Cal­cu­late long ex­po­sures

Digital Photograper - - Techniques -

take A test ex­po­sure

Ex­treme ND fil­ters such as the LEE Big Stop­per (ten stops) are too dark to me­ter and fo­cus with the fil­ter in place. You there­fore need to com­pose and fo­cus with­out the fil­ter and take a test shot to es­tab­lish a ‘base ex­po­sure’.

Shoot­ing long ex­po­sures isn’t dif­fi­cult, but you will need to do some maths

cal­cu­late the fil­tered ex­po­sure

You can do the maths (dou­ble the ex­po­sure time for each stop) or use an app such as the ex­po­sure cal­cu­la­tor in Pho­toPills. Here, an ex­po­sure of 1/10sec at f11 and ISO 100 ‘trans­lates’ to 102 sec­onds with the Big Stop­per.

take the fi­nal shot

Fit the fil­ter and switch to man­ual fo­cus so the cam­era doesn’t at­tempt to re­fo­cus. For ex­po­sures of longer than 30 sec­onds, switch to Bulb mode and use a re­mote re­lease to lock the shut­ter open for the cal­cu­lated time.

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