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Osc narrowband flats at F10 suggestions

Celestron C6 Acquisition Calibration Narrowband Deep Sky
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TiffsAndAstro avatar
TiffsAndAstro avatar
RGB and narrowband flats on my 533 and 72ed were a breeze in Nina so I've hardly put any effort into them

Moving to my C6, RGB flats were trickier and results not as good, but still acceptable to me. Floppy dew shield, not perfect collimation and small illuminated circle being my major excuses

Narrowband however is a disaster. Somehow, even using no flats but bias and darks is also terrible. Stacking with not flats, darks or bias is surprisingly decent one or two (ahem) hot pixels though. Too many donuts too, so I'd like decent flats.

My attempt at sky flats for NB didn't work out, but I took them too early maybe.

Does anyone have any top tips I could try? No astro dark so I'd like to try get this sorted before dark returns in a month or two.

Oh and a budget of like a quid smile
andrea tasselli avatar
andrea tasselli avatar
Take sky (dusk/dawn) flats and you'll be sorted (the below is for NB filters):

" As for sky flats at dusk just wait for the Sun to have just set or be within 5 min of it setting, point the scope away from the Sun setting position by about 100 degrees and nearest to zenith and take flats using NINA". For dawn flats (who's got the strength to take them?) just invert the times.

P.S.: Obviously, no clouds please.
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TiffsAndAstro avatar
TiffsAndAstro avatar
hmmm, dusk flats? that is definitely a good idea, ty smile
Tony Gondola avatar
Tony Gondola avatar
Fix the dew shield, collimate the scope and follow Andrea's suggestions. Fundamentally there really isn't any difference in how you create calibration frames between the two systems.
TiffsAndAstro avatar
TiffsAndAstro avatar
andrea tasselli:
Take sky (dusk/dawn) flats and you'll be sorted (the below is for NB filters):

" As for sky flats at dusk just wait for the Sun to have just set or be within 5 min of it setting, point the scope away from the Sun setting position by about 100 degrees and nearest to zenith and take flats using NINA". For dawn flats (who's got the strength to take them?) just invert the times.

P.S.: Obviously, no clouds please.


You say obviously no clouds, but... that's not obvious my thinking was overcast will diffuse the sunlight.

I think I'm going to to have to try more variations on more methods and hopefully find one that works.

Dusk flats is top of that list though.
TiffsAndAstro avatar
TiffsAndAstro avatar
Tony Gondola:
Fix the dew shield, collimate the scope and follow Andrea's suggestions. Fundamentally there really isn't any difference in how you create calibration frames between the two systems.


Dew shield is fixable at some future time with official aluminium dew shield.

Unless my collimation changes, I can't see how it would break my flats. 

However, you've now made me think a little mirror flop could. Maybe to some extent?
andrea tasselli avatar
andrea tasselli avatar
TiffsAndAstro:
You say obviously no clouds, but... that's not obvious my thinking was overcast will diffuse the sunlight.

I think I'm going to to have to try more variations on more methods and hopefully find one that works.

Dusk flats is top of that list though.


Clouds don't work, already tried that. Both during daylight, at dusk and at night. Reason being that their homogeneity and scattering aren't uniform.
Kristof Vandebeek avatar
Kristof Vandebeek avatar
I shoot with a 10” newtonian. I take dawn flats when I have clear skies, works fine. 

For cloudy mornings or mornings where I had to wait for my tube to dry due to a fogged primary mirror, I use two thick square pieces of white/diffuse plexiglass while my tube is pointing to zenith. It gives a fairly good diffuse light and the flats come out really well. A disadvantage might be that the exposure times for these flats are much longer than the dawn flats. If there’s much variation in light due to changing cloud cover I tend to pick flats with similar ADU values and throw others away.
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Tony Gondola avatar
Tony Gondola avatar
TiffsAndAstro:
Tony Gondola:
Fix the dew shield, collimate the scope and follow Andrea's suggestions. Fundamentally there really isn't any difference in how you create calibration frames between the two systems.


Dew shield is fixable at some future time with official aluminium dew shield.

Unless my collimation changes, I can't see how it would break my flats. 

However, you've now made me think a little mirror flop could. Maybe to some extent?

if it changes the light distribution in any way, it certainly could but I think it would have to be pretty bad.
Tony Gondola avatar
Tony Gondola avatar
TiffsAndAstro:
andrea tasselli:
Take sky (dusk/dawn) flats and you'll be sorted (the below is for NB filters):

" As for sky flats at dusk just wait for the Sun to have just set or be within 5 min of it setting, point the scope away from the Sun setting position by about 100 degrees and nearest to zenith and take flats using NINA". For dawn flats (who's got the strength to take them?) just invert the times.

P.S.: Obviously, no clouds please.


You say obviously no clouds, but... that's not obvious my thinking was overcast will diffuse the sunlight.

I think I'm going to to have to try more variations on more methods and hopefully find one that works.

Dusk flats is top of that list though.

If you look at what the camera is recording when clouds are present, you'll see why.
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TiffsAndAstro avatar
TiffsAndAstro avatar
Thanks all for the help and advice.
Hopefully I can try some variations on Sunday night and go from there.
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