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08-29-2018, 03:44 PM   #1
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The real 645!

The size of 645 film is 56 x 42! But the current generation of medium format sensors are 44 x 33. Why is this? The current generation of medium format cameras are mostly mirrorless. This means, they have a much smaller footprint. My question is, if cameras can shoot at speeds in excess of 20 fps, why can't they integrate a real 645 sensor ?

08-29-2018, 04:01 PM   #2
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I believe it's sensor availability and cost. For the most part, the Pentax 645 lenses (even the new ones) can accommodate full-frame-645, so they're ready if it ever happens. (The newer version of the 25mm f/4 lens is the exception, due to the built-in hood vignetting.)
08-29-2018, 04:03 PM   #3
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There have been backs with larger sensors, just not for the "cheap" pentax 645, fuji etc. Check out Phase one P65+, it's quite old (found a review from 2009) and it has a sensor size of 53.9mm x 40.4mm. The recently announced IQ4 back is also "full frame medium format" and it costs just over 50k
08-29-2018, 04:07 PM   #4
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QuoteOriginally posted by aaacb Quote
There have been backs with larger sensors, just not for the "cheap" pentax 645, fuji etc. Check out Phase one P65+, it's quite old (found a review from 2009) and it has a sensor size of 53.9mm x 40.4mm. The recently announced IQ4 back is also "full frame medium format" and it costs just over 50k
Holy shit! That's expensive! I could buy the k-1 plus all the lenses I ever dreamed about!

---------- Post added 08-29-18 at 04:07 PM ----------

QuoteOriginally posted by Paul the Sunman Quote
I believe it's sensor availability and cost. For the most part, the Pentax 645 lenses (even the new ones) can accommodate full-frame-645, so they're ready if it ever happens. (The newer version of the 25mm f/4 lens is the exception, due to the built-in hood vignetting.)
I hope they do!

08-29-2018, 04:17 PM   #5
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I believe that there will be a Pentax 645 digital body that uses the full-frame 645 sensor before much longer. It’s their obvious answer to the Fujifilm and Hasselblad MF bodies, without considerable R&D and manufacture re-tooling. The only question for me is when – I would have thought sooner, rather than later, would be critical to maintaining sales in this premium market segment.
08-29-2018, 04:22 PM   #6
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8 10 inch sensor backs for view cameras have been on the market for quite some time. A fellow I know from high school uses these for a business he runs making limited prints of artist's original works for the artist to sell.
08-29-2018, 04:36 PM   #7
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QuoteOriginally posted by RobA_Oz Quote
I believe that there will be a Pentax 645 digital body that uses the full-frame 645 sensor before much longer. It’s their obvious answer to the Fujifilm and Hasselblad MF bodies, without considerable R&D and manufacture re-tooling. The only question for me is when – I would have thought sooner, rather than later, would be critical to maintaining sales in this premium market segment.
Well they'd have to develop their own sensor, just like Nikon did! Cuz no one's designing sensors that large!
08-29-2018, 04:42 PM   #8
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QuoteOriginally posted by SunnyG. Quote
Well they'd have to develop their own sensor, just like Nikon did! Cuz no one's designing sensors that large!
You mean, aside from Sony?

08-29-2018, 05:01 PM   #9
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It’s not really about “designing” a sensor that size but more about how many wafers they can cut from a sheet with the smallest amount of waste.
08-29-2018, 06:09 PM - 1 Like   #10
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QuoteOriginally posted by twilhelm Quote
It’s not really about “designing” a sensor that size but more about how many wafers they can cut from a sheet with the smallest amount of waste.
When it comes to such things wasted wafer space ins't the concern, it is yields and cost. I still believe that current state of the art fabs are running 300mm wafers which are mostly round but have a slice out of them so that they get properly aligned in the machines. When I last worked around wafers the current state of the art had just switched to 200mm or was going to switch, but the place I worked was still on 75mm ones (3"). At the time a blank 3" wafer would cost about $20 and bigger blank ones basically scaled with surface area so assuming that a 3" wafer today would still cost around $20 a blank 300mm one would cost somewhere in the low $300s. The major cost in semiconductors is the cost to run the machinery to make them and the engineering for designing them. Larger wafers allow more to be created at a time but even with a 300mm wafer you aren't going to be placing many 60mmx45mm (likely slightly larger) dies on it. Add in that they way the make semiconductors there is never a 100% yield and with larger dies there is an ever greater chance of there being a critical defect. So the number of dies we could fit on a 300mm wafer is going to be substantially less than 30 probably closer to 15. Of those 15 it wouldn't surprise me if 5 were bad. From the time that wafer is loaded in at one end of the process until the time it exits the other end may take a day as it moves from one multi million dollar (probably 10s of millions of dollars) machine to another. Hopefully in all of the baking that is done there wasn't a defect in the wafer that causes it to shatter from the thermal stress.
08-29-2018, 06:26 PM   #11
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QuoteOriginally posted by MossyRocks Quote
When it comes to such things wasted wafer space ins't the concern, it is yields and cost. I still believe that current state of the art fabs are running 300mm wafers which are mostly round but have a slice out of them so that they get properly aligned in the machines. When I last worked around wafers the current state of the art had just switched to 200mm or was going to switch, but the place I worked was still on 75mm ones (3"). At the time a blank 3" wafer would cost about $20 and bigger blank ones basically scaled with surface area so assuming that a 3" wafer today would still cost around $20 a blank 300mm one would cost somewhere in the low $300s. The major cost in semiconductors is the cost to run the machinery to make them and the engineering for designing them. Larger wafers allow more to be created at a time but even with a 300mm wafer you aren't going to be placing many 60mmx45mm (likely slightly larger) dies on it. Add in that they way the make semiconductors there is never a 100% yield and with larger dies there is an ever greater chance of there being a critical defect. So the number of dies we could fit on a 300mm wafer is going to be substantially less than 30 probably closer to 15. Of those 15 it wouldn't surprise me if 5 were bad. From the time that wafer is loaded in at one end of the process until the time it exits the other end may take a day as it moves from one multi million dollar (probably 10s of millions of dollars) machine to another. Hopefully in all of the baking that is done there wasn't a defect in the wafer that causes it to shatter from the thermal stress.
Very interesting information. And it makes sense why larger sensors have a higher cost ratio when comparing to, say an ape-c sized sensor.
08-29-2018, 07:12 PM   #12
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The bigger the sensor/wafer, the higher the cost to make them, the higher the price it is to sell them, smaller profit return.
08-29-2018, 07:47 PM   #13
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QuoteOriginally posted by RobA_Oz Quote
You mean, aside from Sony?
The Sony developed sensor is 44 x 33. Not actually 645

---------- Post added 08-29-18 at 07:50 PM ----------

QuoteOriginally posted by MossyRocks Quote
When it comes to such things wasted wafer space ins't the concern, it is yields and cost. I still believe that current state of the art fabs are running 300mm wafers which are mostly round but have a slice out of them so that they get properly aligned in the machines. When I last worked around wafers the current state of the art had just switched to 200mm or was going to switch, but the place I worked was still on 75mm ones (3"). At the time a blank 3" wafer would cost about $20 and bigger blank ones basically scaled with surface area so assuming that a 3" wafer today would still cost around $20 a blank 300mm one would cost somewhere in the low $300s. The major cost in semiconductors is the cost to run the machinery to make them and the engineering for designing them. Larger wafers allow more to be created at a time but even with a 300mm wafer you aren't going to be placing many 60mmx45mm (likely slightly larger) dies on it. Add in that they way the make semiconductors there is never a 100% yield and with larger dies there is an ever greater chance of there being a critical defect. So the number of dies we could fit on a 300mm wafer is going to be substantially less than 30 probably closer to 15. Of those 15 it wouldn't surprise me if 5 were bad. From the time that wafer is loaded in at one end of the process until the time it exits the other end may take a day as it moves from one multi million dollar (probably 10s of millions of dollars) machine to another. Hopefully in all of the baking that is done there wasn't a defect in the wafer that causes it to shatter from the thermal stress.
I hope some day they become cheap. Just like it happened with FF
08-29-2018, 07:52 PM   #14
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Sony makes both "crop" and "full frame" 645 sensors.

Sony's sensor roadmap includes a 150MP medium-format chip for 2018: Digital Photography Review
08-29-2018, 08:27 PM   #15
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QuoteOriginally posted by SunnyG. Quote
I hope some day they become cheap. Just like it happened with FF
They likely will become cheaper once the general process gets sorted out but they are a very low volume item compared to things like even high end microprocessors so will remain a high cost item unless there is a huge return to medium format by the general population. A die that size is huge at almost 3 times the size of a current high end processor (most recent size I found for those is 42mm x 28mm). With modern processors they can at least bin them and ones that have faulty cores or processors just disable that portion, or if not too severe clock them lower helping with yields but with sensors that doesn't seem like something they could effectively do. There is still a lot of randomness in processor creation as the ion implant is basically like a shotgun with atoms.

Last edited by MossyRocks; 08-29-2018 at 08:28 PM. Reason: incomplete thought
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