Solar Imaging Tutorial, Focus, Flat Calibration, Exposure | Jan 20, 2020
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- čas přidán 5. 09. 2024
- This tutorial for solar imaging is about how to focus your instrument(s), create flat calibration and manipulate parameters for exposure to see various features and record them in one exposure, both the surface and the limb together.
Key elements to know perhaps before watching the tutorial video:
FireCapture: I'm using FireCapture software specifically for this entire process. Huge thanks to the author of this software and that it's free!
Gamma: I use gamma a lot in FireCapture, it's totally software manipulation. I do not use gamma (its off or neutral, neutral is 50 in FireCapture by the way) when recording however. Gamma stretches values that are useful when using your eyeball to see what's on your live feed from your camera, it's handy to stretch up the shadows and mid-tones (moving the slider to the left towards 0) (less contrast, see faint stuff like prominences); it's also handy to crush the shadows and mid-tones so that perceived contrast is higher on things like spicules, plages, filaments, spots, etc (moving the slider to the right, towards 100). Several times in the tutorial I will set exposure and then use gamma to crush shadows and see surface detail to critically focus, and then open up shadows with gamma to then see the prominences on the limb, again, without changing exposure--the key is that exposure wasn't changed to see the surface or prominences, just software manipulation of gamma, and the point of that is that the data is there, so turn gamma off when recording your video. You can get the faint prominences lifted in post processing and you can increase surface contrast with post processing from the same single exposure capture (my previous tutorial, Rapid Workflow). You don't have to use this, I just find it handy to focus and see prominences to know its in my data, then turn it off to actually capture the data.
Flat Calibration, Defocus Method: Defocus method is commonly used and easy when the solar disc fills the FOV of your camera so that there's only sun in your FOV. One can simply defocus the disc until features are gone, somewhere near the center of the disc ideally. I lower exposure values to achieve about 65% histogram fill. FireCapture recommends between 50~80% if you use the hover tool. Exposure time doesn't matter. I prefer not to use gain if possible doing this, but you can use gain if you need to. FireCapture has a default flat frame tool built in, you simply click it, tell it how many frames you want to capture, it will capture them and apply the flat calibration to your real time video stream from the camera.
Flat Calibration, Diffuser Method (Bag Flats): The Diffuser method is an easy way to create a flat calibration frame when the solar disc does not fill the FOV on your camera sensor, and you can see the limb or void of space around the full disc or partial disc. You need an opaque transluscent bag, I'm using a cereal bag. It should not be completely see through, but opaque. Not all bags are equal, so you have to experiement and find one that does what you need. The key is that it diffuses light, as in, it scatters the light. What this does is illuminates the bag itself so that when its in front of your aperture, the light source is now larger and it will fill your FOV on your sensor so that you can create a flat frame even though the solar disc isn't filling your FOV. This works for full disc FOV with a short scope, and for partial disc FOV. The bag needs to be over the entire aperture into your scope, but also it needs to be farther away from the front of your aperture, not directly touching it, I find it needs 2+ inches of space so that there's no hard edge and the diffuser material will be illuminated farther out than what the solar disc would normally appear as. A lens hood or lens shade is ideal for this to provide that space, ideally, larger than your actual aperture. This is key to not have the bag flat up against your entrance to your aperture of your solar scope (you may need to make a small hood or cardboard holder for dedicated solar scopes that tend to completely lack lens hoods). I again target 65% histogram fill. When performing this method, put the disc in the center or near center of your FOV or sweet spot, we focus first to get critical focus, then don't touch the focuser. Then we put the bag on, and raise exposure to fill the histogram to 65% (or 50~80% per FireCapture's hover tool). Gamma off. Capture your flat frames with the FireCapture tool. It will auto-apply the flat frame. Now remove the bag. You will need to lower exposure values again to your recording exposure values. It will still be in focus, no need to change it. You can however still fine focus if you need to.
Software Credit to the Author of FireCapture! Thank you for your awesome work!
Music Credit to TimeCop1983 on BandCamp! Check them out!
Marty, thanks so much! I see the difference between what I was doing (bottom line: nowhere near enough histogram filled up-usually at 0 gain no gamma exposed for ~50-60% instead of higher) and what you’re doing. My proms were just way too faint squished down to almost zero the stacking and noise algorithms almost ignored them.
All good Dennis, I hope it helps!
Excellent information. Great tutorial which as your others videos, go right to the point. Thanks for sharing your experience!!!
Thanks!
Love it. Thank you so much. Do you have a follow up video showing how you processed these captures into images? That would make this complete.
Hello, thanks! Yes, here's that tutorial on processing: czcams.com/video/RJvJEoVS0oU/video.html
I am going to invest in H alpha scope. Have been doing whitelight for more than two years now.
Now's a great time while everything is in stock! When the maximum returns, everything will be constantly sold out and long waiting periods. So the minimum is the best time to buy! :)
@@malsYT best and done 😎
Hi Marty. Great video!!! Thank you!! Just wondering what software package you use to stack the images and load the flats. Very new to this and don't know how to combine both solar images and flats in the stacking process. If you could point me in the right direction it would be greatly appreciated! Thanks. Doug
Hi Doug, thanks, I do the acquisition in FireCapture with real time flat overlay so I can see what the product will be (no guess work). Autostakkert!3 is the software I'm using to align & stack the frames for lucky imaging. All free software.
@@malsYT Thanks Marty. Will check out Autostakkert 3!
Is there any specific reason to target 80-90% histogram? Good video
Hi, you could go for more, you could go for less. It depends on the subject. Right now in active regions there are flares often, and sometimes ellerman bombs near spots, these add intensely white spots which will fool your histogram that looks at the entire FOV and can influence exposure to be lower on everything else. I suggest targeting somewhere in the 70's to 80's really tops for flat field purposes and so that you do not over-expose plage areas. You'll see what I mean when you sharpen a brighter plage and it instantly goes nearly all white--this was due to over-exposure and heavy contrast/sharpening routines.
Great Video! I just ordered a Full Aperture Solar Filter for my 12" dobb. Will I be able to see Filaments and prominences. Or will I need more filters?
Hi, a full aperture white light filter will show the photosphere. This is the brightest layer of the sun's outer layers and will show you sunspots, faculae and convection cells or granulation. The chromosphere is above the photosphere and is many orders or magnitude dimmer than the photosphere, so it requires extremely narrow bandpass filtration to block all that photosphere light to see the firey hellscape that is the chromosphere where you will see prominences and all that. The filter would need to be down to around 1A to begin doing this (0.1nm), or frankly even more narrow, around 0.7A (or 0.07nm) bandpass to show it with good contrast, which is commonly done with an etalon filter and blocking filter system. These are very expensive. So unfortunately that white light filter you purchased will not show you the chromosphere, only the photosphere. Also, a 300mm aperture is probably way too much aperture even for visual for solar because your seeing conditions in day time are likely very poor, like most places in the world. You would be better off with a 4 inch aperture to start, unless you know for measured fact that you have sub-arc-second seeing conditions in day time (this is rare). If you want to see the chromosphere, it won't happen with your 300mm dob without incredibly expensive filtering systems (many thousands of $). So if you're interested in chromosphere viewing, I would suggest you look at Lunt's 40mm HA or 60mm HA dedicated scopes from a budget stand point, or perhaps a Daystar Quark on a smaller refractor (like a 4" refractor).
Nice one Marty 🙂
Hey Marty, if you happen to read this I enjoy your work 👍 Question .. what is the purpose of shielding your mount with reflective material? Thanks for these videos 👍
Hi Chris, I do that to keep heat off the metal mount and stuff and then heat rises off and can effect local seeing
Wise Imaging Hi Marty, ahh hah .. ok got it, maybe I should do the same with my white EQ6-R mount ehh? Also it’d be cool if you did a video sometime showing how you Frankenstein’d your scopes together with PST etalons and stuff .. I find that fascinating. Thanks again 👍
When taking flats do you move your telescope to the center of the sun? Or it doesn't matter where you put your telescope? Thanks
Hi, during the minimum, yes you can use the center of the disc for this. During the maximum you will be hard pressed to find a place that has no active region so that there's no patches from plages, spots, etc involved, in that case, you just use any area that you can that has no features in the FOV that change the brightness/darkness when defocused (such as an intensely bright plage).
Hello! Amazing photos and tutorial. Many thx for it from beginners. But how you guiding sun?
Thanks; Guiding on the sun doesn't require anything special, any tracking mount should have multiple slew rates, side rail (which is virtually everything including planets), lunar (different rate) and solar (different rate). Usually if using a GoTo system, selecting solar will change its slew rate to match (or lunar if choosing lunar; otherwise it defaults to side rail which handles everything else's standard rate).
@@malsYT And before guiding you have to align in night time?
@@user-tw9ve2fm4d If you are setting up an EQ mount, you simply need it roughly polar aligned. If you want it really accurate with minimal drift, then yes, it needs to be done at night and the alignment preserved. Otherwise, if it's done in day time, that's ok too, just roughly polar aligned via the direction and elevation, if it's close, it will still work well enough for course image scales. And many modern mounts have one star alignment options that include solar system objects to use. My mount is permanently setup in an observatory, so I polar aligned it and it keeps alignment indefinitely. I realize not everyone is doing that, and so if setup is required each time, you do not have to do it at night and preserve it, but it will be more accurate of course. You can still just rough align it during the day and it will work ok.
@@malsYT THANK YOU! It's really useful advise for me. I will try to do it!
Good but your flat is very dependent of your (non homogeneous) source of light, that's why as soon as you move from where you took your flat, the flat doesn't really work (e.g. 6:00 major gradients on the right).
Wise Imaging
Marty - some questions, as I am a solar imaging newb.
1. My ZWO 1600 has TEC cooling - is that required to be used with solar imaging? I presume not, since cooling is really only critical for limiting noise in DSO imaging so that the data is above the camera's noise floor. If TEC is not required for solar imaging, what is the ideal normal operating temperature for the sensor? I did a test run on Sunday, the 1600's sensor was around 28 degrees C. Is this acceptable, or will this damage the camera and I should be using TEC cooling?
2. For HA, does the filter need to be set to IR?
Cheers,
Dave
Hi Dave, cooling is not needed and will not provide noise reduction to short exposures. Operating temp, lower is better just for lifetime of components as heat does wear things out faster, but as long as you're withing operating spec of the sensor you should be fine. Setting a filter type makes no difference other than naming for organizing and cataloging, such as designating IR, it doesnt change the data.
@@malsYT Thanks Marty.
ZWO mentions "working temperature" in the manual for their 1600 mm pro camera - do you think that that mean surface temperature of the sensor or ambient air temperature?
Also, how do you align your GOTO mount during the day? No alignment stars, can't see the South (or North) pole etc. Do you just do a rough alignment to South/North direction, set your altitude on your GOTO mount and do a 1 star alignment on the Sun?
@@davepastern I think it specifies ambient temperature. My mounts are on piers, permanently polar aligned, for setup, align well at night or rough align in day, telegizmo 365 covers protect well.
@@malsYT OK! Should be good then in the Australian Winter. Summer perhaps not lol! I don't have the luxury of a permanent observatory or even a permanent pier sadly (variety of reasons). I'll do a rough align vs true South and set the latitude on my GOTO mount.
Many thanks for your awesome tutorial and time to reply, greatly appreciated.
@@malsYT well, first chance to test the Lunt and 1600 mm pro camera today since last weekend - looks like the camera is dead. Exposure set to "1 to 200ms". Gamma set to maximum. Gain set to 0. Sun centred on field view via 20mm eyepiece before swapping to camera (which has a narrower FOV than the ZWO camera I might add). FPS set to maximum 30fps to avoid any USB traffic errors. Image preview in FireCapture is dead Black, nothing showing. No, I don't have the front lens cover on the Lunt, or the 1.25" nosepiece cover on the camera. FireCapture detects the camera without issue. Just no data visible.
I strongly suspect the sensor on the ZWO is DEAD.
Should I be using an IR/UV cut filter when imaging? From what I have read, this is not necessary with a dedicated HA solar scope and imaging. Am I wrong?
FireCapture shows the sensor at 31 degrees C. From what others have told me, this is not an issue, and I should not have to use the TEC 12v cooling on the camera when solar imaging.
FireCapture histogram showed nothing. Dead as a door nail.
The camera was working for nearly all of my session last weekend, when it stopped working last weekend (same problem as today), it was nearly time to pack up as the Sun was about to dip below a neighbour's rooftop. So, I decided that I would test it at a later point of time.
Note: ZWO camera was purchased new, in 2017. Stored in its original box, untouched, unused, until last weekend. Very poor QC from ZWO. Of course, it is now out of warranty, so I am left with a 2 grand dud. I am beyond fucking pissed off.
Is she one of those who took the jab?
Wise Imaging