I see it as being dependent on the field of view at capture time, whether you enlarge it afterward or not. You would normally compare the resulting images at the same size to decide which one is magnified more, yes, but the smaller field of view was always more "magnified" to begin with. At least, that's how our brains see it. Looking at 4x6 images, the one with the smaller captured field of view looks more magnified, even if it was captured with a P&S and you "shrunk" all of the images in resolution terms. If they all had the same output dimensions to begin with, where is the post-capture "magnification"?

DAZ has a very good point about resolution though. That would help explain the physics, since the distance of motion projected for a given field of view should be proportionately larger (so faster) in a physically larger image circle. If a physically larger sensor has the same resolution (and therefore more total pixels and greater physical magnification, in terms of detail), then it would be more sensitive to the motion.

That makes a lot of sense to me: sensor resolution combined with field of view, with both accounting for physical magnification. An FF-sized lens on a APS-C sized sensor doesn't change this relationship, because the smaller sensor sees a smaller field of view as well.

Then the guideline works because of the typical viewing resolution of images at that time. Hmm.




This sub-discussion is in reference to the guideline for avoiding visible camera shake in your images when taking handheld shots. We were trying to figure out how it makes sense physically.

It was originally relevant to the OP because the camera seems to follow it, or something similar, when auto-adjusting shutter speed. We kinda got sidetracked though

Ummm, where have you been for the past half-century? It's a well known photographic maxim that, in order to produce a blur-free handheld shot, the shutter speed should be no slower than the reciprocal of the focal length. Any slower and you need a tripod.

Have either of you two heard of Shake Reduction, Pentax has it you know? With a long lens, 1/40 sec might be the lower limit because any movement is magnified but with a wider lens 1/20 sec should be easy unless you have the DT's. Some steady people can handle a slower speed than that.

Nothing is absolutely set in stone, there are always workarounds, lean against a wall or tree for stability, rest the camera on something, practice your breathing. Sorry, I took it was a given that there are obvious limits when hand holding so I should have been clearer previously.

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Last edited by Damn Brit; 04-07-2009 at 12:46 AM.

[newarts]

Regarding the 1/focal_length rule, there are two practical limitations to image motion smear:
1) Image motion during exposure should be less than one pixel on the display.
2) Image motion during exposure should be less than one pixel on the sensor.

Criterion 1 implies the crop factor should be taken into account in the 1/f rule because the smaller sensor will require more magnification to yield the same sized display.

Criterion 2 implies the pixel pitch should be taken into account in the 1/f rule.

The math assumes a constant rate of camera rotation in which case the distance the image moves during the exposure depends on time and focal length as:
Image_motion = (Focal_length)(Rotation_rate)(Exposure_time)

Therefore,
Exposure_time = Image_motion/(Focal_length)(Rotation_rate)

Iowa Dave

[newarts]

Regarding the wandering exposure problem, I think one root cause lies in the nature of the math used by the camera. Exposure doesn't wander, it jumps.

By convention the camera's exposure is set in factor of two steps of ISO, F_stop, and exposure time (stops). This impiles the exposure jumps by at least one stop as the camera is adjusted. But scene illumination is a contiunous measure. Therefore, camera settings can do no better than to bracket the actual exposure requirement with a tolerance of 1 stop.

Most camera's exposure settings are calibrated in fractions of a stop, but these fractions are fairly large, resulting in obvious jumps of exposure as adjustments are made by the camera or user.

Small differences in metering must therefore lead to jumps in exposure.

Iowa Dave

Dave

[Quension]

Have either of you two heard of Shake Reduction, Pentax has it you know?

Oi, page 2!

Sorry, I took it was a given that there are obvious limits when hand holding

And we were discussing exactly what those limits are. Read thread!

Oi, page 2!

Oi yourself, when I responded, you were talking about shutter speed in isolation without any other parameters.

And we were discussing exactly what those limits are. Read thread!

I did read the thread, you were discussing limits without taking into account your individual ability. What you were discussing is only a general guide, if you abide by that you are limiting yourself, I wasn't being facetious. A smaller aperture can increase your chances of reducing blur, changing from single frame to continuous can increase your chances of getting a shot without blur, even the subject matter makes a difference.
The truth is, within reason, you don't know your limits until you try. back at you and to finish on a friendly note.

[Quension]

Oi yourself, when I responded, you were talking about shutter speed in isolation without any other parameters.

True, this is one of those threads where I kept thinking nested quotes would be useful, but was too lazy to do it.

I did read the thread, you were discussing limits without taking into account your individual ability. What you were discussing is only a general guide, if you abide by that you are limiting yourself, I wasn't being facetious.

Oh, no argument from me here. In my case, I was only considering it from the angle of what the camera does and why, not about what I would do.

I actually find SR changes the way I approach this. I figure there are three blur causes from my hands. There's micro-shake, which I simply can't control, but SR can compensate for. There's larger shake, which I can control to some extent (don't OD on coffee, wear a jacket when cold), and SR mostly can't deal with. And there's drift, where I gradually stop aiming at the right spot, which SR can't fix at all.

So when SR is on, I tend to look at the shutter speed and think, "okay, I'm not OD'd on coffee, can I keep the camera aimed properly for 1/4 second or more?" without even worrying about focal length, and let SR take care of the rest. The results are never 100% guaranteed of course, but it makes things simple for me.

[panoguy]

Have either of you two heard of Shake Reduction, Pentax has it you know? With a long lens, 1/40 sec might be the lower limit because any movement is magnified but with a wider lens 1/20 sec should be easy unless you have the DT's.

I wonder how many people today even know what the DTs are?

Anywho... I can't contribute much to the pretzel logic about focal lengths and hand-holding, but I do know that I got two razor-sharp handheld shots in quick succession at 1/20 with a 77mm on my K20. (At ISO 3200 and f/1.8, so no hope of going faster than that!) The "reciprocal focal-length guideline" is a great one to keep in mind, but like "sunny 16" and "let sleeping dogs lie" it is just a suggestion, not a rule. Ignore it when you feel you need to...

Now, the OP is about changing exposures, so I'd suggest "take as many pictures as you can in Manual mode and use Matrix metering to start out." Compare them on the computer by EXIF data (so handy) to see what was best for each situation, and later on go to center-weighted and spot metering and EV compensation, et al. Eventually those "other modes" on the dial like Av and Tv will make more sense by experience, but those books you mentioned are a *great* head start!

-Mark

[OregonJim]

I got two razor-sharp handheld shots in quick succession at 1/20 with a 77mm on my K20. (At ISO 3200 and f/1.8, so no hope of going faster than that!) The "reciprocal focal-length guideline" is a great one to keep in mind, but like "sunny 16" and "let sleeping dogs lie" it is just a suggestion, not a rule. Ignore it when you feel you need to...

I agree - we were merely discussing whether or not the 1/FL guideline changes with sensor size, all other things being equal. We were speaking in general, not targeting any specific camera. Of course, SR (and an individual photographer's ability) will greatly influence the application of said guideline.

[AndrewG NY]

As far as I know, Pentax doesn't alter their program line based on whether SR is turned on or off.

The 1/FL rule-of-thumb was most likely chosen because it is easy to remember and reasonably effective for the dominant handheld cameras in use--that is, those using 135 film.

This is how I explain to myself that the multiplier should probably be applied when thinking of this:

1) If I am shooting a telephoto lens and shake x-amount, the field of view will shift 2%.
2) The same shake of x-amount will cause a wide angle field of view to shift only 0.5%.
3) Things dependent on field of view would normally incorporate that 1.5x multipler.

[Alfisti]

Have any of you shot with compact cameras??? Sweet jebus of course th emultiplier needs to be applied. A small superzoom might have a 10mm lens that is eq to 500mm ... try hand holding that at 1/10th second and get back to me

[OregonJim]

Have any of you shot with compact cameras??? Sweet jebus of course th emultiplier needs to be applied. A small superzoom might have a 10mm lens that is eq to 500mm ... try hand holding that at 1/10th second and get back to me

Have a look further up the thread. We already discussed that.

[Nico]

When I shoot indoors where lighting is limited, I see that the brightness of the picture varies significantly with the f-stop. And I do not understand why this is the case.

Hi, I had a problem that sounds similar to yours. I examined the aperture lever on the lens and it was getting stuck at the wide open end occasionally. The blades were not closing when it was supposed to, therefore overexposing occasionally. I opened the lens, surely enough the screw holding the mechanism that limits the maximum aperture opening was loose.

I am 99.99% sure that the problem is fixed. I lost one of the AF contact spring during the process. I swept the floor with my hands but could not find it. Hopefully replacement is available.

[OregonJim]

I lost one of the AF contact spring during the process. I swept the floor with my hands but could not find it. Hopefully replacement is available.

Maybe cut down the spring from a ballpoint pen? Last time I had a lens open, the contact springs looked to be about the same diameter.

edit: Got a broken digital watch? There's usully a tiny spring in there that connects to the beeper (if the pen spring is too big).

[Marc Sabatella]

The "magnification" doesn't happen until you enlarge the image 1.5x to match the image size of the FF image. That is done post capture.

True. So if you don't intend to enlarge the image - if you never plan to view it on screen or print it - you can safely ignore the "crop factor".

But if you never plan to view it on screen or print it, you could shoot everything at a 1 second exposure, using a coke bottle for a lens and ISO 6400, and never see any issues with your images. You've *got* to magnify the image to see it. And as soon as you do, the crop factor becomes relevant.

[OregonJim]

True. So if you don't intend to enlarge the image - if you never plan to view it on screen or print it - you can safely ignore the "crop factor".

But if you never plan to view it on screen or print it, you could shoot everything at a 1 second exposure, using a coke bottle for a lens and ISO 6400, and never see any issues with your images. You've *got* to magnify the image to see it. And as soon as you do, the crop factor becomes relevant.

Wrong. You have to REDUCE the image to see it onscreen, unless you happen to have a 10 or 14MP monitor (I don't think they exist yet).

Magnification in the context of thread means enlarging a crop-sensor image to the equivalent size of a full-frame sensor image. E.G, to make 8x10 prints from both (assuming resolution is identical), the crop-sensor image must be enlarged 1.5 time the FF image in order for the images to look "similar" (same field of view).