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Comments on the P30/P30+ digital backs

BJNY

Member
I borrowed a friend's P30 to photograph some moire-prone organza fashion, but an Aptus 75 did better.
 

David Klepacki

New member
David

Thank, extremely helpful. On the rotating back, is that an additional item, so ALL camera adapters work or do you need a special "Contax rotation back adapter" and one for each other

these guys are expensive (though a LOT cheaper than an extra back!

Victor
First, only the square format cameras (e.g., Hasselblad V, Rollei 6008, Sinar Hy6) are capable of rotating adapters. This is one huge advantage of the Sinar system for square format cameras, even though shooting with a 645 format sensor. Unfortunately, you cannot rotate the back on the Contax.

Second, I should point out that while Sinar offers these rotating backs, they also have a special "revolving" adapter exclusively for the Sinar Hy6. The advantage here is that the back does not get removed from the camera, and can easily be rotated from portrait to landscape and vice-versa by just twisting. With the rotating adapters, you have to physically unmount the back, rotate it, and then re-mount it....also very fast and not much effort as it may sound.
 

David Klepacki

New member
I guess I need more info on what microlenses are for/what they do, and how it it is different from an AA filter. Can someone educate me?
In a nutshell, microlenses are used to boost signal sensitivity by capturing light that would otherwise be lost due to oblique incidence on the sensor (between the pixels). Typically, there is a tiny microlens over each pixel, sort of like a catcher's mit. However, there is a limit to how oblique these lenses will be able to catch the light without distorting the wavelength information. Beyond this angle, false colors appear. In my baseball analogy, it would like calling a wild knuckle-ball a strike, even though it did not go over the plate.

For a photo example, if you use an ultra-wide lens on a rangefinder camera (e.g., a 24mm lens on an Alpa), the oblique impact of the light could cause color shifts if the sensor uses microlenses, that you would have to correct manually. Similar situations occur when using large enough tilt and shift movements on a technical camera.

An AA filter is used to suppress the spatial frequencies that exceed the sampling limit of the sensor (known as the Nyquist rate). The Nyquist frequency is determined by the size and spacing of the pixels. In general, the smaller the pixels and more densely they are packed results in higher Nyquist frequencies. In photographic terms, if your image contains very fine detail that exceeds the ability of the sensor to capture such resolution, those frequencies get recorded with false colors and structures, also referred to as moire. Sort of like if your car odometer exceeds its number of digits, the mileage would go back to counting from zero, since there is no place to record those extra miles. Similarly, these high frequencies have no where to go, so get falsely recorded by the sensor, when no AA filter is present.

An AA filter essentially blurs these high frequencies into the higher frequency capabilities of the sensor, but this leads to some loss of the sensor resolution, which is why many people do not like them.

Lastly, some cameras contain both microlenses and an AA filter. They are two things used for two different purposes.
 
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tom in mpls

Active member
Yes. Phase does not use AA filters on any of their backs.

To my knowledge, the only MF backs that have AA filters are the older Kodak backs (discontinued) and the Mamiya ZD back. In each case, these AA filters are optional (removable).
Obviously I was getting confused between AA filters and microfilters. Thanks!
 
T

thsinar

Guest
just some more information about microlenses:

Microlenses are also used to gain sensitivity, which is reduced with smaller pixels.

Smaller pixels have in addition the negative effect/disadvantage that the dynamic range (DR) is much smaller, that those pixels are faster "full", thus leading very quickly to over-exposure. Also details in the shadows get lost.

Thierry
 
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