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 The Lion Nebula SH2-132 I have been trying to capture data using a number of different filters on my OSC camera to allow me to create images that are less dominated by the red Ha when I use only my Optolong L-eNhance filter. For this one I used the following:- 38 x 180 seconds with the L-eNhance, from which I extracted the Red channel only and designated this as the Ha channel- 30 x 300 seconds with the Oiii filter, used for the Oiii channel- 75 x 120 seconds with no filter, from which I extracted the luminance and used it as a Sii channel. I also extracted the stars from this data I then combined the Ha, Sii, and Oiii channels created above, using the Forax PixelMath in Pixinsight. I colour balanced the resulting image in GHS using a linear adjustment on the green and blue channels to align them with the red channel; then used GHS to stretch the image. I did wavelet sharpening on the starless image before adding back the stretched stars. This would be a lot easier with a mono camera I’m sure. I welcome feedback on how I might improve this approach, or this image. Thanks, Keith |
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Okay there is a lot to unpack here. I think before we dive into the image, it is worth considering the data acquisition phase. I perused your images and I can see that you live in bortle 4? If that is the case you then you want to think about much longer sub-frames for narrowband. I am talking 600 seconds at least.This would be a lot easier with a mono camera I’m sure. You are right, this would be much easier with narrowband. However, if you browse around astrobin you can find a lot of beautiful images in narrowband with OSC cameras. It can be done! It does require a lot of integration time. On this image you only have six hours or so. You need to consider bumping that up to double, triple or even quadruple the integration time. Shooting at F/7, in narrowband, with a OSC means you are going to need a lot of integration time to get an acceptable signal to noise ratio. Speaking as someone who started off with a OSC and duo-band filters, I already know 90% of the battle you are facing in the processing phase is caused by a poor signal to noise ratio due to the low integration time. So, if I was you, I would:
I would also just use the duo-band filter. The Oiii filter is not doing anything for you that the L-enhance is not already doing. I suppose the Oiii filter captures more contrast because its a smaller band-pass, but still. |
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Hi Keith, Disclosure - I am not qualified to provide much objective feedback with my limited experience, but hope to offer some helpful tips. First of all, your image turned out really nice. I just finished this target as well - same bortle, camera, L enhance, on less quality glass with similar FL. You can go longer exposures for that sky magnitude on our camera at around 100 gain with that filter. I have found it's much easier to process L Enhance images by separating out clean Ha and OIII data wtih some simple Pixel Math. These formulas come from dark sky geek and are based on the spectral sensitivity of our camera / filter. Done on linear data that has been DBE'd (our whatever you prefer) I do mine starless: Split RGB and rename r,g,b Create OIII in pixel math: Single RGB/K expression Output a new file, name "OIII", grayscale (2*0.9 * ((g-0.1*r) / 0.917) + 0.5 * ((b-0.08*r) / 0.498)) / 2.3 Create Ha, output a new file, name "Ha", grayscale Single RGB/K expression (r-0.03*OIII) / 0.8 Compare your two new files, you will be amazed. To recombine in PM RGB output - R/K: Ha G: 0.9*OIII + 0.1*Ha B: OIII Then stretch and process as you please. I also like the Foraxx script, but Bill Blanshans newest revised process for Narrow Band Normalization (3 weeks ago) is a slick tool for HOO type pictures. Cheers! |
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Thank you for the excellent feedback! Based on both of your inputs, I went back and reprocessed only the L-eNhance data using the approach described by Scott above. If I needed more integration time before, I certainly need a lot more with using only 1/3 of the data, but I think this illustrates what you are both saying - that I can get as good or better results using just the dual narrowband filter and a different processing approach. Here's the result of my reprocessing. I will add another night of L-eNhance data at my next opportunity. |
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For Sii data, Askar makes an Oiii, Sii filter that you can seperate out the Sii data to make true SHO. The other option is to shoot with a real Sii filter. The bonus is you can use an Sii filter with much more moon than an Oiii. I regularly shoot under near full moon (up to about 80% full) with my Sii and Ha filters. As long as the target is not close to the moon. You'll still be at a disadvantage using an OSC but at least you would be using nights you would never shoot Oiii or dualband on so call it free signal. SVBony makes about the cheapest 2" Sii filter at $150 USD. I don't have one but reports on some of their other newer filters have been positive, especially for the price. |
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| I actually have and IDAS NB3 filter which collects Sii and Oiii. They don't make it anymore, but I have used it to collect Sii on other targets. |
