Calibration frames..flat darks

[Craig123]

Hi all

Currently I take flat frames after each session for each filter used and then pop the dust cap on the telescope and take matching flat darks for my Zwo asi 1600 mono camera . There is no real need to do flat darks for each filter every night as one master flat dark should suffice for all filters as long as temp, exposure and gain is the same. I should then be able to use this master flat dark on different flats from different nights on the same target without taking   another set to match the new flats much the same as the master dark frame I already re - use  from my library . Does that sound  right ?

Thanks in advance 

craig

Edited September 9 by Craig123

[geeklee]

21 minutes ago, Craig123 said:

I should then be able to use this master flat dark on different flats from different nights on the same target without taking   another set to match the new flats much the same as the master dark frame I already re - use  from my library . Does that sound  right ?

This is correct.  I do the same (although take less Flats where possible!)

As you say, as long as you have the Flat Darks matching Flat temp, exposure, gain AND offset, you have them covered.

[Craig123]

7 minutes ago, geeklee said:

This is correct.  I do the same (although take less Flats where possible!)

As you say, as long as you have the Flat Darks matching Flat temp, exposure, gain AND offset, you have them covered.

Thanks .What is your approach with flats …re use from night to night if not moving your set up ? I take mine down and in to the house but do not touch the imaging train . Hopefully i will be moving in to WBPP next . It sounds like a dream . 😀

[daz]

As long as you don't move the imaging train, you *should* be OK to reuse flats - but you have to be careful with dust do-nuts ruining that plan!!

I have a DSD Flat panel on my Esprit, so I tend to take them each session...

 

And as geeklee says, provided you use the same exposure length, gain and offset as well...

[Craig123]

12 minutes ago, daz said:

As long as you don't move the imaging train, you *should* be OK to reuse flats - but you have to be careful with dust do-nuts ruining that plan!!

I have a DSD Flat panel on my Esprit, so I tend to take them each session...

 

And as geeklee says, provided you use the same exposure length, gain and offset as well...

Thank you Daz . I will stick to doing flats I think.. just in case. 

[geeklee]

3 hours ago, Craig123 said:

What is your approach with flats …re use from night to night if not moving your set up ?

I'm the same as yourself and take the imaging train off but keep intact.  @daz is of course correct, but I'm a little more loose on my approach with refractors (solid dew shield) and my Samyang lens.  I've successfully reused Flats on those.  With other scopes, I'm usually more careful  

[Ouroboros]

My flats are always of different durations so I always take flat darks of the same duration to match. Helps Pixinsight to marry up the right darks with the right flats.  Maybe this is not strictly necessary if some kind of normalisation is done in the calibration stage, I don’t know. 

I was under the impression that matching temperature didn’t matter much for flats/flat darks because the exposures are generally short. Lights and light darks, yes. I have a library of master light darks at different temperatures. 

[geeklee]

12 minutes ago, Ouroboros said:

My flats are always of different durations so I always take flat darks of the same duration to match.

Agreed, this is the correct way as discussed (if you have Flats of varying durations)

12 minutes ago, Ouroboros said:

I was under the impression that matching temperature didn’t matter much for flats/flat darks because the exposures are generally short.

I find it just good practice.  Why take the risk of calibration not quite working right when you can just match each component (including temp).  I get what you're saying though and if it's working for you, then why change.

Edited September 9 by geeklee

[Craig123]

5 hours ago, geeklee said:

I'm the same as yourself and take the imaging train off but keep intact.  @daz is of course correct, but I'm a little more loose on my approach with refractors (solid dew shield) and my Samyang lens.  I've successfully reused Flats on those.  With other scopes, I'm usually more careful  

After being very thorough on my initial astrophotography journey I feel I will start to chill out a bit this winter, not do flat darks as much and maybe re-use flats too . Great  😀

[ONIKKINEN]

Just a heads up with your method of taking the darkflats, a cap on the scope is often not enough to block all light and you have a real risk of light leaks. Just a few photons will ruin your darkflats (and regular darks) and essentially make them meaningless.

I recommend taking the camera off the scope and taking the darks in a completely dark environment. You can take a set of darkflats of various exposure times and use them later. I put my camera in the fridge where it will be in perfect darkness, and this helps with cooling too.

[Craig123]

2 hours ago, ONIKKINEN said:

Just a heads up with your method of taking the darkflats, a cap on the scope is often not enough to block all light and you have a real risk of light leaks. Just a few photons will ruin your darkflats (and regular darks) and essentially make them meaningless.

I recommend taking the camera off the scope and taking the darks in a completely dark environment. You can take a set of darkflats of various exposure times and use them later. I put my camera in the fridge where it will be in perfect darkness, and this helps with cooling too.

Much appreciated. This didn’t cross my mind. Just assumed the cap would be sufficient. 🙏

[Elp]

If you have a filter drawer in front next to the camera you can also use a dark filter, I've got one which helps me take darks with my Hyperstar setup when I'm using an uncooled camera (not needed when I'm using a cooled camera as I just reuse my dark flat library, I can consistently get my flats to auto expose to 10s (I mostly image NB), otherwise I just take the needed dark flats the next day with the camera resting in a dark place (like in a box, but allow the heat to vent out) face down cap on, cooled down).

[Craig123]

Thanks . No filter draw here , just a filter wheel and while i’m delving in to areas I need to brush up on ..how does the filter draw work in the imaging train ?

I will do my darks again with a little more   care on creating a light free environment. My current library is at least a year old . Thanks 🙏 

[Elp]

2 hours ago, Craig123 said:

how does the filter draw work in the imaging train ?

It simply takes up space in the imaging train backfocus like any adaptor. It has an insert piece which is removable from the side, take out, change filter, put back in. All without disturbing the train. But as a result new flats usually are needed if using an imaging filter. But if taking dark frames with a dark filter newly inserted you simply put the filter in and take your darks.

Edited September 10 by Elp