# Sigma 170-500mm f/5-6.3 DG APO concerns



## davebmck (Mar 10, 2008)

I bought this lens this weekend to use on my Rebel XTi. I want to use this lens mostly for photographing wildlife. I took about 60 shots with it this weekend to see what kind of pictures I can get out of it. The problem I am having is that I cant seem to get good sharp images at anywhere near the full zoom. I do get good sharp, well focused images at 170mm, but that is not why I bought the lens.

Im not a pro photographer and this is my first telephoto lens over 200mm, so I am not sure if the problem is me or the lens. I was shooting in good daylight at iso 400, F8 (which is supposed to be the sweet spot for this lens), distances from 25 to 100 feet, using a tripod and remote shutter release. Shutter speeds ranged from 1/250 to 1/1000.

When I open the images in Camera Raw they look OK at the default 21% zoom ratio, not perfectly sharp, but respectable. However, when I zoom to 100% the image is not sharp and seems not perfectly focused. Sharpening the image doesnt completely fix the problem.

Am I expecting too much from a telephoto zoomed to 500mm or is this lens just not capable of taking sharp images at this setting? I have 10 days to return this lens, and I am currently disappointed enough with it to return it. I just want to make sure it is not what I am doing or that I have expectations that are beyond what is capable with a 500mm lens.


----------



## GTHill (Mar 11, 2008)

Are you on a tripod? I would try it on a tripod and use the timer to make sure it isn't camera shake that you are seeing. 

Gene


----------



## Big Mike (Mar 11, 2008)

Also, it's a good idea to use MLU (mirror lock up) when shooting a long telephoto on a tripod.

Does that lens have OS (stabilization)?  If so, you will want to turn it off when using it on a tripod.


----------



## Mav (Mar 11, 2008)

Yeah what Mike said.  You need a camera with a MLU or at least a shot delay after the mirror opens before it starts taking the photo.  Otherwise you're probably getting mirror vibrations into your shot.


----------



## Mystwalker (Mar 11, 2008)

Can IR (OS for Sigma?) help with the mirror vibration if hand holding?

Maybe my 70-200 isn't considered long enough because I'm not seeing this problem.


----------



## davebmck (Mar 11, 2008)

GTHill said:


> Are you on a tripod? I would try it on a tripod and use the timer to make sure it isn't camera shake that you are seeing.
> Gene


Yes, as mentioned above I am using a tripod and a remote shutter release.


----------



## davebmck (Mar 11, 2008)

Big Mike said:


> Also, it's a good idea to use MLU (mirror lock up) when shooting a long telephoto on a tripod.
> 
> Does that lens have OS (stabilization)?  If so, you will want to turn it off when using it on a tripod.


Good suggestion.  I will try it with the MLU the first chance I get.  No, it does not have OS.  Do you thing manual focusing would help?

Thanks, Dave.


----------



## davebmck (Mar 11, 2008)

Mystwalker said:


> Can IR (OS for Sigma?) help with the mirror vibration if hand holding?
> 
> Maybe my 70-200 isn't considered long enough because I'm not seeing this problem.


My other lens is the Sigma 18-200mm with OS.  I get very sharp images with it when hand holding at all focal lengths.


----------



## Mav (Mar 11, 2008)

Mystwalker said:


> Can IR (OS for Sigma?) help with the mirror vibration if hand holding?
> 
> Maybe my 70-200 isn't considered long enough because I'm not seeing this problem.


Not for this, no.  OS/VR/IS/VC (<-- Tamron) only stabilizes the lens, not the camera body.  And the support system stabilizes the body/lens combo as a whole.  The MLU allows vibrations within the body itself to stabilize before the picture is snapped.  You only need to worry about this once you start getting to pretty serious tele lengths and at relatively slow shutter speeds.


----------



## davebmck (Mar 12, 2008)

Update.  This afternoon I tried manual focus and activating the mirror lock.  I didn't see much difference with the manual focus, but the mirror lock up seems to have helped some.  My tripod is definitely not up to the job.  There was a slight breeze blowing and I could see it causing the camera to shake at 500mm.  I had to wait for breaks in the breeze to take shots.  Anybody got a suggestion for a solid, stable tripod that doesn't weigh a ton?


----------



## DSLR noob (Mar 12, 2008)

focusing at the fully zoomed in length isnm't possible. Canon EOS bodies are designed to focus at apertures of 5.6 or larger. A canon EOS 1 series body can manage f/8 or larger, but simply put, if you know the specs of your camera, you know why it doesn't autofocus at 500mm (because it maxes out at 6.3)


----------



## davebmck (Mar 12, 2008)

I don't understand what your telling me.  I know that the maximum aperture is  6.3 when the lens is zoomed to 500mm, but why wouldn't it be able to focus at smaller apertures, ie F8?  Maybe you can explain this differently so that I can understand what you are saying.


----------



## DSLR noob (Mar 12, 2008)

smaller numbers let in more light, 6.8 doesn't let in a lot, a canon camera (well any camera) needs a lit of light to autofocus properly. This requires an aperture of 5.6 or larger,i.e. 1.4, 1.8, 2.0, 2.2, 2.8, 3.5, 4.0, 5.6 or something of the like. 6.3 is too dark and even if you're in the middle of a desert with TONS of light, the camera is programmed to give up with what it's given after passing 5.6 unless you're using it on an $7000 1 series body, in which case it'll work all the way up to f/8. A lot of people don't look at this in their camera's limitations when buying lenses (usually insanely high range super zooms like this) then complain that it doesn't work. Well, I've no sympathy because quick research would've told you to expect this before hand. Also, what do you expect with a zoom that covers 430mm of range? Sorry if I sound harsh, but researching your gear would've made you a happier person. 

(Note: Nikon, Pentax and Sony are the same way this isn't just some stupid evil Canon scam, they have 5.6 functioning AF modules in the non-pro bodies, usually with a center cross type AF point needs to be used at 2.8 or larger to focus using its cross type capabilities)


----------



## Sw1tchFX (Mar 12, 2008)

What tripod do you have? don't tell me it's an el-cheapo $25 wal-mart tripod, because if it is, that's your problem.


----------



## davebmck (Mar 13, 2008)

DSLR noob said:


> smaller numbers let in more light, 6.8 doesn't let in a lot, a canon camera (well any camera) needs a lit of light to autofocus properly. This requires an aperture of 5.6 or larger,i.e. 1.4, 1.8, 2.0, 2.2, 2.8, 3.5, 4.0, 5.6 or something of the like. 6.3 is too dark and even if you're in the middle of a desert with TONS of light, the camera is programmed to give up with what it's given after passing 5.6 unless you're using it on an $7000 1 series body, in which case it'll work all the way up to f/8. A lot of people don't look at this in their camera's limitations when buying lenses (usually insanely high range super zooms like this) then complain that it doesn't work. Well, I've no sympathy because quick research would've told you to expect this before hand. Also, what do you expect with a zoom that covers 430mm of range? Sorry if I sound harsh, but researching your gear would've made you a happier person.
> 
> (Note: Nikon, Pentax and Sony are the same way this isn't just some stupid evil Canon scam, they have 5.6 functioning AF modules in the non-pro bodies, usually with a center cross type AF point needs to be used at 2.8 or larger to focus using its cross type capabilities)


If you point me to some reading on this, I would appreciate it.  I have read two books on photography recently and have been doing a lot of reading on the internet and have never ran across this issue.  It's also funny that the guy at the camera store (manager) wouldn't have told me about this.

Another question.  Why is it that I get about the same results with manual focus.  This is an autofocus issue, isn't it?


----------



## DSLR noob (Mar 13, 2008)

davebmck said:


> If you point me to some reading on this, I would appreciate it.  I have read two books on photography recently and have been doing a lot of reading on the internet and have never ran across this issue.  It's also funny that the guy at the camera store (manager) wouldn't have told me about this.
> 
> Another question.  Why is it that I get about the same results with manual focus.  This is an autofocus issue, isn't it?


IS your di-opter correct for your eyes? also, the Rebel series uses a very smally viewfinder that is not very good for manual focusing maybe it's just too hard for you OR your camera to focus (not an insult to you, I personally wouldn't be able to MF on a rebel @ f/6.3, I never did when I had mine). The lens could be soft but I doubt it would be THAT soft.


----------



## davebmck (Mar 13, 2008)

Yes, my di-opter is adjusted.  I would agree at this focal length I can't do a better job than the camera by manual focusing.  The point is that the camera is focusing, not hunting and is getting very close if that is the problem with my images.

I still do not understand the principle here.  I know you need light to focus and that this lens will have problems focusing if there is insufficient light.  What I don't understand is why I can't focus at a smaller aperature if the light is adequate, regardless of the maximum aperture of the lens.  I sense that the answer lies in your statement "the camera is programmed to give up with what it's given after passing 5.6", but I don't know what that means.  It seems you are telling me I can only use my camera at apertures of 5.6 or larger, but I know that is not right, so I must be misunderstanding what you are saying.


----------



## Rhubarb (Mar 14, 2008)

DSLR Noob makes a very valid point. Let me try and fill in what appears to be the missing logic step.

When an SLR meters, auto focuses and when you look through the view finder, the lens is at its widest aperture; regardless of what aperture you have set it to. It is not until you press the shutter release button that the lens stops down to the selected aperture and triggers the shutter to make the exposure.

For example lets say you are using a 400mm f4 lens. You want to make an exposure of f8 1/500th. You set your aperture to f8 and set your shutter speed. You look down the lens to compose and focus the shot. What you are seeing is the lens at f4 (its widest aperture) the camera uses this light and aperture to auto focus. You press the shutter release button, the lens stops down to f8 (the set aperture) the shutter releases and the exposure is made.

As DSLR Noob points out a lot of DSLR auto focusing systems are designed to work with the light from f5.6 or wider.

At 500mm your lens' widest aperture is f6.3, smaller than what your auto focusing system is designed to work with. This could be the cause of your problem.

The fact that you are shooting at f8 with this or any other lens is irrelevant, as the auto focus happens with the lens at its widest aperture.

I hope this helps.

I'm not sure exactly how you would test to see if this is your exact problem or not (it sounds like you may also have a tripod issue). I would also be of the mind that if there wasn't enough light for the AF system that it would hunt around, rather than consistently being slightly out of focus.  That said I have never used a lens that slow before  so I have no experience on how they should behave.


----------



## JerryPH (Mar 14, 2008)

DSLR noob said:


> focusing at the fully zoomed in length isnm't possible. Canon EOS bodies are designed to focus at apertures of 5.6 or larger. A canon EOS 1 series body can manage f/8 or larger, but simply put, if you know the specs of your camera, you know why it doesn't autofocus at 500mm (because it maxes out at 6.3)


 
I do not know Canon cameras, but your post makes absolutely no sense.  

Any dSLR camera's ability to focus is NOT based on the F/stop limitations of the lens, its based on available light and focus mechanism inside the camera.  The camera controls the lens... not the other way around.


----------



## Rhubarb (Mar 14, 2008)

JerryPH said:


> I do not know Canon cameras, but your post makes absolutely no sense.
> 
> Any dSLR camera's ability to focus is NOT based on the F/stop limitations of the lens, its based on available light and focus mechanism inside the camera.  The camera controls the lens... not the other way around.



But the f/stop has a direct affect on availble light, does it not?


----------



## davebmck (Mar 14, 2008)

Rhubarb said:


> When an SLR meters, auto focuses and when you look through the view finder, the lens is at its widest aperture; regardless of what aperture you have set it to. It is not until you press the shutter release button that the lens stops down to the selected aperture and triggers the shutter to make the exposure.


Rhubarb, thanks.  That is the piece of information I was missing to understand this characteristic of the camera.  I'm still not sure this is my problem, but it is clear this would not be an optimum lens for this camera.  It does hunt sometime when I don't expect it to.  Any yes, my tripod is definately part of the problem.  I will fix that this weekend.

Thanks again for everyone's help.
Dave


----------

