Why does my Sigma 18-250 Macro do this?

this has happened on and off since i first started using it (brand new). sometimes when i press the shutter half-way to auto-focus, the view in the viewfinder seems to drop down totally messing up my composition and forcing me to readjust the camera. the camera isn't moving because most of the time i'm using the remote and not touching the camera. this sound right? the lens does seem to have some features that i'm not familiar with so maybe i'm missing something.

Does it do that when the VR (OS with Sigma) is turned "OFF"? Might be something is not working right with the VR.

Marcel said:

Does it do that when the VR (OS with Sigma) is turned "OFF"? Might be something is not working right with the VR.

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well right now it's turned on and probably has been since day 1 so i can certainly try turning it off. thx.

Slipperman said:

well right now it's turned on and probably has been since day 1 so i can certainly try turning it off. thx.

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then let us know if that was the culprit...

Is there a switch to lock it into macro? If so, is the switch locked?

It may simply be the OS working. I have read somewhere, either manual or a lens makers website, that you may have to recompose after engaging VR (OS). While a little shift would not matter in a lot of situations, it makes sense a tight macro could easily get out of frame.

Edited to add: If you are not hand-holding the camera, you likely need to turn OS off anyway.

^^^ like Eyelight stated. Having the camera on a tripod or stabilizing it, having the VR on actually will cause some blur in certain situations.

hark said:

Is there a switch to lock it into macro? If so, is the switch locked?

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no switch for macro just for zoom lock (at 18mm only), AF and OS. plus this was a landscape. frankly i'm not sure how the macro capability works on this lens. the only thing i see related to macro are these little indicators on the lens itself as it extends when you zoom in. eg: at 28mm, you see the ratio 1:9.5, at 50mm, 1:5.8, etc. so basically it seems like it's always in macro mode since a ratio appears at every focal length on the lens. but i don't really understand everything about macro so maybe somebody can explain this.

Just put your camera on the tripod, try with and without the OS switch. It has nothing to do with macro except the fact that the image can move more with the OS switched on when you're closer to your subject.

FastGlass said:

^^^ like Eyelight stated. Having the camera on a tripod or stabilizing it, having the VR on actually will cause some blur in certain situations.

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this could explain another problem i had which was the series of pics i took (on tripod) all came out blurry. the subject was about a half mile away (as the crow flies) but up on a hill which gave me an unobstructed view. i cranked the zoom all the way up to 250 thinking it was enough but they still all came out crappy.

When seeing a macro lens listed as a 1:1 ratio, it means that the image recorded from the sensor is the same size as real life. If taking an image of a magazine in a 1:1 ratio. Than the sensor size would need to be the same size as the magazine. The lens you have looks to have a 1:9.5 ratio making it slightly less than what most people would think as a true macro lens.

Slipperman said:

no switch for macro just for zoom lock (at 18mm only), AF and OS. plus this was a landscape. frankly i'm not sure how the macro capability works on this lens. the only thing i see related to macro are these little indicators on the lens itself as it extends when you zoom in. eg: at 28mm, you see the ratio 1:9.5, at 50mm, 1:5.8, etc. so basically it seems like it's always in macro mode since a ratio appears at every focal length on the lens. but i don't really understand everything about macro so maybe somebody can explain this.

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The macro capability is simply that it will focus closer than a non-macro lens. Not sure what the ratios you are seeing would mean, since the macro ratio would also depend on focus distance. Sigma's site is not very forthcoming with info.

Slipperman said:

this could explain another problem i had which was the series of pics i took (on tripod) all came out blurry. the subject was about a half mile away (as the crow flies) but up on a hill which gave me an unobstructed view. i cranked the zoom all the way up to 250 thinking it was enough but they still all came out crappy.

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A shot at that distance and at 250mm would require a fast shutter speed and a great deal of light to overcome camera movement. You would also need a clear atmosphere, because any haze will make an image soft.

I have a much older Sigma 70-210 f/3.5-4.5 macro lens that has a switch that needs to be flipped for macro work. That's why I mentioned it. After doing an online search, your lens appears to work differently.

Eyelight said:

A shot at that distance and at 250mm would require a fast shutter speed and a great deal of light to overcome camera movement. You would also need a clear atmosphere, because any haze will make an image soft.

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how fast? i was using aperture priority where i tried f11, 13, 14, 16 (for greater depth of field correct?) and the shutter speeds came out as 1/200, 1/160, 1/125 and 1/100. ISO 100 on all of them. the sky was totally cloud free with bright sunshine. it was around 2:40 in the afternoon so the sun wasn't straight up in the sky (in fact it was already setting). pretty sure i had at least close to correct settings. correct me if i'm wrong

Slipperman said:

how fast? i was using aperture priority where i tried f11, 13, 14, 16 (for greater depth of field correct?) and the shutter speeds came out as 1/200, 1/160, 1/125 and 1/100. ISO 100 on all of them. the sky was totally cloud free with bright sunshine. it was around 2:40 in the afternoon so the sun wasn't straight up in the sky (in fact it was already setting). pretty sure i had at least close to correct settings. correct me if i'm wrong

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How fast depends on the distance, the detail of the subject and how solid the camera is supported. Distance makes for smaller details and adds atmospheric issues.

Camera movement that twist on any axis that is perpendicular to the line between camera and subject will be greater at greater distances. Mirror slap, for instance, is likely to shake the camera in a pitching motion (rotating on the horizontal axis) which creates and angle of movement. While the movement may be a fraction of a millimeter at the camera, it is magnified by distance and the greater the distance, the greater the blur.