Difference Between a Process Lens and an Enlarging Lens

[neil poulsen]

Does anyone have a clear understanding of the differences between an enlarging lens and a process lens? How are they optimized differently? All the definitions I've been able to find describe them as having the much the same characteristics.

In this regard, what's the problem with using a process lens as an enlarging lens. For example, I believe that Ansel Adams used a process lens for his 8x10 enlarger. Yet, some caution against this.

[Ernest Purdum]

The main difference is aperture. Most enlarging lenses for large format are somewhere around f5.6 or so, the process lenses about f9. The other difference is that process lenses are usually, though not always, optimized for closer image/subject ratios, often 1:1. Enlarging lenses are optimized for differing ratios, depending on what the maker guesses will be the most commonly used enlargement size.



For moderate enlargement, a process lens should work very well as an enlarging lens. Indeed, many have been used that way. For very big blow-ups, an enlarging lens should do better.

[Sal Santamaura]

Process lenses are usually optimized for 1:1, and are slower -- in the f/9 range -- than typical f/5.6 enlarging lenses. Nikon's 300 mm El-Nikkor is designed to perform best at 2X magnification; its 150 mm El-Nikkor at 4X.

That said, if you're interested in enlarging 8x10, a friend of mine purchased both a 300 mm Apo Nikor and 300 mm El-Nikkor back in the 1980s. He tried each on his well-aligned Durst 184 with glass negative carrier and couldn't detect any difference in resulting 16x20 prints. He sent back the El Nikkor. Unless you're planning great magnifications, the only discriminator might be easier focusing using faster enlarging lenses than with process lenses.

[Sal Santamaura]

Ernest, I was typing while you were posting. Great minds think alike...

[Michael S. Briggs]

Some reasons for the differences:

Process lenses were probably frequently used to make same-size copies, reductions and enlargements, while enlarging lenses are almost always used to enlarge. Based on the typical usage, it makes senses to optimize a process lens for 1:1 and an enlarging lens for the enlarging ratio that the manufacture guesses will be typically used. As the format size increases, the typical enlargement ratio decreases and become closer to the 1:1 of the process lens. So a process lens is likely to work better for enlarging 8x10 films than for 35 mm.

Some process cameras were focused based upon measurement rather than observing the image. This is why one sometimes sees with a process lens a data card with an accurate value for the actual rather than nominal focal length and also stating the value of the distance between the principal points of the lens. These values would have been used in setting up the camera so that when the operator set the camera to some reproduction ratio, the camera would produce that reproduction ratio and would be in focus. For cameras that were focused based on measurement, a lens with a fast aperture is not needed.

Both types are used to image flat items to flat items, so being "flat field" is important for both.

[Conrad Hoffman]

I used to bring circuit board artwork to a local repro house to have film tools made and saw much of the other work they did. The usual requirement was to reduce an original by 4X or less. Geometry was critically important, and the lens distortion had to have been small fractions of a percent. I never saw a piece of film smaller than 8x10 used, and focusing was usually by scale, though there was a large ground glass that could be swung into the film plane. Almost no continuous tone work was done- everything was on high contrast lith film and run though an automatic processor. My guess is that if your magnifications are within the design window for the lens, there's nothing wrong with a process lens used as an enlarging lens. The problem is that most available process lenses would be best suited to a very large format enlarger making rather large prints. Also, watch out for the large number of so-called process lenses that were really copy machine lenses. These show up surplus constantly and aren't worth much, though they can be usable for non-critical stuff.

[Armin Seeholzer]

Hi Neil

I'm really sure thad AA used not a process lens because he always stated to use the right tool for what ever is done and he was a perfectionist! To work with a process lens you get the first problem with focusing because it is quite darker then a f 5.6 lens! Just my opinion!

[Thilo Schmid]

neil,

a Process Lens is a lens that is designed for a fixed application, usually within some machinery. A Process Lens does not have to be symmetric or optimized for 1:1. The Process Lenses used in the stepper machines of the semiconductor industry, e.g., are usually optimized for 10:1 and a single wavelength.

The requirements for an Enlarger Lens (or Repro Lens as well) are similar to that of a Macro Lens (~1:20 to ~1:2) with two additional optimizations: distortion and flat field (plane to plane projection).

Process Lenses may share the same design as Copy-, Macro- or Enlarger Lenses. Why should a Lens Manufacturer build a new design, if an existing one will do for a certain application? The Schneider G-Claron, e.g., comes as Camera Lens with a shutter, as an Enlarger Lens with an illuminated aperture scale or as a Process Lens with a fixed aperture barrel. On the other hand, the famous APO-EL-Nikkor is used in circuit board production machines as well. Whether a Process Lens is suitable as an Enlarger Lens or vice versa, depends on the specs and comfort you require.

[Sal Santamaura]

Armin, if you view the film "Ansel Adams Photographer" that was made around 1980, you will see him in his darkroom adjusting the lens on his horizontal enlarger while making a print from an 8x10 negative. The lens is clearly marked as an f/9 Apo Nikkor -- a process lens.

[Bob Salomon]

Another major difference is that process lenses up to 600mm are optimized for use at f22 only. 600mm and longer are optimized for f32 only.

Enlarging lenses are optimized to perform optimally at much larger stops. This makes printing far more convenient as to avoid reciprocity you need a whale of a lot of light to use a process lens at its optimal aperture.

Ever been in a process camera room when they turn on those lights?

[Øyvind Dahle]

What I miss is examples of comparable pictures or prints made whit the different lens types. I have three 150mm lenses, two apo-gerogon and an enlarger lens. I don't see any difference on a Polaroid 55P/N film taking pictures of a CD-collection at 2m.

I did see a difference between a 210 Apo-Symmar and a 75mm Mamiya Polaroid press camera-lens, the 210 was close to 35mm optic, while the 75mm was poor.

I expect almost 35mm film contrast and resolution, so I let the 75mm go.

All my other optic was just under the 210 in achievment on my red wall (shooting at 20x focal length, 1.5m for 75mm, 1.8m for 90mm, 3m for 150mm, 4.2m for 210mm and 6m for 305mm - my terrace is no wider :-)

Øyvind:D

[Jim Cooksey]

Apologies in advance for what may sound like a hopelessly naive question, but I've been out of LF for a few decades (long story) and am looking to get back in a slightly different direction, specifically, VLF - 8x10 or 11x14, carbon transfer printing. I'd like to start with B&W, but color carbon printing appeals to me also, for some perverse reason. To get to the point, would a process lens be useful for creating accurate color separation negatives for such an effort? Any tips on where to go for guidance?
Thanks.

[Doug Herta]

Jim - Sandy King is a frequent contributor here and has a Carbon printing group on yahoo groups. Look around here, unblinkingeye.com and the Bostick & Sullivan site for more carbon printing info.

[Vaughn]

Jim, where are you located?

I give carbon printing workshops on the West Coast, Jim Fitzgerald gives individual workshops down in SoCal, and Sandy King is on the east coast, giving workshops there and elsewhere. Of the three of us, only Sandy has experience with color carbon printing, but you'll probably want to start out with monochrome to get your feet wet.

But please feel free to contact me if you have any questions about the process, or go to the sites Doug mentioned.

Vaughn

[bob carnie]

Could someone here describe the difference between a camera taking lens and a enlarger process lens.
Specifically how it applies to depth of field and depth of focus?
and why one would not expect closing down an enlarger lens will give much or any sharpness increase.

[Ken Lee]

Every lens has an optimum focus distance, and an optimum aperture. Enlarging lenses open wide to make focusing easier in the dark. We stop them down to a better aperture when exposing the print.

That being said, some lenses are so good, that we only notice a substantial difference, under substantial magnification.

What one person deems substantial enough, is a matter of personal judgement.

[Dan Fromm]

Bob, depth of field is the region in front of the lens that's in acceptable focus. Depth of focus is the region behind the lens that's in acceptable focus.

Stopping down most lenses will increase sharpness for a while because most lenses aren't perfectly corrected and have aberrations that are sensitive to aperture. Stopping down reduces their effects, increases the effects of diffraction. At some aperture and magnification, stopping down farther will lose more to diffraction that is gained by reducing coma, improving field flatness, ...

There've been many discussions of using enlarging lenses as taking lenses for distant subjects. With respect to modern enlarging lenses, e.g., Componons, Rodagons, to the extent that there's a consensus it is that long ones are usable as taking lenses. There's no consensus about short ones or about relatively ancient enlarging lenses.

All that I know is only one of the enlarging lenses I've tried out as a taking lens has worked well; that one, the Boyer Saphir BX, is for sure simply a rebadged taking lens. I know for a fact that Boyer rebadged taking lenses for use as enlarging lenses. The only Boyer lens optimized for enlarging is the Saphir B, and it isn't very good; modern 6/4 plasmat type enlarging lenses from, e.g., Fuji, Nikon, Rodenstock, Schneider, are better.

I have no idea whether relatively ancient enlarging lenses, the Saphir B excepted, are optimized for enlarging. One would think they ought to have been but Boyer propaganda asserts that the Saphir B is the first lens optimized for enlarging. It was designed in the 1930s.

[bob carnie]

Thanks Dan

here is a observation which makes me question my understanding of depth of focus when making a print.
When I grain focus a print, my print is tack sharp, I do not see any added benefit of closing down, unless of course if the lens to print combination is not exactly aligned at one or two edges.
My thinking is that depth of focus is not a benefit when you grain focus, what are you gaining by closing down. focused grain is focused grain, some argue that there is a benefit I just don't get it
I understand the depth of field on camera lenses , but never really grasped the benefit/logic of depth of focus on a print as I was always under the impression that a good process lens converges on one single plane.

not sure if I am explaining myself properly here.



Bob, depth of field is the region in front of the lens that's in acceptable focus. Depth of focus is the region behind the lens that's in acceptable focus.

Stopping down most lenses will increase sharpness for a while because most lenses aren't perfectly corrected and have aberrations that are sensitive to aperture. Stopping down reduces their effects, increases the effects of diffraction. At some aperture and magnification, stopping down farther will lose more to diffraction that is gained by reducing coma, improving field flatness, ...

There've been many discussions of using enlarging lenses as taking lenses for distant subjects. With respect to modern enlarging lenses, e.g., Componons, Rodagons, to the extent that there's a consensus it is that long ones are usable as taking lenses. There's no consensus about short ones or about relatively ancient enlarging lenses.

All that I know is only one of the enlarging lenses I've tried out as a taking lens has worked well; that one, the Boyer Saphir BX, is for sure simply a rebadged taking lens. I know for a fact that Boyer rebadged taking lenses for use as enlarging lenses. The only Boyer lens optimized for enlarging is the Saphir B, and it isn't very good; modern 6/4 plasmat type enlarging lenses from, e.g., Fuji, Nikon, Rodenstock, Schneider, are better.

I have no idea whether relatively ancient enlarging lenses, the Saphir B excepted, are optimized for enlarging. One would think they ought to have been but Boyer propaganda asserts that the Saphir B is the first lens optimized for enlarging. It was designed in the 1930s.

[Ken Lee]

Using a grain-magnifying focusing device, you should be able to see the grain become more sharply rendered as you stop down a few stops from wide open. Unless that makes it too dark.

[bob carnie]

I have never noticed that, usually I focus wide open and close down 2 stops, but not sure I will see sharper grain, I will concentrate on this a bit more.


Using a grain-magnifying focusing device, you should be able to see the grain become more sharply rendered as you stop down a few stops from wide open. Unless that makes it too dark.

[Mark Sawyer]

Using a grain-magnifying focusing device, you should be able to see the grain become more sharply rendered as you stop down a few stops from wide open. Unless that makes it too dark.

Agreed. It would depend on that "optimum aperture", which would be different from lens to lens, but I doubt it's wide open even on an enlarging lens.

I always stop down a little, just because presuming perfect film-flatness, curvature-of-field, and enlarger allignment is presuming an awful lot.

[Ken Lee]

The improvement might not be seen in the center of the image. Stopping down a few stops increases the useable circle of coverage, so the difference is probably seen towards the corners. If you use a lens that is somewhat larger than the diagonal of the film, then you use more the center of coverage anyhow.

[Dan Fromm]

Bob, depth of focus is a killer when we're shooting at infinity. It is then very thin, just like depth of field when shooting at infinite magnification (do you see the connection now?), so the least difference between the film's position when the shot is taken and the GG's position while focusing and composing will reduce sharpness in the negative. But this is in taking.

When printing, depth of focus is much greater and anyway the negative stays put. But when printing, depth of field is quite small so small differences between the plane the grain focuser focuses on and the plane the paper's surface is in will reduce sharpness in the print. This is why we're supposed to focus with the grain focusing aid on a piece of paper as thick as the one that we'll print on.

Cheers,

Dan

[ic-racer]

Depends on what you are interpreting when you look. Diffraction starts to rear its head with the first click of the aperture dial. There may be less contrast of the grain wide open, but the grains may be sharpest wide open and stopping down increase the contrast and decreases the sharpness to a point when diffraction totally messes it up.

Depending on the maximum aperture of the lens, different series of events may happen as you stop down. There is no mystery, though, the grain focuser tells all if you believe what you see.

Bob asked about depth of field. The reason it is important (assuming you are using a glass carrier and have a proper aligned enlarger) is that you may not always be at the enlarging lenses optimum magnification. As you move out of the optimum range the field becomes less flat. When exceeding the maximum magnification range of an typical enlarger lens the center of the image focuses on a point much closer to the enlarger head than the outer edges of the image. It is in fact opposite the normal curve of a negative so a curved negative makes the situation even worse.

Again the grain magnifier tells all. If you focus by moving the head up and down you can easily demonstrate this lack of field flatness when you project a 35mm negative to 40" using a "standard" 50mm lens.

The failure of a lenses flat field is also be seen when using an enlarging lens at the other extreme of too little magnification. For example using an enlarging lens for 1:1 reproduction.

[Drew Wiley]

Jim - back to your immediate question: Many process lenses were specifically designed for very accurate flat-field "apo" color separation. In this respect, the better quality models are generally superior to general enlarging lenses. By being
typically one of two stops slower, they were easier to correct in engineering than faster enlargement lenses. If you are beginning with large-format originals, the
effects of diffraction stopped-down are negligible, and often never apparent to the
naked eye. I assume that your mention of such lenses implies you wish to make
enlarged color separations. As an example, I use a 240mm Apo Nikkor process lens
to make 8x10 enlarged separations from 4x5 film, typically from f/16 to f/22. The
results are superb. From 8x10 originals, I make the separation simply by contact.
For enlargement you will need an absolutely ridgid and precisely aligned enlarger,
plus some sort of vaccum filholder which doesn't flex at all in the septum, preferably
with pin registration. Separation filters are a tricker subject, but if they're below the
lens should be glass. Then to keep track of what you're doing, it helps to have a
graphics step tablet and transmission densitometer. Also get the very best grain
magnifier you can find. I won't go into films or developers, because that's a very
complicated subject in its own right, and depends on the exact final output.

[Jim Fitzgerald]

Apologies in advance for what may sound like a hopelessly naive question, but I've been out of LF for a few decades (long story) and am looking to get back in a slightly different direction, specifically, VLF - 8x10 or 11x14, carbon transfer printing. I'd like to start with B&W, but color carbon printing appeals to me also, for some perverse reason. To get to the point, would a process lens be useful for creating accurate color separation negatives for such an effort? Any tips on where to go for guidance?
Thanks.

Jim, as Vaughn said he is up north and I'm in Ventura. Most of the lenses I use for image making in 8x10, 11x14, 8x20 and soon 14x17 are process lenses. My carbon transfer prints from these lenses are quite nice. If I can be of any help let me know. It is wise to try monochrome carbon first to get the mechanics of the process down and then venture down the color path.

Jim

[Cor]

Isn't stopping down an enlarger lens also helping to overcome the curving of some types of FB paper? Some of these papers curve so much that even my baseboard does not keep them completely flat at the edges, and somehow the resulting image is sharp there too.

When I make small test prints, the cut pieces FB paper bow significantly (I "crack" them sometimes), but still these test prints come out more sharp that I expect.

I have a formula somewhere which demonstrates the to me surprising depth of field limits around the paper surface, cannot find them at the moment..

Best,

Cor


Bob, depth of focus is a killer when we're shooting at infinity. It is then very thin, just like depth of field when shooting at infinite magnification (do you see the connection now?), so the least difference between the film's position when the shot is taken and the GG's position while focusing and composing will reduce sharpness in the negative. But this is in taking.

When printing, depth of focus is much greater and anyway the negative stays put. But when printing, depth of field is quite small so small differences between the plane the grain focuser focuses on and the plane the paper's surface is in will reduce sharpness in the print. This is why we're supposed to focus with the grain focusing aid on a piece of paper as thick as the one that we'll print on.

Cheers,

Dan

[Drew Wiley]

For critical work a vacuum easel should always be used. And it takes more vacuum
draw to keep real paper flat than film. Too much vacuum and you've got a problem
too. The pump should have a bleeder valve which is adjustable. I remember an
otherwise exceptional photographer where, if you looked closely, you could frequently make out faint pegboard holes in dark areas of the prints! Not my choice
of a suitable material for a vacuum board. Holes should be a lot smaller and further
apart, and arranged to flat the film or paper from the center outwards as the vacuum pump is turned on, so the material won't get wrinkled.

[ic-racer]

Isn't stopping down an enlarger lens also helping to overcome the curving of some types of FB paper?

Perhaps in some settings. Here are some numbers (based on CoC 0.15mm):
The focal depth on the baseobard side at f5.6 with a 5x enlargement is 2.5mm. When stopping down for a print (f22) the focal depth at the baseboard is 43mm.

[ic-racer]

I actually just got done with aerial image testing a 240mm Componon-S (X-mas present) with my existing 250mm Fujinar 'tessar-style' process lens. Also comparing those lenses to a 300mm Rodagon enlarging lens and a 305mm Eskofot process lens.

Tests done at 3x magnification (30" image) with Peak 1 loupe.

Neither 240/250mm lens is all that good at the corners wide open. In fact neither will resolve grain in the corners when wide open at 3x magnification. Both resolve grain around 22 to 32 with diffraction taking over past f32. Less than stellar performance likely due to pushing these lenses to the coverage limit with 8x10.
Both the 300mm Rodagon enlarging lens and the 305mm Ekofot process lens give sharp grain wide open in the corners, with improving contrast and corner resolution when stopped down.

At f32 to f22 all 4 lenses will give acceptable prints, with the 300mm enlarging lens slightly favored under close scrutiny at the edges.

Relevant points to this discussion:
1)The focal length had much more effect on edge sharpness than the lens construction or intended use.
2) At usual working apertures, the differences between lenses can be small.