tele converter using ttl meter on canon ftb ermm ....

[smiffy_smiffy]

Someone has used a Komura Telemore95  2x tele-converter on their std canon 50mm 1.8 lens with ttl metering. using  a Canon ftbn camera, and all negs are seriously under exposed.    Should they have just opened up 2stops from the indicated ttl meter reading ?  They were under the clear impression that ttl metering would automatically compensate for any tele-converter... the blurb supplied says:  that 'using the converter with ttl metering does not require adjustment' ..

 

[paddler4]

TTL means "through the lens". it should correctly meter the light hitting the photosensor regardless of what's in front of it. I have never had a problem metering with a teleconverter on any of the Canon bodies I've owned. HOWEVER: for the image to be properly exposed, the electronic communications between the lens and the camera have to be maintained properly, and the lens has to achieve the correct aperture. So perhaps something is going wrong there.

[smiffy_smiffy]

Thanks paddler, But pictures taken on the same kit prior to the t/c being attached are perfectly exposed and the t/c is brand new, so they really don't understand what has happened ..nor do I !!

[AJG]

A Canon FTb should have a mechanical connection between the lens and the camera body for the light meter.  There will be less light coming through due to the teleconverter, so there must be a problem with the converter not communicating with the camera if the lens otherwise works well on its own. The t/c may be "new in box" but it is probably at least 30 years old, so dried out lubricants, possibly?

[smiffy_smiffy]

Thank you AJG, we have looked through the camera back whilst on b setting and the lens stops down ok to the selected apertures.

To clarify, the indicated 'correct' ttl exposure is almost the same whether the t/c is attached or not, that's the mystery !!

Edited August 31, 2023 by smiffy_smiffy
typo

[Ken Katz]

As described by AJG, the mechanical linkage between the camera body and the lens needs to be maintained by teleconverter, so that the lens stops down when the shutter is activated.  I would look at the front of the lens, using a 1 second exposure to see the iris in the 50 f1.8 operate with and without the teleconverter.  It should mechanically stop down the same amount when using the same set aperture on the lens.

Since a 2x converter eats about 2 stops of light, at the same aperture the required shutter speed needed to center the meter needle would result in 2 stops slower shutter speed with the 2x.  Make sure the FTB's 12% partial meter is looking at the same subject when you check.  Also, the FTB has a relatively limited low light meter capability, compared with a modern camera, which could impact results with the 2x attached.

[AJG]

6 hours ago, smiffy_smiffy said:

Thank you AJG, we have looked through the camera back whilst on b setting and the lens stops down ok to the selected apertures.

To clarify, the indicated 'correct' ttl exposure is almost the same whether the t/c is attached or not, that's the mystery !!

Then the meter linkage of the t/c must not be functioning correctly.

[smiffy_smiffy]

Yes thanks all for your replies, it now appears the t/c itself was at fault, however the very centrally weighted ttl metering on the Ftb didn't help matters.

Bearing in mind, as you have said,  these items could be approaching 50 years old, so we shouldn't expect perfection, and many thanks again :0) 

[ben_hutcherson]

When in doubt in a situation like this, you can always revert to stop down exposure to double check. On an FTb(or F-1...or TXb/TLb) it's dead simple to do so and doesn't even require you taking your eye from the viewfinder. Push the self timer lover toward the lens mount. The lens should stop down, the "lollipop" will fall out of the metering range, and "correct" exposure is when the needle falls within the red index in the lower right of the metering scale. BTW, this is exactly how the meter on the FT and Pellix operate-they just have a permanently etched circle on the focus screen.

Also, I wouldn't call the FTb(or FT, Pellix, F-1, TX, or TLb) "heavily center weighted." They are strictly 12% partial meters with the metering area indicated by the gray box in the center of the frame. This gray box is actually a semi-silvered area on the focusing screen that is bouncing light to the metering cell just behind the focusing screen. On F-1 focusing screens you can see a cut-out in the frame of the screen for the metering cell to see through.

This is actually quite a capable meter, and I have a lot of perfectly exposed slides to back up my saying that. I was using my F-1 and FTb most heavily in the 2006-2008 time period. The key is fully understanding how the meter works and especially being aware that if it's not in the gray box, the meter doesn't see it. Also, remember that linear polarizers can throw off this meter badly and unpredictably.

[smiffy_smiffy]

Very many thanks ben, very interesting stuff, so good I will print it out !