Exposure times for Lrgb

[Craig123]

Hi all. I have been doing 20 mins with my Atik mono and NB filters through SW Ed80  but now it's galaxy season I hoped to swap filters and try a target like the Pinwheel or the needle galaxy again. I'm not sure how long to go on these targets or how to factor in the brightness of the sky where I am shooting to get decent subs. After trying iriis neb last week I'm not so confident with broadband filters. Any advice here or other good targets would be most welcome. 

Thanks

 

 

[vlaiv]

If you give me some specs, I'll run numbers for you and recommend exposure length.

I'll need camera model (QE, pixel size, read noise) and approximate SQM reading on your location.

[ollypenrice]

I'd just experiment. I make my L exposures longer than my RGB and sometimes use the RGB in greyscale as a short exposure to repair over exposed cores. Typically I use 15 min L and 10 minute RGB from this dark site.

Olly

[Craig123]

8 minutes ago, vlaiv said:

If you give me some specs, I'll run numbers for you and recommend exposure length.

I'll need camera model (QE, pixel size, read noise) and approximate SQM reading on your location.

Thanks Vlaiv. That would be great. Iam at work so will get some info when finished. 

[Craig123]

3 minutes ago, ollypenrice said:

I'd just experiment. I make my L exposures longer than my RGB and sometimes use the RGB in greyscale as a short exposure to repair over exposed cores. Typically I use 15 min L and 10 minute RGB from this dark site.

Olly

Thanks Olly. That is a good starting place. I got alot more gradient than I thought I would  from the neighbours TV (.. I think that was it )  on my Iris shots last weekend. The target was still a good way above the house and it was really dim but the shots are not too good. 

Craig

 

[Rush]

If the focalratio of SW Ed80 with Flattner/Reducer is around F/6 or F7, RG channels 600s©10frames,Blue may be 50 % more (15 frames)

Lum 600s © 20 or 30 frames. If you use fast optics /camera lens, can even get away with less frames. This applicable to most of the Atik cameras in general.

Attaching an example of HRGB at F/2,

R:3,G:3.B:6 © 300s,Ha:12©600s, total IT 3hrs. Hope this is of somehelp.

Cs Rush.

 

[Craig123]

3 hours ago, vlaiv said:

If you give me some specs, I'll run numbers for you and recommend exposure length.

I'll need camera model (QE, pixel size, read noise) and approximate SQM reading on your location.

Hi Vlaiv

Here are screenshots of the Atik 314l + spec. Clear outside has me in a bortle 5 location although we live on the edge of the estate next too fields to the east so I'm hoping it's abit darker where I image.

[Craig123]

19 minutes ago, Rush said:

If the focalratio of SW Ed80 with Flattner/Reducer is around F/6 or F7, RG channels 600s©10frames,Blue may be 50 % more (15 frames)

Lum 600s © 20 or 30 frames. If you use fast optics /camera lens, can even get away with less frames. This applicable to most of the Atik cameras in general.

Attaching an example of HRGB at F/2,

R:3,G:3.B:6 © 300s,Ha:12©600s, total IT 3hrs. Hope this is of somehelp.

Cs Rush.

 

Thanks very helpful. Yes that is the F ratio for the ED80 with reducer. Are you just imaging at bin x1 for all channels? 

I've read that bin x2 can produce blocky images with some pixel sizes and wondered if this applied to the 314.

Very nice pic aswell. 

[vlaiv]

13 minutes ago, Craig123 said:

Hi Vlaiv

Here are screenshots of the Atik 314l + spec. Clear outside has me in a bortle 5 location although we live on the edge of the estate next too fields to the east so I'm hoping it's abit darker where I image.

Bortle 5 is a bit vague for imaging as it corresponds to range of 19-20mag/arcsec^2, but let's go with ~20mag as you say that it will be a bit darker where you image.

Calculation says that you won't see real benefit past 5 minutes per sub, but you can go as low as 2 minutes for brighter targets.

Here are percents of SNR increase over 2 minute exposure (for 2 hours total imaging time, 23mag target, 20mag skies, and camera specs you linked):

3 min: 1.36%
4 min: 2.07%
5 min: 2.5%
6 min: 2.78%
8 min: 3.15%

(after 5 min all further increase by fraction of percent - and this is compared to 2min exposure, so 8 minute exposures will have only 3% better SNR compared to 2 minute exposures for total imaging time after stacking).

 

[Craig123]

32 minutes ago, vlaiv said:

Bortle 5 is a bit vague for imaging as it corresponds to range of 19-20mag/arcsec^2, but let's go with ~20mag as you say that it will be a bit darker where you image.

Calculation says that you won't see real benefit past 5 minutes per sub, but you can go as low as 2 minutes for brighter targets.

Here are percents of SNR increase over 2 minute exposure (for 2 hours total imaging time, 23mag target, 20mag skies, and camera specs you linked):

3 min: 1.36%
4 min: 2.07%
5 min: 2.5%
6 min: 2.78%
8 min: 3.15%

(after 5 min all further increase by fraction of percent - and this is compared to 2min exposure, so 8 minute exposures will have only 3% better SNR compared to 2 minute exposures for total imaging time after stacking).

 

Thanks for looking at that. Great.Much appreciated. 

So effectively with this set up I'd be better off with lots of 5 minute exposures rather than 10 minutes. Can you tell from this if it would be OK to bin x2 for rgb or better stick with x1. 

Clear outside has sky quality as 20.26 so about right if that's accurate. ?

 

[Rush]

56 minutes ago, Craig123 said:

Thanks very helpful. Yes that is the F ratio for the ED80 with reducer. Are you just imaging at bin x1 for all channels? 

I've read that bin x2 can produce blocky images with some pixel sizes and wondered if this applied to the 314.

Very nice pic aswell. 

Thank you, was a test shot for 3 hrs. yes always x1 binning. Was never happy with high binning. Kills the resolution IMHO.

Try a session with those numbers and see what y ur set up produces. From there you can always try new exposure times and sequences.

You need a starting/reference point . Use a good LPS filter if necessary. like IDAS or similar. thats it.

gd lk & lot of fun Craig

Cs

Rush

 

[vlaiv]

13 minutes ago, Craig123 said:

Thanks for looking at that. Great.Much appreciated. 

So effectively with this set up I'd be better off with lots of 5 minute exposures rather than 10 minutes. Can you tell from this if it would be OK to bin x2 for rgb or better stick with x1. 

Clear outside has sky quality as 20.26 so about right if that's accurate. ?

 

I would not bother with 2x2 binning - you are already at very low resolution at 2.6"/pixel

[Craig123]

20 hours ago, vlaiv said:

I would not bother with 2x2 binning - you are already at very low resolution at 2.6"/pixel

Was happy to get 5 or 6 hours luminance using 5 minute subs yesterday. Seems to have worked better than last time and I cleaned the filters ?. I tried throwing in all calibration frames in Astroart aswell so an interesting night

 

20 hours ago, Rush said:

Thank you, was a test shot for 3 hrs. yes always x1 binning. Was never happy with high binning. Kills the resolution IMHO.

Try a session with those numbers and see what y ur set up produces. From there you can always try new exposure times and sequences.

You need a starting/reference point . Use a good LPS filter if necessary. like IDAS or similar. thats it.

gd lk & lot of fun Craig

Cs

Rush

 

Was happy to get 5 or 6 hours luminance using 5 minute subs yesterday. Seems to have worked better than last time and I cleaned the filters ?. I tried throwing in all calibration frames in Astroart aswell for the first time so an interesting night. Thanks

[Craig123]

On 07/03/2019 at 17:29, vlaiv said:

Bortle 5 is a bit vague for imaging as it corresponds to range of 19-20mag/arcsec^2, but let's go with ~20mag as you say that it will be a bit darker where you image.

Calculation says that you won't see real benefit past 5 minutes per sub, but you can go as low as 2 minutes for brighter targets.

Here are percents of SNR increase over 2 minute exposure (for 2 hours total imaging time, 23mag target, 20mag skies, and camera specs you linked):

3 min: 1.36%
4 min: 2.07%
5 min: 2.5%
6 min: 2.78%
8 min: 3.15%

(after 5 min all further increase by fraction of percent - and this is compared to 2min exposure, so 8 minute exposures will have only 3% better SNR compared to 2 minute exposures for total imaging time after stacking).

 

Hi Vlaiv

Having followed the above suggestions on exposure time for Luminance at 5 mins i forgot all about it in a rush after a long day and got a few hours on red filter at 10 mins.. I'm hoping I can still stack with Luminance despite different times. Could I ask what you would suggest for blue and green tonight. Stick with 10 mins or reddo red and hope to get the rest at 5 mins. Many thanks

[vlaiv]

15 minutes ago, Craig123 said:

Hi Vlaiv

Having followed the above suggestions on exposure time for Luminance at 5 mins i forgot all about it in a rush after a long day and got a few hours on red filter at 10 mins.. I'm hoping I can still stack with Luminance despite different times. Could I ask what you would suggest for blue and green tonight. Stick with 10 mins or reddo red and hope to get the rest at 5 mins. Many thanks

Hi, no need to redo red if you already have it captured.

Not sure what you mean by stacking with Luminance, but if you are just registering subs on same stars and stacking luminance to its own stack and red to its own - there should be absolutely no problem. If you are doing something fancy and combining data from different filters to extract particular information - like adding R, G and B to create extra luminance, or doing other math - it can still be done, but you need proper method of calculation - like proper sub equalization methods and stacking capable of weighting on SNR.

If you are happy with 10 minute subs for R just go with 10 minute for G and B - longer subs never hurt in terms of SNR, there will be less data to process. Only drawback is need for good tracking / guiding and possibility of dropped subs.

[Craig123]

3 minutes ago, vlaiv said:

Hi, no need to redo red if you already have it captured.

Not sure what you mean by stacking with Luminance, but if you are just registering subs on same stars and stacking luminance to its own stack and red to its own - there should be absolutely no problem. If you are doing something fancy and combining data from different filters to extract particular information - like adding R, G and B to create extra luminance, or doing other math - it can still be done, but you need proper method of calculation - like proper sub equalization methods and stacking capable of weighting on SNR.

If you are happy with 10 minute subs for R just go with 10 minute for G and B - longer subs never hurt in terms of SNR, there will be less data to process. Only drawback is need for good tracking / guiding and possibility of dropped subs.

Great. Really appreciate the help.I may actullay get it finished tonight but I've only just started to work on flats last night so might have more fun and games  dealing with Luminance dust and vignetting from the older 5 min subs. Hoping I can process them out abit cheers Vlaiv.