Flats essential

[Fieldsy]

Hi guys 

I understand dark frames but flat and bias frames ? .im not over keen on leaving equipment out all night to do flats the next day ( do u have to leave settings and focus same as imaging session) and then wrap a white cloth over scope? And bios isnt that just like a dark?. I’m using dedicated cam not DSLR.

Edited April 18, 2019 by Fieldsy

[RolandKol]

Purpose of Flats: 1) removes vignetting 2) removes any dust shadows produced by dust and etc.

Bias: Yes, the same purpose as Dark, just it removes another kind of bad signal left in the image produced by sensors. If you stretch your MasterDark and MasterBias, you will see the difference. 

For Flats, - you have to be close to the focus, you can be slightly off and yes, you can do it next day if you have not moved your rig around and if you have not removed the camera from the scope.

Deep Sky Stacker help file has explanations in case you need more.

 

 

Edited April 18, 2019 by RolandKol

[Grierson]

Do you have a cooled camera? If so, and in my admittedly limited experience, you can do Darks at any time providing the camera is cooled to the temperatur, exposure and gain used for the imaging session. I have made a library of Darks at various gains and exposures. Saves a lot of time! As far as Bias is concerned there seems to be a debate around whether they are actually needed with a dedicated Astro camera. Depending which side you come down on again your Bias can be made at any time without cooling the camera. 

[Fieldsy]

No I completely strip everything down and pack it away so flats the next day would be impossible. So looks like I need to get a white box thingy .?

[RolandKol]

yep... I have similar to this one.
Just do not throw away the box, - simply cut out the hole for your scope and for USB cable in it.

Add few sheets of paper (3 or 4) and you have a nice USB powered LED panel

Edited April 18, 2019 by RolandKol

[Fieldsy]

2 minutes ago, RolandKol said:

yep... I have similar to this one.
Just do not throw away the box, - simply cut out the hole for you scope in it.

Add few sheets of paper (3 or 4) and you have a nice USB powered LED panel

Thanks that's a lot cheaper than what I was looking at?

[RolandKol]

Just keep the box away from snails!!!

My cardbox was almost terminated by them.

[Fieldsy]

Ordered and on it's way. So just cut a snug hole in box for scope .is the focus and other settings still relevant ?

[RolandKol]

11 minutes ago, Fieldsy said:

Ordered and on it's way. So just cut a snug hole in box for scope .is the focus and other settings still relevant ?

Yep, and of course, do not throw away the internal panel holders which will be in the box.

On DSLR, - switch Camera to Exposure/Shutter Priority Mode (TV on Canon), use the Same ISO as on the Light Subs, - Focus can be not Perfect.
And... Off you go! Easy as that

Take around 40 subs. 
Subs will be below 1sec anyway. 2 minutes and all is ready.

Just, - I try to keep subs above 0.3sec, as a precaution (it is my personal choice, you do not need to do that). To increase the exposure time of subs, simply add more paper into the box.

Edited April 18, 2019 by RolandKol

[Fieldsy]

2 minutes ago, RolandKol said:

Yep, and of course, do not throw away the internal panel holders which will be in the box.

On DSLR, - switch Camera to Exposure/Shutter Priority Mode (TV on Canon), use the Same ISO as on the Light Subs, - Focus can be not Perfect.
And... Off you go! Easy as that

Take around 40 subs. 
Subs will be below 1sec anyway. 2 minutes and all is ready.

Just, - I try to keep subs above 0.3sec, as a precaution. To increase the exposure time for subs, simply add more paper into the box.

My camera is asi178mm not a dslr.

Add more paper into box ? I must be missing something .why do I need paper in the box ? Or will it be evident once I have item.

Edited April 18, 2019 by Fieldsy

[RolandKol]

Oops miss-read.

Target ADU 25k - 30K on any Flat Aid assistant, - APT or SGP.

Same gain,  as Lights.

Keep an eye on Exposure times, as if it will be Very short, the camera will catch how Panel Flickers (you will see horizontal bandings), so add Paper to increase exposures.

I keep only MasterFlats from 100subs per filter.

Once done, try to take some DarkFlats (same gain, exposure time as Flats, but cover the scope as you do for Darks and Bias).

You can try using DarkFlats instead of bias for better results.

If you will go with Bias (as it is a bit easier), do not do Bias subs shorter than 0.3sec.

ASI cameras produce very unpredictable Bias results with subs which are shorter than 0.3sec.

 

Edited April 18, 2019 by RolandKol

[RolandKol]

Paper will serve as a T-Shirt,

1) will dim the Panel Brightness

2) will spread the light and cover some pattern which is on the LED panel.

[RolandKol]

Without paper, you will see these dots on the flats. 

and, I am 100% sure, the panel will be Too bright for any astrocam without paper

[Alien 13]

I dont bother with flats most of the time as I shoot with a DSLR and camera lenses and use either generic lens correction data or one I have made modified to remove any dust bunnies.

The sensor dust is dealt with separately by localized correction in PS or in rare occasions a separate exposure with the lens removed so the camera can effectively be pointed anywhere to produce even illumination. 

The reason I do this is that its almost impossible to keep dust bunnies in the same place on a DSLR due to mirror slap and the sensor cleaning routine when the camera is turned off.

I am also one of the few that leave the long exp noise reduction on to take proper matched dark's but as I dont do many subs its not a waste of imaging time 

Alan

[alacant]

Hi. Software moves on. If you have a clean sensor, I'd say it does a better job correcting what a few years ago could only be tackled by flat frames. The best we've found is StarTools' wipe module; it doesn't care what orientation or focus your camera was at after taking the light frames.

HTH

[Fieldsy]

On 18/04/2019 at 16:01, RolandKol said:

yep... I have similar to this one.
Just do not throw away the box, - simply cut out the hole for your scope and for USB cable in it.

Add few sheets of paper (3 or 4) and you have a nice USB powered LED panel

Item delivered and hole cut thanks

[RolandKol]

Nice! 

And you are almost Ready!

[Fieldsy]

? no laptop is at mates being completely reinstalled for a clean instal as it’s only a notebook not much space .god knows what had been left on it over the years with so many install and uninstalls .get it back today then have to put all the Astro software on it ,so looking at next week for first views  weather permitting ?

[cjdawson]

Dammit, wish I'd thought not to throw the box away.   That's brilliant.

 

As for what all the types of images do.   Here goes.

 

1. Lights - the images, you know the pretty stuff

2. Darks - Exposed for the same time as the lights, but in complete darkness to get an approximation of the noise in the image.  Subtract this from the light frame and you end up with a clear image.

3. Flats - Solves the vignetting problem, also will help to solve issued with specks of dust that get into the imaging train.  (They appear like dark circles and vary in side depending on where they are)

4. Darks for flats - does the same job as dark frames, only for the flat frames.

5. Bias frames - shortest exposure possible on the camera.   These images record the minimum value that can be obtained from each pixel in the camera.  Without this each pixel could have a different minimum value, which would be like looking at a lumpy surface.   By applying bias frames to all the other frames above, you'll even out the image much better.

 

The Darks, Darks for flats and Bias frames can be produced at any time and kept in a library.   You can even do some of the integration work to produce master files, which have the combination work already done - this can save a great deal of time when it comes to your processing.

[Davey-T]

2 hours ago, Fieldsy said:

Item delivered and hole cut thanks

Snap

Dave

[Fieldsy]

47 minutes ago, Davey-T said:

Snap

Dave

I only put gaffer tape on the edge to help it last longer with keep getting it on and of.?

[Starwiz]

4 hours ago, cjdawson said:

Dammit, wish I'd thought not to throw the box away.   That's brilliant.

Also wish I'd known about the box! ?

[Fieldsy]

23 hours ago, Starwiz said:

Also wish I'd known about the box! ?

Have to thank Roland for that bit of advice def wouldn't have thought of it myself ?

[RolandKol]

And I have to thank @carastro, who probably, has to thank someone else  

[carastro]

..... and I have to thank Mike one of the admin on here as I got the idea from his wooden made light box.

Carole