Wow! An excellent and thorough analysis of what is actually happening with these filters. Definitely surprising that the 6nm filters dont suppress a lot more of the background light pollution. Maybe you might get different results in a Bortle 8 or 9 location? I am in a Bortle 6 location so my results should be similar to yours. I think Quiv the Lazy Geek should check out your video. I really really appreciate your attention to detail and I actually understand what's happening now. As a side note, you mentioned corrector plate alignment - it would be great to see a RUclips video on how to collimate Hyperstar on an Edge HD. I am finding it very difficult to achieve round stars over the entire sensor (and I'm using a micro 4/3rds ZWO294mm Pro). You definitely have a new subscriber!
One of the best videos I have ever seen related to this topic. I am currently in the process of selecting narrowband filters for Samyang to be used probably at f2.8. Your video clearly confirms that blue shift risk increases with narrower band width. I was thinking about 6nm non MaxFr filters from Astronomik. Now it's really good question if this makes sense at f2.8.
Incredible work, thanks for sharing. I feel like I just listened to a talk in a scientific conference! If I understand correctly, in 36:13 the histograms for the angle of incidence may be missing the fact that at a larger radius there is more lens/mirror surface (the circumference is proportional to the radius), so I believe that the histogram shouldn't be flat, it should instead increase with the angle and therefore the issues you described are even more important!
I think quiv the lazy geek did a video accounting for some of the angular content. It has been a while since I looked at the calculations, but I think the python script I used accounted for both the primary area and for the secondary obstruction - so i think the radius effect was accounted for, but I would need to dig in to confirm it.
Sorry for the late comment, it's been a while since you worked on this 😂 You need to account for how the surface area is distributed inside the aperture that is not blocked by the secondary. That video seems to incorporate this aspect indeed
@@albertizard the script used ray tracing assuming parallel incidence to the primary mirror and accumulated the rays on the sensor - so the annulus area effect of the mirror should be incorporated.
@@BrentMantooth ray tracing is fine. The issue is the assumptions about the geometry where the ray tracing is taking place. I checked the notebook you linked in the description. In def transmission_chip(), the line R, PHI = np.meshgrid(r_vals, phi_vals) assumes that all r_vals have the same weight in the calculation. Imagine a spider web, the cells farther from the center have more area, which grows proportionally to the radius. Also, in the next line it calls get_theta(), in this function there is a line commented out which seems to have the right maths, the uncommented one ignores the size of the sensor. I think both issues would lead to slightly worse outcomes.
Very informative. I am using the Baader cmos optimised f2 NB filters, 6nm Ha, 4nm Sii and Oiii. Reasonable results so far on Samyang 135@f2 with asi2600mm/mc but early in the testing so far. Would be great to have details on your tilt adjustment rig - I have built one but it is very cumbersome to use. Cheers, Des
hm, I bet you are stopping down your lens to f/2.5 with the 6 nm, and even more with the 4 nm, probably down to f/2.8. I may do a follow up looking at smaller bandwidth filters and for lenses. I think I also want to refine my index of refraction estimate, I thought of a way to get that a bit more accurate. What I learned was that the narrower filter was rejecting more real signal, than it was rejecting background for a net loss in quality.
By far the deepest analysis I’ve found on this topic, Brent. I use the IDAS NBZ for Hyperstar imaging and, according to the specifications, it is also a wider band filter both in Ha and OIII. I have a C9.25 EdgeHD with Hyperstar V3 and the ASI071. When I got this filter the increase in SNR was evident, compared to the previous narrow band ccd filers from Baader (which are engineered for a slower f-ratio). I’m considering going for f10 mono imaging. In that case, I think filters in the 3nm to 5 or 6nm FWHM range would be useful, because of the very low angle of incidence. What’s your opinion on that?
The down sides to narrower band are cost and you may need longer exposures for auto focus runs. Otherwise it seems like 3 nm would be awesome for those focal ratios. Keep an eye out for reviews on halos
That’s something to keep in mind. I’ve seen some threads in CN about halos with even the most premium brands. And definitely those can come from a lot of sources as you have shown. I’ll have to inspect some of my images to check where those halos were produced
Excellent video! I've been looking for something like this for a while. I want to run these calculations for my optolong filters which are 7nm and I use a Hyperstar 3 on an EdgeHD 1100 which is F2 I believe.
Hi Brent, i have a C925 and recently bough a hyperstar v4. i understand about bandpass shift but can i still get useable results with my Altair triband filter v1? i use a Altair 26C imx571 colour sensor. i mean if i could afford theIDEAS NBX UHS or the new Optolong l extreme f2 i would. it would be a shame not to just junk the filter i currently own if it isnt shifted too badly at f2.3 which is my current imaging rig. would be glad to hear your thoughts. thanks Des
this follow on video may answer your question ruclips.net/video/IudhLAjqD8E/видео.html the short version is the more narrow the bandwidth the more signal loss you will have at lower f/. If the bandwidth of your filter is large ( maybe greater than 6 nm) then no problem, if the bandwidth is smaller, then you are throwing away (filtering) the signal you want.
Hey Brent, I really appreciate you sharing the comparisons between the 12nm and 6nm MaxFR filters. I'm considering a set of these and was curious on your thoughts with my two scopes: An Askar FRA300 (F5.0) and a Skywatcher Quattro 150pm (6 inch newtonian) (F3.45 with coma corrector/reducer). So I have an F5.0 and F3.45 system and want to get the best set of filters to use with both scopes to maximize signal to noise and have nice stars with little to no halos. Which set of Astronomik filters would you recommend in my scenario? Thanks.
if budget is no object - go 6 nm. if you want all the signal you can get, go 12 nm. at f3.45 incident angle is ~8.2 degrees - so look at the chart at a time stamp of 35:00 and compare transmittance at ~8 degrees. The 6 nm will have a little attenuation at the higher angles (down to ~80% transmittance). without doing the simulation... the 6 nm filter on your Quattro will probably make its light collection closer to f/4 ish. on my hyper star the 6 nm filter was giving a response closer to f/2.5 so maybe it won't be so bad for you? the 12 nm filter would give you your full f/3.45 signal. My testing was in a bortle 5/6 zone, and some of the comments indicate the benefit of the narrower filter may be more significant in higher light pollution conditions. some drawbacks on the 6 nm are that you may need longer exposures for you AF runs (I was doing ~8 second exposures to get confident and reproducible focus runs) the 6 nm filter will not give you better resolution... it will provide better signal to noise at f/5, and somewhat better signal to noise at f/3.45 compared to the 12 nm filter. Do these differences justify the difference in cost for you? that is up to you. depending on the currency conversion rates it can be cheaper to buy directly from astronomiks in Germany than to buy elsewhere. you may find my updated video of a little more help: ruclips.net/video/IudhLAjqD8E/видео.html
and remember for the chart at 35:00, it is the area under the transmittance curve from where the photons are coming from on your scope - not just the transmittance at the highest angle - your quattro will be somewhat like my hyperstar. if you really want to know, download the python code and put in your scope parameters. my other video gets into this in more detail.
@@the_astro_nerd after all of my filter adventures, I came to appreciate the importance of parfocal filters. on fast systems backfocus is critical, and if your filters are not parfocal, you may need different spacers for each filter. I now use only Astronomic filters for everything. this is also very important if you do OAG. for your Bortle zone... and scopes... I would say go for the 12 nm and spend the cost difference on other things.
I know you said the Hyperstar at f1.9 with the 6nm stops down the optics so it’s better to go with the 12nm. I also noticed you are in a bortle 6 zone. My question is do you believe the same holds true for those of us in a bortle 8 to 9 zone. Or would the 6nm be better due to the extra sky glow?
That is a great question. I think it comes back to the statistics of signal of interest and sky glow, and that you just need 'more data' (more subs) to help remove the sky glow. I don't have a quantitative answer right now, but I think stopping down the scope does more damage to the signal than the narrower filter benefits the signal. The rate of real signal accumulation is the most important (so 12 nm) seems to be the key factor, and being above the read and shot noise of your detector. I provided links in the description for a paper from Abby Road Observatory (see the link for karmalimbo) Some of Jim's other papers on that that server get into simulating sky glow, but not in the context of exactly this question. Look up a video with the title "Deep Sky Astrophotography With CMOS Cameras by Dr Robin Glover" around the 50 min mark is a table based on f/ and bortle that gets at these concepts. I will think on it and see if I can do another video on these topics. I think Cuiv the lazy geek channel has a video about light pollution in Tokyo and signal as well.
Interesting! I image with a OSC and a 5nm dual band filter. I wonder if a 12 nm filter like the L-enhance wouldn't be better when using an f/2 camera lens like the samyang 135mm...? Either that or stopping the lens down to f/4. What are your thoughts on this?
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I have published updated calculations for the hyperstar see other videos on my channel
Wow! An excellent and thorough analysis of what is actually happening with these filters. Definitely surprising that the 6nm filters dont suppress a lot more of the background light pollution. Maybe you might get different results in a Bortle 8 or 9 location? I am in a Bortle 6 location so my results should be similar to yours. I think Quiv the Lazy Geek should check out your video. I really really appreciate your attention to detail and I actually understand what's happening now. As a side note, you mentioned corrector plate alignment - it would be great to see a RUclips video on how to collimate Hyperstar on an Edge HD. I am finding it very difficult to achieve round stars over the entire sensor (and I'm using a micro 4/3rds ZWO294mm Pro). You definitely have a new subscriber!
One of the best videos I have ever seen related to this topic. I am currently in the process of selecting narrowband filters for Samyang to be used probably at f2.8. Your video clearly confirms that blue shift risk increases with narrower band width. I was thinking about 6nm non MaxFr filters from Astronomik. Now it's really good question if this makes sense at f2.8.
I will see if I can setup and run the simulations to see what that would look like, hope to post it soon.
First pass is that the 6 nm will work fine on most 2.8 lenses up to full frame sensors
Thanks for the video. I've read quite a bit on this topic but this is an in-depth treatment of these problems.
Wonderfully detailed and helpful video
Incredible work, thanks for sharing. I feel like I just listened to a talk in a scientific conference! If I understand correctly, in 36:13 the histograms for the angle of incidence may be missing the fact that at a larger radius there is more lens/mirror surface (the circumference is proportional to the radius), so I believe that the histogram shouldn't be flat, it should instead increase with the angle and therefore the issues you described are even more important!
I think quiv the lazy geek did a video accounting for some of the angular content.
It has been a while since I looked at the calculations, but I think the python script I used accounted for both the primary area and for the secondary obstruction - so i think the radius effect was accounted for, but I would need to dig in to confirm it.
Sorry for the late comment, it's been a while since you worked on this 😂 You need to account for how the surface area is distributed inside the aperture that is not blocked by the secondary. That video seems to incorporate this aspect indeed
@@albertizard the script used ray tracing assuming parallel incidence to the primary mirror and accumulated the rays on the sensor - so the annulus area effect of the mirror should be incorporated.
@@BrentMantooth ray tracing is fine. The issue is the assumptions about the geometry where the ray tracing is taking place. I checked the notebook you linked in the description. In def transmission_chip(), the line R, PHI = np.meshgrid(r_vals, phi_vals) assumes that all r_vals have the same weight in the calculation. Imagine a spider web, the cells farther from the center have more area, which grows proportionally to the radius. Also, in the next line it calls get_theta(), in this function there is a line commented out which seems to have the right maths, the uncommented one ignores the size of the sensor. I think both issues would lead to slightly worse outcomes.
Wow! Impressive work. Very instructive. Thanks for sharing.
Very informative. I am using the Baader cmos optimised f2 NB filters, 6nm Ha, 4nm Sii and Oiii. Reasonable results so far on Samyang 135@f2 with asi2600mm/mc but early in the testing so far. Would be great to have details on your tilt adjustment rig - I have built one but it is very cumbersome to use. Cheers, Des
hm, I bet you are stopping down your lens to f/2.5 with the 6 nm, and even more with the 4 nm, probably down to f/2.8. I may do a follow up looking at smaller bandwidth filters and for lenses. I think I also want to refine my index of refraction estimate, I thought of a way to get that a bit more accurate.
What I learned was that the narrower filter was rejecting more real signal, than it was rejecting background for a net loss in quality.
I want f4 f3 test great video as scientific as it gets with out cutting edge technology.
By far the deepest analysis I’ve found on this topic, Brent.
I use the IDAS NBZ for Hyperstar imaging and, according to the specifications, it is also a wider band filter both in Ha and OIII. I have a C9.25 EdgeHD with Hyperstar V3 and the ASI071. When I got this filter the increase in SNR was evident, compared to the previous narrow band ccd filers from Baader (which are engineered for a slower f-ratio).
I’m considering going for f10 mono imaging. In that case, I think filters in the 3nm to 5 or 6nm FWHM range would be useful, because of the very low angle of incidence. What’s your opinion on that?
The down sides to narrower band are cost and you may need longer exposures for auto focus runs. Otherwise it seems like 3 nm would be awesome for those focal ratios. Keep an eye out for reviews on halos
Good threads on cloudy nights about all the filters
That’s something to keep in mind. I’ve seen some threads in CN about halos with even the most premium brands. And definitely those can come from a lot of sources as you have shown.
I’ll have to inspect some of my images to check where those halos were produced
Excellent video! I've been looking for something like this for a while. I want to run these calculations for my optolong filters which are 7nm and I use a Hyperstar 3 on an EdgeHD 1100 which is F2 I believe.
Glad it was helpful!
Hi Brent, i have a C925 and recently bough a hyperstar v4. i understand about bandpass shift but can i still get useable results with my Altair triband filter v1? i use a Altair 26C imx571 colour sensor. i mean if i could afford theIDEAS NBX UHS or the new Optolong l extreme f2 i would. it would be a shame not to just junk the filter i currently own if it isnt shifted too badly at f2.3 which is my current imaging rig. would be glad to hear your thoughts. thanks Des
this follow on video may answer your question
ruclips.net/video/IudhLAjqD8E/видео.html
the short version is the more narrow the bandwidth the more signal loss you will have at lower f/. If the bandwidth of your filter is large ( maybe greater than 6 nm) then no problem, if the bandwidth is smaller, then you are throwing away (filtering) the signal you want.
thanks very much Brent.@@BrentMantooth
Hey Brent, I really appreciate you sharing the comparisons between the 12nm and 6nm MaxFR filters. I'm considering a set of these and was curious on your thoughts with my two scopes: An Askar FRA300 (F5.0) and a Skywatcher Quattro 150pm (6 inch newtonian) (F3.45 with coma corrector/reducer). So I have an F5.0 and F3.45 system and want to get the best set of filters to use with both scopes to maximize signal to noise and have nice stars with little to no halos. Which set of Astronomik filters would you recommend in my scenario? Thanks.
if budget is no object - go 6 nm. if you want all the signal you can get, go 12 nm.
at f3.45 incident angle is ~8.2 degrees - so look at the chart at a time stamp of 35:00 and compare transmittance at ~8 degrees. The 6 nm will have a little attenuation at the higher angles (down to ~80% transmittance). without doing the simulation... the 6 nm filter on your Quattro will probably make its light collection closer to f/4 ish. on my hyper star the 6 nm filter was giving a response closer to f/2.5 so maybe it won't be so bad for you?
the 12 nm filter would give you your full f/3.45 signal.
My testing was in a bortle 5/6 zone, and some of the comments indicate the benefit of the narrower filter may be more significant in higher light pollution conditions.
some drawbacks on the 6 nm are that you may need longer exposures for you AF runs (I was doing ~8 second exposures to get confident and reproducible focus runs)
the 6 nm filter will not give you better resolution... it will provide better signal to noise at f/5, and somewhat better signal to noise at f/3.45 compared to the 12 nm filter.
Do these differences justify the difference in cost for you? that is up to you.
depending on the currency conversion rates it can be cheaper to buy directly from astronomiks in Germany than to buy elsewhere.
you may find my updated video of a little more help: ruclips.net/video/IudhLAjqD8E/видео.html
and remember for the chart at 35:00, it is the area under the transmittance curve from where the photons are coming from on your scope - not just the transmittance at the highest angle - your quattro will be somewhat like my hyperstar. if you really want to know, download the python code and put in your scope parameters. my other video gets into this in more detail.
@@BrentMantooth I also have a similar backyard sky of about Bortle 5/6.
@@the_astro_nerd after all of my filter adventures, I came to appreciate the importance of parfocal filters. on fast systems backfocus is critical, and if your filters are not parfocal, you may need different spacers for each filter. I now use only Astronomic filters for everything. this is also very important if you do OAG.
for your Bortle zone... and scopes... I would say go for the 12 nm and spend the cost difference on other things.
I know you said the Hyperstar at f1.9 with the 6nm stops down the optics so it’s better to go with the 12nm. I also noticed you are in a bortle 6 zone. My question is do you believe the same holds true for those of us in a bortle 8 to 9 zone. Or would the 6nm be better due to the extra sky glow?
That is a great question. I think it comes back to the statistics of signal of interest and sky glow, and that you just need 'more data' (more subs) to help remove the sky glow. I don't have a quantitative answer right now, but I think stopping down the scope does more damage to the signal than the narrower filter benefits the signal. The rate of real signal accumulation is the most important (so 12 nm) seems to be the key factor, and being above the read and shot noise of your detector. I provided links in the description for a paper from Abby Road Observatory (see the link for karmalimbo) Some of Jim's other papers on that that server get into simulating sky glow, but not in the context of exactly this question. Look up a video with the title "Deep Sky Astrophotography With CMOS Cameras by Dr Robin Glover" around the 50 min mark is a table based on f/ and bortle that gets at these concepts. I will think on it and see if I can do another video on these topics.
I think Cuiv the lazy geek channel has a video about light pollution in Tokyo and signal as well.
Interesting! I image with a OSC and a 5nm dual band filter. I wonder if a 12 nm filter like the L-enhance wouldn't be better when using an f/2 camera lens like the samyang 135mm...? Either that or stopping the lens down to f/4. What are your thoughts on this?
I will see if I can setup and run the simulations to see what that would look like, hope to post it soon.
@@BrentMantooth Awesome!! Thank you!
Have you run the simulation? I am very interested to know!!
@@tempusfugit6820 Just posted the Samyang calculations on my channel
Green lasers destroy sensors! Don’t do this!