[aslyfox]

I was only responding to seeing the term, which is almost universally used. I just think that it's an inaccurate analogy. I wasn't mad at anybody, certainly not another PFer.

i didn't think you were

and i agree Spaghetti-O bokeh is better

[MKohoutek]

what happens with mirror ( AKA catadioptric ) lenses:

" No Aperture: The Mirror Lens

The catadioptric or mirror lens—basically a reflector telescope—produces distinctive out-of-focus shapes popularly known as “doughnut bokeh.” Mirror lenses generally do not have adjustable diaphragm apertures. The distinctive shape of the bokeh comes from the design of the lens and the placement of the reflecting mirror in the center of the image. Light enters the optical tube, passes a small mirror, and strikes a concave mirror at the rear of the tube. The light is focused back toward the small mirror and reflected back through a hole in the concave mirror where the camera or eyepiece is mounted.

The result is bokeh with a bright edge and a relatively dark center. Some folks love this effect. Others despise it. Remember, bokeh quality is subjective . . . "

- Understanding Bokeh | B&H Explora

obviously not every photo taken with a " mirror " lens produces bokeh.

[ not my diagram ]

GoatsNDonkey - Thank you for the explanation!

---------- Post added 08-15-19 at 06:59 AM ----------

The dragonfly shot is cool! I haven't really tried exploiting the "macro" abilities of my Tamron 55BB. This makes me want to try it out on smaller, closer subjects.

Thagomiser - I was about 15 feet away from that dragonfly and I did crop the shot in PP, too. So...not really a macro shot - but still fun to use a long focal length for that kind of shot.

[cooltouch]

I just noticed the above quote, where it's written "obviously not every photo taken with a " mirror " lens produces bokeh."

So at first, I was asking myself what mirror lenses don't produce donut bokeh, and I concluded that Newtonians don't. A Newtonian has that tiny secondary mirror in the light path for the eyepiece (or camera) only, so I'm thinking it's not enough to produce donut bokeh. I suppose I could be wrong. I don't have any photos taken with a Newtonian that I can evaluate. There's another, rather uncommon mirror design where the light path is angled so that it isn't occluded by another mirror.

But then I realized that the quote is saying that it's possible for a mirror lens not to produce any bokeh. I suspect he meant to write "donut bokeh." Actually, I've found that a regular cat-type mirror, meant for photography, can produce photos with no donut bokeh. The key is to be focusing on a subject that is at or close to infinity. Then your hilights will contain no donuts.

[aslyfox]

I just noticed the above quote, where it's written "obviously not every photo taken with a " mirror " lens produces bokeh."

So at first, I was asking myself what mirror lenses don't produce donut bokeh, and I concluded that Newtonians don't. A Newtonian has that tiny secondary mirror in the light path for the eyepiece (or camera) only, so I'm thinking it's not enough to produce donut bokeh. I suppose I could be wrong. I don't have any photos taken with a Newtonian that I can evaluate. There's another, rather uncommon mirror design where the light path is angled so that it isn't occluded by another mirror.

But then I realized that the quote is saying that it's possible for a mirror lens not to produce any bokeh. I suspect he meant to write "donut bokeh." Actually, I've found that a regular cat-type mirror, meant for photography, can produce photos with no donut bokeh. The key is to be focusing on a subject that is at or close to infinity. Then your hilights will contain no donuts.

no I mean that I have taken photos without any bokeh being produced

check the photos in the thread many have no bokeh at all

[goatsNdonkey]

no I mean that I have taken photos without any bokeh being produced

check the photos in the thread many have no bokeh at all

Perhaps we need one or more working definitions of "bokeh" to continue this discussion.

* My definition of "good bokeh" is when the out-of-focus areas are rendered in such a way as to either (1) enhance the overall impression of the image, or (2) add additional interest to the image.

* My definition of "bad bokeh" is when the out-of-focus areas are rendered in such a way as to distract from other elements of the image and make the image less interesting, if not annoying.

Note that some people automatically assign donut or Spaghetti-O bokeh from mirror lenses to the second group, while I do not.


So, my question to aslyfox is, when you say some mirror lens shots "have no bokeh" do you mean:
--they have no out-of-focus areas?
--their out-of-focus areas are totally bland and neither enhance nor annoy?
--some thing else?

[aslyfox]

Perhaps we need one or more working definitions of "bokeh" to continue this discussion.

* My definition of "good bokeh" is when the out-of-focus areas are rendered in such a way as to either (1) enhance the overall impression of the image, or (2) add additional interest to the image.

* My definition of "bad bokeh" is when the out-of-focus areas are rendered in such a way as to distract from other elements of the image and make the image less interesting, if not annoying.

Note that some people automatically assign donut or Spaghetti-O bokeh from mirror lenses to the second group, while I do not.


So, my question to aslyfox is, when you say some mirror lens shots "have no bokeh" do you mean:
--they have no out-of-focus areas?
--their out-of-focus areas are totally bland and neither enhance nor annoy?
--some thing else?

how would you describe these photos in this thread that I and others posted ?

The Mirror Lens Club! - PentaxForums.com

The Mirror Lens Club! - PentaxForums.com

https://www.pentaxforums.com/forums/122-lens-clubs/71775-mirror-lens-club-2.html#post4684535

those, and others, is what I was referring to:

that at times, when using a mirror lens - no bokeh is produced

Personally I have no problem with bokeh ( beauty is in the eyes of the beholder after all ) whether " normal " or " doughnut / spaghetti-o bokeh

[goatsNdonkey]

how would you describe these photos in this thread that I and others posted ?

The Mirror Lens Club! - PentaxForums.com

The Mirror Lens Club! - PentaxForums.com

The Mirror Lens Club! - Page 2 - PentaxForums.com

those, and others, is what I was referring to:

that at times, when using a mirror lens - no bokeh is produced

Personally I have no problem with bokeh ( beauty is in the eyes of the beholder after all ) whether " normal " or " doughnut / spaghetti-o bokeh

Of the three examples you provided links to, I'd call the out-of-focus areas of the first one to be bland enough to call "no bokeh." The faint pattern of fence wire in the background is so indistinct as to be barely there, and certainly not busy.

In the second example--the zinnias against out-of-focus gradation between a light green to nearly black--this beholder finds quite lovely bokeh. The greens are absolutely creamy and one could spend a very long time trying to capture that kind of smooth gradation in an garden. I think the out-of-focus area certainly enhances the image while keeping most of the attention on the focussed-on subject matter. A lot of other backgrounds might suit the main subject matter of the picture far, far, less suitably.

In the third example, I find bokeh, just not anything quite as remarkable as in the second example.

[aslyfox]

Of the three examples you provided links to, I'd call the out-of-focus areas of the first one to be bland enough to call "no bokeh." The faint pattern of fence wire in the background is so indistinct as to be barely there, and certainly not busy.

In the second example--the zinnias against out-of-focus gradation between a light green to nearly black--this beholder finds quite lovely bokeh. The greens are absolutely creamy and one could spend a very long time trying to capture that kind of smooth gradation in an garden. I think the out-of-focus area certainly enhances the image while keeping most of the attention on the focussed-on subject matter. A lot of other backgrounds might suit the main subject matter of the picture far, far, less suitably.

In the third example, I find bokeh, just not anything quite as remarkable as in the second example.

it could always be my monitor but I see no bokeh in the second photo

it is a great photo

same as the third

now I am talking about the spaghetti-0 bokeh common with mirror lenses

[luftfluss]

I call it Spaghetti-O bokeh

That's brilliant.

[goatsNdonkey]

it could always be my monitor but I see no bokeh in the second photo

it is a great photo

same as the third

now I am talking about the spaghetti-0 bokeh common with mirror lenses

I was talking about bokeh according to the bokeh definitions I submitted in my previous message.

In your answer to the part of that message asking what you meant by the term bokeh, you did not say that you were only referring to the Spaghetti-O or donut bokeh that mirror lenses can often produce. If that is what you meant by "no bokeh" in you earlier remarks, I would agree, only the third of those examples has a trace of it.

I agree that it is possible for mirror lens shots to have little to none of those circular patterns, but they certainly can produce other kinds of bokeh. A number of lenses are capable of producing what is sometimes called bubble bokeh, but it is possible to get other kinds of bokeh from them (again referring to my definitions for good and bad bokeh to clarify what I mean), and they don't always produce bubble bokeh when one is hoping for it.

To people who trumpet that they would never own or use a mirror lens, because of that infernal donut bokeh they are famously afflicted with, your three examples would help make a case for them to reconsider their extreme decision.

On the other hand, the second example of the three, would be excellent evidence for a bokeh-niac, like any those who post regularly in PF's bokeh thread, to consider getting a mirror lens (if they didn't have one) because of the range of kinds of bokeh it could produce.

[cooltouch]

I found bokeh in most of the shots in the above links. For the sake of definition, to me "bokeh" is defined as out of focus highlights. And by "highlights" I mean anything that adds to the quality of an image.

In the above images, there were several that didn't appear to have any Spaghetti-O bokeh, but they had them, they were just very soft. In a few others, the donuts were there, they were just very small.

Here's a good example of a mirror image with no donut bokeh. I suppose that, since the entire image is mostly in focus, you could argue there is no bokeh. Canon FTb, Sigma 600mm, Kodachrome 64.


An another one in which the donut bokeh are small and rather inconsequential. Canon F-1, Sigma 600mm, Kodachrome 64.


And yet another in which the donut bokeh are so obvious, they're practically the subject of the photo. Canon F-1, Sigma 600mm, Kodachrome 64.


On balance, though, I think that, as long as the image has something important or obvious to say, a few donuts here or there aren't gonna be a bother -- at least certainly not to me.

Canon FTb, Sigma 600mm, Kodachrome 64


Canon F-1, Sigma 600mm, Kodachrome 64


Canon F-1, Sigma 600mm, Kodachrome 64

[marcusBMG]

I've been playing with a couple of PK mount sigma 600's I picked up.




I have to say the more I play with them the less enamoured I am. One thing that's clear is that the contruction is inferior to that of the tamron adaptall SP 500mm's. The white one is the second one I have had with a ring of silvering deterioration, and some discolouration with this one (however there was no loss of resolution in comparison to the black one, my impression is that the main effect is a more rapid loss of contrast as the light gets duller).



In less than ideal light I struggle to get a presentable image. Too many pics exercising the delete button like this (samsung NX20, magnified evf for focus 1/1250th 200asa). IMO if the sun isn't shining you're almost wasting your time, the contrast on these is just too poor.



In best light, PP'ed jpg's (with the blemished white one!) :




Not far off the tamrons, but very distinctly inferior, as these crops show.






But Michaels (cooltouch) scanned slides show these sigmas can be good.

[cooltouch]

Yes, they can be excellent. Unfortunately, as I've probably mentioned in an earlier post, there was some variability regarding quality control. Which is too bad. That one I bought in 1984 was an excellent lens. About five years ago, I bought one in Canon EOS mount -- so a fairly recent build -- that was definitely sub-par. It produces a double image, which ruins things. More recently, I bought an early one that is close to the Tamron in sharpness. Contrast is a bit dull, though, but I think that is because of a fine layer of dust that has accumulated on the inner surfaces. I still haven't gotten around to cleaning that lens yet.

I haven't totally lost confidence in that EOS mount Sigma. I dismantled the rear section of the lens, to see if there were any way to adjust collimation. There isn't any that I can see. It is a very solidly built lens -- in the rear section, at least -- with no movement possible for any of the rear elements. But I'm gonna take it to a very competent local repair outfit here and see if there's anything they can do to improve its problem with the double image it produces. So it may yet be salvageable.

So, Sigma 600s are something of a crap shoot. If I were to buy another, it would only be with returns accepted by the seller, and I'd try it out as soon as I got it. On another forum, the members there and I had a discussion regarding image quality vs. approximate date of production. I was expecting to find that the earlier lenses were, on average, better performers. But that wasn't the case. The variability seemed to persist through the entire product run.

[mlynch53]

My Sigma 600 for Pentax, I think, has been a good, solidly-built lens with good optics. It's the grey one. I think of it as heavy enough that I can use it only on a tripod no matter what the situation. The mirror remains in very good shape, after owning the lens since mid-2017. (I used it for the total solar eclipse that year and posted successful shots of the results in this forum earlier.)

I recently bought (again) a Tokina 500mm mirror lens for my Pentax K-S2, because I wanted to be able to hand-hold a lens of this reach. I've had very good results with it, knowing the limitations of mirror lenses.

My K-S2 brings up another question: It's the first camera I've owned with a live-view screen for photography (not just videography), and I'm wondering if any of you find the live view to be very helpful with careful focusing...

I've used a right-angle, 2x magnifying finder attachment on my camera to help with focus, and it has been very helpful. Wondering about the usefulness of live view for this purpose.

[cooltouch]

I have found that anything that can be done to aid in focusing is a welcome addition. Back in my film days, I bought an eyepiece magnifier for my Canons, which helped some. With my first DSLR, which is a 10.1mp Canon XS with a squinty viewfinder, I bought an eyepiece adapter th at increased magnification by 1.35x. This was a welcome addition. That camera also has live view with a magnification setting that I also found to be very helpful.

More recently I've been using a Sony NEX 7. It has Live View plus it has a focus peaking feature that helps a lot. But I've found that focus peaking is not necessarily the most accurate method. The NEX also has a 2-step magnification function that can be used -- I think the powers are 6x and 11x -- which helps a lot and often reveals that focus peaking can be less than accurate. At these high magnification levels I've found shooting hand-held can be tricky. Especially with longer lenses. For longer focal lengths, when shooting with the image magnification function, a tripod is the best method for insuring good results.