There are adapters available for several camera mounts to use the
lenses of the Pentax 110 SLR system. There is also one for the Sony E
mount, shown here. As these lenses were made to cover 110 pocket
format, which is 13x17mm,
you have to crop the sensor of the A7. There is an easy setting for
APS-C format on the A7, which is about 24x16mm size, a crop factor of
1.5. This is still bigger than 13x17mm, but I used it nevertheless as
it's handy.
There is another problem to use
these lenses: the Pentax camera has the aperture behind the camera
mount. The lenses have no aperture and they all open to f 2.8. So the
lenses are quite
soft.
I have tried the aperture disc system of a lensbaby, which I adapted to
the adapter. A first try did not succeeed, the results are at the
bottom of the page. I will have another try later.
The A7 adapter.
The adapter and the different Pentax lenses, from left: 24mm, the
smallest, 18mm, 50mm, 20-40mm zoom and 70mm.
Focal length: 18mm, a wide-angle
of 27mm in cropped format.
A7 and the lens.
Sample picture: You may click
on the sample image for full resolution. The
full resolution image opens in a new window, so you can keep it open
for comparison. Focus set to infinity.
A little bit of vignetting, but quite o.k., a bit soft towards the
edges which could be avoided by further cropping.
Closest focus goes down to 23cm (!).
Meanwhile I got hold of the rare 18mm PF panfocus lens.
From the front they look the same except the "PF" inscription.
Of course there is no focussing helical on the panfocus lens.
And here is the result:
Similar to the ordinary 18mm,
maybe a tad sharper in the center.
Focal length: 20-40mm, a moderate
wide-angle of 30mm to a slight tele of 60mm in cropped format.
A7 and the lens at 40mm setting.
A7 and the lens at 20mm setting.
Yes, it has to be extended for shorter focal length
Sample picture: You may click
on the sample image for full resolution. The
full resolution image opens in a new window, so you can keep it open
for comparison. 20mm, focus set to infinity.
Vignetting at the edges, overall a
bit soft due to overcast.
Sample picture: You may click
on the sample image for full resolution. The
full resolution image opens in a new window, so you can keep it open
for comparison. 40mm, focus set to infinity.
Good in the center, only a bit
soft for the rest which could be avoided by further
cropping.
Closest focus is 38cm with 20mm setting, 53cm with 40mm setting.
Focal length: 24mm, the standard
length of the system. It's moderate wide angle of 36mm in cropped
format.
A7 and the lens.
Sample picture: You may click
on the sample image for full resolution. The
full resolution image opens in a new window, so you can keep it open
for comparison. Focus set to infinity.
O.K. in the center, a bit soft towards the edges which could be avoided by further
cropping.
Closest focus is only 30cm.
Focal length: 50mm, a portrait
length of 75mm in cropped format.
A7 and the lens.
Sample picture: You may click
on the sample image for full resolution. The
full resolution image opens in a new window, so you can keep it open
for comparison. Focus set to infinity.
O.K. in the center, a bit
soft towards the edges with a hint of colour cast which could be avoided by further
cropping.
Closest focus is 89cm.
Focal length: 70mm, a tele length
of 105mm in cropped format.
A7 and the lens.
Sample picture: You may click
on the sample image for full resolution. The
full resolution image opens in a new window, so you can keep it open
for comparison. Focus set to infinity in the
first picture.
The lens is sharp, but has a
shallow DOF. See the second picture
A second sample picture. Focus set on the crow sitting on the chimey
near the center, which is about 30m away.
It makes quite a difference although it's only a mm or two from
infinity setting. Everything at the same distance is sharp. There is a
hint of colour cast towards the edges.
This is a tele lens, so closest focus is about 150cm.
As promised, I made an adapter with apertures. For
wide open lenses these
perform quite well. They could be interesting for smaller sensor
formats and with the use of aperture disks. This is a first try that
failed. I used the lensbaby aperture disks that I had already and
magnets just behind the adapter opening.
Aperture disk held by magnets.
I used 3 apertures, F5.6...
...F11...
...and F22.
There is increasing heavy vignetting. So this is unusable, that's why
there are no full resolution pictures of the 3 above samples.
The adapter and the original mount.
On the adapter the mount sits deep in a kind of tube.
The original mount has the aperture just behind the mount. On the
picture you see the 2 aperture blades wide open at F2.8. They are at
~5mm from the flange. The lenses protrude a bit more than 4mm from the
flange, so the aperture sits right behind the last element of the lens.
So I will have to try another approach with aperture disks right behind
the lens. This may take some time, but I will report back.
