NEXT STEPS in as­tropho­tog­ra­phy

Some of the ad­vanced equip­ment and tech­niques used by ex­pe­ri­enced as­tro im­agers to cap­ture stun­ning images

Sky at Night Magazine - - NEXT STEPS IN ASTROPHOTO­GRAPHY -

The Moon and plan­ets

While imag­ing the Moon us­ing a DSLR cam­era at a scope’s prime fo­cus gives good images, slot­ting a high frame-rate (HFR) cam­era in at prime fo­cus on a sim­i­lar setup will de­liver WKH EHVW UHVXOWV 7KH OHV FDPHUDV OLNH ZWO’s ASI120MC-S (£151) or the Ce­le­stron NexI­mage Burst Im­ager d FDSWXUH DUHQ W WKH QLVKHG pic­ture, though: they need to be pro­cessed with spe­cial­ist soft­ware.

7KDW V EHFDXVH +)5 FDPHUDV WDNH video rather than still images, which typ­i­cally con­sists of hun­dreds of in­di­vid­ual frames a sec­ond. This helps over­come is­sues with bad VHHLQJ $Q +)5 FDPHUD V YH VHFRQG video with, say, 600 sep­a­rate frames will record many more mo­ments when the tar­get’s seen through a still at­mos­phere than the one ex­po­sure a '6/5 FDPHUD WDNHV LQ WKH VDPH WLPH

6SHFLDOLVW VRIWZDUH OLNH 5HJL6WD[ RU $XWR6WDNNHU­W LV QHHGHG WR VHSDUDWH the video into in­di­vid­ual frames, and then elec­tron­i­cally com­bine these IUDPHV LQ D SURFHVV FDOOHG VWDFNLQJ ,W V ZLWK +)5 FDPHUDV DQG VWDFNLQJ WKDW H[SHULHQFHG LPDJHUV WDNH WKHLU best pho­tos of the plan­ets too.

The Sun

Our star is so bright it poses a real dan­ger to eye­sight and equip­ment, VR FDUH PXVW EH WDNHQ WR NHHS WKH ends of any tele­scope pointed at the Sun cov­ered with ei­ther end caps or a spe­cial­ist VRODU OWHU

There are dif­fer­ent W\SHV RI OWHU WKDW FXW out most of the en­ergy of the Sun’s light. White OLJKW OWHUV XQGHU d al­low a tiny por­tion the Sun’s spec­trum through and show de­tail on the Sun’s vis­i­ble sur­face. Hy­dro­gen-al­pha DQG &DOFLXP . OWHUV RQO\ VKRZ light from those re­spec­tive parts of the Sun’s full spec­trum, but these are ex­pen­sive (around £2,000). They do, how­ever, en­able so­lar im­agers to use large aper­ture tele­scopes to cap­ture stun­ning de­tail at dif­fer­ent lev­els on the Sun’s chro­mo­sphere.

7\SLFDOO\ D OWHUHG WHOHVFRSH VLWV RQ D GULYHQ PRXQW WKDW WUDFNV WKH VN\ at the same rate it would the stars. As for cam­eras, the same ad­vice ap­plies: a DSLR cam­era at prime fo­cus is good but an HFR cam­era is bet­ter.

Gal­ax­ies and neb­u­lae

The chal­lenge with gal­ax­ies is they are so faint that cap­tur­ing enough of their pho­tons to pro­duce de­cent images re­quires long ex­po­sures and LQFUHGLEO\ DFFXUDWH WUDFNLQJ So a sturdy, well-aligned mount and WULSRG DUH NH\ (4 RU (4 W\SH mounts (£550 and £1,250 re­spec­tively) are pop­u­lar choices. Though Go-To isn’t nec­es­sary, a mo­torised RA axis WKDW WUDFNV WKH VN\ GXULQJ ORQJ H[SRVXUHV LV D PXVW ([SHUW LPDJHUV RIWHQ NHHS WKHLU VHWXS RQ WUDFN E\ ‘au­to­gu­id­ing’ it; cor­rect­ing any drift with a sep­a­rate scope, FDPHUD DQG WUDFNLQJ soft­ware. '6/5 FDPHUDV ZRUN well on gal­ax­ies, though their sen­sors can be­come hot dur­ing long ex­po­sures, in­creas­ing un­sightly noise. To com­bat this, spe­cial­ist CCD RU &026 FDPHUDV OLNH WKH ZWO ASI071MC Pro Cooled d RU WKH $WLN +RUL]RQ d have built-in fans to cool their sen­sors. Pro­cess­ing is im­por­tant here too: typ­i­cally many cal­i­bra­tion frames are FRPELQHG ZLWK WKH QDO LPDJH WR re­move noise and hot pix­els us­ing VRIWZDUH VXFK DV 'HHS6N\6WDFNHU

The Atik Hori­zon is an ex­am­ple of what’s known as a cooled cam­era – a fan keeps the sen­sor from over­heat­ing dur­ing long ex­po­sures

A sin­gle frame taken by an HFR cam­era will look like the image on the left, but many such images can be com­bined, or ‘stacked’, to pro­duce the fi­nal image (right)

You can view the Sun with a range of kit, from spe­cial­ist so­lar tele­scopes to fil­tered in­stru­ments

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