Filters for Narrowband Imaging
Posted 17 October 2013 - 04:25 AM
I am going to try narrowband imaging with ST 8300M and AT8RC carbon tube( AP CDT 0.67 reducer).
I happened to get used Astrodon 3nm 36mm Ha filter and Astrodon 5nm OIII filtesr in good condition.
But i still need SI filter for Hubble Palette.
If I can not get used SI filter in good condition, then I may need to order new one.
Is there much difference in performance between Astrodon 5nm and 3nm Si filters?
I need advice on choice between 5nm and 3nm.
Posted 17 October 2013 - 06:21 AM
Posted 17 October 2013 - 06:23 AM
I have no real experience with the 5nm yet though as it is "new-to-me."
One thing you might want to consider is your sky. Dark or light-polluted? Also, do you want to image in bright moonlight?
The narrower filter should be better at rejecting those "unwanted" wavelengths.
I don't think there is ever any reason NOT to go to 3nm on SII or OIII unless you habitually use uber-fast optics. Going that narrow on Ha can have some negative consequences on some objects, in some conditions as that narrow a window pushes the NII emission down.
Myself? I'd eat the $$$ and go for 3nm in all filters. I know the dollar hit hurts.
Lots of excellent info on these matters at this Astrodon site.
Posted 17 October 2013 - 08:37 AM
I am using Baader 2" filters in my QHY9.
was going to buy the 7nm HA filter.
I am interested in being able to image SOME while moon is up.
will this work, the 7nm? before I spend the $$
Posted 17 October 2013 - 08:54 AM
I don't recommend using Baader SII and OIII filters in moonlight.
Posted 17 October 2013 - 09:26 AM
Posted 17 October 2013 - 05:31 PM
I will wait until the end of this year for the used Astrodon SII filter in good condition.
If not, it is not going to be easy decision.
I will try to compare the performance of 3nm Ha and 5nm OII filters.
Posted 17 October 2013 - 07:38 PM
The major issue I have heard is using a 3nm Ha on planetary nebulae tends to clip a lot of the signal and thus a 5nm is a better choice for PN's.
Posted 17 October 2013 - 09:05 PM
Posted 18 October 2013 - 01:02 AM
I also found useful link to Astrodon site. to compare 6nm and 3nm OIII filters.
Here is the link-- http://www.astrodoni...owband/6v3.html
Some people may like 3nm better and other also 6nm.
You judge yourself.
Posted 18 October 2013 - 09:00 AM
I went progressively went from the Baader filters to the 5nm Astrodons and the difference was not insignificant. When I moved to 2" filters, I went 3nm for SII and OIII and recently moved from a 6nm HA to a 5nm HA. I'd probably move to the 3nm HA if one turns up used.
My light pollution is that bad. If you can use wider filters, I'm truly envious.
Posted 20 October 2013 - 01:00 AM
You may be right. The choice of bandpass will depend on seeing condition.
It is going to be tough to do AP in Toronto.
One of my daughter graduated from Univ of Toronto this June with Chemical engineering major and I was there for the ceremony.
My youngest is still sophomore in UT majoring in Mineral Engineering.
Posted 20 October 2013 - 01:39 AM
Posted 20 October 2013 - 01:50 AM
You should read this.
The image below is comprised of a stack of 18 thirty minute 3nm SII exposures of NGC 1491 taken at 2857mm FL F/9 during a full moon. The pixel scales 0.39"/px and the image has only been stretched.
As you can see, there's plenty of signal and contrast using a 3nm SII filter during a full moon.
You might read this recent discussion.
Posted 20 October 2013 - 06:12 AM
Posted 20 October 2013 - 07:17 AM
Your QHY filterwheel will allow you to use the 50mm round unmounted Astrodons. I know this because I've used the QHY filterwheel myself.
The nylon screws and washers are what you use to hold the filters in place. It's a pain to get set up, but once done, works flawlessly. One word of advice; when you have the filters mounted in there and screwed in, you will likely need to cut a bit off the thread end of the screws else they'll prevent the carousel from turning.
BTW, just as an aside, right after I mentioned that if a 3nm HA went on the used market I'd probably get it, guess what happened? I'm now the proud new owner (awaiting delivery) of a 3nm HA filter.
Let's try this again. If a used AP3600/DDM85/Paramount ME comes on the market for $5000, I'd likely buy it
Posted 20 October 2013 - 07:51 AM
About the QHY filter wheel - i have already installed there baader LRGB 2" filter set and i don't want to disassemble it and change filters every time when i need to go between narrowband and lrgb. It has only 5 positions for 2" filters so my idea is to use the fifth blank position together with manual filter drawer for narrowband. I will see if it is possible to use 50mm unmounted filters with the filter wheel. Should be possible.
Posted 20 October 2013 - 08:43 AM
Alas, I don't have the too many filters problem. I've bought and sold LRGB filters a few times and found imaging with them very unrewarding. It might have been my lack of knowledge at the time, it might be that light pollution truly makes wideband imaging impossible, it could be a number of things. I might take a stab at it again at some point, but for now I've gone narrowband only. It makes even the cheapest filterwheel viable.
I've gone with the QHY22 for increased sensitivity and long ago went 2" filters for versatility, but part of me would like to get one of the SBIG STT-8300 or QSI683 rigs all decked out. If I sell off all my imaging accessories I could wind up just about $2,000 short
Posted 20 October 2013 - 09:07 AM
Posted 20 October 2013 - 09:12 AM
Posted 20 October 2013 - 10:46 AM
I posted a image comparing 3nm and 5nm SII (post #5641707) and as you can see in that post there isn't a lot of difference - stars are a little bigger in the 5nm, but that might be good as they will match the OIII better.
Posted 20 October 2013 - 11:41 AM
Posted 20 October 2013 - 03:27 PM
The conclusion is if you want to shoot in full moon, 3nm is a better choice and in other case 5nm may work.
It makes my decision on SII more complicated since I already got 5nm OIII.
I will experiment it myself to see what happens in my condition.
Posted 20 October 2013 - 04:15 PM