Active image enhancer (Is this a new idea?)

[focaldepth]

Active image enhancer (Is this a new idea?)

First off let me admit I am a complete novice to Astro photography.

Secondly this would not be the first time I have "invented" something only to find it in the shops a few months later. We all do it.

So if this is not a new idea I apologise to to real inventors.

If this is a genuine invention then I would like to offer the idea as "open source" free for all to use.

The idea comes in 2 versions:

1) Fully integrated.

2) Quick and dirty

The principle is based on the fact that we need to take long exposures of well tracked targets for well known reasons.

There will be tracking errors. There will be seeing errors.

Guiding can be used to reduce those errors.

Adaptive correction (pseudo adaptive) can be applied i.e. tilting windows etc.

Adaptive correction (true adaption) can be applied by measuring turbulence and corrected by distorting the optical path (expensive).

This idea can be applied to any of the above but I describe the simple guided case only.

During guiding there are times when the image is offset but still being integrated by the CCD array.

This idea uses a simple LCD shutter to filter out those guiding errors give each sub the best data integration possible.

1) The Fully integrated system.

Sensing the error: Using the guide camera or another fast camera we can calculate either or both of FWHM and offset of one or more guide stars.

When ever the measured error is outside pre-set limits we close the LCD shutter to prevent integration of bad data. Image exposure time is increased to compensate. This would need the big boys to build it into a camera although it could be added to say nebulosity or similar with a little bit of hardware and effort.

2) The quick and dirty system.

Firstly we deliberately over expose the images by say a few percent.

Using a standard guide camera driving say an ST4 port we detect the correction signal to the mount. When ever we detect a correction we close the LCD shutter for a while.

To keep the exposure correct we close the shutter from time to time to compensate for lack of corrections.

Simple.

A down side is that LCD shutters tend to polarise the image and you do loose some brightness but if it means better subs who cares.

So my question is has anyone read or heard of such an idea before. Can I buy one?

If not, then I do have the capability to design/build/program the quick and dirty one out of some 3D glasses and a micro controller and and some “glue” chips and an old Barlow. I probably have all the parts in my junk room. Trouble is my SONY 3D glasses were £100 a pair (omelettes and eggs). It would be a simple and fun project.

Unfortunately I am just beginning to learn how to take astro images (only ordered a lode star a few days ago) and it could be months before I have the skills needed to take half decent images let alone assess whether this works or not.

Any feed back good or back would be appreciated.

[Catanonia]

mmmm, nice idea, but might get a few problems with shutter artifacts.

Also it seems a lot of effort in additional time, expense etc and will not get past the noise problem that stacking helps by building up the common peaks in an image.

Put simply, just take an additional few sets of subs and let the stacking programs work it all out.

Interesting idea if you wanted single shot exposures.

Personally I would like to see double star guiding tools. Ie guide off 2 or more stars and take averages to move the mount to get more precision.

[focaldepth]

Thanks for your input.

I don't think shutter artefacts apply as the LCD effectively dims the whole frame to black in a few ms. LCD shutters are becoming common on cameras these days anyway.

The idea is to still use it with multiple subs to take out the noise and increase dynamic range of the image. The idea is to to remove data accumulated while the auto guider is repositioning the mount. Also will remove data while seeing wobbles the image. The effect should be to increase detail and sharpness of the subs.

[Catanonia]

Thanks for your input.

I don't think shutter artefacts apply as the LCD effectively dims the whole frame to black in a few ms. LCD shutters are becoming common on cameras these days anyway.

The idea is to still use it with multiple subs to take out the noise and increase dynamic range of the image. The idea is to to remove data accumulated while the auto guider is repositioning the mount. Also will remove data while seeing wobbles the image. The effect should be to increase detail and sharpness of the subs.

mmmm, might work and I can see the logic.

Only thing to watch for is that the likes of PHD constantly move the mount and you may find the shutter is shut more than it is open.

[FraserClarke]

It's not a silly idea at all -- I've written something similar for an instrument using a laser guide star adaptive optics system. If we lost laser lock for whatever reason, we'd close the shutter and wait until it was reacquired, and extend the exposure time so that we ended up with the same total 'on-sky' exposure time. It was always the plan to have a metric of how well the AO correction was running, and close the shutter if it got bad. We never implemented that though, because we found it didn't vary enough to be worthwhile.

I don't know anything about these LCD shutters. How good are they optically? Would they distort the image going through them?

How quick would want to make the 'on/off' decision? If it is 1/10th of a second or slower, a mechanical shutter might be feasible instead, and offer simplier optics?

How would you measure the error? If you want to do it fast (<1s), you'll need a very bright star to guide on presumably??

[focaldepth]

Thanks TeaDwarf, you obviously have some experience in this area.

I don't know anything about these LCD shutters. How good are they optically? Would they distort the image going through them?

My plan initially was to use half a pair of 3D glasses just to try it out. They can easily operate at 100Hz. They look quite optically good at a casual inspection. Would need to look at IQ and spectral response at some point though.

Companies like LCD Shutters from Liquid Crystal Technologies

offer very fast responses.

How quick would want to make the 'on/off' decision? If it is 1/10th of a second or slower, a mechanical shutter might be feasible instead, and offer simpler optics?

I lack the experience to get a feel for how many and how big the corrections needed by a guide scope are but I would guess we need to react as quickly as practical, probably 1Hz. (1sec/10min exposure = 0.2%)

Mechanical shutters get back to Catanonia's comment about artefacts.

How would you measure the error? If you want to do it fast (<1s), you'll need a very bright star to guide on presumably??

The quik n dirty option works on the st4 signals. The full solution would need a fast guide scope. For example the Starlight xpress can feed directly into an adaptive optics corrector. Have not looked at it yet but I cant imagine it would not take much to modfiy one of the open source guide camera programs to drive a shutter.

Software already exists to calculate both FWHM and sub pixel position error and is not hard to calculate anyway.

Glad you can see the possibilities.

[focaldepth]

Catanonia

Only thing to watch for is that the likes of PHD constantly move the mount and you may find the shutter is shut more than it is open.

A I have said I lack the experience to judge how much correction is needed but I would have thought if it is constantly correcting that the PHD system gain may be a little high. I would have expected for the mount to do 99% of the work and the guider to make minor corrections. Any way I still have a lot to experience in this field.

[focaldepth]

OK now I am arguing with my self.

Actually a simple rotary shutter, a bit like SBIG use on their cameras, would be reliable and work OK.

Just wondering if a simple firmware tweak to an SBIG camera with built in auto guider would achieve the desired effect. Is SBIG reading this?