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Explanation needed

Caz

By Caz
in Imaging - Deep Sky

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daz

daz

Posted
Posted

Pretty much it, really Gaz.

The CCD chip is divided up into pixels and these can be considered little buckets. As the photons of light fall onto the pixels, the bucket gradually filles up. Of course, if too much light is captured, then the bucket overflows into adjacent ones and the details are washed out. Too few, and the detail is invisible.

The eye itself is also part of the equation and is to do with rods and cones (different light receptors) but I'm not sure of the mechanics of them - a quick google would tell you more...

Hope this makes some sort of sense (it does in my head, anyway!)

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GazOC

GazOC

Posted
Posted

Well seeing as I'd typed this any way..... :clouds2:

Yep Caz, if you you look under the images that the guys post then sometimes you'll see something like "20x30 secs" that means they've taken 20 shots of the object, each 30 seconds long - generally the fainter the object, the longer exposures needed.

The reason more than one shot is taken is that any random noise on the camera or any unwanted atmospheric effects that may spoil a single shot can be averaged out if you have many shots. to play with.

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GazOC

GazOC

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Yes Caz, you take many shots (some of the planetary ones will be 100s or even 1000s) and use Registax to stack them, youre unlikely to get the same error or glitch over many images, the really bad images are thrown away automatically anyway by the software.

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CELESCOPE

CELESCOPE

Posted
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The guys have explained it very well Caz , yes like they say planets and even the moon with the type of cameras we mainly use IE toucam pro2 which is a web cam unmodded except the lens is removed to leave the chip open , to this an adapter is used to fit into the scope, and many images are taken up to 5000 if you wanted out of these you would pick the best clearest images which could only be about 800 poss . depends , then you would stack them in registax a free software programme, this however does take a little getting used to , its not all plain sailing so to speak , but some wonderful images can be achieved using this method ,

As for deep sky , this is much harder, the visible ones are not to bad , but for this you need either a modded web cam or another deep sky imager , or a digital camera like the 300d, the draw back with web cams and digital are that they are not cooled , this is required mostly for long exposures to keep what we call the noise level to a minimum, modded web cams are mostly air cooled which is fine for winter and autumn , after that we get whats called hot pixel problem were alot of tiny dots appear all over the image, and if your tracking is out these appear as long streaks, which we have to deal with .

mostly all the images i take are not visible to see on the puter screen , so you have to download a few frames or subs we call them to see where the image is sitting , have to do a few of these sometimes , but once centred , you can now settle back and run off as many frames as you think needed , my target for my setup as i have a fast Ratio, is around 45/ 50 sec each frame and i need normally 50 of them to stack , registax is no good really for this , so other software is best used, like Maxim , i could go on forever its an in depth subject , but hopefully you are now saying, Geeze!!!.

Cheers

Rog

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GazOC

GazOC

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In the beginning, it is very frustrating. Gaz will bear testiment to this, I have no doubt !

I certainly can! My New Years Resolution for the last 3 or 4 years has been to give imaging a proper go, it's just too blumming fiddly and I havn't got the patience!!!

Believe it or not, this is one of my better ones.....my advice would be to start with the Moon, at least you get results that way!!

image.jpg

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The Warthog

The Warthog

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I certainly can! My New Years Resolution for the last 3 or 4 years has been to give imaging a proper go, it's just too blumming fiddly and I havn't got the patience!!!

Believe it or not, this is one of my better ones.....my advice would be to start with the Moon, at least you get results that way!!

So, am I looking at a little trailing in this pic, Gaz, or are the stars slightly oval for another reason? (Not knocking your pic, just trying to learn!)

If you are taking pictures with a film camera, where stacking isn't an option, do you have to track an object for 600 seconds to get the equivalent of a 20x30 stack? And what happens to "noise" on a piece of film? Does it happen?

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daz

daz

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WH

The trailing could be down to three things - polar alignment, error correction in the drive (PEC), or manual guiding.

As for film, yes is the short answer - you would have increase the exposure time. Noise is an electronic things - it's basically the background radiation. What you will get on film is grain. The longer the exposure, the more prominent the graininess.

The repricocity failure of the film is also important - the point at which it stops collecting more light.

Gaz's pic looks like one single image to me - is this correct Gaz?

A stacked image would show a sharper ring, I think.

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GazOC

GazOC

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The polar alignment was off (my polar scope wasn't calibrated), hence the stars :clouds2:. The image is made up of (I think!) 10x15secs as 15 secs was all I could get away with before the trailing got *REALLY* bad!!

I did have another copy that James and Ant had photoshopped for me that sorted out the trailing and enhanced the detail on the ring, unfortuneatly its somewhere in my Inbox along with 15,000 other emails!!

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GazOC

GazOC

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That was the piccy I meant to link to the first time but got mixed up, for some reason I'd given them the same file name and then uploaded them to different hosts and linked to the wrong host.

The second pic is after James and Ant had had a play with it in Photoshop, the first one is just stacked. It just goes to show you may have captured more detail than you first thought. You be amazed what Registax can do with what at first look like very poor lunar shots with my Meade DSI.

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