org/wiki/Airy_disk

For FWHM - look here:

https://en.wikipedia.org/wiki/Full_width_at_half_maximum

It is usually taken that FWHM = 2.355 * RMS as that holds for normal distribution (Gaussian bell shape) - when you have RMS spot radius.

In the end there is handy formula to relate angles and micrometers for a telescope (a bit of trigonometry really) which goes:

angle in arc seconds = size_in_um * 206.3 / focal_length_in_mm

It is handy to calculate arc seconds per pixel - if you for example put some pixel size

3.75 * 206.3 / 700mm = 1.105"/px

(700mm is focal length, 3.75um is pixel size and it solves for angle in arc seconds). Alternatively it can serve to convert micrometers to arc seconds for some focal length - just use pixel size of 1um so you get

1 * 206.3 / 700mm = ~0.295"

So there is 0.295" per 1um at 700mm or 1/0.295 = ~3.4um per arc second.

In the end - if you want to get ideal sampling rate for long exposure - you take FWHM size of star and divide that with 1.6 to get arc seconds per pixel for optimum sampling (explanation for this is rather complex and involves Fourier transform and convolution theorem and Nyquist sampling).

With that we can see that above telescope with x0.6 reducer will produce around 7" FWHM stars without even having influence of seeing or mount guide error. That is ~4.375"/px or at 420mm ideal pixel size would be 8.9um based on that alone.

It is important to remember - shorter the focal length - "tighter" the spot diagram needs to be in micrometers to provide sharper image - because with less focal length - there is more sky covered with every micrometer.

 

Thanks for the explanation. I think I may still have some gaps that I need to fill in but from what I can see the FRA400 is probably not diffraction limited at any wavelength, while the FRA300 seems to be at least in the centre. Now I'm questioning my purchase. I have a TSA120 and Tak states that spots are 10microns across a 35mm sensor with the flattener which is about diffraction limited across the field. So maybe I'm expecting too much from cheaper optics. This is just theoretical of course and maybe seeing/ guiding etc negates much of this but to me it's still surprising.

Edit: Also with processing techniques it’s now easier to reduce stars and recover detail so maybe this also negates it. Plus it’s easier to fix bloated stars, rather than misshapen stars and at least they seem fairly uniform across the files on the Askars. 

14 minutes ago, vlaiv said:

There are spot diagrams published for all combinations - with x1 flattener, x0.8 reducer and x0.6 reducer.

Here we have RMS radius of spot diagram. With focal length of 700mm and reduction of 0.6 - that turns out to be 420mm of effective focal length.

6um RMS spot size is equal to 3" at 420mm - so that is quite low resolution.

If we were to calculate effective aperture it would be

3" RMS radius spot size is equivalent to 3" * 2.355 = 7.065" FWHM which is in turn equal to 2.44 * 7.065" / 1.025 = 16.82" airy disk diameter

That is the same as 16.46mm aperture scope. Like I said - not much of a resolving potential.

 

I’m interested in learning more about spot sizes and how to translate that into imaging potential. Can you direct me to a good source? For example, I just ordered a FRA400, but now I’m looking closer at spot diagrams the FRA300 looks better. How is the aperture and FL affecting this and how can we make objective comparisons?

Thanks for the quick response. Yeah, it seems like it’s a good deal for the money and I haven’t really seen many negative reviews or comments on this in particular. 
 

Wasn’t sure between this and the FRA300. 

Nice review @Lee_P! I’ve just picked up an ex demo FRA400. Seems to tick a lot of boxes for me. Just a question on the star image at the corner you posted. It looks like CA, which the spot diagrams show may be present but it’s also very consistent with CA I’ve seen introduced with the L-extreme filter. Did you see this when not using the L-extreme also?

The Sigma's are top for well corrected, fast wide angle lenses. I have the 28mm and 40mm. Maybe this needs to be added to the collection!

13 hours ago, Pete Presland said:

Stunning looking view there, the modded camera certainly showing some nice detail

Thanks 😊

4 hours ago, FenlandPaul said:

Beautiful images. You’ve really managed to push that exposure time with the Polaris - I hadn’t come across that but of kit before but it looks very interesting.

I’ve noticed a feature of Norway is that ostensibly unspoilt, wild areas can often have very harsh lights at night! A product of long winter nights and cheap electricity I guess!

Thanks 😊

I’m not convinced the Polaris is worth the money, especially if deep sky is your target. I picked it up on a deal with wide automated panoramas in mind. I haven’t really had the chance to test that but I’ve seen some stunning examples from others. 
 

Yeah, it surprised and continues to frustrate me. As you say, it’s a byproduct of the geographical location and nature of the terrain. However, I still think a lot of it is unnecessary. The electricity prices are not so cheap anymore, maybe that will have a positive effect, at least from my own selfish viewpoint!

A two row vertical panorama of the Milkyway, looking out over Fusafjord to the town of Eikelandsosen in western Norway 🇳🇴 

I took the opportunity of a new moon to test the Benro Polaris with a modded EOS R near my home. Really wanted to get the fish farms in the image but had to crop parts out due to a barge with ridiculously strong lighting (see second image)

Happy to see the extra Ha response around Cygnus from the mod. I haven’t really made my mind up on the Polaris but if I can get it to automate panorama’s it will be a winner. Hoping to take it on holiday this year!

EXIF:
Canon EOS R (astromod)
Sigma 28mm ART
Sky: 20x30sec f2.8 ISO1600
Foreground 8x30sec and 8x4sec @f2 ISO100

Hi,

I did get sub arc sec guiding in the end but I’m afraid I can’t remember what I did now. Also, I no longer have that mount. I recommend going onto the PHD2 group. The people there were very helpful and responsive.

https://groups.google.com/g/open-phd-guiding

If you’re guiding at 0.6” RMS I wouldn’t worry too much! Just get the shutter sorted and you’re good to go 👍

17 hours ago, Dark Raven said:

  

I’ve ordered the Seestar. I’m too curious to find out how this is. A 50mm f5 triplet astrophotography package for $399? I must be missing something here. 

Thanks for the kind words all!

9 hours ago, Alan White said:

Very nice image indeed, one to be proud of.
I like widefield images, make you take in the reality of just how much is around us to see.

4 hours ago, saac said:

Beautiful. Never seen Bodes and the Cigar in widefield before, looks great. 

Jim 

I’m kind of glad I was forced into the wide field version. It does give you another perspective on the area. 

The light nights are closing in here and for what would probably be my last time imaging before the summer, I really wanted it to be with my Tak TSA-120 for the first time. Of course, Tak adapter hell hit and I was unable to get my imaging train together. So, I decided to try imaging M81 and M82 in wide field, particularly trying to bring out some IFN. I checked framing and found I could also fit in Coddington’s Nebula IC 2574, which is actually a spiral galaxy. 
 

I went for 5min exposures under a 65% moon and after tossing subs due to clouds I had 5hr 40mm of data. I wasn’t entirely confident of getting a final product I was happy with. Sure enough I had issues processing with the high dynamic range but managed to finally come up with something I’m happy with. Even if I’m not exactly sure how now! Processed in PixInsight. Hope you like it and happy to get some feedback!

Tak FS-60 with 0.72x reducer

Zwo ASI2600MC

Lights 68x300s

10x darks and flats

Thanks! I haven’t tried the Gain script or HDRMultiScaleTransform so I’ll give them a go. I managed to get something a bit more like what I was hoping for by really pushing the IFN in one layer and lightly stretching the  galaxies in another layer in Photoshop then set the top IFN layer at 60% opacity. A bit too much colour mottling for my like though. 

Edit to add: I just had a look at your fantastic version @Fegato. So much detail in the IFN and galaxies very well controlled. I would delighted with that!

I'm wondering if there is a way of doing a form of HDR processing without data of different exposure lengths? I captured some widefield M81/ 82 data with 5min exposures to bring out the IFN. I've managed to do this, however, no matter what I do I can't bring out the IFN without completely blowing the galaxies out. I've tried everything from masking to layers but can't achieve anything with any detail in the galaxies without artifacts around them. Can anyone point me to a good tutorial? I mainly use PixInsight but have Photoshop too. Happy to make the data available if anyone wants it too. Forgive the corner stars though!

Stunning!

I'm sure there are a few threads around. The general consensus is that it is a good binocular for astronomy, particularly if you handheld is your only option. I hve them but have only tried a couple of times but the stabilisation certainly makes a difference.

Here’s the comet picture from the 30s stack. Quite happy with that.