Filming for Photos

[smeech]

Hi all

I'm a little confused. I have a dslr and will soon be getting a telescope - hopefully an Equinox 100 and if not a mak 127. I am puzzled though, I have read that you can use a webcam to film lets say a planet and then use registax to create the picture. I think I understand this bit. But - can you use the HD film mode on a DSLR and do the same thing? Would it be better just to take pictures?

All help is much appreciated.

Thanks

Steve

[Cornelius Varley]

I suppose you could. The advantage of a webcam over a DSLR is that a webcam (SPC880/900) costs a lot less, @£30 v £500

Peter

[ismangil]

Not necessarily.

Proper experts on astrophotography will explain it better.

From what I read in books regarding astrophotography there is an issue of image scale.

Because a DSLR imaging chip is large it is harder to get a small object to register properly on it.

[smeech]

I think my point is, is it really that easy? Got a new tripod (my first ever) today so am going to try out some widefield with my 55-250 lens and see what happens.

I'm guessing long exposure and high iso. It will be unguided so do you have any idea how many degrees the earth moves a minute? Will try and move my tripod manually! It's going to be tough but hey i've got the tools I might as well use them!

[ismangil]

For lower focal length, on a DSLR you can try up to 30s without the star start trailing. Longer focal length, over 3s and the stars would trail.

I would think trying to keep up with the rotation manually is hard without introducing movement to the stars.

The Sky At Night April 2011 has a good intro on DSLR wide field photography.

[ismangil]

On your other point: is it that easy, well yes and no. The equipment is easy enough, the technique not quite. There is a whole book on it by Martin Mobberley.

[Jannis]

for planets, don't count on a dslr unless you are able to record using crop mode to "increase optical zoom" by using only a smaller area of the sensor to record. otherwise the planet will be way too small to see as anything else but a bright dot.

if you Have a crop video mode on the dslr, then yes, it's that simple. get a tripod, a scope, record, and stack good frames in movie later.

be awere it Will be insanely hard to manually track the planet, not to mention even finding it at that high magnification.

in my case for example, with a 1000mm scope, and the canon 550d at video crop mode (640*480 pixels used) the focal lenght is equal to in old standard 35mm FF:

1000mm * 1,6 (APC sensor) * ~7x crop = 11200mm...

now imagine walking around with an 11.2 meter long lens, and manuallt follow an object on the sky, and there you have how hard it actually is without a good tracking mount. oh yeah, and you have no image stabilization on that 11 meter lens either...

[smeech]

Thanks Jannis. Its reassuring you have a 550d. I have one too. Was just going to give widefield a go first. Will progress to planets once i have had scope for a while. Will be getting an equinox100 i hope so am guessing a barlow will be needed also!

Thanks for all the help. Tough to get your head round these things when you are a noob.

[Jannis]

We have all been wondering about these things at one time, hehe

Here's how saturn looks at 1000mm with the 550D:

and made 4x larger:

[smeech]

Blimey! That's really good. Presume it is through a telescope that has a focal length of 1000mm. If I were to buy a 100ed (which is 900mm) would I expect to see the same thing?

Was going to give my new tripod a bash with some widefield tonight but the clear skys of today have now disappeared and all I can see are yellow clouds (because of the streetlighting).

Thanks for you help.

[Jannis]

Yes, you shuold be able to see it very similar. personally i'm looking to get a barlow though, as it's too small even when using the crop mode on the 550D's sensor.