What timespan for a Solar AVI?

[Space Cowboy]

Being a Solar imaging virgin I was just wondering how long I can capture an avi for? I will be using my planetary DFK 21 cam at f11.8 (Skymax 127 scope). Obviously the Sun only rotates roughly once a month so I'm thinking of the Earth's rotation.

Due to hard disk space I wont be going longer than 5 mins per avi.

[Bizibilder]

I've happily taken 4 or 5 min avi's of the Sun. (I use my HEQ5 which is well polar aligned). As you suppose disc space is the real limiter.

[Space Cowboy]

Cheers Roger!

[JamesF]

I'm not sure the Earth's rotation matters because you can track the sun to counter it. The Earth's orbit might. A rough calculation suggests that the earth's orbit should be about two arcseconds per minute. I'm being really hard of thinking this evening though and I can't immediately see how to fit that into my formula for imaging time. I'll see if I can work it out.

James

[Space Cowboy]

Thanks James yes of course the mount tracking cancels out the Earth rotation, silly me lol

[JamesF]

Doh! I'm being daft. I've just realised I can get all Greek and pretend the sun moves relative to us. So, my formula for maximum capture time for planets is:

t = 206265wpk / πfd, where

w is the size of a sensor pixel in metres

p is the period of rotation of the planet

k is the fraction of a pixel acceptable for rotational drift

f is the focal length of the telescope in metres

d is the angular diameter of the planet in arcseconds

if we treat the Sun as having a rotational period of 395 days (365 days for the Earth. plus 30 days of its own in the same direction) and use 0.5 for k, that would give

t = 5.8 x 10^8 w / f

For your DFK, w is 5.6 x 10^-6m, and for the 127 Mak, f is 1.5m, so that gives t = 2179 seconds or just over 36 minutes.

I can't immediately see anything wrong with the maths there, but it's certainly possible.

James

[JamesF]

In case anyone wants to know, I assumed the angular diameter of the sun to be 32 arcminutes. Obviously it varies a bit depending on where we are in our orbit, but not by enough to make a large difference to the interpretation of the result, I feel.

James

[hunterknox]

If you're after capturing granulation then be aware that granules will reorganise themselves over a period of few minutes. I usually try to keep AVIs under 90 seconds for that. If you're aiming for full disc and don't care about the finer detail then longer exposures are fine.

[Photosbykev]

I typically shoot a minute avi with a dmk21 camera giving me 3600 frames to play with in Registax 6 and use the best 50% to stack. With the dmk41 I still shoot one minute videos but only have 900 frames to play with

A lot can happen in a minute

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[JamesF]

That's a good point. The formula I posted above accounts for movement of features across the surface, but doesn't account for them changing. If they're changing on a scale that's possible to resolve with your camera/telescope combination then that is probably the determining factor when imaging the Sun.

James

[Ant]

I normally aim for 2100 frames - which is 35 seconds at 60fps. I have no reason for this number it's just what I do.

Ant

[JamieW]

Is there much point going beyond a couple of thousand frames? Isn't there a law of diminishing returns when it comes to stacking?

Not that I'd know, my software gives up when the avi reaches 2Gb which is roughly 500 frames.

[hunterknox]

I'll defer to Kev any day!

[Space Cowboy]

Terrific information fellas! I would be taking fairly high fl images so maybe it would be best to keep the avis short though I will experiment. I'm guessing noise level is not such an issue with solar as it is with Planetary so long avis may not be necessary.

[Photosbykev]

If you are struggling for disk space you could get a USB external hard drive and store the data on that

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[GreatAttractor]

Remember that large number of frames is not only about increasing signal-to-noise ratio, but also increasing the chance of getting more good quality frames - seeing during the day is worse than at night. Plus even the Sun gets pretty dim when you push the focal length and add a dark filter like the Solar Continuum. For high focal length work I wouldn't shoot for more than a few minutes; in my sunspot time-lapse I used 1-minute videos per each final frame and 5-minute intervals. Filming a sunspot in detail for more than these few minutes would just make it fuzzy.

[Space Cowboy]

Remember that large number of frames is not only about increasing signal-to-noise ratio, but also increasing the chance of getting more good quality frames - seeing during the day is worse than at night. Plus even the Sun gets pretty dim when you push the focal length and add a dark filter like the Solar Continuum. For high focal length work I wouldn't shoot for more than a few minutes; in my sunspot time-lapse I used 1-minute videos per each final frame and 5-minute intervals. Filming a sunspot in detail for more than these few minutes would just make it fuzzy.

Thanks! Interesting to hear seeing is worse during the day.

Cheers Kev, my netbook has enough HD space to keep me happy if i don't get carried away, about 80 gigs is what i normally use on one given session.

[Photosbykev]

My one minute videos are 1Gb in size so its an easy calc to see what space I need i

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[Avdhoeven]

I always take 30s movies at 60fps and that works perfectly...

[Space Cowboy]

Thanks! Just gotta wait for the weather to improve lol Nearly got a capture yesterday evening but the cloud appeared right on cue once the cam was in place!

[thenews24]

I usualy won't capture for more than 30 seconds, even when using my eq mount. Disc space isn't too much of a problem, but loading huge files into registax is.

Here is a vid of the avi files, then the processed images following the recordings. The longest was the first one at about 33 seconds. I can only get 15 fps with my cam, so your looking at about 490-500 frames total, which is more than I need. I'm usualy pleased with the results from even 100 or 200 frames.

http://youtu.be/dBm2A1B8e_Y

[Space Cowboy]

Very impressive! I'm surprised more people in Solar are not following us Planetary guys and using AS!2 (Autostakkert) for stacking and aligning as its so much quicker than Registax.

[Photosbykev]

Very impressive! I'm surprised more people in Solar are not following us Planetary guys and using AS!2 (Autostakkert) for stacking and aligning as its so much quicker than Registax.

I think some people are switching to AS2 but I really struggle with it so at the moment I'm happy using Registax 6 with 1 - 2Gb videos

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