Narrowband imaging help?

[Astroblagger]

Hello iv just started narrowband imaging through baader filters, i have a few questions,

IS it better to get get longer exposures in Ha binned 1x1 then get the S and O binned 2x2 or just better getting equal lenght exposures all binned 1x1? Also iv noticed when i change onto the O filter its gets quite out of focus? is this a common problem as i though the filters were suppose to be parfocal? I have also had afew issues getting the O filter sharp looking in focus on the screen when focusing? Any help appreciated.

[swag72]

While filters are touted as parfocal, it is more likely the scope optics that are focusing the light slightly differently through the different filters. I would make it a habit to always focus between filter changes regardless. As temperatures change the focus will probably drift a little as well, so you are really giving yourself the best chance by a quick refocus.

Regarding binning - Mmm, all I can say is that I don't bin anything. I do 1x1 for everything and try to capture at least the same amount of OIII and SII as Ha, but suspect that this really should be far more in reality. People do bin their OIII and SII though, so I would say give it a go and see how it pans out. What works for me, may not suit you.

Using a Bahtinov mask for focusing should ensure you get optimal focus, and couple that with Bahtinov Grabber and you are well away. Works for me every time.

Hope that helps.

[lensman57]

troublesome

Hello iv just started narrowband imaging through baader filters, i have a few questions,

IS it better to get get longer exposures in Ha binned 1x1 then get the S and O binned 2x2 or just better getting equal lenght exposures all binned 1x1? Also iv noticed when i change onto the O filter its gets quite out of focus? is this a common problem as i though the filters were suppose to be parfocal? I have also had afew issues getting the O filter sharp looking in focus on the screen when focusing? Any help appreciated.

Hi,

I think that Sara has given you good advice, I also find Oiii filter troublesome particularly with ED doublets as these are usually not so well corrected in the Blue range of the spectrum, also the blue light bends quite a bit more in the atmospher than the red, that is why in daytime photography the shadows are always dark in mono or blue in colour photography because the shadows are illuminated mainly by the bendy blue light.  The only time that I have used binning has so far been for frame and focusing, you loose a lot of data and resolution by binning. There may be good reasons for using binning in Lrgb imaging as the resolution is provided by the L channel  ( unbinned ) and the colour data can then be binned to reduce imaging time but these will then need to be rescaled post capture for the data to be compatible for processing.

A.G

[Astroblagger]

Great advice thanks very much, what is Bahtinov Grabber? I have a Bahtinov Mask.

[swag72]

Look on this site http://www.njnoordhoek.com/ and you'll find it to download.

Sadly the guy who did this programme and put it out in the public domain for free passed away in 2012.

[Gina]

I find that I need at least twice the Ha exposure for OIII and SII.  I'm in two minds about binning the OIII and SII and I agree with Sara - try it for yourself and see how you get on.  It does make processing a bit more complicated - for instance the stars come out twice as big and need a lot of messing about with.