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Canon 55-250 STM on M cameras

Started Mar 12, 2022 | Discussions thread
Larry Rexley Senior Member • Posts: 1,238
Re: is it worth it? (TC)
3

MAC wrote:

Larry Rexley wrote:

KevinRA wrote:

Larry Rexley wrote:

The thread mentions modifying the rear mount to work on EF teleconverters instead of only EF-S--- since then some users on this forum have posted about the possibility of buying a replacement part that lets you modify the lens mount in a reversible, non-destructive way just removing several screws and replacing the rear lens mount. It is mentioned in this thread:

https://www.dpreview.com/forums/thread/4623096#forum-post-65817791

just a query here - as an owner of this excellent little cheap lens - is really adding a teleconverter worth it? It is quite sharp at 250mm f/5.6 and even better at f/7.1 - but I doubt 350 f/8 is as good - for me I'd crop on a high density sensor instead.

Absolutely using a good 1,5x TC is worth it - the particular 1.5x teleconverter I use (Kenko 1.5x 5-elements SHQ) has very little loss of sharpness and contrast when used with the EF-S 55-250mm IS STM, in fact I have a hard time telling the images apart with and without the TC even at the pixel level. I think what you said would probably be true of the cheaper MC4 teleconverters which are not as good optically.

The point of diminishing returns appears to be going to an MC7 2x teleconverter with this lens, in that case there is little difference between cropping a 1.5x TC image and using the 2x TC.

I’d like to see a controlled test of this

I haven't done detailed comparisons of daytime photography, but have posted many images with the TC that show it's pixel-sharp.

The closest thing I have is that I've done controlled comparisons shooting the Moon at the same ISO with the 55-250 IS STM alone, with the 1.5x Kenko SHQ TC, and with a Kiron MC7 2x TC, plus at prime focus with a Meade ETX-90 telescope.

The 55-250 images were all shot at the same ISO and processing using identical DxO settings for exposure, contrast, and sharpness. The Meade telescope obviously has no lens profile in DxO so I adjusted sharpness using unsharp mask setting best I could, but exposure settings were the same as for the 55-250 images (the scope image is a little noisier as it was shot at ISO 800 vs 400 for the 55-250 images).

Al images below were cropped but not downsized at all --- they are at full 'pixel' resolution. The rest of the frame was just black, of course. View in a web browser at 100% size to compare.

There appears to be some benefit for the Moon of going from the 1.5x to the 2x teleconverter, but to my eyes it isn't as large as the increase in detail as the difference between the bare lens and the 1.5x TC.

EF-S 55-250 IS STM with no teleconverter

EF-S 55-250 IS STM (modded to EF mount) with Kenko 1.5x SHQ teleconverter

EF-S 55-250 IS STM (modded to EF mount) with 2x Kiron MC7 teleconverter

Meade ETX-90 telescope (1250mm f. l., f13.8)

 Larry Rexley's gear list:Larry Rexley's gear list
Canon EOS M6 II Canon EOS M200 Canon EF-M 18-55mm f/3.5-5.6 IS STM Canon EF-M 22mm f/2 STM Canon EF-M 11-22mm f/4-5.6 IS STM +21 more
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