Sigma 50-150 lens on a Canon 7D

[hee]

Spurred by an upcoming trip to Alaska I have notionally made the jump from entry level to enthusiast by going from a faithful EOS 350 lens kit to ordering a Canon 7D kit (18-85mm lens) and a Sigma 50-500mm OS lens together with 95mm UV filter and polariser. However my lack of knowledge is already showing - why does the Sigma box contain a step-down ring ("for APS-C cameras") and is there a problem with just using the lens on an APS-C camera with a 95mm filter?

[ameerat42]

Welcome aboard - AP, as well as your upcoming trip.
So that way you can attach the appropriate (hopefully included) lens hood for the APS-C sensor cameras.
Am.

[Epoc]

You state you have bought a 50-150 and a 50-500 Sigma. I don't think Sigma do a 50-150, but they do do a 150-500 OS and a 50-500 OS. So which is it? I have the 150-500 and have no such adapter. Works equally well on my D700 and D7000.

[hee]

Thanks guys but I'm still a bit puzzled
Ian - The lens in question is a Sigma 50-500mm OS (which I think is what I wrote. The other lens is a Canon 15-85mm which comes with the camera kit).
CC - I would have thought that the lens hood that comes with the lens would fit the 95mm thread, which I assume would be the default setup for a full-frame camera.
My query revolves around why reviews refer to the step-down ring "for use with APC-S cameras"
I guess ultimately I'm trying to work out if the lens will work ok on the 7D without the stepdown ring, given that I have bought 95mm polariser and UV filters.

- - - Updated - - -

Sorry, my mistake, I see that I wrote "50-150" in the heading which was an error

[agb]

I think this is what you need to know.
Hood Adapter HA1030-01 (Supplied)

Hood adapter extends the length of the lens hood and provides more effective shading when used with digital cameras with an APS-C size image sensor.

* When using the APS-C Hood Adapter HA1030-01 with digital cameras with larger than APS-C size image sensor, vignetting will occur. Please remove the hood adapter if you are using these cameras.

[ameerat42]

Better said than I, Graham.
Am.

[agb]

Better said than I, Graham.
Am.
Much better than I could say it too. Sigma gets the credit.

[Wayne63]

Welcome to AP, enjoy the site and look forward to seeing some of your pics in the forums

[ricktas]

I moved your thread from Introductions as it isn't really an introduction, but rather a gear related question.

Now that we have given you your answers, hope we get to see you and your photos on the forums.

[hee]

A final word on this now that the lens and filters have tuned up (note that my heding should hve read Sigma 50-500 OS
1. the step-down ring (95mm-86mm) appears to serve no purpose at all other than allowing you to purchase slightly cheaper and small filters. It apparently can't be used with a polariser so I'm not sure why they bother including it,other than to confuse new-chums like me.
2. Both the lens hood and the APS-C hood adapter (basically an extension tube to the lens hood for APSC cameras) fit to the outside of the lens, or each other, via a bayonet fitting and seem to have no relevance to the step-down ring which thread-screws to the the inside the lens rim (as do the 95mm filters)w
3. Crucially for me, I am able to use the 95 mm UV filter and polariser that I had already ordered and paid for. Phew.
4. I'll be interested to see what practical difference fitting the APS-C hood adapter makes - can't quite work out the physics!