First Attempt with ZWO ASI120MM-S -- Moon - Many Questions

[gnomus]

I finally managed to try out my ZWO ASI120 MM-S (USB 3.0) mono planetary camera last night.  I decided to try the moon through my Celestron 8 inch scope mounted on a CGEM.

I am using Firecapture.  First off - I had the option of shooting 1280 x 960 at 8 bits (frame rate just shy of 60FPS) or 1280 x 960 at 16 bits (down to 30 FPS).  Which should I choose?  I went for 8 bits - was this incorrect?

Next - focussing.  I was surprised to see what a small FOV I had.  Obviously due to the size of the chip.   With my DSLR, I could just about get the whole moon on the sensor.  With the ZWO, I got only a portion of the lunar disc.  It was not all that easy to know precisely where I was.  Well, I went to somewhere near the limb that looked vaguely interesting (I think I got a small bit of Copernicus in the final shot - see below)

Focussing on screen looked like it would not be easy.  The image was extremely .... well ... fluid is probably the best word for it.  It was like looking through shimmering water.  I know .... I'll break out my Bahtinov Mask that I got the other week.

Bahtinov Question 1: How critical is the placement of the mask? I hung mine over the front of my home-made dewshield.  This takes it out some 16" or so from the front glass of the telescope.  Is that still OK, or does the mask need to be nearer the front glass?

Bahtinov Question 2: I was able to get the three lines on screen.  When I shifted focus, the middle line moved back and forth between the two outer lines.  I was unable to tell exactly where they all intersected, however, because of "blobs".  The "blobs" were star-like in appearance.  There was a white "blob" (?star?) in the central region of the three lines.  There were also "blobs" on each of the lines a little way out from the centre so that the central "blob" was surrounded by 6 other "blobs".  Nevertheless, by moving the focusser back and forth, I was pretty confident that I got the central line, centralised.

I locked focus using the knobs on the Edge HD.  The lines still appeared to be intersecting.  I slewed to the moon.  It was still very "soupy" in appearance.  However, I decided to press on, and I shot 4 lots of video L, R, G, & B.  (I wasn't sure if I needed 'L' on the moon, but I did it anyway.)

I decided to capture 2000 frames through each of the 4 filters.  This gave AVIs just shy of 3GB.

This proved to be problematic in Registax.  Whilst the AVI would load, I could not scroll through the still frames.  Registax would tell me that I was on Frame 500 (for example),but the image on the screen did not change one iota from frame 1.  I was able to ingest and scroll through frames in smaller AVIs (shall we call them my 'test' shots - though in reality they were things I had set up wrong).  Does anyone have any solution to the Registax issue?

I had no problems loading and viewing the frames in AS2, and this allowed me to align and stack the AVI.  I decided to keep only 5% of the best frames for stacking (I'd seen something on YouTube about using only a small percentage of frames when shooting the moon).

I then played around with the "wavelets" of the resulting TIFFs in Registax.

I have to say that I was a bit disappointed with the results.  They did not appear very sharp to my eyes.  I was not sure whether the issue was that I did not nail the focus, or if the "seeing" last night (5 Dec 2014) was so poor that I was never going to get a decent result.  As a beginner, I don't really know how to rate "seeing".  There was not a cloud in the sky.  However, there have been nights when I have been able to use my highest magnification eyepieces, and I was still able to achieve sharp focus when visual observing.  Last night was not one of those nights.  I wonder, therefore, if there are some nights when I should just stick to visual, since I am never going to get decent results using the planetary cam.  

I attach a JPEG of the red filtered AVI (which was probably the best of the bunch).  

There were a fair few questions in there,so let me list them for convenience:

1) 8 bit or 16 bit captures?

2) Is it OK to hang the Bahtinov off the end of the dewshield?

3) Does anyone else get the "blobs" (I know ... if I'd been smart, I could have photographed them so that you wouldn't have had to listen to my awful description).

4) How many frames?

5) Does anyone have a solution to the Registax issue?

6) Is the result a "seeing" problem or a "focus" problem - are there some nights when I should give up on the idea of imaging?

7) Any other comments?

Here's the picture (he muttered, shamefacedly):

[knobby]

I was out last night using similar equipment ( C8 edge / as I 120 mc ) also struggled with focus . suspect it might not have been as clear as it looked and the seeing was pretty poor . I was imaging Jupiter and it was leaping all over the frame .

So your moon image is fine ... Well done

[glowingturnip]

1) 8 bit or 16 bit captures?

2) Is it OK to hang the Bahtinov off the end of the dewshield?

3) Does anyone else get the "blobs" (I know ... if I'd been smart, I could have photographed them so that you wouldn't have had to listen to my awful description).

4) How many frames?

5) Does anyone have a solution to the Registax issue?

6) Is the result a "seeing" problem or a "focus" problem - are there some nights when I should give up on the idea of imaging?

7) Any other comments?

I'll have a go...

1) 16 bit, I would say.  Multiples better bit depth = much better pictures and much better data to process

2) I think so

3) I assume you were using the bahtinov whilst pointing at a star, then slewed to the moon, because it will only work on point light sources, but I think you did that.   if you're using a laptop and seeing your bahtinov diffraction pattern on the laptop screen, then try Bahtinov Grabber, which takes the guess work out of whether the spikes are aligned or not.  Available here - http://www.njnoordhoek.com/  (and while you're at it, raise a glass to Niels).  If you're not using a laptop, it can be tricky, just use a really bright star, one of the famous ones.

4) Lots.  I usually go for about 2 mins worth of 30fps or 60fps, and then go for a small fraction of the best for stacking.

5) no, afraid not.  I like AS2! better anyway though

6) seeing, definitely - "The image was extremely .... well ... fluid is probably the best word for it.  It was like looking through shimmering water" and "soupy" sounds like a perfect description of poor seeing to me !  Focus looks ok

7) other comments - if you're getting lost, use a moon atlas (seriously !  it's quite fun driving round the moon if you've got a close-up view).  Not sure you need to do LRGB, very little colour on the moon - you could probably just go for monochrome L unless you have loads of time.  You've been a little too heavy-handed with the wavelets to be honest, it's a little over-sharpened.

It's a good pic though !  try again another night when the seeing is good

[Luke]

First up, nice shot! The Edge 8 is the favourite of my scopes for imaging or observing the moon

1) I don't think it will make a huge difference either way. The main benefit I have found of 16 bit is that it works great on dark parts of the image if you massively brighten them up. I do that a lot for solar imaging, so it's a big plus there. With lunar, I tend to keep dark parts dark, so don't feel the 16 bit has that much benefit.  The exception could be if Iam using a Barlow and keeping gain down (to limit noise) and the image is very dark. I might think 16 bit could be handy there as I will be making very dark parts of the image much brighter.

4) It's tricky to know what the best number of frames is. These days, after the capture has been analysed, I tend to Ctrl-click in different parts on the graph and find where abouts the frames are still decent (sharpest frame should be left-most on the graph, and most blurry frame should be right-most - at least, that's the theory!), then that's how many I stack. I get the feeling that sometimes it doesn't matter hugely, fewer sharper frames might still end up giving a similar result to more frames that are slightly less sharp as the latter has less noise so perhaps can take more sharpening, ending up roughly a draw. That's just my impression from stacking and sharpening many movies.

6) Sometimes focus can be off, sometimes the seeing just wasn't great. As you get more experience, you'll get a feel from what you see on the laptop screen how good the seeing is and e.g. whether it is okay to ramp up the mag using a barlow. Sometimes the seeing is not really good enough for the 2m focal length of the Edge and the results will be poor. I then either use the 0.7x Edge reducer (costs a pretty penny, I must try my 0.5 reducer that cost a fraction of the price...) if I think that is enough reduction, or I switch to a much shorter focal length refractor. Lunar imaging I find is almost always possible at about 500mm focal length. Seeing last night was okay our way, but it will vary from place to place.

7) I only shoot in mono and don't do colour capture, hopefully someone else can chip in. Without actually having done it, my idea would be to use either the red as the luminance or use a filter like a red longpass to do luminance. The longer wavelength should generally be less affected by the seeing.

Some folks get great results from wavelets but I've never really got anywhere with them. If you can, try Smart Sharpen in Photoshop (with Remove set to Lens Blur) and see how that works for you - try setting Amount to 500% and adjust the radius to whatever looks best to your eye. You might be able to apply a second dose of Smart Sharpen, try a smaller radius and as high an Amount as you can without lots of noise appearing. I am also experimenting with Lucy Richardson deconvolution in Astra Image, but Smart Sharpen is fast and pretty easy to use.

Hope that helps.

Luke

[ArmyAirForce]

I normally shoot at least 4000 frames on the Moon, however this test was just 2000 frames. Camera ASI120MM, ZWO Luminance and Red Filters, Astronomik 742nm IR Pass Filter.

Each AVI was 2000 frames, shot through cloud in less than ideal seeing conditions. 30% of each AVI was stacked in Autostakkert 2, with identical wavelets and histogram stretch in Registax v5.1.

The first image was with the Astronomik 742nm IR Pass filter. This gave the most sharp image.

The second was with the ZWO Luminance filter, and is the softest image.

The third picture was with the ZWO Red filter. This is more sharp than the Luminance image, but still softer than the IR Pass.

If you don't have an IR Pass filter, then I would shoot the Moon through the red filter, as these wavelengths pass through the atmosphere better than green and blue.

[gnomus]

Thanks to all for the responses.  I will give it another go when the seeing improves.  Another thing that occurred to me was that when took the AVIs, the moon was high in the sky, but was almost directly overhead a coal-fired power station that is some 4 miles from my house.  

I will be more aware of this next time and try to get the moon when it is in a more suitable location.  Unfortunately the power station seems to be located almost exactly at the highest point of the ecliptic.  

Knobby: Thanks for the encouragement (I think it probably was mostly a seeing issue).

Stuart: thanks for the link to the Bahtinov grabber - I will try that out next time.

Luke: I think that I will soot mono (perhaps through an IR filter - as suggested by Stephen) - and capture more frames.

Stephen: thanks for the images - the IR filtered one is clearly sharper - I may get one of those IR filters. 

[gnomus]

Just in case anyone may be interested, I have a solution to the Registax issue mentioned above.  That is to shoot SER files rather than AVIs.  Registax was quite happy with the 3000-frame SER files I shot last night.  (Unfortunately, the images were no better, but that is not down to a software problem!!)

[TiTanecd]

What is the quality / size comparison between .avi and .ser?

[gnomus]

What is the quality / size comparison between .avi and .ser?

Jings - you are asking then wrong person    I've only been at this a few nights.  I checked the files, however, and I found that my 3000-frame SER files were around 7.2MB in size, whereas my 2000-2500 - frame AVIs were just under 5GB.  Also the AVIs were 8-bit compared with the 16-bit SER files.  I know bigger ain't always better, but this suggests that the AVIs can potentially produce better quality.  

I cannot do a quality comparison since all of my results have been poor so far.

I would be grateful if someone could tell me whether I should be using AVI or SER - I'd never heard of SER prior to trying this astrophotography business and I, probably foolishly, assumed that SER was the preferred format.

[Blazar]

I have pretty much the same set-up as you (and Knobby). I shoot the 120MM-S at 8 bits (along with a Baader IR pass filter). keeps the frame rate high to help combat poor seeing IMO vs greater number of brightness levels available per pixel (256 for the 8 bit, 65536 for 16 bit...though I guess it does depend on the bit welll depth in the ASI).  I will have a go with a 16 bit version and see what happens.

You have done a good job there on that shot, so don't stop its a learning journey.

From stuff like this (afocal first shots I did though the EP of my TAL):

To recent stuff (same target) through the Edge800 and the 120MM-s (at 8 bits)....seeing plays a major role!  though learnt a lot from more recent stuff...:

Its an awesome hobby....

You might want to use PIPP as well first off then go through your usual processing routine.

2) I usually take the shield off to use the Bahtinov mask...not sure it makes much difference though.

4) Up to you. I usually stick to around 1100 or so sometimes higher. I only stack the best quality frames though, so sometimes I might have shot a 1200 frame AVI, yet only stack around 50 or so. its down to how good the quality graph is. If you start stacking poor frames in with your good ones, then it will degrade the finished article you have worked hard to capture. It is also depends how much free space you have on your hard disk. I came away one evening having to clear off work to squeeze over 50GB of data onto it. a separate overflow drive is now what I have if my startup disk is filling up!

5) Use AS!2...much easier.

6) seeing has been pretty poor recently. it can only improve!

[gnomus]

I have pretty much the same set-up as you (and Knobby). I shoot the 120MM-S at 8 bits (along with a Baader IR pass filter). keeps the frame rate high to help combat poor seeing IMO vs greater number of brightness levels available per pixel (256 for the 8 bit, 65536 for 16 bit...though I guess it does depend on the bit welll depth in the ASI).  I will have a go with a 16 bit version and see what happens.

.....

Steve

Thank you for replying.  I wanted to thank you for posting your images.  That second shot is absolutely stunning - I would be "over the moon" (sorry, I couldn't resist it) if I were able to achieve something like that.  I have an Astronomik IR filter winging its way to me, and I will keep at it.  I do think that some of my issues are related to seeing.  

I have an additional question.  I have noticed that over the course of a 3000 frame (a little less than 2 minute) capture, the position of the moon on screen may shift somewhat - perhaps by as much as an inch or so on my 17" laptop screen.  I am tracking at the sidereal rate, but of course that is not quite the speed that the moon is moving, is it?  Do I live with this, or is there something (probably obvious) that I am not getting?

Thanks again for that excellent moon shot.

Steve M  

[ArmyAirForce]

Not sure about your mount, but the Skywatcher GOTO EQ mounts have options for Lunar and Solar tracking rates too. You need to look for a Lunar tracking rate in your menu.

[gnomus]

Not sure about your mount, but the Skywatcher GOTO EQ mounts have options for Lunar and Solar tracking rates too. You need to look for a Lunar tracking rate in your menu.

Oops - how embarrassing.  It's on page 24 of the manual that came with my mount (CGEM).  

I can have: Sidereal; Lunar; and Solar.  

Erm ....  

[glowingturnip]

if you don't have good polar alignment, you'll get that drift with the moon too.  I have to admit I do tend to just plonk my mount down pointing in roughly the right direction if i'm doing lunar stuff.  There's a lot less drift if you do take the time to polar align though.

[strutsinaction]

Hi Gnomus

To help with Bahtinov focussing you might like to try the Bahtinov Grabber tool (the version without autofocus):

http://www.njnoordhoek.com/?cat=10

Enter your telescope focal length (in metres, not mm), aperture (again, in metres, not mm) and the camera pixel size (in microns) then click the Set Capture Area button. You then click and drag the centre of your Bahtinov image in FireCapture to grab a portion of the image for analysis. The tool then tells you how close t perfect focus you are!

Regards

John

[gnomus]

if you don't have good polar alignment, you'll get that drift with the moon too.  I have to admit I do tend to just plonk my mount down pointing in roughly the right direction if i'm doing lunar stuff.  There's a lot less drift if you do take the time to polar align though.

Thanks Stuart.  I have to admit that I am a "plonker" too - of course that will be obvious from my posts!

[gnomus]

Hi Gnomus

To help with Bahtinov focussing you might like to try the Bahtinov Grabber tool (the version without autofocus):

http://www.njnoordhoek.com/?cat=10

Enter your telescope focal length (in metres, not mm), aperture (again, in metres, not mm) and the camera pixel size (in microns) then click the Set Capture Area button. You then click and drag the centre of your Bahtinov image in FireCapture to grab a portion of the image for analysis. The tool then tells you how close t perfect focus you are!

Regards

John

John: Thanks.  I had downloaded Bahtinov Grabber, but it did not seem as stable as the version you have linked too - it seemed to crash after a couple of minutes.  I wonder if I had previously downloaded the "autofocus" version.  Also thanks for the instructions.  I will give this a go the next time we have clear skies (hopefully some time in 2015!!!)

[Blazar]

Steve

Thank you for replying.  I wanted to thank you for posting your images.  That second shot is absolutely stunning - I would be "over the moon" (sorry, I couldn't resist it) if I were able to achieve something like that.  I have an Astronomik IR filter winging its way to me, and I will keep at it.  I do think that some of my issues are related to seeing.  

I have an additional question.  I have noticed that over the course of a 3000 frame (a little less than 2 minute) capture, the position of the moon on screen may shift somewhat - perhaps by as much as an inch or so on my 17" laptop screen.  I am tracking at the sidereal rate, but of course that is not quite the speed that the moon is moving, is it?  Do I live with this, or is there something (probably obvious) that I am not getting?

Thanks again for that excellent moon shot.

Steve M  

 You are most welcome. I have not been doing this for too long (a couple of years). Have you had a look at some of the Lunar images in the 'Imaging Lunar' section on this forum, will give you some idea of what other people use as well. The IR filter is it an IR "pass' or an IR 'cut'? The IR pass one is the one that is most useful I believe.

I don't usually bother switching to lunar tracking as without a barlow it does not appear to move too much. When you throw a barlow on then thats when it appears to fly across the screen IMO. I will follow your progress on the forum. Look forward to seeing you progress  and your images (if we ever get some more clear nights!)

Good luck!

[gnomus]

 You are most welcome. I have not been doing this for too long (a couple of years). Have you had a look at some of the Lunar images in the 'Imaging Lunar' section on this forum, will give you some idea of what other people use as well. The IR filter is it an IR "pass' or an IR 'cut'? The IR pass one is the one that is most useful I believe.

I don't usually bother switching to lunar tracking as without a barlow it does not appear to move too much. When you throw a barlow on then thats when it appears to fly across the screen IMO. I will follow your progress on the forum. Look forward to seeing you progress  and your images (if we ever get some more clear nights!)

Good luck!

Thank you.

According to the bumf, the filter I have ordered "only allows infrared light with wavelengths of more than 742nm to pass".  I assume that that is a "pass filter" therefore.