Author Topic: Adapter stack height (Read 784 times)

tom-ep1 · « **on:** August 03, 2011, 12:59:17 AM »

Hi guys

i was just wondering, i have an mFT to Minolta MD Adapter. So this adapter has an effektive height of about 24mm. Why is it that long?
We know the distance is making the zoom even more higher, one thing we dont actually need, because legacy lenses have a lot zoom and we need more wide angle.
But even more important, with more distance, less surface from the lens is used, picture quality gets worse.

How i came to this, because its the same when you compare mFT 2x Crop to Fullformat. The sensor is smaller, so it gets a smaller cut out of the lens field.

So why it should matter to have the same distance as on the old Minolta MD ? I dont get it.

cosinaphile · « **Reply #1 on:** August 03, 2011, 03:37:25 AM »

the distance between the rear element of your MD lens and the micro 4\3 sensor has to be the same as the distance between the rear element of the lens and the film plane in the slr film camera bodiesin order for it to achieve correct infinity focus.

the reason it is the size it is ,is because slrs have a large mirror box assembly sitting between the lens and the film plane [pressure plate\ digital sensor], and this distance must be mimiced by an adapter so that the lens works properly

more extension of the lens [achieved with extension tubes or bellows] will not give more "zoom"... but it will give more magnification , essentially turning any lens into a "macro " lens ,..... the more extension , the more magnification

actually when you use a legacy lens on micro four thirds only the "sweet spot"or central portion of the lens is used, so light falloff from the edges is not a problem and the sharpness across the frame is increased because the softer edge of the frame is cropped off by the micro four theirds sensor

this cropping by the sensor does kill the wide lenses

, that is so true!!!

tom-ep1 · « **Reply #2 on:** August 04, 2011, 03:18:50 AM »

i totally missed infinity focus !

So this would also mean, in mirrorless cameras the lens can be even smaller because its used better. But then we got more problems with light falloff in edges

cosinaphile · « **Reply #3 on:** August 04, 2011, 05:39:55 AM »

i hope the designers will design in a way that it isnt a problem, its more apparent when considering optical properties of lens across formats

Em5 Pete · « **Reply #4 on:** August 04, 2011, 05:49:30 AM »

Quote from: tom-ep1 on August 04, 2011, 03:18:50 AM

i totally missed infinity focus !

So this would also mean, in mirrorless cameras the lens can be even smaller because its used better. But then we got more problems with light falloff in edges

If you have a camera repair near by, adj the lens for INF with for the adapter you will use with it is a 2m fix with the lens INF stop point.. bring a m4/3 body also.

Adapter stack height