ASI120MM first light

Hi,

After seeing Tony's Saturn images with his ASI120MC I decided to get the mono version to update my now aging webcam for planetary photography.

First light was with my Coronado PST. Since we finally have some sunshine I should make the most of it!

I've always found imaging with the PST very tricky. The eyepiece holder does not separate on my model so, webcams can't get focus without a barlow, DSLR's need eyepiece projection, and even then getting the exposure right on colour chips is hard. I never really got images i was happy with.

The ASI120MM suffers from the same focus issue as webcams so a barlow is needed if you use the nosepiece adapter. Looking at the live frames to focus (I used firecapture) is quite easy with a monochrome camera and it's also easy enough to get a well exposed image. For the first time with a camera and the PST I was able to spend quite a bit of time just looking at the sun on the laptop monitor and slewing to look at different features.

I took some video frames from firecapture, with different exposures to being out different features, and after running through registax and gimp produced this:



Not bad for a first effort. Though I need to come up with a better focusing method. Also newtons rings are very obvious, I may be able to remove those, or at least widen them so they are not so obvious by moving the camera's plane slightly. Thats work for another day.

Next I decided to see if I could get focus without a barlow. You can't with the nosepiece. However if you unscrew that and connect it to the scope with duck tape (patent pending ) it focuses fine:


With that setup you can almost capture the full disk in the frame:


Focusing is a bit more forgiving without the barlow. There are no newtons rings this time, possibly due to the lack of barlow, but I suspect mostly because the camera isn't as accurately perpendicular to the light path so the interference just doesn't occur. More experimentation needed there.

Anyway I'm happy with it so far. The resolution is quite high at 1280x960, with 3.75um pixels, so the sensor itself is quite small. It does support 'region of interest' so at a 'standard' webcam resolution of 640x480 it can do 113fps. So I'm looking forward to trying this on planets now that I have a filterwheel to play with.

I've never used any other dedicated planetary cameras, DMK etc., so I cant give a comparison, but for $298 +shipping etc. it's certainly one of the cheaper options and so far has performed better than I'd expected.

Hi Albert,
Good to hear you got the ASI 120mm form Sam and nice first light report. Yeah you got to work on the those newtons rings but good capture all the same, second image is excellent, you could be right about the camera not being square or the like. I can’t remember maybe 3 or 4 months ago there was a lot talk and advice on cloudy nights on how to correct this, worth checking it out.

Enjoy your new camera.
Well done,

Tony

Thanks Tony. Sam was great to deal with, he answered the couple of questions I had and the camera arrived quickly.

Good to know the rings issue was mentioned on cloudynights. I'll have a search over there. There is so much contents on that site now that it's hard to search and find the little gems of great advice that are on there.

Cheers,
~Al

Really great pics Albert. Looks like your PST is a very nice sample. That second pic is worthy of a Spaceweather frontpage feature.

Those ASI's are excellent. I've just been doing the same thing with a QHY5L-II mono. Same chip as the ASI120. It was a tossup between the two which one to get for me but already have another QHY and stuck with the brand.

Not sure if it's the same with the ASI but I noticed that the Newton rings depended heavily on what exposure/gain settings I used and were far more obvious in Firecapture when using 16-bit mode

Trev