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09-14-2019, 06:34 AM   #1
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Hacking the 60-250 SDM/screwdrive fix

Ok, probably everyone knows that the da* 60-250 cannot be converted to screwdrive when the SDM fails, as the hack that works on the other lenses does not work on the 60-250.

But why?

I have a theory, (for which there may only be a smidge of supporting evidence) as to why it doesnít work.

I donít actually have a 60-250, but itís been bugging me....

Observations:

a) The 60-250 has the biggest zoom range of all the SDM/screwdrive lenses.
b) There are multiple records in the firmware that require the C0 -> 80 change in the different lenses. It seems to be that the camera can/will/may read these records from the lens at any time when the focus or zoom rings move. This data may include current zoom position, and current focus distance.
c) The amount of filled in data in the firmware seems to vary from lens to lens (for example the da* 300) has much less, but it is not a zoom, so perhaps not surprising.
d) When applying the hack to the 60-250 it kinda/sorta works until the focus changes or perhaps the zoom changes, which implies a non modded record was read from the lens.

Theory:

The fix doesnít work because the rom table in the 60-250 is larger than the camera debug options can read or write. When the fix is applied, some, but not all of the rom is modified. When the 60-250 lens is modded and used, the camera quickly reads in a non modified record and switches back to sdm, which causes failure.

The fix:

Somebody needs to modify the firmware to read and write more than 2k bytes of rom, which is how much the debug options are currently able to read and write to/from the lens, 4kb would be good I think.

Or, perhaps easier, modify the interactive lens rom editor (another debug menu option). Currently this debug option allows changes to be made only to the first 1kb of the rom (highest allowed offset 0x03FF) it should ideally be perhaps 0x0FFF (4kb). It is notable that the rom sd card read/write routines can handle 2kb of rom, but the interactive editor is restricted to 1kb, which really highlights the fact that the lens debug options are old code that may not handle changes made to lens rom size over time. Plus they took them out altogether in the later cameras.

Regrettably this is only a theory, it would require someone quite skilled to even find out if the reasoning is valid.

I have seen some old Ďhackerí threads, are any of these people still around?

If the theory is correct, the community would only need one modified camera to fix 60-250 lenses... It may not be correct, however...

09-14-2019, 06:54 AM   #2
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It would be awesome if somebody could figure it out. I love my 60-250 but I would be much happier if it was screwdrive
09-14-2019, 07:30 AM   #3
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I can check again. But as I recall. The erratic behavior occurs without changing zoom and without pointing at a new object.

It is possible you are correct, but it will be hard to test.
09-14-2019, 08:26 AM   #4
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I agree, it’s like trying to figure out what’s in Pandora’s box without being able to open it.

However, for all I/we know the camera downloads the entire rom at once, and then uses that, which would still cause consistent failure. I guess....

09-15-2019, 11:33 PM   #5
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QuoteOriginally posted by UncleVanya Quote
I can check again. But as I recall. The erratic behavior occurs without changing zoom and without pointing at a new object.

It is possible you are correct, but it will be hard to test.
Has anyone tested the modded firmware while also preventing the SDM pin from shorting? It would see the lens as an F/FA lens, potentially working as a screwdrive only?
09-16-2019, 06:03 AM   #6
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QuoteOriginally posted by ZombieArmy Quote
Has anyone tested the modded firmware while also preventing the SDM pin from shorting? It would see the lens as an F/FA lens, potentially working as a screwdrive only?
I'm not sure. In the other focal length lenses I know people tried disabling the SDM connection which failed.
09-16-2019, 09:17 AM   #7
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QuoteOriginally posted by UncleVanya Quote
I'm not sure. In the other focal length lenses I know people tried disabling the SDM connection which failed.
Just thought it'd be worth testing.
09-16-2019, 07:25 PM   #8
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QuoteOriginally posted by ZombieArmy Quote
Just thought it'd be worth testing.
It might. I am going to try later when I have time.

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