Pre-requisite:
you have adapted your M42 lens with an adapter ring.
Set up you DSLR to shoot witout a lens.
With the Sony A700 you have a menu item "release w/o lens" : set to enable (it was the same with the Minolta D5D)
For the Sony A300, you will only shoot in M mode (no specific menu item to tel the camera that there is no lens)
For most of the DSLR set the exposure mode dial to Aperture Priority (A or Av).
Do not take care of the aperture setting of the body and reported by the vewfinder.
Set the aperture ring of the lens to wide open (e.g. f/2.8) This is the actual aperture value wich will be used by the metering of the body independently of the aperture set value set on the body. The lens does not communicate to the body the aperture value.
Manual focus with the focus ring. If the deep of field is very norrow, you can use neck movments to slightly adjust the focus (this is also a good practice for macro shoot focusing)
Check the AF confirm in the display panel of the viewfinder by half pressing the shutter button :
The green plot appears when the focus is OK (liveview in this case but also works in viewfinder)
Once the focus is OK, you will also notice that the speed is updated each time you half press the shutter button. That mean the metering is real time computed.
If you close the lens aperture ring to have a wider deep of field, you will notice that when half pressing the shutter button, the speed is real time updated.
Then press the shutter button. Normaly the exposure is OK : ensure with the histogram.
Because of the narrow deep of field of fast lenses at wide aperture, a good technique to ensure you will have good shots is to take 3 shoots, the first at wide aperture then you will quicly close more and more for the next shoots to enlarge the deep of field.
With the Sony A700, you do not need to half press the shutter button to see the speed being reel time computer (just move aperture ring on the lens). Same with the focus ring: you do not need to half press the shutter button to see the focus confirmation in the viewfinder information area.
Some DSLR are only working in M mode. This is the case with the Sony A200, 300, 350. But the metering of the body is working: when you move the aperture ring, the EV scale is update. So, once the focus is OK, you just have to set the aperture ring on the lens. The on the body, set the speed in order to have the EV scale centered at 0 :
On this sample of EV scale, the camera metering detect that your picture will be under exposed of 1.3 EV. So adjsut the speed with the front dial to center the EV scale on the 0.
Then shot and ensure with the histogram your exposition is OK. If no adapt the speed for EV compensation.
