Question on enlargers in relationship to normal lens?

[Kevin Crisp]

A 150 El Nikor covers 5X7? I'm going to have to try this.

[Chauncey Walden]

Kevin, the old one with the 53mm flange does. I have no idea about the newer ones.

[Gene McCluney]

In larger than 4x5 format, many people choose a somewhat wide-angle enlarging lens, due to the amount of distance needed from negative to print. Particularly in a home-darkroom situation with 8 ft. ceilings. It is very easy to exceed this height with an 8x10 format enlarger when making a moderately large print with a "normal" focal length enlarging lens for the format. In a pro darkroom, of course the ceiling height can be "built" to allow for full rise of the enlarger.

[Clay Turtle]

Thank you for your insight so far & I would ask you to bear with me a few moments longer
1) Ran search & found one thread that dealt with home-made enlarger but the guy was asking or stated that he was using a cold light source. He didn't go into details as to the construction . . . alignment considerations?
2) Considerations of producing 5x7 format gives rise to question of available out sourcing . . . as I had not been doing any 5x7 negative processing, I was reluctant to start with my initial exposures which I had to mail out of state to have processed.
Now as to printing . . . I do know or did know of one place that printed 4x5 but I don't know that they do 5x7? I don't know that they are still in business & if they are I know that they did b&w and color negatives but I don't think they did positive printing processes? These concerns (general) arise as an aspect of a particular instance or exposure. [See attahed photos]
As part of camera build I wanted to make trial exposures but not having gg for back, I used subsitute of photograph frame glass. It didn't work well, I could focus directly though the len opening (like a telescope) or by getting at an extreme angle under the hood (dark cloth) I could make out a small circle on the (sg-1) substitute glass.
Normally one would set up for 5x7 negative then move easel to print cropped area. but I wae questioning, why not physically cut down the negative (slide) to a 4x5 format? Which extends itself to considerations of multiple format in 5x7 like that of the 8x10 format & what adversely it would effect the sharpness of the print?

[Clay Turtle]

Enlarging lenses are optimized for flat field. Most "normal" lenses are not.

You can use shorter lenses, but even if a shorter lens has enough coverage, it's generally best to employ the center of the lens's image circle, where the best quality is given.

I had heard that statement before that there is a difference between enlarging len & camera len and had accepted it without relating what was being implied by the statement . . . flat field? Both the enlarger & the camera project an image on to a flat field or plane . . . unless you are shooting one of those rotating camera using mirrors to project the image onto roll film => ie 180 degrees panoramic?
Rethinking it I wonder if that which I am not understanding has to do with the relative angle at which the light enters the film or printing medium?
Noting that if I take the glass beaker I use the processing chemicals & fill it with water then putting the plastic stirring rod into it. I note the rod appears bent when it extends from one side to the other but as I move it into the vertical parallel & perpendicular with the surface the angle changes . . . so if I relate this to the len aspect then the further (greater the angle) from the center the more the image (light) has to bend (is bent) to form the focused image?
Is this what is meant by the "flat field" statment?

[Bob Salomon]

I had heard that statement before that there is a difference between enlarging len & camera len and had accepted it without relating what was being implied by the statement . . . flat field? Both the enlarger & the camera project an image on to a flat field or plane .

The enlarging lens assumes that the thing that you are projecting is flat. A taking lens assumes that the scene that it is photographing does have depth. A process lens, like an enlarging lens, also assumes a flat original but it is corrected to work only at f22 or f32 depending on focal length. An enlarging lens is corrected to work at much wider apertures.

[ic-racer]

Is this what is meant by the "flat field" statment?

One way to look at it is to think of LENS-to-FILM and LENS-to-SUBJECT distances. When a lens is 'optimized' for a certain LENS-to-FILM and LENS-to-SUBJECT distance, frequently that means that the field will be flat. That is a flat subject will project in focus from edge-to-edge on a flat film surface.


Typical 'pictoral' lens for photograpy is frequently optimized for all points at infinity to be projected in focus on the film plane.

A typical 'macro' lens for photography is frequently optimized to project a flat surface at a LENS-to-SUBJECT distance less than infinity, onto the flat film surface.

A 'process' lens is frequently optimized to project a flat surface when the LENS-to-SUBJECT and the LENS-to-FILM distances are equal.


A 'low magnification' (typical) enlarger lens will be optimized (flat field) for distances similar to a process lens.
A 'high' magnification enlarger lens will be optimized for distances somewhere between the 'process' lens and the 'macro' lens.

You can certainly go beyond the design boundaries of any lens and get acceptable results by stopping down. You can easily check this with an 'edge viewing' grain magnifier under the enlarger prior to making a print. When using a camera, it is not so easy to check the edges without exposing an image.

[aduncanson]

Clay,

When you are projecting a flat negative onto a flat piece of photographic paper, it is critical that the lens have a flat field in order to keep the image sharp to the corners. Therefore, process lenses and enlarging lenses optimize this characteristic. In a camera, the subject is frequently not flat even though the film is. Therefore there is little to be gained from optimizing the lens for a flat field and lens designers trade that characteristic off in favor of some other characteristic that is more important in general photography, possibly better coverage or better performance at larger apertures. (I don't know, I am not a lens designer.)

Therefore a flat field process lens is a lens that has been optimized for a characteristic which is not likely to be important in general use. That said, I still love my Artar.

[Clay Turtle]

Well that seems to satisfy the question of what enlarging lens for a particular formats . . just seems strange that the "normal lens" for enlargers seem to be directly related to format of the enlarger. I assume that the cone of light (image) relates to the lens, itself & therefore the (degree) angle which the light intersects the paper would be the primary relationship, not the format? As with the previous image form the 5x7 format, I could cut it down to a 4x5 format which would be easier to have enlarged or printed than the 5x7. But if this were true then when using a long lens on the 35mm format would be best to use the same (similar) focal length on the enlarger.
Yet if I were to cut down the LF format to print as small or medium format then I would use the normal lens for that format to print an enlargement? Of course I am assuming that the light angle of incidence is not constant at 90 degrees (right angle) to the paper or film as the case may be . . . I just find it a bit strange is all, afterall I never heard of anyone using a 300mm enlarging lens as they had shot the 35mm negative with a 300mm lens.

[aduncanson]

Clay,

The enlarging lens is typically sized for the format being enlarged. The primary issues are: 1) Does the lens have sufficient coverage for the format being enlarged? and 2) Does the lens allow sufficiently large enlargements given the limits of the enlarger column? Another concern is if the enlarging lens performs well at the print magnifications you will be making.

The enlarger could constrain the lens choice if you have a fixed condenser, where the lens is assumed to be a specific distance below negative stage. I have a 4x5 enlarger (Omega D2) and I replaced the fixed condenser with an Aristo cold light. The cold light does not constrain the lens choice in this way. I use a Rodenstock 120mm wide angle enlarging lens for both 6x9cm and 4x5 inch negatives. I also use a 80mm lens for 645 and 6x6 negs. If I was willing to suffer enlarging 35mm negs, I would be looking for a shorter lens. If I wanted to greatly enlarge a small portion of a 4x5 neg, and I was able to center that portion in the enlarger's light path, I would certainly use a shorter lens.

Because the lens and the paper are flat and typically parallel, changing the focal length of the enlarging lens has no effect on the perspective of the print. Using a 300mm enlarging lens for a 35mm negative would do nothing but severely limit the size of the enlargement you could make and almost certainly give performance inferior to a lens optimized for the smaller format.