I found that flats will over-correct when not being used in tandem with bias. My tool of choice is Siril and on its website they explain it pretty clearly. I also wrote some lengthy comments recently on Facebook ;-) Basically if you apply only flats to your lights you get L/F which will lead to over-corrections. If you apply bias to your lights only ((L-B)/F) you get over correction too. But once you apply bias to both the flat and the light you'll get a proper corrected image ((L-B)/(F-B)). Better still is to apply Darks to your lights and use the bias in the flat calibration ((L-D)/(F/B)). One of my cameras is the ASI294MC Pro. Not only does it produce pretty strong amp-glow - which makes darks a necessity - it also has inconsistencies when shooting short exposures. Shorter than 3 seconds is too short for consistent results. Therefor I never shoot bias with the 294MC Pro. I do use a synthetic bias to prevent the over-correction I mentioned earlier.
Yes I think you are correct. The 294c is a very complex beast to tame. My 294 version is a nightmare to calibrate. Thanks for the info and for watching.
Hi Andy very informative video mate, do you thing this was some of the problems you had with the 200 PDS you had to return? , how you getting on with the new scope?
Hello, I tried and restacked some of the data from the 200PDS, using the Darkflats as Bias and the results where the same. The slop/mirror movement in the mirror and the flex in spider had to great an influence and caused the imaging issues. I've not currently tried the 8 inch Stella Lyra, I've been working on wider field subjects. Clear Sky's!
I was told and figured that either use this or that. That means, either use only bias + flats +darks OR use flatdarks +flats +darks. But don't use both. I haven't tried using both but I might give it a go and see what happens. I did have some failed images, just not long ago with the 533mono, and looked pretty similar to your poorly calibrated image and for the life of me I couldn't figure out what I was doing wrong. Re-shot the flats at least 3 times, tried different options and new darks and so on, and yet I had poorly calibrated stacked image anyway. Also with the darks, there are more than one time, when the dark adds noise back in, instead of removing it. I just know, because stacking it without the darks resulted in a much better image. Sometimes I'm totally lost what I should or shouldn't be doing , this hobby can be a migraine inducer for sure haha!
Yes I found that using all of them is best. However I need to test my 294c sensor camera as it is not capable of creating bias, therefore I'll use dark flats for bias and well as for calibrating the flats.
How incredibly timely! I have just begun to wonder if my approach to calibrating images from my 533MC-Pro is wrong, since the resulting images don't seem to be all that well calibrated. Like you, I also was not using bias frames, using only dark flats/flat darks in my WBPP process. I will give it a try with the bias frames included and see what happens. Many thanks!
Let me know how it goes and if your images stack together ok. Remember to tick Optimize Dark Frame to enable the bias in the Lights calibration. Try just putting a Darkflat in the Bias and restack, see if this makes any difference. Good luck and I hope this helps.
I also read somewhere some time ago that you should do bias frames with the 533MC anyway. I’m certainly going to try it with my 533MC and my 183MM. With mono would you need to do bias with each filter?
The bias is independent from filter, therefore only one set of bias frames are needed. However for flats they are dependent upon filter and potentially that also means individual darkflats as well per flat duration, however potentially bias and darkflats are very similar and therefore this needs testing. Thanks.
Newbie. Did my 1st flats last week. Got a 2600 duo. Spoiled myself w/all things ZWO. Got a usb lite pad. At lowest setting I had to add 5 layers of tshirts to get a 1.9s exposure time, which pushes my spot on this histogram 3/4 of the way to the right instead of a nice center. Using Asair to auto take flats gives me a super fast exposure time w/ 1 tshirt layer and perfect center on histogram. Tried Cloudy Nights, but still confused. What's your thoughts on using flats w/ at least 3s exposure time? This is something I picked up on other tutorials. I wish I would have taken the fast dark flats to experiment with and see what the difference is, but I cleaned all my glass. And I did do biases, darks, and dark flats. Covering all my bases. Thanks.
The Duo is an IMX571 and it is known to be a well behaved sensor, I think it copes well with short Flats or longer Flats. I managed to get longer exposures for flats by using drawing paper sheets, however I think experimentation is required to get the workflow settled. If you are finding that the ASIair is giving you good data then don't change anything! However if you have issues it is worth experimenting. Certainly with older sensors, longer flats seem to be easier to calibrate (such as with the 294C sensor which is hard to calibrate.) Good luck and clear sky's!
Very interesting Andy weirdly enough I found that darks used to give me more agro so I just stack lights flats & dark flats only & it seems to work ok for me. I do however only shoot colour & not mono so I don't know if that makes a difference.
Hi Tich, Hope you are well. I did find that my darks had to be updated every month or two, because they didn't work well. I think the sensors change in a short time and need updating. I never knew Bias would make such a difference until I tried it, hopefully going forwards this will improve the calibration. Best wishes and clear sky's!
Bias frames are good. No harm in doing them at all, I had read that they were not required, but in reflection there is no harm and clearly they can have a big impact on imaging. Thanks for watching, clear sky's!
I am not sure of the algorithm in APP. However it does have a Bias tab and I would experiment with inputting Bias into that and see what happens with your stacking results. Clear Sky's!
Thank you.
I found that flats will over-correct when not being used in tandem with bias. My tool of choice is Siril and on its website they explain it pretty clearly. I also wrote some lengthy comments recently on Facebook ;-) Basically if you apply only flats to your lights you get L/F which will lead to over-corrections. If you apply bias to your lights only ((L-B)/F) you get over correction too. But once you apply bias to both the flat and the light you'll get a proper corrected image ((L-B)/(F-B)). Better still is to apply Darks to your lights and use the bias in the flat calibration ((L-D)/(F/B)).
One of my cameras is the ASI294MC Pro. Not only does it produce pretty strong amp-glow - which makes darks a necessity - it also has inconsistencies when shooting short exposures. Shorter than 3 seconds is too short for consistent results. Therefor I never shoot bias with the 294MC Pro. I do use a synthetic bias to prevent the over-correction I mentioned earlier.
Yes I think you are correct. The 294c is a very complex beast to tame. My 294 version is a nightmare to calibrate. Thanks for the info and for watching.
Thanks for this interesting video. What telescope & camera were you using? Thanks
SW 130pds and Altair 269c, thanks for watching!
Hi Andy very informative video mate, do you thing this was some of the problems you had with the 200 PDS you had to return? , how you getting on with the new scope?
Hello, I tried and restacked some of the data from the 200PDS, using the Darkflats as Bias and the results where the same. The slop/mirror movement in the mirror and the flex in spider had to great an influence and caused the imaging issues. I've not currently tried the 8 inch Stella Lyra, I've been working on wider field subjects. Clear Sky's!
I was told and figured that either use this or that. That means, either use only bias + flats +darks OR use flatdarks +flats +darks. But don't use both. I haven't tried using both but I might give it a go and see what happens. I did have some failed images, just not long ago with the 533mono, and looked pretty similar to your poorly calibrated image and for the life of me I couldn't figure out what I was doing wrong. Re-shot the flats at least 3 times, tried different options and new darks and so on, and yet I had poorly calibrated stacked image anyway.
Also with the darks, there are more than one time, when the dark adds noise back in, instead of removing it. I just know, because stacking it without the darks resulted in a much better image.
Sometimes I'm totally lost what I should or shouldn't be doing , this hobby can be a migraine inducer for sure haha!
Yes I found that using all of them is best. However I need to test my 294c sensor camera as it is not capable of creating bias, therefore I'll use dark flats for bias and well as for calibrating the flats.
How incredibly timely! I have just begun to wonder if my approach to calibrating images from my 533MC-Pro is wrong, since the resulting images don't seem to be all that well calibrated. Like you, I also was not using bias frames, using only dark flats/flat darks in my WBPP process. I will give it a try with the bias frames included and see what happens. Many thanks!
Let me know how it goes and if your images stack together ok. Remember to tick Optimize Dark Frame to enable the bias in the Lights calibration. Try just putting a Darkflat in the Bias and restack, see if this makes any difference. Good luck and I hope this helps.
Thanks, I will. I should say my stacking worked ok but I wasn’t happy with the results. I’ll report on my findings!
I also read somewhere some time ago that you should do bias frames with the 533MC anyway. I’m certainly going to try it with my 533MC and my 183MM. With mono would you need to do bias with each filter?
The bias is independent from filter, therefore only one set of bias frames are needed. However for flats they are dependent upon filter and potentially that also means individual darkflats as well per flat duration, however potentially bias and darkflats are very similar and therefore this needs testing. Thanks.
Newbie. Did my 1st flats last week. Got a 2600 duo. Spoiled myself w/all things ZWO. Got a usb lite pad. At lowest setting I had to add 5 layers of tshirts to get a 1.9s exposure time, which pushes my spot on this histogram 3/4 of the way to the right instead of a nice center. Using Asair to auto take flats gives me a super fast exposure time w/ 1 tshirt layer and perfect center on histogram. Tried Cloudy Nights, but still confused. What's your thoughts on using flats w/ at least 3s exposure time? This is something I picked up on other tutorials. I wish I would have taken the fast dark flats to experiment with and see what the difference is, but I cleaned all my glass. And I did do biases, darks, and dark flats. Covering all my bases. Thanks.
The Duo is an IMX571 and it is known to be a well behaved sensor, I think it copes well with short Flats or longer Flats. I managed to get longer exposures for flats by using drawing paper sheets, however I think experimentation is required to get the workflow settled. If you are finding that the ASIair is giving you good data then don't change anything! However if you have issues it is worth experimenting. Certainly with older sensors, longer flats seem to be easier to calibrate (such as with the 294C sensor which is hard to calibrate.) Good luck and clear sky's!
Very interesting Andy weirdly enough I found that darks used to give me more agro so I just stack lights flats & dark flats only & it seems to work ok for me. I do however only shoot colour & not mono so I don't know if that makes a difference.
Hi Tich, Hope you are well. I did find that my darks had to be updated every month or two, because they didn't work well. I think the sensors change in a short time and need updating. I never knew Bias would make such a difference until I tried it, hopefully going forwards this will improve the calibration. Best wishes and clear sky's!
Would it hurt doing bias frames anyway.
Bias frames are good. No harm in doing them at all, I had read that they were not required, but in reflection there is no harm and clearly they can have a big impact on imaging. Thanks for watching, clear sky's!
For ASTAP simply put your BIAS frames in the flat dark tab.
Would this work with Astropixel processor?
I am not sure of the algorithm in APP. However it does have a Bias tab and I would experiment with inputting Bias into that and see what happens with your stacking results. Clear Sky's!