This is from David Glover@ Hasselblad from a previous thread.
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( I add to this thread with some information regarding the HCD28, HCD35-90 and the H3D 60MP...
The Hasselblad HCD lens line (28mm, 35-90mm zoom) has been designed to deliver outstanding lens performance (high resolution, low lens errors) on a Medium Format sensor area, in a lens design that is relative compact and light. In the process of optimizing design for all the performance criteria Hasselblad has carefully chosen its design elements with the following logic.
We have chosen a target sensor format of 36 * 49mm for the optimization of the lens performance for the HCD lens line in order to achieve a compact design with fast focusing as well as high performance. Top performance is reached even with sensors larger than 36 * 49mm. The only restriction is that a marginal crop is introduced with the HCD28 and the HCD35-90 in 35 mm setting. On a full frame 60 Mpix camera, the crop will result in an effective pixel count of 55 Mpix and a focal length factor of about 1.1. This means that the HCD28 will be equal to a 31 mm lens and the HCD35-90 will be equal to a 38-90 mm.
We have chosen to allow a level of basic optical imperfections (color aberration, distortion and vignetting) within the capability for our DAC lens corrections to handle it afterwards. We can therefore make a better design compromise and concentrate on minimizing optical errors that cannot be corrected by DAC, for example edge to edge sharpness. The results will not be as good for film use, which we therefore have excluded.
Our estimate on benefits with regards to size, weight and price are as follows: Compared to using the original full 645 film format (41.5 * 56mm) we are able to deliver a lens design that is around 30% more compact, and 30-40% less expensive.
To support the achievements of Hasselblad’s HCD lens design please compare the HCD28mm with other Medium Format lenses of the same focal length. Check the image detail and lens performance at the edges. Add to the comparison that all HC/HCD lenses include internal AF motor (fast, accurate focus), central lens shutter (flash sync at shutter speeds up to 1/800), and manual focus override. The difference in price between the HCD28 and the main competitor’s product is currently a 40% advantage for the HCD28.
I spoke to our lens designer about this and even though the difference between a 49mm sensor and the 645 format 'seems' relatively small in terms of lens construction it is a big step.
Therefore our new zoom lens would be significantly larger, heavier and much more expensive if expanded to the 645 format. So much so that its use would become unattractive and uneconomical.
You will notice though that with the 60MP sensor its effective length becomes 38-90 - the top end is not affected. Using the HCD lenses with the H3D-60 will automatically crop the image. No interaction is required by the user.
David ) End Quote
