Video Shooters are Learning the Wrong Exposure Triangle

Video Exposure Triangle

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What if you remove 'Aperture' from the triangle as well?

artsmith's picture

 I am currently adapting a 500mm 'Tamron' Mirror (Catadioptric), lens to work with a Lumix GH5 for wildlife shooting. Those with a knowledge of this lens will realise that it features a fixed aperture of f8.0, and that an ND4 Neutral density kit came with the lens as supplied originally. I shoot video at 50 frames/sec. and a 180deg. shutter opening. It's almost a case of my options not being a triangle, but a two-sided figure if that is possible. Since my video is a semi-hobby retirement interest, (although also a full-time occupation), and must be financed out of superannuation, the operation is thin on finance, more or less ruling out a variable ND filter of around 82mm for the foreseeable future. (And even that is conditional upon a filter being able to be mounted on the front of the lens, since a quick measurement of the thread diameter comes up with 81mm instead of 82mm).

 At the same time, the ND-4 filter screwed into the rear of the lens, plus adjustments I have made to the GH-5 settings now see me within spitting distance of being able to cope with highlights on pure white feathers of White Herons and Royal Spoonbills, even in the brightest sunlight. Recently as an experiment I placed my hand with fingers extended, partly across the lens while in use, and obtained, without any other detrimental effects, an effective reduction in aperture of around one stop without any downsides I was able to see. I am contemplating making a do-nut shaped ring to fit in front of the lens and be trapped in place by the lens-hood when screwed into position. The lens is of such obscenely long focal-length, especially when used on a MFT camera, that a restrictor of the type I have mentioned almost up against the front glass and held securely in place ought to allow me to claw back 1.5 to 2 stops, which would solve my problem based upon my recent experiences. So out-of-focus would the 'do-nut' be that I would not even anticipate very much vignetting, although I would be prepared to settle for a small amount rather than blown out highlights. Has anyone else had experience of this or a similar problem and would my solution work?. I realise that the dimensions of the 'do-nut' would be critical, but I have machine-shop facilities allowing me to finish things off tidily and time to experiment and optimise results. What do the 'experts' out there think? I'd rather like to know.

Ian Smith

Dunedin, New Zealand.

 

 

 

 

 

 

You are, actually, adjusting

jleinung's picture

You are, actually, adjusting the "apeture" with your disks.  The "apeture" of a catadioptric lens is determined by the diameter of the mirror. Your disks are casting a shaddow on the outer edges of the mirror, effectively lessening the diameter, and hence the "apeture." It's an interesting approach. At some point I'm sure you will begin to see some vignetting in your images, and you will have to determine the effective "apeture" of your disks via measurement of your resulting exposures from a common reference, such as a gray card.

Good Luck!!

shutter speed for high motion sports

richa's picture

I wish to disagree in very strong terms with Mr. Wilhelm.  I shoot basketball in gymnasiums and the control of shutter speed is critical to getting sharp, crisp images.   My artistic objective is the ability to review a shot to see a foot on a line, the hand on a ball, and get to as fine a detail as possible.   Slow shutter equals blurry useless footage.  I always shoot 1/120, and go to 1/250 whenever possible. 

I refer to camcorders with 1/60sec shutters as "wedding video" where all detail is washed out.  Such a setting under high motion conditions is not a suitable artistic match up.   

I've recorded basketball for the last 15 years and it has always been a struggle to get equipment and settings which match the needs of this medium.  In earlier years for example Sony used to say "there is no market demand for progressive scan" video.  Try to image how poorly interlace video of basketball looks.  Whatever you image, the reality is worse.  The belief system of "blurry, soft focus images" continues to harm sports shooting options today. 

You can take a look at some of my recent work on youtube, search for Pinewood basketball vs Menlo Jan 12 2018. 
If this comment system permits links, it is here: 

 
Most gyms don't have the light to support 1/250s shutter, but Menlo does.