What is....How do I.....

[Space Bat]

OK Got a Canon DSLR and have had little time to do anything other than a 30 minute window about 4 days ago....

Couldn't load into Registax as it kept hanging and took absolutly ages so now have DSS and this is far better...

I have tried searching the site but can't find out a simple explanation(for the simple...thats me... ) on what and how to do the following....I know it probably sounds stupid to most of you experienced digital camera buffs...but what is and how do I do the following....

Dark Frame

Flat frame

Bias frame

............ETC

Yes I could go and by a book

But if a kind soul could explain what all this means and what I should be doing and how...that would be really great

Chris

[greenkat]

Hello Chris

I would have a go at explaining dark frames but I have this knak of making people more confused than when they started

Here's a link to a page that makes a better job of explaining than I would

AAVSO: CCD Observing Manual: Camera Skills

[dark knight]

Hi Chris, which software you use is dependant on what images your trying to stack. Deep Sky Stacker (DSS) is for stacking DSO's (deep space objects) where'as Registax is for lunar and planetary images.

hth

carl

[themos]

First of all, a "light" frame is what you start with: say 10 60-second exposures of the Orion nebula, captured in RAW format (stay with that format for all others).

A "dark" frame is an exposure of the same duration, same ISO settings, same temperature but with no light hitting the sensor: put a cap on the scope or something and shoot. Get at least 10 of those. It takes some time, that can't be helped. But you can shoot those on cloudy nights.

A "bias" frame is even simpler, just reduce the exposure time to the minimum value available (1/4000 sec?) but keep the same ISO and shoot. They take much less time to do so shoot 100 of those.

A "flat" frame is a pain. Unlike the last two you need to capture light for this one. You need to provide a uniform illumination to your scope. People do that with white t-shirts in front of the aperture and a flash gun. Keep the same ISO, same focus and optics as with the "light" frame. The exposure time is up to you (depends on the intensity of the flash) but you should be careful not to saturate any pixel but have a strong signal (the histogram's peak should be as centred as possible but remember : no saturating). Shoot as many as you can, 10, say.

Then feed those to DSS and read the DSS help and tutorials.

[Space Bat]

Many thanks.....

Much appreciated...I am now a little further up on the curve

Chris

[jgs001]

Chris, Themos has explained that really well. The DSS help contains very good information on them also. With the SLR, set it to Av mode for flats, that way the camera will determine the correct exposure (although it won't work with a flashgun), it puts the peak on about the 75% point on the display histogram. I did read somewhere that DSS works better with an odd number of calibration frames (although I don't know why), I use at least 11. Although for darks, that can take a really long time to complete.

[Space Bat]

Only got DSS last night...a bit bewildering - but produced some lovely pics - for what I had which wasn't v.much Will have a another go later where I remove some of the poorer shots or too dark the 20-30s subs and see what that does - then re-introduce some of the 20-30s subs back.

I suppose it is too late to improve things with adding Darks/flats...etc as if I am reading and understanding should be done at the same time due to temperatures of the camera (CMOS sensor) ???

I just wish I spent more time taking shots than trying to suss the eos utility... - wasn't to know the clouds/mist was about to roll in and cut the session abruptly

As a first stab - I am pleasently suprised it is a shame I was hampered alot with dew - my improv dew shield was working well up to the other night...but as the scope is near all the fens...I fear dew will be a constant nemesis until we move...

Chris

[jgs001]

If you're using mixed length subs, then I think you need to be using the Entropy combine method, the others work best for subs of identical settings. Yes, ideally darks and flats should be done at the time, but don't worry too much about those for now. They will help, but...

Dew shields help a lot, but there are limits... a hairdryer on low heat and blow from some distance, waved across the optics works as a bit of an impromtu dew control mechanism (it's what I've been using), but ideally a full set of dew strips and controller is the way to go. They are on my ever increasing shopping list

[Space Bat]

If you're using mixed length subs, then I think you need to be using the Entropy combine method, the others work best for subs of identical settings. Yes, ideally darks and flats should be done at the time, but don't worry too much about those for now. They will help, but...

Dew shields help a lot, but there are limits... a hairdryer on low heat and blow from some distance, waved across the optics works as a bit of an impromtu dew control mechanism (it's what I've been using), but ideally a full set of dew strips and controller is the way to go. They are on my ever increasing shopping list

Hi Chap,

I have a cheap dryer which I use...however it is when I notice the corrector dewing up...which seems to be take image all good - take image - better check corrector - damn its dewed up...

It was my first and only go on the new camera - was no supprise to see the cloud cover and fog....as it was pretty wet evening dew wise, worst I have seen it

[dark knight]

Just a quick tip Chris, set up separate folders to keep your flats, darks and bias frames in, make a note of the settings used for each batch, that way if you are imaging the same object at roughly the same temperature, exposure and ISO you won't need to take all those flats, darks etc again. Just build up a well organised library of folders. This will save loads of time allowing you to just concentrate on subs...

HTH

Carl

[Space Bat]

Great tip...

Will do...so if I am understanding this correct.

Pic ISO's I would use... so

400 / 800

Take flats and darks for this... and batch them on temperature?

So

Flats and Darks...at ISO 400 at -5 degrees.. one libary

Flats and Darks...at ISO 400 at 0 degrees.. one libary

Flats and Darks...at ISO 400 at 5 degrees.. one libary

Etc...

Is this correct?

Chris

[dark knight]

Yep, you hit the nail on the head, just be sure to label them correctly so you don't get mixed up and can differentiate between your flats and darks...

[Space Bat]

Thanks guys...I think I have got it covered now...

Chris

[jgs001]

If DSS is used, it creates a Master Dark with the exposure duration and ISO in the file name already, just save that and add the temperature to the save file.

[Space Bat]

I feel like Johnny 5

Chris

[themos]

I think a library makes sense only for the bias and dark frames (as they require no light). For bias, the only variable that matters is ISO setting. For darks, ISO + exposure time + temperature all matter.

Flats must be taken at each session, don't make libraries for them.