Flats SOLVED

[Earl]

Now Then !

Steppenwolfs thread got me thinking and a penny dropped. my issue looked not to dissimular mybe a touch more exagurated.

The first flats I took last week which I thought were for my Luminance were in reality Ha Flats (this is important as if they were Lum this would of been noticed then.)

I took a 5 second Luminance Flat...... Lines I then took a posistion 8 Flat (empty filter) Lines.

I took 5 second flats for RGB Ha OIII SII all fine and as expected.

I inserted 6 sheets of white paper between my Gerd flat field jobby and my glass 5s Flat on Lum and Empty.... Both FIne.

Problemo Solved.

I need to either get a dimmer for the Gerd jobby or use papper to calm it down.

Lets see if I can get some OIII subs again tonight and see if that Line is there !!!

[swag72]

Glad you got to the bottom of it Earl

[martin_h]

I made a lens cap, similar to that used for solar film but with 2 sheets of copy paper......does the job!

[Earl]

Good plan

[steppenwolf]

Yup, this is all about the EL panel being too bright, necessitating exposures that are too short. Sheets of paper will do the trick just fine as they attenuate the light.

[Earl]

Yup, this is all about the EL panel being too bright, necessitating exposures that are too short. Sheets of paper will do the trick just fine as they attenuate the light.

Was your issue with just luminance too?

[steppenwolf]

No, I noticed it with my OSC camera BUT, I would probably have got away with it with NB filters because, by their very nature, they attenuate the signal allowing longer exposures to achieve the same ADU.

[martin_h]

I find I need 1 thickness of paper for NB and 2 sheets for LRGB.

[Ant]

Surely as long as you get the required ADU, why is the exposure length inportant?

Ant

[Earl]

Surely as long as you get the required ADU, why is the exposure length inportant?

Ant

I think on faster setups it saturates the sensor too quick, so you need a less powefull light but a longer exposure, a mechanical shutter also complicates it i belive. (in my case of a 8300)

[ollypenrice]

Surely as long as you get the required ADU, why is the exposure length inportant?

Ant

I don't think it is unless your camera has a shutter, in which case the 'wipe' will introduce a gradient and also affect the real exposure that you actually get. (Part of it might be shuttered.)

Regarding all these flats, I no longer bother. One (master) flat fits all for me, and for a number of experienced guests who come here. Since moving to a closed electric wheel I found no difference whatever been separate flats and a lum-for-all. There's not much point in agonizng over the theory, I don't think. I'd just suggest trying it in practice. It certainly works for me but, if ever it doesn't, I'll think again.

To further the heresy I now use exactly the same calibration files for every sub, whatever the exposure, and I get the cleanest stacks I've ever had. In AA5 I load up a lum flat, a master bias used as a dark and a bad pixel map made from a clipped 30 minute master dark. (2000 ADU taken off the bottom as per AA's instructions.) The time and tedium this saves is prodigious though having lots of data in the morning is a nice problem to have!

Bit of thread creep here, Earl. Hope that's OK but it did seem to follow on.

Olly

[Earl]

Its a fair point, and your incorrect flats (LOL) seem to work very well for you