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Thread: Canon RP with EF-S effective focal length

  1. #1
    Junior Member
    Join Date
    Jan 2009

    Canon RP with EF-S effective focal length

    Hi all!

    I'm currently using the Canon 80D (which i upgraded from the 60D) with the Canon EF-S 17-55 2.8 (great lens!)

    I have considered upgrading to full-frame before, but the price and size threw me off. Now with the new EOS RP (this might be rushed but..) I'm thinking this could be it.

    If I get the new EOS RP and use it with my current lens EF-S 17-55 2.8 will it effectively be 17-55mm full-frame or will it be the conversion ?
    In other words, will the field of view be the same, or will it become ultra wide?

    Thanks in advance for the answers!

  2. #2
    Super Moderator Kayaker72's Avatar
    Join Date
    Jan 2009
    New Hampshire, USA
    There are several aspects to this.

    First, if using the Canon EF to RF adapter, the focal length will be the same. The RF cameras have a flange distance of 20 mm. The EF (and EFS) cameras had a flange distance of 44 mm. The adapter is 24 mm. Thus, using the adapter plus an RF body your flange distance for EF and EFS lenses will still be 44 mm.

    All that means, the focal lengths will stay the same.

    Now, the field of view. Field of view is a function of the focal length and sensor size. From what I've read, the R series goes into a crop mode as soon as an EFS lens is attached. So, it will behave similar to your 80D, but you will be getting a lower resolution file. The R and RP have a crop mode for 4K video. And that crop factor is 1.6x, the same as an EFS lens. So, when shooting 4K video with an EFS lens, the focal lengths will provide the same field of view as you get on a crop sensor body at full 4K resolution. I haven't heard what happens with 2K video with an EFs lens.

    I've only read this once, but it is a potential interesting feature to the R/RP bodies. If true, you can effectively use as a lower resolution camera with EFs lenses or a full resolution camera with EF/RF lenses.

    EDIT...yep, I wanted to confirm, page 119 of the RP manual. It has a "crop mode". Page 121 of the RP manual, the data outside of the crop mode area are not saved. So, confirming it is a lower resolution image (approx. 10.1 MP).
    Last edited by Kayaker72; 03-12-2019 at 02:21 PM.

  3. #3
    Junior Member
    Join Date
    Jan 2009
    damn... so basically I will be buying a full-frame to use it as crop. That sucks! might just sell the whole pack then, and get the rp with a new lens.
    Thank you for this. Glad I didn't make the purchase yet.

  4. #4
    This is of course because the EF-S lens doesn't necessarily light up the whole full-frame sensor. It's not designed to have to do that.

    The flange distance isn't important for the focal length, but is for the lens' ability to focus at infinity.

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