Has anyone got any webcam focussing tips - JUpiter?

[TerryW]

Hi,

I've been trying to image Jupiter for a while now. I've had numerous distracting issues such as moisture inside my Celestron 9.25 OTA. These are all sorted out now. However, I am still getting fuzzy-brown-melon Jupiter imaging results and I think it may be focus related.

The seeing hasn't been brilliant from Hampshire and I realise this may be a major factor. Does anyone know a clear way of differentiating poor focus from poor seeing?

Currently, I use an spc900 attached to my laptop and Sharpcap to get an image on the screen. I've read and watched every tutorial I can find so I can handle the software (I think).

To focus, I get some moons into focus and then adjust Sharpcap gain and brightness so that I can see equatorial belts clearly. Then I refocus as best I can. The planet is always shimmering wildly using a x2 Barlow which I suppose is down to upper atmosphere moisture and movement. I take a few thousand frames but there is never anything I'd even remotely use as a reference frame.

I am wondering if I have focussing issues and whether there is a tip or trick I can use to avoid wasting time and effort when the seeing just won't support imaging.

Terry

[Psychobilly]

Bahtinov or simple y mask on a nearby star and slew back...?

[lukebl]

I try to focus on a bright star first using a Bahtinov mask, then slew to Jupiter. That does require pretty accurate GOTO, given the tiny field of view, but as you've got an NEQ6 I assume you're using EQMOD and a program like Carte du Ciel?

Having said that, despite getting pretty good focus, I still can't get particularly good Jupiter images! There are obviously other factors which I haven't bottomed out yet.

[Psychobilly]

On the rare occasions that I had a dabble with planetary I used to cheat and autoguide on the planet...

Peter...

[TerryW]

I try to focus on a bright star first using a Bahtinov mask, then slew to Jupiter. That does require pretty accurate GOTO, given the tiny field of view, but as you've got an NEQ6 I assume you're using EQMOD and a program like Carte du Ciel?

Having said that, despite getting pretty good focus, I still can't get particularly good Jupiter images! There are obviously other factors which I haven't bottomed out yet.

I think it is the fine focussing where I am having difficulty. I see the moons as nice points of light which gets me 99% there but Jupiter is still really fizzy.

I guess what I am looking for is something that will categorically indicate that the seeing the issue and there is no way I will get a clear view however hard I work at the focus. Sometimes I mess around for 20 minutes without getting any improvement (or maybe that is the "indicator" that the seeing is too poor).

[lukebl]

I think it is the fine focussing where I am having difficulty. I see the moons as nice points of light which gets me 99% there but Jupiter is still really fizzy.

I guess what I am looking for is something that will categorically indicate that the seeing the issue and there is no way I will get a clear view however hard I work at the focus. Sometimes I mess around for 20 minutes without getting any improvement (or maybe that is the "indicator" that the seeing is too poor).

Not sure how you can definitively test for seeing quality, apart from experience. I think that the low frame rate of the webcam sensor, plus the relatively long exposures required to image (I usually can't image at better than 1/33 or 1/50 second) means that you are more at the mercy of good seeing than one of the dedicated planetary cams like the Imaging Source cameras.

[Anweniel]

Figure that with the C9.25 FL 2350 (4750 barlowed) and the spc effectively c.7mm? you should be getting Jupiter at approx 670x, I'm not 100% but it would suggest to me that atmospheric conditions will be VERY intrusive at this power and I'm not convinced there would be much way around this.

[WayBig]

To focus I tun the brightess right up, aim at a (now very bright overexposed) moon and focus to get the edge of the moon as sharp as I can. Then lock the focuser and adjust the gain, exposure etc. I've made a bahtinov mask, but haven't used that for imaging yet.

Picking up on your point about reference frames. registaxx creates one from a small stack of frames which you then sharpen using the wavelets - so the reference frame ends up looking sharper than individual frames...

Hope that helps a bit. If you posted up some images then I'm sure someone could offer more specific advice.

[michaelmorris]

One thing you might want to look at is exposure. Over exposure can wash out detail really easily. The sharpening process can make this even worse.

Try to underexpose quite a bit. In SharpCap, try to ensure that the black area in the histogram does no intrude more than about 3/4 to 4/5 of the way across the graph (i.e. leave about 1/4 to 1/5 of the histogram as yellow on the right hand side as you look at it)