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 Changing f stop during shooting 
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Joined: Thu Nov 27, 2014 11:39 pm
Posts: 2
Post Changing f stop during shooting
Hello everyone,

Since I'm new to all this, first of all I want to thank you all for the detailed information related to the time lapse photography. Almost all of your posts I have read and I decided to ask a few questions regarding the holly grail of photography. To give you a short scenario. If i want to take pictures of the sunset and get sharpness across the entire image and its expression of sun rays F number should be above 11. To slow down my shutter speed i need to use ND filters and i understand that part. Combination of those two (F number and ND filters) will give me desired speed of 100 and bellow. When i start the transition itself from day to night in order to achieve clear and sharp stars and the milky way, F stop should fall at or below 2.8, the shutter should go above 20 seconds, ISO should go beyond 1600 and ND filter should be removed from the lens. My question is, how do all of this while the camera takes photos? How do i change F stops during shooting or do i change it at all and when is the right time to do so? Do i have to do everything manually or there is a better procedure? Thank you.


Mon Dec 01, 2014 1:00 am
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Joined: Fri Oct 21, 2011 3:25 pm
Posts: 153
Location: North Bend, Washington
Post Re: Changing f stop during shooting
I think most people *avoid* changing aperture (f-stop) during a timelapse. Remember, unless your subject is really, really close to the lens - you can still get everything in focus at f/2.8 or f/4 - especially on a wide-angle lens. Make sure you understand & know how to look up "hyperfocal distance" (via a chart or smartphone app).

Example - full-frame camera sensor, with 16mm lens @ f/2.8:
Hperfocal distance = 10 feet.
So focus on something 10 feet away, and everything from 5 feet to infinity will be in focus (or at least "acceptably sharp").

On the other hand, if you're deliberately using a needlessly small aperture to create diffraction artifacts (like a sun-star) - then you'll probably have to figure out some way to change your f-stop during the timelapse. Maybe one of the more expensive USB-based intervalometers or a PC app can do this? Or punt and add fake sun-rays later in Photoshop or your video-effects program, if they're really important to you.

Also note that changing f-stop via camera settings means you can't use the "lens-twist trick" to reduce aperture flicker (you'd need full communication between lens & camera).


Mon Dec 01, 2014 11:25 am
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Joined: Thu Mar 10, 2011 11:38 pm
Posts: 585
Location: Exmouth, Western Australia
Post Re: Changing f stop during shooting
Samyang (aka Rokinon) make a range of prime lenses intended for SLR cameras taking video. These have click-free, manual aperture controls complete with 'industry standard' gears which can be driven by standard follow-focus motors. Genuine aperture ramping! The focus ring is also geared.

I've had a look at some reviews of these lenses and they generally get favourable comments.

Kit


Sat Dec 06, 2014 2:31 am
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