Bokeh, Specular Highlights, Guess The Lens - A Surprising Result

[Rico]

Here is one. It looks like the buttons on the coat of the woman is showing all three kinds of bokeh at once.

[d.bradley]

Sean,

To get back to your STF lens filter idea, here is the dyxum post. Unfortunately the images have been moved since posting time, but they were promising indeed:

Would it be possible to modify a lens to be a STF lens?: Dyxum forums

Cheers,
D

[d.bradley]

And Gubbe (Arto), the dyxum user who tried this out, has the jpg's from his test loacted here

Enjoy.

[carpents]

Originally Posted by d.bradley

Sean,

To get back to your STF lens filter idea, here is the dyxum post. Unfortunately the images have been moved since posting time, but they were promising indeed:

Would it be possible to modify a lens to be a STF lens?: Dyxum forums

Cheers,
D

Absolutely fascinating. Why didn't I think to print a gradient on a transparency? (Yeah, it isn't quite the same as having a variable-density piece of glass.)

I'm curious, though, why mounting it on the front of the lens wouldn't work. That thread talked specifically about opening up the lens and placing the transparency near the aperture blades. (Which I assume your link shows...but sadly it won't appear for me.) Maybe because I'm primarily interested in improving wide open and at most 1 stop down, whereas they were talking about getting bokeh smoothed out at f/8.

[d.bradley]

I can't figure that one out Sean...I think is has to have something to do with the angle of incidence of the light entering the lens. I still think that a gradiant spot filter at the front of the lens would simply produce a vignette, possible in addition to smoother bokeh. It would be an easy test to try, fortunately. Other than my guess about the angle of incidence though, I don't know enough about optics to say why putting the filter closer to the focal plane is better.

Obviously the minolta STF has it internally...the second aperture would probably block the gradiant edges of the glass, thus controlling the smooth transition effect.

I have revived the thread at dyxum and asked the author...


**Wouldn't it be cool to try this with a catadioptric lens? Or I wonder if it would just end up working like a regular ND filter given the path of light...

[Jonas B]

Originally Posted by creampuff

Jonas, thanks for the images. Very informative. Both the Sigma and Pentax have aspherical elements and it does seem that both have concentric circle oof points from you pictures. Obviously the lens construction and aperture blades have a part to play too.
BTW the second image (FA35mm?) is so much nicer

Hi,

Yes, they are both sporting aspherical elements. The concentric circles are more pronounced with the Sigma lens, very faint with the Pentax. And sure, the second image is more "eyecandy" than the Sigma (the top one).

The good thing with the Sigma is that the bokeh is neutral where the FA35 shows bright rings. Thin smaller bright spots in the background and the Sigma will make make much better than the Pentax in this case. Then again, when these bright spots are near the edges/corners they get a weird shape with the Sigma, and much less (and softer) with the FA35.

What are the designers thinking of?

[Jonas B]

Originally Posted by d.bradley

And Gubbe (Arto), the dyxum user who tried this out, has the jpg's from his test loacted here

Enjoy.

I enjoyed. Thank you for the links! The flower shot is pretty promising. Now we have the question: Why don't Pentax or Sony or anyone more STF lenses, and in shorter focal lengths?

[blende8]

Originally Posted by Jonas B

I enjoyed. Thank you for the links! The flower shot is pretty promising. Now we have the question: Why don't Pentax or Sony or anyone more STF lenses, and in shorter focal lengths?

Perhaps we should push BOKEH more in the online fora, so that it becomes the single most important lens property, leaving behind sharpness and CA.

Pentax, give us better bokeh!

[Jonas B]

Originally Posted by carpents

Absolutely fascinating. Why didn't I think to print a gradient on a transparency? (Yeah, it isn't quite the same as having a variable-density piece of glass.)

Hi,

I'm curious, though, why mounting it on the front of the lens wouldn't work. That thread talked specifically about opening up the lens and placing the transparency near the aperture blades. (Which I assume your link shows...but sadly it won't appear for me.) Maybe because I'm primarily interested in improving wide open and at most 1 stop down, whereas they were talking about getting bokeh smoothed out at f/8.

In reply #87 I mentioned that a filter just in front of the lens won't work. I also said that I don't know why it works when the extra set of aperture blades are placed closer to the standard aperture blades.

That was intuition. I don't know more about optics than a five year old kid playing with a magnifying glass in the sun.

My guess: Imagine a simple lens with two elements and an aperture mechanism in the middle somewhere, the lens focused to infinity.
Just in front of the front element we have the filter threads. Aim the lens towards the sun and we have the sun in focus at one extreme and the imagener at the other. By stopping the lens down, from, say wide open and one stop, we close the aperture rings a bit. This is done somewhere where we have "no focus" optically. We just lessen the light by stopping rays coming from the sun hitter the outer parts of the front element. The net result is that the picture gets darker.
Now the tricky part. The STF set of aperture blades makes two things: it darkens the picture, just as the ordinary aperture, and it has an pleasing effect on the OOF parts of the picture by smoothening them. My guess is that the STF aperture blades are placed pretty close to the standard ones but still at a "plane" where we have a little more focus, sort of speaking. I think you can understand how I am thinking, but I have of course no grip of this.

It would be fun to try something with a short tele lens with some air inside it between the lens groups. I'm thinking of a way to add apertures (cut out from paper possibly) in different sizes and move them a little forth and back to see what happens.
Maybe this is why the STF lens is a tele lens; they might have needed space in there to get a good aperture mechanism fit. I would like to have a FF sensor and a 24mm, a 50mm and a 90mm STF lens to go with it...

regards,

[Jonas B]

Originally Posted by blende8

Perhaps we should push BOKEH more in the online fora, so that it becomes the single most important lens property, leaving behind sharpness and CA.

Pentax, give us better bokeh!

Aber natürlich!
We live in the times of oversharpening anyway. Besides of the megapixel race there is a freak'n resolution race going on, on the lens side. That serves us with axial CA and bright rings and harsh rendering.

blende8, is that avatar you?

regards,

[blende8]

Originally Posted by Jonas B

blende8, is that avatar you?

I'm afraid so.

[Jonas B]

Originally Posted by blende8

I'm afraid so.

I have no opinion on that... But, I think the picture is cool!

kindest,

[carpents]

Originally Posted by Jonas B

What are the designers thinking of?

You answered yourself (as did blende8) - sharpness.

Originally Posted by Jonas B

I enjoyed. Thank you for the links! The flower shot is pretty promising. Now we have the question: Why don't Pentax or Sony or anyone more STF lenses, and in shorter focal lengths?

Damian, I did get the link to load. (Must have been weighed down by all the PentaxForums traffic to it, ha ha.) I agree with you Jonas - that flower picture shows incredible promise given how that 50/1.7 renders naturally. (Which is to mean, quite poorly.)

Originally Posted by blende8

Perhaps we should push BOKEH more in the online fora, so that it becomes the single most important lens property, leaving behind sharpness and CA.

Indeed. My 'Normal Lens Shootout' was likewise criticized for undervaluing sharpness and overvaluing bokeh. For most, I think that sharpness is more important - and that is even among the small minority who care enough about photography to participate in on-line forums!!

If Pentax made a lens undercorrected for spherical aberrations just so it would render backgrounds nicely, I'm afraid it wouldn't really sell well. It would be relegated to the smallest of niche consumers.

Originally Posted by Jonas B

Now the tricky part. The STF set of aperture blades makes two things: it darkens the picture, just as the ordinary aperture, and it has an pleasing effect on the OOF parts of the picture by smoothening them. My guess is that the STF aperture blades are placed pretty close to the standard ones but still at a "plane" where we have a little more focus, sort of speaking. I think you can understand how I am thinking, but I have of course no grip of this.

Yes, yes, this makes perfect sense. What we are really trying to do is 'soften' the light around those sharp-edged aperture blades. But I wonder if the front-mounted filter would have an effect on some of the CA effects we see even if it doesn't help with the shape or distribution of the highlights.

I suspect you are correct about needing the room in a telephoto design to fit the STF portion. I guess this means your wide-angle dreams are not realistic. Maybe if they made a bigger-than-FF camera??? (Just kidding, even I don't think this will ever happen.)

[carpents]

Lensbabies?

See the picture in this post:
CJCram's 'Finally figuring out this lensbaby' Thread

[kenyee]

Originally Posted by carpents

What we are really trying to do is 'soften' the light around those sharp-edged aperture blades.

If that's true, they should attach another set of blades at an N degree offset to the regular blades. This would give you a better approximation of a circle which it seems is what they really want for better bokeh? I.e., the more blades/sides to the simulated circle, the better the bokeh?