RedCat 51 Master FLat Problems...

[Nikolas74]

Hello, 

i am having so many difficulties as far as i remember to make some nice flats to match my images.For some reason it it impossible for me to find the secret spot in time and adu for my Flats.

This is my equipment :

Telescope: Redcat 51

Camera: Atik 383l+ mono (i know the shutter problem that's why i always aim for 3sec and above for taking my flats)

Filter Wheel: Atik EFW2 (36mm)

Filters: Astrodon Ha & Oiii 36mm 3nm

FlatBox: Geoptic flat field generator 164mm (dimmable)

Image aquire software: APT Tool v3.71

Software: Astro Pixel Processor

 

This is what i get...i am uploading some images converted in jpeg for the site...

Photo A is a MASTER FLAT Ha (Bin 1x1) created with 30 Darks, 50 FLats (3.7sec adu 22000), 50 Dark Flats, 100 Bias 

Photo B is a MASTER FLAT Oiii (Bin 2x2) created with 30 Darks, 50 FLats (5sec adu 46000), 50 Dark FLats, 100 Bias

Photo C is an example result of stacking my fits of Helix Nebula at Bin 2x2 , with the above calibration master frames (this is the Oiii in this case)

 

Are my calibration frames Over correcting ? if yes what can i do ?

Is the Optical path problematic ? as i can see at photo A ? what can i do , what to check ?

I have checked also the filter wheel position related to filter change , but it comes centered...i couldn't see a fault on it.

i Believe i have a problem also finding the correct ADU value....i made any experiments by changing the adu value and i have tried at 22000, 32000, 47000 by using the CCD Flats Aid.......but nothing all come out the same.

I hope someone can help cause i am loosing my mind and my fits 😥

[Adam J]

Its they are over correcting, it looks like an issue with settings in APP to me. 

I suggest that you go through APP setting on calibration line by line and see if you can find something out of place. 

Are your flats being correctly calibrated with bias?

Edited October 3, 2019 by Adam J

[Nikolas74]

Adam thank you for your reply , 

Yes my Flats are corrected with Bias in the procedure of creating Master Flats (if that's what you mean) , also i have discovered now by experimenting that 16bit master calibration frames work better than 32bit , i don't know if that should be correct or not....

If they are over correcting , does that mean that i should use less calibration frames to create my Masters ? although someone told me the more the better......

[Adam J]

On 03/10/2019 at 16:46, Nikolas74 said:

Adam thank you for your reply , 

Yes my Flats are corrected with Bias in the procedure of creating Master Flats (if that's what you mean) , also i have discovered now by experimenting that 16bit master calibration frames work better than 32bit , i don't know if that should be correct or not....

If they are over correcting , does that mean that i should use less calibration frames to create my Masters ? although someone told me the more the better......

Only just seen this. It's not the number of frames it's something wrong with the exposure and or your calibration process. 

[Laurin Dave]

Did you sort this out?  Wonder if this was caused by internal reflections.. Had something similar and sorted it out with some flocking 

[Nikolas74]

10 hours ago, Adam J said:

Only just seen this. It's not the number of frames it's something wrong with the exposure and or your calibration process. 

I think too....till today I am still fighting to find what is going on....

[Nikolas74]

10 hours ago, Laurin Dave said:

Did you sort this out?  Wonder if this was caused by internal reflections.. Had something similar and sorted it out with some flocking 

Really don't know.....I have to experiment more....what I know is that I never had these issues before.

[ollypenrice]

You say,

 

Photo A is a MASTER FLAT Ha (Bin 1x1) created with 30 Darks, 50 FLats (3.7sec adu 22000), 50 Dark Flats, 100 Bias 

Photo B is a MASTER FLAT Oiii (Bin 2x2) created with 30 Darks, 50 FLats (5sec adu 46000), 50 Dark FLats, 100 Bias

but if I'm reading your post correctly this is not at all the right way to make flats. 1) There is no need for '30 darks.' These darks are there to calibrate your images, not your flats. 2) You can calibrate CCD flats by either subtracting bias or by subtracting proper dark flats but certainly not both, because they are almost identical and will double-subtract if you do this.

I never make my flats in the same pre-processing pass as used to stack and calibrate my images. I want to have a look at any master flat I use before applying it. So I load up all my individual flats as if they were images and load up a master bias to use as a dark flat. I then average-combine my flats and look at the result. If you want to go by the book you can make dedicated darks for flats (AKA Flat darks) but with CCD cameras I really wouldn't bother. A master bias will give the same result as a master dark flat.

Olly

[Nikolas74]

Olly thank you for your answer  , what i do is to load everything in APP and start the whole procedure from scratch , this is how i end up with the masters.....i use a different approach when doing it at Pixinsight.

So what i am posting as an example is the result from APP...but the same happens with other software.

Maybe its too much to use DARKS and DARK FLATS...i don't know i have lost it totally , my brain is spinning now 😀

[Adam J]

On 22/10/2019 at 14:15, ollypenrice said:

You say,

 

Photo A is a MASTER FLAT Ha (Bin 1x1) created with 30 Darks, 50 FLats (3.7sec adu 22000), 50 Dark Flats, 100 Bias 

Photo B is a MASTER FLAT Oiii (Bin 2x2) created with 30 Darks, 50 FLats (5sec adu 46000), 50 Dark FLats, 100 Bias

but if I'm reading your post correctly this is not at all the right way to make flats. 1) There is no need for '30 darks.' These darks are there to calibrate your images, not your flats. 2) You can calibrate CCD flats by either subtracting bias or by subtracting proper dark flats but certainly not both, because they are almost identical and will double-subtract if you do this.

I never make my flats in the same pre-processing pass as used to stack and calibrate my images. I want to have a look at any master flat I use before applying it. So I load up all my individual flats as if they were images and load up a master bias to use as a dark flat. I then average-combine my flats and look at the result. If you want to go by the book you can make dedicated darks for flats (AKA Flat darks) but with CCD cameras I really wouldn't bother. A master bias will give the same result as a master dark flat.

Olly

Yes Dark flats are for use in place of Bias for flat calibration on CMOS cameras not for CCD chips. In that case you only use Bias.  

[Nikolas74]

Thank you...that's something I didn't knew.

[Nikolas74]

Is it normal that the shadows from the light path don't look round and instead they have this weird shape ? Shouldn't it be round ? I was thinking that maybe the flat panel was not centered because it's a bit bigger than the Redcat lens diameter....but I try to center it the best way I could.

[Adam J]

6 minutes ago, Nikolas74 said:

Is it normal that the shadows from the light path don't look round and instead they have this weird shape ? Shouldn't it be round ? I was thinking that maybe the flat panel was not centered because it's a bit bigger than the Redcat lens diameter....but I try to center it the best way I could.

I know your camera has a shutter and that flats need to be sufficiently long so as to minimize the effect of the shutter opening and closing.

[Nikolas74]

Yes , my Flats are taken over to 3 seconds...the Ha was 3.70 if I remember....sorry but my English is not as good as yours and generally I hope i can make my questions clear as possible.....the shadow/light pattern between the Ha flat and Oiii flat is so different ....is it normal ?it's not concentric....another strange thing is that , this Ha master flat is doing a better job than the Oiii master flat when used accordingly to the light frames....

[Nikolas74]

This is from yesterday , a stacking of 8x1200sec Oiii filter( no claibration frames).....I believe this a reflection of something but its round so it must be from the filter.....so tonight i will swap sides to see what happens...

[Laurin Dave]

Looks too large to me to be from a filter and wonder if it’s a reflection from a surface or one of the elements within the Redcat.. suggest you use the dust donut calculator to work out how far away it is (just google dust donut calculator, I’d estimate at least 80mm from the sensor) also take the camera off and look through the scope at a bright light and see if there are any shiny surfaces that need blackening..  or whether it needs to be returned..   

[Nikolas74]

That's what I am afraid of.....an element misplacement in the Redcat....but then again I don't see to have a star problem.....in the Ha filter this pattern don't show....tonight I will check with the filter flipped side.....

[Laurin Dave]

Your stars look good so hopefully nothing to do with the glass..  remember though that surfaces do not necessarily reflect all wavelengths the same so the issue could easily be different on different filters

[Nikolas74]

Goodmorning , ok this is a stack of 6x1200sec Oiii filter( no claibration frames).........strange how the pattern/gradient changed....

Oiii filter is flipped side now.....

Light Pollution is more visible on the right....

What you make out of it ??????

Edited October 26, 2019 by Nikolas74
correction

[Simon Pepper]

Hi,

 

Did you ever get to the bottom of this?

 

Thanks

[Nikolas74]

2 hours ago, Simon Pepper said:

Hi,

 

Did you ever get to the bottom of this?

 

Thanks

Hello , unfortunately no I couldn't find the reason , still have on my mind a couple of tests I would like to do when I will have the time...and we will see the results....I thought about many possible problems but can not come to a conclusion. The only filter I had good success is the Ha 3nm Astrodon...all the others give me a short of reflection or I don't know how to call it..

[ollypenrice]

On 29/04/2020 at 16:22, Nikolas74 said:

Hello , unfortunately no I couldn't find the reason , still have on my mind a couple of tests I would like to do when I will have the time...and we will see the results....I thought about many possible problems but can not come to a conclusion. The only filter I had good success is the Ha 3nm Astrodon...all the others give me a short of reflection or I don't know how to call it..

I would try this: Make a new master bias out of 50 bias frames stacked using a simple 'average' algorithm. Save it as Dark Flat because that's how you're going to use it. Save a copy as Master Bias if you like. All this is for mental clarity!

Shoot a set of flats.

What I now do is lie to my stacking software and tell it the flats are images (sometimes called Lights) and the Flat Dark is a dark for the 'images.' Nothing else. Tell it to stack and calibrate and now you know you have a genuine, simple, standalone Master Flat.

Now stack your images with only the following files: Images (often called Lights), Master Dark (same exposure and temperature as your Images) and Master Flat. No bias anywhere.

I really don't like throwing all the files into one huge stacking and calibrating operation. I like to do it step by step.

Olly

 

[Nikolas74]

I will give it a try when I will have the time, thank you for the suggestion.