To Sigma: SD Quattro manual focus at the shooting aperture?

[Tom Schum]

Or autofocus for that matter.

As it is, the camera can be focused in manual mode and then when the shot is taken the focus is off. I am having this problem with certain settings of the 50mm f2.8 DG Macro lens, one of many legacy Sigma lenses not found on the official compatibility list.

If during manual or aperture priority, we had the option to actually operate at the chosen shooting aperture, focus could become certain manually, and maybe even automatically if there was enough light for that in the scene.

This could be enabled by a menu item to be added in a new revision of firmware, unless I am missing something that is already there. If I am missing this please let me know what setting to change.

The main thing for me is to have the certainty that optimum focus is actually attained, before triggering the shutter.

As it is, the Sigma lenses focus at full aperture then stop down to shooting aperture, and if there is no compensation table in the camera the focus can be off.

About the only way to focus these lenses with complete certainty is to focus at maximum aperture so that the camera won't stop down during shooting.

The other way to do it is to use a completely manual lens such as a Samyang, which does not allow the camera to control its aperture. I guess for Sigma use, I'd have to buy a Nikon mount Samyang and use an adapter to get to SA mount. Or, I can use my 40-year-old M42 lenses, but I won't be getting modern performance out of most of them.

Yes I know that all I have to do is buy a global vision lens from Sigma (A, S, or C), but that's going to get expensive.

 

[Scottelly]

Don't the lenses all have a switch to set them to manual focus mode? If so, you can switch off auto-focus, and the focus will not change as the camera shoots the photo, right?

 

[dr.noise]

Don't the lenses all have a switch to set them to manual focus mode? If so, you can switch off auto-focus, and the focus will not change as the camera shoots the photo, right?

Not quite right.

The usual focusing method is doing it with the aperture fully open. That way you will get all the available light to better see the details, and also narrower depth of field so you would easily see where the focus is.

AF cameras with AF lenses all use this method, as far as I can tell. Actual aperture close happens at shooting time.

OP's concern is about the focus shift that may happen after the aperture is closed (Without physically refocusing the lens).

This sounds unbelievable, but is technically possible. I have an old manual lens that behaves exactly that way - on different aperture settings it need to adjust the focus differently. I don't know the mechanics of this, all I can say these lenses are extremely rare and perhaps are all in the past.

Modern AF lenses should not behave like that so I think OP's concerns are not as real as they seem. Except he's got that exact rare lens.

 

[xpatUSA]

Or autofocus for that matter.

As it is, the camera can be focused in manual mode and then when the shot is taken the focus is off.

That sucks, big time.

Zeiss says:

" Spherical aberration in lenses leads to so-called focus shifts. This term refers to the fact that changing the aperture causes a shift in the optimum focus position. This effect is particularly conspicuous in the case of fast prime lenses. You can find a more detailed description of focus shift in the article "Measuring lenses objectively" which appears in Camera Lens News Nr. 30 starting on page 24.

In order to take into account the effect of focus shift on precise focusing, the user should – as far as possible – carry out focusing at the aperture at which the shot is subsequently to be taken."

In other words, they agree with you:

http://www.zeiss.com/camera-lenses/en_us/website/photography/what_makes_the_difference/manual_focusing.html

I am having this problem with certain settings of the 50mm f2.8 DG Macro lens, one of many legacy Sigma lenses not found on the official compatibility list.

This may not help at all but the first Sigma 50mm f/2.8 DG Macro lens that I ever owned had an aperture ring where you had to set it to f/max before the camera could control the aperture. It did not do AF at all. A very good lens for what I was doing (watch shots).

Maybe there are still some out there . . .

 

[JohnLindroth]

If during manual or aperture priority, we had the option to actually operate at the chosen shooting aperture, focus could become certain manually, and maybe even automatically if there was enough light for that in the scene.

The main thing for me is to have the certainty that optimum focus is actually attained, before triggering the shutter.

As it is, the Sigma lenses focus at full aperture then stop down to shooting aperture, and if there is no compensation table in the camera the focus can be off.

About the only way to focus these lenses with complete certainty is to focus at maximum aperture so that the camera won't stop down during shooting.

Tom, are you concerned with the range of focus increasing when the lens stops down? I didn't notice a switch for DOF preview, like most SLRs have. I rarely worry about this, but you've got a valid point if you want to know what is in focus in your field of view.

The manual says this (pg 51):

After you set the aperture, the camera will determine the appropriate shutter speed. If you select smaller apertures, depth of field will be greater. Larger apertures tend to blur the background, as depth of field will be shallower.

1 Set the Exposure Mode to the A position.

(In the Viewfinder, the aperture value indicator is illuminated in green.)

2 Set the desired aperture value by rotating the Front Dial.

3 Press the shutter button “half-way” to verify the focus and take the picture.

Does this imply that the aperture stops down on a half-way shutter press?

-John

 

[JohnLindroth]

The manual section is for Aperture priority mode (A)

 

[JohnLindroth]

Since I don't have any lenses that work with AF, here's how I have the system set up

Shutter button, half-way is AEL lock

AF/AEL button is set to LV Magnification

That way, as long as appropriate for the subject, I can magnify to make sure that at least the main subject is in good focus.

Not sure if this helps.

-John

 

[Tom Schum]

Thanks to all who have responded.

I've noticed a small amount of focus shift vs aperture with my Samyang 85mm F1.4 for Fuji X mount (not used on Sigma of course) so I have to focus it at the shooting aperture to get exactly precise focus. This lens is fully manual. It is also current production, a modern design, and insanely sharp when focused well.

John, if none of your lenses support AF, they must be fully manual, is that true? If so, you set the aperture on the lens and the camera knows nothing about it. And you would be focusing at whatever aperture you want to use for the shot.

Shooting the SD Quattro in Aperture Priority mode or in Manual mode with a Sigma SA mount lens that supports automatic operation, the camera operates and focuses at full aperture (even in manual focus mode), then stops down only for the actual exposure.

The specific lens I am using at the moment is the 50mm f2.8 EX DG Macro. It is not possible to set the aperture on the lens; it is necessary to set it using the camera either in Aperture Priority mode or in Manual mode. It seems to work adequately well when manually focused in either of these modes, but the nagging impression is staying with me that the focus is not as good as it could be at any aperture smaller than f2.8. I need to do some serious focus checks before being able to say what's what. Deviations will be small if there are any, but this bothers me.

In the SD Quattro there is no DOF preview button and so far as I know no way to actually look thru the lens while it is set to anything other than full aperture.

This method is very good for film SLR and DSLR operation because it gives the user the brightest viewfinder image possible, but for mirrorless we should be able to set the aperture of the lens, focus at that aperture if desired, then shoot.

The only way to do that now is to use a fully manual lens, and Sigma doesn't make any of these.

I'd like to see a menu item that will set actual shooting aperture at all times, so if I have any doubts about focus shift I can use the camera this way. Yes I understand that trying to focus at f5.6 is going to be far different than trying to focus at f1.4, but I want to know what I am getting BEFORE triggering the shutter.

--
Tom Schum
Celebrate mediocrity (in moderation)

 

[Johan Borg]

Modern AF lenses should not behave like that so I think OP's concerns are not as real as they seem. Except he's got that exact rare lens.

I had the Sigma 50mm f/1.4 (pre-Art) which had enough focus shift on the SD15 to remain in my muscle memory years later. It's not uncommon even among Sigma lenses.

 

[JohnLindroth]

Tom,

All my lenses are Sigma AF SA mount, but none work correctly with AF on the sdQ.

 

[Tom Schum]

Modern AF lenses should not behave like that so I think OP's concerns are not as real as they seem. Except he's got that exact rare lens.

I had the Sigma 50mm f/1.4 (pre-Art) which had enough focus shift on the SD15 to remain in my muscle memory years later. It's not uncommon even among Sigma lenses.

Thanks for posting. I had the same lens for my Canon 30D and it performed very well.

Modern lenses can definitely have a little bit of focus shift with aperture, and this new menu item for the SD Quattro would allow us to cope with it successfully.

 

[Tom Schum]

Tom,

All my lenses are Sigma AF SA mount, but none work correctly with AF on the sdQ.

 

[JohnLindroth]

Tom,

All my lenses are Sigma AF SA mount, but none work correctly with AF on the sdQ.

 

[Tiger1]

Sorry to ask, but doesn't the camera stop down in Live View?

My other cameras (with live view) do that and if I need critical focus then live view on the rear lcd is the only way to be sure that focus shift is not occurring.

Cheers.

 

[Tom Schum]

Sorry to ask, but doesn't the camera stop down in Live View?

My other cameras (with live view) do that and if I need critical focus then live view on the rear lcd is the only way to be sure that focus shift is not occurring.

Cheers.

SD Quattro does not do this.

I would guess the SD Quattro is full-time live view, since it is mirrorless.

So far as I know the only time it stops down to shooting aperture is during the exposure.

This is the problem.

I have Fujifilm mirrorless cameras, specifically the X-E1, and when I operate the 23mm F1.4 lens in manual focus, aperture priority, and half-press the shutter button, it stops down to the shooting aperture and stays there until I fully press the shutter button to take the picture. This gives me access to depth of field preview, and to focus better if I want.

The SD Quattro does not do this. In Manual and in Aperture Priority mode, with manual focus, I half-press the shutter button and there is no change in the lens aperture. It remains fully open until I fully press the shutter button to take the picture. So there is no way to look at the scene thru a stopped-down lens, unless I use a non-Sigma fully manual lens.

What camera do you have that stops down to shooting aperture full-time in live view? Please tell me more about this camera.

 

[Tiger1]

My D810 definitely stops down in live view.

It is the only way to combat lenses which suffer from focus shift. Of course there are stellar lenses that have very little focus shift out there ( 35mm Art) but even some good ones have it (50mm Art).

 

[Tom Schum]

My D810 definitely stops down in live view.

It is the only way to combat lenses which suffer from focus shift. Of course there are stellar lenses that have very little focus shift out there ( 35mm Art) but even some good ones have it (50mm Art).

Thanks for the information. Now I know the best cameras do it right.

It wouldn't be hard for Sigma to put this feature into a menu item in a new revision of firmware. I think it is needed. Maybe call it "full time DOF preview".

I sent this idea to Sigma USA yesterday, and if I get a response I'll publish it in this thread.

 

[Tiger1]

As someone seriously considering the SDQ-H I await your future post on this matter.

Cheers.

 

[kthxjapan]

This is for most Canon, Olympus, Nikon, etc users the first thing they remap to something else because manual focus is for cavemen.

The lens release is right where the DOF preview button is on practicality every other camera.

When you hold down a DOF Preview button the camera instructs the lens to close to the selected aperture.

I was also frustrated by this until I realized the 18-35 has easy zone focus areas around 6ft of focus distance which is marked. Sigma not marking DOF distances AT ALL by aperture on lenses has irritated me since I bought my first Art lens.

 

[Tom Schum]

My inquiry sent via web submission: "SD Quattro would focus better manually if I could set it to focus AT THE SHOOTING APERTURE in Aperture Priority or Manual mode. Can this be added to the camera firmware?"

Sigma USA response Mon, Aug 29: "Thank you for contacting Sigma. Please explain how the camera would focus better stopped down. Usually you get sharper focus by focusing wide open and having more DOF when it stops down. Are you looking for DOF preview?"

My answer Wednesday Aug 31: "Some lenses have a focus shift when focused at full aperture then stopped down for the exposure. That is, in spite of greater DOF when stopped down the image is just out of focus. For this reason I want to set the lens to the shooting aperture, then focus it and shoot. Is this possible?

If not, DOF preview would be desirable as a second choice. In my Fuji X-E1 in manual focus, the lens stops down to shooting aperture when I half-press the shutter button. This would be easy to implement, but does not solve the focus shift problem. The focus shift problem is a lens problem."