Filroden

You've all cursed me. Having not dropped a sub for tracking for I don't know how long...after 45 minutes tonight my tracking just stopped and I couldn't get it going again! I suspect battery issues but I need to investigate further.

20 minutes ago, Gina said:

More reading of the "Inside PixInsight" book has been very interesting and I have learned a lot more.  I can see better ways of processing my data and learned more about the relationship between bias, dark and light frames as well as shortcuts to taking and calibrating both lights and flats.  I know the calibration I have been using has left a lot to be desired and I can see ways it can be improved including SuperBias. 

Before you go down the superbias route I'd suggest reading alternative views on its usefulness. There is a really good thread on Cloudy Nights. Based on that thread I created a normal master bias using over 250 subs and it has worked much better than the superbias I created. Given how easy it is to take many bias frames, statistically, you're going to get a better result integrating real frames rather than trying to mathematically simulate that same result from fewer frames.

7 hours ago, parallaxerr said:

Fortunately the wetness was dew not rain, so no harm done.

Here's the result of last nights attempt, second go at M42. This time I gathered more subs, although only an extra 30mins or so despite being out for an extra 2hrs. I had some serious PE (I think - major star trailing on Alt axis for 4-5 frames each time) every 10mins or so, so lots of subs got binned. Also had about 15-20° field rotation at a guess, so lots of cropping was required.

WO ZS66SD unguided on Nexstar SE 6/8 Alt/Az, Nikon D3200 w/Baader Semi-Apo filter. 198x30s subs, 50 dark, 50 flat, 50 dark flat.

That's a really good image with a clear man running! I do like the field of view on your WO. Frames it nicely.

3 hours ago, parallaxerr said:

I had some serious PE (I think - major star trailing on Alt axis for 4-5 frames each time) every 10mins or so

I used to get this but I increased the weight to the back and it stopped. Now I can image for hours and it keeps rock solid on the target. 

8 minutes ago, Nigel G said:

Ken

Glad to hear you have sorted your mount, never nice when something like that happens. 

I went to a deep sky astrophotography talk this week, apart from the usual " you need a heq5 mount minimum " it was very interesting,  the guy had a mono CCD with filter wheel and auto focuser.  He said each colour filter needs to be focused individually,  the auto focuser stores the focus for each filter and automatically focus with each filter, not sure how much they cost though.

He also said about duel band and swapping colours in processing. .. using the red as blue and blue as red which had interesting results.

Good luck for tonight,  unfortunately there's broken cloud here, getting heaver. 

Cheers 

Nige 

I've been looking for an auto focuser but I can't find one that will fit my scope. I think I'm ok so long as I get the luminance filter focused spot on.

Clouds blew in here too. Got about 100 subs but I had to discard over half of them because of the clouds. It's now raining

Also just discovered that using SGPro, you can track your focus by measuring the HFR for each image. I was able to (I think) improve my focus using my mask by monitoring the HFR until it reached a minimum (it worked with the spikes too). It felt better than just eyeballing the focus based on the centre spike bisecting the outer ones but the proof will be in the processing. The HFR varies between filters but I suspect that's because the stars naturally look smaller or larger depending on the filter, e.g. all light passes through the L filter so it should show the largest star size, whereas the stars look smallest in the blue filter.

Would be nice to be able to more accurately check my focus before I commit to a long night of imaging!

1 minute ago, Stub Mandrel said:

You could find that hot turbulent air destroys your seeing as well... can you cap it off for a few hours?

I'm going to test it first. I think it's bad now because the temperature has been dropping quickly. I'm hoping it stabilises. My HFR on the blue filter was about 2.5 so it seems to be okay.

Finally another clear night and a little time before the moon rises to capture a few more frames of NGC1333. In the meantime I've been playing with the scope and discovered:

- my StarSense fits my refractor after changing its mounting plate so all this time I've been fighting to do three star aligns and I could have been doing it automatically!

- I think I've figured out how to link and control my scope from within my image capture software including automatically plate solving to make re-alignment of images easier. However, in experimenting with it m mount threw a very big wobbly and would not turn off, either with the power switch or even pulling out the power cord. Very Scary. However, after a mild panic in which it looked like I'd reprogrammed the mount to be something it wasn't I finally managed to fully reset it. More experimenting needed but it could make setting up and controlling the gear from indoors much easier.

- My blue and green filter are reasonably parfocal but the red looks to be way off - not sure it matters for colour data given you can bin colour data but I need to check the luminance filter too. It could mean refocusing between filters which changes how I'd have to image.

I've also discovered that my kitchen vent blows directly across where I have to sit the scope. In these temperatures it's venting lots of steam making me worried that I'm going to suffer more from cloud pollution than light pollution.

3 hours ago, david maitland said:

M82 taken with an 8" lx90, it isn't very recent. It's something like 10 x140sec lights along with calibration frames. Processed in images +.  Best one I capture with an alt. Az. Since moved on to an Eq.

How did you manage to track for 140s at that focal length? Or did you mean 140 x 10s lights?

On 11/15/2016 at 18:58, Nigel G said:

Hi guy's

I have been working on a YouTube channel , Alt-AZ Astrophotography. for a day or so and would like your opinions, maybe how to improve and suggest videos to post or even if its worth it.

So far I have uploaded a few processing video's and a showcase video.

I'm planning to post video's on type of kit and capturing images.

Here's a link if your interested

https://www.youtube.com/channel/UCchMWf52QIubmbDcXYOP1Bw

I would appreciate your honest opinions.

Thanks for the link Ian, going to read it now.

Cheers

Nige.

 

I've just watched the star spike removal video (sorry, I had to turn off the music!) and I had two thoughts:

- when you used lasso to mask the spikes, at first I thought you were being very inaccurate with the lasso until you completed the heal and I saw that you didn't need to be very accurate! Maybe worth pointing that out

- you could put a process step list in a smaller font in one of the corners so the viewers can see the steps you're taking, letting the list build down as you start each step - stops you needing to focus too much on which options your mouse is selecting

e.g. 1) Use Lasso tool to roughly mask spikes

2) Use Heal tool with xxx option

Likewise. I keep my tripod as low as possible. It kills my back during alignment but I think it's more stable. I also have vibration pads below the tips which speeds up how quickly it settles.

Isn't it better to reduce ISO before exposure? You'd only want to reduce exposure if you couldn't reduce ISO far enough to avoid clipping.

I see what you mean. So you're balancing the input range wanting lower ISO to output range wanting higher. 

So the test would be to start at the highest ISO and work down until no clipping occurs?

7 hours ago, parallaxerr said:

OK, I wasn't going to post this just yet but I have a question - in comparison to other M42's I've seen, there seems to be quite a lot less stars in mine. Probably a result of setting ISO to 400, but I really do like the dark background. What do you think? Stars vs noise?

 

I've just compared your star field with one of my first images taken last year. This, I think, was with the 9.25" SCT at f6.7. I think it was from a stack of 15s subs. The field of view is different but I see 100% overlap of stars.

11 minutes ago, Stub Mandrel said:

If you avoid clipping using a higher ISO increases the dynamic range in the image.

For example, an 8-bit mono image can have up to 256 levels or shades o grey, 0 to 255.

Say a mono 8-bit image at ISO 100 covers the range 0 to 70, it will contain 71 shades of grey (not fifty!)

At ISO 200 it would cover the range 0 to 140, and have 141 shades.

At ISO 400 it would require the range 0 to 280, but 280 is more than 255.

In this case the 200 ISO image would clearly capture the most detail without losing data.

Bear in mind this is true for astro images that typically start near the black point (0) and will only approach high values at the centre of the brightest stars.

 

This also shows why a 14-bit DSLR like my 450D (16,384 levels) shows much more detail than my 10-bit 10D (1,024 levels) at the same ISO setting.

 

This is why, at face value, it makes sense to use the highest possible ISO rating without clipping.

 

But working against this is noise, both read noise and thermal noise. If noise doubles from, say, ISO800 to ISO1600 then because the signal doubles as well the signal to noise ratio doesn't change and the extra detail revealed gets lost in the extra noise.

Curiously the noise/ISO relationship appears to be different for every type camera or sensor, and perhaps in detail for every individual camera.

My reading of various websites is that you need to find the 'sweet spot' for your own camera using online data as a guide to find the likely range (ISO800 and 1600 are quoted as 'best' for the 450D by different websites) and then do some experiments. My own experimentation on this is inconclusive, for my camera any given exposure 800 is less noisy than 1600, but if you stretch an 800 image to match a 1600 one, the 1600 version shows marginally less noise.

What to do?

I think it's the other way around: dynamic range reduces with increasing ISO. Here's a chart for the Canon EOS 50 from http://photonstophotos.net/Charts/PDR.htm

However, I think ISO is non-linear in its effect on signal and what I think it does at higher ISO is use more of the dynamic range for the lowest signal, therefore giving it an apparent "boost" - something that can be achieved in post-processing. However, because it has less range to play with, it therefore has to compress the highest signals, so increasing the likelihood of saturating stars.

38 minutes ago, parallaxerr said:

Same here but I don't have the blinky option. I have a feeling I was nowhere near saturating the sensor at ISO400 which is why I didn't capture some of the higher end of the range, i.e. fainter stars.

So long as your background has cleared zero then you have all the data captured regardless of increasing ISO. Increasing ISO just multiples the strength of data that already exists. So I wouldn't increase ISO and expect to see more (once processed). However, lower ISOs would result in the histogram being lower overall and require more stretching (develop in StarTools) than a higher ISO.

The only reasons I can see why you would not capture fainter stars - the exposure time is not long enough and/or they are fainter than the background signal - neither of which could be solved with increasing ISO.

You've almost resolved the trapezium at 30s. I'd have thought it might be overexposed! 

I personally prefer to see a non-black background as there will be very feint detail which will be lost if you clip the shadows. It does mean leaving noise visible but that can be reduced. 

Otherwise it's looking good. You've almost closed the loop of nebula and the running man is just visible. 

Darks and flats should deal with the corners. 

Yes, the peak will move right with longer expo or higher ISO. But even at 10s you've cleared the left side so I'd try 1600. I'd even be tempted to test 800.

I aim to get the left of the histogram clear of zero; I.e. The darkest part of the raw image is >0. After that, I want to avoid over exposing stars so I reduce ISO until I get as much between those two limits. Sounds like ISO 1600 might be ok.

I'd agree and go with the reducer on this one in order to 'go faster'. I can't imagine you'd beat seeing; at least not down to 1.4"/pixel. The other advantage is that the shorter focal length will be less sensitive to tracking errors and allow you to squeeze even more seconds per sub. Plus the wider field of view gives you more options to frame/crop. If the target is small within the image you could always produce a wide field image (sampled down to reduce it's scale) with an insert panel at normal resolution (or even slightly enlarged) to show the target.

You're doubling the focal length of the scope, and given the aperture is fixed your slowing the scope down, needing longer exposures. As you say, you're also making tracking more difficult making it more difficult to achieve even equal exposures let alone longer ones.

But, there are possibly occasions it's better. Planetary imaging, and maybe some bright planetary nebulae which are such small targets the longer focal lengths are worth it. I can get 15s exposures at 2350mm and over 90s at 400mm. I've not tried the 2350 with my 2.25x Barlow for anything other than Jupiter but I could probably get 4s. However, at f22.5 I don't know what I'd get in that time.

just finding my target with such a small fov makes me horrified! It was bad enough at f10 and f6.7 using a reducer!

5 minutes ago, Gina said:

I'm afraid I missed this post when you posted it Dave   But I agree with you - a suitable directory structure would be a good way of organising the master calibration files., or at least the bias and dark.

I guess top level will be gain then temperature and exposure. 

I don't think you need subfolders for master calibration files. Just include the gain, temp and exposures in the file name and they will sort themselves within a single folder. I can't imagine you'll have hundreds of master bias and dark calibration files.

31 minutes ago, parallaxerr said:

Thanks for the encouraging words Fil. The green seems to be a problem for me, in both scopes. When I use the colour tool in ST the image has a heavy green tint to it, same with my M31 attemp. I cap green to yellow and reduce green further with the sliders but then then struggle to balance red an blue.

I just reprocess the same data in an attempt to remove more noise and address the ca, but I think the image is too soft now.

I also didn't drizzle in DSS and only binned 50% which I think has proven to remove the noise a bit better.

I don't think it is soft. I think it's just a problem with the colour balance and CA. Otherwise it's the start of a nice project to add more data (especially with the new filters).

I had a quick play with the jpg in Photoshop. As it's very black clipped I had trouble manually adjusting the colours. I did find (for the second image) that reducing the red a lot and the green a little using curves helped. I then tried PS' autocolour and it did a much better job with one click!

StarTools remains a mystery to me so I don't know the equivalent way to do the above. 

4 hours ago, parallaxerr said:

Here's the result of Monday nights session with the ST120. M33, about 1hr of 30s subs, x50 darks, x50 flats and x50 dark flats.

The light frames suffered heavy LP so I'm not suprised there's still significant gradient in the image. I'm still learning startools so maybe more could be removed? Due to the noisy light frames I used x2 drizzle in DSS, which left me with a 12068x8024 image @ 1.08GB  I then binned to 25% in startools which did seem to smooth things out a bit.

The CA is there, as expected, but I don't find it overly offensive. Hopefully the semi-apo filter will help address it and the skyglow when it arrives.

Most of my attempts so far have been with about an hours worth of data, early in the evening. It's becoming clear I really need to capture more data, later at night, when the lights have gone off, target altitude allowing. Oh for a clear night on a weekend...and a new moon..and a target between 30° - 60°!!!!

 

As you say, there is noticeable CA which hopefully the filter will reduce. There is also a colour balance issue with a definite green tint across the whole image. You can see it most strongly on the galaxy core and on the yellow/orange stars which all have a slightly acid tint! I could remove the green tint in Pixinsight but I don't know how you'd adjust colour in StarTools. Other than the CA, your stars are nice and tight, so adding more data should be a breeze. You've done a good job with any light pollution, as I can't detect any gradient (other than a flat colour shift).

I used to drizzle and reduce but I found it just added more processing time and little benefit. I think it's usually only recommended if you're seeing square stars. There are probably other, more efficient, ways of smoothing backgrounds within StarTools, allowing you to skip the drizzle steps.

12 minutes ago, Gina said:

The weather forecast is not good for the next few days so maybe going through a whole lot of data and making a database or spreadsheet could be worthwhile.  But which - database or spreadsheet or maybe just a table.

Can you not handle it through file naming and stucture?

I record the target, filter, time, exposure, gain, offset and temperature in each sub's filename. I can then link them to the appropriate master bias, dark and flat files which are similarly named. I store all subs in folders based on target and all calibration masters in their own folder structured by equipment.

It's still a pain loading the right files into the right boxes during calibration and that could be simplified by saving only the calibrated images, but it's manageable without the need for additional files linking the data. If Pixinsight could import files based on a script driven by a database/spreadsheet I might go down that route, but given you have to manually select files anyway, I don't see it saving time.