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oldannie

software for a beginner and taking flats

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First of all hope I've posted this on the right forum - not sure! Hope to set up a newly received HEQ5 pro synscan in the next week (as soon as I receive the upgraded bolts I've ordered) and am intending to use it with my Nikon D600 and various lenses. Am wanting to get into the habit of taking darks, bias and flat frames. For the flat frames am thinking on the lines of a piece of foam cor board but am going to have to buy it on-line I think. The most commonly available size is A1 (approx 23"x33") - will this be okay?

I've downloaded Carte du Ciel, Stellarium and DSS. Bearing in mind am not going to be linking my set up to a computer is there anything else I should consider? For my general photography I use Lightroom for post processing - will this suffice, Photoshop is expensive!

Cheers

Annie

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For flats I stretch a white t-shirt over the lens backed by a piece of new printer paper and aim at a white wall or grey skies. Just be sure to save a file for each camera lens combination. Adjust exposure to just over 1/3 of range of histogram. Welcome from another beginner to imaging--Jack

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What are you going to use for the light source for the flats?

You can take the bias frames already, set the camera to manual, minimum exposure time, ensure the lens and viewfinder are capped, and take lots of raw pictures at the ISO settings you intend to use.

You can even then stack these in DSS to make master bias files.

I've not used Lightroom, I'm not sure if that has the right tools to process astro images.

Doesn't the D600 suffer from star eating? Have you looked into that?

TSED70Q, iOptron Smart EQ pro, ASI-120MM, Finepix S5 pro.

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Hi Annie,

If 'Lightroom' does not give you the expected results, there is always 'GIMP', (and it is another freebie). :angel4:

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Thanks for your replies and D4N - once I know exactly what you mean by ' star eating ' I'll be able to tell you whether the D600 is afflicted by it - got to get used to all these terms yet!

Cheers

Annie

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Was assuming I would use the twilight skies Nigel - thanks for reinforcing that.

Annie

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Just remember that flats and darks are temperature sensitive, if it gets a lot colder when you come to take your lights the flats could become useless.

Oh and star eating is a problem some cameras have with noise reduction that cannot be fully turned off. Effectively the camera decides that the stars are hot pixels and removes them for you. I was going to buy a second hand Nikon until I read about this.

TSED70Q, iOptron Smart EQ pro, ASI-120MM, Finepix S5 pro.

Edited by D4N

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My understanding is that bias and flats are not temp sensitive. As to the "star eating", that is a correctable firmware issue. Google Nikonhacker website. I have their package installed with no problems and pleased with the results.--Jack

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Yeh I guess it depends on the duration of the flat, if they need to be a few seconds to provide enough exposure then you will start to get noise. I always take mine at the end of the session since I don't set up until it's dark anyway and might change my mind on what filters to use.

I don't profess to be an expert on calibration frames, I just do what works for me ;)

Firmware hack sounds like a good idea, I couldn't find anything that would work for the model I was looking at before.

TSED70Q, iOptron Smart EQ pro, ASI-120MM, Finepix S5 pro.

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Shamelessly copied from DSS help file: "

Light, Dark, Flat, Bias... What are they and how to create them?
(if you are wondering how all the files are used during the calibration process you can have a look here)

Light Frames
The Light Frames are the images that contains the real information: images of galaxies, nebula...
This is what you want to stack.

Dark Frames and Dark Flat Frames
The Dark Frames are used to remove the dark signal from the light frames (or the flat frames for the Dark Flat frames).
With DSLRs and CCD Camera, the CMOS or CCD is generating a dark signal depending of the exposure time, temperature and ISO speed (DSLR only).
To remove the dark signal from the light frames you use a dark frame that contains only the dark signal.

The best way to create the dark frames is to shoot pictures in the dark (hence the name) by covering the lens.
The dark frames must be created with the exposure time, temperature and ISO speed of the light frames (resp. flat frames).
Since the temperature is important try to shoot dark frames at the end or during your imaging session.

Take a few of them (between 10 and 20 is usually enough). DeepSkyStacker will combine them automatically to create and use a clean master dark or master dark flat.

Bias Frames (aka Offset Frames)
The Bias/Offset Frames are used to remove the CCD or CMOS chip readout signal from the light frames.
Each CCD or CMOS chip is generating a readout signal which is a signal created by the electronic just by reading the content of the chip.

It's very easy to create bias/offset frames: just take the shortest possible exposure (it may be 1/4000s or 1/8000s depending on your camera) in the dark by covering the lens.
The bias frames must be create with the ISO speed of the light frames. The temperature is not important.

Take a few of them (between 10 and 20 is usually enough). DeepSkyStacker will combine them automatically to create and use a clean master bias/offset frame

Flat Frames
The Flat Frames are used to correct the vignetting and uneven field illumination created by dust or smudges in your optical train.

To create good flat frames it is very important to not remove your camera from your telescope before taking them (including not changing the focus).
You can use a lot of different methods (including using a flatbox) but I found that the simplest way is to put a white T shirt in front of your telescope and  smooth out the folds. Then shoot something luminous (a flash, a bright white light, the sky at dawn...) and let the camera decide of the exposure time (Av mode),

The flat frames should be created with the ISO speed of the light frames. The temperature is not important.

Take a few of them (between 10 and 20 is usually enough). DeepSkyStacker will combine them automatically to create and use a clean master flat frame.
"

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Some really helpful info here - thanks for taking the time to respond.. Fortunately it seems that the Nikon D600 is not one of those cameras that 'eats up' stars. On reflection I would like to try and take flats as D4N does, straight after a session so I do after all need to think about a suitable light source other than the twilight sky. From reading other stuff I also gather that if I take flats I need to take bias frames otherwise the maths don't add up - but dont ask me to explain that!

Thanks again - upgraded bolts arrived today so no excuses for any further prevarication!

Annie

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Unless the HEQ5 turns out to be an EQ1 in truth, you have not 'prevaricated' although if you wait until the dark skies of Winter before installing the new mount bolts, you will have 'procrastinated'.

Sorry but I couldn't think of a half sensible way to subscribe to a very interesting thread.

Also working through this learning experience. (camera arrived last Tuesday)!

All the best Annie, from Rich

Edited by RichM63

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It's darks that should be taken at end of session, You need a fair amount of light to do proper flats, so take flats and bias in daytime when convenient. I make a calibtation folder with sub folders for the different ISO and lens combinations in the case of flats, and the different ISOs for bias. Once you make a run involving members of each class, DSS will generate a "master" flat, bias, and dark. In future just use the master. It saves stacking time and HD space too. Eventually, if you record ambient temperature at time of taking darks, you can keep master darks at different temps in your calibration library too. This saves a ton of time on imaging nights.--Jack

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Thanks Jack - but am afraid I still have a couple of uncertainties! Reading Steve Richards, Making Every photon Count' it's suggested that flats should be taken at exactly the same orientation of the camera and the same focus position as the lights which implies they should be taken immediately after the Lights - or does it! The notion of taking them during the day when convenient is appealing. Have also read that as DSLRs are not temperature stabilized the use of darks is questionable? perhaps I just need to concentrate on flats and bias!

Annie

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I only take flats a few time a year. But I do mount the camera at roughly the same orientation on the telescope each time.  It works pretty well - yes, strictly you should do them after every session, but, hey, life's too short ...

NigelM

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It's the orientation of the camera to the rest of the imaging train that's important for flats to help remove dust bunnies, etc. Daytime or dawn/dusk is better for flats as more light is available to get the histogram up to 1/3 saturation. DSLRs are indeed not temp stable, but darks taken at the end of the session will be fine, as ambient temp is the same as the subs. I just bought an outdoor digital thermometer so I can build a library of master darks at different temps, so I don't have to waste imaging time (or sleep time) taking darks every session.--Jack

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You can reuse flats if you have left your imaging train complete.

You need to redo your flats if you remove the camera or change its orientation.

They are semi-temperature sensitive but nothing like darks. Your focus point changes slightly with temperature so flats taken at +20°C would not be ideal for -10°C. I do a fresh set every month as my camera is in a permanently fixed position.

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It's the orientation of the camera to the rest of the imaging train that's important for flats to help remove dust bunnies

Surely dust bunnies are fixed relative to the camera so it doesn't matter what orientation for those?  It is the overall vignetting pattern that comes from the OTA (and hence why you need the same orientation).

NIgelM

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The most pronounced dust bunnies are close to the ccd but there can be ones on filters and lenses too.

These will move if you rotate the camera.

TSED70Q, iOptron Smart EQ pro, ASI-120MM, Finepix S5 pro.

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Thanks for all the info. I may just concentrate on trying to take good Lights and how to stack them and worry about flats and bias frames later. I do take the point that life's too short!

As usual have learnt a lot from this post.

Cheers

Annie

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