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Author Topic: Lens Diffraction Test, with Hasselblad HC lenses  (Read 14968 times)
James R Russell
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« Reply #20 on: June 06, 2009, 06:07:11 PM »
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Quote from: gwhitf
I just feel like I've learned a good lesson by doing these tests. I just never in a million years thought it would affect the golden brand, , (I mean Fuji). I thought that bad stuff like this only affected "those other guys that live across town", like Sigma, or Tamron, or the like.

(Actually, I have a Sigma 70mm 2.8 for the Canon, and it's the sharpest lens in my Canon case, so go figure).

Multiple tests so far, and the sweet spot with the 35, 50, and 80 HC are between f5.6 and f11. If resolution and absolute sharpness is the goal. At least these are my findings. Scary, scary territory past f16; only venture into those woods with extreme caution.


A friend of mine recommended the Sigma.  At first I spewed coffee and choked, thinking about actually owning a Sigma lens, but thought I'd give it a try and though I'm not somebody that pixel compares this stuff, the Sigma is the sharpest "smaller than larger sensor format" lens I own.  On the d3 and D700 it's brilliant and well built.

Kind of scary actually.

JR
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hcubell
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« Reply #21 on: June 06, 2009, 06:26:56 PM »
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Quote from: gwhitf
I just feel like I've learned a good lesson by doing these tests. I just never in a million years thought it would affect the golden brand, , (I mean Fuji). I thought that bad stuff like this only affected "those other guys that live across town", like Sigma, or Tamron, or the like.

(Actually, I have a Sigma 70mm 2.8 for the Canon, and it's the sharpest lens in my Canon case, so go figure).

Multiple tests so far, and the sweet spot with the 35, 50, and 80 HC are between f5.6 and f11. If resolution and absolute sharpness is the goal. At least these are my findings. Scary, scary territory past f16; only venture into those woods with extreme caution.

I have not personally verified it through my own tests, but no less an authority than Joe Holmes personally assured me that f/16 is  the limit and it provides excellent sharpness IF you use what he believes are the very best capture sharpening programs. He likes Raw Developer's R-L Deconvolution, Focus Magic and Smart Sharpen. Since he forgets more about this stuff in a minute than I will ever know, I follow his advice. Oh, and I am happy with the results I get with each of these programs. The one hangup with Focus Magic is that it is not a Universal Binary, so I go to CS3 if I want to use it.
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ThierryH
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« Reply #22 on: June 06, 2009, 06:44:58 PM »
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with "other parameters" was meant the reproduction scale, resp.the distance lens-sensor/film, or in other words, the shoooting distance, resp. the focal length.

That are all the parameters affecting the diffraction, with the exception of the blades' shape, which IMO has no real visible difference and can be considered as minime.

Obviously, if you are using a bottle glass in front of your camera, that doesn't matter anymore, it will be bad anyway and your IQ is already affected by the built-quality: I wouldn't say that the Digitars are badly designed lenses.

Thierry

Quote from: Jack Flesher
I think you actually answered why with the last 7 words above, "provided that all other parameters are equal;"  in most cases, all of the other parameters are not generally going to be equal...
« Last Edit: June 06, 2009, 08:21:20 PM by ThierryH » Logged

Jack Flesher
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« Reply #23 on: June 06, 2009, 07:00:14 PM »
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Quote from: ThierryH
I wouldn't say that the Digitars are badly designed lenses.

I didn't say that either, in fact I said the opposite.  What I did say was that diffraction is easier to spot sooner in lenses that are sharper.

« Last Edit: June 06, 2009, 07:01:42 PM by Jack Flesher » Logged

Ray
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« Reply #24 on: June 06, 2009, 07:41:18 PM »
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Quote from: carstenw
All lenses of equal focal length set to an equal aperture are affected equally by the laws of physics. Are you talking about the same focal lengths? The determining factor is the size of the hole, whose diameter is focal_length/aperture. View cameras generally use lenses of greater focal length and so the hole is larger, i.e. less diffraction.

I think you might be confusing DoF requirements with diffraction effects here. When using different format cameras, in order to get equal DoF on equal FoV images on equal size prints, the physical aperture sizes should be equal on the respective lenses used. This entails using different focal length lenses to achieve the same FoV, and different f stops on those lenses of different focal lengths to achieve the same DoF.

For example, an 8"x10" field camera used with 400mm lens will produce the same FoV as a 35mm format used with 50mm lens (ignoring differences in aspect ratio). In order to get the same DoF using the 8x10 format without using tilt and swing, you would need to stop down by a factor of 8. If you use F8 with the 35mm format, you would need to use F64 with the 8x10 format (50/8=400/64).

When using different FL lenses on the same format, the longer focal length, at say F16, will have a larger physical diameter and therefore should produce less diffraction effects as the light passes through the opening. However, as Thierry mentioned, the entire image is enlarged at the sensor when using the longer focal length, including the initially smaller effects of diffraction.


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ThierryH
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« Reply #25 on: June 06, 2009, 08:09:22 PM »
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I did refer to Dustback's remark about his Digitars.

However, I fully disagree with your statement about "affecting" sooner with better lenses: what is already spoiled by the glass in terms of sharpness can't be spoiled more by diffraction. In that perspective, a bad lens remains bad, a good lens gets its produced images affected, the more with f-stops becoming higher.

It has nothing to do with "earlier" or "sooner": that is misleading and leads to think that the effect is bigger on good lenses.

Thierry

Quote from: Jack Flesher
I didn't say that either, in fact I said the opposite.  What I did say was that diffraction is easier to spot sooner in lenses that are sharper.
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Jack Flesher
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« Reply #26 on: June 06, 2009, 09:09:58 PM »
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Quote from: ThierryH
I did refer to Dustback's remark about his Digitars.

However, I fully disagree with your statement about "affecting" sooner with better lenses: what is already spoiled by the glass in terms of sharpness can't be spoiled more by diffraction. In that perspective, a bad lens remains bad, a good lens gets its produced images affected, the more with f-stops becoming higher.

It has nothing to do with "earlier" or "sooner": that is misleading and leads to think that the effect is bigger on good lenses.

Thierry


 Must be a language barrier... Please re-read what I wrote.  I said, "diffraction is easier to spot sooner in lenses that are sharper."  Note that I did NOT say it is "affecting" sooner in sharper lenses, only that it is easier to *spot* sooner

PS: Just curious Thierry, what are you doing for work now?

Cheers,


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ThierryH
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« Reply #27 on: June 06, 2009, 09:20:27 PM »
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Must be!

However, my comprehension of your sentence

Quote from: Jack Flesher
... In actuality, the best lenses will show diffraction more readily than lesser lenses" ...

is that better lenses show it more, faster, whereby I have to admit that I don't understand the word "readily": the Italian translation gives "faster", the German "already", and the Spanish "easier".

Thierry

PS: I have not yet decided about my professional future, simply enjoying my time and the present.

Quote from: Jack Flesher
Must be a language barrier... Please re-read what I wrote.  I said, "diffraction is easier to spot sooner in lenses that are sharper."  Note that I did NOT say it is "affecting" sooner in sharper lenses, only that it is easier to *spot* sooner

PS: Just curious Thierry, what are you doing for work now?

Cheers,
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Jack Flesher
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« Reply #28 on: June 06, 2009, 09:52:15 PM »
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Quote from: ThierryH
I have to admit that I don't understand the word "readily": the Italian translation gives "faster", the German "already", and the Spanish "easier".

In English, the word "readily" is an adverb that means, to do without difficulty or easily. Being an adverb it is also implied as an action, hence the to do...
« Last Edit: June 06, 2009, 09:55:41 PM by Jack Flesher » Logged

ThierryH
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« Reply #29 on: June 06, 2009, 10:10:48 PM »
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Alright, in this case we do agree.

I simply wish to emphasize here the importance of the lens, not in relation with diffraction: it is the most critical element in the quality chain, hence if you wish best image quality use the best lenses.

Thierry

Quote from: Jack Flesher
In English, the word "readily" is an adverb that means, to do without difficulty or easily. Being an adverb it is also implied as an action, hence the to do...
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EricWHiss
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« Reply #30 on: June 06, 2009, 11:46:00 PM »
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Definitely there are some differences from lens to lens even considering the same mount and focal length etc. at least from my testing.   While these differences could be chalked up to aperture design and placement in the lens, my guess is the magnification factor is more important.     I think this was touched on but image circle or magnification factor are important to consider with regard to diffraction effects.  I would expect the lenses with larger image circles to be limited at higher numerical f-stop values all else considered.   I guess I could test this out with my rollei 150mm apo macro which purportely has a huge image circle against my 150mm tele-xenar both the same focal length and made by Schneider.
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carstenw
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« Reply #31 on: June 07, 2009, 02:01:15 AM »
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Quote from: Ray
I think you might be confusing DoF requirements with diffraction effects here.

No, I meant it as I wrote it. DoF is clearly a separate issue. I wasn't aware that the same size hole in lenses for different formats would result in identical depth of field. I will have to work through the math to verify that for myself.

Quote
When using different FL lenses on the same format, the longer focal length, at say F16, will have a larger physical diameter and therefore should produce less diffraction effects as the light passes through the opening. However, as Thierry mentioned, the entire image is enlarged at the sensor when using the longer focal length, including the initially smaller effects of diffraction.

Right, I was only speaking to the first sentence here. I haven't yet worked through the effect of using similar focal lengths on different systems. I was writing about using lenses designed for different uses on the same sensor. In this scenario, it doesn't matter what the size of the image circle is, or any other parameters. If the focal length is equal, the diffraction is equal at equal apertures for different lenses. That doesn't mean that the image is equally blurry though, just that the part attributable to diffraction is equal.

Diffraction is always present. It is not something that "kicks in" at larger apertures. Diffraction happens when light passes an edge. What happens at smaller aperture openings is that this part of the light passing through the lens starts to dominate the overall photo.
« Last Edit: June 07, 2009, 02:05:34 AM by carstenw » Logged

Ray
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« Reply #32 on: June 07, 2009, 10:32:10 AM »
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Quote from: Jack Flesher
In actuality, the best lenses will show diffraction more readily than lesser lenses; the sharper the lens is, the easier it is to see when and where diffraction anomalies kick in.  (As to why it's more of a problem with digital than film, I suspect it's because we can easily view our direct digital captures at 100%, where with film one would have to have a perfect scan or perfect analog enlargement first to view it, and perfect scans are difficult enough where perfect analog enlargements are rare to non-existent.)  So in this case, I would submit the Schneider Digitars (or Rodenstock HR digitals) being among the best glass available for digital sensors, will show diffraction issues more readily than even the best MF lenses, regardless of brand.

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.


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gwhitf
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« Reply #33 on: June 07, 2009, 10:41:08 AM »
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After testing, I could make a case to just have TWO fstops on a "serious" lens -- one of the fstops would be wide open, for focusing and composing, and then once you nailed that, you'd push a button, and it would stop the lens down to it's sharpest Fstop. That might be f5.6 and two thirds, or F8 and a 5/16's, or whatever each particular lens design peaked out at.

I'm putting the final touches on my own new Hasselblad firmware update today -- when you're shooting in the range of f4 - f11, the areas around the frame, in the viewfinder, flash green. But when you stop down to f16, the area in the viewfinder outside the frame begins to turn bright red, to caution you. And if you're man enough to stop down past f16, then all kinds of warning lights flash off and on in the viewfinder, to get your attention. At f32, a Smoke Machine is activated, inside the viewfinder, and the entire viewfinder fills with smoke, to purposely block your vision of the frame. With the 120 HC lens, when you go to F45, the H2 body simply detonates in your hands, to keep you from blowing the job.

I'm also filing suit against my college professor that taught me, "just shoot at f22 if you want to carry focus throughout the entire frame, for maximum depth". After that, I'm heading to Retouching University, to learn how to shoot Foreground Focus Layers, and Background Focus Layers, and then stitch them together.
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Jack Flesher
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« Reply #34 on: June 07, 2009, 11:06:46 AM »
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Quote from: gwhitf
After testing, I could make a case to just have TWO fstops on a "serious" lens -- one of the fstops would be wide open, for focusing and composing, and then once you nailed that, you'd push a button, and it would stop the lens down to it's sharpest Fstop.

Now you need to read up on another common lens design anomaly -- "focus shift."  
« Last Edit: June 07, 2009, 11:07:35 AM by Jack Flesher » Logged

Dustbak
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« Reply #35 on: June 07, 2009, 12:19:38 PM »
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Ah... such a delight for focus bracketing
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capital
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« Reply #36 on: June 07, 2009, 04:57:48 PM »
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Here's a link to an aperture study I had done of one of my large format lenses on film:

« Last Edit: April 07, 2013, 12:33:55 AM by capital » Logged
David Grover / Phase One
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« Reply #37 on: June 08, 2009, 12:38:53 AM »
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Quote from: Jack Flesher
Now you need to read up on another common lens design anomaly -- "focus shift."  

Fortunately corrected on all H cameras.


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David Grover
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David Grover / Phase One
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« Reply #38 on: June 08, 2009, 12:42:05 AM »
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Quote from: gwhitf
After testing, I could make a case to just have TWO fstops on a "serious" lens -- one of the fstops would be wide open, for focusing and composing, and then once you nailed that, you'd push a button, and it would stop the lens down to it's sharpest Fstop. That might be f5.6 and two thirds, or F8 and a 5/16's, or whatever each particular lens design peaked out at.

I'm putting the final touches on my own new Hasselblad firmware update today -- when you're shooting in the range of f4 - f11, the areas around the frame, in the viewfinder, flash green. But when you stop down to f16, the area in the viewfinder outside the frame begins to turn bright red, to caution you. And if you're man enough to stop down past f16, then all kinds of warning lights flash off and on in the viewfinder, to get your attention. At f32, a Smoke Machine is activated, inside the viewfinder, and the entire viewfinder fills with smoke, to purposely block your vision of the frame. With the 120 HC lens, when you go to F45, the H2 body simply detonates in your hands, to keep you from blowing the job.

I'm also filing suit against my college professor that taught me, "just shoot at f22 if you want to carry focus throughout the entire frame, for maximum depth". After that, I'm heading to Retouching University, to learn how to shoot Foreground Focus Layers, and Background Focus Layers, and then stitch them together.

Hi Mr T,

Further to your original post then I guess you have highlighted something that you have heard is not unknown and wasn't news to me.  Sorry to disappoint. ;-)

But anyway, the lesson is I guess to find the limits of your own gear so not caught with your pants down.

I have forwarded your firmware ideas to R&D for comment.

Best,


David


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David Grover
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« Reply #39 on: June 08, 2009, 01:41:33 AM »
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Quote from: David Grover / Hasselblad
Hi Mr T,

Further to your original post then I guess you have highlighted something that you have heard is not unknown and wasn't news to me.  Sorry to disappoint. ;-)

But anyway, the lesson is I guess to find the limits of your own gear so not caught with your pants down.

I have forwarded your firmware ideas to R&D for comment.

Best,


David


David,

In all seriousness, let's say you wanted to go Gursky and shoot a scene in times square where you pulled tight detailed 50mpx focus from front subject to background on a very large print, (think moving people that are sharp.

How would you do this with a 80mm or even a 50mm lens in digital?

B
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