T90, second viewfinder image

[gregory_nicholson]

Hi Folks,

I'm looking at a T90 in a local camera shop. Everything is "mint-

minus" except there are two images in the viewfinder.

 

The second image is basically the center of the original image,

about 1/8th that height and the same width. It is getting projected

as a rectangular stripe under the normal viewfinder scene. I'm

puzzled, should I avoid this camera or is it possible it's a simple

mirror adjustment like with Aaron James focusing problems on his

T90? Thanks in advance.

[alan_swartz]

Greg,

 

Wild guess is that something's going on with the prism. I'd think that the mirror would have to be grossly out of position to cause this, if it were possible at all. If so, focus would be very far off from the indication on the lens.

 

My guess is, though, that if the focusing screen is OK and is properly installed, a grossly misaligned mirror would only create a dark band in the viewfinder, like happens with the extreme telephotos. This double image sounds like it must be happening above the screen, something to do with angles of reflection. Are the LED readouts at the bottom of the viewfinder OK?

 

Has someone taken the screen out of its frame and replaced it incorrectly? The lip of the frame is the bottom, and that should be the glossy side of the screen. The matte side faces the prism. The lens-mount edge of the screen has a long relief in the middle, the rear edge has a short one. Or is it an AE-1P screen? They will install. Does the frame have the white "T" on the edge, and does the screen have the partial metering circle?

 

Weird problem!

 

Regards,

Alan

[jomar_haktorson1]

I think this is normal?

I have checked my F1N (AE-finder), T90 and an AE1-P

 

By looking slope downwards into the finder it's possible to see a stripe of the focusing screen under the regular viewfinder picture, just as you describe. If you look streight forward however, the stripe should not be visible.

That counts for all of my cameras.

 

Jomar Haktorson

[awahlster]

Alan the Matte side of the screen should face the mirror not the Prism!

[gregory_nicholson]

Well what do you know, I just checked my most used camera, the mechanical F-1, no stripe. Then I checked my Pellix, FT, EF, F-1N and A-1 and they all have this similar stripe. In the early book "An Introduction to the Canon F-1" is a statement "ghost images are completely corrected" for this camera. I never knew what that meant. This must be what they're talking about. The camera may have some type of light baffle in the prism. I guess the T90 must be okay, anyway, thanks for your comments.

[John Crowe]

Thanks Greg, now I am going to have to actually get up from my computer, dig out my T-90, and see what the heck you are talking about!

 

 

Just fire off the T-90 shutter a bunch of times to make sure it does not EEE! When you spin the selector wheel it should change the settings with each little detent. Mine has not done this for years which is annoying, ...just something to watch out for. Take care!

[alan_swartz]

Mark, I've got every screen for the T90, several of them NOS. Nobody has flipped the screens in the frames, and they all have the matte surface up, next to the prism, when installed. The installation tool will not snap onto the matte side, since there is no lip on the frame. No installation problems, no focusing problems. Matte goes up.

 

AE-1 Program screens orient the same way.

[gregory_nicholson]

Alan's right, I just put a "D" screen in my A-1. With no instructions, I first tried to put the matte down like an F-1 screen. It wouldn't go, matte up and it fit right in and focuses perfectly.