[Medex]

Hello,

Yesterday I tried to access Sigma lens ROM file. There is not much numbers and letters, and they all are organised in 8 sections. First section differs from other 7. The first and second sections ar displayed in the picture attached.
Does anybody know the meaning of those numbers and letters? Let's say, I have aperture number f4.5 as minimal and would like to change it to f1.9 (to be displayed on the camera's dysplay). How do you think, is it possible to make this by changing some parts of the code in ROM file?
I know some people make Pentax lens conversions from SDM to screw drive and they access ROM file data to modify some places in the code (C0 -->80).

Thank you.

Attached Images

 

[K1N8]

It usually helps to have multiple variations of a ROM file, to compare changes and commonality.

[Medex]

It usually helps to have multiple variations of a ROM file, to compare changes and commonality.

Are you suggesting to access the ROM file on another Sigma lens and compare code?

[Hank]

The data that you are showing is really bare.

For those who do not know how to read the information being shown:
The row header is the hex offset, 0 to 15 (or 1 to 16).
The column is the memory offset of the program, starting at 0000 and ending.
The first set of characters is A0 (space) and 00 (null). The 94s in the second set are a nothing character.

[K1N8]

Are you suggesting to access the ROM file on another Sigma lens and compare code?

If the ROM keeps the state and current configuration of the Lens, then the usual process is: get a ROM dump, change one single setting, get another ROM dump, compare. Repeat.

Comparing ROM's from different lenses can also give some insights, when the feature set is known. The smaller the difference between the Lenses, the better.

[UncleVanya]

What would the point be of having the lens lie? EDIT: The example given on f/stop just doesn't make sense to me. I do edit the files for SDM conversion and in that case you are changing the bits that report the type of focusing system the lens is capable of using so that the lens lies and says it doesn't have SDM. I can't imagine a similar desired change to make - unless you can edit the focus at a given mm/distance.

[stevebrot]

Does anybody know the meaning of those numbers and letters? Let's say, I have aperture number f4.5 as minimal and would like to change it to f1.9 (to be displayed on the camera's dysplay).

The "numbers and letters" are hexadecimal numbers (data) from set locations in the lens' read-only memory. Whether your task is doable is hard to say, but since your understanding is minimal, you may not be the person to do the attempt. Failure may brick the lens. Rather than start with hacking the lens ROM, it might help to share why you want to do such a thing.


Steve

[Medex]

The "numbers and letters" are hexadecimal numbers (data) from set locations in the lens' read-only memory. Whether your task is doable is hard to say, but since your understanding is minimal, you may not be the person to do the attempt. Failure may brick the lens. Rather than start with hacking the lens ROM, it might help to share why you want to do such a thing.


Steve

I made manual lens adapter for Pentax camera. It is projection lens with helicoid and m65 adapter on the end. The adapter has PK mount and contacts to imitate autofocus lens, and the chip, that transfers focal distance and aperture data. Now I have 170mm f4.5. But want to do 170mm f1,9 or 1,8.
Such an adapter allows the lens to work in Live View with face detection function. It is more convenient way to make precise focusing there where the face is (no need for reframing to achieve good composition). Look here:
Pentaxians Public Group | Facebook

---------- Post added 10-29-18 at 08:10 PM ----------

What would the point be of having the lens lie? EDIT: The example given on f/stop just doesn't make sense to me. I do edit the files for SDM conversion and in that case you are changing the bits that report the type of focusing system the lens is capable of using so that the lens lies and says it doesn't have SDM. I can't imagine a similar desired change to make - unless you can edit the focus at a given mm/distance.

look here for more info:
Pentaxians Public Group | Facebook

[UncleVanya]

I made manual lens adapter for Pentax camera. It is projection lens with helicoid and m65 adapter on the end. The adapter has PK mount and contacts to imitate autofocus lens, and the chip, that transfers focal distance and aperture data. Now I have 170mm f4.5. But want to do 170mm f1,9 or 1,8.
Such an adapter allows the lens to work in Live View with face detection function. It is more convenient way to make precise focusing there where the face is (no need for reframing to achieve good composition). Look here:
Pentaxians Public Group | Facebook

---------- Post added 10-29-18 at 08:10 PM ----------


look here for more info:
Pentaxians Public Group | Facebook

Sorry - I'm not joining a facebook group for more info on this. I am unlikely to be that helpful in this case. I am not certain that the f/stop data is even transmitted in a way that isn't an offset against a known minimum. I was under the impression that the lens id was transmitted and the focal length and so forth and from this the camera determined the f/stop but I'm likely confused. I know that with manual focus A series lenses the entire thing is done via the contacts not the data pin - but since you have a data pin then that may be ignored?

[Medex]

Sorry - I'm not joining a facebook group for more info on this. I am unlikely to be that helpful in this case. I am not certain that the f/stop data is even transmitted in a way that isn't an offset against a known minimum. I was under the impression that the lens id was transmitted and the focal length and so forth and from this the camera determined the f/stop but I'm likely confused. I know that with manual focus A series lenses the entire thing is done via the contacts not the data pin - but since you have a data pin then that may be ignored?

ok, I will copy / paste
"The manual focus lens and Face Detection feature in the Pentax body are already a reality
Who do portrait photography with non-traditional manual focus lenses (let say, projection lenses), probably knows that Face Detection does not work as one of the autofocus modes in Live View. Normally we use center focus point to acquire focus, we enlarge the image, then do focusing more precisely, then diminish the image, recompose and press shutter button. This is NOT CONVENIENT. Try the autofocus lens and see how comfortable it is to shoot people when their faces are recognized by the camera, you are able to compose the image ant shoot.
It's even harder to use any kind of lens with Petzval optical schema. Those lenses have curved area of focus. If you do focusing in the center, then reframe the picture and shoot, the face will be out of focus.
Well, that's it. I decided to cheat the camera. I made the m65 adapter with a chip and now my manual focus projection lenses are able to work with face detection feature. No need to recompose the image after focusing with central point, because focusing is done where you choose the face to be.
I made adapter for my Visionar 168 mm and Kipronar 165 mm lenses. The EXIF shows 170 mm focal distance. But it is possible to make 70, 80, 90, 100, 110, 120, 135, 150, 170 and so on until 300 mm focal lenght. Aperture is f4,5 (should be f1,9), but exposure is right. Maybe I will try to reprogramm the chip if I find the way to access ROM data.
This adapter is for m65 focusing helicoid.

[K1N8]

Interesting. So the chip does connect to the camera body, but does it also connect "up" to whatever lens sits on this adapter?

[Medex]

Interesting. So the chip does connect to the camera body, but does it also connect "up" to whatever lens sits on this adapter?

it does not need to connect to the lens, because it is projection lens without iris diaphragm. The chip transfers focal lenght and max to min aperture data to the camera via 7th pin (digital information) and this allows to use the MANUAL focus lens in Live View with face detection function. The chip is needed for this and for portraits only. Such an adapter also allows to use manual focus lens with the flash in HSS mode.

[Riggomatic]

Would this allow you to select focus points, like an AF lens as well?

Interesting project!

[K1N8]

The chip transfers focal lenght and max to min aperture data to the camera via 7th pin (digital information)

So blocking the digital pins and only leaving the PK-A "aperture" pin is not an option.

Hacking the ROM data is not going to be easy. As said before it can easily brick the chip. How did you read the ROM data anyway? You have a flashrom programmer?

You also need to verify, that you can read and write the unmodified ROM image. Next is finding the exact chip, all available manuals and if possible any emulators that can execute the binary ROM data. Which is also difficult because something has to "pretend" to be the camera body, or at least that specific circuit. The chip is probably expecting an answer or some basic communication between chip and camera body.


You said you can set the focal distance the chip reports to the camera? How is that done?

[stevebrot]

Aperture is f4,5 (should be f1,9),

Are you sure maximum aperture/aperture range is transmitted by the data pin with the chip you are using?* Default is to use the mount contact pattern, even on AF lenses. This can be tested by masking the data pin and seeing what maximum aperture is detected.


Steve

* The camera body determines available apertures by calculation from minimum aperture and aperture range as encoded by the mount contacts or provided by polling the data contact.