I am just starting out in Astrophotography and have a question............

Instead of stacking many images to assemble a final image, wouldn't work as well to take one good image, make a hundred copies and stack them?

I bought a Supercurcuit 0.003 lux PC164C b/w camera a couple of years ago.....from stuff I read on the web it ought to work well for prime focus imaging.

Between that camera, my Nikon FG (35mm) and a Nikon 4500 Digital (Afocal) I ought to be able to make some purdy pictures..............

Digital works both ways. You can take a single 5 minute image or 5x1 minute images. The information build up would be the same. Reasons for the shorter exposure would be your tracking abilities. Errors occur with longer exposures. The other advantage of more exposure is to keep the noise down with faint objects like a small comet or DSO. It is like pouring salt from a shaker---the more you pour the more information you get and the less amount of noise. Hope this helps
Mike

Another reason to use multible short exposures for example is the Orion Nebula. It is a fairly bright object and taking too long of an exposure could blow out (over expose) the core and what Mike said about tracking errors. Long exposures will increase the risk of star trails and camera noise. You can get alot of data from 1min. Unforntunatly I do not have those problems, because none of my camera equipment is capable of more than 15sec. Maybe after I get my 8" Newt, but don't tell my wife...

Larry

But my original quest was, could you take one 15 second clean image of, say the moon, make 100 copies, and stack these............wiould this work?

Sorry, I didn't understand the question. I don't know about that. From my own experience if you duplicate an image and then combine them, you end up with the same image that has flaws twice as bad. I am sure someone has a better answer for you.
Mike

That answers it.............thanks.

Hey Leonard,

Have you had a chance to do any imaging yet? I hope you will post your efforts.

Larry

I got one picture with my Nikon 4500 through my 10"SCT of Saturn.............You can tell it is Saturn, but that is about all.

During the Mulberry Mnt Star Party, I hope to try some Wide Feild shots with my Nikon FG 35mm with a 55mm f1.4 lens, piggybacked on my 10" SCT / CG5 AGST and mayhap some prime focus. I will also have my Nikon 4500 digital camera/adaptor. The moon will be visible and I may try to take some of it.

Hey Leonard,

When you gonna show us some of them images from MM? I sure wished we could have been there... I have not had my scope out since May 9th. but, tonight the scope is outside equalizing and I'm going to try raw images of the moon. I've installed a raw mod for my meb cam hoping to improve the quallity.

Clear skies,
Larry

On Saturday, about 2am, I took several Afocal photos of Jupiter with my Nikon Coolpix 4500, a universal camera adaptor and 10" SCT/ASGT mount. I was using a 2" 30mm eyepiece with a 13% moon filter. I set the camera exposure to 2 seconds. after I centered Jupiter in the frame, I set the camera zoom to 3X so it would be a little bigger in the finished picture.

The pictures turned out great...........Now I need to figure out how to post pix in this forum...................

On Sunday, about 3am, I piggybacked my 35mm Nikon FG (with 400 speed film - 50mm F:1.4 lense) on my 10" SCT/ASGT mount and took several exposures.

The first pix I took were centered on Jupiter in the eastern section of Sagittarius. Since bright Jupiter was in the shot, I limited the time exposures to 1 minute, 1.5 minutes, and 2 minutes.

The next group of pix were centered on Sadr, the central body star of Cygnus. 1 minute, 2 minutes, 3 minutes, 5 minutes and 10 minutes.

The last group of pix were centered on the Lagoon Nebula again in Sagittarius . 1 minute, 2 minutes, 3 minutes, 5 minutes and 10 minutes.

I think I had a pretty good polar alinement and I hope the pix come out OK.........I will have them developed later this week.

To post the pix, I guess I need a website to post the pix to and reference with the "Img" command above, Correct?

Figured it out........................







I think the last one is the best image!!!!!!!!!!!!!

That's a great afocal image with lots of cloud band detail and it looks like you got a few of it's moons too...way to go Leonard! This Sunday the GRS will be in view around 12:30AM to 3AM Hopefully the cloud gods will be happy...

Hi Leonard,

Each individual frame you take has a related signal to noise ratio, where signal is the light you capture from the object in question and noise is randomly generated from the camera to gain brightness.

So, when you capture several frames and stack them, since the signal is always present in the same pixels they are preserved while the noise kind of cancels.

Now, the longer the exposure the less noise it generates.

You can think of it in terms of film. If you were taking a shot of a dim object and use for example a 1600 ISO film you might need only say 1 second, while using an ISO 100 film you might need 5 sec. But the size of the grain of the ISO 1600 is much bigger than the one of the ISO 100 film, right?

Think of the size of the grain as the noise of the digital camera. If you were able to use 5 sec. it would be better to use 100 ISO, but in reality you might better use 1600 just to be sure you get a picture at all
Now, imagine you can take several pics at 1 sec using 1600 film. The grain on the film will never be the same (that is the noise equivalent) so at the end if you stack them you would get a picture very similar to the one using 5 sec at ISO 100.

If at the end you were able to take as sharp an image using 5 sec instead of 1 sec you should, several times and stacking them.

All this applies for dim deep sky objects.

For the moon and planets you never need exposures longer than a fraction of a second. You can try to stack many of them using programs like registrax.

Finally for objects like the Orion nebula whose core is very bright but the nebula outer part is dim, you might want to try short exposures for the core and longer ones for the outer part. Then use photoshop or similar and masking technics as found here:http://starizona.com/acb/ccd/software/ps_dynmask.aspx

Best,
Pablo