image

[j w guy]

just some help, I have a 383l and when in use my images are always over ex. no matter how low the ex time is the images are poor. I have tried to image Saturn with poor result,I am using windows seven. At times the imager fan makes a different pitch sound and exposures change from light to dark, is it possible concern with imager, computer or user error. any help please
  regards J G

[NickK]

Can you give more info? focal ratio, target etc?

The 383L has a mechanical shutter (like many KAF 8300 based cameras) which limits it's minimum exposure time.

I can't use the 383L on the moon or for solar because the target is too bright, even at f/13 with a 4" refractor.

[NickK]

The KAF 8300 sensor needs a shutter hence every design (regardless of vendor) using one - the issue is that they will cause shadows or uneven lighting on very fast exposures. I find that any image less than about 3 seconds results in a shutter shadow. Lunar is possible - with filters and a very very early crescent.

A camera with an interline sensor, without a mechanical shutter would be better for brighter targets - which is why I have the Titan for solar/lunar and planets. I can't comment on the new sony 4xx cameras - perhaps someone else could share their experience with high luminosity targets.

[NickK]

I wanted to slightly correct your understanding. 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..

[ReedDower]

Can you give more info? focal ratio, target etc?

The 383L has a mechanical solar panel shutter (like many KAF 8300 based cameras) which limits it's minimum exposure time.

I can't use the 383L on the moon or for solar because the target is too bright, even at f/13 with a 4" refractor.

So which camera is best suited under those conditions.. I am facing similar problem so can you help me out?

[NickK]

Can you give more info? focal ratio, target etc?

The 383L has a mechanical solar panel shutter (like many KAF 8300 based cameras) which limits it's minimum exposure time.

I can't use the 383L on the moon or for solar because the target is too bright, even at f/13 with a 4" refractor.

So which camera is best suited under those conditions.. I am facing similar problem so can you help me out?

It's down to the amount of light. So there's a few options:
a) Using a Sony sensor where the image is transported into a special transit channel (protected from light), often called "electronic shutter" is better suited for coping with very bright targets.
b) Reduction of light through higher focal ratio - I've used a 383L on bright targets by increasing the focal ratio such as a 5x Televue Powermate whilst imaging Jupiter. However this depends on the aperture of your scope.
c) Reduction of light through filters, narrowing the band for wideband targets; or; narrowing the bandpass for narrowband helps reject unwanted light.

I've managed to use the 383L directly on a 4" APO natively on a very very early moon. Also using a 5x on Jupiter - I could have reduced this more by using RGB filters.