Quote:
Originally Posted by gregbradley
The extra data has made a lot of difference to the contrast and detail. Nice.
I often wonder if I should go for 3nm Ha and O111 filters. I thought you were using 3nm until I saw this thread. The 5 is good. Have you considered the 3nm? I wonder what the advantages/disadvantages are? Longer exposure time is the disadvantage but how much more detail, if any, does the 3nm achieve?
Greg.
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I believe that Paul Haese uses 5nm Ha & S2, and 3nm O3 - Al Sam has just ordered the 3nm O3 as well (wasn't cheap!). Under full moon in Melbourne, I've found the 5nm O3 is most affected by gradients etc. Certainly considering the 3nm O3 in future for this reason alone.
Quote:
Originally Posted by Atmos
The most important difference between the 3&5nm Ha filters is the NII emission line. A 3nm Ha has only the Ha emission while 5nm+ will also contain the NII emission. With the extra emission it will bring make some objects brighter but it isn't a "true" Ha filter.
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Yes Colin, Bert (Avandonk) previously on this forum used the N2 filter extensively with great results. 656.3nm for Ha vs 658.4 nm for the N2 filter - they're pretty close together but certain objects appeared to respond very well to the N2. It would be creatively interesting to see colour images mapped RGB 3nm S2 Ha N2 or in combinations including the O3.
Quote:
Originally Posted by gregbradley
Thanks for that. Yes I knew that and its why I decided for my Honders not to switch to 3nm at my dark site on the advice of Don Goldman. But my home site, whilst fairly dark, does have some easterly pollution and I wonder how much of a gain you get from the 3nm. They are very expensive.
3nm narrowband filters seem to be used on this site often with the QSI683 as 30mm filters are far less expensive than the 50mm square ones.
Greg.
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Greg, you've probably already seen this but for other reading, this post from Astrodon is interesting -
http://www.astrodon.com/uploads/3/6/...rowbandfaq.pdf
Slawomir uses 3nm filters with great results from his LP affected home base, and I think ultimately that's the way to go.
I made a financial compromise to get the 3 x 5nm filters at the time of my QSI purchase. Having used them extensively over the past year, I may well move to a full set of 4x 3nm filters in future as I expect more creative opportunities will result.
However, aside from the extra cost, the required exposure times will increase as well. I'm currently using 20min subs, but I expect 30mins to be the minimum with the 3nm filters. Having realised that 30hrs plus data is now the minimum for many targets with my backyard rig, I dread the fact that it will probably increase further with the 3nm filters!
Quote:
Originally Posted by Atmos
I've just started using Astrodon 3nm Ha filters, not sure how other passband ones compare as I've never used them but I have a sky limit of ~12-13 minutes with a full moon in the light polluted burbs of Melbourne.
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Out of curiosity Colin, when you get a chance, could you perhaps post some examples of your results with various exposure times in the 15-30min range? I know you did post those amazing 1hr subs recently and it's probably a technical thing but I'm curious as to why you're limited to 12-13 mins here in Melbourne.