D-FA 50mm f/1.0 SDM - Page 14

ogl · 05-26-2009, 11:21 PM

I has only some doubts about DFA*50/1.0 SDM....
But other lenses could be real.

DA35/2.8 is LIMITED, but not pancake.
To make compact 135/2.8 in metal body is not a problem.
DA won't be big. Minolta had compact 135 mm lens.

*falconeye* · 05-27-2009, 01:42 AM

Originally Posted by ogl

I has only some doubts about DFA*50/1.0 SDM....
But other lenses could be real.

ogl, you are so easy to excite

As my girlfriend keeps saying: "There is no True in the False"

ogl · 05-27-2009, 01:46 AM

It seems to me that parts of new roadmap is not fake...
Ask me - WHY?
I answer - BECAUSE.

I had a dream.

I hope that DA135/2.8 will be announced this year. With new camera - September-October.

janneman · 05-27-2009, 04:23 AM

Originally Posted by ogl

It seems to me that parts of new roadmap is not fake...
Ask me - WHY?
I answer - BECAUSE.
I had a dream.

I hope that DA135/2.8 will be announced this year. With new camera - September-October.

Ofcourse parts of it are not fake, it does list current lenses

vinzer · 05-27-2009, 05:17 AM

Originally Posted by tinyt187

Agreed... they need to be able to attract the canikon FF userbase (prestige) to make the switch. In a down economic climate, even the NFL photogs might give Pentax a second thought if they can get quality gear for half the price with the 400mm... as long as they don't care about FPS ;-)

Maybe they can entice some with such a product, but I think a lot of those NFL sideline photographers don't own the lenses they shoot with. I believe those are owned by the media outlets they working for, or maybe loaners from Canon/Nikon professional services.

I wonder if Pentax still intends to push through with the pro service they said they're working on in the past. That would really go a long way towards earning some faith from the pros who, understandably, are reluctant to shoot with a system that doesn't offer them pro services.

Pål Jensen · 05-27-2009, 07:07 AM

Originally Posted by ogl

I has only some doubts about DFA*50/1.0 SDM....
But other lenses could be real..

Disagree. The D-FA645 25/2.8 is even more unreal than the 50/1.0. They would probably cost the same and be equally difficult to design. However, it is possible to make a case for a 50/1.0; far more diffucult to make a case for the extra cost, size and weight of the 25/2.8 for a lens that will be mostly used for landscapes.

GoldenWreckedAngle · 05-27-2009, 07:18 AM

Originally Posted by vinzer

Maybe they can entice some with such a product, but I think a lot of those NFL sideline photographers don't own the lenses they shoot with. I believe those are owned by the media outlets they working for, or maybe loaners from Canon/Nikon professional services.

I wonder if Pentax still intends to push through with the pro service they said they're working on in the past. That would really go a long way towards earning some faith from the pros who, understandably, are reluctant to shoot with a system that doesn't offer them pro services.

I wonder that myself. I'm not yet earning 51% of my income from photography (one of the requirements) but if I'm still shooting Pentax when I do I'll be very interested in that program.

*OregonJim* · 05-27-2009, 10:19 AM

Originally Posted by RawheaD

(a) as I've said elsewhere, I'm 99.9% positive that it is physically impossible to make an f1.0 lens for PK mount;

Care to explain why? I don't see the relationship between lens mount and diaphragm size - and the size is dependant on focal length. What am I missing (besides the $$$ to buy such a beast)?

*falconeye* · 05-27-2009, 01:09 PM

Originally Posted by OregonJim

Care to explain why? I don't see the relationship between lens mount and diaphragm size - and the size is dependant on focal length. What am I missing (besides the $$$ to buy such a beast)?

RawheaD recently explained this here:
http://www.pentaxforums.com/forums/598686-post107.html

The argument lacks some considerations for tele and retro-focus designs. But as it turns out, as long as a lens' entrance and exit pupil are the same, RawheaD's argument still holds true. So, I agreed to RawheaD's statement.

I am not aware of any SLR lens which has unequal entrance and exit pupils.

*Jonson PL* · 05-27-2009, 03:22 PM

Originally Posted by RawheaD

Yeah, I can confirm that.
That it's a fake :-D For obvious reasons; (a) as I've said elsewhere, I'm 99.9% positive that it is physically impossible to make an f1.0 lens for PK mount;

Fast lenses for K-mount are easy to make.
The prototype 20/1.4 is the fastest in its wide-angle segment :
K 20/1.4 AL

The 300/2 is an exceptional fast tele lens :
K 300/2

The 8.4/2.8 birds-eye; is a uniquely fast super wide :
K 8.4/2.8 Bird's-Eye

The 50/1.2 is not a super big lens, in the Pentax system. It should not be all that difficult to make a faster f/1 lens.
Likewise, the 85/1.4, and 135/1.8 are easy to produce in the K mount. And they function fine.

Here are some even faster lenses for Nikon :
Rodenstock TV-Heligon 50 mm f/0.75 lens.
Repro-Nikkor 85 mm f/1
Rodenstock TV-Heligon 42 mm f/0.75.
Kowa 55 mm f/0.8.
Rodenstock XR-Heligon 75 mm f/1.1
MATI 86 mm f/1.2

"So, at least as an alternative, other visual approaches might be explored, and while doing so technical trade-offs should be accepted. My preferred choice is shooting with fast lenses at wide aperture settings. In fact, the wider the better and don't let the f/1 barrier hold you back....

Remember f-numbers are specified for infinity focus. Moreover, due to the various optical designs, even greater variability is introduced. Thus, when the pupil magnification (p) is factored into the equation, some of the seeming blindingly fast lenses fade into the not-so-extreme category. However, any of these lenses still are much faster than a Micro-Nikkor set to an equal magnification.

The advertised large-aperture value of fast lenses is valid only for infinity focus and when they cover their designated image format. Step way outside these parameters and the effective aperture may be significantly reduced (as shown in the Table above)."

Rodenstocks : 64 mm f/1.25, 95 mm f/1.4 and 100 mm f/1.5 lenses.
Need for Speed: Very Large Aperture Lenses

Some of these, could likely be used on Pentax as well.

And the Canon 50/1 lens, was 985 grams. 8,1 cm length, with USM.

A K-mount 50/1 lens would not be difficult to make. But they need to look at production cost, compared to how many would buy. I would much prefer that the 20/1.4 went into production instead. But some might like the large aperture 50/1, when used on crop cam.
And the variaty of special primes, are what set Pentax aside from other brands.

*falconeye* · 05-27-2009, 04:27 PM

Originally Posted by Jonson PL

The 50/1.2 is not a super big lens, in the Pentax system. It should not be all that difficult to make a faster f/1 lens.

You really should go back one post and read the post by RawheaD I had linked there.

muvideo · 05-27-2009, 04:45 PM

Originally Posted by falconeye

RawheaD recently explained this here:

I am not aware of any SLR lens which has unequal entrance and exit pupils.

Hello, usually I dont' post because of my pooor english.
I'm curious about the statement above, perhaps I dont' understand
correctly, but isn't entrance pupil of 200/2.8=about71mm?
And so for 300/2.8=107mm, 85/1.4=60.7mm.
I haven't seen exit pupil of these lenses, but I think that it's of
smaller diameter than entrance pupil.
Or have I made wrong assumptions on what are entrance and exit
pupils?

*falconeye* · 05-28-2009, 11:57 AM

Originally Posted by muvideo

Or have I made wrong assumptions on what are entrance and exit pupils?

The topic about entrance and exit pupils isn't very intuitive. Still, it is key to a proper understanding of optics. E.g., entrance and exit pupils not only have an aperture, they have a position along the optical axis too. And this position may be entirely outside of a lens ...

The entrance pupil determines the point of parallax-free rotaton (yes, it is NOT the nodal point!) and f-stop, the exit pupil determines DoF.

The ratio P = exit pupil diameter / entrance pupil diameter is called pupil magnification. So-called symmetrical lenses are defined by P=1.

As a matter of fact, a symmetrical lens with f/1.0 is impossible for the PK-mount. Period.

(Of course, asymmetrical lenses do exist (but are rare). The argument by RawheaD applies to symmetrical lenses.)

A good starting point for further reading is

Pupil magnification - Wikipedia, the free encyclopedia and the links therein.
The DOF equations

Addendum:
I found this statement:

Wide angle lenses frequently have P>1

Such a lens has an exit pupil larger than the entrance pupil and therefore, possible apertures are even smaller.

An f/1.0 lens for PK mount would require P<1 and I don't know if such lenses do exist at all.

muvideo · 05-28-2009, 12:39 PM

Originally Posted by falconeye

The topic about entrance and exit pupils isn't very intuitive.

...

An f/1.0 lens for PK mount would require P<1 and I don't know if such lenses do exist at all.

Thank you for explanation.
Fabio.

ogl · 05-28-2009, 09:33 PM

Originally Posted by Jonson PL

Fast lenses for K-mount are easy to make.

Here are some even faster lenses for Nikon :
Rodenstock TV-Heligon 50 mm f/0.75 lens.
Repro-Nikkor 85 mm f/1
Rodenstock TV-Heligon 42 mm f/0.75.
Kowa 55 mm f/0.8.
Rodenstock XR-Heligon 75 mm f/1.1
MATI 86 mm f/1.2

Good post