28mm dot on Sigma zooms

Started Jan 29, 2007 | Discussions
Shop cameras & lenses ▾
kirbysdl Regular Member • Posts: 108
28mm dot on Sigma zooms

On my Sigma 17-70, there's a little dot on the barrel's focal length scale at 28mm. There's also one on the 18-200 lens, and other Sigma DC zooms print the actual numbers instead of using a dot. Why is 28mm so important? On a Canon 1.6x sensor, its 35mm film equivalent length is only 44mm, so it's not even an indicator of the "standard film" 50mm view.

 kirbysdl's gear list:kirbysdl's gear list
Canon EOS 70D Canon EF-S 17-55mm f/2.8 IS USM Canon EF 70-200mm f/4L IS USM Canon EF 35mm f/2 IS USM
SNGX1327 Veteran Member • Posts: 5,186
Re: 28mm dot on Sigma zooms

not sure. on the canon kit lens, 28mm is marked as the focal length where the lens is the shortest physically. that particular lens extends when zoomed to any of the extreme focal lenghts

nickleback Forum Pro • Posts: 11,111
Re: 28mm dot on Sigma zooms

kirbysdl wrote:

On my Sigma 17-70, there's a little dot on the barrel's focal
length scale at 28mm. There's also one on the 18-200 lens, and
other Sigma DC zooms print the actual numbers instead of using a
dot. Why is 28mm so important? On a Canon 1.6x sensor, its 35mm
film equivalent length is only 44mm, so it's not even an indicator
of the "standard film" 50mm view.

28mm is the approximate diagonal of an APS-C sensor.

Standard view on a camera is where the diagonal measure of the capture medium equals the focal length. 35mm diagonal is 43.3mm, pretty darn close to 44mm. 50mm is used as the "standard" lens on most SLRs because that's about the shortest near-symmetrical design you can do on a 35mm SLR, which makes it inexpensive.

-- hide signature --

Seen in a fortune cookie:
Fear is the darkroom where negatives are developed

kirbysdl OP Regular Member • Posts: 108
Re: 28mm dot on Sigma zooms

nickleback wrote:

Standard view on a camera is where the diagonal measure of the
capture medium equals the focal length.

A-ha, very concise. So I guess the reason old 35mm film cameras came with 50mm kit lenses is because 35mm lenses were too expensive to make well.

Thanks!

 kirbysdl's gear list:kirbysdl's gear list
Canon EOS 70D Canon EF-S 17-55mm f/2.8 IS USM Canon EF 70-200mm f/4L IS USM Canon EF 35mm f/2 IS USM
nickleback Forum Pro • Posts: 11,111
Re: 28mm dot on Sigma zooms

kirbysdl wrote:

nickleback wrote:

Standard view on a camera is where the diagonal measure of the
capture medium equals the focal length.

A-ha, very concise. So I guess the reason old 35mm film cameras
came with 50mm kit lenses is because 35mm lenses were too expensive
to make well.

The true normal for 35mm format is 43.3mm, so substitute "43 or 44mm lenses" for "35mm lenses" in your statement above and it is correct.

Thanks!

You're welcome!

-- hide signature --

Seen in a fortune cookie:
Fear is the darkroom where negatives are developed

strikeback03 Senior Member • Posts: 2,892
except...

lenses from long before digital also have the dot. Here is an EF 24-85 originally marketed in Sept 1996.

-- hide signature --
nickleback Forum Pro • Posts: 11,111
Re: except...

strikeback03 wrote:

lenses from long before digital also have the dot. Here is an EF
24-85 originally marketed in Sept 1996.

Lack of space to write 28? Beats me. I was just commenting on 28 actually having a little bit of significance. Don't know if that's why it is a dot on the barrel.

-- hide signature --

Seen in a fortune cookie:
Fear is the darkroom where negatives are developed

strikeback03 Senior Member • Posts: 2,892
Re: except...

I'd assume that for whatever reason it is just tradition to mark 28 - if the numbers don't fit then with a dot. Also I don't believe it is the point of minimum extension on the kit, IIRC mine was shortest at around 33mm.
--
http://www.linelight.org/

kirbysdl OP Regular Member • Posts: 108
Re: except...

Yeah, the 17-70 is shortest at 17mm grows continuously until 70. Thanks again for all the replies. I'm gonna shoot a bit at 28mm so I can grow accustomed to what a 28/30mm prime should look like.

 kirbysdl's gear list:kirbysdl's gear list
Canon EOS 70D Canon EF-S 17-55mm f/2.8 IS USM Canon EF 70-200mm f/4L IS USM Canon EF 35mm f/2 IS USM
Keyboard shortcuts:
FForum MMy threads