Jupiter GRS Transit 25.11.13 ASI120MC

[catman161]

ASI120MC, 200P, NEQ6 Pro, Televue 2x Powermate. Best 1300 frames of 1500 captured in sharpcap 2 at max resolution and frame rate and stacked/tweaked wavelets in Registax 5.1.

Second time using the ASI120MC and still need to get used to it. I have just recieved and fitted a moonlite focuser since taking these and the DC motor should arrive tomorrow which wil be great as it takes ages focusing by hand and waitng for the scope to stop shaking only to have to tweak the focus again!

Anyway, comments/help welcomed

Capture 25_11_2013 22_37_01 by Gattouomo161, on Flickr

Jupiter 25_11_2013 22_23_35 by Gattouomo161, on Flickr

[Johan L]

Looks good! You have nice detail there. I think you could try a 3x barlow or even a 4x barlow.

Johan

[catman161]

Thanks yes a 4x powermate is on the purchase list-will be in new year sometime now though.

I am hoping the moonlite focuser and DC motor will help with getting the images that bit sharper as it has really been hit and miss with focusing by hand

[JamesF]

An excellent start.  Having come from using an SPC900 I did find the ASI120MC took a while to get the hang of.

I'd suggest reducing the frame size and going for a faster frame rate for more total frames I think.  You could also get a bit more image scale by adding an extension between the barlow and the camera.  I used an old Skywatcher kit 2x barlow that I've removed the lenses from.

It might also be worth giving AutoStakkert!2 a go for the stacking and then use Registax for wavelets.  I reckon AS!2 almost always does a better job than Registax.

The ideal focal ratio for imaging with this camera is probably between f/20 and f/25, so a 4x or 5x barlow/powermate would probably work quite nicely.  It can be a pig to get the image on the sensor at that point though.  An illuminated reticle eyepiece can be very handy for getting the image dead centre.

James

[catman161]

That's brilliant advice thanks James I'll check the other software out. I also use a flip mirror I help with gettin it on the sensor more easily. I used the SPC900NC until very recently so am sure that with right conditions and maybe trying to extend the focal length a little I can maybe get a bit eyed quality images. I have also purchased the 1.5 inch moonlite extension tube for my new focuser so I will try adding that uti the image train to see what effect it has. Thanks for the advice

[Space Cowboy]

Nice images Mr Catman! As James says more frames is the key. If you capture around 10,000 frames at 640x480 then you can be more selective when stacking, personally I'd stack 1-2000 in poor seeing and 5-6000 in good conditions.

[catman161]

Thanks Cowboy Thats something I had not thought of doing. Do you mean getting up to 10,000 frames in smaller say 1000-1500 avis and joining together? If i went for 100,000 frames all in one go would I not encounter rotational error?

[catman161]

*10,000 not 100,000 lol!

[jambouk]

I'd emailed damian peachy earlier in the year when i started out with planetary imaging, and he suggested to get 5-6 minutes of data on saturn, and that has a similar rotational period as jupiter, though admittedly less surface detail. I guess it depends on your frame rate... If you can get jupiter on a really small area of the sensor, and get the frame rate up to 60fps, you could capture 10000 frames in less than 3 minutes.

Right, back to scrubbing my sensor clean....

James

[Space Cowboy]

Rotational blur is not an issue at these focal lengths when capturing a 3 min avi. The stacking software corrects the small rotation during this time. Too many people worry about this when they should be capturing more frames. Basically Jupiter is 3 mins, Saturn 6 mins and Mars 6 mins.

You can use the program "Winjupos" to de-rotate the stacked 3 min avis into one image covering 10-15 mins of capture time but thats a more advanced level of processing.

[JamesF]

You can actually calculate a theoretically optimal capture time depending on what level of error you're willing to accept, so I did  It's documented in the second half of this page: http://www.tanstaafl.co.uk/2012/03/focal-ratio-capture-length-planetary-imaging/.  Speed of rotation is only one factor.  Focal length and pixel size are others.

Under UK skies I reckon you can easily double my calculated figures in all but the most exceptional of conditions because whilst you might not want any feature to move more than half a pixel during the capture the limit of resolution just isn't that good to start with.  It might be interesting to redo the calculations with the limit not on how much a feature may be allowed to move on the image sensor, but what (seeing-limited) angle it may move through.  If your average seeing means you can't resolve below two arcseconds for instance, it might be interesting to redo the calculations to give a capture time that allows no feature to move more than one arcsecond.

Working at the sorts of effective focal lengths we're using with the level of kit we have access to, I'm in agreement that the figures Stuart gives are definitely the right kind of ballpark and they're what I'd recommend to people.  I might go a bit shorter on Jupiter, but generally only if the seeing was very good and I could sustain a high frame rate.

James

[Space Cowboy]

Yep if you can see rotational blur on a 3 min avi you must be capturing one hell of a detailed image.

Here is what happens in practice :

http://stargazerslounge.com/topic/169898-jupiter-dec-1st-de-rotate-comparrison-update/

[catman161]

Great stuff, thanks guys I will try this out for sure once I have got used to how to sort the frame rate out on new camera-I've only used it twice and just set the frame rate to maximum both times. Cheers

[si@nite]

Nice capture catman!

[catman161]

Thanks Si

[jambouk]

My primitive understand of the frame rate for the camera seems to be dependent upon:

Exposure time (shorter exposures allow fast fps).

Gain (again I think maybe less gain may allow faster fps, but that may just be making it up).

Amount of the sensor in use (smaller area = faster fps).

Laptop / connection (though I am using a 15m active USB lead from my laptop to the camera, running on its own internal battery and I was still getting nearly 50fps the other night).

I'm looking forward to your next clear night Felix. I'm expecting high things with the focus now

JD

[catman161]

Oh man now I feel pressured James! I need to get my head down and read a bit more about planetary imaging instead I just learning as I go and seeing what happens. Maybe I'll get better results but quicker

Thanks for explanation re:frame rates I've got something to mess about with now.

[JamesF]

My primitive understand of the frame rate for the camera seems to be dependent upon:

Exposure time (shorter exposures allow fast fps).

Gain (again I think maybe less gain may allow faster fps, but that may just be making it up).

Amount of the sensor in use (smaller area = faster fps).

Shorter exposure times allow you to take more exposures in the same period of time, so yes, in general you'll get a higher frame rate with shorter exposures (though some cameras allow the frame rate to be set separately).  Gain is the "amplification" applied to the captured signal, so it won't affect frame rate but it will make the image brighter.  Where it can come into play is because shorter exposures give a dimmer image which may then be corrected by increasing the gain.  Unfortunately with increased gain comes increased noise.  It's a balancing act.

The smaller the number of pixels in use the smaller the amount of data that has to be transferred to the host computer.  In some circumstances that can fix an effective maximum frame rate because the camera just can't shove data down the pipe fast enough to keep up with its own capture rate.

James

[JamesF]

Oh man now I feel pressured James! I need to get my head down and read a bit more about planetary imaging instead I just learning as I go and seeing what happens. Maybe I'll get better results but quicker

Thanks for explanation re:frame rates I've got something to mess about with now.

I'd always recommend people get out there and do it.  Nothing counts so much as experience and practice, even if this time the results aren't as good as you want or were expecting.  Only after a couple of years did I reach the stage where I was confident that I could go out and spend several hours imaging and be sure to come out of it with something passable, and then I changed cameras and had to start learning all over again  The important thing is to keep at it and learn from the bad days (of which I've had plenty).  Getting to understand the physics of what was going on really helped get me through some of the times when it just didn't seem to go right.  When you've spent four hours sitting out in the freezing cold one night only to find the next day that all your data is rubbish, it's encouraging to know that you are at least learning something from it and can move forward next time.  It's just a shame that in the UK, "next time" might be several weeks away  It's amazing how much better you get if you get five or six clear nights on the bounce.  At least until the exhaustion takes over

So don't feel pressured.  Go out, enjoy it (most importantly), get as much data as you can and think of "the ones that got away" as just a natural part of the learning process.

Actually, now I come to think of it, there's another thing... Many capture applications (my own, FireCapture and SharpCap for certain) allow you to save a text file with the camera settings for each capture run.  Always leave that turned on.  When you're learning the ropes, even if you think you've got the best data you can (and I'd always say "do more runs than you think you need"), it's always worth doing some more capture runs varying the settings to learn what effects they have.  You may even find you actually end up with better data from different settings, but either way you have a record of what they were and potentially can reproduce them in the future.

James

[catman161]

Great advice thanks James I do leave the txt file of settings on and often look at them-well mostly when people ask what settings I used and then I go back and have a look

[U Cyg]

Nice image Catman!

Angie

[jambouk]

In fact felix won the photo of the month competition on the east midlands stargazers forum with this image:

http://www.eastmidlandsstargazers.org.uk/topic/6450-picture-of-the-month-november-2013/

Well done felix

Jd

[catman161]

Thanks Angie

Oh man JD, you're embarrassing me!

[todd8137]

hi these look brill hearing a lot about these cams ,i'll stick with the dmk 21 and filter wheel for now but a fore see some great images coming are way

pat