# Why EVF will never replace OVF for me

Started Jan 14, 2014 | Discussions thread
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 Re: science, math, disprove? In reply to canonagain123, Jan 15, 2014

canonagain123 wrote:

let's go the mathematical way then. The EVF has to have a refresh rate of at least 1/24, right? Because the same EVF is used for video in the cameras that have EVF. So the maximum exposure it can get is 1/24s, ISO X, f/X, right? If you take the exposure from my test above, f/1.4 iso 3200 10s, at 1/25s you'd need 30/2^8.5 = 3200 * 2^8.5 ISO 1,158,523 to achieve the same exposure at 1/30.

That's fairly simple math. Can you disprove it?

Human visual sensitivity is on the order of ISO 500-1000 [1][2][3]. We integrate over a 15 second period in very low light situations to see very dim objects. [3][4]

Likewise the refresh rate of the EVF can be independent of the integration time for the sensor. You would end up with ghosting but for slow moving or static scenes (like your white leg of the clothes dryer) this doesn't matter.

Every 1/24th of a second (or whatever desired refresh rate) I can show the image produced by integrating over the prior 10 seconds of time.

Real-time exposure preview tries to simulate this but generally does so by boosting the signal rather than integrating over time. Integrating over the whole 10 seconds and producing a constant output better replicates what the eye/brain is doing but in any sort of normal lighting condition with movement this is a smear. Predictably nobody wants this as the default behavior in their EVF.

The olympus OMD "live time" long exposure feature can kinda sorta do this. [5][6] Since you can get up to 24 previews then for a 12 second exposure you can get a preview every half second. It's not a constant refresh but it's a more useful feature the way it's done. I wish more cameras could do this.

Your math is incorrect because of the incorrect premise. You aren't seeing the white leg of the clothes dryer instantaneously (or 1/24th of a second) but integrated over a longer period of time by your brain. To replicate this behavior is possible in a EVF but generally undesirable.

References:

[3] BLACKWELL, H RICHARD Contrast Thresholds of the Human Eye, OSA, Vol. 36 Issue 11, pp.624-632 (1946)

[4] Clark, R.N., Visual Astronomy of the Deep Sky, Cambridge U. Press and Sky Publishing, 355 pages, Cambridge, 1990

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