14. Dark, Flat, and Bias Frames with the ASIAir Pro

over the past couple of weeks I've gotten a lot of questions about how to take dark flat and bias frames with the ASI or pro so that's we're going to talk about in today's video before we get started though I want to stress that this isn't tend to be a general overview of how to take these three calibration frames with the ASIO Pro as you'll learn if you do your own research things will change slightly depending on the software you're using if you have a CMOS or CCD sensor if sensors color or monochrome and a whole lot more you can even have two of the exact same camera model side-by-side and they might not perform exactly the same and that leads us into a whole rabbit hole that I'm not going to deal with where this entire concept is so technical you can spend hours if not days really trying to comprehend the finer points of bias frames or dark frames or flats or anything else so I'm not going to get into the weeds with all that technical detail because I'm trying to keep it simple give you something to start off with and then for those of you who really want to go above and beyond you can continue to do your own research first let's start out with bias frames because these are by far the easiest to do and they should only take you about a minute so if you have your ASR Pro ready to go you can follow along and generally I recommend taking these after your imaging session at the end of the night like I said only take about a minute to do first make sure that the gain matches what you used for your light frames in my case a gain of 200 this is really the most important thing simply is that the gain matches between your bias frames and your light frames everything else isn't as important once you've made sure that the gain is correct it's really all you have to do and again if you're taking these immediately after your light frames at the end of the night everything should be set up and ready to go next we can go to the autorun feature here and then we'll click the three little dots and lines and that'll get us into the auto run menu now if you have anything here you can clear it out reset the progress do whatever you have to do and then we're going to create a new sequence right here first up we have our exposure or our shutter speed this needs to be as fast as possible so you can have to do the preset here of 0.01 or if you click that box with a slash through it you can enter a manual value and I want to go even faster so I put 0.001 and there we go for our filter it really doesn't matter because we're gonna be blocking off the camera sensor anyway in the telescope so no lights gonna be coming through therefore you can have any filter on there doesn't make a difference for the amount of photos we need to take I would say 100 usually the more photos you have your the better it's gonna give you a cleaner result at the end of the day so you don't have to take 100 you could take more than 100 but for me that's kind of a good round number and it tends to do a good job finally make sure you click that bias button at the bottom of the screen that way it's labeled properly and then you can hit OK now we can click the little back arrow in the top left of the screen to get to our actual shooting menu from there all you really have to do is click the circular button over on the right and it's gonna go through and take in this case 100 bias frames I don't want to be clear here when you're taking your bias frames you want to make sure that no light reaches the camera's sensor that's why I put the lens cap on the front of my telescope that way no light could reach the camera now obviously I'm recording this video during the day you don't want to take your bias frames and broad daylight you're better off taking these at the end of your imaging session it's in the middle of the night or I mean with a dedicated Astro camera or DSLR even you can take these at any time your bias frames they're not time sensitive so as long as there's a darkroom you can put the camera in or just if you're doing these middle of the night that's fine but the big thing here again is that no light reaches the camera sensor and then in this case the asar pro is gonna go through it's gonna take the hundred photos show you a little preview you can see all that electronic noise being generated there and once it's complete we've now done our bias frames and we can move on to taking dark frames next before we get to dark frames though I want to do a quick recap and make sure we're all on the same page so for our bias frames you need to make sure that the game or your eye self using a DSLR the same as your light frames you also need to take a very fast exposure that fast as possible if you're on a DSLR that'd be like one four thousandth or 180 thousand of a second on our dedicated Astro camera here it's like point zero one or point zero zero one then you want to take about a hundred pious frames making sure that no light reaches the camera sensor that's the most important thing the final point I want to make about bias frames is that you can reuse these in the future as long as you're using the same game with your light frames in other words I took my bias frames at a gain of 200 if I photograph the Andromeda galaxy a month from now using a gain of 200 I can reuse these bias frames I don't need to take a whole new set that night so that's one of the nice things about bias frames is that provided the gain stays the same you can use them for months at a time without needing to take new ones next let's talk about dark frames and the great thing is these are very similar to bias frames you only have to change a few things and you're ready to go so once you finish taking your bias frames again usually want to take these event of the night now we can swap over to our dark frames if that we're still on auto run but I'm gonna click the three dots with the three lines that's gonna give me back into the shooting schedule from here usually you need to click reset progress down the lower left that way you can just edit your original shooting schedule so there we go I cleared out the progress now I'm gonna click on my shooting schedule where it says bias there and now we need to enter our settings for the dark frame this time I'm going to start at the bottom and work our way up so you want to specify dark that way the naming structure makes sense when you get to the computer for the amount of photos I usually recommend taking 20 dark frames you can take more but you're gonna be wasting a lot of time if you do that if you take any less it might actually cause some artifacts and your photos the filter doesn't matter because just like our bias frames no light is gonna reach the sensor therefore it doesn't matter what filters in front of the camera finally the exposure needs to be the exact same as your light frames so if we took a two minute long photo 120 seconds of Andromeda you need to make sure that the exposure here is also 120 seconds now as I mentioned these dark frames take quite a while to complete if you look at the bottom of the screen says estimated time 40 minutes and 2 seconds so this is a big time investment but one of the great things is that since we're using a dedicated Astro camera with a cooling system and the asar Pro you could theoretically take your dark frames whenever you want it doesn't have to be immediately after your light frames so if you go to your main camera settings here in the S air Pro you want to make sure that the game is still the same as it was when you take your light frames also verify that the cooling system is turned on and that your target temperature is also the same as it was when you take your light frames if you do those two things correctly then you can begin your auto run take your dark frames and like I said I'll take quite a while to complete but once that's done you can incorporate those into your stacking process on the computer all right let's do a quick recap of our dark frames and then we will move on to flats so for our dark frames you need to make sure that they gain the exposure or the shutter speed and the sensor temperature matches your light frames any one of those three things is not the same as your light frames these are not gonna work as well as they should you also want to take about 20 dark frames for the best results that's kind of like the sweet spot between wasting time and not having enough dark frames and most importantly you got to make sure that no light reaches the cameras sensor if it does it's gonna really screw things up that's why we usually recommend taking these in the middle of the night with no bright light shining on the camera the lens if you want to take these during the day since we now have that ability with the cooling system just make sure you put in a darkroom and no light is able to reach the camera at all finally we have flat frames and I've saved these for last because on the assayer Pro they're surprisingly difficult to take before we get into that though let's talk about how to take your flat frames number one you need to make sure that the gain is the same between your light frames and your fly frames number two if you use multiple filters throughout the night you need to make sure that you take a set of flat frames for each filter number three the focus needs to stay the same between your light frames and your flat frames so if you were to take the camera inside and the next morning you try and take your flats you need to make sure that you put the focus back to where it was the night before and if you have to change the focus ring quite a bit between your L RGB filters and your narrow band you should factor that in as well also if you're using a telephoto lens you need to make sure you're at the exact same focal length the main reason we're so adamant about the focal length and the focus staying the same is because that can throw off how large the nest appears and also it will change the vignette especially if you have a telephoto lens and you're zooming in and out so verify and that the focus and the focal length are the same before you start taking two flat frames finally number four you need to make sure you're photographing an evenly lit light source if you mess this one up and it's easy to do you're really gonna be setting yourself up for a lot of problems once you get into the stacking and if you do your own research online you'll find a lot of different options for photographing and evenly lit light source personally I want something simple easy and free so I decided to photograph my TV screen unfortunately when I did that I had banding in my flat frames because my camera was picking up the refresh rate of the TV even if I put a t-shirt over the front of my telescope and did this I was still picking up the banding I don't have that just because the TV was so bright it was penetrating through the shirt or what but then I tried photographing my laptop screen with the t-shirt rubber-banded over the front and this time I didn't have any more banding so for me personally I'm gonna use my laptop screen from now on now that you understand the basics of taking your flat frames let's talk about how to do all this inside the ASI air Pro app with the app started up you can enter all your normal information hit enter and then we're going to be in our main workspace here however for a lot of you you might be in the auto run menu because you're digging your light-dark or pious frames today though for our flat frames we want to start off in the preview menu right here don't forget the gain needs to be the same for the flat frames as it was for your light frames if you go to the main camera settings you can see the game right here and for those of you who use different filters throughout the night with different gains don't forget you have to come in here and change the game for every filter if that's what you did for your light frames last night for me I used a gain of 200 the whole night regardless of the filter so I'm good there finally we want to go to the filter wheel settings and pick out the first filter we're gonna create for our flat frames if you were doing narrowband then you might want to start off with sulfur oxygen or hydrogen alpha if you're doing L RGB imaging then might as well start with L either way get a filter that you use last night and then we can get started provided you're pointed up it's your evenly lit light source you got your gain dialed in and your filter selected we can now start here in the preview menu first click on the exposure button the lower right we need to find our shutter speed or the exposure that's going to give us a flat neutral gray image however this is where it's really tricky on the asar Pro because we have to just keep clicking different exposures until we find the correct one thankfully we have a histogram here in the app that's really gonna help us out see if you click the histogram button it will bring it up at the bottom of the screen but it's really not very intuitive so let's explain what's going on here in the very lower right you should see information with max min and average and then there's some values next to that 65,000 in this case what that corresponds to is that 65,000 is pure white oddly enough though you're seeing a black image there in the background so I don't know why the ASI our app is showing you a black photo when it should be pure white but it is that's why you shouldn't rely on the picture you should rely on the numbers and again 65,000 is pure white what we're trying to do is get a flat gray image therefore the values in this case should be around 32,000 if you look towards the bottom center of the screen you'll see 32,767 that's kind of our center point here in the app if you can get that spike to center up with that value you'll be in good shape if you look over on the right you'll notice my exposure set to 0.01 seconds so with that shutter speed a gain of 200 my ELF filter photographing my TV screen if you look very closely you'd see the average number here on the histogram is about 25,000 that's right about where we want to be for our values that we were getting a flat gray image that's not too bright or not too dark for our flat frames your challenge is going to be adjusting that exposure to get similar values if the values are too high or too low your flat frames are not gonna work out properly and that's exactly what we see here I switch the exposure down to just 0.001 seconds and now my new average value is only 3000 the spike has also moved almost all the way to zero it's no longer near the center at 32,767 so in this case I would have to increase the exposure or the shutter speed to capture more light increase the average value and move that spike on the histogram towards the center of the screen that's really what we're trying to do here is pick different exposure values until you meet all those requirements at this point I'm sure some of you're saying okay if it's that much of a pain just use another application for the flats and that's what I thought of too so I loaded up sharp cap and then there's a really nice slider here for your exposure rather than screwing around clicking those buttons manually you can just move this slider left and right very quickly look down at the histogram on the lower right and once you get it near the center you're done then he gets or taking your flats that would be a much faster and easier way to do things unfortunately there's a very important problem here and that is the fact that the game does not correspond with the asi or pro app remember I was using a gain of 200 in the app and if we go back and look real quick you can go from 0 to 300 in the a as a hair Pro app however here in sharp cap the gain settings are completely different and they don't correspond with what we see in the app therefore it would be impossible for me to use sharp cap for my 5 frames because I can never get the game to match up properly with my light frames taken in the asar Pro alright let's get back on track and finish taking these flat frames so we're back in the SAR app I've adjusted my exposure here until I find a value that's between 20 on the low-end and about 35,000 on the high-end I'm mainly looking at the average value and the lower right there it looks like it's about 20 6,000 that's good enough now I'm gonna switch from my preview window to my auto run from here I'll click the three dots and the three lines to get to my shooting schedule then I'm gonna click on the shooting schedule button there first we need to adjust the exposure to what we figured out it was in the preview just a minute ago make sure you choose the correct filter as well we're gonna take 20 of these and you want to make sure you specify these as flat frames if you did all that you can click the start button and begin taking your photos in my case though what I'm doing is that I couldn't remember the number I that was point 2 is actually point zero two if you're starting to see all these weird numbers starting to get confusing you really got to make sure you remember what you're doing now they've gotten all dialed in though I'm gonna click the center button over on the right to begin taking my photos it's gonna go through take 20 images and if you still have your histogram up it will show you the correct values there our average is 26 thousand that's really good once this completes with my 20 photos then I can swap over to my our G or B filter if I'm doing l RGB imaging the night before for that we want to go back to our preview and find the new exposure because remember every time you change filters the amount of light coming into the camera will change so you have to figure out new values for every single filter and this can be kind of a pain now that I've switched to my RF filter I'm going back to preview and I'm gonna take another test photo my current exposure is 0.02 seconds which is what it was for the L filter however the L filter lets in a lot more light than they are so that's exactly what we see here now my average value is all the way down to 8,000 that's very low it's not bright enough so I need to click on my exposure button use a longer shutter speed maybe 0.2 or point zero five something take another photo look at the histogram trying it up around 30,000 roughly in this case this case is about nineteen thousand that's not high enough so I'm gonna click on my exposure again put it to maybe 0.1 seconds take another photo you see how much of a pain this is if you had sharp cap you'd have already been done by now just by moving the slider you won't have to come in here and keep guessing back and forth now I'm at 39,000 that's okay but it's a little bit high but I'm just gonna deal with it now so I'll go back to my auto run like the three dots three lines then I have to reset my progress before let me continue so I click the reset progress button click on my button there switch to the our filter make sure run flats I think my exposure was what was it I can't remember that's the problem I keep losing my train of thought here so I put it to zero point two seconds I wasn't quite sure if that was right so I'm back to preview in fact it was zero point one now that I remember the correct value I can come back to my how to run click the three dots in the three lines and what I'm doing here is that rather than choosing one of the presets which might not give you the proper exposure you can click the box with a slash through it and enter your own so let's say you're going between like 0.5 and 1 and now there's working you can just put in 0.6 manually and get things exactly where you need to be it's really important you know how to do that then you can click OK click the back button in the upper left and take your set of photos now for the our filter and once it starts taking them and transmitting you'll be able to make sure when the average value updates on the lower right that things are correct and in this case they were at 65,000 so I knew they were wrong so I stopped it went back into the outer run had to reset the progress and then enter a value that was actually correct and I keep getting my decimal places mixed up so I did do 0.06 not 0.6 this is why I hate using the asar app for this flat frames it's way too complicated than what it should be they should take it five minutes to do it shouldn't take yet half an hour and with all the troubleshooting here I spend the whole afternoon once I really didn't know how I was doing and even now I'm just barely trying to get the hang of it so I've showed you the process very vaguely like I said this is so much of a hassle that it was very hard for me to thoroughly explain it clearly to you because it's so convoluted to begin with and I'm sure I lost a few of you along the way so let's do one more recap using a green filter and then we'll call it a day because I've had enough flat frames I don't know about you so I'm gonna go to my green filter now and we need to adjust our exposure to get a properly exposed image again around 30,000 roughly in this case so I'm gonna start off just taking maybe a 0.05 exposure again because between R and G you should really shouldn't lose that much light and I'll take my shot right here once it finally loads up it'll give us our new average value if it's anywhere from twenty to thirty-five thousand I'm happy let's see what it is twenty one thousand that's okay and I know I can always adjust my exposure a little bit using that feature I showed you a minute ago in the auto run so now that we verified were at about 21,000 for the average at 0.05 I'll go back to auto run I want to give that average value up a little bit so I'll reset my progress here in Auto run click on the box change it to green then I'm going to manually enter a value here of let's see what I do is 0.08 that'll give me a little bit more light and that should overall do a better job so now I can take my photo if I notice that the average value using correct during the auto run I'll just stop it go back and try something different and in this case let's see what happens and it looks like it's gonna stay at 21,000 852 because I guess I just got lazy and said forget it it's close enough ideally it would have been closer to 30,000 just to let you know but once I got that done then I swapped to my B filter repeated the process until that was done as well if you're gonna be doing narrowband flat frames those will let in a lot less light so you have to factor that in if you're only doing like point zero five for your exposure with narrowband your exposure might be as much as one and a half seconds if not two seconds that's how much light they're gonna cut out all right I'm done I've had enough of this I'm sure you're probably equally is worn out from this video the whole point originally was to show you how to photograph your dark flat and bias frames of the asar Pro an eidetic head Astro camera as we learned it's very easy to take your bias ramps can take you more than a minute your dark frames are equally as easy to take but those will be a lot longer anywhere from 40 minutes to two hours you'll spend taking your dark frames your flat frames on the other hand are a huge hassle especially here in the app is way more complicated than it needs to be so I want to make sure you at least have some idea of what's going on here before we go the way I take my flat frames on the asar Pro is I pick my filter make sure the gain matches the light frames from the night before then I go to the preview window next I click on exposure and take a photo with my histogram active once the photo completes I looked down at my histogram and more importantly the average number in the lower right I want it to be around 30,000 right now with my hydrogen-alpha filter and a half setting exposure it's at 9500 47 that's way too dark which is crazy because that's a half second exposure pointed in a bright laptop screen so I change it to one second that should theoretically double the average value from nine thousand to about nineteen thousand let's take a look yeah eighteen thousand 393 so once you can do some basic math and you start to understand what's going on it should make things easier if I know I made eighteen thousand now if I do two seconds that should put me up around thirty six thousand for my average value which is a little high let's see what it gives us yep we're at thirty six thousand at least now that math is starting to work out now once I have that value in mind I can go out of the preview and go to the autorun menu once I'm in the autorun menu I can go back to the settings reset the progress and then change the filter from B to hydrogen-alpha then for my exposure time I know that two seconds was too high one second wasn't high enough so I can click the box with a slash through it and enter a manual value of maybe one point five cut it right in half and then I'll hit OK then I could click the back arrow and begin taking my photos in this case my flats for the hydrogen-alpha filter once the first image completes and it loads up I double-check the average value there in the lower right make sure it's around thirty thousand in this case twenty seven thousand five hundred ninety-four good enough I'll let it run for all twenty photos and I repeat that process and it looks like there's a oddly heavy vignette up on that corner with that filter that leads me to the final problem with flat frames is that if you're photographing a light source that isn't evenly illuminated you might be getting these false vignettes that when you include it in your stack it actually causes your final image to try out way worse that's why I personally don't bother with flat frames because my final images look great and more likely than not I'm gonna screw it up or rip my hair out with this really complicated process that shouldn't be this difficult and for me the little value mini of it is not worth the hassle you using some type of other astrophotography software like we saw a sharp cap to take your photos you can take your flag rooms much more easily and there's plenty of other laptop applications that will work just fine but today we're using the SI air in our smartphone so it does come with some drawbacks one final thing I want to caution you want is that if you're like me and you're starting to think about using another piece of software to handle your dark flat and bias frames that might not work as we saw with sharp cap the gain settings in there are completely different from what they are here in the asar pro app in other words whatever software used to take your light frames use that to take your calibration frames as well we're gonna be using the SAR Pro to take your light frames then you'd want to make sure you take your bias darkened flats in there that way there's no discrepancies as I was going back and editing this video I realized it was one final point I want to make about flat frames and that's the fact that these are also used to remove dust spots from your final image and that brings up another unique problem because if you wait too long between your light frames and your flat frames it's possible that the dust and your photos will change as well and when the dust spots don't line up properly between your light frames and your flat frames you will get problems in the stacking software that's just one more hassle with the fly frames and that's personally why I don't bother taking them because I don't really even notice any dust in my photos the vignette is negligible too so why would I spend all this time and frustration taking them and also if I screw one thing up I'm actually going to cause more problems on the final stack because maybe it's trying to remove dust that's not actually there or it's trying to remove a vignette that isn't actually there because I didn't take my flat frames perfectly that's just something you want to keep in the back your mind and always remember take a new flat frames pretty often that way the dust spots line up between your flats and your lights for every single filter as well [Music] [Music]

Channel: Peter Zelinka

Views: 41,963

Keywords: flat frames, dark frames, bias frames, vignette, dust spots, remove, astrophotography, nebula, galaxy, photography, asiair, asiair pro, zwo asi, how to take flat frames, how to take dark frames

Id: xfFqZTLmpMU

Length: 27min 46sec (1666 seconds)

Published: Wed May 20 2020