# When should ¹/EFL become ¹/(2 × EFL) to avoid camera shake

Where is the boundary when I should set my shutter speed to ¹ / (2 × EFL) instead of ¹ / EFL to avoid camera shake? (EFL = Equivalent 35mm Focal Length). Let's assume the lens has no image stabilization.

Is it certain megapixels amount? Then how many megapixels should my matrix be to stick the first formula?

Is it a size of pixel on the matrix? Which size this pixel should be then?

Something else?

UPD: The only answer I found is here: Stopping Camera Shake and the 1/(Effective Focal Length) Formula.

• Commented Jul 13, 2016 at 0:03
• Didn't find any exact numbers or certain explanations when should I multiply EFL by two or more. Just general idea to make shorter shutter speed if I have problems. Commented Jul 13, 2016 at 7:24
• Yes, actually — the point in referring to that other question is a) to show that there aren't exact numbers and b) to give background on why. Commented Jul 13, 2016 at 9:26
• Yes, there are no exact numbers, but the general rule which was correct for years (1/EFL is usually enough) now becomes not so correct for hight megapixel cameras (when EFL should be multiplied). This is a kind of a new phenomenon and there should be some signs when should it be rather expected. There should be no exact signs or numbers (like on 20Mp camera you'll going to face it and rather not on 10Mp camera), but at least approximate (you'll find it for 5Ds, but not for 400D). Commented Jul 13, 2016 at 9:39
• Commented Jul 13, 2016 at 17:00

When should ¹/EFL become ¹/(2 × EFL) to avoid camera shake?

When you plan to display at twice the magnification needed to create an 8x10 print to be viewed at distance of 10" by a person with 20/20 vision.

The original 1/FL rule of thumb was based on the assumption of a 36x24mm frame of film being enlarged to an 8x10 print. Even then, if you were planning on printing twice as large many photographic textbooks recommended shooting at 1/(2xFL). The same was (and is) true of depth of field. If you are printing twice as large you need to halve the size of the circle of confusion, which results in DoF half as deep for the same focal length, aperture, and subject distance.

In the current environment, if you are displaying a 24MP image at 100% (one screen pixel per one image pixel) on a 96ppi monitor (a typical 23" 1920x1080P HD monitor, for instance), you're looking at the equivalent of a section of a 60x40 inch print! In that case you would need to use the 1/(6xEFL) formula to reduce the same amount of camera motion allowable for an 8x10 display size to be undetectable.

• Good answer, but the phrase twice as large is potentially confusing. Do you mean 16x20" instead of 8x10", so that the image is twice as large in each dimension or 4x larger in area, or do you mean 11.3x14.1", so that the area is increased 2x? Commented Jul 13, 2016 at 17:00
• Prints are near universally expressed in terms of their linear, not areal, size. Printing twice as large as 8X10 has pretty much always meant printing at 16x20. Commented Jul 13, 2016 at 22:34
• Why leave room for confusion when it's easy to say something unambiguous like "double the dimensions"? What's obvious to you might be misconstrued by a less knowledgable reader. Commented Jul 13, 2016 at 23:02
• Because any 1/FL rule of thumb isn't anywhere near an exact science to begin with. It will vary highly from one individual to the next based on the ability to use proper handholding techniques by several orders of magnitude greater than the difference between 11x14 and 16x20. Commented Jul 13, 2016 at 23:29
• Further, the dimensions included in the final sentence of the answer could be used to infer that references to size are linear: 60x40 is roughly 6 times the linear size of 10x8 (allowing for the different aspect ratio). If we were using areal size the the needed formula would be 1/(30xEFL)! Commented Jul 13, 2016 at 23:32

If you use higher end lenses and 20+ MP sensor, the 2x rule is safer. Safer meaning that there are many factors. Weight distribution of your lens, your camera body, your current physical condition, your current level of adrenaline, your sniper/biathlon training etc. So it is best to watch your shots closely and develop your personal rule.

• > your sniper/biathlon training I guess I need take a couple of lessons :) Commented Jul 13, 2016 at 14:26
• Or just use your longer lens, turn IS off and see what you can do to keep it steady. Your position, breathing, holding... @igorp1024 Commented Jul 13, 2016 at 15:40
• Yes, I use a fairly heavy lens hand held and reckon that the IS basically makes up for the weight difference compared to my previous lighter lens. After hiking uphill you probably need to allow another stop or 2. Commented Jul 15, 2016 at 6:42

If you had a consistent and measurable amount of camera shake, then I suppose you could determine exactly the required shutter speed, and that would depend not only on focal length, but also the lens resolution, sensor properties (crop factor, pixel resolution/density) and how large, and from what distance, you will view the final image.

However the amount of camera shake is highly variable. One photographer may be able to hand hold at 1/15th while another would get blur at 1/60th. So I think figuring in crop factor or pixel size is really pointless when the camera shake is the big variable.

So IMO you start with the 1/EFL as a guide and adjust based on your experience with how that rule of thumb works with your ability to hold a camera steady in your hands. Do some test shots on a wall chart and see for yourself what you're capable of.

• Sorry, but nothing certain. Let's assume, I (and most of the people) can hold the camera still on 10Mp with 1.6 crop-factor. Should I do this on 22Mp FF camera? Should I do this on 55Mp FF camera? Let's say, I'm not looking for my own experience, but experience for most of the people. Commented Jul 13, 2016 at 7:25
• I've updated the question. Commented Jul 13, 2016 at 7:32