need help with adobe photoshop!

blazingice · Post by **blazingice** » Sun Jul 18, 2004 1:21 pm

Cool. That's much better than the original one you posted - can see much more although it looks somewhat blur. How long was the exposure for this photo?

MooEy · Post by **MooEy** » Sun Jul 18, 2004 1:43 pm

not my pic, i merely edited it for hlyf. i think i tried to push the pic too much liao.

~MooEy~

hlyf · Post by **hlyf** » Sun Jul 18, 2004 1:49 pm

whoa.. what did u adjust to get this?? hmm quite patchy, but def than my original

well if i use photoshop's autocontrast alot more stars appear, but much much more noise appears too... so i just need a way to improve contrast of the stars without bringing out all the noise....

carlogambino · Post by **carlogambino** » Sun Jul 18, 2004 5:36 pm

mak,pple dun do one time exposure, they tack short exposures using registax then edit using photoshop...

gwenyi · Post by **gwenyi** » Sun Jul 18, 2004 6:23 pm

carlogambino wrote:mak,pple dun do one time exposure, they tack short exposures using registax then edit using photoshop...

Not exactly. For planetary work, people usually take about 200-300 to stack them using registax and the results can be quite pleasing . Whereas for constellations + DSOs, people usually take a very long exposure usually varying from 20 mins to 40mins. However, you can also take 3 pics of each 10mins to stack them (eg. for globulars).

IMHO, i'll rather go for the conventional slr cams as they do not have noise. So, the things that will interfere with how well the pics turn out are

1. the sky

2. quality of lens

3. film

4. tracking time

In comparision, ccd cams are good for long exposures, but they produce a relatively large amount of noise unless you have a cooling fan. slr cams are good for long exposures, but they need tracking to show the same amount of detail as the ccd cam pics which are processed.

cheers,
wenyi

carlogambino · Post by **carlogambino** » Sun Jul 18, 2004 7:38 pm

hmm... but i thought the reason why pple use ccd cams are cos of the short exposure, so that very precise tracking is not required.(no need to polar align within a few arcminutes). However, due to noise build up for long exposures, they do short exposures instead(with tracking,but no need so precise polar alignment) and stack them... true?

gwenyi · Post by **gwenyi** » Sun Jul 18, 2004 10:30 pm

nope. people usually use ccd cams becos there isn't a need to track manually at all. The computer does all the calculations for PEC(periodic error correction) and so they can do long exposures as well. However, due to the noise build up, the exposure time is limited to usually < 10 mins.

cheers,
wenyi

Post by **weixing** » Mon Jul 19, 2004 10:57 am

Hi,

hmm... but i thought the reason why pple use ccd cams are cos of the short exposure, so that very precise tracking is not required.(no need to polar align within a few arcminutes). However, due to noise build up for long exposures, they do short exposures instead(with tracking,but no need so precise polar alignment) and stack them... true?

Those short exposure shot is suitable for planetary imaging only. The main reason for taking a lots of short exposure images and stack them together is to capture the details of the planet without over exposure... it had nothing to do with tracking accuracy or CCD noise. For DSO, you still need long exposure. How long the exposure depend on your tracking ability and how well your CCD camera handle with noise.

nope. people usually use ccd cams becos there isn't a need to track at all. The computer does all the calculations for PEC(periodic error correction) and so they can do long exposures as well. However, due to the noise build up, the exposure time is limited to usually < 10 mins.

CCD or film, you still need to do tracking or guilding if you take long exposure, unless you are taking star trail astrophoto.

Have a nice day.

gwenyi · Post by **gwenyi** » Mon Jul 19, 2004 6:51 pm

didn't add 'manually'.

nope. people usually use ccd cams becos there isn't a need to track manually at all. The computer does all the calculations for PEC(periodic error correction) and so they can do long exposures as well. However, due to the noise build up, the exposure time is limited to usually < 10 mins.

cheers,
wenyi

Post by **weixing** » Mon Jul 19, 2004 7:06 pm

Hi,

nope. people usually use ccd cams becos there isn't a need to track manually at all. The computer does all the calculations for PEC(periodic error correction) and so they can do long exposures as well. However, due to the noise build up, the exposure time is limited to usually < 10 mins.

I think you get mix up with the CCD camera on the guide scope or the off-axis guider and the camera that take the picture. You can still use the auto-guider system when using Film camera. You are not using the guiding CCD camera for taking pictures.

Have a nice day.