Lights, Darks and Flats revisited

[jkrah]

Ive been reading up about the virtues of taking darks and flats and the like and am wondering about tricks people might use to do this more efficiently (time/effort wise)..

My basic understanding of the process is .. (please excuse my cryptic summary)

1. Lights - define standard Temp / ISO / Exposure / Full Optical Path
2. Flats - use lights ISO / (Exposure for balanced histogram) / Full Optical Path
3. D/Flats - use lights Temp / ISO / (Flats-Exposure) / (no opt path)
4. Darks - use lights / ISO / Exposure / (no opt path)
5. Bias - use lights Temp / ISO / shortest possible exposure (max gain?) / (no opt path)

where..
(full opt path = scope focused on target + any filters)
(no opt path = equiv. of lense cap on)


I'm wondering if this is a correct/efficient order of steps ?

How critical is temperature for the Darks /Bias ?
eg.. can I use a pre-made set if the outsite temp differs by say 5' ?

Using flats and darks sure sounds (and looks) worth it..
but I'm also sure there must be some tricks available to minimize the actual effort involved..

(thanks in advance for any hints)
Jason

[Octane (Humayun)]

No minimisation of steps is allowed.

You do that, and your images will lack that little something which will set them apart from everyone elses.

As mentioned in another thread, I stick by what I said about creating image libraries; darks -- how are you to account for the decay of the sensor over time, unless you create regular dark frames (which defeats the purpose) and flats -- this idea is preposterous.

For the high-end dedicated astro-CCDs, the creation of dark libraries may be a viable solution to saving time out in the field, but, for us DSLR users who take their astrophotography seriously, nothing beats the real deal of creating your darks immediately after the lights, and flats and their associated darks after that, or even before the lights.

As for the sequence of steps, what I've done in the past is the following:

1. lights;
2. darks;
3. flat lights;
4. flat darks

Regards,
Humayun

[Geoff45 (Geoff)]

Originally Posted by jkrah

How critical is temperature for the Darks /Bias ?
eg.. can I use a pre-made set if the outsite temp differs by say 5' ?

Very critical. Dark signal doubles for every 6 deg rise in temp (or halves for every 6 deg drop).

[jkrah]

Hi ghsmith45,
Thanks heaps for the info.. thats interesting to know.. and certainly justifies fresh darks when possible..

Hi H, just wondering, do you remove your cam from the scope for steps.. 1,2,3 (specifically step 2 (darks) )?

thanks again for the advice
Jason

[Terry B]

I do it in the reverse order.
Flats first.
I don't bother with flat darks but do use bias/offset frames that I take next.
Lights
Darks last.
My reason is that my flats are taken with my observatory closed and a flash reflected off the roof towards a white wall.
I then opent the observatory and take my lights.
The darks are taken when I'm packing up or sometimes left to do by themselves when I'm finished depending on how late it is and how sleepy I am.

[Geoff45 (Geoff)]

Originally Posted by jkrah

Hi H, just wondering, do you remove your cam from the scope for steps.. 1,2,3 (specifically step 2) ?

thanks again for the advice
Jason

No