Darb Flats!

[Daniel-K]

i have added flats to an image and now when i stacked it, the image is really dark and the faint detail isnt there. even when i stretch the image?

[andyo]

i have added flats to an image and now when i stacked it, the image is really dark and the faint detail isnt there. even when i stretch the image?

The master flat should be divided into each light frame.If you post more info on how the flats where taken and what calibration software was used with what settings someone may be able to help.

[Daniel-K]

Thanks Andy. They were taken on av mode iso800 with the laptop screen open on notebook. I used DSS this is the 2nd time I have tried flats and both have been unsuccessful. The scope was an ed80 so the screen covered the end of the dew shield easily. I took 30 flats in total. I have tried stacking them with nearly every possible setting in dss to no avail.

[ollypenrice]

Did you expopse the flats to about a third of the way to saturation (the histo peak a third of the way to the right?)

And did you calibrate them using a master bias as a dark frame?

Both steps are important. I don't use DSS so I can't help on how to do this in that prgramme.

Olly

[Daniel-K]

I took darks but what's a master bias?Yes they were slightly over exposed. I thought that I could just load them into DSS :/

[andyo]

Bias frames are taken with the exposure set to the shortest possible setting and the end of the scope covered like darks.Take about 35 and combine to get your master bias.This records the thermal current that all sensors have and the master bias can then be subtracted from your flats.backyard eos has a setting called av flats that sets the exposure time automatically for taking flats

[Daniel-K]

Bias frames are taken with the exposure set to the shortest possible setting and the end of the scope covered like darks.Take about 35 and combine to get your master bias.This records the thermal current that all sensors have and the master bias can then be subtracted from your flats.backyard eos has a setting called av flats that sets the exposure time automatically for taking flats

ah! i never knew that! i was wondering why i had to do it manually i will have a look as i could not see it the other night

[Jannis]

Just curious, i keep reading you guys use an LCD display for flats.. Does this actually work well in the end? I mean, since the LCD isn't 100% evenly illuminated, i'm guessing it would never be "perfect", but i've never tried myself - i've always waited untill right before the sun comes up to take flats...

[andyo]

ah! i never knew that! i was wondering why i had to do it manually i will have a look as i could not see it the other night

Yes check the drop down menu and you will see an av-flats option then set your camera to av mode if I remember right a low iso setting is best I think I use to use iso400.Cant help with DSS.Take about 35 as Olly said the histogram should be about a third of the way to the right,overexposing your flats would cause problems.

Als lightbox may be better than notebook for taking your flats here is a link

http://www.iceinspace.com.au/forum/showthread.php?t=30188

I use one of earlsmans light panels sandwiched between opaque Perspex sheets

[andyo]

Just curious, i keep reading you guys use an LCD display for flats.. Does this actually work well in the end? I mean, since the LCD isn't 100% evenly illuminated, i'm guessing it would never be "perfect", but i've never tried myself - i've always waited untill right before the sun comes up to take flats...

in short yes it does work most of the time