C
ChrisJ
Guest
For the last week I've been pondering using the Pentax 110 lenses on the G1, the problem is, as you all know, that there is no aperture adjustment on these lenses, but they are optically superb.
Heres my design criteria,
It must be able to focus on infinity.
Be able to change aperture without removing the lens off the camera.
Be fairly strait forward to make.
Use any available Pentax 110 lens.
I found that to avoid vigneting the aperture had to be directly behind the lens as it was in the original camera. There is not really enough room to fit a conventional aperture mechanism behind the lens.
As every different focal length needs a different sized hole for say f8 it wouldnt be easy to calibrate a normal aperture mechanism.
After a lot of midnight oil I finally hit on the idea that the really old turn of the century photographers used and make slide in apertures. These are made of Plasticard which is available in thin sheets, in black and is cheap.
Here are some first results, all are shot with the lens focussed on the front red berries at their closest focussing wide open, the focus wasn't changed when stopped down ;-
First the 18mm lens wide open (f2.8)
Then with a 2mm diameter aperture
The 24mm lens wide open (f2.8)
With the same 2mm aperture
Finally the 50mm lens wide open (f2.8)
and with the same 2mm aperture which on this lens is about f25 !!
I'll post pics of the adapter if anyone is interested.
Chris
Heres my design criteria,
It must be able to focus on infinity.
Be able to change aperture without removing the lens off the camera.
Be fairly strait forward to make.
Use any available Pentax 110 lens.
I found that to avoid vigneting the aperture had to be directly behind the lens as it was in the original camera. There is not really enough room to fit a conventional aperture mechanism behind the lens.
As every different focal length needs a different sized hole for say f8 it wouldnt be easy to calibrate a normal aperture mechanism.
After a lot of midnight oil I finally hit on the idea that the really old turn of the century photographers used and make slide in apertures. These are made of Plasticard which is available in thin sheets, in black and is cheap.
Here are some first results, all are shot with the lens focussed on the front red berries at their closest focussing wide open, the focus wasn't changed when stopped down ;-
First the 18mm lens wide open (f2.8)
Then with a 2mm diameter aperture
The 24mm lens wide open (f2.8)
With the same 2mm aperture
Finally the 50mm lens wide open (f2.8)
and with the same 2mm aperture which on this lens is about f25 !!
I'll post pics of the adapter if anyone is interested.
Chris
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