View angle on Pentax *ist DS compared to a 35mm camera

I'm studying the *ist DS manual and I came across the section where
they describe that the view angle, the captured area of the *ist DS is
about 1.5 times smaller than a 35mm camera. When you would use a 150mm
focus point lens with a 35mm camre, you should use a 100mm lens with
the *ist DS to get the same view angle. Since I haven't bought the
camera yet, I'm not sure if I'm understanding this correctly: does this
mean that a 200mm lens would function as a 300mm lens and that the same
lens would bring the subject of the photo "closer up" on the *ist DS
than it would on my MZ-3? Is there any impact on the lens opening when
switching to digital? Is an f2.8 lens still f2.8 on the *ist DS?

On another subject, I have auto focus lenses for my Pentax MZ-3 but I
don't remember what mount that is. How can I figure that out? The same
question for my old Pentax ME lenses. I understand that I can use even
the ME lenses with the *ist DS without converter ring, etc, right? (No
auto focus, obviously)

Thanks!

"Hoshisato" wrote in message
oups.com...
I'm studying the *ist DS manual and I came across the section where
they describe that the view angle, the captured area of the *ist DS is
about 1.5 times smaller than a 35mm camera. When you would use a 150mm
focus point lens with a 35mm camre, you should use a 100mm lens with
the *ist DS to get the same view angle. Since I haven't bought the
camera yet, I'm not sure if I'm understanding this correctly: does this
mean that a 200mm lens would function as a 300mm lens and that the same
lens would bring the subject of the photo "closer up" on the *ist DS
than it would on my MZ-3? Is there any impact on the lens opening when
switching to digital? Is an f2.8 lens still f2.8 on the *ist DS?
All that changes is the angle of view which is the result of the smaller
image size of the digital camera. The same principal applies to the use of
view camera lenses on smaller cameras.
Since the image size as captured by the camera has no influence on the size
of the diaphragm in the lens, there can be no change in the fstop. This
princpal also applies to the use of view camera lenses on smaller cameras.
Jim

Hoshisato wrote:

I'm studying the *ist DS manual and I came across the section where
they describe that the view angle, the captured area of the *ist DS is
about 1.5 times smaller than a 35mm camera. When you would use a 150mm
focus point lens with a 35mm camre, you should use a 100mm lens with
the *ist DS to get the same view angle. Since I haven't bought the
camera yet, I'm not sure if I'm understanding this correctly: does this
mean that a 200mm lens would function as a 300mm lens and that the same
lens would bring the subject of the photo "closer up" on the *ist DS
than it would on my MZ-3?

Yes indeedy. There's also less vignetting and other such problems, since
the image you're shooting is basically a center crop of the image you'd
get from a 35mm film camera.

Is there any impact on the lens opening when switching to digital? Is an
f2.8 lens still f2.8 on the *ist DS?

Yes, it is, since the focal length is the same from camera to camera.

On another subject, I have auto focus lenses for my Pentax MZ-3 but I
don't remember what mount that is. How can I figure that out? The same
question for my old Pentax ME lenses. I understand that I can use even
the ME lenses with the *ist DS without converter ring, etc, right? (No
auto focus, obviously)

There's a really great web site that lists all the variations of the
mounts, and a whole lot of other stuff as well:
http://www.bdimitrov.de/kmp/

You'll be able to use MZ and ME lenses on the *ist DS. In fact, the MZ-3
has a KAF2 mount, which the *ist DS also has. For the ME lenses, you'll
have to change the 'custom' setting 'Using aperture ring' to
'Permitted.' One wonders why this setting even exists, but you have to
switch it if your lens doesn't have an A setting on the aperture ring.

The problem you might run into is some third-party lenses, specifically
Ricoh, which have their own variation of the k-mount and will get stuck
on your camera.

: Yes indeedy. There's also less vignetting and other such problems, since
: the image you're shooting is basically a center crop of the image you'd
: get from a 35mm film camera.

Right. It's unfortunate that many people care calling them 1.5 "zoom
factors," etc. All the factor of 1.5 means is that the image sensor is 1.5 times
smaller than the piece of film the lens was designed for. Just think of cropping out
only the center of the image the lens projects on the film. Everything else remains
constant... a 200mm/f2.8 lens is still a 200mm/f2.8 lens. The picture taken, however,
will be from just the center of it, so the actual angle of coverage will be equivalent
to a 300mm lens. The DOF will be the same as 200/f2.8.

: You'll be able to use MZ and ME lenses on the *ist DS. In fact, the MZ-3
: has a KAF2 mount, which the *ist DS also has. For the ME lenses, you'll
: have to change the 'custom' setting 'Using aperture ring' to
: 'Permitted.' One wonders why this setting even exists, but you have to
: switch it if your lens doesn't have an A setting on the aperture ring.

Although it's possible to use a non-'A' lens, it's one more step. In addition
to making the change above, you need to use 'M' manual mode on the camera.
Fortunately, when you hit the 'AE' button, it will stop the lens down, meter, release
the aperture, and set the f-stop/shutter speed to what it deems appropriate. All of
that takes about 1/2 sec. You do, however, lose the ability to use matrix metering on
such lenses... it's spot or center-weighted.

: The problem you might run into is some third-party lenses, specifically
: Ricoh, which have their own variation of the k-mount and will get stuck
: on your camera.

Yes. There are (AFAIK) two different issues. One is a small pin on the
flange of a Ricoh lense that can fall into the AF drive hole. The other issue that
the flange on the end of the lens can be larger than what the camera wants. In some
cases, the lens can go on, but not come off (badness!).

I had a Vivitar 28-105 that had both problems. It was a 1-hour job to remove
the Ricoh pin, and file down the flange to make it work perfectly on my -DS. I've got
a few pictures I can post if there's enough interest.

-Cory

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Thanks to all of you; I have some Sigma APO KAF2 lenses, is there any
known problem with those? They work fine on my MZ-3.

I have received my *ist DS and the Sigma APO KAF2 lenses work just fine
with it.