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Ivan J. Eberle
15-May-2009, 06:56
Assuming all else to be equal (focal length, grinding and polishing accuracy, glass formulation, collimation/manufacturing tolerances), would a lens that is optimized for a larger image circle than 4x5 inherently have lower resolution than one optimized for the format?

ic-racer
15-May-2009, 07:05
Light passing through the center is not bent as much by the glass, therefore, can retain resolution. Thats my thought based on empiric data.

Arne Croell
15-May-2009, 07:08
Does "all else" include the price/manufacturing cost?

Gem Singer
15-May-2009, 07:55
I'm not an optical engineer, but this is what I have discovered. A lens with huge coverage ability is not less sharp when used with a smaller format.

In fact, it seems to be sharper when used with the smaller format, since it is only using the center section of the image circle.

For example, I have a Nikkor f8 120SW and a Nikkor f9 300M. both lenses have image circles and will cover 8X10. When used for the 4X5 format, they are extremely sharp.

Emmanuel BIGLER
15-May-2009, 08:18
would a lens that is optimized for a larger image circle than 4x5 inherently have lower resolution than one optimized for the format?

It is very difficult to give a clear answer to the question because it depends how you compare the final results.

The first answer that comes to mind would be to say : yes if you compare the same lens design, same glass, same manufacturer, larger lenses for larger formats have lesser resolution than shorter lenses for smaller formats, with the same angular coverage.
The reason is that the residual geometrical aberrations scale exactly like the size of the lens elements.
However, diffraction effects do not scale like this since the wavelength of light is the same for all lenses. So for short focal lengths used on small image detectors in order to avoid diffraction you cannot stop down as much as you can do in large format.
So this makes the comparison difficult between lenses of similar design but optimised for different detector sizes since the best f-stop is not the same for different focal lengths.

For top-class lenses operating close to the diffraction limits, the best f-stop number N, for a given family of designs like the 6-element standard view camera lenses, actually follows an empirical law that you can derive by compiling the best f-stop recommended by manufacturers for the same design offered on catalogue in different focal lengths.
For older 6-element standard lenses we have N_best approx equal to the focal length in mm divided by 8 mm : N_best is betwwen 16 and 22 for a classical 150 mm standrda LF lens.
For top-class recent lenses like the apo-sironar-S, the apo-symmar L and "digital" lenses covering approximately the same angle (70-75) N_best would be something like the focal length in mm divided by 11 mm, yielding something between 11 and 16 for the best 150 mm available today, something between 5.6 and 8 for the best 75mm lenses, a range of best f-numbers actually corresponding to old planar/xenotar designs in medium format for decades, and not far from what modern digital view camera lenses demand in order to keep the image with as little diffraction effects as possible.

If we use the various lenses for various formats at the best f-stop and consider that in this situation the actual resolution limit combining aberration and diffraction is something like 1.4 times the size of the diffraction effect alone, we get a simple scaling law, the minimum detectable spot size scales like the focal length also.

As you see the question of using with the same image format various lenses of same focal lengths but various angles of coverage is not an easy one. Arne is right to mention price and manufacturing costs. If we do take into account only a reasonable cost for the lenses in use, I would expect a standard 150mm lens covering 70-75 on the 4x5" format to perform better in this angle that the central portion of a 150mm/110 ultra-wide angle lens covering the 8x10" format.

But in practice there are some good surprises and I agree totally with Gem Singer.
I use regularly a 75 mm Grandagon-N lens, 6 elements, covering 102. The image quality delivered by this lens stopped down to f/11 is superb, on the central portion of a 6x9 image or rollfilm is by no way poorer than what I am used to see with a Rollei or a Hasselblad MF camera fitted with a standard 75 or a 80 stopped down to f/11...
But the full aperture of the wide-angle grandagon is only 6.8, while planars or xenotars for 6x6 (5 or 6 elements) offer 3.5 or 2.8. The optimisation was different.

Dan Fromm
15-May-2009, 10:04
I'm not an optical engineer, but this is what I have discovered. A lens with huge coverage ability is not less sharp when used with a smaller format.

In fact, it seems to be sharper when used with the smaller format, since it is only using the center section of the image circle.

For example, I have a Nikkor f8 120SW and a Nikkor f9 300M. both lenses have image circles and will cover 8X10. When used for the 4X5 format, they are extremely sharp.Apples to oranges because they're different designs.

That said, I shoot a number of lenses made for larger formats on 2x3 and in practice all of the better ones shoot about equally well.

Its fun to theorize about how wonderful a lens can be, but the emulsions I use aren't better than my lenses and my technique is often less than perfect. I doubt that many of us routinely get the best our lenses can give. So discussions like this one have an air of, um, unreality, bring the mythical debate about the number of angels that can dance on the head of pin to mind.

FWIW, I just shot a 4"/2.0 TTH Anastigmat, ex-F95, against a 100/2.5 Uran-27, ex-RA39, and a 105/5.6 Zircon (6/4 plasmat type). At apertures larger than f/5.6 the TTH won, from f/5.6 down the Zircon was no worse than the better of the other two. The Uran-27 isn't horrible, but the other two are better.

So what? I mean, if I'm going to be shooting in the range f/11 - f/22, the Zircon is the clear winner; its no worse that the others at those apertures, is much lighter than either, and stops to f/22 while the aerial camera lenses go only to f/16.

I can imagine situations in which the TTH would be the lens of choice, and it is certainly better pour epater les bourgeois than the Zircon. The Uran-27 is even more outrageous and is usable. But as a practical matter I'd hardly ever use either in place of the Zircon.

Cheers,

Dan

Emmanuel, please don't remind me that I'm an ignorant barbarian. I'm a birthright barbarian and every day the whole world shows me how little I know.

Gem Singer
15-May-2009, 10:56
Dan,

I stated openly that i am not an optical engineer.

I was attempting to answer the OP's question based on my sixty-three years of experience with many different lenses.

BTW, those lenses that you mentioned must be before my time. I have never heard of them.

Dan Fromm
15-May-2009, 11:49
Gem, they're all post-WWII. The aerial camera lenses were designed in the 1950s, the Zircon some time after 1972. You've been around longer than they have. Of the three, only the Zircon is a conventional LF camera lens.

The TTH is discussed in the VM; these days they bring silly money on eBay. The Uran-27 is very little known; a cross-section is shown in the 1963 GOI catalog. Boyer lenses are also poorly known even in their native France. Boyer had a US distributor, Rolyn Optics, when Boyer closed in 1982; several years ago Rolyn had new old stock Zircons.

You're ok, Gem, but I should have been clearer that I think the OP's original question is, um, misguided.

Cheers,

Dan

Ivan J. Eberle
15-May-2009, 12:39
I sincerely don't appreciated your "misguided" remarks, nor the flaming, not one bit, sir. If you don't like the question, Dan Fromm, move along.

I'm using LF versus MF primarily for greater resolving power in order to make larger prints for the galleries I'm represented in. Already have MF gear capable of 80 lp/mm resolution. I've been using smaller formats for over 30 years (20 professionally) and have been achieving film-limited resolution using excellent technique. So naturally I approach LF expecting superior results, not just looking for enough overhead in a 16x20 that I can afford to be sloppy.

But back to the reason for asking the original question. I have a Meridian 45B technical field camera with back moves (swing and tilt only) Back moves allow using a lens of smaller coverage, unlike front standard moves for tilt and swing, at least. Frankly, I'm non-plussed about the resolution I'm achieving with a 210mm APO Plasmat with huge coverage (Caltar IIN f/5.6, AKA Rodenstock APO Sironar N with 301mm image circle or thereabouts). Reasonably happy with my Nikkor 90mm SW, however.
If it's a matter of simple physics, I soon may be looking for a modern 150-210mm lens with similar apochromatic design but less coverage.

venchka
15-May-2009, 13:31
I know just enough about all of this to get in trouble.

If the only criteria you are using is lp/mm, large format lenses will rarely equal the better medium format lenses.

Your 80 lp/mm figure for your medium format lenses is at the beginning of the upper range for the best lenses. The best large format lenses will top out at or below 80 lp/mm.

Folks don't go to the trouble of using large format equipment just for lp/mm.

You are correct in using the "sweet spot" in the center of a huge image circle to obtain higher lp/mm over the area you are using.

Large Format Lens Tests (http://www.hevanet.com/cperez/testing.html)

Medium Format Lens Test (http://www.hevanet.com/cperez/MF_testing.html)

Enjoy!

Dan Fromm
15-May-2009, 14:06
I sincerely don't appreciated your "misguided" remarks, nor the flaming, not one bit, sir. If you don't like the question, Dan Fromm, move along. Ivan, please reread Dr. Bigler's thoughtful response carefully. Then read his short biography on this site, it is located at http://www.largeformatphotography.info/users-directory/people/ebigler.html . Then visit www.dioptrique.info and compare Eric's results for lenses within the same design family; his calculations, one set per prescription, make it clear that not all lenses in the same family, let alone all lenses covered by a single patent, are equal. Also please see http://www.hevanet.com/cperez/testing.html; their resolution measurements are somewhat startling. Then look in your soul and ask yourself whether touchiness is appropriate.

I'm sorry that y'r 210/5.6 Caltar IIN doesn't meet your requirements. If it isn't clear, I also have some lenses that aren't quite good enough. Many, many rejected macro lenses ...

Since not all lenses in the same design family are equal and since, alas, not all lenses of the same make and model are identical either, the best thing for you to do is stop theorizing and start being more empirical. Beg, borrow, rent, or buy some likely lenses and ask each one if it is good enough for you. After you've settled on one, get rid of the others.

Now do you understand why I think your question is misguided? No answer to it will get you a lens that you can be sure will meet your needs. No matter which lens you acquire, it will have to go through acceptance testing. Why not start there?

Good luck, have fun,

Dan

Paul Kierstead
15-May-2009, 14:13
So naturally I approach LF expecting superior results, not just looking for enough overhead in a 16x20 that I can afford to be sloppy.


Finding technically-competent very large prints done from LF is quite easy. I am sure you have come across a few in your lifetime.

Go look at a few carefully. It will answer you question regarding superior results conclusively/

bglick
15-May-2009, 14:48
Hope I am not jumping into a hornets nest!

The OP question is a fair one.... At best, this question can only be answered in general terms, otherwise a book can be written on all the qualifiers...

Without getting too technical..... I will revise the OP's question to make the fair comparison I think he is after. Where he mentioned same fl, I will change this to.... same composure on the larger format. It's only fair to compare a 75mm MF lens, to a 150mm 45 lens and a 150mm 810 lens.... now they all have the same angle of coverage on both sides of the lens. This was mentioned by others. This is a HUGE variable in sharpness potential. The wider the angle, the harder it becomes to control aberations.

With those caveats, the answer is YES. Larger Image circle lenses will resolve less in a given area of the film....with the rare exception of the very center of the image, and even then, only at times. However, the larger format has more image area, so it wins. how much does it win by? That depends on the next big caveat.... DOF!!

If you must match DOF, you, must continually stop down the larger format lens, 2 stops per format jump (per same composure). And this is the Achilles heel of larger formats. OTOH, if you are shooting infinity, or flat subjects with no significant DOF, now the larger image format lens can really shine. Several years ago I prepared a generalized comparison that demonstrated this..... I never bothered to update it with the new digital formats, but you can follow the 6x7 / 4x5 / 810 formats, both infinity based, and DOF based to get a feel for the net resolution benefit at the same final print size.

The bar group to the far right, show the lenses shot at optimum f stops focused at infinity, using modern lens designs of course. Each format jump is VERY significant, not quite 2x, but close.

The first 4 groups of bars shows different f stop relations between the formats for same DOF.... the 4th set, shows typical landscape DOF requirements..... (f32 for 4x5) as you can see, each format increase does not significantly add resolution.


http://www.pbase.com/bglick/image/50899836/large

So when comparing the potential of "recorded resolution" for different lenses, for different formats, the actual "application" the lens will be used for, will significantly effect its potential benefits....

Also, this represents recorded resolution on film, not aerial resolution of the lens. Aerial resolution by itself is not that significant for photographers. Its the combining of the lens aerial resolution with the films MTF via 1/R equation that provides the max. possible recorded resolutions. Film type is significant as well, as some films resolve much greater than others.... in the chart I provided, it assumes color chrome film using common contrast ratio subjects.


OTOH, Chris Perez tests demonstrate what a lens can resolve using B&W targets (ultra high contrast), with B&W high resolving film, in studio conditions. Very unrealistic for real world shooting, but nonetheless, his results make for excellent apples to apples comparison between lenses. (of course there is variances in samples) But don't think you can use color neg film in landscape settings and resolve these kinds of values.... the fall-off is dramatic. Often half or more...


please keep machine gun fire down to short bursts.....
(running for digital cover)


...

Dan Fromm
15-May-2009, 15:30
Bill, in the end the OP is going to have to commit himself and acquire a lens. What's the point of agonizing over which lens to get first when whatever he buys will have to pass acceptance testing? Just get a lens, test it, and if necessary repeat until one that's good enough is found.

He hasn't told us how large he wants to print, what the viewing distance will be, how he'll enforce the viewing distance, ... And he hasn't explained why sharpness is so important.

I make this last point because, although I'm a somewhat obsessive lens tester, the Ektachromes that I have printed are selected for more than just sharpness. In fact, I have a few fairly soft prints on my wall that please in spite of being much less sharp than ought to be possible.

You of all people should know that calculating and reasoning and spinning theories, perhaps trying to extract moonbeams from cucumbers, is much more fun than actually doing. I think, though, that you're learned that doing gets better answers unless the point of the theorizing is to determine what can't be done.

Do you remember H. Lou Gibsons absolutely terrifying book Photomacrography? Its one gigantic limitative theorem, with photographs to demonstrate that the theory works.

Cheers,

Dan

bglick
15-May-2009, 15:44
> Bill, in the end the OP is going to have to commit himself and acquire a lens. What's the point of agonizing over which lens to get first when whatever he buys will have to pass acceptance testing?


I interpreted the OP question as a general question about how larger image circle lenses effect resolution vs. smaller image circle lenses. Often people don't want to buy gear, or even test gear, till they have a better understanding of the effect such gear will have on their final product.... Then after that threshold is met, you more into the more nitty gritty issues you suggest...




> I have a few fairly soft prints on my wall that please in spite of being much less sharp than ought to be possible.


Agreed, resolution is relative... so many variables from capture to final print.... but for some, this is part of the art form they enjoy pursuing. Yep, I am guilty of this myself... for others, its all about composition, they don't care much for how technical the final print is.... this is why photography is a great mix of art n science, it attracts all types.




> I think, though, that you're learned that doing gets better answers unless the point of the theorizing is to determine what can't be done.


Theorizing, if you understand the fundamentals of what you theorizing about, will get you 80% there.... I consider it a form of orientation, to know what direction is best to pursue for further testing. I constantly battle between format sizes, shutter speeds, resolution issues, etc. Of course, all based on final image size, working backwards from there...


> Do you remember H. Lou Gibsons absolutely terrifying book Photomacrography? Its one gigantic limitative theorem, with photographs to demonstrate that the theory works.


Sounds interesting, never read it.... I will look for it...

Wimpler
16-May-2009, 00:15
While the answers so far have illustrated users experience, I, as I think the original poster, are more interested by more fundamental physical evidence.

Two things I can think of:

1. If you have two identical lenses, one you wish to use on large format, one on small format. In the small format lens you could get away with more baffling. Some elements can be made smaller. If this is not done, internal reflections (in the lens or in the camera) will degrade the image (lower contrast, flare, ghost images).

2. Again take 2 identical lenses. To control the abberations (spherical, curvature of field, ...) for large format you DO NOT want optimal correction in the middle. You want it somewhere halfway so that the middle and the corners of the image will be acceptably sharp. Now if you want to use the lens for small format, you would want the optimal correction much closer to the center of the image circle.

These two considerations make me believe that small format lenses will perform better on small format then large format lenses will. Not only will the image quality be better, cost and weight can be saved.

Mark Sawyer
16-May-2009, 02:04
Might as well throw my thoughts in too...

Any good modern lens should be very sharp, especially in the center. Very good resolution isn't that hard for good modern designers. And agreed that within design families, there is often significant variation from lens to lens, sometimes even from example to example of the same manufacturer.

Going for that last little bit of resolution can be easily overshadowed by other variables like diffraction, the "wrong" f/stop, a cheap filter, very minor camera shake, bad processing, imperfect enlarger alignment, an enlarger lens that doesn't live up to the taking lens, and a zillion other things. It's more a theoretical, even philosophical exercise. But if we must, and yes, we must... :D

The big change in going to a wider coverage lens is going to a different design family. Examples: The widest coverage is a Hypergon design, and it's never going to rate as a "super-sharp" lens. Those two thin, very spherical lenses just won't do it.

A Dagor is a wide coverage lens, and it can be very sharp but (in theoretical absolutes) it's not as sharp as a plasmat. The plasmat is a dagor lens modified by separating two of the cemented surfaces, so the designer has two more surfaces to play with, two more levels of design freedom. But the plasmat has a little less coverage...

Go to an Artar, and you lose even more coverage, but you have a design with potential to be even more sharp, which is why some people love Artars...

But in practice, a lot of very demanding photographers are very happy with the sharpness of those Dagors, and even the "not-so-sharp" Hypergon will be sharper than even good eyes will resolve in a contact print.

If you want the absolute sharpest lens possible without regard to coverage, that design is, believe it or not... a Petzval! Which is why high-end refracting telescopes are still Petzval designs. But that sort of "sharpness without regard for coverage" is impractical in a large format lens, which is why no one makes lf petzval lenses anymore, and the old ones are prized for how they fall apart outside the sharp center...

Emmanuel BIGLER
16-May-2009, 02:25
At this point of the discussion I realize that we did not mention the image detector itself.
20 years ago, all photographers used film and the rule was simple : the same grain and film resolution is offered by film manufacturers whatever the size of film might be (all films being actually cut to any final size from huge rolls), hence, the larger film size was, the lesser you had to enlarge and the better the final image was.
But film performance increased continuously in the XX-st century, and 35mm and MF camera & lens manufacturers never stopped to claim that due to improved film resolution, grain & sensitivity, there was no need for larger format cameras (35mm aficionados laughed at old timers using the rolleiflex TLR and Hasseblad aficionados claimed that they performed better than old timers with their view cameras), except in some specific "niche" situations like architecteure or advertising with wide-angle lenses or for artistic purposes e.g. platinum palladium or other technique based on contact prints. Or any reason that we are discussing here : the number of posts on this forum proves that there are many, many reasons to continue to use the large format camera !

But now that digital imaging has become the main stream in commercial photography, we are forced to re-consider the old (lens + film) approach since new silicon detectors outperform film in terms of noise and photon detection efficiency. Not in terms of resolution since we do trust the tests made by Chris Perez and Kerry Thalmann. OK for 100 lp/mm but which is the signal to noise ratio @100lp/mm in the film image recorded on T-max behind a top-class 80 mm lens designed for MF ?
But we are forced to re-consider what a good image is; we were used to film grain after decades of living with it, we were not used to grainless digital images. Hence the questions of final image resolution have to be re-visited, I would say : painfully revisited for those who have to admit that silicon has won the battle.

A real example of the real world.
I know a French professional photographer who used to work for demanding clients in architecture shots including interiors (advertising shots for furniture and kitchen equipement for example).
Due to the very special job he was doing for very special clients, he continued to work with large format slides in 4x5" and above until he realized that his annual expenses in film and lab services could be balanced with the investment in a medium format silicon sensor. So he made the jump and he will not go back. For the same demanding clients now he shoots with a medium format specialized view camera, the very best "digital" lenses from a famous German manufacturer and a 39x47 mm digital back from a very famous silicon foundry.

So if we want to make the comparison complete, we should take into account the new player in the game : silicon sensors.
And a top-class "digital" view camera lens lens coupled with a top-class medium format sensor will clearly outperform the classical (LF lens + F slide) combo, at least when the client demands a digital file and not only a large format print that could be made with a top-class colour negative traditionally enlarged on colour paper witha top-class lens. The fact that we have to scan the slide in order to deliver the file to the client is an important point. Any amateur here, familiar with excellent B&W images enlarged optically at home, who has been disappointed by scans delivered by his amateur-grade flatbed scanner knows what I mean.

And the debate, eventually, is not only a question of pure lens resolution, my understanding is that if you consider only the optical resolution, the total number of resolved points in the image delivered by a medium format "digital" lens or a top-class "film" lens covering a larger format has no reason to be very different when both lenses are used at the optimum f-stop.

My feeling is that the total number of points that can be recorded behind a top-class lens of a given angular coverage is the same for all formats provided that the lens is top-class and used at the best f-stop. The reasons being in the practical best f-stop values that we can read from manufacturers data-sheet.

I would be interested to see a side-by side comparison for top-class image of paintings between a "film" lens & LF camera fitted with a 4x5" scanning back and MF "digital" lens+technical view camera combo.
In this case of taking the best possible image of a flat object, depth of field questions are not the main problem.
But doing so we would play with the same kind of silicon-based image detector.
Very probably we could discover that older large format lenses were not totally corrected from lateral chromatic aberration, a defect which seems to be enhanced by RGB Bayer patters for which old timers of the coulour film era did not care. No idea whether thos defects show up in scanning backs : probably some of our readers know about that.

I would really be interested to see the comparison between, say, an apo-sironar-S, 150mm focal length coupled with a modern scaning back for 4x5" and the recent 70mm "digital" lens (from the same manufacturer as the apo-sironar-S) coupled with a recent 645 silicon sensor.

My conjecture is that : used at the best f-stop, I do not see any reason why one or the other system could outperform the other.
Simply because, as Arne Croell mentions speaking about price, we are in the same league in terms of application aimed at photographers and not in the military optics game !

Ken Lee
16-May-2009, 05:19
"Several years ago I prepared a generalized comparison that demonstrated this... http://www.pbase.com/bglick/image/50899836/large "

I find that chart very interesting !

If we double the size of the print - to a 16 inch vertical print - do the numbers go down by a factor of 4 ?

If we were to add a horizontal line, above which is "acceptable" resolution, and below which would be "unacceptable" resolution... where would that line be ?

Thanks !

bglick
16-May-2009, 11:40
> If we double the size of the print - to a 16 inch vertical print - do the numbers go down by a factor of 4 ?


no, if you double the print height, you cut the resolution in half, not 4.




> If we were to add a horizontal line, above which is "acceptable" resolution, and below which would be "unacceptable" resolution... where would that line be ?



That all depends.... what do you find acceptable? What is max. resolution your printing media will hold? What is the view distance of the final print (major factor) This is where the level of variables starts to creep in, and everyone must evaluate on their own.


As a general rule, recording 5 lp/mm to a print is considered tack sharp, even under ultra close inspection. With normal view distances, where user stands at a distance equal to the print diag. measurement, you can easily shoot for 1/2 the resolution, or 2.5 lp/mm to print. Remember, as you double your view distance, you double the retinal resolution.


Emmanuel, your points are well taken..... I will toss one zinger at ya..... the more pixel dense a sensor becomes, the great resolution potential (assuming you stay below the noise threshold). However, to exploit that resolution capacity, better lenses are required.... which must be shot at lower f stops (lower than the format jump suggests) Herein is where the balancing act starts.... if you need DOF, you can't be so selective about the f stop you use, now the lens becomes the limiting factor again.

As it relates to this discussion, their is 3 kinds of photography.

1) Shallow DOF photography requiring fast ss.

2) Shallow DOF photography where slower ss are acceptable

3) Deep DOF photography.

For shallow work... portaits, wildlife, where fast shutter speeds are required, digital beats the pants off film (assuming the best FAST lenses re in use for that given format).

For shallow DOF photography where slow shutter speeds are acceptable, LF beats "most" digital. AT the high end, a 4x5 or 5x7 format can at least match the best of MF digital, at a lot less cost. 810 will still exceed it, and blow it away if using high resolving B&W film. (this rambling uses color capture as the default)

For extreme DOF photography (landscapes)..... LF is still the cats meow... but if you have the $$, MF digital is an equal contender with 60 MP backs...That is what my chart demonstrates, which IMO, most people miss when making the comparison.....i.e., there is NO ONE comparison, it is application based.

But now, if scene is cooperative enough, (static) and you can take multi captures and stitch in PS, this changes all the rules. DSLR is KING, it wins in every category, resolution, convenience, fast shutter speeds, size and weight of total package, etc. etc. CS4 has taken this to a new level. IMO, LF will be threatened more by this, than MF digital... The limitation is, you must be selective in the scenes you shoot.... I have shot some waterfalls, with the center of the image being the waterfall, one snap, then shoot all around the waterfall where everything is static.... Stitch it, and BINGO.... sometimes you need a little imagination.... our options today are nearly endless.... unfortunately, all the new break throughs keep chipping away at film based photography.

Ken Lee
16-May-2009, 12:16
"CS4 has taken this to a new level".

So far, I have avoided upgrading from CS3. To what new or improved feature do you refer ?

bglick
17-May-2009, 00:24
> To what new or improved feature do you refer ?

The reference was about stitching....

Bernard Kaye
17-May-2009, 16:47
Leica's 135mm. f 4.5 Hektor produced excellent B & W and good but cold color. They came out with 135mm. f 4 Elmar which produced fine B & W and brilliant color; word was that it was a 4 x 5inch lens, that we were shooting 35mm. down the center, whatever, photographers admired it for both B & W & color though it was long like the previous lens, the Hektor. So Leica produced a shorter f 4, 135mm. that was very expensive and according to Leica, far better than the Elmar. But, and I am not sure of why, photographers never took to it; perhaps the Leica guys know why. When in California, I used the Elmar for color, found it superb; when on the Rhine, I used the more modern and more expensive more modern lens; it was good but perhaps I am not able to see an improvement that is there.
Bernie

Lynn Jones
20-May-2009, 13:23
Hi Ivan,

In my several decades of photo/optical experience, there has been a "rule of thumb" that focal length for focal length, the wider the angle of view the lower the contrast, the narrower the angle of view, the higher the contrast.

I have accepted that for my uses since the people stating this had degrees in optics or optical physics and my poor lonely little BA is in photography/cinematography.

Lynn

bglick
25-May-2009, 11:18
Lynn, as a general rule, I agree...however, technology keeps advancing, and as with some rules, there is always some exceptions....

Contrast is the one of the strong benchmarks of recorded IQ, but its not the only benchmark. Edge sharpness also comes into play..... but this is not so easily defined as MTF, which is the % of a targets contrast which a given lens projects. The greater the resolution in the target, a lower % of contrast which can be transfered. This entire generality is effected by image circle projection size. The larger the image circle, the less contrast.

Getting back on track.... lens designs / glass types / toerancing, etc. keep improving as optical software is removing much of the labor involved in such. As a result, there is some very impressive lens designs with wide angles. A few that come to mind are the Mamiya 7 43mm for MF and the SSXL 110 and 150.

When a lens has the same Angle of View on the front assembly as the rear assembly, (symmetrical) the lens is confronted with much less aberations vs, a lens that has a wide angle on one side, and a much lower angle on the other side. Hence why there is certain sweet spots in lens fl's for each format size.

Your assertion that less angle of view, equates to higher MTF is very true.... specially when it combines with the same angle of view on both sides of the lens. However, this is theoretical, not always a reality. For example, a 200mm fl lens on 35mm camera has about a 10 deg FOV on both sides of the nodal point. This alone does not assure a GREAT lens, but it certainly "sets the stage" per say, for a great lens.

This is evidenced in many of Canons 200mm offerings. But to really squeeze very bit of performance potential, the lens design becomes quite elaborate. Consider the 200mm f2 from Canon, its MTF is above 95% throughout the entire image height. To accomplish this, it required 18 elements and some exotic glass. Certainly no easy task, but IQ is like nothing I have ever experienced in my 25+ years of photography. Hence it's $5500 price tag.

Also, f stop plays an important role in MTF. As apt. opening becomes smaller, its easier to correct for aberations, but at the same time, the % MTF will lessen (vs. its max. potential). Most lens designs compromise at some point, to reduce the complexity of the design.... allowing less elements, smaller size, lower weight, lower cost glass, lower tolerances, etc. This is the beauty of LF lenses... they are natural compromises as they require use at very high f stops to allow for some reasonable DOF.


Of course, in this digital age, if you scan your film, contrast can be pumped up very nicely with post processing. The same can be said for edge sharpness... IMO, post processing has trumped the advances in lens designs by a long shot. When you consider PS costs ~ $150 a year to own, (upgrade fees) and it works with every lens in your arsenal, its way cheaper than buying the latest and greatest glass. Of course, for those purist who print direct from film, they must rely "mostly" on the capture process only for the best possible IQ. To increase quality of darkroom prints, you must use the better enlarging lenses, which are best suited for a specific print task, as well as good darkroom technique. I salute the darkroom printers of today... :-)

Ben Syverson
25-May-2009, 12:14
Major manufacturers are slaves to consumers, who all want fast glass.

Don't get me wrong, I love f/1.4 for low-light photography, but when the sun is out, I would love to mount a very simple plasmat to my DSLR for a neutral, ultra sharp view.

Such a lens would be six elements, around 40-50mm, symmetrical or near-symmetrical, around f/4 or f/5.6, and ultra light weight. In terms of image quality, it would blow every other SLR lens out of the water.

But it wouldn't sell because of the aperture, which is a horrible shame.