EOS RP Auto Focus Woes

[n0fumar]

I'm wondering if i'm being overly fussy about this. I've got an EOS RP with an EF adapter and a Tamron 28-75 XR DI LD f2.8 (the older one, not the newer one) and I just can't seem to get sharp pictures using auto focus. I set up a brief test to try and see if I was going crazy or if I was justified, and I'd like some feedback.

About the test;

• Pictures taken in AV mode.
• Aperture set at f5.6 and all other settings set to manual
• Auto focus pictures taken using Spot AF with the box right on the text
• Candle is about 2' away
• Self timer for 2 seconds and camera on a tripod to limit shake

I'm wondering if I'm being way too much of a pixel peeper here.

Here are images of the RP with the Tamron lens comparing auto focus to manual focus

I've run a few extra tests using my older t2i and can confirm the images are *MUCH* sharper when using auto focus.

Here are the same type of images on my t2i

I then ran the same test using my 50mm f1.8 II on both the RP and t2i and got *MUCH* better focusing on the RP.  It's comparable to the t2i in this case.

Images on RP with 50mm at f1.8 and f4.0

Images on t2i with 50mm at f1.8 and f4.0

Anyone have any thoughts on what might be happening?  Am I expecting too much here?

[n0fumar]

Did some more testing and can confirm the lens is back focusing during auto focus by what looks like 16-24mm range (not sure on the terminology here).

I wanted to test if I was back focusing, so I put a book in a vice and put a ruler next to it on a 45 degree angle.

See images here. Auto focus is on the left and manual focus is on the right.  It's a little difficult to see at wide open f2.8, but as I stop down to f8.0 you can see the focus is farther back on the ruler more towards the 7" mark.

I then tested this against the t2i with the same lens. Lens is sharp on the t2i, still backfocus on ...

I also did a test here with the 50mm. f1.8 is soft, but f4.0 and above show a drastic improvement an....

So after plenty of testing, it would seem that this is isolated to the lens when mounted on the RP.  The lens itself is fine, but the communication between the lense and however it autofocuses is not happy.  Anyone want to confirm what I found?

[Waddizzle]

You should also be able to confirm the location of the locked AF point when you call up the image in the camera.  Finally, always be cognizant of the MFD of your lenses, and the DoF that you are working with.

[EDIT]. If you are using a tripod, then you may also want to try manually focusing the lens, using the zoom functionality on the rear LCD screen.

[Waddizzle]

First and foremost, are you using the Canon RF/EF mount adapter?  What was the actual shutter speeds for the test shots?  Did you use a tripod?

Why are you using Spot AF?  That focus mode is probably looking at a much larger area than you might think.  The same is true for Spot Metering,

Finally, front and back focusing has no real meaning with MILC bodies.  Try a more recently released lens, too.

[n0fumar]

Hey There.  Yes it's the Canon mount adapter, I also tried a third party adapter and had the same results.

Yes I was on a tripod, the shutter speed was probably between 1/60 and 1/30, I used a two second timer to eliminate any shake.  Also, Spot AF is the smallest focus box you can use on this camera.

[Waddizzle]

Spot focus is NOT the smallest AF point that you can use.  Like I said above, the actual AF area is larger than people realize. You can use the Canon DPP4 app to verify exactly where the AF point was locked in he image.  It will also show you how large the AF area is.

I suggest that you retry your tests using the more conventional AF point modes.

[n0fumar]

I'm going based off what comes in the manual.  You may be thinking of another mode?

[n0fumar · Accepted solution]

Hi all,

I wanted to make a quick follow-up here in case anyone comes across this.

Somewhere in another thread, a few of us determined the older 28-75 f2.8 was not fully compatible in autofocus mode. This was a bummer because I really liked that lens due to it's size and constant aperture through the focal range.

So I looked through for some newer standard zooms and finally settled on the Tamron SP 24-70mm f2.8 G1 lens. Watched ebay listings and picked one up for $300.

I ran a few tests (same as before) and have them linked in this album. It is VERY clear that the new lens is autofocusing properly. I didn't even bother running a test with manual focus since it was so apparent the autofocusing was working as intended.

I'm making this update in hopes that someone may find it later down the line and benefit from the testing I did. If you have another lens which is performing like this, maybe it will help too.

Thanks for the help everyone!