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<math display="block"> {(f/\#)}_\mathrm{microlens} \le {(f/\#)}_\mathrm{objective} \times \mathit{ff}\,.</math>
Thus if shading is to be avoided the f-number of the microlens must be smaller than the f-number of the taking lens by at least a factor equal to the linear fill factor of the pixel. The f-number of the microlens is determined ultimately by the width of the pixel and its height above the silicon, which determines its focal length. In turn, this is determined by the height of the metallisation layers, also known as the 'stack height'. For a given stack height, the f-number of the microlenses will increase as pixel size reduces, and thus the objective lens f-number at which shading occurs will tend to increase.{{efn|This effect has been observed in practice, as recorded in the DxOmark article 'F-stop blues'<ref>{{cite web|last=DxOmark|title=F-stop blues|url=http://www.dxomark.com/index.php/Publications/DxOMark-Insights/F-stop-blues|work=DxOMark Insights|access-date=29 January 2012|archive-date=25 January 2012|archive-url=https://web.archive.org/web/20120125061948/http://www.dxomark.com/index.php/Publications/DxOMark-Insights/F-stop-blues|url-status=dead}}</ref>}}
In order to maintain pixel counts smaller sensors will tend to have smaller pixels, while at the same time smaller objective lens f-numbers are required to maximise the amount of light projected on the sensor. To combat the effect discussed above, smaller format pixels include engineering design features to allow the reduction in f-number of their microlenses. These may include simplified pixel designs which require less metallisation, 'light pipes' built within the pixel to bring its apparent surface closer to the microlens and '[[Back-illuminated sensor|back side illumination]]' in which the wafer is thinned to expose the rear of the photodetectors and the microlens layer is placed directly on that surface, rather than the front side with its wiring layers.{{efn|The relative effectiveness of these stratagems is discussed by [[Aptina]] in some detail.<ref>{{cite web|last=Aptina Imaging Corporation|title=An Objective Look at FSI and BSI|url=http://www.eetrend.com/files-eetrend/newproduct/201101/100029156-17249-fsi-bsi-whitepaper.pdf|work=Aptina Technology White Paper|access-date=29 January 2012}}</ref>}}
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}}</ref> later models of the 645 series kept the same sensor size but replaced the CCD with a CMOS sensor. In 2016, [[Hasselblad]] announced the X1D, a 50MP medium-format [[Mirrorless interchangeable-lens camera|mirrorless]] camera, with a {{convert|44|x|33|mm|abbr=on}} CMOS sensor.<ref>{{cite web|url=http://www.dpreview.com/news/1988725790/medium-format-mirrorless-hasselblad-unveils-x1d |title=Medium-format mirrorless: Hasselblad unveils X1D |first=Allison |last=Johnson |publisher=[[Digital Photography Review]] |date=2016-06-22 |access-date=2016-06-26}}</ref>
In late 2016, [[Fujifilm]] also announced its new [[Fujifilm GFX 50S]] medium format, [[Mirrorless interchangeable-lens camera|mirrorless]] entry into the market, with a {{convert|43.8|x|32.9|mm|abbr=on}} CMOS sensor and 51.4MP.
<ref>{{cite press release | title=Fujifilm announces development of new medium format "GFX" mirroless camera system | publisher
<ref>{{cite web | title = Fujifilm's Medium Format GFX 50S to Ship in February for $6,500 | url = https://petapixel.com/2017/01/19/fujifilms-medium-format-gfx-50s-ship-february-6500 | date = 2017-01-19}}</ref>
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