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

Started Jun 15, 2014 | Discussions thread
Eric Nepean
Eric Nepean Veteran Member • Posts: 4,427
Re: Crop Factor, Low Light and Aperture with m4/3 lenses?

oneohone wrote:

I am in the market for a DSLR/mirrorless camera and after initial research and trying various cameras the Olympus M10 has made my final shortlist. Now I have some experience shooting 35mm film and in my experience I often take my 50mm f1.7 lens which I enjoy a great deal and it s a good fit for the types of photography I do, candid street, a little landscape and also portraits.

Now I wonder, I have mostly shot film (not counting snapshots with my cellphone) and then crop-factor never enterted my mind. The M10 has a larger crop factor than the other cameras on my shortlist (1.5 or 1.6) how does that impact the choice of lenses? To get something similar to the 50mm focal length I would need a 24mm lens, but what about aperture? If I understand correctly (and maybe I don't) aperture is also influenced by crop factor, then how is it possible to get a f.2.8 lens or lower for the m10? And how does that further influence low light performance? I often take pictures in low light without flash or tripod and from my experience with the film camera I often use f.2.8 or lower.

I know the M10 is a good camera, and the m4/3 system is also really good, and obviously people are satisfied using this system, but I just need a little help understanding the problem with low light and lens selection for the m4/3 system.

The effective aperture (considering DoF) can sometimes help and sometimes hinder.

On the one hand, if the very narrow depth of field from a 50mm F1.7 lens is something you use a lot to separate your subject from your background, you will not get as much of that with M43 lenses.

On the other hand, if your style of photography doesn't demand narrow depth of field, and you use your 50mm F1.7 for its low light capabilities, then you will find that you get more depth of field for the same wide aperture in M43 - which you might consider a bonus.

For example, lets use the 50mm F1.7 35mm film lens focused at 15 feet as the basis for comparison, it will give you a depth of field of about 2.75 feet for 35mm film.

A 25mm F1.8 M43 (Olympus) lens focused at 15 feet would give you the same field of view, and allow you to use the same shutter speed and ISO, but give you a depth of field of 6.1 feet - and your background will be somewhat less blurred. Some people would like that, other would not.

But there are some alternatives:

The 25mm F1.4 M43 (panasonic) lens would give a depth of field of 4.75 feet, and allow a slightly faster shutter speed or lower ISO.

The Cosina Voigtländer Nokton 25mm f/0.95 M43 lens would give a depth of field of about 3 feet, and allow almost two stops faster shutter speed (but it won't have autofocus, nor auto exposure except in aperture priority mode)

Another choice would be to buy a Metabones speedbooster to adapt your 50mm lens to M43. This neat gadget (I think of it as an inverse teleconvertor) will reduce the focal length of your 50mm  to .71x, and increase aperture by stop - so your 50mm F1.7 will become a 35mm F1.2 lens, focused at 15 feet it will have a depth of field of 2 feet (but it won't have autofocus, nor auto exposure except in aperture priority mode)

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Eric

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