Total Frames before it becomes an overkill

[Intergage]

Afternoon all,

Just checked out the cloud cover for tonight and saw the magical '0%' so I'm going to attempt another Saturn shot at about 6:30 - 7pm tonight.

I took these a couple of night ago http://imgur.com/a/rIAQo
The Saturn picture is 3000 frames in total and using the best 85% of the frames.
I have worked out I should be able to get about 10k - 15k frames of Saturn before I start to see rotation from the earth in the images.

What I am wondering, is it worth taking so many frames or does it get to a point where adding more data isn't going to make it any more sharp or clear?

Sorry about the awfully written post, got a bit confused myself while typing it haha.

[Camelopardalis]

Nice one mate :thumbsup:

The seeing is the important thing for bring out any detail in Saturn.

I'm no expert, but I don't see anything wrong with lots of frames, but flip the processing on its head and if you get say 10k frames, try stacking just the best 10-15% and see what happens. You should be able to see a difference. If not, then the seeing is magically consistent.

You should find that stacking so many frames is actually blurring the image, if the seeing is all over the place like it is whenever I try :lol: so by recording so many more frames it gives you a larger selection of frames to choose from.

I'm sure there is a point of diminishing returns...but the more good frames you capture the better IMO. Just make sure your scope is cooled, etc, to maximise your chances.

Btw, field rotation doesn't matter as Registax will take care of that during stacking.

[tonybarry]

Saturn is a planet which rotates on its axis every 10 hours 39 minutes (at the equator). If you are looking for surface features, you really need to limit your session duration to somewhere around two to three minutes, or any feature will get blurred.

Field rotation should be handled by the stacker.

If all you want is the Cassini Division, you can image for much longer session duration.

The earth's rotation will affect you every 12 hours when the sun comes up.

Regards,
Tony Barry

[Intergage]

Hey! Yeah! Completely missed that. Spent all day pondering this too.. If I take as many as possible before Saturn leaves the field of view for my horribly aligned dob that should give me a large number of AWESOME frame rather then a large number of mediocre frames?

I am understanding this correctly, right? haha.


Hey TonyBarry,

Yeah just trying to get the Cassini Division and at least a little detail on Saturn would be nice. The fact I have a dobsonian goto mount and not an EQ tracking mount (Or is it EZ?...) will that effect the duration of my session?



Thanks again for both the replies.

[Camelopardalis]

Well, the more frames you take, the more of them will be mediocre but the proportions should be more or less the same, and by laws of averages you should get more awesome frames :D of course, it's entirely possible that you click the record button just as the seeing deteriorates and you get a higher proportion of mediocre ones...

Take a bunch of sequences. Hard disk space is cheap. Good night under the planets, not so much :D

But also, spend the extra couple of minutes getting the alignment right with your Dob so the object stays closer to centre for longer. Mirrors aren't perfect, especially as they tend to the edges. And you'll be able to take longer sequences with more accurate tracking.
Doesn't matter whether you're using a Dob or an EQ for planetary, so long as it's tracking well....reason being is that the individual frame exposure time is very short - I'm using 15-20ms but it depends on what your camera will support - and in that time there's very little field rotation, or noticeable rotation of the planet in question. I found with Mars though he features do move within a few minutes though, so faster = better if there are high contrast surface features.

[tonybarry]

Hi Matt,

Goto Dobs are good for tracking, but not so good for long exposures. Since you are on Saturn, long exposures are irrelevant. You will have quite short exposures (e.g. 1/500th second to 1/100th second). What will matter is the seeing - how good the air is above you.

The knowledgeable people say that Lucky Imaging (which is what you are doing) has an upper limit of (about) 1/100th sec per exposure. That is where the sky is effectively "frozen" and if something is clear it will stay clear for the duration of the image. Now the whole planetary disk will not be clear, but parts of it will be, and that is what AutoStakkert will use.

The Canon will take perhaps 4 frames per second until the CF or SD card is full, and at that point you probably call that one session. Change cards, start another session while you copy the first card to disk. Repeat until weary. You could download to disk straight away (using EOS utilities), but that takes maybe five to ten seconds per image. You are better off just doing a burst to CF. Much quicker to get some numbers under your belt.

Then come inside and stack sessions.

Hope this helps,
Regards,
Tony Barry

[archioptic]

OT: I thought these images looked familiar. I saw your post on the r/astrophotography sub on Reddit and asked about your set up details. Good to see some Aussies in there.