Flats - Forums - AstroBin

Topic starter

11 days ago

GDay all

I have a creek running behind my place and hence lots of trees. I image between them and on my deck. Some nights I can only get ten subs if Im lucky and anything quite high no dramas getting a decent amount.

Many times Im lucky for ten. In that ten my EAF may change once or twice due to temp change. So would I take 20 flats say for just three subs at that EAF step range and then another twenty flats at the other step range? Crikey if it changes three times sixty odd flats for say ten subs.

I have never bothered before but I see colour shifts in some of my stars after an RGB combo. Yup I can edit some of them in PS, but more curious to know about the flats and what some of the gurus would do.

I have a modest setup and dont expect Tak stars.

I have some tilt but thats strange as well. I throw subs at ASTAP and one night that particular filter may have extreme tilt but another day none. I gave up on that as I do see some tilt in the lower left corner.

More interested about the flats, how many is too many and do I take them on every EAF change? I have set the ASIAIR+ for the EAF to change at 2celcius change. Hate to set it at one…

Step size in one night for example :

Blue Filter: 20919…EAF change that night 20887. I place my scope on my kitchen bench and dont even see the focuser move when trying the steps out.

I take flats with a Giotto on an Askar FRA500. Camera ZWO6200

Regret long blurb. Regards

bigCatAstro

11 days ago

My long time understanding is that you should take flats for each change of filter, not really for a focusing change. Ten to twenty flats per filter used are generally enough. Since you have a short period of time to image, you could probably get away with ten per session—just depends on your rig.

I take 40 flats per session object (overkill) since I don’t change filters with my OSC. When I go to an electronic filter wheel, I will take more flats according.

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Stephen Jones

Topic starter

11 days ago

GDay bigCatAstro

Yup got it. I always take 20 odd because thats what the net comes up with also….and Chatgtp. I have never done per filter. Only been doing astro for a short time. I do them all up at the end which Im I now know is incorrect. Just that I notice now looking at photos on Astrobin. Ta for the response.

Paul Macias

11 days ago

If you have a refractor, you only really need to retake flats if you open up your imaging train, which can let in and shift dust.

If you’re physically moving your rig everyday, it wouldn’t hurt to take flats for that day, if you think there’s a big enough chance there is dust that will move around.

However, your actual focus level isn’t going to matter for flats at all. Or rather, you don’t need to take flats for each different EAF step.

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Médéric Hébert

11 days ago

Paul Macias · Nov 15, 2025, 02:03 AM
If you have a refractor, you only really need to retake flats if you open up your imaging train, which can let in and shift dust.

Even with a newt, unless you live in a dirty environment, I haven’t found taking flats every day to be necesary.

Only on moving/dissassembling the rig or rotating the imaging train.

Paul Macias

10 days ago

Médéric Hébert · Nov 15, 2025, 02:16 AM
Paul Macias · Nov 15, 2025, 02:03 AM
If you have a refractor, you only really need to retake flats if you open up your imaging train, which can let in and shift dust.
Even with a newt, unless you live in a dirty environment, I haven’t found taking flats every day to be necesary.
Only on moving/dissassembling the rig or rotating the imaging train.

I haven’t used a newt for imaging, so I didn’t want to speak for those. Part of me assumed dust would be much more of an issue, with a closer piece of the glass being open to the air, but I guess not! Good to know!

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bigCatAstro

10 days ago

Paul Macias · Nov 15, 2025 at 02:03 AM
If you have a refractor, you only really need to retake flats if you open up your imaging train, which can let in and shift dust.

If you’re physically moving your rig everyday, it wouldn’t hurt to take flats for that day, if you think there’s a big enough chance there is dust that will move around.

However, your actual focus level isn’t going to matter for flats at all. Or rather, you don’t need to take flats for each different EAF step.

Indeed, I agree with this generally.

I forgot to add, since I open my filter drawer to exchange out my dual narrowband for a uv/ir when polar aligning, I just go ahead and take new flats anyway.

Paul Macias

8 days ago

One thing I started doing was creating a custom keyword in NINA for my lights and flats, to help match them in WBPP. Basically, in the NINA filename output, you just make up whatever word you want, put that word in the end of the filename, followed by an underscore, and then a number. Whenever I open up my imaging train for any reason, I just increase the number that follows the keyword.

Then, in WBPP, I just use that keyword as a keyword when stacking, and it will match any lights and flats that have the same number.

For example, lets say a filename of a light frame is “DATE_TARGET_FILTER_SPECIALMAGICFLATSKEYWORD_2”

For your flats that you took, it would be “DATE_FILTER_SPECIALMAGICFLATSKEYWORD_2”

Your WBPP Keyword that you would add is SPECIALMAGICFLATSKEYWORD. I recommend using a shorter keyword, but hopefully you get the idea. A bit unrelated to the topic, but I thought it was a corny neat idea to share that might help some. When I was doing flats more often, it was sometimes a pain to match which flats to use for which lights if I wasn’t remembering to do flats each session. This was my solution for that.

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Craig Rairdin

2 days ago

My rig is permanently mounted on a pier at Starfront Observatories, so there’s no assembly/disassembly. But I’ve seen my flats change (just a bit) from night to night. I shoot OSC, either wideband (no filter) or narrow (dual narrowband filter). I arrange targets and filter changes so that I start in one configuration and end in the other. Whatever configuration is first, I’ll cool the camera and shoot flats in that configuration before nautical dusk. Then, in the morning, I leave the scope in its final configuration with the cooler on and shoot flats in that configuration after nautical dawn. I use ASIAIR; shooting 20 flats in auto mode takes less than a minute; so no big deal.

I realize I’m a little spoiled because even if it starts raining in the middle of the night and the roof closes, when I wake up the rig is still there and I can shoot flats and shut things down. But you get the general idea — I don’t change filter configuration before I have taken flats. That’s the important thing — even with the filter wheel, dust can move when the filter wheel moves.

Just to round out the process — in the morning I download all my subs from ASIAIR, store the master flat file with the subs for each target, then run APP and save the calibrated files. After that I can build for that night or after several nights from the calibrated subs and don’t have to worry about calibration frames.

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Stephen Jones

Topic starter

2 days ago

Craig

Out of curiosity what is the average ADU? Auto is very bright so I lower my light panel so I get around that 24000-26000.

Craig Rairdin

2 days ago

Stephen Jones · Nov 23, 2025, 11:22 PM
Craig
Out of curiosity what is the average ADU? Auto is very bright so I lower my light panel so I get around that 24000-26000.

ASIAIR in “auto” mode like I use usually targets around 28–32k ADU, but I don’t have the raw flats because ASIAIR does not save them. I had an ASI2600MC Pro on the scope for a while at gain 100 and I gave it full brightness on my Deep Sky Dad OFP2 and it was happy. I recently swapped in an ASI183MC Pro temporarily. It runs at gain 200 and I have to reduce the light to 75% or it complains about not being able to find a suitable setting.

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Stephen Jones

Topic starter

1 day ago

Craig thanks for the info. Mid 30000s was what my Asiar Plus would do in auto as well., depending on the filter. My flats are saved in auto? I use a very long ethernet cable as Im in the back yard and grab flats etc via IP address on my PC.

Craig Rairdin

1 day ago

Stephen Jones · Nov 24, 2025, 06:59 AM
My flats are saved in auto? I use a very long ethernet cable as Im in the back yard and grab flats etc via IP address on my PC.

It’s my understanding that the individual exposures might be saved if you have an SD card or flash drive inserted. I don’t. It’s also possible that older versions of the firmware saved them or saved them in a different place. I connect the same way you do but with a shorter cable, as the Mac on which I run the ASIAIR software is on my pier. It’s the connection to the Mac that is at the end of a 1000 miles of Ethernet cable. :-)

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