Long VS Short Exposures in Astrophotography - Broadband

Part 1 of what will most likely become a multi-part series attempting to address this question! :-) Follow for more!

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#astrophotography #space #stars #nebula #pixinsight #seestar #zwo #asiair

[miguelmorales]

As I'm sure you know, if the stars are oblong, there will always be less fine detail. If the system is blurring the stars into a other than round shape, then it is doing the same with the fine details as well.

[mschmalenbach]

Nice job Luke, as always. My sense is that the shorter exposure / more frames stacked image has smoother noise, but the other seems to have slightly better colour AND slightly better contrast.

I think the lesson for us all is to get a minimum of 20 frames to stack, with exposures that are as long as our gear AND environmental conditions will allow for that still deliver perfectly round stars. In other words, the answer to the question is, as always "it depends!!!"

[GoldenJackalTutorial]

I also did a similar comparison a while back, I shoot in Bortle 3-4 and the dark sky really works well with longer subs, but not too long. For instance, I have found out that 300s LRGB and 600s SHO gives me the most detail. Drop lower and I start losing fine detail, go higher and there is no gain in any detail, it actually seams there are worse results since external factors (such as wind) have higher impact on overall sub quality in longer exposures. I think the sky darkness as well as aperture size and speed are all three very important in deciding the sub frame length. Great video as always.

[hawkesworth]

I know you probably like the red border around your Youtube thumbnails because it sets them apart from others but unfortunately it's the same colour as the red line that appears under thumbnails of videos once I've watched them and it would be easy for me to skip over a new video.
I think it's the reason why not many people do it.

[RumourHasitYT]

Thanks for giving over a very rare clear night to do this for your viewers. Much appreciated

[annikasoraya]

Hey mate,

You are a right legend! Thank you for sharing your tips and experiences here at YouTube-You sure are gifted at this universal hobbie we all share a strong affection for. Your talent and dedication is most appreciated and your presentations are extraordinary. May you continue such exceptional work well into the future buddy.

Sending you many blessings and light from Australia!

[Jacq_Deepsky-Villa-Karimunjawa]

What I found out is that in most cases it's enough to shoot 120-180 seconds shots at broadband (OSC) and 180-300 on Narrowband (like the L-Ultimate). Most of the times I shot 30 seconds shots for the stars. To many different exposure times, will make the processing traject longer :) Nice video by the way !!

[mikemarcus]

Thanks for doing this. I see more stars on the Left... I see more resolution on the Left... stars appear brighter on the Left.

[Lord_Volkner]

The one on the right definitely seems to have more detail and contrast ... at least to me. Maybe not when zoomed in on the tiny galaxy, but for sure when zoomed out all the way.

[jerryg]

One thing i think is a benefit with shorter exposures is that when seeing conditions are a bit poor as they often are in Florida’s west coast, the images tend to be a slight bit less blurred. The comparison between the faint galaxy in those pics looks similar to what can be experienced.

[Wheeljack]

Really interesting. Thanks for taking the time to do this experiment.
I've found that a sort of sweet spot is often around 3 minutes, especially with OSC. Star colors seems to be very decently perserved, and detail in the background doesn't seem to take a hit.
Downside is that it will increase the number of individual subs by 8 pr hour. When you have projects often spanning 20+ hours, those extra subs all add up both in terms of processing time and storage.
As an example using a camera that produces 51mb fits:
- 20 hours of data using 300s subs = 240 files / 12gb
- 20 hours of data using 180s subs = 400 files / 20, 5 gb
Of course... a way around that is to take say 15 minutes worth of 1m subs only for the stars.

[gabewrsewell]

good comparison luke! i think the things like elongated stars and satellite trails aren’t a shortcoming of your comparison here, i feel like it’s an important thing to include because that’s exactly the risk you take with longer subs. less chance for dithering to help out, less of a loss if you lose a frame to a wind gust or guiding spike, et cetera.
for those who want to dive deeper, Deep Sky Detail has a great video on Signal to Noise Ratio And Number of Subframes, i’d recommend checking it out for a better more fundamental understanding on how many and how long your subs should be! and clear skies luke!

[dmccallie]

I do live stacking for public outreach at a local observatory. We live-stack and project to a large screen outside the obsevatory. We have an old, home-brew large (30”, F5) Newtonian, with rather poor tracking, so the exposures are limited to 20s max. We get great results with the short exposures. I can take the captured fits and post-process with PI for even better results. We do end up using higher gain that is ideal, but a few blown-out stars don’t bother me.

[davidthompson]

Excellent video. Surprised me with the results.

[Wombatzone]

I did a 10min test on Tarantula and compared it to my usual 5min subs, I can say I did collect a lot more data, but also collectted a lot more satellite trails as for in the Southern Hemisphere it is busy to the south, so the shorter exposures allow me to get clean subs without too many getting satellite trails. Was cool to see the target clearly without having to stretch the 10min sub.

[misaelescobarruiz]

Bonita la toma de la galaxia remolino buen procesado

[AstroQuest]

Fantastic video Luke. I love real experiments like this rather than BS opinions that people often spew out. You learn much more and there are always surprises. Cheers

[adaster]

The way I see it. The more subs you take the lower the normalised noise floor of the image. As long as you expose long enough to bring fine details slightly above that noise floor, then your good. So then it becomes a balancing act. Too long exposures and you don't get as many subs and therefore have more noise but stronger signal. Too short exposures you get many subs so lower noise floor but a weaker signal so might lose details to the normalisation process. I personally find for emission nebulae 300s is enough, granted I'm using a very sensitive cooled camera. For bright wideband stuff like Orion, Galaxies etc, 60s or even 30s is enough. 60 would blow Orions core out for me. Awesome testing!!! Really interesting video

[frankmm]

Processing time and data storage, overall data collection efficiency etc. they can sway me away from too short of a sub.

[JeffHorne]

Excellent experiment! Would love to see a narrowband version of this experiment.