question about planetary detail

mark3d · #1 07-03-2008, 10:23 AM

i understand that photographs of DSOs are more spectacular than the objects appear visually, because the long exposure catches much more light than our eyes can.

with planets though, i dont see how this can be as much of a factor - planets are so bright that any photo would have to be short exposure.

therefore i dont understand how a 12" dob can take images like this:

http://www.iceinspace.com.au/mygalle...turn-150px.jpg

but all we see with a 10" dob is a small white disc with lines out the side? granted we are only looking at 150x, and the seeing has not been great, but there is a huge difference. is the photo just taken with very high magnification?

if thats the answer, i have more EP shopping to do!

so far the DSOs have been very impressive but the planets a bit disappointing.

if i could see images like that photo i would be ecstatic! if its just a combination of getting the right conditions with the right magnification then thats a challenge im happy to undertake

goober (Doug) · #2 07-03-2008, 11:08 AM

I'm not an imager, but I think those stunning planetary shots are composed of many, many images, run through some processing software. Don't ask me what happens at that stage, but the results out the other end are stunning.

For the visual astronomer, we have to wait for that magic moment when the seeing steadies for a split second, and you see the stunning detail. The better the seeing, the more often those split seconds come along.

rmcpb (Rob) · #3 07-03-2008, 11:42 AM

Doug is right. Imagers take LOTS of images and stack them together to get more detail with each image. In this process images that are affected by bad seeing are dumped so only the good ones are stacked. With each layer more of the constant signal is added and the noise from seeing effects and from the chip are reduced finally producing a very detailed image.

Our poor old eyes can only use the image that is presented to them at the time.

mark3d · #4 07-03-2008, 12:34 PM

thanks guys that makes sense.. it sounds like the stacked images bring out the detail and colour. being able to discard the ones with bad seeing sounds great!

they do still seem to get very high magnification even from 80mm APOs.. do they just use high power EPs and/or are the images scaled in the software too?

rmcpb (Rob) · #5 07-03-2008, 02:23 PM

They use all sorts of bits to get higher and lower magnification. They often use barlows and powermates to increase the magnification and focal reducers to get wider fields of view with the corresponding lower magnification.

Of course the final image can be scaled by software as well BUT to get the detail you need the raw data from the initial images, hence the hardware used.