[Michael Piziak]

I like reflex lens as they can be super telephoto with a smaller/lighter size.

I'm curious, is there a way to predict when and when not one would get the doughnut shaped bokeh with these reflex lens.

Currently, I'm craving the SMC Pentax 400-600mm Reflex Reviews - K Zoom Lenses - Pentax Lens Reviews & Lens Database


Michael

Addendum: I previously owned a 500mm Tamron reflex lens, but either I had a bad copy or the lens isn't that great. My photos using my Pentax 55-300mm lens provided better cropped photos than the Tamron delivered at 500mm.... As seen in this older thread: https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/437054-tam...omparison.html

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Last edited by Michael Piziak; 02-02-2023 at 05:30 PM.

[MarkJerling]

Bokeh is a result of the shape of the aperture, and, for mirror lenses the bokeh is almost always rendered as donut shapes. For me, almost all mirror lenses produce quite a "messy / busy" bokeh, but I think it;s highly subjective, of course. I don't think there's a way to predict when or when not you'll see donuts, but you will most likely see donuts in your out of focus areas when using a mirror lens. The extent of this is likely aperture size related.

[photoptimist]

The basic design of mirror lenses means 100% of them create donut bokeh. That doesn't mean the donuts will appear in every picture, just any picture with any small, bright, out-focus objects.

Reflex lens have a folded optical path with a large primary mirror at the back bouncing the gathered light to a small secondary in the center of the front of the lens. However because that secondary mirror blocks incoming light, it creates a hole in the bokeh thus forming a donut.

P.S. There is a telescope design known as a Schiefspiegler that avoids this blockage but I've never heard of a camera lens built on the Schiefspiegler principle.

[Michael Piziak]

The basic design of mirror lenses means 100% of them create donut bokeh. That doesn't mean the donuts will appear in every picture, just any picture with any small, bright, out-focus objects.

Reflex lens have a folded optical path with a large primary mirror at the back bouncing the gathered light to a small secondary in the center of the front of the lens. However because that secondary mirror blocks incoming light, it creates a hole in the bokeh thus forming a donut.

P.S. There is a telescope design known as a Schiefspiegler that avoids this blockage but I've never heard of a camera lens built on the Schiefspiegler principle.

I read that wikipedia article you linked us to. That's a very interesting article and I wonder why no camera manufacturer has designed a reflex/mirror lens with the Schiefspiegler principle.
It seems as if most camera manufacturers, including most lens manufacturers, have stopped making reflex lens; although, I think I did see one that was recently released, but that's just one.

On another topic. It seems as if the Pentax reflex lens I'm looking at, seems like it is less sharp at the 600mm focal length of the lens. I haven't been able to find many photos, however, from the lens at the 600mm range....

I suppose Live View would come in handy at determining if ones photos are likely to have lots of doughnut shaped bokeh.

[luftfluss]

Tokina just released 300, 600, and 900mm mirror lenses for several APS-C mirrorless* platforms.

*Which are no longer "mirrorless" when one of these lenses is attached, I guess.

[Michael Piziak]

Addendum: I found the focal lengths of the images on this page to be good ones to judge the lens at 600mm
The focal lengths of the 7 images on the page are as follows:

1st image = 600mm (the Catkin image is the first image I'm starting at)

2 = 600 (the pigeon image then so forth)... In this one, I think it illustrates how you need to nail focus and focus is razor thin some times as feathers are in focus but head isn't...

3 = 600
4 = 600
5 = 500
6 = 500
7 = 500

and the link to those 7 images is: https://www.pentaxuser.com/forum/topic/smc-pentax-reflex-zoom-1-8-12-400-600...ent--65783/p-0


Comments please: What do you guys/gals think of the images at the 600mm and 500mm focal range ?

When I think of using this lens, I think of whether or not I would come across the same results that I did with the Tamron, which is that cropping photos from my Pentax 55-300 lens would or would not yield photos just as good or better than the reflex lens images uncropped....

---------- Post added 02-02-23 at 08:18 PM ----------

Tokina just released 300, 600, and 900mm mirror lenses for several APS-C mirrorless* platforms.

*Which are no longer "mirrorless" when one of these lenses is attached, I guess.

Yes, there website even has a new 900mm. Probably not for k mount, but there are adapters....

I don't quite understand your thought "no longer mirrorless" though - ?

[luftfluss]

I don't quite understand your thought "no longer mirrorless" though - ?

Just a corny joke by me... take a mirrorless camera, add a mirror lens, and suddenly you are no longer shooting mirrorless

[Michael Piziak]

Just a corny joke by me... take a mirrorless camera, add a mirror lens, and suddenly you are no longer shooting mirrorless

Oh, that's actually a good one that went above my head !

lol

[GUB]

Addendum: I found the focal lengths of the images on this page to be good ones to judge the lens at 600mm
The focal lengths of the 7 images on the page are as follows:

1st image = 600mm (the Catkin image is the first image I'm starting at)

2 = 600 (the pigeon image then so forth)... In this one, I think it illustrates how you need to nail focus and focus is razor thin some times as feathers are in focus but head isn't...

3 = 600
4 = 600
5 = 500
6 = 500
7 = 500

and the link to those 7 images is: https://www.pentaxuser.com/forum/topic/smc-pentax-reflex-zoom-1-8-12-400-600...ent--65783/p-0


Comments please: What do you guys/gals think of the images at the 600mm and 500mm focal range ?

When I think of using this lens, I think of whether or not I would come across the same results that I did with the Tamron, which is that cropping photos from my Pentax 55-300 lens would or would not yield photos just as good or better than the reflex lens images uncropped....

---------- Post added 02-02-23 at 08:18 PM ----------




Yes, there website even has a new 900mm. Probably not for k mount, but there are adapters....

I don't quite understand your thought "no longer mirrorless" though - ?

If you look two images below the yellow flower one in the link - they represent the range in bokeh a given lens can do. I have the 400 - 600 and I consider it is capable of pleasant background results. To answer you first question the variables in what make the donuts harsh or not are; lens to subject distance , background separation distance and the relationship of these to the physical size of the front element and it's f stop and focal length. An obscure formula of course aggravated by highlight spots in the background. EDIT (I forgot) and one other variable is the size of the texture of the background.
Given the ease to miss focus and the temptation to hand hold I wouldn't buy a mirror for it's sharpness. But they are fun and in some situations a practical choice

[GUB]

400 - 600 Pentax . I don't know what focal length these were taken at but it was probably 600mm. Linked from the mirror lens club. As you can see the technical sharpness of the images is secondary to the over all effect.

[JohnMc]

The basic design of mirror lenses means 100% of them create donut bokeh. That doesn't mean the donuts will appear in every picture, just any picture with any small, bright, out-focus objects.

MMM... Spectacular Specular donuts.

[AstroDave]

I had the Pentax 400 - 600 reflex lens once upon a time. I don't have it any more.

i.e. Not a big fan of this lens.

[biz-engineer]

I'm curious, is there a way to predict when and when not one would get the doughnut

Biggest problem with these lenses , is you don't get a freshly brewed coffee with your doughnut.

[Michael Piziak]

I believe, sometimes, just a little smudging can reduce the predominant affect of the dougnut bokeh. I dunno, maybe I made it worse - smiles...




from

[gofour3]

I like reflex lens as they can be super telephoto with a smaller/lighter size.

Also note all the Pentax reflex lenses are pretty slow and have a fixed aperture......


Phil.