[JohnBee]

...it is great to see all the pics of, and thoughts about 28mm lens bokeh! This is definitely a subjective topic, and it seems there are many factors which influence the out of focus character in photos...

I like the 28mm focal length on my Pentax DSLR because it is a 'normal' focal length. It really is different than using a normal lens on a 35mm camera, as im sure using a normal lens in medium format is, since depth of field at comparable apertures gets narrower as the format size increases...

I have been out taking more pictures with the 28/2 A lens：

That 28/2 is magical!
The only one could find(without looking to hard) was for F mount.
Which raises the question as to how well it would perform under a FF sensor...

[blende8]

Just to clarify, the format that a lens is created for does not change the size of the "circle of confusion" at all, it is solely dependent on the focal length, aperture, and distances to the focal point and the background elements.

This is not correct.
Below is a quick comparison between the DA16-50@50 and the FA50/1.4 (both at f2.8):
Same scene, tripod, focussed on something in the foreground, observed the circle in the background.
Originally I noted it first with the DA70, but other DAs show this, too.
Interestingly the DA55 does not show it. This lens covers FF.

[Pentaxor]

This is not correct.
Below is a quick comparison between the DA16-50@50 and the FA50 (both at f2.8):
Same scene, tripod, focussed on something in the foreground, observed the circle in the background.
Originally I noted it first with the DA70, but other DAs show this, too.
Interestingly the DA55 does not show it. This lens covers FF.

is this an FA50/2.8 macro or the two other FA50's (1.4 and 1.7) stopped down ?

there is no reason for it to look like that if it's wide open as the blades aren't closed down. did you carefully checked the blades on that particular lens? this is just odd, IMO. FA's are also FF lenses, so the DA55 being a FF could be easily dismissed.

[blende8]

It's the FA50/1.4.

FA's are also FF lenses, so the DA55 being an FF could be easily dismissed.

As I said.
I only noticed this effect on some DA lenses that definitely do not cover FF.
I am no optics expert, but perhaps it has to do with the exit pupil?

[arpaagent]

This is not correct.
Below is a quick comparison between the DA16-50@50 and the FA50/1.4 (both at f2.8):
Same scene, tripod, focussed on something in the foreground, observed the circle in the background.
Originally I noted it first with the DA70, but other DAs show this, too.
Interestingly the DA55 does not show it. This lens covers FF.

--image snipped--

Interesting. I also have the DA16-50. I'll do some tests of my own tonight with it against DA50-135, FA50 Macro, F50/1.7, A50/1.2, etc. Maybe I'll also do a test at 24mm against some others. Not that I don't full trust your results but I am certainly curious and would like to see for myself.

[Pentaxor]

It's the FA50/1.4.


As I said.
I only noticed this effect on some DA lenses that definitely do not cover FF.
I am no optics expert, but perhaps it has to do with the exit pupil?

Yes, that is the most probable reason. COC's shape is influenced by aperture opening.
as far as the DA55 is concerned, I believe it is greatly influenced by it's rounded aperture blades which makes the COC shape consistent in all apertures.

[Jimfear]

To go back to the original purpose of this thread I have dug up two photos taken wide open with two different lenses.


First one is by the K28/3.5, probably the same design as the S-M-C Takumar 28/3.5 above. Pretty good overall but getting a little harsh in the highlights.




Second one is with the Vivitar 28mm f/2 (Kiron made), georgweb had a sample before that looked fine, this one taken at f/2 though and the bokeh going crazy (not to speak of distortion...)

---

Last edited by Jimfear; 01-07-2010 at 02:17 PM. Reason: images too wide...

[JohnBee]

Second one is with the Vivitar 28mm f/2 (Kiron made), georgweb had a sample before that looked fine, this one taken at f/2 though and the bokeh going crazy (not to speak of distortion...)

So same lens(es) but different bokeh's?

[gofour3]

I agree with what Steve said, a 28mm focal length lens would not be my first choice for expecting nice bokeh shots. Try the K50/1.2, it has the nicest that I have seen.

I have the K series 28/2.0 and it is unique as having floating lens elements, which eliminate distortion. Nice bokeh nope, 3D effects on close objects yes.

Phil.

[Class A]

These are from my Sigma 28/1.8 (full frame, nine blades, blades never show jaggies like many Pentax lenses). Some Picasa PP but no extra blurring.

Hand-held while it was windy -> not as sharp as it could have been but shows bokeh @ f/3.5.
Attachment 51393
f/3.2:
Attachment 51394
f/5.0:
Attachment 51397

EDIT: I exchanged the original images with others that I sharpened for this small size. They now look a lot more like the originals. The grain in the OOF is from the sharpening but I prefer that to the mushy appearance the previous sharpening method resulted in.

[JohnBee]

These are from my Sigma 28/1.8 (full frame, nine blades, blades never show jaggies like many Pentax lenses). Some Picasa PP but no extra blurring.

The second one looks nice.
1.8 sounds pretty darned impressive for a 28mm too.
How do things look around 2.8?

[arpaagent]

This is not correct.
Below is a quick comparison between the DA16-50@50 and the FA50/1.4 (both at f2.8):
Same scene, tripod, focussed on something in the foreground, observed the circle in the background.
Originally I noted it first with the DA70, but other DAs show this, too.
Interestingly the DA55 does not show it. This lens covers FF.

--image snipped--

Please see a post I made in another thread regarding OOF highlights and lens format. I don't want anyone to be misinformed about stuff. Weiland, no offense meant, but I find that your example is misleading. In my tests in the post below, I have shown my setup and explained exactly what I did, so anyone should be able to reproduce my results.

Basically, from my testing, lens format does not affect the OOF highlight sizes.

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/85864-out-focu...tml#post873435

[Jimfear]

So same lens(es) but different bokeh's?

Same lens, different aperture, different bokeh. Georgweb's photo was stopped down a bit, and the background was also mostly green (and red) which usually produces smother bokeh.

[Asahiflex]

The lens is rare, but here are a few samples made with the SMC Pentax 1:2/28, which is optically the same as the Carl Zeiss 28mm f/2 Distagon 'Hollywood', designed by Erhard Glatzel. The lens features floating elements to provide better results at closer ranges.

[gofour3]

Beautiful shots Peter, that's exactly why I love the K28/2!! You can only appreciate how good this lens is if you own one.

Nice work,

Phil