Author Topic: Tamron Adaptall-2 question  (Read 706 times)

Chulster

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Re: Tamron Adaptall-2 question
« Reply #15 on: July 03, 2020, 03:10:57 »
Damn.

I received the Dandelion chip today. But I can't install it just yet.

It turns out that the light baffle of the Adaptall-2 mount, from which I need to remove some material in order to fit the Dandelion, is made of rather tough metal. The job would take forever using my cheap needle files. I'm going to have to buy a Dremel.

Chulster

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Re: Tamron Adaptall-2 question
« Reply #16 on: July 06, 2020, 00:12:16 »
Ugh. So I cut and filed away a piece of the light baffle to make room for the Dandelion. It was a good fit.

Unfortunately, I forgot that the light baffle on this Adaptall-2 mount rotates several millimeters when you put the mount on the lens. As a result, the Dandelion's contacts do not align with the camera's. Not at all. I'm going to have to remove more material to allow shifting the location of the Dandelion by several millimeters.

Doubly unfortunately, I had already glued the chip to the mount. And I was unable to remove the chip without destroying it.

So now I have to order another Dandelion and wait some more.

I think I should give up photography.

Erik Lund

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Re: Tamron Adaptall-2 question
« Reply #17 on: July 06, 2020, 09:18:28 »
I would recommend to buy some spare Dandelion if you plan on installing more of them, they are quite fragile and prone to damage in all sorts of ways; breaking off, splitting, pins sticking or falling out,,,  :o :o :o

Good luck!  ;)
Erik Lund

Chulster

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Re: Tamron Adaptall-2 question
« Reply #18 on: July 08, 2020, 08:38:38 »
It turns out my Dandelion chip had not been destroyed after all. The plastic casing was damaged, but the chip was still operable. So I fortified the casing with some epoxy and reinstalled the chip on the Adaptall-2 mount after removing more material from the light baffle to get the chip into the right position.

I now present the results of the exposure test. I took two sets of exposures from f/2.8 through f/22 at whole-stop intervals. Manual exposure was used in order to eliminate metering variation as a factor. ISO was a constant 100. For each stop change in aperture, I simply changed the shutter speed by one stop to get the same theoretical EV every time.

The first set of seven exposures was done using a command dial on the camera to control aperture. The second set (the control set) was done using the lens's aperture ring to control aperture. Both sets can be found at the following URL:

https://drive.google.com/drive/folders/1EffrCxTsWboDwtgkyY5gcl2sevk7b896?usp=sharing

Spoiler alert: it is obvious that this lens, or the combination of this lens and this Adaptall-2 mount, does not provide linear control of aperture via the stop-down lever. (Again, I am using "linear" here in the sense that a constant increment in the position of the stop-down lever will produce a constant increment in the f-number. For example, one millimeter of change in position of the stop-down lever will result in one stop of aperture change.) You can see how the photos become progressively overexposed as aperture is changed from f/2.8 to f/16. There is a slight drop in exposure going from f/16 to f/22 for unknown reasons, but the overall conclusion of non-linearity is inescapable.

Curiously, you can also see some inconstancy of exposure in the control set. Exposures get slightly darker as you go from f/2.8 to f/22. But not enough to really matter.

I am going to keep the Dandelion on this lens but use the aperture ring since it obviously produces much more consistent results. Oh well! At least I get to retain some of the other benefits of the chip: correct lens identification in EXIF and the enabling of highlight-weighted metering.