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I have a bit of a mess with mount converters and their effect on focus distance, focal length, etc (alien.top)

submitted 10 months ago by Aqui_Menda@alien.top to c/photography@viewfinder.pro

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So I have a Canon m200 (ef-m) and I bought an Ef-s / Ef-m mount adapter. Nothing special, just a piece of plastic and electronics from Meike. However, I recently came across a YT reels making a review of a extension tubes: a device that one could install between the lens and the body in order to get a smaller minimum focus distance. (The guy even stacked several of them, largely minimizing the focusing distance and increasing the focal length). That device look very similar to a mount converter -the only difference being that the input and output mount is the same-. So, I have the following questions:— Do mount converters affect focal length? (I have a ef-s 55-250mm lens and even if it's just 10mm longer than my kit lens, I feel like it is much more. Maybe I just need to get use to it, but I could swear that it is too long.)

— Do mount converters minimize focus distance? Since they enlarge the distance between the sensor and the lens, I thought it would maximize the focus distance.

Thanks a lot for your help :D

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[–] JayEll1969@alien.top 1 points 10 months ago

OK you have two different thing.

Mount convertors take lenses meant for a different camara system and let them be used on yours. They dork because the flange distance (the distance between the lens and the sensor) is greater in the original system than on the new system - if you look at DLSR then they had a big mirror in between the sensor and the lens so adapting these lensed to a mirrorless camera means you need to hold the lens the same space away from the sensor as it would have been on the DLSR.

So that gap in the mount adapter is to make sure that the lens is the correct normal distance away from the sensor to get infinity focus.

Macro tubes are meant to be put inbetween a camera sensor and a lens that is already at the correct distance from the sensor.

This means that it is now pushed forward to the "wrong" distance. Because of the way lenses work when focusing at the closest working distance items that are closer to the lens will be focused to a point behind the sensor, these tubes pus the lens forward from their normal positions so that the focus points for these closer objects end up on the sensor.

The down side to this is that the focusing points for infinity or far away objects are pushed forward too much and you can no longer focus on these to bring them sharp on the sensor.

The amount it lets you get closer depends on the size of the tubes, which then influences the magnification you can get. To get true macro 1:1 magnification you need to add tubes of the same focal length as the lens.