Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2

Started Jun 16, 2014 | Discussions thread
Anders W Forum Pro • Posts: 21,468
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2

noirdesir wrote:

Ulric wrote:

bobn2 wrote:

Ulric wrote:

The larger format lens does not have to resolve as many lines per millimeter on the image plane, thus it can be (but need not be) optically inferior to achieve the same output image quality compared to a smaller format lens. The reason is in the lesser need for enlargement from the image in the image plane to the output image of arbirtary size.

OTOH, what matters is not resolution per millimeter but per image, and the larger format lens has to perform over a larger image circle. It evens out.

In practice, no it doesn't - the advantage is to the larger image circle.

To even out means to become even or more even, and yes it does.

You mean all (D)SLR tele lenses automatically get a 50% higher centre resolution when used on a DX camera compared to be used on an FX camera?

I don't think that's what Ulric means. He refers to lenses made for different image circles, not the same lens used on a sensor with a smaller diagonal than that for which the lens is made.

(Or is this just all lens manufacturers without exception refusing to release DX tele lenses?)

I don't know why the Nikon don't make long teles specifically for DX. Most likely, they are just trying to keep costs down. As I think you are aware, MFT teles are made for the MFT image circle.

The problem is that we cannot fully test any hypothesis because so far with the exception of the Nokia 40+ MP phone cam, larger sensors come with higher pixel counts and we cannot verify whether a m43 lens in front of a 80 MP sensor would deliver the same resolution per picture height as MF lenses in front of a 80 MP back. We can compare a m43 lens in front of a 16 MP sensor with a MF lens in front of a 16 MP sensor (Phase One P20) but while we know that the MF lens has a lot of reserve resolution as visible when used in front of a 80 MP sensor, we cannot test whether the m43 lens would do equally well in front of 80 MP sensor because there is no such sensor.

If two lenses do equally well when tested on sensors with 16 MP, then we can predict with pretty good accuracy that they will also do equally well on a sensors with 80 MP. The following approximation is known to be a pretty good one:

1/i = sqrt(1/l^2 + 1/s^2)

where i is image resolution, l is lens resolution, and s is sensor resolution.

The closest we can get is to compare 'equivalent' DX with FX lenses adapted to smaller-sensored (and thus higher pixel density) cameras. For example the Nikon 40 mm f/2.8 DX vs the Nikon 60 mm f/2.8 G FX or the Nikon 35 mm f/1.8 DX vs the Nikon 50 mm f/1.8 G FX tested on the 10 MP Nikon 1 V1 (as done by Photozone), the 10 MP correspond to a 32 MP DX sensor. We see that DX lenses have a somewhat higher resolution but nowhere 50% higher than they would need to deliver the same resolution when used on DX and FX with the same number of MP.

On a variety of grounds, that does not strike me as a particularly good comparison. What is known based on the laws of optics is that if we take a lens design for a certain format, say a 50/1.8 for FF, and scale it down in all relevant dimensions so as to make 25/1.8 for MFT, the two lenses will deliver the same resolution if we measure per image diagonal (and the MFT lens twice as much as the FF lens if we measure per mm) at the same f-stop as long as resolution is limited by lens aberrations only.

 Anders W's gear list:Anders W's gear list
Panasonic Lumix DMC-G1 Olympus OM-D E-M5 Olympus E-M1 Panasonic Lumix G Vario 14-45mm F3.5-5.6 ASPH OIS Panasonic Lumix G Vario 7-14mm F4 ASPH +28 more
Post (hide subjects) Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow