The ISS will transit the Moon this evening (in Sydney), in the Northwest sky, about 30 minutes after official sunset. I am wondering what exposure to set on my ASI1600MC. I will use a 0.5x reducer making the focal length about 1,000 mm and will set the gain quite high, at say 300, to enable a faster frame rate. The obvious thing would be to set exposure time for the Moon, in the very low millisecond range. What I am not sure about is the brightness of ISS in comparison to the Moon. Will is be visible as it approaches and passes the Moon? Will it show in silhouette or simply vanish as it actually transits the Moon, which will take less than a second?
Hi Richard- I’ve never captured a transit before (although it is on my wish list) but from what I’ve seen the ISS will just be a silhouette against the bright moon and I think that’s really the shot you’re looking for anyways. So adjust your video frame exposure and gain to get nice lunar detail and that’s all you need to worry about. If you had a second setup or want to attempt an ISS capture separate from the moon you could attempt with higher gain.
I just checked the predictions and it’s just missing the moon from my location but i get another go on the 23rd which will be right on target
It was 23 seconds later than advertised but I did manage capture it in 5 frames, one of which is attached. The ISS was sunlit during transit and was much brighter than the moon, over exposed in fact. At a focal length of 1,000 mm, the ISS is quite small. Against a black background, a hint of structure is discernible but not to the point of identifying solar panels.
The attached image has reduced resolution to keep the file size down. The ISS shows as a bright spot more or less in the middle of the moon, just above a prominent crater.
Edit: The second image shows detail (or lack thereof) when zoomed in on the ISS with a black background. There's no detail but I think at least a hint of some structure.
Hi Richard- I’ve never captured a transit before (although it is on my wish list) but from what I’ve seen the ISS will just be a silhouette against the bright moon and I think that’s really the shot you’re looking for anyways. So adjust your video frame exposure and gain to get nice lunar detail and that’s all you need to worry about. If you had a second setup or want to attempt an ISS capture separate from the moon you could attempt with higher gain.
I just checked the predictions and it’s just missing the moon from my location but i get another go on the 23rd which will be right on target
Good luck and please post your results!
Thanks for your comments. I have posted one of my images.
Thanks for posting your pic. Glad you were able to catch it and not a bad effort for your first attempt but yes shame it’s a bit over exposed. I think however the moon is also quite overexposed so had that been adjusted with a bit lower gain I think it may have yielded a bit more ISS detail. I forgot to mention before that when I adjust my gain/exposure for lunar shots I’m aiming for about 40% on the histogram
Thanks for posting your pic. Glad you were able to catch it and not a bad effort for your first attempt but yes shame it’s a bit over exposed. I think however the moon is also quite overexposed so had that been adjusted with a bit lower gain I think it may have yielded a bit more ISS detail. I forgot to mention before that when I adjust my gain/exposure for lunar shots I’m aiming for about 40% on the histogram
Yes, it was definitely a learning experience. The ISS vanished in the second frame as it crossed the over exposed, right hand edge of the moon, which is to be expected. Next time, I will keep the exposure lower and ditch the 0.5x reducer so that the focal length will be 2,032 mm.
The frame rate could to be USB limited. The computer is USB 3.0 and the camera USB 3.0/2.0. According to ZWO, I should be able to achieve 23 games per second (10 bits) and 15 frames per second (12 bit) with full resolution (16 MP). I am only getting 3 frames per second at the moment. The PC has an SSD drive. It could be a dodgy USB C to USB A adapter perhaps.
Richard I'd suggest the USB-C to USB-A adapter be the first thing you check, they are far from equal and I'm particular to only buy a couple of brands.
Plus USB-A doesn't have the transfer speed capabilities of USB-C.
Richard I'd suggest the USB-C to USB-A adapter be the first thing you check, they are far from equal and I'm particular to only buy a couple of brands.
Plus USB-A doesn't have the transfer speed capabilities of USB-C.
Thanks for the suggestion Leo. I have in fact ordered a USB C 3.0 to USB B 3.0 cable with a claimed bandwidth of 5 gigabits per second, no adapter required. On paper I think that it could deliver 50 frames per second, twice the camera output.
When I get it, I will do some "bench testing" looking also for bottlenecks relating to CPU loading, memory usage (32 GB onboard) and disc writes (SSD). Due to my last minute RDP/Windows Hello issues I had very little time to look at frame rate issues.
Don't be discouraged, any transit capture is a good one. I've attached the prediction of the event and it is low and as a consequence very distant. All those amazing ISS shots are taken when the moon (or sun) is overhead and the ISS is only about 400km away and therefore much larger in angular size.
As it is a moving object, exposure length is critical and needs to be as short as possible even at the expense of gain noise. Use ROI too which will increase frame rate, there is no point capturing blank space around the target.
Keep practising on any events you can - when that really good one comes along, you want to be on top of your game
Richard the SSD theoretically shouldn't be a bottle neck but I believe they are not all created equal. I studied IT back before SSD's were a thing and don't have one myself but I don't need it for my slow gear but worth looking into. I do find brand name items generally better than little known things and there's plenty of information on the specific models with full technical specs.
As mentioned, any capture of the ISS crossing the moon is an amazing capture, not something I'd ever have the eyes or reflexes for now.
Richard the SSD theoretically shouldn't be a bottle neck but I believe they are not all created equal. I studied IT back before SSD's were a thing and don't have one myself but I don't need it for my slow gear but worth looking into. I do find brand name items generally better than little known things and there's plenty of information on the specific models with full technical specs.
As mentioned, any capture of the ISS crossing the moon is an amazing capture, not something I'd ever have the eyes or reflexes for now.
Thanks Leo. I didn't rely on my reflex's or eye sight. In fact, I saw nothing in real time, it was only by viewing the images later (in sequence) that I found the 5 out of 200 frames that showed the ISS.
The basic idea is to wait with the Moon in view, capture images 60 seconds either side of the nominated time and hope for the best. A Moon transit is a good way to image the ISS because you know where to point to scope.
I want to get the frame rate up purely to capture more images in the second or two that the ISS takes to pass through the FOV.
As for the SSD, I think that it is a good brand, may Kingston. When my USB 3.0 cable arrives thus week, I will do some structured testing to gauge hour all think links in the image capture chain are performing. Hopefully, I will be better prepared next time. This time around, I was happy just to see the ISS in five images.
Kingston are generally considered a good brand but it's not just down to brand, as mentioned, I studied IT before SSD's were a thing and I haven't kept up with the technology but I believe brands of reputable standards also have higher quality and cheaper versions in the range.
Who knows, if the cloud ever disappears locally I may attempt an ISS transit one night. Much of my photography has been based around taking multiple shots and hoping for the best (I have a thing with chemical fires in a coffee tin in total darkness. I call them fire spirits).
I was near tempted to take a scope and camera out last night, just for the moon, clearest I've seen it in 3 weeks. I didn't though thinking maybe today but not with the weather again.
Kingston are generally considered a good brand but it's not just down to brand, as mentioned, I studied IT before SSD's were a thing and I haven't kept up with the technology but I believe brands of reputable standards also have higher quality and cheaper versions in the range.
Who knows, if the cloud ever disappears locally I may attempt an ISS transit one night. Much of my photography has been based around taking multiple shots and hoping for the best (I have a thing with chemical fires in a coffee tin in total darkness. I call them fire spirits).
I was near tempted to take a scope and camera out last night, just for the moon, clearest I've seen it in 3 weeks. I didn't though thinking maybe today but not with the weather again.
The camera can deliver 23 FPS @ 16 MP X 10 bits = 3,680 Mb/s, less than the new USB 3.0 cable's 5,000 Mb/s rating.
The documentation for the Kingston SSD claims write speeds of "up to" 2,800 Mb/s which will drop that frame rate to 17 or 18 FPS. This represents the best that I can hope for.
When the USB cable arrives, in the next few days, I will be able to see what real world frame rate is. Factors such as CPU capacity and USB infrastructure capacity could further reduce the frame rate. Hopefully it will be significantly higher that the 3 FPS that I saw the other night.
EDIT: Looking more closely at the SSD specs, my 1 TB SSD has a write speed of 2,100 Mb/s which reduces the maximum theoretical frame rate down to 13 FPS.
The cable arrived this morning and the difference was immediately apparent.
While not recording, the frame rate was 22.5 FPS. With image capture under way, TIFF recording was at a maximum of 15 FPS and was variable, falling as low as 5 FPS.
Both SER and AVI stayed pretty much at 22.5 FPS and were quite steady. AVI had the advantage of using half the storage space. Regardless, the consumption of storage space was quite rapid.
As far as computer resources were concerned, CPU and memory were less than 50%. SSD "usage" was notably higher for SER but not actually saturated. It was less than 50% for SER and AVI. There seems to be no doubt that the USB cable was the bottle neck.
That's the best outcome for you Richard!
Sadly playing with a lot of computer related stuff I've long learned all cables are not created equal.
I too have noticed a wide variation in USB cable performance over the years.
I haven't been too concerned about frame rate until now, even though I noticed it was not very good. The higher FPS will be useful for planetary imaging.
USB 3.0 is 5Gbps … 5000 megabits (Mb) per second => roughly 500 megabytes (MB) per second.
If your SSD is NVMe, then its write speed is likely 2100 megabytes (MB) per second … about 4 x more than the USB speed. While many SSD can’t sustain the maximum for long, the sustained speed is usually more than 1000MB/s.
Fwiw, I feel your pain… I tried a similar capture some years ago and got about 3 frames as the ISS passed over the Moon, and the camera was also a 1600 at max frame rate. It’s not an easy challenge
USB 3.0 is 5Gbps … 5000 megabits (Mb) per second => roughly 500 megabytes (MB) per second.
If your SSD is NVMe, then its write speed is likely 2100 megabytes (MB) per second … about 4 x more than the USB speed. While many SSD can’t sustain the maximum for long, the sustained speed is usually more than 1000MB/s.
Fwiw, I feel your pain… I tried a similar capture some years ago and got about 3 frames as the ISS passed over the Moon, and the camera was also a 1600 at max frame rate. It’s not an easy challenge
Yes, that very thing was niggling at me and I meant to check the Kingston data sheet but I didn't get around to it. It does say 2,100 MB/s which comfortably exceeds both the USB 3.0 cable rating and the maximum anvailble output from the camera.
The bottom line is that I can capture 16 MP at 22.5 FPS, a vast improvement on the 3 FPS that I was getting the other night. It means 20 images or so during a moon transit which will be much better. All I need now is another transit.
