Rotational Blurring "Myth or Real ?"

[Clayton]

Further to my attempts to de-mystify this black art

I conducted an experiment by stacking the results from 2 avi's

The first beginning at 20:55 and running for 120sec till 20:57.

The second beginning at 21:00 and running for 180sec till 21:03.

Both taken on the 22nd November through a 200mm Newt at a total of 2.4m focal length. I will leave the judgement of the results up to you.

With the disclaimer that I firmly believe that rotational blurring is real and should be considered in high end rigs. I simlpy wish to ask if maybe we are taking it too far at the lower end ??

Also the total length of data may be less than 8min due to me not being aware of the actual temporal extent of the frames chosen by Registax for this test.

[Clayton]

For comparison this is the earlier (20:55) more conventional 120sec image by itself

[GazOC]

I agree, the figures seem to come from people imaging at crazy (for us mere mortals) focal lengths. I think most of us could get away with quite a bit longer.

I can't seem to remember the maths behind the figure but, along side rotational speeds and pixel size, focal length is a major factor.

I think people are taking that x minutes is the maximum length of time without making allowances for the decreased focal length.

The above could, of course, be complete codswallop!!

[Ant]

I've always worked on the principle that the maximum for Jupiter is around 1 minute before the increase in frames is negated by the rotation of the planet itself.

But it was a figure that I picked up through chatting with people rather than any scientific method.

You guys are probably right, you need to me imaging at very high focal lengths before it becomes an issue.

Ant

[GazOC]

I have a book somewhere with the formula in. I'll try and dig it out....

[GazOC]

maximum time = (206265*P*T)/(2pi*F*R)

P = pixel size in mm

T = Rotation period of the planet in seconds

F = Focal length in mm

R = Radius of the apparent diameter of the planet in arc seconds

[Tim]

ow ow ow numbers..........make my head hurt and my eyes bleed.

Great pics btw.

[Clayton]

This formula tells me I have 74 seconds which I think is far too stringent. Other factors like seeing and focus will extend this time. even the "big boys" will capture for at least 90sec

[GazOC]

So much for that book!!