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The ultimate which ATIK ccd thread.


ncjunk

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One thing not shown in the spec for the 383 is the minimum exposure. I use 1ms (0.001s) for setting up in daylight with NB filter.

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One thing not shown in the spec for the 383 is the minimum exposure. I use 1ms (0.001s) for setting up in daylight with NB filter.

Good point, no chance with a 383 due to the shutter. Its 0.02s minimum i think.

You start seeing shutter shadow lower than that.

That means i couldnt use it for the odd cheaky planet.

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Good point, no chance with a 383 due to the shutter. Its 0.02s minimum i think.

You start seeing shutter shadow lower than that.

That means i couldnt use it for the odd cheaky planet.

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I had a feeling that was the case - I thought there was a good reason for rejecting the 383 as in other respects it looks pretty reasonable.
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The minimum time with the 383L is 3 seconds from my experience.

To explain why it uses a shutter.. here's my post from elsewhere..

It is possible to use a sensitive sensor with imaging lunar/planets/solar, however it is down to how quickly the image can be read from the CCD sensor itself and not allowing further light to impact the image that's the problem (the shutter is just part of this)..

A CCD is made up of CCD pixels arranged in columns and rows. Imagine a grid of squares on a piece of clear plastic - each dot (pixel) charge adding more dark ink to the square.

When a CCD is read, the charge (built up by light hitting the CCD pixel) is moved, amplified and converted into the number you see as a pixel value.

CCDs are usually in two designs for this draining process - interline and full frame - which defines how the sensor drains it's charge for each pixel.

An interline CCD has alternating CCD pixels (columns) and drain for that column. This means that the sensor can be drained very very quickly (in parallel).

Now imagine the plastic in strips with a space next to it. When the image is taken, the exposure finishes by all the plastic strips jumping into the 'drain' space. Meanwhile the light hitting the CCD starts adding electrons to the pixels but does not impact the image sat in the drain space.. the plastic pixels are then read out from the space quickly and is then converted into pixel values.

So this doesn't require a shutter but has a gap between each column.

A proper full frame CCD moves the charge down row by row on the CCD sensor to the end where it is read off. So going back to the plastic analogy - This reads the plastic by sliding the image down.. row by row and reading the last row of plastic. Any light hitting the CCD will then add to the image - this is why a shutter is required to prevent additional light hitting the CCD as the image is read.

The image read is slower but the quality of the image is better because the there are no gaps for any drain spaces.

Once you add anti-blooming of very bright objects to either of these it adds an additional space between the pixels. Now before anyone mentions - the KAF 8300M is a hybrid with a micro lens over each pixel to focus light hitting any space towards the CCD pixel and not hit the related bloom control 'drain space' on the chip.

So the KAF8300 is more suited to longer exposures..

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You can use .001 sec with the 383 but you will see a shadded patch at one corner. This does not matter with planets as you stick the planet in the middle and only download a small box around it anyway.

The shutter makes flats a bit more unfriendly needing about 3sec but you find simple ways of getting around at.

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What about pixel size effecting that qe graph? The 8300 has 5.4umX5.4um and the 694 has 4.54umX4.54um so thats 21% more photons? Same thing goes for the 9um kodak 10000000000000002 and thats why that sensor insn't as bad as the qe says?

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Its not quite as simple as bigger pixels equals more photons. At this point I lack informatiin but pixels contain lenses as well and the structure of the ccd is such that each pixel is. Very close to its neighbour minimising the gap, I think there is a slight gap in the pixels but no gap in the lenses above which focus the light to the pixel.

I also don't know if qe is per pixel or ccd, I suspect per pixel. But a previous question I had was along similar lines.

I'll see what info I can dig up on the ccd structure.

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Reaity tells me that the KAF11002 is actually very fast in Ha. I don't have enough experience, yet, to comment on RGB sensitivity but the Ha pours in fast, around 4.67. (That's in SUOPP.)*

Olly

*Standard Units Of Photon Pouring

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You can use .001 sec with the 383 but you will see a shadded patch at one corner. This does not matter with planets as you stick the planet in the middle and only download a small box around it anyway.

The shutter makes flats a bit more unfriendly needing about 3sec but you find simple ways of getting around at.

If you sub-frame then the camera will only download the subframe too. So a higher overall frame rate is possible.

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The pixel size is often almost directly proportional to the full well capacity. That is a parameter that gives better resolution and more dynamic range and should not be forgotten. Since it is so closely coupled with pixel size you more or less get what you ask for when you decide on image scale through pixel size.

/p

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The pixel size is often almost directly proportional to the full well capacity. That is a parameter that gives better resolution and more dynamic range and should not be forgotten. Since it is so closely coupled with pixel size you more or less get what you ask for when you decide on image scale through pixel size.

/p

I can't say I've noticed much difference between the 314L+ and the 460EX in dynamic range. When I get the dual or triple imaging rig working I should be able to do a direct comparison. With the 314L+ pixel size of 6.45 and 460EX at 4.54 that's 50% each way or about twice the area with the 314L+. That should be noticeable.
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The figures i found were icx285 (314l) = 17000

Icx674/694 (428, 460) = 15000

Not sure if they are correct as i've seen a few other figures as well.

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the 8300 faults can all be processed out or have the relevant number of needed subs, I still think its FoV makes it far better than the new batch of 4's

I can see your point but it may depend on the target. For a big one, the 8300, for a faint one the 4 series? Edit; When I say faint I do mean faint - the really difficult ones.

Olly

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I can see your point but it may depend on the target. For a big one, the 8300, for a faint one the 4 series? Edit; When I say faint I do mean faint - the really difficult ones.

Olly

This is why i am leaning towards a 428 the extra sensitivity may give me a bit of an edge on the faint galaxies and i'll take whatever i can get.

There's so little in it that i feel like a judge at a painting competition "it really was a very high standard but..."

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I can see your point but it may depend on the target. For a big one, the 8300, for a faint one the 4 series? Edit; When I say faint I do mean faint - the really difficult ones.

Olly

Thats a fair point Olly, but I really cant get my head round all these ickle chips, its a step backwards imo

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Thats a fair point Olly, but I really cant get my head round all these ickle chips, its a step backwards imo

I don´t think it´s a step backward they are just going for high QE and reduced noise as much as possible at the expense of size of sensor.

If you like imaging Galaxies then size of sensor isn´t going to be the most important requirement. Only M31 doesn´t fit, with M33 a bit tight.

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Thats a fair point Olly, but I really cant get my head round all these ickle chips, its a step backwards imo

I couldn't tear myself away from chip size either. Small pixels only go so far as a substitute for aperture. Aperture brings focal length and focal length means a big chip! So big scope and big chip on small target beats small scope with small chip on small target...

So here at my place my TEC140/Atik 4000 had a similar field to Yves' 14 inch/full frame. It couldn't compete. But the TEC with a full frame taking a larger object is a different story.

We want everything and we can't have it!

Olly

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I couldn't tear myself away from chip size either. Small pixels only go so far as a substitute for aperture. Aperture brings focal length and focal length means a big chip! So big scope and big chip on small target beats small scope with small chip on small target...

So here at my place my TEC140/Atik 4000 had a similar field to Yves' 14 inch/full frame. It couldn't compete. But the TEC with a full frame taking a larger object is a different story.

We want everything and we can't have it!

Olly

Watch it, or i'll scream and scream and scream until i'm sick....

I want it ALL!

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