Ad
Ad
Ad
Pages: « 1 2 3 [4]   Bottom of Page
Print
Author Topic: Lens Diffraction Test, with Hasselblad HC lenses  (Read 13467 times)
David Grover / Phase One
Sr. Member
****
Offline Offline

Posts: 940



WWW
« Reply #60 on: June 09, 2009, 12:52:06 AM »
ReplyReply

Quote from: Jack Flesher
Nice! Can you post an example to show us how well it works --- with say the 100 focused on something relatively close, like at about 1 to 1-1/2 meters away, wide open and f5.6 or 8?

...but how would know where I focussed?  You would have to trust me.  

Essentially, the theory is simple.  Aperture related focus shift is a known factor (if you are the lens designer) so can be corrected by a) knowing the working aperture and  knowing the focus distance.

The H1 had two zones in the focus range which related to two different corrections for focus, in the H3D there are several more for greater accuracy.

We are talking bee's dick corrections but every little helps, especially (as I keep saying) as the resolution increases on digital sensors.

Best,


David


Logged

David Grover
Business Support and Development Manager, Software.
David Grover / Phase One
Sr. Member
****
Offline Offline

Posts: 940



WWW
« Reply #61 on: June 09, 2009, 12:55:26 AM »
ReplyReply

Quote from: gwhitf
Yes, it was an issue with a 120 Macro HC last month, on a tabletop shot.

If I ever track down your email address, I'll give you the details.

In the end, with enough Smart Sharpen it was fine, but I was nervous there for a while; thought I had a defective lens.

So yes, it's been an issue.

Sounds like you need an HTS?

Logged

David Grover
Business Support and Development Manager, Software.
Jack Flesher
Sr. Member
****
Offline Offline

Posts: 2595



WWW
« Reply #62 on: June 09, 2009, 02:40:21 AM »
ReplyReply

Quote from: David Grover / Hasselblad
...but how would know where I focussed?  You would have to trust me.  

Essentially, the theory is simple.  Aperture related focus shift is a known factor (if you are the lens designer) so can be corrected by a) knowing the working aperture and  knowing the focus distance.

The H1 had two zones in the focus range which related to two different corrections for focus, in the H3D there are several more for greater accuracy.

We are talking bee's dick corrections but every little helps, especially (as I keep saying) as the resolution increases on digital sensors.

I understand the theory... What I am not so sure about is the implementation of said corrections

Oh, and I'd trust you Dave.

Cheers,
« Last Edit: June 09, 2009, 02:45:12 AM by Jack Flesher » Logged

David Grover / Phase One
Sr. Member
****
Offline Offline

Posts: 940



WWW
« Reply #63 on: June 09, 2009, 02:50:02 AM »
ReplyReply

Quote from: Jack Flesher
I understand the theory... What I am not so sure about is the implementation of said corrections

Oh, and I'd trust you Dave.

Cheers,

Next time I have a 100 in my hands ill take a wide open and an f8 and we'll see.  

Essentially the AF drive knows to + or - the setting based on working aperture set.  Same goes for Manual Focus (if you are using the focus confirmation arrows in the VF) as these light up based on the same data from the AF system.

Thanks for the trust!

D


Logged

David Grover
Business Support and Development Manager, Software.
Ray
Sr. Member
****
Offline Offline

Posts: 8812


« Reply #64 on: June 09, 2009, 05:41:36 AM »
ReplyReply

Quote from: gwhitf
But in general, my advice is to NEVER shoot an HC lens any smaller than f11. Even f16 shows noticeable softness, and 22 is a joke, and let's not even talk about 32 or 45.

I guess now we know why Michael did not use F22 when doing a quick comparison of the Canon G10 P&S and the P45+. The results might have enraged you all.

He used the P45+ at F11 and the G10 at F3.5. On A3+ size prints, both images looked virtually indistinguishable, except for the shallower DoF of the P45+, which sort of gave the game away.

I've always been a bit suspicious of the resolution of 8"x10" film when using F64, which gets you approximately the same DoF as 35mm at F8. I think it's understood that you cannot get tack sharp images at F64, even with Large Format. But what you do get with such a large format is better tonality, smoother gradations and far less grain. These qualities are sometimes more important than the ultimate in resolution.

It's also a fact that, whilst at F64 the plane of focus will not be as sharp as it would be at F22, the parts furthest away from the plane of focus will be far sharper at F64 than they are at F22.

In fact, the difference in sharpeness at the plane of focus, between F22 and F64, will be far less than the difference in sharpness away from the plane of focus, depending on the depth of the scene of course.
Logged
ThierryH
Sr. Member
****
Offline Offline

Posts: 409


« Reply #65 on: June 09, 2009, 07:41:51 AM »
ReplyReply

Hi Ray,

You forget one important factor concerning lenses used for large format film: they have been built and optzimized for an optimal f-stop around 22. In fact, they give no noticeable difference (according to MTF curves) between f16 and f45, most of them. That is when used at infinity, on 4x5". Using a larger format, e.g. 8x10", an aperture of f64 is still within the limit (under) of the critical aperture where diffraction "circles" starts to be bigger than the allowed confusion circles and affecting the overall sharpness, at infinity. For sure, f64 is not in the optimal reproduction range of large format lenses, as you have said, but not that much of a problem when DoF is needed and not reachable with a plane adjustment.

Best regards,
Thierry

Quote from: Ray
I've always been a bit suspicious of the resolution of 8"x10" film when using F64, which gets you approximately the same DoF as 35mm at F8. I think it's understood that you cannot get tack sharp images at F64, even with Large Format. But what you do get with such a large format is better tonality, smoother gradations and far less grain. These qualities are sometimes more important than the ultimate in resolution.

It's also a fact that, whilst at F64 the plane of focus will not be as sharp as it would be at F22, the parts furthest away from the plane of focus will be far sharper at F64 than they are at F22.
« Last Edit: June 09, 2009, 07:42:41 AM by ThierryH » Logged

gwhitf
Sr. Member
****
Offline Offline

Posts: 811


« Reply #66 on: June 09, 2009, 08:42:13 AM »
ReplyReply

Quote from: David Grover / Hasselblad
Sounds like you need an HTS?

Mr G,

Can you confirm whether the HTS works with an H2/P45+ with the 35mm HC lens, even if some of the Pheatures were disabled?

Will it physically work, and take a photograph with an enemy back and a body that's been disowned?

Thanks.
« Last Edit: June 09, 2009, 08:50:57 AM by gwhitf » Logged
PeterA
Full Member
***
Offline Offline

Posts: 123


« Reply #67 on: June 09, 2009, 08:52:28 AM »
ReplyReply

tis a fine balance - selling lenses and HTs's that work with competing backs on discontinued body strategy  - I wonder at the economics of it all..given the stats on known sales and projected sales both segmented by camera in use type  I could optimise your close out "the free loading competition totally" timing for you David. At a guess i'd suggest oh maybe another 18 months...
Logged
tho_mas
Sr. Member
****
Offline Offline

Posts: 1692


« Reply #68 on: June 09, 2009, 08:58:08 AM »
ReplyReply

Quote from: gwhitf
You stop down, thinking you're going to carry focus deeper into the frame, when in truth, it's like you're laying a Gaussian Blur layer over the entire photograph. Even the subject area that you wanted tack sharp.
If focus stacking is too complicated due to the conditions but you have the time to shoot at least two shots you can shoot the first shot at f8 to get your main subject very sharp and a second shot at f16 for more DOF and merge the two shots in Photoshop.
So you take the f16 shot and add in the sweet spot of the f8 shot. That works very well and might be a good compromise in some situations.
Logged
gwhitf
Sr. Member
****
Offline Offline

Posts: 811


« Reply #69 on: June 09, 2009, 09:13:13 AM »
ReplyReply

Quote from: PeterA
tis a fine balance - selling lenses and HTs's that work with competing backs on discontinued body strategy  - I wonder at the economics of it all..given the stats on known sales and projected sales both segmented by camera in use type  I could optimise your close out "the free loading competition totally" timing for you David. At a guess i'd suggest oh maybe another 18 months...

I agree with you. You can feel the battle lines being drawn -- and the only two armies will be Hasselblad and Phocus, marching face to face toward the PhaseOne/CaptureOne army, (with PFC Gomer Pyle Mamiya bringing up the rear). You can feel the showdown about to happen soon.

If I was a betting man, (and a working photographer), I'm putting my money on Hasselblad, long-term. They continue to refine, tweak, and add new features almost every few months, that apply to working photographers.

At some point, a man's gotta choose, and you can feel the two camps splitting more and more every day. I'm stuck right in the middle, with this mutant camera/back. I feel like I'm the child of Divorced Parents, and Mommy ain't talking to Daddy. I gotta go to Big Brother David or Big Brother Dougie to get any answers about the family.
« Last Edit: June 09, 2009, 09:24:45 AM by gwhitf » Logged
Ray
Sr. Member
****
Offline Offline

Posts: 8812


« Reply #70 on: June 09, 2009, 09:16:52 AM »
ReplyReply

Quote from: ThierryH
You forget one important factor concerning lenses used for large format film: they have been built and optzimized for an optimal f-stop around 22. In fact, they give no noticeable difference (according to MTF curves) between f16 and f45, most of them. Thierry

Thierry,
That sounds a bit odd to me. I cannot understand why a lens would have the same performance at F16 as at F45, unless it was a really lousy lens with lots of aberrations which were so bad that there's no difference between F16 and F45. In other words, at F16, all the other aberrations are greater than the diffraction effects. At F45, diffraction is greater than all the other aberrations.

Add the total aberrations, including diffraction, at F16 and at F45, then the sum is the same. You must be referring to some very old lens designs. No?

There are a few 35mm format zoom lenses which are sharpest at F16, usually at the long end. When a 35m lens is sharpest at F16, it's a sure indication it's a low quality lens.
Logged
Dick Roadnight
Sr. Member
****
Offline Offline

Posts: 1730


« Reply #71 on: June 09, 2009, 09:51:17 AM »
ReplyReply

Quote from: stewarthemley
Dick, Port Izzac (sp?) looks as interesting as ever. Taken from the Doc's house?
Yes -  Port Isaac, 20 or 30 meters below the Doc's House... and there are dozens of equally photogenic harbours, estuaries, bays etc. around the British coastline...

The pic is a compromise with:
 
not a short enough exposure to stop movement of waves, people and vehicles
not a small enough aperture for sufficient DOF
not a large enough aperture to eliminate diffraction
Logged

Hasselblad H4, Sinar P3 monorail view camera, Schneider Apo-digitar lenses
Nick_T
Jr. Member
**
Offline Offline

Posts: 88


« Reply #72 on: June 09, 2009, 02:41:38 PM »
ReplyReply

Quote from: gwhitf
Mr G,

Can you confirm whether the HTS works with an H2/P45+ with the 35mm HC lens, even if some of the Pheatures were disabled?

Will it physically work, and take a photograph with an enemy back and a body that's been disowned?

Thanks.

Yes George it will work. Obviously you won't get the distortion corrections and you'll have two carry two battery chargers for life but at least you won't have to learn Phocus
Nick-T
Logged

gwhitf
Sr. Member
****
Offline Offline

Posts: 811


« Reply #73 on: June 09, 2009, 03:34:35 PM »
ReplyReply

Quote from: Nick_T
Yes George it will work. Obviously you won't get the distortion corrections and you'll have two carry two battery chargers for life but at least you won't have to learn Phocus
Nick-T

Ouch. Below the belt.

Leaving for the desert next Wednesday. Will have to hire an extra Sherpa just to carry the required battery chargers for my broken-marriage system...
Logged
David Grover / Phase One
Sr. Member
****
Offline Offline

Posts: 940



WWW
« Reply #74 on: June 09, 2009, 03:35:55 PM »
ReplyReply

Quote from: gwhitf
Mr G,

Can you confirm whether the HTS works with an H2/P45+ with the 35mm HC lens, even if some of the Pheatures were disabled?

Will it physically work, and take a photograph with an enemy back and a body that's been disowned?

Thanks.

Yes it will work.  You will need your H2 on the latest firmware mind.  So send to NJ for update or find a friend with an ixpress or CF back and they can do it through Phocus.

David

Edit Ps.  Oh didn't see Nick's reply. Thanks... and yes TWO chargers.  Tsk tsk.
« Last Edit: June 09, 2009, 03:37:52 PM by David Grover / Hasselblad » Logged

David Grover
Business Support and Development Manager, Software.
stevesanacore
Full Member
***
Offline Offline

Posts: 214


« Reply #75 on: June 14, 2009, 12:49:38 PM »
ReplyReply

Quote from: Ray
I have to agree with Jack Flesher here.

Diffraction is a constant that varies only with aperture diameter. It exists to some degree at all apertures, in proportion to physical aperture diameter. It exists at F2.8, but is so small that it's irrelevant compared with diffraction effects at F16 which begin to rear their head.

Diffraction is something we can do little about. Its effects are proportional to F stop.

If a lens is sharpest at F5.6, it's because all the other lens distortions types have been reduced below the diffraction limit  that applies to the aperture. (Is that clear, or is it gobbledegook?)

If a lens is sharpest at F16, (and some 35mm zooms are), it's because all the aberrations other than diffration, coma and astigmatism etc, are so lousy, that the lens is lousy.

Diffraction effects are completely embedded in the laws of Physics. But at F2.8 they're so small as to be insignificant.
At F16, resolution is limited by diffraction. One could say, all lenses are equal at F16, no matter how hard the lens designers work.

This is exactly why I use Leica glass on my Canon's - at f5.6 my Leica's are razor sharp from edge to edge at infinity. Past f11 (where my Canon zooms need to be), most 35mm glass gets diffraction softening.  I would assume this applies to most new MF glass also because of the sensor quality. I just can't imagine software sharpening will make up for poor sharpness from the optics, but I guess it helps a bit.

There is no substitute for knowing what you are doing and using the appropriate f stop for ultimate image quality for each photograph.





Logged

We don't know what we don't know.
Pages: « 1 2 3 [4]   Top of Page
Print
Jump to:  

Ad
Ad
Ad