Angry Sun - Sunday 21st August

[markt]

Bit late posting this, but here's my full disk from Sunday...

full disk Ha copy by Mark Townley, on Flickr

Hope you like,

Mark

[smerral]

Hope you like,

Certainly do!

[Sam]

Yeah, nice image and a lot going on - very apt title!

[johnh]

Quite remarkable collection of features you got there.

John.

[markt]

Thanks guys!

[PH-R]

Excellent pic, what equipment did you use?

[Carbon60]

Another great image Mark. Love the detail.

Stu.

[markt]

I use a pair of 40mm Coronado etalons @ f20, camera is a DMK31. This is a mosaic of 6 panes.

Just wish the sun would come out long enough again to let me grab somemore images!

[Carbon60]

Hi Mark,

On your Brierley Hill blogspot you mention the use of a flat field image to reduce artefacts (and enhance some detail). Excuse my ignorance, but for the 6 pane mosaic did you produce a flat field for each pane and then combine to make the whole disc image, or did you make the whole disc mosac first and then subtract a whole disc flat field from this?

Thanks

Stu

[markt]

Hi Stu.

At the start of each imaging run I take a flat and dark frame. This is applied to each of the 6 panes automatically in avistack2, each of these panes is then assembled in IMerge and final post processing done in PS CS4.

Thanks,

Mark

[Carbon60]

I see. Thanks for clarifying. Something else to try......

Regards

Stu

[PeterW]

Nice.... Yep I need to hope for some clear skies.

Cheers

Peterw

[markt]

Thanks Stu and Peter!

[stolenfeather]

and an angry sun it is! Mind you, a calm and collected one never offers us good pictures right?

Isabelle

[Photosbykev]

Hi Mark, how are you shooting the flats through the PST?

[markt]

Thanks Isabelle! You're right, an angry sun is the best from an imaging / observing point of view.

Hiya Kev. I'm not using a PST, i'm using a pair of 40mm coronado etalons mounted on a IKI 70mm f6 frac. To get the flats, as i'm imaging with a 2x barlow nosepeice, I can fill the field of view if I centre right in the middle of the solar disk, then defocus the scope so that all surface features melt away, what this leaves is a 'grey image' that still shows up all the dust motes, the dimming at the field edges caused by the barlow, any newtons rings and banding caused by the etalon. I then take an avi of this and avistack2 turns this into a flat frame that it uses when processing the actual data files.

This technique would not work if you are using a cam that gives a full disk view of the sun at the scopes native focal length - eg PST & DMK41, however if you barlow up the focal length so that you fill the chip with sun then it should work. I've not tried it with a PST yet, but hope to soon, in theory it should work though and could get rid of the uneven illumination caused by the PSTs sweet spot... In theory(!)

It is important to remember though, when you have shot your flat frame you should not alter the tuning of your etalon in anyway.

I would wholeheartedly endorse the use of dark frames too for solar work - these show noticeable improvements to an image especially if you are using your cam at higher gain settings and require little extra time or effort to implement.

Thanks, Mark

[Photosbykev]

Thanks for getting back to me Mark. I'm using a DMK41 and 2.5x Powermate so I can centre on the sun and then defocus. I'll have a play next time

[markt]

I'm using a DMK41 and 2.5x Powermate so I can centre on the sun and then defocus. I'll have a play next time

Definitely worth doing Kev