Jupiter 4SE first time with SPC

[ChrisEdu]

So, this is my first ever atempt at doing anything with footage captured by my SPC900NC attached to a NexStar 4SE.

It is from an avi containing about 23 frames (a short clip!) and stacked in Registax 5.1 following the AstronomyShed YouTube basic tutorial. I then did some further messing around in CS4 and Capture NX2.

I'd appreciate any advice on how to make future images larger and how to get a nice smooth circular edge - I used a sharpening tool in NX2, selecting to edge, to try to achieve this.

[Mike Hackenbacker]

very well done.i have the same scope maybe you could tell me how you do it,

[JamesF]

It's possible the edge looks odd because you're at (or perhaps beyond) the limits of magnification for the seeing. You probably need lots more data too.

I'd try to get a couple of thousand frames at 1/10th of a second each or something like that and then stack those to see how they come out (or use the C11

It's a good start though -- far better than my first images of Saturn were.

James

[ChrisEdu]

Thanks folks!

I would certainly use far more frames next time, as this was kind of just trying to get the camera working, what with my documented issues on that front!

Mike, I found the video tutorial from Astronomy Shed to be really excellent for guiding me through the process of the stacking, and I think they do one on getting the avi but haven't searched for that yet. To do this image, I used my 4SE and SPC900NC webcam. I pointed the scope at Jupiter and then ran inside to check the focus on the comuter screen. I then went back out to adjust the focus and repeated this process until I was happy enough with it. Then I used SharpCap to capture about 4seconds of video (just guessed at what settings to use by playing with them until it looked alright on the screen!). Next, I went to YouTube and found the AstronomyShed video on how to use Registax for planets and just followed the video whilst processing my image. I did a little extra tweaking in CS4 and Nikon's Capture NX2, to try to enlarge the image and smooth the edges. If you want to try it and find you get stuck, PM me and I'll try to help from my very clueless perspective!

[Stephen]

good start - now increase that 4 seconds to 4 minutes or so, maybe leave the sharpening tool alone as that may introduce more pixellation than the original

oh and larger jupiter, try sticking a barlow under the camera

[ChrisEdu]

try sticking a barlow under the camera

Hmm.... I've been thinking I ought to buy one! Any recommendations for a decent one?

[JamesF]

But don't overdo it. If you take images for too long then Jupiter's rotation will start to cause distortion.

James

[Stephen]

Hmm.... I've been thinking I ought to buy one! Any recommendations for a decent one?

a good 2x will probably sort you out (for doubling your eyepieces and pushing the scope to F26 for imaging.)

In the £40 bracket, a TAL 2x

In the £80 bracket, a Celestron Ultima 2x

above that, Powermates ... but they ain't cheap

[Stephen]

But don't overdo it. If you take images for too long then Jupiter's rotation will start to cause distortion.

James

Absolutely. Working half drunk here, 4 mins is about doable though isn't it?

[JamesF]

Hmm.... I've been thinking I ought to buy one! Any recommendations for a decent one?

Depends how much you want to spend. The Celestron Ultima 2x barlow and Orion Shorty 2x are "reasonably" priced at the cheaper end of the scale and I've never seen a bad review. I'm happy with my Ultima. They come up in the for sale section every now and then, but are rarely available for long. At the other end of the scale there's the Tele Vue Powermate. Tele Vue also do a 2x barlow, but I'm not sure it's worth the difference in price over the first two.

James

[JamesF]

Absolutely. Working half drunk here, 4 mins is about doable though isn't it?

I reckon most smaller scopes should be ok with four minutes. I can't recall the calculations I saw for Jupiter. At the time I read them it wasn't in the sky, so I didn't pay too much attention. If the cloud would lift long enough to make an extended imaging session a possibility I might have gone back to check already, but there appears to be precious little hope of that happening in the near future

James

[ChrisEdu]

In the YouTube video, the chap suggests capturing no more than 1000 frames to avoid rotation issues.

[Stephen]

In the YouTube video, the chap suggests capturing no more than 1000 frames to avoid rotation issues.

Is it possible you got the context wrong? The number of frames alone is irrelevant, it's the duration of time they are taken over that is.

[ChrisEdu]

Is it possible you got the context wrong? The number of frames alone is irrelevant, it's the duration of time they are taken over that is.

From what I recall, I don't think he mentioned the frame rate, just the number of frames. However, I agree, it must be the amount of time you are capturing data that is important, rather than necessarily the number of frames. I think, what he was getting at was that, assuming a reasonably slow frame rate, 1000 frames would be at the upper end of the time taken to capture that many.

[JamesF]

Exactly so.

In a clear image, every element of the chip in the camera is going to "see" a given area of the surface of Jupiter. Ideally you want to stop imaging before the surface has moved too much across them, so the image doesn't start to mix up the colours when they're overlaid. You may need to allow for the maximum theoretical resolution of the scope in there, too.

Jupiter rotates about once every twelve hours, so you can work out how long it takes for the any given part of the image to cross pixel boundaries.

I'm fairly tired at the moment and my memory isn't at its best, but I'll try to look up what it says in my planetary imaging book over the weekend.

James

[Stephen]

Exactly so.

In a clear image, every element of the chip in the camera is going to "see" a given area of the surface of Jupiter. Ideally you want to stop imaging before the surface has moved too much across them, so the image doesn't start to mix up the colours when they're overlaid. You may need to allow for the maximum theoretical resolution of the scope in there, too.

Jupiter rotates about once every twelve hours, so you can work out how long it takes for the any given part of the image to cross pixel boundaries.

I'm fairly tired at the moment and my memory isn't at its best, but I'll try to look up what it says in my planetary imaging book over the weekend.

James

Headache inducing.... Don't forget all calculations will depend on your focal length and sensor dimensions.

Maximum movie length for planetary imaging

[ChrisEdu]

I'm fairly tired at the moment and my memory isn't at its best, but I'll try to look up what it says in my planetary imaging book over the weekend.

James

That will be interesting to know. Thanks.

Likewise, too tired to think now, so off to bed!

[JamesF]

Ten hours. Jupiter rotates about once every ten hours. No idea why I wrote twelve.

James

[Nathan_Pembs]

The latest issue of Astronomy Now magazine has an article on imaging Jupiter, according to that scopes sized 150-250mm gives you a 2 min max before cloud details being to blur.

As you scope is smaller, you could perhaps get away with a 3-4 min capture.

[Stephen]

The latest issue of Astronomy Now magazine has an article on imaging Jupiter, according to that scopes sized 150-250mm gives you a 2 min max before cloud details being to blur.

As you scope is smaller, you could perhaps get away with a 3-4 min capture.

I've not got to the article yet, does it factor in sensor (pixel) size?

[Nathan_Pembs]

I've not got to the article yet, does it factor in sensor (pixel) size?

No mention of sensor size, quite a general watered down article to be fair. Dipping the toe in as it were

Brief mentions about frame rates, but that's about it.

[Cloudwatcher]

........how to get a nice smooth circular edge ............

You could try making another layer of the background as a mask,place on top of original and expand Jupiter until the frilly edges disappear.......

[JamesF]

TBH I think that one looks less "real" than the original.

James

[JamesF]

Just found some stuff in Martin Mobberley's "Lunar and Planetary Webcam User's Guide" about capture periods. He suggests that to prevent smearing of the image you need to stop capturing before the fastest-moving part of the image has covered 0.5 arc seconds of your field of view. I'm not sure where that figure comes from as I've just skimmed through to find the maths. He gives the following formula:

time window = drift limit / (( pi . apparent planet diameter ) / rotation period )

where the drift limit is 0.5 arc seconds and the apparent planet diameter is measured in arc seconds as seen from your point of view. Personally I'd prefer to write it as:

time window = drift limit * rotation period / pi / apparent diameter

but it's the same thing.

I don't know what the current width of Jupiter is, but he suggests 45 arc seconds when it is in opposition, and the rotation period is 590 minutes, which gives:

time window = 0.5 * 590 / 3.14 / 45

or two minutes plus a few seconds.

Compare that with Mars, which might be 25 arc seconds wide and rotates in 1477 minutes:

time window = 0.5 * 1477 / 3.14 / 25

giving you almost nine and a half minutes.

The question now is whether you should stick with the 0.5 arc second resolution figure or change it based on your combination of camera and scope. The Dawes limit for your scope suggests you wouldn't even be able to resolve detail down to one arc second across, so a limit of four minutes sounds perfectly reasonable for Jupiter. You also need to account for the resolution of the camera, but I haven't got that far yet.

James