Cuiv, I am rather a user of cooled astrocams, but I wonder, how can average thermal signal (which is not noise btw, noise is the just the square root of the average level, which U ofc know) swamp signal? Signal grows linearly with time, and thermal noise grows square rooty with time. No matter what multiplicative constant, the signal will asymptotically win. How can that problem be real? I suspect someone has misconceptions in misconceptions and they really mean "amp glow" and related effects (which are signal! and grow linearly) not averaged thermal noise. (btw, just thinking out loud, why using multiband filters with OSC sensors and DSLR's, when it is pretty affordable nowadays to use cooled mono+NB. the first option is cutting tons of light and resolution, and doesn't have any flexibility)

This is a great video and was something I too have struggled to understand in the past. The clarification of the two sentences "I need to expose longer/I can expose longer" is gold.

Awesome content and approach Cuiv! Great videos - keep up the great work!

Thank you for tackling a complex subject there are dozens of folks who are addresing the entry level problems and only a handful willing to go to the next step. Thanks and please keep up the good work.

Good to see you cranking the info.

It has to be the most common rookie mistake regarding exposure time. I think it comes when someone imaged the Orion nebula and it shows up on nearly all cameras nicely with/without any filter. So moving on to a fainter object, the rookie WANTS to see the nebula on each sub, although many fainter nebulae will not show up like that unless the image is severely over exposed and the stars are over saturating and bloating like a big flashlight. So, moving on to a light pollution filter or narrow band, and the "ahhh, finally, I can shoot 10 minute subs so now I will be able to see the nebula in each of my subs" . Meanwhile the nebula emit the same amount of light , the narrow band filter letting through the same amount of light too, with the exception of the wavelength that are blocked. You are still receiving the same amount of light at the sensor. Some blocked, others lights allowed through, the nebulae or the stars aren't emitting less or more. People asked me "why are you only taking 180second subs with the narrow band? " I'm like, because I tried 300 seconds and my stars were bloating. Plus if I got an airplane or cloud ruining my sub, I don't have to throw away a whole 5 minute exposure, only 3 minute. It adds up!

My God Cuiv, you are such the Geek! Thank you for that!!!

It makes totally sense what you say. I do use a DSLR and will move to a much more polluted area, so your advice is highly appreciated, thanks!

I use a ZWO 533MM camera with LRGB, Ha, O-III and S-II filters. I run the cooler at -10C. I find longer exposures to be advantageous to a point, but there are factors that limit that advantage even with cooled cameras. 300-second subs in hydrogen alpha generally have the same noise levels as 180-second subs. I have yet to expose O-III and S-II subs for less than 300 seconds. What limits the benefits of going 300 seconds or longer for me are the hordes of satellites and aircraft passing overhead, and my mount's ability to track accurately. Light pollution is another limiting factor. Poor seeing also messes with your auto guiding too. What seems to work best for me so far is exposing through the LRGB filters subs for 30 to 120 secconds depending on the object and filter, and 180 to 300 seconds through the 7nm narrow band filters depending on the object. In this way a passing satellite or glitch in the auto guiding results in less lost integration time. I am using an 80mm F/6 apochromatic refractor with a .8X focal reducer/flattener.

Awesome info bro! Extremely helpful in understanding the narrow band filters. I almost got tricked too into thinking I need to expose longer or raise the ISO but it makes perfect sense what are you saying.

Great info Cuiv. I wish I had viewed something like this four years ago - Would have saved a lot of disappointing imaging sessions with my DSLR until I finally figured it out by trial and error.

Another great video with useful info. Content is key and you just opened a few doors for me. Thanks again Cuiv. Keep them coming. HJ

Makes perfect sense! Good advice, thanks

Clear explanation, it makes sense. I believe I am better prepared to shoot Astro photo.

Very interesting. Thanks.

CTLG nails it again. Many thanks Pal

Excellent explanation Cuiv! 👍👍

Thank you for a great explanation. It makes sense and is very useful info.

Excellent lesson! I've been schooled. :)

Great explanation Cuiv, the exposure time is always an issue

Exactly so and we’ll put! Thanks!

Excellent video!! I’m a beginner (& starting to get some decent results with my DSLR) and this was easy to understand, along with being very informative. Thanks!

Thank you - hugely interesting explanation.

Thanks Cuiv! Great info. I'm using a DSLR right now but plan to move to a dedicated astro cam. This is great info, thanks again. ps.. I lived in Japan for 2 years. Loved it. It's not all raw fish ;-)

Thanks for making this video! This was explained very well! Appreciate it! 😃

This has saved me lots of effort. Thank you!

Glad you’re back and doing better. I would love to see a video on how do the initial setup in NINA with an auto focuser. I bought and installed a Senso quite a while back and although I was able to get it installed and see that the motor would drive my focuser I’m completely lost on what to do next to actually make AF work. Every video I’ve seen always assumes certain knowledge and skips over steps making it impossible to figure out. A short simple tutorial showing all the steps with NINA would be very helpful. I’ve been using NINA for a while and have all the other basic functionality working but AF is the final piece. Anyway, keep up the great content!

Thanks for the video. I'm new to narrowband filters so found the video interesting but left me a bit confused. Perhaps it would be helpful to share specific examples of solutions on what settings and exposure times would be good? In my case I'm getting an h alpha modded canon EOS R and a drop in narrowband L extreme filter.

Glad you're back!

Nice, thx for this explication!

Well explained Cuiv!! You've probably seen this, but for those that haven't, a talk by Roger Glover (of SHARPCAP fame) giving an in-depth talk on the 'dynamics' of CMOS astroimaging.

Thank you, Prof. Cuiv ;-) Very Interesting 👍

That is true only if the nebula emission is limited to that narrowband. If there is a certain emission close but out of that band you will lost data there. I do prefere to capture with and without and blend them

Thanks for the explanation! I was really falling for that misconception "If I get an L-Extreme I will have to expose longer and my camera is already at it's limit!". It's well explained, that's a new sub for you :D

Cuiv going crazy with the videos :D

Hello Cuiv, I l Really love your video's. Have seen a lot of them and learnt a lot. In the meantime, Optolong has the L-Ultimate out. What about this one for OSC camera's ?

Nice video, great explanation. Question or tips. I have a 450D canon modified myself (remove IR\UV filter). I am using 12nm halpha filter. I notice that I have a lot of bandings (horizontal) in my raw images @ 400mm (refractor). Compare to my camera lens 50mm I don't see bandings. Is there a way to avoid the bandings? Why do I see them @ 400mm but not @ 50mm? Maybe it's still there ? Thanks!

Top video…👍💪pls make a video with Seestar s50 and Lenses… what’s there the difference? Ect…😊 thx

Great video pointing out a common misconception. However if I heard correctly, at one point you imply that increasing exposure time will increase thermal noise. The opposite is true, sensor thermal noise will decrease in each frame as the square root of exposure time. For the stacked image it is the total exposure time that matters. For the same total exposure time the sensor thermal noise component will be the same. P.S. Kn addition to increasing image contrast the NB filter will also decrease the shot noise in the final image that comes from the sky glow. Keep up the good work. I always enjoy your videos!

Had to abandon my modified DSLR and jumped to a cooled osc due to the thermal noise. I now use the L-Extreme. What a difference! Thank you, sir.

This video is gold! 🥇

Thanks Cuiv, great video! I was working my way to your conclusion but you got me over the line! I'm a DSLR user and just starting out - I wonder if there is an issue using the very narrow bandpass filters with manual focusing with a Bahtinov mask?

I worked as a radiometrologist (retired, physicist). We would use a multi-channel analyser (MCA) to examine the spectrum of say, X-rays. By setting a region of interest (ROI), your narrowband filter's window, we would exclude the unwanted data either side, and its noise too. That may mean you can expose for longer, because you have less noise and can count for longer because you have less signal too. Can does not mean you necessarily want to. That depends on your signal to noise ratio with a camera (& counting statistics). A smaller camera sensor will produce less heat, which is proportional to its area (& design a bit too), and that is noise to be removed somehow. You still need to determine your optimum ISO and exposure time, tracking may be a factor with the latter. But you may not need to increase your exposure time because you are still getting the same count in your ROI, you have simply got rid of the rubbish on either side.

Depends on how tall the peak is, on the spikes in the graphs y-axis. Moving from no filter, to a filter, you're getting less light because some of it is lost on the y-axis but the aim is to cut light out on the x-axis. Moving from one filter to another, you're probably not losing any of the light on the y-axis (which will depend on the filters you choose to use). So it makes sense that you don't need to increase exposure times. You're still getting (pretty much) the same amount of light in the wavelengths you want light from, unless those peaks are a lot lower. However, increasing exposure time means you're gathering more light and less of it is light pollution.

Newbeone here. Still learning, no HW yet. Is exposure time to capture nebulae based on equipment you are using, trial and error, or are there some basic guidelines to start out with? My current HW plan is edgehd, AM5 and a 2600mc pro(maybe the duo).

I think using these on a unmodded DSLR is kind of a waste- The blocking filter on the camera blocks out most of what you're paying for the filter to pass. Great video and great to see you feeling a little better. Welcome back!

Excellent, clear explanations as always ! In the video you mentioned that narrowband filters are not a good idea for OSC cameras - why is this ? Thanks

Hi! This might be a dumb question after what you said, but because of the response i've gotten from asking store owners about filters i still wanted to ask. I use a star tracker with an HA-modded Nikon dslr and lenses between 50mm to 300mm and f1,8 to f8. I do this unguided and get between 1-5min exposure time. I want a filter to be able to do astrophotography i full moonlight and in summertime when it doesn't get as dark at night. Because what you say makes sense to me i believe that i could go with a narrow bandpass filter like, for example, the L-extreme for this, but several store owners have said it's not a good idea. Do you think i should go for 7nm, or would you suggest a wider bandpass in my case? I should add that i want to mount the filter in front of my lenses as that makes most sense to me with camera lenses. If you know a filter that makes that possible with normal camera step down rings i would love suggestions as this is not an easy topic to get clear answers on either!

This interesting video is focused on DSLRs, right? It doesn't apply to dedicated cooled astronomical cameras, correct? Thanks!

great advice. Great video as always. So happy you are back with a vengeance.

This is the perfect explanation of what I asked a few days ago. Thanks so much, Cuiv! One more thing: what is the real relationship between band pass and telescope speed, i.e. focal ratio? Why are there filters designed for f/2 telescopes for example?

I never dial up the ISO. It heats the camera. It does not increase the number of photons collected. I leave my ISO at the values where read noise, DR are optimized. I can increase the gain in post.

Interesting topic! I have the f/2 3.5nm Baader narrowband pass filters for Rasa. I am wondering if they can be used for normal scopes > f/4 and if they are better than using my older 12nm narrowband filters.

I have a hyperstar for my C6 scope. What do you recommend me for my monochrome camera, filters 2'" vs 1.25". .?

Yes, you can't deceive the laws of physics, but knowing them, you can better understand how to use them to achieve your goal. My first Canon 550D, I myself am a lover of the Sony system, I turned into a Frankenstein) He could sing and dance and even cool down at a delta of -26 °. The reason was simple, there was no money for an astro camera. However, it was then that I realized all these relationships when using narrow band filters. Now my astro-Canon is in my "museum", I do not sell it, as a memory of where it all began. And comparing his raw footage today with what I'm getting now from Toptek 571, I don't always see a huge difference. Cooling is a big advantage for digital cameras. Not counting, of course, high-aperture optics.

Thanks for the explanation.. but what exactly does "dithering" do?

could you review some of the best astrophotography cameras for low budget and the enthusiast? - thanks

Hi Cuiv, I'm a lazier amateur astrophotographer here and following your channel since your AZ-GTI tuning video :) , what are your thoughts of using narrowband and an unmodified regular camera? I am planning to use the Optolong L-enhance with my 61mp Sony Camera, am I to expect terrible results with a regular camera and narrowband filters?

I think that this video, even beeing more suitable for DSLR users, adresses a little my question about the L-Extreme and the ASI533MC. I've used that filter on M31 and took about 50 120s frames (out of 75 due to a wall on my line of sight 😭) and I'll now combine those with a bunch of 120s or 180s frames to be taken with the Baader Neodymium (I live under a Bortle 7/8).

I have a full spectrum modified 60D and find when I shoot everything is very red. I know I can process much of this out… but… I think I am missing a filter… what clip in filter do you recommend for someone just starting out? I will be attaching my camera to a FLT91 (when ever it arrives) 😊

Can we assume that the 18nm vs the 12nm vs the 3nm filters all have the same transmission value?

What about with the HCG-mode of the 2600, 533 cameras with ZWO saying we should either shoot at 0 gain or 100 gain, 100 gain being the HCG-mode. Would really love to pick your brain on something Cuiv maybe I will try an DM you on discord

Hello - when I use my DSLR , I was under the impression that I need to have my histogram 1/3 of the way for the peak value - otherwise , the image is underexposed . I have been following this rule of thumb When I use my multi band pass filter , The histogram is too far to the left , so I increase my exposure time to get it back to 1/3 . So are you saying that I don’t need to increase exposure time ? If the histogram peak is all the way to left , that is ok ? I feel like it will be too dark . A 30 second exposure with and without a filter is not the same on the histogram Can you please elaborate on this ? Thank you - and thank you for all the great content ! Regards

Cuiv, I know you are on a hiatus right now and will be back in a few months and all, however, perhaps it would be funny to do a very short video in french when you are back! Just short 1 minute stuff. Just an idea

The OPT affiliate link takes me to spammy stuff. Is there a typo? If i copy the text of the link it works all right, but if i click on it i get redirected to stuff that wants to show me notifications and install software, and never arrive at OPT.

Hi Cuiv. A question regarding NB imaging. I'm starting working with monocrom from a light polluted area (Bortle 7/8) and I'll try the Horse Head Nebula as HaRGB. The question is shall I use short exposures in RGB and larger ones in Ha or can I go to longer ones in RGB. From your experience with light pollution what will be the best approach?

I am using these techniques with my DSLR. Hopefully, Santa Clause will bring me a dedicated cooled camera for next summer! Until then I’m just trying to improve my skills.

👍🏻

Well, not completely the same. There's about a 3% loss to the filtering material and another 5% loss to the glass plate it is on... so you ARE losing about 9% of the narrowbandpass you want as opposed to not using a filter at all, but in the end its usually less total loss than using a broad band-block like the pollution filters. Additionally if you're going for deep galaxies the 5 to 7nm narrow filters are a better option. Using an actual astrograph instead of an "astrophoto telescope" will make a much greater difference in your light gain overall but not many people are willing to do the tiling and knitting that RCs need for broad objects.

Actually the person who teaches me astrophotography is wrong. I was wondering why I have to exposed longer for Ha. It totally didn’t make sense for me. Thanks for the clarification

Maybe I need to come back with a fresher head but I didn't really pick up a whole lot of what was said. Just went in through one ear and out the other. Maybe someone can explain it to me in an even more simple way.