Method
Flats Calibration using the “white t-shirt” and light method (no, I don’t have a flat box).
Situation
I am running the flats calibration wizard, enter the data per the help file (and / or manual) after first reading the Atik Manual to make sure my camera specs are good.
On running the wizard, I get the following error (on all filters) “Time below Minimum”.
For info, I followed the instructions left on another forum as follows:
I had a post from Joel Short at SGP. I will now type out what Joel specified for my Atik 383l.
The 383L uses a shutter so you need to take flats that are at least 2 seconds long. Your light source needs to be bright enough (or dim enough) to get around 3 seconds for good flats with the 383L.
You only need to take flats at the binning you take your lights. So if you only shoot 1 X 1 with the 383L (which you should) you will only need to take flats at 1 X 1. In the wizard, click the drop down menu next to each filter and just choose 1 X 1 and leave the other bin modes unchecked.
In the wizard, in the parameters section, use a target mean of 25,000 adu and a minimum exposure of 1 second (but it really should be above 2 seconds). Also, change the tolerance to +/- 1000.
Your imaging system doesn’t need to be in perfect focus when taking your flats, so if you take flats at some other time of the day as long as your focuser is close to where it usually is focused your flats wil be fine.
5 The wizard will do all the work for you, and will increase or decrease the exposure time to get your flats to the target mean ADU value.
I thought I was on to something but alas!! Still the same error.
Your problem is actually your ‘Maximum Exposure’ which is set at Zero (and hence, below the minimum value). You should bump that up… you may need 30 or 40 seconds for the NB filters…depending. Once you get going you will see what is required.
Sorry Pete…disregard that last one. Looking closer at your screen shot…I now see that your 1st shot yielded way above the 40,000 ADU you wanted. Is that a very bright light you are using…or is there any chance that the shutter is ‘acting up’…???
I think you might be right - the light I suspect is too bright. I will try with an ordinary torch light rather than the LED from my power tank. I might have been too enthusiastic.
I will try and pull down the max exposure too. The manual said to leave it if your camera has infinite max (which the Atik does) but I might start small and broaden it out.
Pete,
First, the “maximum exposure” time does not matter. I never touch that and keep it at zero. This just means that SGP will expose the flat image for as long as necessary to reach your target ADU.
You’ve got two problems:
Your light source is WAY too bright.
Your minimum exposure time is way too short.
What’s happening is that SGP will not go below 0.2s exposure time, but the light source is so bright that even at 0.2s the resulting flat is still above your 40,000 ADU threshhold.
All you really need to do is find a dimmer light source and follow my instructions that you quoted above.
Are you taking twilight flats, or what kind of light source are you using?
I was using a torch shining towards the rig a la “t-shirt” style. I take your point and will dim down the light source significantly and follow your directions accordingly. Will post back with how it goes.
