Flats blowing out center of live capture image

[stbkaiser]

Equipment
Celestron SCT 9.25, Celestron OAG, ZWO ASI200MC pro, Starizona SCT corrector IV, iOptron_iAFS SCT focuser
LED Light Pad ( sketch pad ) 410mm x 300mm , adjustable intensity
Set gain at 26, exp 120s , no cooling
Preprocessing set to "Apply Flat" pointed to Master flat file

Flats created using the FLATS capture menu in SharpCapInstall-4.1.14310.0-64bit, pro
Gain and exp settings adjusted to "OK" level indicated by Sharpcap.
35 Flat exposures taken :
Create Monochrome , Capture and subtract bias
Separate Flats created for Starizona only and Starizona with Ioptron setup.

Flats and imaging with Starizona
I began using the Starizona SCT corrector and created a Master flat using (SharpCapInstall-4.1.14310.0-64bit, pro)
When I tried doing Live stacking , the Flat is blowing out the center of my live capture image.

I experience the same issue when using the iOptron_iAFS focuser in line with the Starizona .
(should not matter but I wanted to test results)
Although the center of the image is even more blown out during live stacking.

Am I not applying this correctly.
Thanks

[Howardk]

When creating flats make the hustogram approx 50-80%

Use 1s or less exposure
Gain and everything else same settings as your lights
Adjust light panel to get histogram as above

[stbkaiser]

Humm
from Sharpcap forum- ROBIN
On the settings,

A) Flats and dark flats must use the same settings as each other (gain/offset/exposure/colour balance)
B) Light frames and dark frames must use the same settings as each other.

There is no requirement for the settings for A) to be the same as those for B). If you are using bias frames in A) instead of dark flats then the only difference should be the exposure.
------------
must be something else
Maybe a way to adjust intensity of the Flat as it is applied?

[admin]

Hi,

first step is to check the flat frames - normally you would expect the brightest area to be in the center, with darker areas around the edges/corners due to vignetting and also from any dust shadows. SharpCap will try to adjust everything up to the brightness of the brightest area of the flat, so if there is some anomalous bright area in the flat (brighter than the center) then that could be the problem. The algorithm that evaluates the brightest value in the frame is supposed to be able to ignore the odd hot pixel, but a larger bright area may trick it.

You can also get issues if your dark frames are not correctly matching the light frames - that can cause the flat frame to under or over correct, but that usually shows in the darker areas - not sure if it could also affect the brighter center of the frame significantly.

Feel free to share the relevant frames for me to have a look to see if I can spot anything out of the ordinary - sometimes that turns out to be much easier than trying to describe the problem in enough detail

cheers,

Robin

[stbkaiser]

Sorry about this.
I believe I messed up my Darks .
Will do a new set of darks and flats and see if that does a proper correction.
Take care