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Finally got a clearish sky so I thought I would have a crack at the horsehead again. Took all of 3 minutes to get the mount out and PA'd. Put on the scope and camera on and manually aligned with the target. Then spent half an hour trying to get APT to work. I could connect with the camera and put it in live view so I could trim the focus. Could not see a thing in live view. No stars, no nothing.

Went back and forwards checking camera then APT. Nothing!!!! Tried looking through the camera viewfinder and could not see anything either. Check lenscap, yes its in my pocket. WHY CAN'T i SEE ANYTHING!!!!

Flash of lightning hits the brain and I realise I have my new Ha clip filter in the camera and its blocking the light. DOH!!

Anyways, I tried a few things and still could not see anything in APT liveview, so I removed the filter, focused and replaced the filter again. Took some test subs to get a decent exposure limit and set APT running.

The subs are very red....is this normal??

Edited by Stephen
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No you need to focus with it in. If you focus without and then put it in, your focus will have changed by the width of the filter. Doesn't sound a lot but will make a massive difference.

The only way I ever found to focus with the Ha filter in was to focus on a particularly bright star, then slew to my target. As I recall, even focusing on Vega was tricky as it was so difficult to see anything.

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I don't have Ha filter, but discussed the problem with two friends some time ago. They also confirm that is needed very bright star in order to see something on the LiveView. If it still doesn't help, the method that Andy suggests will work :)

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The subs are very red....is this normal??

Erm, well, yeah that is the whole point. Ha is in the red part of the spectrum and since the filter is blocking everything except Ha then you will end up with a red sub since only the red pixels in the Bayer pattern will receive any light.

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Erm, well, yeah that is the whole point. Ha is in the red part of the spectrum and since the filter is blocking everything except Ha then you will end up with a red sub since only the red pixels in the Bayer pattern will receive any light.

looks like I will have to learn new processing techniques then. Oh the joys of imaging.

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No you need to focus with it in. If you focus without and then put it in, your focus will have changed by the width of the filter. Doesn't sound a lot but will make a massive difference.

As the filter is installed into the camera and doesn't add to the length of the imaging train I wouldn't have thought the filter made any difference to the focus point. I might be wrong though.

Cant you take, say, a 10 sec sub and use the focusing aid in APT, thats the way I do it and works well

I can try that method when I get another clear sky.

I don't have Ha filter, but discussed the problem with two friends some time ago. They also confirm that is needed very bright star in order to see something on the LiveView. If it still doesn't help, the method that Andy suggests will work :)

There are a few things left to try out with APT that might help, but as always we are waiting for clear nights to test stuff. We get so few clear nights lately, that the last thing i want to do is spend time testing instead of imaging, but if thats whats needed to succeed then so be it.

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As the filter is installed into the camera and doesn't add to the length of the imaging train I wouldn't have thought the filter made any difference to the focus point. I might be wrong though.

Even though the filter is inside the camera, putting an extra piece of glass in between the camera sensor and focuser will move the focus point - Perhaps only a little, but critical focus is important unless you want soft looking images.

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