# Sensitivity (or other) gains from BSI?



## 3kramd5 (Jun 10, 2015)

What kind of differences can one legitimately expect from a BSI sensor? Is circuitry generally large enough that having it on the front makes a significant impact on light-gathering capabilities?




Are we prohibited from discussing the A7R2? My previous thread was deleted, but perhaps because I just posted a press release with an itchy posting finger. I went back to add to this question, but it was gone. If they've really fixed the shutter (electronic 1st curtain) and BSI makes a real difference, I may not take delivery of my 5DS and sell my A7R. 

Thoughts?


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## msm (Jun 10, 2015)

We'll have to wait and see actual tests before we know if it does make a significant difference in sensitivity. Part of the benefits from BSI are the faster readouts enabling 4K on a high resolution sensor like this.

And the shutter shock issue is fixed, not only does it have EFCS but also a full electronic shutter mode with absolutely no sound or vibrations, though I expect that to have a rather slow scan speed like on the A7S.


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## psolberg (Jun 10, 2015)

Since there is no BSI sensor this large from ANY camera manufacturer, you'll find out later. But again, keep in mind sony was going to have improvements regardless of it being BSI or not, so simply comparing it to the A7R is not really fair.

But one thing is clear: They obviously went this direction because it provided them with a competitive advantage over old school CMOS. At 42MP, they were probably going to match the noise levels of their 36MP sensor just on technology and process advances alone anyway. The BSI is probably going to rock it.


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## drjlo (Jun 10, 2015)

I'm thinking that future Sony BSI FF sensors in the 24-36 MP range may be even yummier


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## Sporgon (Jun 10, 2015)

Look what higher QE has done for larger sensors.........

It must further improve very high ISO performance. On a FF sensor at low ISO I think we will see about zero benefit in reality.


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## 3kramd5 (Jun 11, 2015)

psolberg said:


> Since there is no BSI sensor this large from ANY camera manufacturer, you'll find out later.



No I won't, unless they also release a non-BSI sensor of the same generation. But certainly there must be comparisons between BSI and traditional sensors, no (obviously not at this scale, but that should not matter much).


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## Marsu42 (Jun 12, 2015)

3kramd5 said:


> psolberg said:
> 
> 
> > Since there is no BSI sensor this large from ANY camera manufacturer, you'll find out later.
> ...



I'm keen to see the real-world benefits too, and if they roll out this type of sensor to their whole range of cameras or if there are some hidden drawbacks vs. the legacy design.

My speculation is that there will be a significant gain, or they would just go on researching and not take the pain to put a new sensor tech (costing lotsa $$$) out on the market.


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## jrista (Jun 12, 2015)

dilbert said:


> According to the wikipedia page
> 
> https://en.wikipedia.org/wiki/Back-illuminated_sensor
> 
> ...



Given the context of the article, which actually states "+8dB signaling" not "signal", I believe they are actually referring to improvements in the electronic control signals that are used to perform sensor reset and readouts, not the actual image signal. It directly attributes the improvement to materials advances in the photodiode and process (probably the move to 180nm and copper wiring). That to me tells me they are talking about electronics, circuitry, and control signals rather than image signals. 

As much as we are all concerned about the image signal, the quality of the control signal that operates the circuitry is still very important to giving us the IQ we look for. The materials and process used to manufacture the sensor play a big role in that. However, I do not believe that the BSI design improved image signal DR by 10dB...that would be a significant improvement for sure. (If we went from say 84dB to 94dB, that would be a jump from 14 stops to 15.7 stops...very significant.)


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## Mt Spokane Photography (Jun 12, 2015)

There is a diminishing return on performance as sensors get larger. At one time, it was said that APS-C was the largest to have any noticeable benefit.

However, as photosites get smaller, the game changes. The percentage of space taken up by the wiring gets larger, and even for FF, there is a improvement. The sensor technology is mature, so small improvements are the best we can hope for. Stacked sensors are yet another type of small improvement that were originally aimed at the cell phone cameras, we will see them move into the large sensor cameras in a couple years. The 1 inch sensors are now here. They may yield APS-C noise performance, or nearly so, so it will be interesting to see.

As sensors move to higher MP's, BSI is going to be common or even standard.


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