Rejoice !!! Yet another equivalency thread :D Locked

Started Jan 31, 2014 | Discussions thread
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Jay Ell Regular Member • Posts: 256
Re: Rejoice !!! Yet another equivalency thread :D

goblin wrote:

The slow fading of the other threads about equivalency being a thorn in my natural thirst for knowledge, I can not feel but compelled to open a new one

So here it is:

Apples for apples, and excepting out of the ordinary products (such as shg f2 zooms)

- Would a 24mm 1.8 4/3 lens be as easy / inexpensive to build as a FF 50mm 1.8 lens (given both are the quasi "Standard" focal for their respective sensor size ?)

A "slow" normal is just about the easiest lens to design (especially for mirrorless) for most systems.

The 4/3 has awfully long flange focal distance for the sensor size complicating the design of "normals" needlessly. Add the requirement of higher quality due to larger output picture enlargement, and you need quite a bit more effort to make a decent 4/3 normal than a FF nornal.

Also the larger format lens with same aperture number would be about two stops faster. (ie. for a desired image SNR, or technical the FF could use about four times faster shutter speed.)

- Or, at the contrary should it be considered as "25mm is 25mm", hence the 25mm 1.8 4/3 lens would follow the optical configuration and technical solutions applied on a FF 25mm lens ?

The wide angle FF 25/1.8 is hard to design for mirrorfull camera, much easier for mirrorless. Compared to 4/3 normal lens a FF mirrorfull more difficult. A FF mirrorless could be simpler though with the caveat that current sensors might not like the design.

- Or, if the comparison in sensor coverage between FF and 4/3 plays too much in the equation and flaws it - STAYING WITHIN THE 4/3 STANDARD - would a 4/3 25mm lens be still more expensive to conceive / build than a 4/3 50mm lens ?

The 50 would be easier to make for 4/3 as you could make is almost symmetric. The 25 would need to be an inverse telephoto design.

Basically - would the rule "50mm lenses are the least expensive and simpler to build" work across the board (not depending on sensor coverage), or will it have to be adjusted for equivalency ?

50mm lens for a large format or medium format is much more difficult than a "normal" for such format. 50 is not a magic number which works from cell phone to large format. Instead if you can keep the lens very symmetric, the design can be simpe and effective.

The "50 is cheap" comes from film full frames and is slightly inaccurate as even for them (assuming SLR and not rangefinder) 55 or 58mm is even easier to design if speed is needed. The wider lenses needed to be inverse-telephoto, thus complicating design.

When it comes to mirrorless it's not trivial to say what lens is easiest to design as one can make almost symmetric lenses of exremely high performance with relative ease, though the current image sensor technology can be problem with those.

Basically, if the more symmetric the lens design is the easier it is to make. There are a couple of practical limitation which one needs to remember: the CMOS sensors don't like light which hits the sensor at a non-perpendicular angle (thus exit pupil is nowdays often further away from the sensor making the design more complex), and if the objective is forced to be far from the sensor (by mechanical issues for example like the mount being far from the sensor) the symmetic designs can't have a small focal length).

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