pipnina

14 hours ago, Elp said:

Its a bit confusing, I thought they removed the front IR filter as an initial mod but on astronomiser it states an IR filter remains on which doesn't make sense. There's also usually an anti aliasing filter which remains on. You can test it on an emission nebula, but likely you will need a UV/IR cut filter or a luminence filter in the image train otherwise you'll get bloat especially around stars.

Some cameras have multiple filters, some only have one. Dichroic coatings can be used to make a single glass surface allow 400-650nm to pass to the sensor while blocking both the UV and IR that the sensor is otherwise sensitive to, so multiple pieces of glass is sort of unnecessary.

My Nikon only had one filter, but the canon I modded had two. interestingly both filtered the light from my NIR optical mouse! (light I can see with my eyes, faintly)

I wonder what target is best for this type of camera... Perhaps a dusty region like the iris nebula or ghost nebula? As those IFN clouds seem to be visible at many many wavelengths.

I think planetary imagers often use IR to get higher contrast in some situations, but for deep sky there is limited use.

You can use it to capture stars through dust clouds, as well as more distant galaxies that would otherwise be invisible at optical lengths, but your sensitivity is going to be much lower and most of the "interesting" stuff is going to be gone with the optical information!

19 hours ago, VNA said:

Hello, sorry, that is a lot of money, I bought a GSO focuser, 2 speed that works great on my lowly CR6.
It is a 2" and rotable  focuser for about $200.00! It fits perfectly, yes it is Chinese, but in the dark you can't tell. ;- )

I picked up a £400 3" R&P by TS. I figured for visual I might like a super-smooth and high quality focuser, but for imaging I could cut the corner a bit as smooth feeling when focusing wouldn't matter when it's only moved by stepper motor!

Unfortunately the 3" TS R&P is a little floppy, and unless the brass screws are done up TOO tightly to allow it to rotate, it flops position in an optically detrimental way as the telescope slews... Maybe there's a middle ground here but it's very frustrating!

I have thought since, if the extra spend on the FT equivalent would have been worth it...

It says 500+ sources found, yet claims to have no stars... Hmm

Might be a good idea to share an image that is failing, I (and others here) will likely have a try at it ourselves and see if we have the same issue, or if we can find good settings for it.

Looking good! I dare say as well, that I think despite the short exposure you have detected a little IFN!

I recognise this very faint 'M' shape, barely visible. But it is part of the IFN around M81! Not bad for only 1.5 hours of RGB

To take it a little further, I could recommend tweaking the colour balance to make the image a bit warmer, as it seems a bit cool at present.

Happy imaging!

I've attempted something similar. My focuser has a built in rotation feature but sadly it slops when not done up so tight, that it won't rotate any more 😕 (3 brass screws allow rotation, another one thumbscrew locks and unlocks rotation, the brass ones need to be done up every time it's moved for some reason)

Glad yours is working however! That looks like roughly what I wanted to achieve with mine!

15 hours ago, Sunshine said:

The pretty and well manicured green space caught my eye, the telescope is also nice!

My dad (retired) takes the garden as his baby, in previous years I've grown things in there too (only things I could eat later mind you) but I got tired of sowing 25 plants and only getting a few ears of corn for it quite quickly.

Now I just take over his potting shed with astro bits.

The tree in the background is an apple tree that predates the house (used to be an orchard). Sadly while it looks to have character from a distance, it is likely to die in a few years as the trunk is hollow in various places (big enough for birds to nest in, and they have! Though with little success due to resident cat)

At this point, I would suggest maybe getting a mini PC that's X86 based?

For example: https://www.ebay.co.uk/itm/114733154309

Select the core i3, 4GB of RAM and the 120GB SSD. it costs less than many RPI boards and kits with the same memory, probably has a faster CPU and also includes storage, and a fair bit of it which is going to be faster than the SD card on a PI. And as a bonus it's still quite small!

I am tempted to give this a go myself!

Simply use the provided windows install on a lot like these (for N.I.N.A users) although for that it might be worth getting them config'd with 8GB ram and enjoy!

Myself, I'd be putting something like Ubuntu MATE or similar on them, and configuring X11VNC to open at boot. This would let me control it remotely as I do with my RPI and use Kstars + PHD2.

Given the stock issues with the RPI it might be worth a go!

32 minutes ago, John said:

SET optics rings a bell for me and I can't quite remember why 

Nice looking scope though 🙂

You might be the first person I've spoken to, who has any familiarity with the name at all!

The people at FLO, as well as Es Reid the optical specialist they partner with, had no idea what the company was. They'd never heard of it!

I got it basically third hand so my chain of knowledge to the scope's origin is broken. I don't know how old it is or anything!

I just know it has been a source of great pain, and I may as well have bought a new triplet instead of this second hand one with all the money I spent getting it up to standard 😕

My SET Optics 130mm triplet after a night of imaging

Cable management is hard, but at least it works!

I seem to always end up with scopes comically oversized for my poor abused HEQ5, those two 5kg counterweights don't come close to balancing this!

The best advice I can think of is to use a program like Stellarium to find objects you want to see on a given night, make a note of them and what constellation they're in, and then draw out some star hopping routes so you can find the object in the eyepiece when you're finally in the field.

It will take some practice as star hopping is a skill, and the telescope AND finder (on most dobs) will have their field flipped vertically and horizontally!

I'd look at brighter objects like M81/82, M51, Leo Triplet etc at the moment, and soon you'll be looking for the ring nebula and such. Happy hunting!

13 minutes ago, gorann said:

Here is my recent image of it with RASA8 and no filter. Looks like IFN with a bit of reddish tone than may indicate some Ha that you managed to pick up. Actually a lot of IFN all around:

https://www.astrobin.com/uahkpy/

Also a cracking image!

I notice a good trend of RASA owners and this object emerging. Starting to think I should have picked one up and put up with manual filter swapping back in september when I went with my APO instead! Certainly it's very hard to pass up the speed of f2 imaging given the UK's weather!

How have you balanced the colour in this image? I notice the other two examples in this thread have a very neutral grey colour in the IFN while you have an almost golden colour in yours. I can only assume at least some of this comes down to artistic interpretation in the various images. I can only guess that the most accurate interpretation we could make would be using PixInsight's SPCC tool after background extraction? I can see some reddish hints in areas of your image though which as you say, could be little bits of hydrogen?

1 hour ago, Fegato said:

Ha ha!  Yes it is quite a bright - I had a go at it last month. I had some advantage though - dark skies, no moon, a very fast scope, and more to the point, no 3nm filter!

https://astrob.in/6n78xm/0/

Cracking shot Robin! Definitely looks like IFN to me, I think I might have to suggest something on the Stellarium GitHub or something because it's currently down as a HII region...

1 hour ago, ollypenrice said:

This is indeed surprising. Apparently it was included in the Sharpless catalogue 'erroneously' classified as an emission nebula, whereas it is now regarded as IFN.  I wonder if there might not have been some truth in the original classification since you've captured Ha in a filter which would not, I don't think,  pick up faint reflection nebulosity.  Perhaps the object contains both ionized hydrogen and the stuff of molecular clouds?

As a control, you could take a test run on some bright (or less faint!) IFN in the same filter.

Olly

I could possibly give it a try, what regions could you recommend I point at? I chose this area because it is one of few non-galaxy objects I can point at at the moment haha.

I know there is IFN around Polaris and near m81/82, but is it bright(er) than this object I wonder?

7 hours ago, symmetal said:

You confused me as the title says Sh2-76 while the image is Sh2-73. 

Sh2-73 is in fact a reflection nebula and classed as IFN. It was included in the Sharpless catalogue by mistake. You managed to get something though which is quite a feat. 😊

Alan

Whoops! Thankfully I can correct the title haha.

Given how hard it has been for me to pick out IFN in the past, I am very surprised to have caught some while using a Ha filter!

It must be a very bright piece of ifn!

With the big moon and uncertain weather last night, I decided to try and find a narrowband target to make use of the relatively clear weather. At this time of year of course that is no easy task!

I eventually found in Stellarium two objects, in the LDB and SH2 catalogs, which seemed promising, in a good sky position and would fit in my scope's FOV! Perfect.

One night's imaging later (and half my subs thrown away due to a frosting sensor window! not doing -15c again!) I have my subs and put the scope to bed before heading to work.

At work I look up these objects to see what I might expect from my images. To my horror they look like IFN objects, which I was shooting with a 3nm Ha filter!

Fully expecting a blank void, I download the subs to my PC when I get home, calibrate and stack them. The SNR is poor... but is this an object I detect anyway?

It looks like *something*, but even binned 4x4 the image has such a low SNR it's hard to make out. I will need more assistance!

So I use RawTherapee's denoise features and turn them up to 11, and in a separate attempt I use Pixinsight's annotation feature. The grainy blob in the middle of my image DOES line up with where pix expects SH2-73 to be!

My image is not pretty, but given I only ended up with 2h40m of subs to include, and possibly of the wrong wavelength bandpass, I think I am pleased!

I'll include the downsampled, unedited tiff if anyone else wants their own look.

Now I wonder if Stellarium is lying about the objects being HII regions, or if my idea of what a HII region is, is wrong! In my mind HII regions are clouds of hydrogen that glow in mostly H-alpha!

master.tif

Whenever I had issues like this with DSS, I did a factory reset and stacked things again.

Set everything back to default and uncomplicated settings. Use the stacking mode where DSS won't do any cropping, use bicubic debayering, don't use dark pixel removal or anything, also only use "average" stacking methods and make sure the output directory is set correctly.

Also as Elp says, ensure the issue isn't in the images being fed to DSS too!

DSS is a wonderful free program but I did also do my fair share of cursing at it as well haha.

I've never heard of someone using a Ha filter for visual successfully, maybe with night vision scopes it could be effective.

The problem is that while the colour vision of humans is relatively sensitive to 656nm, our night vision is not.

Our cones (colour-seeing cells) are not very sensitive in general, and become useless below a certain light level. To allow us to maintain some night vision, we evolved to have rod cells too. These are much more sensitive but only see one colour, which turns our vision black and white.

Note also, how the grey curve (the rod cell response spectrum) loses all sensitivity above 600nm, this means any Ha object would need to be bright enough to be visible to our cones if we were to observe it with our eyes! An object of such brightness does not exist besides bright stars/sun.

However most (all?) objects that emit Ha also emit Hydrogen Beta, which is around 480nm. While this band is only 1/3 as bright as Ha, it falls in our rod's most sensitive wavelength band, which means some hydrogen nebulae can be observed much easier with a HB filter! M42 is likely to be one of these nebulae.

1 hour ago, WolfieGlos said:

Are insects, particularly spiders and their webs a problem? 

Our large garden shed, which was built and left by the previous owners is full of the things, I’ve even known mice to run under it. One day I’d like to try using/converting it to an observatory as it’ll give me a shielded view of the southern sky, but those things concern me somewhat! 

I'm sure there are sprays and such we can use to deter them... I hope!

My dad's shed has had a spider or two but thankfully it has stayed mostly arachnid-free. Or at least the spiders are hiding and small...

3 hours ago, ollypenrice said:

Well, I think the full set was good. Total integration time is not long by galaxy standards, especially when there are tidal tails involved, but the data were very workable.

 

Olly

Wow that really shows what a competent processing wizard can do!

What denoise algorithm are you using? I have struggled to find one that doesn't make the whole image look like a jpeg artifact, even the one pix includes.

1 hour ago, ollypenrice said:

I can't download 300meg of data but O's post (the first response) shows an obviously better S/N in the left hand image. Maybe consider cropping the images to make file sizes more reasonable? Dark skies and poor internet tend to go together! 

Olly

I just re-calibrated the data with the proper input pedestal and re-stacked twice. First dataset is all subs from both nights thrown into WBPP, second is only the first night's subs (so 12 subs per channel for first night only vs 45-ish for all data image).

I cropped them down to 1280x1024 so this is now only a 30MB total download.

I will be honest when I look at individual channels from the stack, autostretched, I can see the difference in SNR much more easily. I guess it all threw me off because it doesn't look like a 5x integration difference in SNR!

All_data_correct_calibration_crop.tif First_night_only_correct_calibration_crop.tif

14 hours ago, ONIKKINEN said:

On flats; you can drop darkflats if you want to and use bias or even the dark master as a darkflat. You can also subtract offset by some other method, i know APP does some kind of pedestal thing for flats and if i recall correctly WBPP in PI also had an option like this. Its important that the offset gets removed, just not very important how with how little dark signal there will be in flats. In principle its the same thing for your lights, you could drop darks and just subtract offset. With 180s lights you are getting less than a tenth of an electron per pixel on average if you cool down to -10 so up to you to decide if that's worth taking darks over.

I did some looking through the settings: WBPP has an output pedestal which adds a certain ADU *post* calibration, and the separate ImageCalibration tool has both output *and* input pedestal.

Setting the input pedestal to match my camera offset does appear to reduce the overcorrection, albeit a bit hard to see given how dark and noisy the subframe is to begin with!

I stacked the blue frames that I calibrated with input pedestal and hit autostretch (right), and compared it to autostretched blue on a previous stack with no pedestal in calibration (left)

Thank you very much for telling me this exists! I have been banging my head against this flats problem for what feels like forever haha.

1 hour ago, vlaiv said:

I think that easiest way to combine two datasets to reveal SNR difference is to create "split screen" scenario.

Both stacks need to be registered against the same sub and calibrated / integrated in the same way (as to have same intensity - to be compatible).

Then half of either stack is copied and pasted directly over the other. This will create "split screen' scenario for linear data and provide you with means to process both stacks in exactly the same way (whatever you do to process the image will equally affect both sides of the image).

As in normalise both stacked results with a linear fit, and register them so flicking between them in an image viwer or photoshop will let me see a flickering 1:1 comparison?

It'd be worth a shot!

1 hour ago, ONIKKINEN said:

Hmm, the differences really do seem suspiciously small. If i had to guess which one had 5x the data im not sure i would make the right call blind.

Your flats are overcorrecting by the way and that could throw a spanner into the works with normalization of the subs which will ruin all hopes of getting the best possible image especially if conditions are different on both nights. Without working normalization adding more subs might not necessarily improve the stack. Maybe something to do with it?
Also looks like you have some pretty heavy light pollution judging from the levels of the stacks. Was one of the nights just with better transparency? I have seen transparency affect an imaging locations bortle rating by more than 1 (from 4 to 3).

Transparency might have been lower for night 2, but I don't know about a whole bortle lower!

Might help here to see the subs:

The sub with the full date stamp in the file name is the second night, the sub that's just M51_Light_Blu is from the first night.

I notice putting them to the same stretch level in Kstars that the subs from night one are definitely darker, but I am not sure how much the signal in M51 is being attenuated by, it doesn't look like a 5x loss to me but my eyes are not so keen for this sort of thing.

I found two of the darkest subs in the middle of each dataset and put them side-by-side at the same stretch and they look similar in terms of signal and noise, but the new dataset is definitely brighter:

And looking at the stats, given my offset of 256 (which yeilds minimum ADUs around 40-60 on my cam), it seems that the average ADU value difference between the two nights is only about 80-90 ADU. It seems a bit suspicious that it would make such a big difference in the final product.

As for my overcorrecting flats... I am still experimenting with the issue. I think I need to apply darks to my main data and bias frames to my flats (flats are around 0.05 to 0.01 second exposures so flatdarks maybe not so necessary?) Getting good, uncontaminated darks is quite hard though. I've burried my camera before and still seen light get in (I even stuck some socks over the front of it in a dark room once trying haha)

It is a bit odd because my much noisier and stronger dark current DSLR had no issue with flat calibration, despite me never using darks or bias frames!

M_51_Light_2023-04-23T23-43-01_001.fits M_51_Light_Blu_001.fits

44 minutes ago, ONIKKINEN said:

Difficult to measure objective things about noise when the data is stretched, but to my eyes the image with both nights is noticeably better. Not that i know how to make those measurements objectively anyway .

 

Could be just a difference in level of stretch of course, but just a preliminary eyeball-only measurement makes me think the left image has a much better signal to noise ratio. The core parts of M51 are incredibly bright so i dont think there are obvious SNR improvements to be seen there. Look at the tidal tail parts for example, they are smoother with significantly less RGB noise. Also many of the Ha regions and bright blue clusters look tighter in the left image.

By the way, when you say sticking the 2 stacks together do you mean actually just stacking the stacks instead of the data from the 2 nights? Stacking stacks will be less effective than integrating the subs to a new stack.

Hm ok maybe the processing will mask it a bit

I just put the two nights together into a simple LRGB combination without stretching, and the second night by itself in another simple LRGB combination

I stacked the two nights combined by adding all the raw files into the WBPP script, so I avoided trying to stack two master lights (PIX refuses to stack fewer than 3 images anyhow)

Maybe this makes it a little easier, I don't really see any appreciable difference myself

both-night-raw.tif 2nd-night-only raw.tif

I have been trying to capture a nice and clean image of M51, and in my first session I caught an already quite nice image with only 1.5 hours in RGB.

On the 23rd, night 2, I managed to bring in over 5 hours! I figured I would see a big improvement sticking the two stacks together... Alas there appears to be no improvement at all 😕

Could it simply be a matter of the second night having that much worse SNR per sub, or could it be difficulty getting multiple nights to work well with eachother in pix in general?

When I stack night one and night two individually, they do look very similar, I am struggling to tell a difference SNR wise.

Is it just bad luck or am I realistically limited to one night per image or per colour?

Thanks

Image13 is both nights together with a quick pix process (ABE, SPCC, stretch and colour boost only), The other Image13 is, as described, only data from the second night.

Image13-2nd night only.tif Image13.tif

A lot of heavy technical discussion in this thread.

I'm happy to enjoy the great picture myself!