[falconeye]

The didn't say whether it was 60 for a horizontal or diagonal AOV. If it is for horizontal, it would put it in the ball park for a DA* for the 645d system. The time line fits for that also.

They don't need to. This is a lens patent. So expect some technical speak.
AOV in lens design always is diagonal. Actually, it is not. It is just a diameter as everything is round

And if you would have done the math, you've obtained crop factors of 1.44, 1.54 and 1.52. Other Pentax patents when examined in the same way (like DA*300) yield crop factors of 1.00.

There really is no need to continue speculating about what are clear statements in the patent document. Esp. read table 5. Also note the small flange-back distance of ~39mm only. The rear element actually protudes a few mm into the mirror box.


Anybody found the patent for the DA*60-250?

---

Last edited by falconeye; 05-17-2010 at 09:11 AM.

[falconeye]

More patents for you:

• DA 70 f/2.4 Ltd.
• Unknown DA 12-35mm f/3.6-5.8 lens (for APS-C, from 2005)
• DA* 60-250mm f/4 (I comment below)
• Unknown DA 12-28 f/4 (made for APS-C, from 2005)
• DA 21 f/3.2 Ltd.

The patent for the DA* 60-250/4 describes several versions, like
61.5 - 243mm f/4.1 or 56.1 - 243mm f/4.1.

The crop factor in all versions is ~0.98/1.03/1.02 at wide/medium/tele zoom.


So, this is the official confirmation from Pentax that the DA*60-250/4 lens is a full frame lens indeed.


BTW: where is all your help?

[Supernaut]

Not much but here's my contribution.

DA35 Macro: Macro lens system - Patent 7715118

Alternative kitzoom? 18-70/4-5.6: Standard zoom lens system - Patent 7609456

Both with crop factor ~aps-c.

[RuiC]

More patents for you:

• DA 70 f/2.4 Ltd.
• Unknown DA 12-35mm f/3.6-5.8 lens (for APS-C, from 2005)
• DA* 60-250mm f/4 (I comment below)
• Unknown DA 12-28 f/4 (made for APS-C, from 2005)
• DA 21 f/3.2 Ltd.

The patent for the DA* 60-250/4 describes several versions, like
61.5 - 243mm f/4.1 or 56.1 - 243mm f/4.1.

The crop factor in all versions is ~0.98/1.03/1.02 at wide/medium/tele zoom.



So, this is the official confirmation from Pentax that the DA*60-250/4 lens is a full frame lens indeed.


BTW: where is all your help?

Thanks Falk well done. Great research job there.

Rui

[youky63]

Thanks for your analysis Falconeye. But I am not a specialist in optics, so could you please explain to me how you get the crop factor from table 5? I would be very interested to be able to investigate on my side too! ;-)

[falconeye]

Thanks for your analysis Falconeye. But I am not a specialist in optics, so could you please explain to me how you get the crop factor from table 5? I would be very interested to be able to investigate on my side too! ;-)

I'm not a specialist in optics either

In the text preceding the tables, they explain symbols W (half angle of view) and f (focal length). The rest is using your pocket calculator. Image diagonal = 2f tan(W) and divide by sqrt(24^2+36^2) to get 1/crop factor. BTW, the other tables are equally ok. Look at the table's headers. The tables describe configurations Pentax has actually examined in detail. One of them would describe the product. Fortunately, they are all very similiar. It may be they provide several tables to obfuscate the actual production parameters (protection against Chinese lens makers). Some of the lenses are P&S and all their lens patents seem to look like this.

[youky63]

I'm not a specialist in optics either

In the text preceding the tables, they explain symbols W (half angle of view) and f (focal length). The rest is using your pocket calculator. Image diagonal = 2f tan(W) and divide by sqrt(24^2+36^2) to get 1/crop factor. BTW, the other tables are equally ok. Look at the table's headers. The tables describe configurations Pentax has actually examined in detail. One of them would describe the product. Fortunately, they are all very similiar. It may be they provide several tables to obfuscate the actual production parameters (protection against Chinese lens makers). Some of the lenses are P&S and all their lens patents seem to look like this.

Of course, I don't even know how I have missed it!
So if this 26-340mm lens is for APS-C camera, I really don't see the point for a such glass! Not wide enough to be used on wide landscape, and probably not good enough to be used as a long telephoto lens. And not very fast even a only 100mm (f/5.2). People that want it probably better look at the 50-300mm for quality.
About the alternative designs, I think it is also to protect their design from any other companies (even/especially japanese) trying to produce an equivalent one as close as possible if successful.

[Supernaut]

I used this link for calculations http://www.tawbaware.com/maxlyons/calc.htm
But I realize that Falks method is far more elegant

There are a few lenses that hasn't and probably won't reach the market. I hope this is the case for this lens as I don't see the point with it either. If people want a "Bigma" for crop they still want maximum reach of 500mm and not something that reaches 500 with crop factor. Imo. I surely hope that this isn't the super tele that was mentioned on the roadmap previously.

[ogl]

More patents for you:[LIST][*] DA 70 f/2.4 Ltd.

What is the crop-factor of DA70?

[Supernaut]

What is the crop-factor of DA70?

About 1.5x is used in the patent.

[ogl]

About 1.5x is used in the patent.

But I saw pictures from film with DA70.
It covers FF. Not at 2.4, but at all other apertures

[thibs]

But I saw pictures from film with DA70.
It covers FF. Not at 2.4, but at all other apertures

At f/2.4, does it vignette or is the border really black? I mean, can it be corrected acceptably in LR/PS or not ?

[gazonk]

At f/2.4, does it vignette or is the border really black? I mean, can it be corrected acceptably in LR/PS or not ?

Don't forget the DA on FF thread!

As I understand it, it's usable even wide open, but very soft in the corners.

[thibs]

Don't forget the DA on FF thread!

As I understand it, it's usable even wide open, but very soft in the corners.

Thank you, forget that one...

[falconeye]

DA70 patent's crop factor: 1.43x

Don't forget the DA on FF thread!

As I understand it, it's usable even wide open, but very soft in the corners.

The bad news is: I'll have to recreate most of its content as the free image hoster with unlimited archival time deleted all of my content ...


The good news is: Meanwhile I learned how to run numeric resolution tests.

MTF50 DA70, f/5.6
center: 3200 LW/PH
short FF edge 1950 LW/PH
extreme FF edge 1100 LW/PH
extreme FF corner 680 LW/PH

The decay in resolution is most likely due to CA as I see double contour lines and a big difference between sagital and tangential resolution (which I averaged). But using B&W film, I cannot really measure the resolution after CA correction ...

Note that the center resolution above is one you cannot see with a 14MP sensor and is about the limit of my measurement setup ...

The attachment shows the deleted image DA70 wide open. Even the outermost extreme corners receive light fully open, so, the ray thru the lens center passes thru. I cannot measure the amount of vignetting in stops as the film used (ADOX) has a very steep response curve and renders vignetting in a dramatic way

So, I added the same shot, but with Gamma=5 applied.