Calibration frame strategy for multi-session narrowband imaging projects

The slight focus shifts involved will not affect your flat frames.

Some people will say that if the system is sealed and you never change rotation then one set of flats will last forever. I suppose that is true however, it’s a risk. You never know if there is a bit of dust or a hair that will suddenly decide to visit your sensor window or filter. Taking flats is so quick and automated if you use NINA, I just can’t really see a good reason not to take them for every session, as insurance if nothing else.

Since you’re using NINA why not automate your sky flats by including that in your sequence? If you throw in a flat session at the beginning and at the end of the night, you’ll have protection if clouds show up in the morning. In any case, you can sleep in!

I use my dark library for darks and bias. I’ll shoot flats most mornings, but for sure if I have torn down the set up between sessions. I shoot sky flats and even if I have to take them for all 7 filters it only takes 5-10 minutes tops.

nadz11.ns · Aug 18, 2026, 08:45 PM

One question on the “flats at start and end of sequence” tip, wouldn’t start-of-sequence flats miss any dust that lands on the front element during the actual imaging run? Seems like end-of-session flats are what actually protect against that, since they reflect the train’s state after the night’s imaging rather than before.

That was really more about clouds, not changes in the state of the dust.

In your case, new dust is probably more likely right from the beginning but if you double up the flat session, you’re covered both ways.

Also, it should be noted that dust on the front element has no effect and doesn’t show as a dust mote. It’s dust much closer to the focal plane that you need to worry about.

Tony Gondola · Aug 18, 2026 at 06:07 PM

Since you’re using NINA why not automate your sky flats by including that in your sequence? If you throw in a flat session at the beginning and at the end of the night, you’ll have protection if clouds show up in the morning. In any case, you can sleep in!

I could do that, but when I say I shoot sky flats, what I really mean is that I shoot white t-shirt flats. So I need to be up to place the white t-shirt ( actually use white t-shirt material in an embroidery hoop).

Tony Gondola · Aug 18, 2026 at 08:54 PM

nadz11.ns · Aug 18, 2026, 08:45 PM

One question on the “flats at start and end of sequence” tip, wouldn’t start-of-sequence flats miss any dust that lands on the front element during the actual imaging run? Seems like end-of-session flats are what actually protect against that, since they reflect the train’s state after the night’s imaging rather than before.

That was really more about clouds, not changes in the state of the dust.

In your case, new dust is probably more likely right from the beginning but if you double up the flat session, you’re covered both ways.

Also, it should be noted that dust on the front element has no effect and doesn’t show as a dust mote. It’s dust much closer to the focal plane that you need to worry about.

ah, i didn’t know that front element dust doesn’t affect much.

I will incorporate flats in the beginning of the session into the sequence and try to double up where possible.

Thanks

Tony Gondola · Aug 18, 2026, 08:59 PM

Some swear by them, some swear at them. They are pricey and the sky is free.

The other thing is that if your OTA doesn’t have any light leaks, and if you have a camera that behaves well with short exposures, you can actually take them in the middle of the day if you have to.

I have used either scope mounted flip style panels for my refractors or wall panels for the larger scopes for decades. I have never had any issues with any of them except once. That was with a wall panel which sadly attracted a large moth one night! Fixed that by running a bug zapper for a few minutes before each flat session. ⚡️

A well sealed flip panel for refractors can also make darks a breeze for the 90% of cameras that do not have shutters. I prefer the Deep Sky Dad units due to their tight light/dust seal and their ability to get very bright which means you do not need a lot of longer flat exposures for narrowband. Very well thought out units and better than the old Optecs and the less well sealed Wanderers.

I abandoned sky flats decades ago and have never looked back. They are just too fussy in terms of gathering them and were not any better (and sometimes worse).

With a well sealed system (and any other kind is not acceptable) that has not been broken down (which is a PITA anyway) I do not take new sets of flats very often, maybe every few months.

Gotta do some tonite though. We just came out of a wildfire evac status 🚒🔥so I reassembled my AP 155 system today after boxing it to take with me. 🚚

Bill McLaughlin · Aug 18, 2026 at 10:25 PM

Tony Gondola · Aug 18, 2026, 08:59 PM

Some swear by them, some swear at them. They are pricey and the sky is free.

The other thing is that if your OTA doesn’t have any light leaks, and if you have a camera that behaves well with short exposures, you can actually take them in the middle of the day if you have to.

I have used either scope mounted flip style panels for my refractors or wall panels for the larger scopes for decades. I have never had any issues with any of them except once. That was with a wall panel which sadly attracted a large moth one night! Fixed that by running a bug zapper for a few minutes before each flat session. ⚡️

A well sealed flip panel for refractors can also make darks a breeze for the 90% of cameras that do not have shutters. I prefer the Deep Sky Dad units due to their tight light/dust seal and their ability to get very bright which means you do not need a lot of longer flat exposures for narrowband. Very well thought out units and better than the old Optecs and the less well sealed Wanderers.

I abandoned sky flats decades ago and have never looked back. They are just too fussy in terms of gathering them and were not any better (and sometimes worse).

With a well sealed system (and any other kind is not acceptable) that has not been broken down (which is a PITA anyway) I do not take new sets of flats very often, maybe every few months.

Gotta do some tonite though. We just came out of a wildfire evac status 🚒🔥so I reassembled my AP 155 system today after boxing it to take with me. 🚚

donld · Aug 19, 2026 at 04:32 PM

Deep Sky Dad works great in my experience. On a pier, flats don’t necessarily have to be taken each night. But people on piers are usually automated so flats take no effort. I’m curious what standard practice is for people on piers, either home observatory or remote. I have seen a few people with home observatories mention SD cards, which is surprising .

Thanks both.

Good to hear the Deep Sky Dad panels are working well for you. Given my situation, I think a flat panel is the right call for me. Sky flats just aren't reliable given how little control I have over timing. Going to look into the Deep Sky Dad units.