STEP BY STEP

Sky at Night Magazine - - THE SKY GUIDE -

STEP 1

For this process we’ll as­sume we’re us­ing a DSLR at­tached to a tele­scope, shoot­ing sin­gle (non-stacked) images. For best fram­ing, a tele­scope fo­cal length of 1,000mm or shorter is rec­om­mended. Plac­ing M43 close to the mid­dle of the long frame edge works well but make sure it’s got enough ‘space-bor­der’ so the fi­nal image doesn’t look cramped.

STEP 3

Con­cen­trate on the outer re­gions. Take test ex­po­sures to en­sure you’re cap­tur­ing the faint de­tail. Don’t worry if the over­all image looks bright. If the core is look­ing white be­cause of over­ex­po­sure you’re prob­a­bly on the right track! A sim­ple way to cor­rect such an image is to dim it us­ing the lev­els mid-point slider, then tweak the bright­ness and con­trast.

STEP 5

You should end up with one deep image with lots of faint stuff vis­i­ble and an­other which only in­cludes the core re­gion. Open both images in a layer-based ed­i­tor, the deeper re­sult on top. Align them so the stars match. Draw a se­lec­tion re­gion, roughly trac­ing the bor­der of the over-ex­posed core. Copy the se­lec­tion to the clip­board.

STEP 2

Now fo­cus as ac­cu­rately as pos­si­ble. The Trapez­ium clus­ter in the cen­tre of M42 is ideal for this. Us­ing Live View, the four bright­est clus­ter stars should ap­pear sharp and sep­a­rated. Once done, set the cam­era ISO to a low or mid­dle value. Low gives bet­ter tone and image qual­ity, but if your track­ing isn’t per­fect, a mid­dle value al­lows shorter ex­po­sures.

STEP 4

Cap­tur­ing the in­ner Thrust re­gion is more straight­for­ward be­cause it doesn’t re­quire such a long ex­po­sure. A good tech­nique is to bracket your ex­po­sures. Iden­tify what you think is the op­ti­mal ex­po­sure then use in­cre­men­tally shorter ex­po­sures, fol­lowed by in­cre­men­tally longer ones. Now you’re cov­ered if your orig­i­nal as­sess­ment was a bit off.

STEP 6

Paste the se­lec­tion as a layer mask for the up­per layer. In Photoshop, this means hold­ing down the alt key while click­ing the new layer mask but­ton. Click the layer mask in the lay­ers dis­play and ap­ply a fairly large Gaus­sian blur so the sharp edges dis­ap­pear. Tweak each layer us­ing Curves un­til the com­bined re­sult looks nat­u­ral to the eye.

Layer mask but­ton

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