Venus!

[Peter Reader]

In my 2 years of doing this I'd only ever imaged Jupiter and Saturn. But yesterday evening on my casual glance skywards I noticed Venus below the crescent moon and hurried to give it a go.

Mirrors were definitely not correctly cooled as Venus was zooming towards the neighbours' roof.

Very windy, my DSLR shots of the moon were bad so I presume seeing wasn't great (or the wind was too much for the EQ5).

150 stacked frames out of just over 100, processed in registax 5.

The planet doesn't look perfectly spherical in my image... any ideas?

Thanks for looking

Pete

[King]

Nice to see more Venus!

Venus is at gibbous phase at the moment so it's not going to appear spherical. This is a pretty fair first shot at the planet (which is very challenging without certain filters - which I currently lack).

I'd be inclined to use at least 1000 frames (certainly no less than 500) for Venus, particularly while it's low and affected by atmospheric impurities (hence the "rainbow" flicker when viewing in colour).

Aside from that, it's getting nowhere but easier in the coming months so you can expect to fare much better.

I've noticed that in spite of the low frame count your background appears very lacking in noise, which is great although it's an indication that you could go for a higher histogram?

[Peter Reader]

This was the best 100 of just over 100 frames, no filters. I recognised the gibbous stage, what I meant to ask was: how come the lower left looks more bulbous that the top right?

Apologies if I'm about to insult all the imagers here: I've never looked at or changed the histogram in registax... sorry! :/

What does it do / what does it represent exactly?

Thanks for the input King.

[King]

Venus is very twinkly at low altitudes so the frames won't all show the full disc. The trick is to get enough frames that capture enough of it so you wind up with a better whole.

It's essentially during capture time when you most need to check the histogram so it gets quite near the end without going past (which indicates over-exposure). The more you fill the histogram, the more diversities of brightness you are getting and hence (hopefully) more detail.

Basically the histogram shows what variations of light you're seeing with the left being darkest (space) and the right side being the lightest.

I gather the best way to go about Venus is with a W47 colour filter or an IR blocker that doesn't also block UV. I also gather good seeing is required for either method, as is a decent aperture (which I also lack and I imagine you could fare better with.)

This is a solar imaging page but it's good for the purpose of knowing what you should be seeing in your histogram: http://www.hapb.net/Solar/histogram/histogram.html You can even use it to see how in focus you are...

[Peter Reader]

Thank you for all this information. I can't Find a live histogram on Sharpcap. Is there a solution to this? What capture software do you use?

[King]

Actually SharpCap does have a histogram option. It's been a while since I used it now but check the headings along the top that give different options. There's a "histogram" in there. However, I find it weirder looking at it on that than on say... IC Capture (which came with my DMK/DBK cameras).

[Clayton]

Not too bad peter

Definitely you need more frames to work with. Usually 80% at least are substandard, more if the seeing is bad. I recently had to throw out 99.9% of my frames to get an acceptable result in some poor seeing even at 45 degrees elevation.

I can't help with Sharpcap but wxAstroCapture has a Histo display

[Pete Presland]

nice picture and fascinating article on the histogram well worth a read!

[Peter Reader]

I'm probably being dopey, but I can't find this live histogram...

Would love to use it!

[King]

In SharpCap you have the top headings File / Cameras / Focusers / etc.

Under that you have Start Capture / Stop Capture / Object Name / etc.

Right of the Object Name text box is a dropdown which defaults at No Transform. Histogram is the 6th option in the dropdown.

[Peter Reader]

Found it, thank you! I've noticed that when focusing on a bright point of light in a pitch dark room the best focus is when the histogram is "longest".

Thank you very much King, and others!