60D Program Mode Shutter Selection

[crojai]

My question concerns program mode with 60d/ 18-55mm stm lens - my understanding is that in program mode the camera tries to use a MINIMUM shutter speed compatible with focal length selected, ie at 18mm...1/18sec...55mm...1/55sec approximately. When I tried it, at 18mm it selected 1/30sec which is ok, but at 55mm it selected 1/15 sec!!! way too slow for handheld at 55mm.  Does anyone have any ideas on this. I put ISO on 'auto' so it would not be a factor.  Thanks as this is driving me nuts!

[TCampbell]

I have not come across anything that documents the algorithm for how Canon program mode choose the exposure settings.

It's unlikely that it is as simple as always going for the minimum shutter speed and a quick test with my f/2.8 lens attached (while using Program mode) reveals that it's often happy to use a middle aperture even when a lower aperture would allow for a faster shutter speed.

My "guess" (and this is purely a guess because as I said... I've never seen anything that documents how the algorithm works) is that it's looking for "safe" exposures.  In other words... avoid extremes.  Try to get the shutter speed fast enough to deal with the focal length of the lens when possible.  I suspect it tries to avoid shooting with a wide-open aperture and also tries to avoid shooting with an excessively stopped down aperture.  But this presumes there's enough light that the camera has lots of adjustment latitude.

If you back the camera into a corner by depriving it of light to see how it behaves when it's desperate to get anything at all...  you may see different behaviors.

Don't forget that the camera offers "program shift" and that's sort of the whole point of Program mode and what separates it from shooting in full auto.  In "program" mode the camera comes up with an initial set of exposure settings just as in auto.  But unlike auto, you can roll the main-dial (the one near the shutter button) to scroll through all the equivalent exposures which are also possible given the metering... as well as using the rear dial to use exposure compensation.

[crojai]

Actually I did find some information on the programming of the program mode which gave rise to my question.  If you google 'program mode program line canon' you get a link to cpn.canon-europe.com which gives a really good explanation of this.  It's just that I can't find the charts for the the 18-55mm.  I've read before that the system is suppposed to try to select a shutter speed compatible with handheld shots as a start so I was pretty surprised it was so far out.   I would really like to find the 'program line' for the 60d/ 18-55mm. 

Thanks for all the input. I'm hoping someone out there can point me in the right direction.

[hsbn]

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@crojai wrote:

Actually I did find some information on the programming of the program mode which gave rise to my question.  If you google 'program mode program line canon' you get a link to cpn.canon-europe.com which gives a really good explanation of this.  It's just that I can't find the charts for the the 18-55mm.  I've read before that the system is suppposed to try to select a shutter speed compatible with handheld shots as a start so I was pretty surprised it was so far out.   I would really like to find the 'program line' for the 60d/ 18-55mm. 

Thanks for all the input. I'm hoping someone out there can point me in the right direction.

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I think you mis-understand the "program line". It pretty much gives you an idea of how the camera calculate aperture and shutter speed for automatic exposure if you are curious. By knowing the line of your lens, it would not help you with anything. But if you want, you can calculate and graph it for your lens.

Back to your original question, you asked why at 18mm your shutter speed is 1/30s and at 55mm your shutter speed is 1/15s. The Canon "program line" in short says that Aperture will not be increased at least until reciporal of focal lenght is reached. At 18mm, your lens aperture is 3.5 and and at 55mm your lens aperture is 5.6 which is 1 1/3 stop slower. Thus, for a given scene, your 18mm f3.5 1/30 will be 55mm f5.6 1/5s.

This is purely my speculation but I think the camera takes into account the IS on your lens. The camera thinks that with IS enable, you can shoot handheld at 2-stop slower. So instead of having to pump up the ISO (or the ISO already reached its limit), they just low down the shutter speed. The correct exposure is F5.6 1/5s. But the camera thinks "it's too slow, the shutter speed need to reach 1/focal length taken IS into account. So ISO will be increased until 1/15s". Again this is just purely speculation.

[hsbn]

I think you are missunderstanding the Program Mode (P on the dial). Program mode is just a fully automatic shooting mode but you can override many different settings like TCampell said.

What are you referring to (I think) is a feature of the AUTO ISO. Newer Canon cameras has an option in AUTO ISO where you can choose when the camera bump up the ISO (Not sure if 60D has this function). Under this options, you'll have several settings (1/125, 1/250, 1/100, AUTO, etc.). For example, if you choose 1/125, then the camera will increase the ISO whenever the shutter speed fall under 1/125 to maintain the exposure. If you choose AUTO setting, the iso will be increased based up the reciprocal of the focal length.

[Skirball]

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@hsbn wrote:

What are you referring to (I think) is a feature of the AUTO ISO. Newer Canon cameras has an option in AUTO ISO where you can choose when the camera bump up the ISO (Not sure if 60D has this function). Under this options, you'll have several settings (1/125, 1/250, 1/100, AUTO, etc.). For example, if you choose 1/125, then the camera will increase the ISO whenever the shutter speed fall under 1/125 to maintain the exposure. If you choose AUTO setting, the iso will be increased based up the reciprocal of the focal length.

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I'm pretty sure only the 1Dx, 5d3 and 6D offer that.  Although, Magic Lantern also has similar functions and I believe it allows more customization.

[cicopo]

I've never ever read that the camera would use 1/focal length or faster either. It may have on some occasions but I doubt it's a built in function.

[hsbn]

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@cicopo wrote:

I've never ever read that the camera would use 1/focal length or faster either. It may have on some occasions but I doubt it's a built in function.

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It's a built-in function for Auto ISO. You can read more HERE

Here is an excerpt:

"Until now, one problem that kept many pros away from Auto ISO was that there was no meaningful control over how slow a shutter speed might be selected in low-light conditions. But with Canon’s recently introduced SLRs, the photographer can tailor Auto ISO to give exactly this type of control. A separate menu entry, Minimum shutter speed, provides the following settings:

• Auto: Camera will continue to try to maintain a shutter speed of at least 1 over the lens focal length, changing ISO to maintain this as long as possible. The camera will tend to pick lower ISOs and slower speeds when using standard or wide-angle lenses.
• User-defined shutter speed: Photographer can pick a speed from 1 second to 1/250 of a second and the camera will only go below this shutter speed after it has raised its ISO to the highest available setting, based on Maximum ISO set by the user under Auto ISO range."

[cicopo]

Good thing we hope to learn something new every day because I've done it now. Thanks.

[TCampbell]

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@hsbn wrote:

It's a built-in function for Auto ISO. You can read more HERE

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That's really good to know.  I'm one of those people who _never_ uses auto-ISO because I have no control over it.  I tend to learn about and use most of the features of a camera, but up until you posted this, had no idea that this was available on my 5D III.  I think I may just have to give this a test spin and see how it works.

Thanks!!