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Occasional Contributor
Posts: 8
Registered: ‎02-16-2017

Having problems with a Sigma DG 28-300mm 3.5-6.3 lens - just not quite right in focus.

He everyone,

 

I have a Canon 450D (Rebel I think in the US) dating back to 2009.
The Canon 18-55mm lens won't focus and it looks like the Flex Cable has died so I've got one on order.

 

I have a Sigma DG 28-300mm 3.5-6.3 lens and while it works, the image quality just isn't 'quite right'. It always seems to be that little bit fuzzy.

Has anyone found some little bit of 'magic' to get it right ?

 

Kind regards,

Chris

Esteemed Contributor
Posts: 3,402
Registered: ‎02-17-2016

Re: Having problems with a Sigma DG 28-300mm 3.5-6.3 lens - just not quite right in focus.

You have to determine whether it is focus or camera/subject movement.

 

You might ask Sigma whether there is a firmware update to the lens.

VIP
Posts: 8,319
Registered: ‎08-13-2015

Re: Having problems with a Sigma DG 28-300mm 3.5-6.3 lens - just not quite right in focus.

Try turning off the OS, optical stabilization, if it has it.  Use it only if you are moving the camera, such as when panning.  Otherwise, leave the OS turned off, and try to maintain a high enough shutter speed where you don't need OS.

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"I don't rent software. I use Photoshop CS6, ACR 9.8 and Lightroom 6.8 ."
Occasional Contributor
Posts: 8
Registered: ‎02-16-2017

Re: Having problems with a Sigma DG 28-300mm 3.5-6.3 lens - just not quite right in focus.

Thanks for the suggestions.

I have determined it is the lens. On 28mm and comparing it to a canon 18-55mm lens, there is quite a difference.


Where I can view the picture and zoom in well on the Canon lens, I cannot come anywhere even close with the Sigma.

It doesn't have Image Stabilization.

Even using a tripod and remote trigger doesn't improve the image.

 

I'm at a loss as to what to do.

 

Regards,

Chris

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Posts: 8,319
Registered: ‎08-13-2015

Re: Having problems with a Sigma DG 28-300mm 3.5-6.3 lens - just not quite right in focus.


@ChrisMadog wrote:

Thanks for the suggestions.

I have determined it is the lens. On 28mm and comparing it to a canon 18-55mm lens, there is quite a difference.


Where I can view the picture and zoom in well on the Canon lens, I cannot come anywhere even close with the Sigma.

It doesn't have Image Stabilization.

Even using a tripod and remote trigger doesn't improve the image.

 

I'm at a loss as to what to do.

 

Regards,

Chris


Not so fast.  Use a simple focus target.  The lens could be back focusing, or front focusing.  Also, what aperture setting are you using?  I suspect the lens may be front or back focusing.  Well, at least I am hopeful that's all it is.

 

Basically, go through all of the motions of making test shots for a "Dot Tune" AFMA adjustment.  If the images are still soft when shooting a target at a distance of 50x the focal length, while mounted on a tripod and an aperture of f/8, then it can be concluded the lens is soft.

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"I don't rent software. I use Photoshop CS6, ACR 9.8 and Lightroom 6.8 ."
VIP
Posts: 11,334
Registered: ‎12-07-2012

Re: Having problems with a Sigma DG 28-300mm 3.5-6.3 lens - just not quite right in focus.

First off a lens is what a lens is. It can not change after it is manufactured.  It can't get any sharper or any less.  It can suffer from alignment issues.  Only Sigma is likely able to perform this adjustment.  I have never used this Siggy in question but I can tell you lenses with a zoom ratio of 11 to 1 are never going to be the sharpest tack in the box.

 

Now for focus adjustment.  Like I stated you can not make it any sharper.  This adjustment simply moves the pin point focus distance.  If this is off, something in your photos will still be in focus. Just not where you thought.

 

Lastly is user technique.  How you are actually using the lens.  In other words it could be you and not the lens.

 

"I'm at a loss as to what to do."

I do have a extra question for you.  Was the lens ever real sharp and has this happened recently?

EOS 1DX and 1D Mk IV and several lenses!
Occasional Contributor
Posts: 8
Registered: ‎02-16-2017

Re: Having problems with a Sigma DG 28-300mm 3.5-6.3 lens - just not quite right in focus.

"a lens is what a lens is"

 

That was my thought as well but I was after a means where I could do something about it.

I can understand focus problems when zooming but even at 28mm and F3.5 it just doesn't have "it".
A handy lense while I await the flex cable for the Canon 18-55mm but I've always wondered why it was nowhere near as focussed.
To answer your question, "Was the lens ever real sharp and has this happened recently?" - it has always been this way since I have owned it.  I bought it second-hand.

 

The problem was bought to light when I woul;d focus on someones eyes for a photo and it would never be quite in focus.
I'd love to have the money for a really good lense but I'm not in that position due to health problems in the past.

I've heard of doing focus adjustments but how is this done ?
My camera is one of the early EOS 450D - bought in 2009.

 

Thanks for the reply and kind regards.

 

Occasional Contributor
Posts: 8
Registered: ‎02-16-2017

Re: Having problems with a Sigma DG 28-300mm 3.5-6.3 lens - just not quite right in focus.


@Waddizzle wrote:



Not so fast.  Use a simple focus target.  The lens could be back focusing, or front focusing.  Also, what aperture setting are you using?  I suspect the lens may be front or back focusing.  Well, at least I am hopeful that's all it is.

 

Basically, go through all of the motions of making test shots for a "Dot Tune" AFMA adjustment.  If the images are still soft when shooting a target at a distance of 50x the focal length, while mounted on a tripod and an aperture of f/8, then it can be concluded the lens is soft.


Back focussing / front focussing - Sorry, I don't get it.

I have some camera knowledge and I suspect I am going to add to it Smiley Happy

 

Also, what is a " "Dot Tune" AFMA adjustment" ? How does one do it ?

 

I've capmpared the two lenses to each other and would loke the Sigma to be sharper - expected that it should be much sharper that it is. It is very poor compared to the Canon 18-55mm lense even without IS being turned on.
I can zoom in on the cannon lens generated image far more that I can zoom in on the Sigma generated image.

 

That includes on a tripod as well as hand help.
The ccanon lens needs the auto-focus flex cable replaced and I'm waiting on it's arrival and in the meantime I'm using the Sigma DG lens.

 

Thanks for the reply Smiley Happy Kind regards.

VIP
Posts: 8,319
Registered: ‎08-13-2015

Re: Having problems with a Sigma DG 28-300mm 3.5-6.3 lens - just not quite right in focus.


@ChrisMadog wrote:

@Waddizzle wrote:



Not so fast.  Use a simple focus target.  The lens could be back focusing, or front focusing.  Also, what aperture setting are you using?  I suspect the lens may be front or back focusing.  Well, at least I am hopeful that's all it is.

 

Basically, go through all of the motions of making test shots for a "Dot Tune" AFMA adjustment.  If the images are still soft when shooting a target at a distance of 50x the focal length, while mounted on a tripod and an aperture of f/8, then it can be concluded the lens is soft.


Back focussing / front focussing - Sorry, I don't get it.

I have some camera knowledge and I suspect I am going to add to it Smiley Happy

 

Also, what is a " "Dot Tune" AFMA adjustment" ? How does one do it ?

 

I've capmpared the two lenses to each other and would loke the Sigma to be sharper - expected that it should be much sharper that it is. It is very poor compared to the Canon 18-55mm lense even without IS being turned on.
I can zoom in on the cannon lens generated image far more that I can zoom in on the Sigma generated image.

 

That includes on a tripod as well as hand help.
The ccanon lens needs the auto-focus flex cable replaced and I'm waiting on it's arrival and in the meantime I'm using the Sigma DG lens.

 

Thanks for the reply Smiley Happy Kind regards.


Do a web search for the phrases you don't understand.  You can begin with " depth of field ', for a camera and lens.  Basically, when a lens focuses on a subject, the creates what is known as a "plane of focus".  Imagine an invisible wall at a fixed distance from the lens.  

 

Objects that are at a distance from the lens that is equal to the plane of focus will appear razor sharp to the camera.  As you move the object away from the plane of focus, either towards or away from the camera, objects will gradually fall out of focus.  There is a zone beginning in front of the plane of focus and extending beyond and behind the plane of focus where objects are not in perfect focus, but have what is described as acceptable focus.  This zone is called depth of field.

 

The size of the zone of acceptable focus, depth of field or DOF, can vary widely depending upon the focal length being used and the distance to the invisible plane of focus.  Depth of field is most strongly affected by your aperture setting.  Do a web search for depth of field table.  A narrow aperture [higher f/stop value] creates a wider DOF than wide aperture [lower f/stop value] would.  This is why I asked what aperture value are you using when photos seem out of focus.

 

When an auto focus lens focus on a subject, it tries to adjust itself so that the plane of focus is at the precise distance to the subject that it is focusing on.  Lenses are mechanical devices, and as such they are not always perfect.  Sometimes a lens will lock focus with the plane exactly on a subject, and sometimes it will be just ever so slightly off.  But, because of the nature of DOF, should a lens lock focus that is slightly off, we do not notice it.  This type of behavior is normal for mechanical lenses.

 

However, sometimes a lens may lock focus and set the focus plane at a distance that is great enough for the subject to be at the edge of the DOF, or even outside of it.  This results in a subject appearing out of focus, but other parts of your photo may appear to be in focus.  When a lens consistently places the plane of focus behind the subject, or target, then this is described as back focusing.  When a lens consistently places the plane of focus in front of the subject, then this is called front focusing.  The keyword here is consistently.  However rare, it is not uncommon for a lens to occasionally miss focus, especially inexpensive lenses.  Temperature extremes can cause a lens to be slightly off when it focuses, for example.

 

I am not suggesting that your lens is not focusing properly.  You can do a web search for a YouTube video about dot tune, which describes how to conduct focusing tests.  What you really need to do is find a test target, and print it out.  Even a yardstick might suffice for shorter focal lengths.  Take pictures of the test target with the camera on a tripod, and the target slightly angled to the camera.  This will allow you to see where the plane of focus is, and the extent of the DOF.

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"I don't rent software. I use Photoshop CS6, ACR 9.8 and Lightroom 6.8 ."
VIP
Posts: 8,319
Registered: ‎08-13-2015

Re: Having problems with a Sigma DG 28-300mm 3.5-6.3 lens - just not quite right in focus.


@ebiggs1 wrote:

First off a lens is what a lens is. It can not change after it is manufactured.  It can't get any sharper or any less.  It can suffer from alignment issues.  Only Sigma is likely able to perform this adjustment.  I have never used this Siggy in question but I can tell you lenses with a zoom ratio of 11 to 1 are never going to be the sharpest tack in the box.

 

Now for focus adjustment.  Like I stated you can not make it any sharper.  This adjustment simply moves the pin point focus distance.  If this is off, something in your photos will still be in focus. Just not where you thought.

 

Lastly is user technique.  How you are actually using the lens.  In other words it could be you and not the lens.

 

"I'm at a loss as to what to do."

I do have a extra question for you.  Was the lens ever real sharp and has this happened recently?


The only person around here making the claim that AFMA can make a lens sharper is YOU.  While you may not want to recognize it, there is a difference between compensating for the focus behavior of a given lens, and "making it sharper".  As always, I find your false and condescending assumptions to be offensive.  

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"I don't rent software. I use Photoshop CS6, ACR 9.8 and Lightroom 6.8 ."
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