What determines integration times?

[RayD]

If you are imaging a new object, how do you determine what integrations to use?  For example, I am heading off to Spain next week and hope to get "proper" first light on my TS80.  I have set up a LRGB sequence in SGPro to image M81, but am pretty much guessing on the integration times for each filter.

How do you work out whether you need 300, 600, 900 seconds for example, or even a combination of some/all?  I seem to search for a guide on each target but get wide differences, so I'm guessing there is no hard and fast rule, even on a specific target?

[wimvb]

Integration time is only determined by patience and perseverance.

Single sub exposure time is very much determined by your setup, conditions and target

With guiding, I would start with 10 mins and exoeriment from there.

Good luck

[RayD]

4 hours ago, wimvb said:

Integration time is only determined by patience and perseverance.

Single sub exposure time is very much determined by your setup, conditions and target

With guiding, I would start with 10 mins and exoeriment from there.

Good luck

Thanks Wim.  Thing is I can easily get 900s subs (that's the longest I've done so far) with no star trailing at all, but I don't know how I would determine if I actually need 900s on a particular target, or whether a specific target needs shorter as I often see comments about shorter subs blended in areas such as cores to prevent it looking blown out.

It's all very confusing, but I suspect you're saying just persevere with each target and I'll come up with my own integrations that suit my specific set-up (camera, filters, OTA etc.).

[Davey-T]

Been having a hack at M81/M82 the last couple of clear nights and they are bright little devils, been taking LRGB 600sec subs using QSI683 and WO110FLT and the cores are well burnt out.

Dave

[RayD]

8 minutes ago, Davey-T said:

Been having a hack at M81/M82 the last couple of clear nights and they are bright little devils, been taking LRGB 600sec subs using QSI683 and WO110FLT and the cores are well burnt out.

Dave

Thanks Dave that's really helpful.  So in this instance would you say it is best to also get some shorter, say 300s subs, to blend in so the cores are suppressed a little, but keep longer ones for the fainter parts of the galaxies?

I'm hoping to have a good run of at least 3 full nights (he says with fingers firmly crossed) so getting the data shouldn't be a problem time wise.

[wimvb]

Done the same with a dslr at iso 400 and barely got usable subs at 10 minutes exposure time, due to light pollution and noise. The histogram on the camera display peaked at 1/3 from left side, but after background extraction in PixInsight, I got mostly noise left.

At my dark site, I can easily double the exposure time, andstill have a dark background.

Sky conditions determine how deep you can go. In my image of the pleiades, I got faint dust at 10 min exposure time, as compared to almost no result at my light polluted site.

That's why I'm saying that there is no golden rule for (single sub) exposure time.  It's too much dependent on setup and local conditions. So, @RayD, keep experimenting. As you get more experienced, you'll develop a feel/knowkedge for what works best for you.

Good luck

[RayD]

2 minutes ago, wimvb said:

Done the same with a dslr at iso 400 and barely got usable subs at 10 minutes exposure time, due to light pollution and noise. The histogram on the camera display peaked at 1/3 from left side, but after background extraction in PixInsight, I got mostly noise left.

That's why I'm saying that there is no golden rule for (single sub) exposure time.  It's too much dependent on setup and local conditions. So, @RayD, keep experimenting. As you get more experienced, you'll develop a feel/knowkedge for what works best for you.

Good luck

Thanks Wim.  I'll set up the sequence to do 300s and 600s first and if needed I can then add longer ones after.

[Davey-T]

Just had a play with one in P'Shop levels and doesn't look too bad from exposure point of view.

No calibration so excuse the snow and blobs.

600 secs red

 

[swag72]

I find it's down to experience.... in that, I always do 30m subs for narrowband. My sky conditions allow 1200s for Luminance, but that was only worked out through trial end error. For RGB I tend to do 300s, but made a mistake on my current target and put 600s in by accident, so 600s in RGB it is then LOL!

[Nova2000]

I feel bright galaxies need 2 different exposure sets? Ex. Cigar has a red cloud which I don't feel it can get captured in 5min exposures but it's and bodes core is very bright. Please correct me if I'm wrong

Rajesh 

 

[RayD]

31 minutes ago, Davey-T said:

Just had a play with one in P'Shop levels and doesn't look too bad from exposure point of view.

No calibration so excuse the snow and blobs.

600 secs red

Thanks Dave, that actually looks pretty good exposure wise as you say, so doing 600 and 300 is probably a good starting point.

26 minutes ago, swag72 said:

I find it's down to experience.... in that, I always do 30m subs for narrowband. My sky conditions allow 1200s for Luminance, but that was only worked out through trial end error. For RGB I tend to do 300s, but made a mistake on my current target and put 600s in by accident, so 600s in RGB it is then LOL!

Thanks Sara.  That's actually interesting with the Lum as my skies there are probably not much different to yours, but I've never considered using subs of that length (not even sure my AZ EQ6 on a tripod would cope with it).

Could have been a worse mistake I guess, but I take it you don't think this will trash the images?

17 minutes ago, Nova2000 said:

 

I feel bright galaxies need 2 different exposure sets? Ex. Cigar has a red cloud which I don't feel it can get captured in 5min exposures but it's and bodes core is very bright. Please correct me if I'm wrong

Rajesh 

 

Thanks Rajesh.  I thought maybe this when Dave said about the cores looking blown out, so will do some 300s anyway as well as 600s, but looking at Dave and Sara's advice, doing both of these exposures means I'm definitely going to be in the ball park with data available for a reasonable image.