STM lens on non-STM camera

Hello everyone (first post in the new forum software - weeee!)

There are a number of benefits to STM focus compared to the regular (non-USM or otherwise special) focus mechanisms.

However, I understand that in order to fully benefit from the silent focus, constant focus rate, focus speed, etc... one needs a camera which was designed with the STM in mind.

What happens when the camera pre-dates STM (i.e 7D)? What is the focus like in that case? What is the difference between the focusing?

Thanks,
Robert.

I haven't tried video but STM works fine on my Rebel T3. It feels a little weird still having to hold down the focus button (I use back-button focusing) in order to manually focus.

DGStinner wrote in post #17304926
It feels a little weird still having to hold down the focus button (I use back-button focusing) in order to manually focus.

I didn't know about this. Do all STM lenses focus with the AF motor even when using the manual focus ring?

yellowt2 wrote in post #17304955
I didn't know about this. Do all STM lenses focus with the AF motor even when using the manual focus ring?

Curious about that as well... first time i hear about this.

According to Wikipedia "Unlike USM, STM lenses use focus-by-wire to enable full-time manual mode. Two main disadvantages are linked to focus-by-wire: First, the need to computationally process the input before the intended action is executed leads to a sometimes perceptible lag. Second, using the motor needs power, so when an STM lens is not connected to a camera or the camera is switched off, changing the focus is impossible."

Wow, didn't realize that; never had an STM lens.

Off topic, but does anyone know how well STM lenses work on adapters? Obviously a non-powered adapter will not allow focusing.
I assume the EOS-M with Canon EF adapter will still allow normal operation? Does manual focus work? Do you have to hold down a button (like DGStinner mentioned with the T3) to enable it?
What about other combos? For example I use Canon EF lenses on a Sony A7 with Metabones adapter; auto-focus works (slowly) and IS works, so I know power is sent to the lens; would I be able to manually focus an STM lens? The Metabones description doesn't seem to mention STM anywhere.

I think I'll just stick with USM lenses...

primeone wrote in post #17304893
Hello everyone (first post in the new forum software - weeee!)

However, I understand that in order to fully benefit from the silent focus, constant focus rate, focus speed, etc...one needs a camera which was designed with the STM in mind....?

Thanks,
Robert.

Well yes; the STM is just a different type of focusing mechanism! It's major advantage is that it offers silent, smoother and constant focusing ability; which is better for camera's that have video capability.

USM, as I've read and understand, is still slightly faster and considered professionally oriented. It doesn't offer the smooth focus or silent focus ability; but instead snaps into focus very quickly. This is perfectly acceptable for still photography but too jerky/noisy for video.

Hypothetically speaking, IF Canon made two lenses completely identical but one with STM and the other with USM; you'd simply select the lens that best suited the camera you have.


Having said all that, the STM lens will perform perfectly fine on any DSLR that doesn't have video ability. You can go to the following website for a direct and interesting comparison.

http://petapixel.com …g-the-70ds-dual-pixel-af/

Ralph

The four types of focus drive Canon offers are:

1. Manual only (i.e., Tilt Shift lenses, 65mm Macro).

2. Micro motor (i.e., 50/1.8 II, many others that aren't marked USM or STM)... Least expensive, but slower, noisier, and it can be more erratic. For example, the 50/1.8 is said to be virtually impossible to Micro Focus Adjust, because it rarely refocuses exactly the same way with successive attempts. Cannot/should not manually override focus while the lens is set to autofocus. Have to turn off AF at the switch first, otherwise there's risk of damaging the lens' focus mechanism.

3. STM or Stepper Motor drive is relatively new and was developed especially with videography in mind, but certainly works fine for still photography too. Adds a little cost (approx. $50 per lens), but is a little faster and a lot smoother than micro motor. It's also very quiet. It is "focus by wire", which means that the manual focus ring will merely turn unless power is applied to the lens (half-press of the shutter release button, unless using Back Button Focusing method in which case that button must be pressed). This probably won't work in what Canon calls the Basic Exposure mode settings found on many of their cameras (the highly automated "Scene" modes: "Running Man/Sports", "Mountain/Scenic"). Camera needs to be in what Canon calls the Creative Exposure modes (Tv, Av, P, M).

4. USM or Ultrasonic Motor drive has been around for quite a while and is the fastest and most accurate/consistent. Usually the most expensive form of drive, found mostly on mid-grade to premium lenses. Not as quiet as STM, but very quiet none-the-less. In most cases it allows for what Canon calls FTM or Full Time Manual override of autofocus, meaning you can manually operate focus at any time without harm to the lens (but see Note 1 below). This is useful when refocusing, for example, and wanting to throw the lens out of focus.

Note 1: Some USM lenses use what's described as a "hybrid" form of drive. The EF 50/1.4 is one example. Some folks feel this drive system is prone to rapid wear and tear if FTM is used a lot with it.
Note 2: A few USM lenses are "focus by wire", too, but can be manually focused so long as they are mounted on a camera and the shutter release button is half-pressed. The EF 85/1.2L II is an example of this. This is same as STM lenses.

I don't use any STM lenses so really can't say about "STM-compatible" cameras.... My understanding was that STM is fully usable on all EOS for still photography, can be used to shoot video on any EOS capable of it, but had some unique advantages for videography, in particular, when used in combination with "STM-compatible" cameras. Since I don't shoot video with my DSLRs, either, I really don't know the advantages offered by using an STM lens on an STM-camera.

In cases where there are both micro motor and STM versions, the STM version of a lens is often the latest and most updated, so might also benefit from other improvements optically or functionally.

You don't have to half *hold* the shutter button. The difference between focus-by-wire (STM, 85/1.2, 800/5.6) and regular lenses (everything else) is that your camera has to supply power to focus. Do this by tapping the shutter button to start the metering. As long as your meter is showing, the focus should work.

In my experience STM lenses are generally just as fast or faster than USM lenses of the same size.

http://youtu.be/pmrvBc​XYcwU

From slrgear.com for the Canon 24mm STM:

Whatever "full-time manual focus" means

Edit: "The final control on the lens barrel is a focus mode switch with the usual AF/MF settings. Note that this lens offers full-time manual focusing even when AF is selected." (from photographyblog.com)

Cgb628 wrote in post #17307514
You don't have to half *hold* the shutter button. The difference between focus-by-wire (STM, 85/1.2, 800/5.6) and regular lenses (everything else) is that your camera has to supply power to focus. Do this by tapping the shutter button to start the metering. As long as your meter is showing, the focus should work.

Just to add to this, I've got my 7D and 24 2.8 STM pancake sitting right next to me, so I tried this out. Tapped the shutter, activated the meter, and could manually focus no problem. I kept racking it back and forth, after the meter went inactive (I think I've got mine set for 6 seconds), I could continue racking focus. Once I stopped racking back and forth, though, I couldn't resume focus until I reactivated the meter. Interesting behavior..

The camera will explode.

Here is what I have noticed with all my STM lenses:

In One-Shot Auto Focus, the focus can be fine tuned (Full Time Manual focus) anytime the shutter is half pressed. As soon as you take your finger off the shutter the STM AF goes dead. (really more like part-time manual focus)

In AI Servo Auto Focus the focus ring is always dead and you can't do manual focus over-ride or fine tune the focus.

In Manual focus the focus ring will be active while your finger is on the shutter button, OR while the metering is active. It will also continue to operate with your finger off the shutter button, but the lens will "go to sleep" after approximately 5 seconds after the metering stops. You won't be able to focus again until you half-press the shutter and start the metering.

But......If you continually adjust the focus ring, the STM Manual Focus will continue to operate for as long as you keep moving it. (even long after the metering has stopped). If you stop adjusting the focus ring, the lens will go to sleep again after 5 seconds. A quick tap on the shutter button starts the metering again and the STM focus will operate again.

amfoto1 wrote in post #17305475
.... For example, the 50/1.8 is said to be virtually impossible to Micro Focus Adjust, because it rarely refocuses exactly the same way with successive attempts. Cannot/should not manually override focus while the lens is set to autofocus. Have to turn off AF at the switch first, otherwise there's risk of damaging the lens' focus mechanism.

This part is incorrect. The 50 f/1.8 MFAs consistently and just fine, at least the three I have tried do; any inconsistencies are not due in any way to the micro motor, which (while slow and noisy) is very accurate and repeatable. The focusing problem is due to residual aberrations which affect the AF algorithms reading the AF sensor. And there is no confirmed case of the lens being damaged by manual focusing in AF mode; it is very prone to backlash and feels terrible, but it doesn't damage the gear train or focus helix.

Here's a good article on the lens (scroll down further for details on breaking the lens by turning the focus ring) :

http://www.dpreview.co​m …digital-photography-myths