28-135mm EF vs. 55-250mm EF-S, please help me understand crop factor.

[klavender]

Sorry for the newbie question but I've searched Google and couldn't really understand this. I have a 40D with a 28-135mm EF lens. I understand this is a APS-C camera and since the lens is an EF that the effective zoom is 44-216mm. I would like to get more zoom but the EF-S telephoto is 55-250mm. 250mm doesn't seem like much more that 216mm and I'm not sure it's worth it. I've also looked at the EF 70-300mm which would be 112-480mm. It's twice as much money and would think I would want it slightly wider at the low end.

Also, if I go with the EF-S 55-250 would the STM be worth it over the standard? I want a quick focus as this will be used mainly for wildlife. How does the standard and STM compare to the USM of my current lens?

[diverhank]

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@ebiggs1 wrote:

"I noticed something strange about my refurb. 55-250mm lens I just bought."

It is the IS.  It is also most likely why the lens was returned and is in the refurb store.  If I were you, I would return it tomorrow. It may be in spec so Canon will not fix it more.

BTW, no Canon lens I know of turns the IS off when attached to a tripod.  Certainly none of the consumer lenses.  Plus I have never seen it hurt to leave it on.  The IS is way better than it used to be and perhaps there was a time that was true. I almost never turn it off.

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There seems to be some misconception regarding Canon IS...per Canon's writeup, for certain lenses, especially older ones, leaving IS on when mounted on tripod is detrimental to sharpness...Here is an excerpt:

Using IS with a tripod

When using certain early models of IS lenses with a tripod it was necessary to turn off the IS function. This is because of a phenomenon known as ‘Shake Return’. Shake Return occurs when the IS system tries to correct vibrations to which the system itself contributes. When the IS lens sits on a tripod, the IS detection gyros pick up any tiny vibrations or movement; these might be caused by the tripod being knocked, or the photographer adjusting a camera setting.

The IS system then swings into action to correct that movement. The movement of the IS lens group causes its own minute vibration, which is in turn detected by the movement sensor, which triggers another correction. This ‘feedback loop’ can continue endlessly, resulting in the addition of unwanted blur to images that would be sharper if the IS function was switched off.

Link to whole article: http://cpn.canon-europe.com/content/education/technical/image_stabilization_lenses.do

Tamron lenses with Canon mount has warning in bold in their manual to turn VR (their version of IS) off.  I tried to leave it on using my Tamron 150-600mm lens and IQ was noticeably worse with VR on while mounted on a tripod.  When in doubt, turn IS off.

[ebiggs1]

"Canon IS...per Canon's writeup, for certain lenses" "When in doubt, turn IS off."

Yet again I report on what I personally see in my use of the gear.  It is not from some report or others review.  I shoot both the big Sigma and Tamron.  I rarely turn IS off.  if it makes any difference it is slight to none. If you feel you need to turn it off there is a switch for just that purpose.

I also see reports from others that claim the lens is sharper with IS turned off.  But this, too, seems to be somewhat faulty.  if it does make a lens sharper with IS off, it to is again slight to none.

You see you can't make a snap observation because you got a photo, or even several, that was better with IS off.  You need to make many, many photos.  And over differing situations and circumstances.

[diverhank]

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@ebiggs1 wrote:

You see you can't make a snap observation because you got a photo, or even several, that was better with IS off.  You need to make many, many photos.  And over differing situations and circumstances.

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Does a couple thousands count? :).  I'm a BIF shooter. I take a thousand per outing. I'm also an engineer, I understand statistics.

[ebiggs1]

A birder with a 55-250?  OK!

[klavender]

I had the camera on a tripod and zoomed all the way out, so it was stable. IS was turned on, I will try it tonight with the IS turned off. But I really need to be able to use IS. When looking through the viewfinder and shutter button pressed halfway, the focal points move slightly. When the shutter button is released, the focal points return to original position. It's something happening inside the lens. I guess I need to contact Canon and get a replacement.

[diverhank]

It's hard to tell just from your description of the lens dipping down (or image shift) but most likely it's because of the IS compensating.  IS is activated when the shutter button is half way down.

Since you put your camera on tripod, I highly recommend turning IS off.  Most Canon lenses automatically turn off IS when on tripod but there's no guarantee.  There are always a bit of noise in any electronic sensors so even on a tripod without any movement the IS mechanism will read some numbers (noise) and wrongly compensates for it, resulting in more blurred pictures.  You don't need IS if you don't shake and usually when the camera is on tripod, there is no shake.

[klavender]

My 28-135mm IS USM kit lens doesn't do this and I leave IS turned on.

[RobertTheFat]

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@klavender wrote:

My 28-135mm IS USM kit lens doesn't do this and I leave IS turned on.

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That may not be significant. The IS mechanisms of the two lenses may work slightly differently.

BTW, I doubt that the 40D's viewfinder has 100% coverage. It may be that what your lens sees isn't changing when you press the button, but rather just the exact portion of the view that's presented to you. But even in that case, it's probably the IS mechanism that's causing it. It may be that the behavior you're seeing is perfectly normal for that camera/lens combination.

[klavender]

Gotcha. I will try turning IS off tonight and see if it still does this. If this lens operates this way, then it is what it is. It's not a deal breaker. I just thought it was odd.

[Waddizzle]

Another factor could be the camera's AF mode, One Shot or AI Servo.  Test the lens in "One Shot" mode, and only the center AF point active.  I have had a lens where Optical Stabilization could cause the image to "shift" if the camera where trying to track a subject in AI Servo mode....Sigma 150-500mm did that.  OS and AF would get into a tug of war, it would seem.