Old Eyes

[Quiet]

I recently got back into photography with a Rebel T7 (not T7i). All is marvelous until I put one of my old M42 mount manual lenses on it. I just can't focus well on the cut frame viewscreen without a microprism/split image focusing screen.

I can find one of those online for 20-ish dollars but I'm not doing surgery on my new camera and the local Canon dealer told me it won't fit a T7 anyway. The screen in question is advertised as fitting a T5.

Can the dimensions or mounting frame of aT7's viewscreen really be different from all the preceeding "T" iterations before it? I'm kinda passionate about using old glass on this marvelous new camera and would appreciate any help.

[Waddizzle]

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@jrhoffman75 wrote:

"There is no guarantee that AF would still be operatble.  All indicators suggested that AF would never be the same.  Changing focusing screens on more advanced cameras involves telling the camera what type of focusing screen you are using, and the T5 had no provision for such an accommodation. "

The autofocus path has nothing to do with the viewfinder focus screen. The autofocus light path is directed to a sub mirror below the main mirror. 

The reason for the custom setting for some screens is that the difference in light transmission could affect the exposure metering. If more or less light is being transmitted the camera needs to know. 

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Maybe, but we're talking about the least expensive Rebel sold.  One of the first, and the least expensive, way to display AF points is to use the focusing screen combined with an LCD projector.  This works fairly well for just a handful of AF points.

The focusing screen in most Rebels are not user replaceable because they are within a sub-assembly, probably similar to this.

[jrhoffman75]

There is no "Maybe " involved. The Canon AF system has nothing to do with the viewing screen:

The Rebel series focusing screens are not designed to be user repalceable because Canon doesn't provide alternate screens. They can be replaced by simply removing one screw however.

I would not recommend getting involved with thirs party replacement screens since a very important adjustment is made when the cmaera is manufactured. It is very important than when the AF system says the lens is in focus that the image in the optical view finder also looks in focus. This is controlled by shims when the camera is manufactured.

There is no guarantee that a third party screen would meet the specs of a Canon screen. If that adjustemnt was off then a true in-focus image would appear off in the OVF. If the user then performed a manual adjustment to focus in the OVF the actual image could be out of focus.

The focus points that are shown in the optical viewfinder are a representation of where the actual focus sensors are - they are not real devices.

[Waddizzle]

John,

That is good to know.  Like I said, there were too many unknowns when I first looked into it.  And, the deeper I looked the more complicated it began to look.  There were just too many unknowns, and if I could not change it myself .... why bother.

[EDIT].

But, the conclusion that I had drawn was pretty simple.  If you cannot see the AF points, then you do not have an AF system!