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[quote name=isaac;278134

for (i = 0' date='j = 0x117c;i < 15;i++,j += 0x800)[/quote]

 

Umm, an insider.

I do speak C, but I'll need to think about that - why 0x117c is not immediately obvious to me....

 

Sandy

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Nor me...

 

For those that don't speak C, this statement initiates a program loop which will run 15 times, with a program variable "j" taking an initial value of 4476, incremented by 2048 each time.

 

Maybe isaac is saying the sensor is divided into 15 concentric rings with a table of 2048 corrections per ring. Who knows!

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Hello Sandy!

I do speak C, but I'll need to think about that - why 0x117c is not immediately obvious to me....

Ok, next hint:

117C 197C 217C 297C .....

0 0 0 0 ....

8 0 0 0 ....

10 8 8 8 ....

13 10 10 8 ....

15 10 10 10 ....

18 13 13 13 ....

19 15 13 13 ....

20 16 15 15 ....

22 16 16 15 ....

23 18 16 16 ....

25 19 18 16 ....

26 20 19 18 ....

28 20 19 18 ....

29 21 20 19 ....

... and so on untill all are 255 ... exactly 2048 steps in 15 tables

 

You can not look into the camera, but....

 

greatings, Harald

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Hello Mark!

Maybe isaac is saying the sensor is divided into 15 concentric rings with a table of 2048 corrections per ring. Who knows!

Maybe....

The sensor is divided - from its center - into 2048 concentrics rings. And - as far as I assume - there are 15 different functions for all the (supported Leica) lenses (and maybe stops).

The 'correction functions' are a linear combination of 1st, 2nd, 3rd and higher order polynomes. And we know, that EACH curve can be represented by a polynom...

Extract them, plot them and you will see a kind of mirror curve of all the plots we have seen here already...

 

greatings, Harald

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Hello Mark!

 

Maybe....

The sensor is divided - from its center - into 2048 concentrics rings. And - as far as I assume - there are 15 different functions for all the (supported Leica) lenses (and maybe stops).

The 'correction functions' are a linear combination of 1st, 2nd, 3rd and higher order polynomes. And we know, that EACH curve can be represented by a polynom...

Extract them, plot them and you will see a kind of mirror curve of all the plots we have seen here already...

 

greatings, Harald

 

Harald,

 

Do you any feeling for the data is actually encoded - where is the info for separate colors, for example?

 

Sandy

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Hello Sandy!

Do you any feeling for the data is actually encoded

What exactly do you mean - or want to know?

- where is the info for separate colors, for example?

Which info for which separation? You mean the cyan color shift or what?

If you mean the compensation of the cyan shift, than I would highly recommend to better speak about the reconstruction of the cutoff red in the corners!

The amount of this cutoff depends highly on the used filter (the one filter you have in use).

I have done some investigations on these UV/IR cutoff filters (Leica brand and also B&W) by doing measurements in a 'recording UV-visible-IR spectrophotometer' with filter set in various angle from 90 to 45 degree. Because of the fact that such interference filters are pure cutoff filters, the cutoff wavelength is going down from IR to the red wavelength. And keep in mind, it is a CUTOFF, not a dampening. The angle of 45 degree is the point, where almost all red (for wich the sensor is sensitiv) is reduced to 0 (zero), so the only information for the red color of an object is build up from rays below 45 degree (and therefore we have to visual impress of cyan).

I have measured two Leica and two B&W filters. All of them have a different cutoff shift depending on angle. There are more differences between the two Leica filters than to the B&W filters... the two B&W filters behave very similar. Maybe this works 'as designed' so a Leica filter is only useable for the Leica lens it is made for.

So in theory (and also in practice) we can compensate the corners only for blue and green, because there is no more red signal. Well, there is some red signal from light entering the lense outside its center (as it will do, when stopped down) but than, we need also high resolution data and not the decompressed 8-bit data... remember, the decompressed data has only high dynamic, but no high resolution!

Beleave me, I have done a lot of work on this issue long before I have bought my M8. I have thousends of scanned negatives from my Contax T2 (Zeiss Sonnar 2.8/38) which vignettes up to stop 5.6... Corner compensation worked only with 3x16 bit scanner data, no chance with 3x8 bit scanner data. So I am realy experienced.

Do not hesitate to ask me, but try to make you free from the idea, to use the 8-bit data...

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I have measured two Leica and two B&W filters. All of them have a different cutoff shift depending on angle. There are more differences between the two Leica filters than to the B&W filters... the two B&W filters behave very similar. Maybe this works 'as designed' so a Leica filter is only useable for the Leica lens it is made for..

 

Thanks for speaking up. It sounds like you have some useful information for this discussion. The only Leica filters that are currently in wide circulation are 39mm and 43 mm (with hints that the 46 and 55 are starting to ship). What sizes did you measure?

What cutoff wavelengths did you find for all four?

 

 

I'm sorry to hear that the Leica filters exhibit large variability, and it sounds as if you are using the right equipment to test for this. I don't believe that they can design a filter for a specific lens. For example, the 39mm filter fits the 28/2.8, the 35/2.0, some of the 50's and perhaps even the 90/4.0 macro lens. These would have very different vignetting correction requirements.

 

scott

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Hello Scott!

The only Leica filters that are currently in wide circulation are 39mm and 43 mm (with hints that the 46 and 55 are starting to ship). What sizes did you measure?

Leica 46x0.75 and 43x0.5

B&W 77x0.75 and 72x0.75 (which falls down and crashes totally :-(

What cutoff wavelengths did you find for all four?

Have thought the plots will be in my office, they are not here and hopefully at home. Will report tomorrow in detail.

I'm sorry to hear that the Leica filters exhibit large variability,

Please do not overrate my statement. I have started to measure at 45 deg., because this is the maximum angle of a 21mm lense. On 1.3 crop this will be reduced to 38 deg (from center) and the almost totaly cutoff of the red channel does not matter.

The difference between Leica and B&W filter cutoff at 45 deg. is app. 20nm and in the range of app. 2 deg. of angle. So for the practical useage of the filters, there is in fact no difference between Leica and B&W except the measureabel difference.

I don't believe that they can design a filter for a specific lens.

I agree. I think the differences result from the production or even the fact, that I tried to position them in 45 deg and have failed +/- 1 deg.

For example, the 39mm filter fits the 28/2.8, the 35/2.0, some of the 50's and perhaps even the 90/4.0 macro lens. These would have very different vignetting correction requirements.

Please do not mix up the (multicolor) vignetting and the angledepending (partial) cutoff of the red channel. These effects are additiv, but the red channel cutoff follows a quite other physical legality (? sorry, English is not my nativ language) than the known vignetting.

The lens and stop depending vignetting could be approximated by a polynom (1st, 2nd and maybe 3rd order) the red cutoff depends on the one hand of the tangens of the angle and on the other hand of the wavelength range of the single cutoff band and has points of discontinuity which means the ray is totally suppressed (phase difference 180 deg.)

You can imagine such a filter as a number of single filters, each for a wavelength range of app. 20 +/-10nm realized in different layers on the surface of the filter glas.

If I do not find my plots, I can easyly repeat my measures (axcept the brocken filter), because the spectrophotometer is in the lab next door.

And luckyly, I had saved the plots (43, 46 and 77) in the equipment :-)

I will scan the plots and put them here in the forum...

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Nice. If you have time, it would be interesting to see the cutoff behavior at 30 degrees as well. After all, there is a visible effect even with 35mm lenses on the M8.

 

thanks,

 

scott

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Hello Scott!

If you have time, it would be interesting to see the cutoff behavior at 30 degrees as well. After all, there is a visible effect even with 35mm lenses on the M8.

I will measure this angle tomorrow, for today the already done plots:

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That's - strange. Very similar performance at at 0 degrees, but very different at 45 degrees. Not what I would have expected. Looks almost like the two Leica filters are from different manufacturers.....Didn't Sean (or someone) pick up some scuttlebutt that some Leica filters were B&W, but some not?

 

Sandy

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It wasn't scuttlebut exactly. Leica's initial filters *were* 486s but then the design changed a bit. They're all variations on the 486, I believe, but I'm not sure about what ways the various size filters differ from a 486.

 

Cheers,

 

Sean

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Hello Scott!

If you have time, it would be interesting to see the cutoff behavior at 30 degrees as well.

Here is a plot of the E43 filter at 0, 30 and 45 deg.

More than 45 deg are not possible in the used equipment, will try tomorrow to measure the E46 again...

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Didn't someone mention they'd received Leica filters made in Japan (Hoya)?

 

My E39's are packed Leica style but the carrier's package and documentation said 'Japan'.

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Hello Sandy!

That's - strange. Very similar performance at at 0 degrees, but very different at 45 degrees. Not what I would have expected. Looks almost like the two Leica filters are from different manufacturers.....Didn't Sean (or someone) pick up some scuttlebutt that some Leica filters were B&W, but some not.

Now I have proofed the difference between my two Leica filters (E43 and E46).

I have repeated with the same test arrangement as yesterday with E43 the E46 filter (and also included the 30 deg. angle).

The shift of the cutoff wavelength is quite different and all but linear. But make your onw interpretation...

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