Question about Tamron Di II (ASP-C) lenses

I know that I have several of these lenses, which I am quite happy with, but I have a question about their construction, particularly how they compare to Canon EF-S lenses wrt the rear element of the lens extending into the camera body. The extra length of Canon EF-S lenses makes them physically incompatible with full-frame cameras, but is the same true for Tamron Di II lenses? I seem to recall reading, long ago, that these Tamron lenses did not have this limitation, as the rear element did not extend as far. I no longer own a Canon ASP-C lens to compare to my Tamron Di II lenses, so does anyone know if my recollection is correct?

Now, before everyone starts telling me about the problems I would have using an EF-S lens on a full-frame body, I am aware of those issues, and in fact do not own a full-frame body. I am asking because I am considering the merits of an Astronomik Clip filter (https://www.astronomik​.com …p-filter-canon-aps-c.html). Because of the position of this filter within the camera body, they are not compatible with Canon EF-S lenses, even on ASP-C bodies. However, if Tamron (or other third-party) ASP-C lenses do not extend into the camera body farther than Canon EF series lenses, this sort of filter should work.

If Tamron Di II lenses have the same physical characteristics in this respect as EF-S lenses, I still have my two 50mm EF lenses, but I would prefer something wider for night sky photography.

Thanks in advance for any info you have.

I am not sure why, but all 3rd party crop lenses (Sigma, Tamron, Tokina, etc) do not protrude into the mirror box like Canon brand EF-S crop lenses.

All 3rd party crop lenses can be safely mounted on Full Frame cameras without interfering with the mirror. They should be fine with your Clip Filter.

Thank you. I thought I recalled reading this sort of info about third party lenses, but could not find it when I went looking recently. Without an EF-S lens to compare my Tamron Di II lenses to, I wanted to be certain. Thanks again.

I just measured a Canon 17-55mm EFS, and from the mating surface of the mount to the rearmost surface of the lens is 8mm
In contrast, a Tokina 11-20mm (IF) DX lens (image circle for APS-C) from the mating surface of the mount to the rearmost surface of the lens (the electrical contact surface) is 6mm

It would be interesting if someone on POTN owned the Canon EF-S 10-18mm f/4.5-5.6 IS STM and could measure how far back it protrudes.

I believe that 3rd party do this for cost savings x3;
A - So they don't get in trouble for wrecking your camera should you repeatedly bash your FF mirror box into the back of their lens.
B - So that one design can work with multiple 1st party bodies with differing APS-C size sensors and mirrorbox clearances.
(keep in mind, most "normal" companies did not feel the need to create a different mount for APS-C. Canon is "special" )
C - So they don't have to make yet another mount (EF-S) to prevent people from doing "A"

Anyway, it was always fun to experiment with 3rd party APS-C sized lenses on FF and more so, APS-H (1D) bodies and see what you could get. The 1D APS-H was win win with these lenses, often getting full sensor coverage at all focal lengths but the widest on zooms.

I have a EF-S 10-18 that I have modified for use on full frame. https://photography-on-the.net …p?p=17035833#po​st17035833

On my 5D Mk III it hits the mirror at 10mm to about 10.5mm and won't take a photo. 11-13mm works fine but vignettes heavily. 14mm to 18mm is quite usable.

Here is a quick photo to show how it looks with the EF-S mount plastic protrusion removed. The end of the lens element looks to be about 8mm above the lens mating surface when the lens is at the 10mm focal length.

Thanks for the measurement, Mike (to Title Fairy: change his title to 'the POTN Ace of the EF-S mount modifiers')