Flats

[carpman]

i hope peeps can help me out

i want to try and add flats to my pics using als virtual lightbox and my laptop but i cant find any reference to how the histogram should look !

i know they reccommend using using av then replicate the settings in manual but my camera ( d5000 ) wont allow me to use av without a lense being attached , i have taken some tonight with the histogram peaking in the middle ....

cheers in advance Dan

[AndyUK]

Hi Dan - I'm not familiar with Nikon Cameras, but the Histogram sounds more or less correct, but they might be better if they were just a tad less.

I always used to aim for a histogram around 1/3 across from the left (which equates to c. 22,000 ADU), but I know that some go as high as 30,000 ADU (with the max at the far right side equalling c. 65,000). If yours are in the middle, then they'll be equating to 32,500... (Hope that helps...?)

[ollypenrice]

If it's peaking n the middle then that's fine. Andy's right. In fact anything from 1/3 to 2/3 will work well.

Olly

[carpman]

cheers guys

sorry to be a pain in the rear but i do i need to take flats for my multi session m42 ?

is there a recommended amount of flats to take ( ie i know they recommend 30 darks )

[ollypenrice]

If your multi session M42 included very short subs for the Trapezium, these are unlikely to need flats because you'll only be keeping a few bright parts of those images.

But the rest will need flats if you want to stretch the faint data into becoming visible. Flats ae utterly essential.

How many? Take 30 and a set of bias to use as darks for your flats - say 50 to 100 bias. That way your flats won't introduce noise. Flats should be exposed to be around half way to saturation. (Histogram peak around half way, say 1/3 to 2/3 of max.)

Olly

[carpman]

my subs are 25s @ iso 1600 with only 5s for the core this is my first attempt at doing the core seperate (i'm using skywatcher 150p on an eq3 with my d5000 on time lapse )

do i need to take flats in every session ( i am taking darks for each session) but have been told if all sessions are taken in the same temperature i would be able to stack the all of the sessions photos in one go

i have never taken or know anything about taking bias shots

here is a shot of my falts histogram taken from photoshop