Coverage of lenses - what you need read before you start to write

So many adapters are popping up for the Fuji gfx, for lenses from systems with similar, bigger and smaller frames. So many people are venting their opinions on this and frankly, they need to read up a bit on what coverage is before advocating this or that. I hope to bring some sanity to this debate.

Lenses and their image circle

If you point the front of a photographic lens towards a light source and the back to a shady area, it will (unless shaded off by a square shade) produce a circular bright area behind it. If you keep the lens at its intended flange to film distance, you will get a circle that is big enough to fit its frame size. It will also have a certain margin, how much depends on the type of lens, but also on the quality of the lens. In general, a cheaper lens will have a smaller circle than a more expensive lens and a zoom or a lens that focuses by moving the whole optics backwords and forward will have a variable sized circle.

Image circle is usually nothing the small- or medium format photographer has to have his mind on, since the lenses are built to cover the frame of the camera they fit to or it will be pretty obvious that only the center of the image has any picture in it, like with a Nikon dx lens on an fx camera.  For the large format photographer, on the ohter hand, the image circle is just another variable to consider when to use or buy a lens, much like a small frame photographer knows what focal length or aperture he wants. A lens that works perfectly for macro work, may never cover his film at infinity and if he want to tilt or shift he may have to stop down or switch to a lens with a wider coverage. When it comes to adapting lenses to the 44x33 senser, its pretty much the same.

What does people say and why is it irrelevant enough for me to write this article?

A lot of people argue that:

1. Bigger format lenses never produce as good images when used on a smaller framed camera since since some of its resolution is wasted outside the frame
2. Optics for smaller frames are never as good when used for a bigger frame since the image circle is too small
3. Adapted lenses are never any good, since they have two mounts and thus, can never be stable enough

For a gadget geek that want the best specs on his gears for its own sake, these may be kind of relevant arguments, but for a photograper they are not. A photographer don't care if the resolution is higher than she or he needs or the microcontrast is better than needed (rather the other way around in that case) or if the lens in sharper in the center or in the corner then the next lens if there is no need for top nodge sharpness for the intended shot. What the photographer is looking for is reliable gear that produces repeatable results and freedom of choice.

I'll go through the above cases and tell you why these are all valid choices.

1.
a: Sometimes one dont need all the resolution to achieve the goal of the shot
b: Sometimes a lower resolution lens actually produces a more pleasant images, with an adapter you can get it from now instead of waiting for fuji to release a soft focus lens
c: Sometimes one wants to tilt or shift, use rise or fall or even shift the image. Then bigger coverage is simply needed, but there are no tilt/shift lenses available for the gfx as of yet, only adapters
d: Sometimes the lens formula was optimized for a smaller frame, but was found to work on a bigger one too and thus sold like such a lens

2.
a: Sometimes the lens formula was optimized for a bigger frame, but was found to work well on a smaller frame as well and thus sold like such a lens
b: Sometimes one is looking the loss of micro contrast or light in the corners the produce a better portrait frame or making the viewer turn her eyes to an object frame in the middle.
c: Sometimes one dont intend to use the optics wide open and the smaller lens has perfect coverage stopped down.

3: Just google some large format images. Allmost all of them uses a lot looser mounts than a medium format camera with even a series of adapters. This is not a problem if you handle it right.

So are the adapters any good?

They are like any other gear, if you know how to use them and play at their strengths, they will give you more options. If you what those options provide, they are the tools that makes is possible for you to take the photo you want to. If you try to use them for every thing, you may end up with them preventing you from doing just that.

Conclusion

Most people that spend the amount of money that a modern medium format camera costs are usually in one of two categories of people, the rich gadget geek group or the photographers group.

If you are in the former, you may feel better off with only the fuji lenses for the GFX.

If you are a photographer, you most likely know when and why you need an adaper. Go get it!

If you are just in it for the debate, clearly state whome of the above groups of people your advocacy is intended for!