Enlarging lens questions

[trooper]

I've been pondering my enlarger lens performance and would invite any

insights.... I use a Beseler 23 w/Aristo cold light and a voltage

stabilizer. My MF optics are a 80mm Rodenstock Rodagon �4.0 and a

105mm Componon �5.6. I have used the Rodagon for some years with

great satisfaction on 645 and 66 formats and purchased the Schneider

to better suit 6X7 negs when I was using Koni-Omega (currently have a

P67 system). I recently experimented with printing some 8X10's with

6X7 negs and the Rodagon along with the same negatives printed to the

same size on print orientation with the 105mm. Even under

magnification of the print, I cannot tell the prints apart. The

negatives were quite sharp group shots, umbrella lit on FP4+ film. I

expected to see some advantage with the Schneider in combo with the

larger negatives (especially at the edges). Should I? Is there

reason to suspect the Schneider not being as sharp as it could be?

The prints are exceedingly crisp and sharp and easily show the

threads in the clothing of groups of 15-20 people in these prints.

 

I know I should just be happy that the prints are good, but it makes

me question how critical matching these formats to enlarging optics

really is. Have any of you had similar equipment experience?

[tim_brown5]

What you have here are two excellent lenses. Unless you got a bad sample it will be exceptionally difficult to see a difference in the prints. A glass neg carrier, carefully aligned enlarger, super sharp negatives on a film such as Tech Pan and prints at least 16x20 will get you in the ballpark of the potential of these lenses. I have a web page <a href="http://home.flash.net/~brownt/optical.htm">here</a> I'm working on that, among other things, shows print sections of images projected with a 80/4 Rodagon and APO Rodagon. I've made (sections of) 24x24 prints with detail too fine to see without a loupe, too fine to scan with a 600dpi flatbed scanner. Be happy that your prints are good.

[bob_salomon]

All 80mm Rodagon lenses cover 67 so this isn't too surprising.

 

As for the lens test page.

 

The Apo Rodagon is a discontinued lens series. It was replaced several years ago with a new formulation. The Apo Rodagon N. Which series are you comparing?

 

If the latest why not indicate so in your posts?

[tim_brown5]

Yes Bob, it's an APO Rodagon N. It's about 3 years old.

[roger_michel]

You did not mention the apertures at which you are making your prints. Both lenses you mention work best WIDE OPEN. I suspect that the larger image circle of the Componon will produce better off-axis results at f5.6 than the Rodagon can muster at f4. You may be surprised that I suggest using these lenses at full aperture. However, diffraction effects swamp improvements in optical distortion even closed down a single stop. Howard Bond has done extensive testing in this area (as readers of Photo Techniques will recall), and I concur with his conclusions. I should also mention that most LF lenses (with the possible exception of certain fast -- i.e. faster than f5.6 -- press lenses) are sharpest wide open (assuming you have adequate coverage for your chosen format at that aperture). If you were comparing prints made with your lenses stopped down, you were not seeing either at its best. Try them both wide open, compare them against each other and against prints made at smaller apertures. Then decide which you prefer.

[bob_salomon]

"Both lenses you mention work best WIDE OPEN"

 

No way.

 

Apo Rodagon N lenses reach optimal aperture within one stop from wide open. Rodagon lenses within two stops.

 

The lens that comes closest to performing best wide open is the G series and that is because it is made for mural enlargements and not normal sized prints.

 

But it is inferior to an Apo Rodagon, a Rodagon or a Rodagon WA at normal print sizes. Just as they are inferior to the G at mural sizes.

[roger_michel]

With all due respect to the esteemed Mr. Salomon of HP Marketing, I know the theoretical optical performance of the both lenses can be improved somewhat by stopping down slightly (as both Schneider and Rodenstock recommend), but this improvement is swamped by the increase in diffraction distortion. Both Ctein and Howard Bond have independently reached this conclusion. I have verified their results through experimentation with a carefully aligned Beseler 45 enlarger and a number of (mostly borrowed) lenses (on the subject of enlarger alignment, the Versa Dynamics laser tool is fantastic!!). I encourage readers of this forum to simply test for themselves. Align your enlarger (depth of focus can be a problem with an enlarger lens used wide open and a misaligned enlarger), then make prints wide open and stopped down. Pull out the loupe, then decide. You might want to check both center and edge performance since the Rodagon has marginal 6x7 coverage wide open. However, if the center is sharper in the prints made wide open, my point is proved.

[bob_salomon]

Roger,

 

Just check the MTF cirves.

 

Ctein is tilting at windmills again with this gem.

 

Lenses like the ones you mention perform best at stope other then wide open.

 

Don't you think that if the lenses perform optimallt wide open the manufacturers would be the first ones to tell you that?

 

Then there is another issue.

 

Using a lens wide open leads to very short exposure times. Times so short that manipulation of the print simply won't be possible. Unless ND is added. Most enlargers do not have ND built in unless you use all 3 colors at once on a color head.

[roger_michel]

I don't know if MTF curves are generated from actual aerial tests or are extrapolated from theoretical performance -- I frankly believe the latter, in which case diffraction effects would not be factored in. I should add that I too doubted Bond's and Ctein's results, and wrote an acerbic letter to PT containing a large number of challenges to the methodologies and conclusions of both authors. I subsequently engaged in a lengthy exchange of letters with Mr. Bond, who took me through his complete testing regimen. I duplicated his tests, and to my consternation discovered that he was right, plain and simple. Diffraction, I think, is a very much underexplored phenomenon, despite its critical importance in determining lens performance. One of the interesting upshots of Bond's work is that it appears that smaller formats have an inherent advantage over larger ones: shorter focal length lenses produce greater depth of field at a given aperture (i.e. at 35mm lens will have more dof at f5.6 than a 105mm lens at f5.6), but both apparently will suffer equal diffraction distortion when set to the same stop. I say "apparently" because I personally (unlike Bond) am not sure that the only factor at play is diffraction (needless to say, the actual lens opening will be larger in a 105mm at 5.6 than a 35mm at 5.6, suggesting LESS diffraction in the longer lens since the size of the wavelengths of light will be the same for both). However, it doesn't matter for practical purposes what causes the distortion, the bottom line is that it is the same at a given f stop for all focal lengths. Since the shorter lens has more dof, it will produce a greater range of acceptible sharpness, and so a greater margin of error when focusing, and therfore more sharp pics. This also means that for view camera photogs, who go for allover sharpness, relying in part of dof (along with altered plains of sharp focus through camera movements), that 4x5 may have some advantages over 8x10 or larger (if nothing else, you can shoot at wider apertures, get the same dof, and use a shorter exposure, reducing shake/movement problems). Anyway, I digress. The conventional wisdom has always been stop down a little for max sharpness. You do reduce spherical/chromatic aberrations thereby -- no question -- but you also increase diffraction. Bond and Ctein are among the first to seriously question whether this is a sensible tradeoff. The bottom line is that this phenomenon is very easy to test. Just make two prints, one wide open and one stopped down. Then compare the center sharpness. At the very least, you probably should start thinking more about how much you routinely stop down your lenses. By the way, Mr. Salomon, if I believed everything Schneider told me I would never have tried my 110 XL on my 8x10 -- a format the lens easily covers at f22.

[bob_salomon]

Rodenstock.s MTF curves are from production lenses. Not from theoritecal designs.

 

Why would a manufacturer produce theoretical curves? It is self-defeating since they would promote a quality level that is unobtainable in the field. As an ISO 9001 qualified company Rodenstock's claims have to be reachable by the user.

 

As to diffraction there are 2 apertures with MTF for each lens. One at open aperture and one at the diffraction limited stop.

 

I don't care what witchcraft Bond and Ctein may be putting forth it is nonsense.

 

We carry a book of prints made on a Durst 45 enlarger carefully aligned with a Zeiss Parallel Mirror Alignment Set and equopped with an AN glass carrier.

 

One negative was used made on a Leica M mounted on a Linhof 003323 Heavy Duty Pro tripod.

 

The center and the edge of that negative was printed at 2x and 4x and 8x and 20 x on the following series of lenses: at open aperture and f8.

 

Rogonar, Rogonar S, Rodagon, Rodagon WA, Apo Rodagon N, Rodagon G.

 

There are dramtic and easily visible differences between the different series and even more dramatic difference between open aperture and f9. Also dramatic are the changes at different scale sizes.

 

You are welcome to examine these prints at trade show we attend in the US.

 

We will be doing the DPIX show in Chicago in May, Showbiz Expo in LA in June, PRO in Dana Point in July (members only), Hunt, Photo East, etc.

 

If you want to see them just let us know prior to the show so we are sure to have it there.

 

These will show that your theory as well as Ctein's and Bond's are flawed.

 

Of course if the tests that were conducted by Bond and Ctein did not have a high quailty, detail rich negative, a properly aligned enlarger, a rigid and stable enlarger or a glass carrier they could get any results they want due to flawed technique.

[roger_michel]

In view of your impeccable reputation (and my good personal experiences speaking to you on the 'phone and at Photo Plus East on a number of occasions), I will certainly take your word for your test results. Bond and Ctein do not contend that EVERY lens performs best wide open, merely that many achieve max sharpness stopped down much less than the common wisdom suggests. Both noticed in particular that many "slow" LF and enlarging lenses are already diffraction limited wide open. All G-Clarons and Apo-Ronars, for example, fall into this category. It certainly may be the case that the two enlarging lenses under discussion here are NOT diffraction limited wide open. I only meant to suggest with my initial comment that aperture is relevant to sharpness, and wider is better sometimes. As I have said several times, readers of this forum should simply test their lenses by making enlargements at various apertures (including wide open), examine the prints with a loupe, and make their own judgments. IT IS NOT GOOD PRACTICE, HOWEVER, AUTOMATICALLY TO STOP DOWN EVERY LENS A FEW STOPS THINKING THAT SHARPNESS WILL BE IMPROVED THEREBY!!! As for your comment that wide apertures result in unacceptably short exposure times, I have not found that to be true. I use a Zone VI Cold Light enlarger for MF and LF, and find that I get typical exposure times of 20 secs or more even at f5.6. In any event, I have a variable voltage regulator that lets me dial in reduced lamp intensity -- a great outboard device available for many enlargers. It is useful for adjusting exposure times when using wider apertures, and also good for compensating for "dry down" once you make a print that looks perfect wet. Highly recommended!!

[tim_brown5]

My technique is not perfect, but it agrees more with what Bob is saying. My test prints, center sections of a 11X enlargement, show with my setup that: The sharpest prints are with my lenses (Rodagon and APO Rodagon N 80/4) closed down 1 stop to F5.6 with a glass carrier. Using a glassles carrier and stopping down to F11 degraded the sharpness, but not dramatically. These lenses, with a 6x6 neg, also have more even illumination closed down 1 stop vs wide open. Diffraction is a factor, but not the big deal Ctein et. al. make it out to be.

[michael_briggs2]

My tests with several top-quality modern enlarging lenses show that the performance is excellent wide open at the center. Stopping down approximately two stops results in a small increase of sharpness at the center, a very small change for some lenses. Stopping down approximately two stops results in a substantial increase in sharpness in the corners. This is very easily seen with a good grain focuser. One could say that the lens is almost diffraction limited at the center wide-open, but this isn't a very useful statement unless you only care about sharpness at the center of your image.

 

Incidentally, it is not enough for a lens to be sharpest wide open for it to be called diffraction limited. There is a theoretical best-performance of a lens based upon the diameter of its aperture and the wavelength of light. Rodenstock shows these values on their MTF graphs with symbols plotted on the vertical axes.

 

Another reason not to use an enlarging lens wide open is that the illumination won't be very uniform.

[bob_salomon]

"many "slow" LF and enlarging lenses are already diffraction limited wide open. All

G-Clarons and Apo-Ronars, for example, fall into this category. "

 

But these are not enlarging lenses. They are process lenses developed for 1:1. The Apo Ronars are narrow field for horizontal cameras and the G Claron, like the Apo Gerogon are wide field for vertical process cameras.

 

Enlarging lenses easily outperform them for enlarging.

[roger_michel]

I didn't mean to suggest that they were enlarging lenses. I said "many LF and enlarging lenses . . . ," with the two examples I gave obviously in the former category. Please remember, I'm not asking anyone to take anything on faith, just test -- it's very easy. I think many people may just dial in f8 or f11 when they enlarge without giving it a second thought. This MAY well be a mistake. And while a little off-topic, I also think there are many, many LF types who are members of the "f64 club"; i.e. they routinely stop way down for max depth of field -- whether or not they need it after movements -- and pay a huge AND UNNECESSARY diffraction penalty (Mercklinger's recent book is very good on this point). Finally, I think there are a lot of general photography/35mm types who think nothing of stopping down to f8 or f11 with a moderate wideangle, completely oblivious to what this does to sharpness. One final point, as for the comment regarding uniform illumination at wide apertures, this is really a coverage problem at bottom.

[wieslaw1]

I have read the above discussion with much amusement - good entartainment during the holiday season:

 

 

�...The prints are exceedingly crisp and

sharp and easily show the threads in the clothing of groups of 15-20 people in these prints�...

 

Yet another guy (RM) has a problem with the lens opening. According to his believe the prints could show molecules in the material the threads were made from if only we followed the theory of Bond et al.!

 

Bob - your reasoning, how sane it might be, will not stand out to the crusader. He is backed by DOUBLE O SEVEN himself!

 

Roger - you seem to like the extreme situations, printing wide open - God bless you. Why not trying another extreme - making prints with the lens cap on.

 

Marry Christmas everybody.

PS. I suggest you use electron source in your enlarger.

The wavelengths of electron beams are several orders of magnitude shorter than the light, and of course you now what that means for diffraction, don�t you?