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07-11-2012, 08:24 AM   #1
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camera metering not correct with M42-EOS adapter

Hi everyone,

I have a 5d Mk II and a few M42 lenses (Samyang 28mm f2.8 and some old Sears 135mm f2.8). I have the fotodiox M42 to EOS adapter (Amazon.com: Fotodiox Lens Mount Adapter, Black M42 (42mm x1 thread Mount) Lens to Canon EOS DSLR Adapter, fits Canon EOS 1d,1ds,Mark II, III, IV, 5D, MarK II, 7D, 10D, 20D, 30D, 40D, 50D, 60D, Digital Rebel xt, xti, xs, xsi, t1i, t2i, 300D, 350D, 400) which works fine. The camera's light meter picks up the exposure correctly and all is good.

The downside obviously to using the manual lenses is having to focus manually. I thought i might try an adapter that has the Focus Confirmation chip on it (Amazon.com: Fotodiox Pro Chrome V.2 Lens Mount Adapter with Programable Dandelion AF Focus Confirmation Chip, M42 Lens (42mm x1 thread Screw Mount) Lens to Canon EOS cameras, fits Canon EOS 1d,1ds,Mark II, III, IV, X, 5D, MarK II, 7D, 10D, 20D, 30D, ). I bought this second one. The focus confirmation works, but the metering is all off. It's overexposing my images. I think it has something to do with the programming on the chip? I'm not quite sure how it works. My camera is reading the aperature as "f4" when I have this 2nd adapter on.

New to the forum, looking forward to meeting some other manual lens users.

07-11-2012, 09:16 AM   #2
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I am curious to know the solution to this as I have always considered that this is the ultimate fall back if pentax stops making cameras. I have both a K mount and M42 kit, each containing upwards of 15-20 primes.

One thing to try is to carefully measure the camera's metering.

I do this by using a block wall or paved road (does not matter as long as the surface is uniform over the frame, and uniformly lit (I like normal skylight or daylight) Shoot each aperture letting the camera pick shutter speed, or at least match the shutter to zero the metering (not sure how canon works in this respect)

then plot greyscale value (measured using your photo editor) vs aperture and see how consistent it is.

You may find that the metering is not as good as you think. Clearly with pentax cameras, the metering needs to know the aperture, especially the K10 and K20, and this has long been a topic of discussion.

It may be that with the focus confirmation chip, the camera is making an assumption of open aperture value and getting screwed up. if this is the case, you may find that each lens either is completely wacky, or each lens may have a different offset compensation required.
07-11-2012, 10:08 AM   #3
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I came across these rather intimidating instructions:

Dandelion programming instructions


I assume though once programmed, you can only use the adapter for the lens programmed? Meaning a separate adapter would have to be bought for every lens.
07-11-2012, 11:17 AM   #4
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what it looks like, is as you suggest, you either reprogram for each lens, or have one for each lens.

Note however, the following.

If I interpret the explanation correctly, it seems as though the adaptor requires you to set the camera aperture to match the lens. I suspect that this is because the camera is then setting up other functions such as for use in flash mode. the non focus confirmation adaptor was simply setting exposure using the TTL metering,

the other functions are related to EXIF data, like focal length etc. the really interesting one is the focus adjustment. it looks like you can program FF/BF into the adapter.

interesting.

What is the shooting process you do with the non confirmation adapter? do you enter the aperture in the camera?

07-11-2012, 11:41 AM   #5
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Lowell,

My process for the non-confirmation adapter is pretty simple. I just focus with my eye and shoot. Exposure (light) meter on the camera works correctly. The EXIF data won't be correct, but I don't really care too much about that.


With the focus-confirmation adapter, the EXIF data should be correct, but I'll have to test after I program it.
07-11-2012, 12:06 PM   #6
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QuoteOriginally posted by bimbom Quote
Lowell,

My process for the non-confirmation adapter is pretty simple. I just focus with my eye and shoot. Exposure (light) meter on the camera works correctly. The EXIF data won't be correct, but I don't really care too much about that.


With the focus-confirmation adapter, the EXIF data should be correct, but I'll have to test after I program it.
I think if you program the adaptor, except for focal length, as long as you set the aperture on the camera to match shooting aperture you should be OK
11-15-2012, 09:10 AM   #7
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you can either program your adapter to your lens (aperture, focal range). or use it without recording real aperture value, basically the same way as the other adapter without the dandelion chip.

according to fotodiox's instruction manual, this method is recommended (especially when using multiple lenses with the same adapter).

A. Taking Picture Without Recording Real Aperture Value
(Recommended: No Programming Required)
a. Set Camera in Either AV or Manual Mode
b. Set Camera to Max Aperture Value (DO NOT Change
Aperture Value on Camera Body)
c. Compose and Focus
d. Set the Aperture Value on Lens
e. In AV Mode, the Shutter Speed Will Be Set Automatically.
In Manual Mode, Set the Shutter Speed accordingly.
f. Take Picture

copied from here http://www.fotodioxpro.com/manuals/fotodiox-canoneos-chip-manual.pdf
11-15-2012, 09:19 AM   #8
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QuoteOriginally posted by Lowell Goudge Quote
I think if you program the adaptor, except for focal length, as long as you set the aperture on the camera to match shooting aperture you should be OK
Nope. ideally it should work like you've mentioned. however, when you match aperture value on the camera to the aperture value on the lens, in aperture priority mode - all pictures come out overexposed. looks like, dandelion chip is somehow confusing the camera exposure meter....

11-15-2012, 06:12 PM   #9
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QuoteOriginally posted by L&D Quote
Nope. ideally it should work like you've mentioned. however, when you match aperture value on the camera to the aperture value on the lens, in aperture priority mode - all pictures come out overexposed. looks like, dandelion chip is somehow confusing the camera exposure meter....
Maybe the camera is metering thinking the lens is wide open, and then changing shutter speed to match the stopped down setting but since you are already stopped down it is over exposing by the number of stops you stop down.
11-15-2012, 06:45 PM   #10
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In the same Fotodiox Instruction Manual:

QuoteQuote:
Taking Picture With Real Aperture Value in Manual Mode
(Required: Set Max Aperture of the Lens)
(Refer to the Programming Section to set the Maximum Aperture Value)
a. Set Camera Manual Mode
b. Wide Open Lens Aperture
c. Set Aperture Value and Shutter Speed on Camera
Body According to Camera Meter, While
Aperture on Lens is at Max.
d. Focusing and Composing
e. Set Aperture Value on Lens and Camera to be the same
f. Take Picture
11-16-2012, 08:53 AM   #11
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QuoteOriginally posted by Lowell Goudge Quote
Maybe the camera is metering thinking the lens is wide open, and then changing shutter speed to match the stopped down setting but since you are already stopped down it is over exposing by the number of stops you stop down.
it's happening only in the opposite scenario, to be precise when aperture values of lens and camera match, then pictures come out over-exposed. but, when you set aperture to the max on the camera (say 1.0) and stop it down directly on the lens, then metering is correct.
11-16-2012, 09:06 AM   #12
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QuoteOriginally posted by rhodopsin Quote
In the same Fotodiox Instruction Manual:
yup...

i don't even bother recording the aperture value anymore, just set it on the camera to the max, and stop it down on the lens.

Last edited by L&D; 11-16-2012 at 09:30 AM.
11-17-2012, 03:44 PM   #13
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QuoteOriginally posted by L&D Quote
it's happening only in the opposite scenario, to be precise when aperture values of lens and camera match, then pictures come out over-exposed. but, when you set aperture to the max on the camera (say 1.0) and stop it down directly on the lens, then metering is correct.
That is exactly what I meant.

The camera is subtracting shooting aperture from F 1 and then metering off the set aperture, making the adjustment Twice
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