YOUR OPINIONS AGAIN PLEASE

Nice picture. Some great nebulosity.

Thanks for comments all.

to david, you mentioned "bias" frames....i know that dark is dark and flat is white... wat is bias and how do you take them.... How many of each would you recomend??? did you look at the first whirlpool picture? why is it so dark do ya recon?? hope all well with you by the way, and did you enjoy galway astrofest??



kevin

I HAVE NOW ACTUALLY PUT THE MENTIONED PHOTOS ON FLIKR SRY :oops: :oops: :oops: :oops:

can anybody tell me wat is a bias frame and how improtant are they... and how do you take them? also how do you take a flat? (flat is white i assume)...

would results be VERY different using and not using these??

thanks all

Hi

Hope this makes sense

There is three types of noise that you get in imaging. First of all there is the electronic noise that arises simply from reading off the data from the chip. These are dealt with by Bias frames. The second kind of noise is that which occurs depending on the length of the exposure taken. This is dealt with by dark frames. Then there is noise which arises due to imperfections in your set up, and imaging train etc. These are dealt with using flat frames.

Bias frames are taken with the shortest possible exposure possible with your ccd/dslr with the cap kept on and are supposed to capture and isolate the first kind of noise. You take about 11 or so frames and average them to get your master bias frame which you subtract from your light and dark frames.

Dark frames are taken with the cap kept on your ccd/dslr but with the exact same temperature and exposure time as your light frames. Again you take about 11 or so and average them to get your master dark to subtract against your light frame.

Flats are used to identify imperfections in the image train such as dust bunnies etc , and are taken with the cap off but with the exact same orientation as your light frames.You semi illuminate your flat frames by puting a item such as a white t-shirt over the FOV and shine a light at the image so that the the dust bunies are shown up in the flat frame. You need to take the same exposure length and again take 11 or so and average them to subtract from your light frames also.

Pheeewwww

As to whether it makes a difference, it will depend very much on the camera used. Some cameras may be very noisey and the taking of flats, darks and bias may be essential. Other low noise cameras do not need such frames.

Improperly taken darks can also introduce noise into your image.

Hope this helps. But there is plenty of stuff about this elsewhere on the boards and the internet.


DB

Hi David,

Thank you VERY much for your reply... It does make sense, and also fills in a lot of gaps... Jus the kind of reply i needed. ,

1 problem still remains though... Does the following Image look like wat you would expect to see in a SINGLE 80sec exposure?? I am gettin ok results for easy targets such as orion dumbell etc...but Crap results in pretty much anything else...
Maybe Im expecting too much from a prime focus unguided (but tracked) setup.. I just dont know if bad results being got at lens or in processing...
That is why i need somebody to tell me if this image looks correct or not...
Hope I didnt waste money on DSLR when I needed a CCD ... have a look anyway.. wat u think?


Cheers and thanks farm3.static.flickr.com/2084/2284610848_ef69247228.jpg?v=0