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Solar Transits of ISS

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#1 StarAlert

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Posted 20 January 2021 - 02:53 PM

I just picked up a portable pier to chase down solar transits of the ISS close to me. I’m planning on using an AR152 with Baader Solar film and my ASI533 camera.

It’s either the AR152 or my Tak FC100DZ. I figured the extra aperture would help with image scale.

Any thoughts on my setup? Would I be better off using the APO instead of the Achro?

#2 dragracingdan

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Posted 23 January 2021 - 10:58 AM

I've captured a few transits. My opinion is to use the scope/camera combination that lets you capture the full disk as that better ensures your change of success. After some experience, your longer FL scope could be used to try and capture the ISS near a sunspot for a unique composition. The APO vs. achro is this case is a non-issue. Transits are definitely fun to capture and nothing helps more than practice. Another bit of advice is to make sure your laptop time is synced with NIST time so you don't click the capture button too late. I just did a lunar transit and my laptop was off by over a minute and would have completely missed the event if I didn't sync with NIST time prior. Just my thoughts

Best,
Dan
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#3 MalVeauX

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Posted 23 January 2021 - 11:33 AM

I just picked up a portable pier to chase down solar transits of the ISS close to me. I’m planning on using an AR152 with Baader Solar film and my ASI533 camera.

It’s either the AR152 or my Tak FC100DZ. I figured the extra aperture would help with image scale.

Any thoughts on my setup? Would I be better off using the APO instead of the Achro?

Heya,

 

I would use the AR152 but I would mask it to either 80mm (F12.35) for use with red filters or 100mm (F9.8) for use with near IR and IR filters, for sampling purposes with your 3.76um pixels of your 533MC and use a red filter on your sensor's nose (like a red imaging CCD filter or 610nm long pass filter, etc). You could even use a near IR filter, like 685nm or 742nm to assist with calming the seeing conditions; that's in addition to your Solar Film for energy rejection. Remember to crop (region of interest) around the solar disc to increase the potential FPS of your camera. The transit happens really, really fast, so you want to be running as fast of FPS as you possibly can with your setup with zero dropped frames, so use the shortest exposure you can with the fastest exposure you can (relative to each other) and fill your histogram via gain (if needed; you may not need this at all); capture as 8 bit mono/RAW.

 

Transits happen at specific times, and it will likely be a time with poor seeing, so instead of trying to get a high res image with a 6" aperture and under-sampling it, instead, you can try to sample with moderate resolution with a controlled smaller aperture and better sampling matching so that if you catch the ISS, it's at least going to be better resolved with more ideal sampling matching.

 

You could use your Tak too, but it's a little faster and you need a longer focal-ratio for sampling, so you'd have to either over-sample (this is risky business in poor seeing with a super short capture period) or reduce its aperture with a mask to best sample with your pixel size, again, in red or near IR or IR wavelengths for best chance in poor seeing.

 

Seeing again will most likely be bad, and the transit is a one-shot deal, you don't get another chance per session. And it happens in an eye blink. Literally. So you have to already be rolling video at fast FPS before the transit begins. Your best chance for a sharp capture in poor seeing is luck and to support that luck use red or near IR and IR wavelengths that are less effected by seeing conditions, with smaller aperture (as mentioned above) to well sample to your pixel size. You could try to use full aperture and simply double your effective focal length with a barlow to get the focal-ratio needed to sample, but you'd then be asking for sub-angstrom-seeing on-demand to benefit that. Not likely. I'd play it safe on this to not miss the chance.

 

Very best,


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#4 PhotonJohn

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Posted 23 January 2021 - 11:44 AM

This is not the same image scale, but I used a Lunt 60/50mm double stacked and ASI174mm. This combination gave me a full disc image. Started my capture 90 seconds before the predicted transit time. Set the capture rate in SharpCap at 30fps for the 0.52 second pass and caught 15 frames with the ISS evenly spaced across the disc. Just so happened that the center of the chord was directly over my house that day. There were no active regions on the disc and a lot of passing clouds, but a hole opened for five minutes. One minute after capture the clouds covered the Sun. Click image for full size.

[attachment=1698338:SISS82720pjpgcn

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Edited by PhotonJohn, 23 January 2021 - 03:13 PM.

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#5 chemman

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Posted 23 January 2021 - 12:04 PM

I love that shot John.

 

Chuck


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#6 StarAlert

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Posted 23 January 2021 - 12:58 PM

Heya,

 

I would use the AR152 but I would mask it to either 80mm (F12.35) for use with red filters or 100mm (F9.8) for use with near IR and IR filters, for sampling purposes with your 3.76um pixels of your 533MC and use a red filter on your sensor's nose (like a red imaging CCD filter or 610nm long pass filter, etc). You could even use a near IR filter, like 685nm or 742nm to assist with calming the seeing conditions; that's in addition to your Solar Film for energy rejection. Remember to crop (region of interest) around the solar disc to increase the potential FPS of your camera. The transit happens really, really fast, so you want to be running as fast of FPS as you possibly can with your setup with zero dropped frames, so use the shortest exposure you can with the fastest exposure you can (relative to each other) and fill your histogram via gain (if needed; you may not need this at all); capture as 8 bit mono/RAW.

 

Transits happen at specific times, and it will likely be a time with poor seeing, so instead of trying to get a high res image with a 6" aperture and under-sampling it, instead, you can try to sample with moderate resolution with a controlled smaller aperture and better sampling matching so that if you catch the ISS, it's at least going to be better resolved with more ideal sampling matching.

 

You could use your Tak too, but it's a little faster and you need a longer focal-ratio for sampling, so you'd have to either over-sample (this is risky business in poor seeing with a super short capture period) or reduce its aperture with a mask to best sample with your pixel size, again, in red or near IR or IR wavelengths for best chance in poor seeing.

 

Seeing again will most likely be bad, and the transit is a one-shot deal, you don't get another chance per session. And it happens in an eye blink. Literally. So you have to already be rolling video at fast FPS before the transit begins. Your best chance for a sharp capture in poor seeing is luck and to support that luck use red or near IR and IR wavelengths that are less effected by seeing conditions, with smaller aperture (as mentioned above) to well sample to your pixel size. You could try to use full aperture and simply double your effective focal length with a barlow to get the focal-ratio needed to sample, but you'd then be asking for sub-angstrom-seeing on-demand to benefit that. Not likely. I'd play it safe on this to not miss the chance.

 

Very best,

Thanks, Marty! 
I appreciate the advice. 
I imaged a lunar transit a couple days ago so I’m very aware of the preparation needed to get a good shot and how important it is to get a high FPS rate.

 

A blink of an eye is exactly right. I saw it zip across my laptop screen but my 5yo daughter missed it completely. She didn’t realize how fast it was going to be going. 

 

It looks like I need to pick up a filter. I am considering the Astronomik ProPlanet 642. Would that be sufficient? Would you suggest a similar filter for daytime lunar transits? This is a single frame from Thursday with no filter, using my f8 DZ. 
 

9D25F0AA 2956 4DCD 976D E0342A7FA73E

I admit I’m hooked on chasing the ISS. It gives me some really fun stuff to do during the day. 
 


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#7 MalVeauX

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Posted 23 January 2021 - 01:27 PM

Really awesome capture there! ISS looks great! Super!

 

642nm is just a red filter with some IR passage (up just past 800nm). It will work for anything you want to use it for. If you want to go a little longer, explore the 685nm. It's possible to go longer into IR with 742nm and more, but a lot of sensors begin to lose sensitivity fast as you go deeper into IR, so while you calm seeing more with longer wavelength, it costs you signal to noise and dynamic range which can be a bear for images which are not going to be stacks mostly since it will be a single frame, so having the noise issues and/or loss in dynamic range may not be worth going that far. You can also look at the Baader 610nm long pass filter. Or just any red imaging filter that is approximately 600nm~700nm and cuts off IR.

 

Daytime lunar transits are best done with IR filters to get more contrast because with just a red filter, you'll still get all the sky glow. With IR wavelengths, you can get a black sky in day light on the moon, compared to a low contrast moon with a blue or light sky surrounding it making it even harder to see visually. So for daytime lunar, I would definitely look at 685nm to 742nm IR filters for this. The beauty is, you can use the same thing for solar with solar film as the energy rejection filter.

 

Very best,


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#8 StarAlert

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Posted 23 January 2021 - 03:08 PM

Really awesome capture there! ISS looks great! Super!

 

642nm is just a red filter with some IR passage (up just past 800nm). It will work for anything you want to use it for. If you want to go a little longer, explore the 685nm. It's possible to go longer into IR with 742nm and more, but a lot of sensors begin to lose sensitivity fast as you go deeper into IR, so while you calm seeing more with longer wavelength, it costs you signal to noise and dynamic range which can be a bear for images which are not going to be stacks mostly since it will be a single frame, so having the noise issues and/or loss in dynamic range may not be worth going that far. You can also look at the Baader 610nm long pass filter. Or just any red imaging filter that is approximately 600nm~700nm and cuts off IR.

 

Daytime lunar transits are best done with IR filters to get more contrast because with just a red filter, you'll still get all the sky glow. With IR wavelengths, you can get a black sky in day light on the moon, compared to a low contrast moon with a blue or light sky surrounding it making it even harder to see visually. So for daytime lunar, I would definitely look at 685nm to 742nm IR filters for this. The beauty is, you can use the same thing for solar with solar film as the energy rejection filter.

 

Very best,

I just ordered the Baader 685nm. Thanks for all your help. 

 

I have two upcoming, nearby transits. A solar transit on 2/7 and a lunar transit on 2/14. 

Keeping my fingers crossed for clear skies. 



#9 StarAlert

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Posted 23 January 2021 - 03:09 PM

This is not the same image scale, but I used a Lunt 60/50mm double stacked and ASI174mm. This combination gave me a full disc image. Started my capture 90 seconds before the predicted transit time. Set the capture rate in SharpCap at 30fps for the .052 second pass and caught 15 frames with the ISS evenly spaced across the disc. Just so happened that the center of the chord was directly over my house that day. There were no active regions on the disc and a lot of passing clouds, but a hole opened for five minutes. One minute after capture the clouds covered the Sun. Click image for full size.

[attachment=1698338:SISS82720pjpgcn

Nice image!!

I think you meant 0.52 second pass. 


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#10 PhotonJohn

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Posted 23 January 2021 - 03:14 PM

Nice image!!
I think you meant 0.52 second pass.


I stand corrected.

#11 StarAlert

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Posted 23 January 2021 - 11:43 PM

 

 

You could use your Tak too, but it's a little faster and you need a longer focal-ratio for sampling, so you'd have to either over-sample (this is risky business in poor seeing with a super short capture period) or reduce its aperture with a mask to best sample with your pixel size, again, in red or near IR or IR wavelengths for best chance in poor seeing.

 

 

I just re-read your post and I'm wondering what you meant by I'd "either have to over-sample". Are you referring to adding a 2x barlow? 

 

Also, am I correct in that the focal length of my rig will determine what kind of filter I should use? Faster scopes need IR filters while slower scopes just need red or near IR? 


Edited by StarAlert, 23 January 2021 - 11:49 PM.


#12 MalVeauX

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Posted 24 January 2021 - 07:18 AM

I just re-read your post and I'm wondering what you meant by I'd "either have to over-sample". Are you referring to adding a 2x barlow? 

 

Also, am I correct in that the focal length of my rig will determine what kind of filter I should use? Faster scopes need IR filters while slower scopes just need red or near IR? 

Yes, adding any effective-focal-length multiplier such as a barlow resulting in a focal-ratio that is over-sampling for your pixel size relative to the wavelength being sampled.

 

Focal length is just part of it, it matters again what pixel size and what wavelength you're sampling, all subject to whatever your atmospheric seeing conditions are. Since seeing conditions are typically poor during the day, the longer wavelengths will have better chances of having acceptable seeing conditions for the sub-second transit time of the ISS. If seeing is poor during that time, less than a second, then it will just be a mushy mess. But if seeing is average due to using longer wavelength, while the angular resolution is lower, the improvement in seeing means at least you have better chances of it being a fairly sharper less blurry capture. This matters a lot since you're not going to be stacking frames, and it really truly is relying on getting a single frame capture which will not have the same latitude in processing as a stacked file.

 

Very best,


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#13 StarAlert

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Posted 24 January 2021 - 05:12 PM

Ok. I clearly need to learn a lot more about photography and wavelengths. 
 

I appreciate your taking the time to explain some of this stuff. 
 

So let me ask you this. I’m thinking a lot about this “5x the pixel size” for the ideal focal length for good seeing. With my Tak DZ, that would give me a focal length of 1,880 and result in a sampling of 0.41”/pixel. At that FL, I should use a red or near IR filter.

 

Let’s say, instead, I use my TEC160. If I barlowed this to get it to f18.8, I’d be at a focal length of 3,008 and the sampling would be at 0.26”/pixel. Does the seeing have to be better with TEC to pull this off? Alternatively, if I run, the TEC at f11.75 (FL = 1,880), would I get essentially the same result as the DZ at f18.8? The seeing just wouldn’t have to be as good to get the same result as the DZ at f18.8? 
 

I find this is all very fascinating. I dig this technical stuff. 
 

On another note... I currently have two Tak 4”ers, two mounts, two laptops, two cameras. I’m thinking about setting them both up at the next transit. One set up for good/avg. seeing and one set up for the possibility of excellent seeing. Good plan? 

 

 

Yes, adding any effective-focal-length multiplier such as a barlow resulting in a focal-ratio that is over-sampling for your pixel size relative to the wavelength being sampled.

 

Focal length is just part of it, it matters again what pixel size and what wavelength you're sampling, all subject to whatever your atmospheric seeing conditions are. Since seeing conditions are typically poor during the day, the longer wavelengths will have better chances of having acceptable seeing conditions for the sub-second transit time of the ISS. If seeing is poor during that time, less than a second, then it will just be a mushy mess. But if seeing is average due to using longer wavelength, while the angular resolution is lower, the improvement in seeing means at least you have better chances of it being a fairly sharper less blurry capture. This matters a lot since you're not going to be stacking frames, and it really truly is relying on getting a single frame capture which will not have the same latitude in processing as a stacked file.

 

Very best,



#14 MalVeauX

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Posted 24 January 2021 - 06:32 PM

Ok. I clearly need to learn a lot more about photography and wavelengths. 
 

I appreciate your taking the time to explain some of this stuff. 
 

So let me ask you this. I’m thinking a lot about this “5x the pixel size” for the ideal focal length for good seeing. With my Tak DZ, that would give me a focal length of 1,880 and result in a sampling of 0.41”/pixel. At that FL, I should use a red or near IR filter.

 

Let’s say, instead, I use my TEC160. If I barlowed this to get it to f18.8, I’d be at a focal length of 3,008 and the sampling would be at 0.26”/pixel. Does the seeing have to be better with TEC to pull this off? Alternatively, if I run, the TEC at f11.75 (FL = 1,880), would I get essentially the same result as the DZ at f18.8? The seeing just wouldn’t have to be as good to get the same result as the DZ at f18.8? 
 

I find this is all very fascinating. I dig this technical stuff. 
 

On another note... I currently have two Tak 4”ers, two mounts, two laptops, two cameras. I’m thinking about setting them both up at the next transit. One set up for good/avg. seeing and one set up for the possibility of excellent seeing. Good plan? 

Heya,

 

Think about it, if you're using a larger aperture, finer image scale, the angular resolution potential is higher, so you need better (finer) atmospheric seeing conditions. It will be magnitudes more difficult, to the point of not possible unless your seeing is excellent, and likely not, to image the potential resolution of your 160mm aperture instrument, even in red wavelength. You'd need sub-arc-second sustained seeing (0.9" seeing, sustained). You need to see what your common seeing conditions are. Start with this. Work within this ultimate limit.

 

Here's a great place to start:

 

https://www.meteoblu...america_4699066

 

Plug in your location, then on the left side menu, look at Outdoor tab then Astronomical seeing. See what it is is predicted (look at the arc-seconds column) through the day from morning to evening (day time). Look at the trends. See what is likely potentially common for your location and the times you might image. That seeing value in arc-seconds directly translates into what you could potentially resolve, it's your limit, and unless it's a value less than 1 arc-second, you won't be benefiting the resolution potential of a 6" or larger instrument even in red wavelengths.

 

For what you're trying to do, at the limit of seeing, you'll need to use a smaller aperture and sample it appropriately to a pixel size via a controlled focal ratio, as described above.

 

Don't try to go bigger, unless you have extraordinary seeing conditions during the day commonly.

 

Two setups for twice the chance at the same data is a good idea. I wouldn't push it for high resolution though, not until you have definitive data and an idea of what your seeing conditions are commonly going to be capable of. Otherwise, you'll use a big aperture, fine image scale, and the result will not even be able to focus due to the bad seeing conditions (you'll see a rolling boil on your screen).

 

Very best,


Edited by MalVeauX, 24 January 2021 - 06:34 PM.

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#15 StarAlert

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Posted 24 January 2021 - 08:16 PM

Heya,

 

Think about it, if you're using a larger aperture, finer image scale, the angular resolution potential is higher, so you need better (finer) atmospheric seeing conditions. It will be magnitudes more difficult, to the point of not possible unless your seeing is excellent, and likely not, to image the potential resolution of your 160mm aperture instrument, even in red wavelength. You'd need sub-arc-second sustained seeing (0.9" seeing, sustained). You need to see what your common seeing conditions are. Start with this. Work within this ultimate limit.

 

Here's a great place to start:

 

https://www.meteoblu...america_4699066

 

Plug in your location, then on the left side menu, look at Outdoor tab then Astronomical seeing. See what it is is predicted (look at the arc-seconds column) through the day from morning to evening (day time). Look at the trends. See what is likely potentially common for your location and the times you might image. That seeing value in arc-seconds directly translates into what you could potentially resolve, it's your limit, and unless it's a value less than 1 arc-second, you won't be benefiting the resolution potential of a 6" or larger instrument even in red wavelengths.

 

For what you're trying to do, at the limit of seeing, you'll need to use a smaller aperture and sample it appropriately to a pixel size via a controlled focal ratio, as described above.

 

Don't try to go bigger, unless you have extraordinary seeing conditions during the day commonly.

 

Two setups for twice the chance at the same data is a good idea. I wouldn't push it for high resolution though, not until you have definitive data and an idea of what your seeing conditions are commonly going to be capable of. Otherwise, you'll use a big aperture, fine image scale, and the result will not even be able to focus due to the bad seeing conditions (you'll see a rolling boil on your screen).

 

Very best,

That's an awesome website. Thanks! 

 

I live in SoCal and the skies are usually pretty steady, but I've never actually looked for a fine measurement of the seeing. I usually just put a zoom in my diagonal and see how far I can zoom before the image gets soft. This website will allow me to compare what I see and what it's predicting. Sweet!!! 


Edited by StarAlert, 24 January 2021 - 08:33 PM.


#16 StarAlert

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Posted 24 January 2021 - 08:31 PM

So if this website predicts seeing at 0.80" - 0.90", that would mean it's time to set up the 6 inch? smile.gif

And if it predicts seeing at 1.0"-1.2", the 4" scope is plenty.



#17 MalVeauX

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Posted 24 January 2021 - 09:00 PM

So if this website predicts seeing at 0.80" - 0.90", that would mean it's time to set up the 6 inch? smile.gif

And if it predicts seeing at 1.0"-1.2", the 4" scope is plenty.

If your seeing is truly 0.8~0.9 arc-seconds, then yes, you could potentially reach critical sampling of the angular resolution of 656nm with a 150mm aperture. You may not see that seeing. It's predicted, not measured, on these websites. But it's a nice way to at least get an idea of what's potentially possible. But I would always take a smaller aperture option as well, like 100mm or 80mm even just in case (especially for shorter wavelengths). When you get it setup and you're looking at the disc, if it's not a high contrast pencil like drawing then seeing doesn't support that image scale in reality (assuming you're on band of course). But you can try to lucky image it. I wouldn't try to push it with a 150mm though. Again, the transit is less than 1 second. Even in good seeing there are fluctuations of poor seeing moments averaged in. If you're going to just try the 6 inch anyways, I would advise having the 4" or something small setup as well to handle it for when seeing is not great to have a chance at something less blurry with more contrast (again, you won't be stacking frames for this, this will just be a single shot, so it needs to be a good match for the seeing or it will be a boiling fuzzy mess).

 

Very best,


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#18 StarAlert

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Posted 24 January 2021 - 09:17 PM

If your seeing is truly 0.8~0.9 arc-seconds, then yes, you could potentially reach critical sampling of the angular resolution of 656nm with a 150mm aperture. You may not see that seeing. It's predicted, not measured, on these websites. But it's a nice way to at least get an idea of what's potentially possible. But I would always take a smaller aperture option as well, like 100mm or 80mm even just in case (especially for shorter wavelengths). When you get it setup and you're looking at the disc, if it's not a high contrast pencil like drawing then seeing doesn't support that image scale in reality (assuming you're on band of course). But you can try to lucky image it. I wouldn't try to push it with a 150mm though. Again, the transit is less than 1 second. Even in good seeing there are fluctuations of poor seeing moments averaged in. If you're going to just try the 6 inch anyways, I would advise having the 4" or something small setup as well to handle it for when seeing is not great to have a chance at something less blurry with more contrast (again, you won't be stacking frames for this, this will just be a single shot, so it needs to be a good match for the seeing or it will be a boiling fuzzy mess).

 

Very best,

Thanks again!!

I've got lots to think about. 

I just picked up an ASI178MC to compliment my ASI533. I can't wait to compare the two. 



#19 StarAlert

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Posted 25 January 2021 - 10:50 AM

Heya,

 

I would use the AR152 but I would mask it to either 80mm (F12.35) for use with red filters or 100mm (F9.8) for use with near IR and IR filters, for sampling purposes with your 3.76um pixels of your 533MC and use a red filter on your sensor's nose (like a red imaging CCD filter or 610nm long pass filter, etc). You could even use a near IR filter, like 685nm or 742nm to assist with calming the seeing conditions; that's in addition to your Solar Film for energy rejection. Remember to crop (region of interest) around the solar disc to increase the potential FPS of your camera. The transit happens really, really fast, so you want to be running as fast of FPS as you possibly can with your setup with zero dropped frames, so use the shortest exposure you can with the fastest exposure you can (relative to each other) and fill your histogram via gain (if needed; you may not need this at all); capture as 8 bit mono/RAW.

 

 

Very best,

Is this actually possible with the ASI533? It’s a 14 bit color camera. 



#20 MalVeauX

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Posted 25 January 2021 - 11:33 AM

Is this actually possible with the ASI533? It’s a 14 bit color camera. 

You're certainly welcome to use 12bit/14bit/16bit of course; my comment was merely to imply there's no benefit to using the color output of the sensor as it will not be the true color of the star, so it's better to use mono so that you can see the contrast and features better (light red color on the LCD in sunlight is low contrast); and that there's really not a compelling reason to use higher bit depth for this either. When you're trying to keep the fastest FPS, if you have 8bit available use that. If there's no FPS difference on your system, use the highest bit depth that you want. But for sub-second ISS transits, I would go for max FPS each time to have best odds of capturing a good frame during a moment of good seeing.

 

Very best,


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#21 Bob3137

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Posted 25 January 2021 - 01:15 PM

This is not the same image scale, but I used a Lunt 60/50mm double stacked and ASI174mm. This combination gave me a full disc image. Started my capture 90 seconds before the predicted transit time. Set the capture rate in SharpCap at 30fps for the 0.52 second pass and caught 15 frames with the ISS evenly spaced across the disc. Just so happened that the center of the chord was directly over my house that day. There were no active regions on the disc and a lot of passing clouds, but a hole opened for five minutes. One minute after capture the clouds covered the Sun. Click image for full size.

[attachment=1698338:SISS82720pjpgcn

Nice capture John! I have a Lunt 60 & same camera. I had the exact opposite happen to me a 2 years ago. Not a cloud in the sky except for 1 lonely cloud. I kept watching it and sure enough, it drifted over & started to covering the sun just as the transit happened. I just looked at my monitor & then up and went "Seriously!?" Lol! What are you going to do! :-)


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#22 lorenzo italy

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Posted 25 January 2021 - 01:29 PM

Thanks again!!

I've got lots to think about. 

I just picked up an ASI178MC to compliment my ASI533. I can't wait to compare the two. 

Hello,
take it as an example ...
My first and only transit of the ISS, with a 90mm refractor and 500mm focal length.
ZWO ASI178mm, Herschel Baader prism with ND 1.8 and Contunuum filter.
I was lucky from a calm and clear day with the sun very high (it was August).

 

post-290225-0-30142000-1598175356_thumb.jpeg

 

Lorenzo


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#23 StarAlert

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Posted 25 January 2021 - 01:42 PM

Hello,
take it as an example ...
My first and only transit of the ISS, with a 90mm refractor and 500mm focal length.
ZWO ASI178mm, Herschel Baader prism with ND 1.8 and Contunuum filter.
I was lucky from a calm and clear day with the sun very high (it was August).

 

attachicon.gifpost-290225-0-30142000-1598175356_thumb.jpeg

 

Lorenzo

Wow! That is fantastic! You shot that at f5.5? 

I think my 4" Tak will be plenty aperture. 



#24 StarAlert

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Posted 25 January 2021 - 02:21 PM

Hello,
take it as an example ...
My first and only transit of the ISS, with a 90mm refractor and 500mm focal length.
ZWO ASI178mm, Herschel Baader prism with ND 1.8 and Contunuum filter.
I was lucky from a calm and clear day with the sun very high (it was August).

 

attachicon.gifpost-290225-0-30142000-1598175356_thumb.jpeg

 

Lorenzo

You were sampling at  0.99"/pixel.

Were you using the whole sensor (the whole sun easily in the FOV) or did you use ROI to increase FPS?

What does ND 1.8 mean? 



#25 lorenzo italy

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Posted 25 January 2021 - 02:32 PM

Yup,
I was at 500mm focal length.

 

I used the ROI (I don't remember the format ...) because with the whole sensor I would have had a few fps, at most 5.
I was using an old laptop.
ND means neutral density filter, it is a gray filter that serves to attenuate sunlight.
It is usually used with the Herschel prism.
There are various "gradations" ND3-1,8-0,9-0,6 and others.




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