Astronomik 6nm Ha filter

[emyliano2000]

Hi guys. First of all I would like to apologise for the clouds, it's probably me buying more astro stuff, my latest being an Astronomik 6nm Ha EOS clip filter.

I have a question for the people who successfully used a narrowband filter with a dslr.
When taking flats with only a light pollution filter I usualy check them to have the mean value for the entire image of around 25000ADU and everything works great.
When using a Ha filter I presume that I should aim for this value for the red channel only as this is the one being extracted. Am I right? If I use the same settings used with a light pollution filter the red channel is way overexposed and I'm thinking that the flat frames won't do their job.
I took a few test flats and this is where the red channel should be on the hystogram to get a value close to 25000ADU for yhat channel.
Am I right to do that or I should do something else to make sure the flats are good when shooting in Ha?

Thanks.

Emil

[rigradio]

2 hours ago, emyliano2000 said:

When taking flats with only a light pollution filter I usualy check them to have the mean value for the entire image of around 25000ADU and everything works great.

 

What software did you use to quantify? Is it in 16bit?

[emyliano2000]

4 hours ago, rigradio said:

What software did you use to quantify? Is it in 16bit?

I check the raw files in nebulosity 4.

 

[Art Gecko]

15 hours ago, emyliano2000 said:

When using a Ha filter I presume that I should aim for this value for the red channel only as this is the one being extracted. Am I right? If I use the same settings used with a light pollution filter the red channel is way overexposed and I'm thinking that the flat frames won't do their job.
 

 

I'm not a narrowband imager so I may be wrong here... but the way I understand it, flats are to even out vignetting in your luminance and remove dust bunnies... when taking flats I've always aimed for luminance with No saturation.. I've heard that when some people do LRGB they only apply flats to the L channel as they do very little to the RGB channels anyway... so at a guess I'd say try regular flats without the filter but hopefully someone with more experience will pop in soon and confirm whether that's correct or not?! 

Hth, Art.

[newbie alert]

1 hour ago, Art Gecko said:

I'm not a narrowband imager so I may be wrong here... but the way I understand it, flats are to even out vignetting in your luminance and remove dust bunnies... when taking flats I've always aimed for luminance with No saturation.. I've heard that when some people do LRGB they only apply flats to the L channel as they do very little to the RGB channels anyway... so at a guess I'd say try regular flats without the filter but hopefully someone with more experience will pop in soon and confirm whether that's correct or not?! 

Hth, Art.

Emil is using a DSLR with a clip in filter,but helpful info on the luminance..thanks for that 

[geordie85]

Don't remove the filter. Flats must be taken with the same light path as lights. 

2 hours ago, Art Gecko said:

I'm not a narrowband imager so I may be wrong here... but the way I understand it, flats are to even out vignetting in your luminance and remove dust bunnies... when taking flats I've always aimed for luminance with No saturation.. I've heard that when some people do LRGB they only apply flats to the L channel as they do very little to the RGB channels anyway... so at a guess I'd say try regular flats without the filter but hopefully someone with more experience will pop in soon and confirm whether that's correct or not?! 

Hth, Art.

This is not quite correct, flats are taken through the luminance filter but are still used with the rgb filters. If you don't then you can still have dust bunnies and vignetting in your rgb subs.

I'd just take flats and use them as is and not separate the channels 

[emyliano2000]

I did try  friends 36nm Ha filter once and the flats taken as I usualy do didn't work. I think it's because the red channel was way overexposed in the flats and when I extract it, it doesn't have the 25000ADU value that I'm aiming for.

Don't know any other reason. My flats had always worked.

[emyliano2000]

I'm imaging the rosetta as I write here so I will take a set of each of the flat frames, 25000ADU for the rgb image and 25000ADU for the red channel only to see which one works.