Mallincam and bloated or blown out stars
Posted 04 May 2013 - 01:07 PM
Posted 04 May 2013 - 03:05 PM
There's a variety of reasons why you'll see stars like that with Mallincam or other video cameras.
The vast majority of folks using video gear are looking for as fast an image display as possible so very high gain is often used. This allows the faint fuzzies to be displayed in only a matter of seconds but does over do the stars a bit.
High gain with video is also often coupled with extra sharpness and this can lead to dark halos around brighter stars ... the "owl effect" some call it.
In the quest for speed very fast optics are often used. In some cases this means aggressive focal reduction which is often at the expense of some optical quality, so the stars are sometimes a little larger than necessary.
If someone wanted smoother images (rather than the fastest possible reproduction) from a video camera all they would have to do is adjust down the gain and sharpness and possibly dial back the focal reduction (this depends on the focal reducer used and how aggressively it's setup). You can produce very nice smooth "CCD like" images with a Mallincam Xtreme camera by using what is called CCD mode.
If you are curious about better images specifically from a Mallincam I would suggest joining the Yahoo Mallincam group and have a look at Chris Applegate's (postings and NSN broadcasting also under the name of Astrogate) images taken in CCD mode (he has quite a selection of images posted, you'll need to look specifically for the ones taken with CCD mode). There are also a few other folks on the group who have posted really nice images using CCD mode.
Overall using CCD mode isn't that popular, most folks want speed above all else but it does show what a Mallincam Xtreme video camera is capable of.
Posted 04 May 2013 - 03:36 PM
I am still learning and playing with this thing. I love it though!
Posted 04 May 2013 - 04:31 PM
Posted 04 May 2013 - 08:36 PM
Posted 05 May 2013 - 12:07 AM
Posted 05 May 2013 - 11:35 AM
The less dynamic range you have the more the stars will clip or blow out.
You can simulate more dynamic range through HDR images. However, the final image still has the same dynamic range it is just that you are compressing the dynamic range of the scene you are capturing.
You can also block out some of the light from the stars with very strong filters. Although you also have to make sure that you don't take out the light from the object you are looking at as well as the light from the star.
Posted 06 May 2013 - 11:18 AM
If one wishes to compare devices, crop from the bigger-CCD image a same-size array as that of the smaller CCD, and display to the same scale. Now you will be examining relevant differences.
And on top of the low resolution (as a function of image width), analog video suffers the smearing of chroma bleed, among other not-so-garish artifacts.
Posted 08 May 2013 - 08:20 PM
Posted 09 May 2013 - 06:56 AM
Thanks Glenn, I hadn't thought about the "digital zoom" effect of using far fewer pixels. I ordered a NexIMage 5 and have downloaded DeepSkyStacker Live. I'm anxious to see what result I'll get using them on DSOs if the skies ever clear here in sunny Colorado
I can tell you the results... If you can get the NexImage down to a fast focal ratio, f/3 or f/4, you can capturebrighter objects pretty well. I used one to get Comet Holmes some time back. But it will not be an Xtreme.