QHYCCD QHY5-III-462M 2MP Near Infrared Monochrome Planetary CMOS Telescope Astrophotography Camera with Expansion Kit - QHY5-III-462M

Logically, one would think, each generation of Exmor sensor would be built upon and incorporate all of the improvements of the generation immediately preceding. However, this was not the case with the fifth generation Exmor R sensors.

The first back-illuminated sensors used shallower pixel wells (like the third-generation front- illuminated designs) than the physically deeper pixels of the fourth generation. So, while the back- illuminated structure increased the sensitivity in the visible range by 2X, the shallower pixels did not improve the NIR. The answer to this is seen in the latest, sixth generation, Sony Exmor R sensors, like the IMX462. Using physically deeper pixels in conjunction with the back-illuminated structure has dramatically improved the sensor’s sensitivity to both the visible and near infrared wavelengths.

Another advantage of the QHY5III462 is the camera’s “Super High Conversion Gain” capability. By using a lower capacitance, a small amount of charge can be converted to a high voltage resulting in higher sensitivity in low-light conditions. The readout noise of the QHY5III462 in high gain mode is as low as 0.5 electrons!

The test exposures below demonstrate the low light improvement over the IMX290 sensor. The QHY5III462C image is on the left and the corresponding QHY5III290C image is on the right. The low light conditions and exposures are identical for each top and bottom pair of images and a UV/IR filter was in place for each camera. So this test demonstrates the QHY5III462C’s increase in sensitivity and SNR over the QHY5III290C under the same conditions in the visual light spectrum alone.

The filter matrix in the IMX462 uses organic dye filters. These filters are very efficient at visible wavelengths but become completely transparent in the NIR. For this reason, good RGB color balance requires an external UV/IR filter that blocks NIR wavelengths.

Many color cameras build this UV/IR filter into the camera or optical window for normal color imaging. However, in order to fully exploit the capabilities of the 462C sensor, in the QHY5III462C camera the optical window is AR coated only with no UV or IR blocking. Instead, the QHY5III462C camera includes two 1.25″ screw-in filters, a UV/IR cut filter to isolate the visible wavelengths for normal RGB imaging and an IR850 filter that will cut the visible wavelengths but pass wavelengths above 850nm.