Light frames/dark frames etc.

[Nimrodel]

Took some photos of the Orion Nebula a couple of nights ago; my very first attempt. Used my DSLR only placed on a tripod and with a remote.

Now I realize I need to take light frames, dark frames etc. Can someone please explain to me how to do that?

Tried to stack my photos in DSS - but since I don't have any light frames I only got a message saying I need to check the light frames...?

[michael.h.f.wilkinson]

I assume you mean flats. Flat frames are created by taking an image of a uniformly lit area. The simplest way to do this is by placing some diffuser (like a piece of white plastic shopping bag) over the scope or lens, shining white light onto that, and taking a series of frames (usually auto exposure). Special flat panels exist for the job. Darks are simpler: put a cap on the lens and take a series of exposures. I always use the same exposure settings and temperature as the lights (which are the data frames).

[Nimrodel]

Thanks! Also I have to ask - is it recommended to photograph the Orion nebula with a telescope or only the camera lens? I have several lenses - small and big, not sure if it's better to use the smallest or the biggest...

[happy-kat]

Try both :-)

The bigger the lens the shorter the exposure before star trails.

[ollypenrice]

A focal length of about 500mm with an APSc chip gives comfortable coverage of the whole nebula, though you can be either side of 500mm if you wish.

However, without a tracking mount, long focal lengths become too badly affected by the rotation of the earth. First you need an accurate motorized equatorial mount and, ideally, an autoguider to correct its errors.

If you are just using a fixed tripod keep your focal length short and use camera lenses to capture the whole constellation, or a large part of it.

Try the book Making Every Photon Count by Steve Richards for a good over view of astrophotography. (Available from FLO, the sponsors of SGL.)

Olly

[Nimrodel]

This is only 4 seconds and it's still star trails. The photo is one single shot, not edited in anyway (just cropped out the nebula) and extremely bad Just wanted you to have a look. Is it caused by the exposure time or is it just out of focus?

[wxsatuser]

105mm on crop sensor covers the belt, main nebula and a bit more.

8x300sec thru bad LP.

[Nimrodel]

Crop sensor? Is it the same as hitting the zoom in button on the live view?

[nicks90]

no, its the sensor size they are refering too.

some DSLRs come with full size 35mm sensors, others come with APS-C or micro two/thirds. The latter two are called 'crop sensors', as they are physcially smaller and give you a 'cropped' image using the same lenses compared to a fullframe camera.

for instance using a 35mm camera with a 50mm lens will give you a certain field of view. Using the same focal length lens on a APS-C camera will give you approx 1.5x crop factor = to a 35mm camera using a 75mm lens.

dont sweat it. Nothing wrong with using an aps-c sensor.

edited to add:

Ignore the word 'crop'. That makes it sound like it is physically cropping the image and you are losing light. You are not. All that is happening is its focusing the same amount of light on to a smaller square.

[Nimrodel]

Which one of these three lenses would you suggest? Canon Zoom Lens EF 70-200 mm 1:2.8, Canon EF-S 18-55 mm f/3.5-5.6 or Canon EF 50mm F1.8? I have three cameras; Canon EOS 450D, Canon EOS 1100D and Canon EOS 7D. Unfortunately I don't have a remote for the 7D for the moment, so I'll use the 1100D for now since it's got liveview.

[wxsatuser]

Try them all.

Best to stop down a stop or two on the EF lenses, you may be able to use the EF-S wide open.

Experiment and see how the stars turnout, look especially in the corners for odd looking stars.

[Nimrodel]

Will try tonight but right now the polar light is "destroying" my view It's really beautiful so I don't complain