All sky camera - aberrations

[festoon]

Just testing out my ASI224MC camera last night with the wide angle lens that came with it. I noticed how the stars in the centre of the field were focused but the stars towards the edge were out of focus. 

Is this common to see this much spherical aberration with a wide angle lens with the one supplied by ZWO? Also any recommendations for a lens that gives better results would be much appreciated.

[paul mc c]

I cant answer your question,but really like your pic,could you tell me how you took it please.

[festoon]

1 minute ago, paul mc c said:

I cant answer your question,but really like your pic,could you tell me how you took it please.

Thanks @paul mc c. It was taken using my ASI224MC with the wide angle lens with an exposure of about 25 seconds. The image was auto stretched using AllSkEye which is a fantastic piece of software for all sky cameras.

[AngryDonkey]

A lot of people are using the Arecont 1.55 for their all sky cameras which seems to work well. Also, it looks like either the camera or the lens is at a bit of an angle as the aberration only appears at the bottom of the image. If you get it all centred it will probably be better all round. I went for a Fujinon 1.8mm lens (which is even more expensive) and even then you get some aberration: https://www.allskeye.com/allskeye-live/

Mike

[paul mc c]

42 minutes ago, festoon said:

Thanks @paul mc c. It was taken using my ASI224MC with the wide angle lens with an exposure of about 25 seconds. The image was auto stretched using AllSkEye which is a fantastic piece of software for all sky cameras.

Thanks mate,just downloaded it there,so will give it a go.

 

[festoon]

57 minutes ago, AngryDonkey said:

A lot of people are using the Arecont 1.55 for their all sky cameras which seems to work well. Also, it looks like either the camera or the lens is at a bit of an angle as the aberration only appears at the bottom of the image. If you get it all centred it will probably be better all round. I went for a Fujinon 1.8mm lens (which is even more expensive) and even then you get some aberration: https://www.allskeye.com/allskeye-live/

Mike

Thanks Mike, I noticed that too about the lens potentially being at an angle. Not sure how to fix that as the lens screws into the threaded mount on the camera and the focus is achieved by rotating the lens in the housing.

Thanks for the info on the arecont and Fujinon lenses I'll take a look at them. 

[festoon]

So I got hold of a Fujinon HF1.8HB-L1 1.8mm focal length Fish Eye lens, and indeed it does seem to improve significantly the off axis aberations. Also has given me signifcantly more field of view which is great.

The only strange thing is the exposure times are signifciantly longer than what I've used with the other lenses to get the same image brightness. With the standard ASI224MC lens I was taking exposures of 20s with a gain of 0 (the images in the first post), here I'm taking ~100s exposures with a gain of 135. When I left the gain at 0, the software (AllSkEye) was going beyond 180 seconds to try and achieve a median image brightness the same as before. If anything I was expecting the exposure to go down as the Fujinon lens is 'faster'. Does that mean the transmission or losses of the Fujinon lens are much worse than the fish eye lens that comes with the ASI224MC?

[AngryDonkey]

I think it has more to do with the fact that you have more houses and trees on your image now and less of the sky which reduced the median brightness of the image significantly.

For your night images it is quite normal that the median target is not reached. I would set the max exposure time to 45s and let the auto clip stretch lake care of the image brightness. If you find it is too dark then adjust the auto stretch parameters to give you a brighter image (and/or increase the gain). 

Great image though!

Edited May 27, 2020 by AngryDonkey

[festoon]

Thanks for the advice Mike @AngryDonkey

I'm convinced that in the most recent image I can see M13 in Hercules! Probably I'm wrong but it does look about in the correct place and a bit fuzzy  

[festoon]

Thanks to Jason at Allsky Optics I managed to buy an Arecont Vision 1.55mm 1/2" f2 all sky lens

I have to say its a fantastic lens giving a superb widefield view on my ASI224MC 1/3" sensor. Whats more the sharpness of stars appears great throughout the whole field of view. In my opinion it gives better results that the Fujinon HF1.8HB-L1 1.8mm fl and is light and day better than the all sky lens that was supplied with the ASI224MC camera.

As a comparison the first image is using the Fujinon lens (30/05/2020). This was taken almost a month ago so had much darker conditions. And secondly picture from last night with the Arecont lens (17/06/2020) - still not really dark due to it being mid June UK, but I was very impressed with the images taken

Edited June 17, 2020 by festoon