16-45. Wow


MattMatic

Link Posted 31/07/2008 - 13:30
IIRC, f/16 is about the smallest you can go with APS-C sensors before diffraction starts kicking in. (But I stand to be corrected!)
Matt
http://www.mattmatic.co.uk
(For gallery, tips and links)

Mongoose

Link Posted 31/07/2008 - 14:51
Matt, it deppends on how good the lens is.

A Perfect lens would perform best wide open, with angular resolution given by theta=arcsin(1.22*(lambda/aperture))


where theta is the minimum angular separation of two bearly resolved objects and lambda is the wavelength of light.


Even the best lenses are imperfect, so performance degrades wide open, but since imperfections tend to be worse at the edges of the lens matters usually improve for the first couple of stops as you stop down.

At some point the benefits from cutting out imperfections in the lens are outweighed by the diffraction limit and performance decreases.
you don't have to be mad to post here



but it does help

johnriley

Link Posted 31/07/2008 - 15:56
Diffraction limted yes, but there are huge variations in performance levels between lenses. Diffraction is not the only consideration.
Best regards, John

missmarple

Link Posted 31/07/2008 - 15:58
[quote:3496ace15f="Mongoose"]Matt, it deppends on how good the lens is.

A Perfect lens would perform best wide open, with angular resolution given by theta=arcsin(1.22*(lambda/aperture))


where theta is the minimum angular separation of two bearly resolved objects and lambda is the wavelength of light.



I was gonna say that

johnriley

Link Posted 31/07/2008 - 16:02
And you'd have been right.

There may be no perfect lenses, but there are plenty of perfectly good ones.
Best regards, John
Last Edited by johnriley on 31/07/2008 - 17:55

justgetoutandride

Link Posted 31/07/2008 - 17:35
johnriley wrote:
And you'd have been right.

There may be no perect lenses, but there are plenty of perfectly good ones.

you are quite correct, I can't find anything on google about them.

Perhaps we do need to increase the time limit on edits after all.


Please call me aj,

I use a Pentax K10D, on a MacBook with LightRoom (vers 1.3 + beta 2)

http://www.ba-joseph.co.uk/gallery

Mongoose

Link Posted 31/07/2008 - 22:39
johnriley wrote:
Diffraction limted yes, but there are huge variations in performance levels between lenses. Diffraction is not the only consideration.

By diffraction limited, I mean limited only by diffraction. By F22 I would be surprised if anything else makes much difference because the physical limit on placed on resolution by diffraction renders other considerations meaningless.

Obviously at F8 there are large variations between lenses, by F22 I doubt you could see the difference even if it's measureable.
you don't have to be mad to post here



but it does help

johnriley

Link Posted 01/08/2008 - 00:22
Published lens tests do show significant variations even at f22.
Best regards, John

Mongoose

Link Posted 01/08/2008 - 12:40
I stand surprised
you don't have to be mad to post here



but it does help

beginner

Link Posted 01/08/2008 - 22:50
I was lost off with all the technical jargon!....but my 18/55 is still cracking at F22.....AND MY 16/45 has a sweet spot at 19mm...........just thought I would add that as a talking point!...night,night folk!............
K20D...ist DS ,DA18/55,DA16/45.DA* 50/135,"A"1.7 50MM..."A" 70/210..M 50mm f2...Tamron 90mm macro,28/300 Tamron,200/500 Tamron 6.9....A Pentax DA*300... Sigma10/20,FA31mm 1.8 Ltd*********,FA 77mm Ltd!

Niloc

Link Posted 06/08/2008 - 15:44
Hi every one I have just bought my self a Samsung GX20 wich I like very much the reason I jioned this foram was to find the best Pentax lenses that I shoud buy

ChrisA

Link Posted 06/08/2008 - 15:51
Niloc wrote:
Hi every one I have just bought my self a Samsung GX20 wich I like very much the reason I jioned this foram was to find the best Pentax lenses that I shoud buy

Welcome!

The best Pentax lenses that you should buy depend a lot on how much money you have to spend.

If you're loaded, get the '*' and limited lenses.

If you're skint, the kit lens is great for what it is.

Have a look round here, see what you think.

A lot of people here (myself included) think the best place in the UK to buy them is here.
.
Pentax K-3, DA18-135, DA35 F2.4, DA17-70, DA55-300, FA28-200, A50 F1.7, A100 F4 Macro, A400 F5.6, Sigma 10-20 EXDC, 50-500 F4.5-6.3 APO DG OS Samsung flash SEF-54PZF(x2)
.

Malo1961

Link Posted 06/08/2008 - 15:56
Niloc wrote:
Hi every one I have just bought my self a Samsung GX20 wich I like very much the reason I jioned this foram was to find the best Pentax lenses that I shoud buy

Hi Niloc, welcome to the Pentax(Samsung) User Forum.
Good to have another new member from.........?
Before we can answer your question it is helpful to know which lens you already have, and what sort of subjects you like to photograph. And a hint of available budget might help also.


Martin.

edit: of course Chris beats me by an inch, sorry
Best regards,

Martin.


Curious about my photography?? Just Follow the Light.
Last Edited by Malo1961 on 06/08/2008 - 15:57

George Lazarette

Link Posted 06/08/2008 - 19:20
Hello,

Please edit your profile to show your location - country is enough.

Presently I am assuming from your name that you are from West Nile.

G
Keywords: Charming, polite, and generally agreeable.
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