New Idea, Pause image while guiding.

[deepsky]

Hi,

When taking 20-30minute images, there is all ways a stray cloud popping in to say hello.

I was thinking. the guide camera show a star qualitity and if the cloud rolls in and the phd2 guide star changes qualitity could you pause the image,
stop the image timer, move the filter wheel to dark blanked filter so no light is taken. Then when cloud move out the way. Start the guiding, move filter back and continue imaging.

Is it an update you could test and explore with. I had a go but phd2 times out after a few seconds.

Every think worked for my quick test by blocking the guide and telescope for 30 seconds.

Hope you like the idea.

Paul

[admin]

Hi Paul,

are you taking 20-30 minute single frames? If you have a CMOS camera with low read noise then there is no need to take such long exposures - you will get just as good a final result by stacking 30 x 1 minute frames as from 1 x 30 minute frame (OK, this depends on the read noise of your camera and how dark your skies are for exact guidance on how long an exposure to use, but super long exposures for astro are *only* required if you are using high read noise cameras - ie CCDs with typical read noise of 8-10 electrons.) Unfortunately the idea of very long exposures (and everything that goes with it, like guiding) have become part of the 'wisdom' of Astrophotography with many people recommending them without actually understanding the reason for them in the first place and why that reason does not apply to all cameras.

So, first option is that if you are taking very long exposures with a CMOS camera then try taking more shorter exposures and let your stacking software (DSS, etc) throw out the frames with cloud due to higher FWHM of stars.

If you are already taking a number of shorter exposures and then stacking, consider using the live stack option in SharpCap. This has options to filter the frames by both FWHM and brightness, again allowing you some control to stop the cloud affected frames from getting into the final stacked image.

cheers,

Robin

[deepsky]

Hi Robin,

Thanks for the reply.

Im using narrow band and images take longer to collect the detail in the images. But i an now taking 5 min images instead of 20min.

But could the system pause while the cloud moved and move to a blank filter? When imaging in a city with bad weather in the UK. This idea would help if taking long images.

If you can get the idea working it could catch on. Would it work?

Many thanks Paul.

[admin]

Ah, narrowband and long exposures makes more sense as your sky background will be very low

I see where you are coming from, but there are practical issues - not least that for most cameras it's not possible to change the duration of the exposure while the exposure is actually in progress, so you couldn't extend an exposure to take account of time lost due to changing to the dark filter. I don't think that different frames of apparently the same exposure would stack very well

If you have some programming skills you could always try to build your own solution for this using SharpCap's built in Python based scripting language - you can control almost all the functions of SharpCap and have general code that could do things like talk to PHD2 to pull this sort of feature together. Unfortunately right now I have a list of things to do on SharpCap that is going to take me all the way through the next two or 3 versions, so I'm afraid there's no realistic chance of me adding this to the core of SharpCap in the near future.

cheers,

Robin

[deepsky]

Hi,

Thanks for the info. I see your point, if you can;t change the time on the camera it would not work.

But a possible idea for the future cameras for cloudy sky's.

I will keep the images to 5mins and this will save time in the long run.

Thanks again for the reply.

Paul.