Settings for Planetary Imaging - ASI1788MM

Discussions of using SharpCap for Planetary Imaging
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Stub Mandrel
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Settings for Planetary Imaging - ASI1788MM

#1

Post by Stub Mandrel »

I have just come by an ASI178MM and I am struggling to decide what the best settings are.

The recommended 'lowest read noise' settings are high values for gain and brightness/offset.

I found the high brightness just made everything very noisy, and in the end used high gain, minimal brightness and a stretch so I could see what was happening. I was imaging R, G, B, L (UV/IR cut) and IR pass, all had similar sensitivity except IR cut which needed twice the exposure (which was OK as it improved the seeing a lot).

Results seemed OK but noisy. I am using an x3 barlow with a 150 x 1200 mm scope so obviously quite a slow combination, but the results seem rather dark compared to my ASI120MC. I guess this is partly due to smaller pixels (about half the area) but the effect seemed more severe than I would have expected.

What sort of settings (gain, brightness, exposure) do you use for this camera for typical targets (e.g. Jupiter, Saturn).
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oopfan
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Re: Settings for Planetary Imaging - ASI1788MM

#2

Post by oopfan »

Hi Stub,

Other members can speak more authoritatively on the topic of planetary (and lunar) photography, but I'll give it a go:

1. For planetary (and lunar) photography, you want to select a combination of gain, exposure, and region-of-interest (ROI) that achieves a high frame rate; a good target is 40 frames per second (fps). Things that increase the frame rate include: a smaller ROI, a shorter exposure, and higher gain. Dave (turfpit) can explain what the ideal histogram looks like.

2. Regarding gain, you are correct that high gain produces the lowest read noise, but the planets are much brighter than deep-sky objects, so read noise is a minor factor. Generally, I choose the lowest gain setting for the primary reason that it offers the highest dynamic range. That leaves you to tinker with ROI and exposure. After you find a combination that yields a high frame rate, then I would tweak the gain until the histogram looks about right.

3. Lastly I would adjust the offset according to the gain you chose. There is an inverse relationship between gain and offset, regardless of the type of photography you are engaged in. The rule of thumb is "the lower the gain, the higher the offset needed." Dave (turfpit) can point to many past posts that discuss how to discover the optimum setting. All CMOS camera owners should keep a cheat sheet of the minimum offset needed vs gain setting. There is no need to increase the offset higher than the minimum, in fact it is discouraged.

Brian
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oopfan
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Re: Settings for Planetary Imaging - ASI1788MM

#3

Post by oopfan »

One final thought:

Years ago I had a 75mm x 1200mm refractor. It was great for planetary even without a Barlow. In your case I suggest not using the Barlow, at least to begin with. It will yield the brightest image and a high frame rate. Process, then see how it looks when you zoom in. Then try 2x or 3x drizzling to see if it helps. Good focus is very important. Also you should capture at least 5 minutes of video (SER file format). During processing, reject 80% of the frames.

Here is a video I made about lunar processing. Many of the same tools and techniques are valid for planetary:
https://rumble.com/ve87ot-how-to-proces ... a-pro.html
I used a 71mm x 418mm refractor. It is not the best scope for this type of work, but the results are gratifying.

Brian
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turfpit
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Re: Settings for Planetary Imaging - ASI1788MM

#4

Post by turfpit »

Stub

https://www.thelondonastronomer.com/it- ... ry-imaging will get you started. The author of the article will have gone through much to get to that level of final result.

This was my first attempt with Jupiter at 14° elevation viewtopic.php?f=16&t=2940.

Note the shape of the log histogram - the classic 'whale' shape indicates the settings for gain/exposure/brightness are about right. Generally, set brightness/offset/black_level to 0 for planetary/lunar as we will lose no faint data with a bright object against a black background.

5 sets of LRGB data is probably ambitious - it might be better to start off capturing a set of L data and process that to understand the workflow. If you use the Barlow then exposure will need to be increased which lowers the fps. Capture in 8-bit mode to ensure fastest fps. The Barlow can always be added later. As Brian mentioned, drizzle is worth looking at, drizzle 1.5x and 3.0x can be found in Autostakkert.

A search on damian peach LRGB planetary will turn up useful background material for this aspect of astro-imaging.

This Astrobin search for ASI178 https://www.astrobin.com/search/?q=asi178&page=1 gives some idea of the camera's capability - the images seem predominately solar.

Dave
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Stub Mandrel
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Re: Settings for Planetary Imaging - ASI1788MM

#5

Post by Stub Mandrel »

Thanks folks, I've been doing planetary for a long time now, with webcams and then an ASI120MC. I experimented with mono using a Toupcam but struggled with settings.

There are some useful tips in those links, especially about histogram settings for different targets. I really struggled to get a good histogram at the same time as a decent frame rate (I was getting 40-80 fps, using RoI) and I appreciate this is in part due to the x3 barlow on an already slow scope, but I am used to getting a pretty decent live image with the ASI120MC (at least before Windows changes made it really unstable).

I worried the ASI178MM was turning out like the Toupcam, in the end I did get some decent data.

I am comfy with issues like focusing, use of ADC, processing etc. My concern is that despite decent final results, I felt that the captures were rather noiser than I expected and didn't seem to be anywhere near as bright as with the ASI120MC. That said they seem to show a bit more detail than ASI120 images.

The Saturn is 3x drizzle, then downsampled to 1.5, Jupiter is just 1x.

Image

Image
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turfpit
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Re: Settings for Planetary Imaging - ASI1788MM

#6

Post by turfpit »

Stub

I saw these images on an iPhone which gives a much tighter display. I would say these are pretty decent images.

Dave
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Stub Mandrel
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Re: Settings for Planetary Imaging - ASI1788MM

#7

Post by Stub Mandrel »

Thanks, I'm sure they could be even better if I can get the settings sussed though :-)
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