lens question

[David Woods]

Hi
I have just aquired a Durst 138S, I have a 210mm Rodenstock Apo Gerogon lens, and also a 150mm Scheider-Kreuznach lens, now when I load my 5x7 neg and put the Rodenstock lens on the enlarger, the image is much smaller than the Scheider, is this right, I thought the larger lens would produce the larger image.

Regards
David

[seabird]

David,

Hi from another Sydney-sider. That's what I'd expect to see. For a given negative size and same column height, think of the shorter focal length Schneider lens as being a wide angle, while the Rodenstock is like a telephoto with a narrower angle of view.

Cheers

[Emmanuel BIGLER]

Hello from France

When you take a picture of a far distant objet, it is true that the longer the focal length, the larger the image on film.
When you enlarge a negative with an enlarger, things are very different, the object and the image are very close to each other if you compare with the situation where you take a picture with an object that can be located at 50 times the focal length.

With the enlarger, if you work with a constant negative-to-board distance "D", the first thing you should keep in mind is that the longest focal length that will allow you to get a sharp image is D/4.
So in order to get a sharp image with your 210 mm lens, the total negative-to-board distance should be longer than 4x210 = 840 mm. And in this situation, called the "2f-2f" setting, the image has the same size as the object, magnification is 1:1
Now imagine that from the previous 2f-2f situation, magnification = 1:1, we keep the total distance of 840 mm constant, and we substitute a 150 mm focal length to the 210.
The laws of optics tell us that we now have two possibilities to get a sharp image,
- either by placing the 150 mm lens at a distance of about 200 mm from the negative, the image will be about 3.3 times bigger than the negative size
- either by placing the 150 mm lens at 645 mm from the negative, with an image size 3.3 times smaller than the negative. This solution is not accesible to the usual bellows of your enlarger !
hence, the apparent paradox:
with the same negative to board distance, say, 840 mm, the 210 mm lens gives you access to the 1:1 ratio only whereas the 150 mm lens will deliver an image 3.3 times bigger than the negative.
You could even use a 135 mm lens covering the 4x5" format and have access to a magnification slightly bigger, about 4 times

With a given focal length, of course you can have access to any magnification, but at the expense of the total distance between the negative and the enlarger board...
There exist 120 mm "wide angle" enlarger lenses covering the 4x5", this kind of lens will give you access to bigger magnification ratios than the 150.. or the 210.

[ic-racer]

I thought the larger lens would produce the larger image.

Regards
David

Now you know :D

Use that 150 if you need to enlarge any 4x5 negatives.
The 210 will work good for 4x5 also, if you make small prints.

If you have the condenser head, make sure you adjust it to match it to the focal length of the lens you are using.

[Bob Salomon]

That 210 is a wide field process lens designed for graphic arts use and optimized for f22 only. A 210mm enlarging lens will give far better performance.

[David Woods]

Thanks Guys
Sometimes the most obvious needs to hit you with a sledge hammer, before it becomes clear, for some reason my mind kept telling me, larger lens larger image,
Regards
David

[Greg Blank]

I am not sure anyone really answered you correctly. A 210 lens is about 8.5 inches or 210mm in focal length. You draw the lens away from the negative that amount and project your image on the base board at an equal distance and you get a 1 to 1 image for 5x7 *If* the lens is designed to cover 5x7. My guess an older process lens will do that. Then you raise your enlarger and refocus at the projection size you want, typically a 210 would be nice and wide for 5x7 *If* the lens is designed to cover 5x7.

Case in point: I recently bought a 240 mm Componon S, for my 810 enlarger + lens plate fer 150 smackers. The lens easily projects 24x30 in a short distance. The 240 cover 8x10 nicely and making bigger images is possible where as my 300 Rodagon (which is a fine lens also) Will just give me a 24x30 at the highest set up of my enlarger with a further distance from my basement floor to enlarger top distance.

I bought the 300mm lens on Ebay 5 years ago for 200 dolares, both lenses new at one point were in the $1,ooo-2,000 range- each.

*A standard disclaimer*


Hi
I have just aquired a Durst 138S, I have a 210mm Rodenstock Apo Gerogon lens, and also a 150mm Scheider-Kreuznach lens, now when I load my 5x7 neg and put the Rodenstock lens on the enlarger, the image is much smaller than the Scheider, is this right, I thought the larger lens would produce the larger image.

Regards
David

[Emmanuel BIGLER]

I am not sure anyone really answered you correctly

Oops ! Forgot to post the useful formulae in order to be comprehensive ! :D

- for a desired magnification M, if the enlarger lens has a focal length f, the total distance D between the negative and the enlarger board is :
D = f . (M + (1/M) +2)

example : I need M=2 in order to get a 8x10" print from a 4x5" negative, if f=210mm, then D = 210x(2 + .5 +2 ) = 945 mm

- for a given fixed distance D between the board and the negative, D should be bigger than 4f (otherwise no sharp focus can be found), and the two possibilities for focusing are given by
x = (1/2) . (D (+ or -) SQRT(D^2-4.f.D))
where x is the distance between the lens and the negative; the corresponding magnification ratio is M = (D-x)/x

Example : take D = 900 mm and f = 210 mm ; the two focusing possibilities are x1=334 mm ; M1 = 1.7 and the (useless) other solution is x2=566mm ; m1 = 1/1.7 = .59

[Dan Fromm]

I am not sure anyone really answered you correctly. A 210 lens is about 8.5 inches or 210mm in focal length. You draw the lens away from the negative that amount and project your image on the base board at an equal distance and you get a 1 to 1 image for 5x7 *If* the lens is designed to cover 5x7. My guess an older process lens will do that. Then you raise your enlarger and refocus at the projection size you want, typically a 210 would be nice and wide for 5x7 *If* the lens is designed to cover 5x7.

Case in point: I recently bought a 240 mm Componon S, for my 810 enlarger + lens plate fer 150 smackers. The lens easily projects 24x30 in a short distance. The 240 cover 8x10 nicely and making bigger images is possible where as my 300 Rodagon (which is a fine lens also) Will just give me a 24x30 at the highest set up of my enlarger with a further distance from my basement floor to enlarger top distance.

I bought the 300mm lens on Ebay 5 years ago for 200 dolares, both lenses new at one point were in the $1,ooo-2,000 range- each.

*A standard disclaimer*Arithmetic error or typo, Greg. At 1:1, negative to lens rear nodal plane distance is 2f = front nodal plane to print distance. At infinity, negative to lens rear nodal plane distance is 1f and front nodal plane to print distance is, um, extremely large.

[Allen in Montreal]

David,

The long and the short of this is, you want to print 5x7 negs, the vast majority of the job will be handled very well by a 180mm or 210mm Rodagon. E bay will provide you with chances to buy either already mounted in a Durst Lapla board for very little.
Don't shy away from the older Rodagons if they are in very good shape, they are still great lenses.

Do not mess up the corresponding combination of the condensors as shown in the diagram by Durst for any given format/lens. Use the 240 top and bottom.

4x5, stick to a 150mm until you are very familiar with the unit.
You do not mention which model it is, I assume it is a Componon?
Use the 240 on top and the 200 on the bottom, curved side facing each other.

What other formats do you plan on shooting and printing on the 138?

[Leonard Evens]

The question doesn't amke sense unless you say just what you are doing.

For example, if you make the same size final print, the ratio of print size to image size is the same, so the magnification doesn't depend on the focal length. However, the longer focal length lens will have to be higher up to achieve that magnification.

Emanuel's answer tells you what will happen if you keep the total distance between lens and easel constant while focusing the image.

[David Woods]

David,

The long and the short of this is, you want to print 5x7 negs, the vast majority of the job will be handled very well by a 180mm or 210mm Rodagon. E bay will provide you with chances to buy either already mounted in a Durst Lapla board for very little.
Don't shy away from the older Rodagons if they are in very good shape, they are still great lenses.

Do not mess up the corresponding combination of the condensors as shown in the diagram by Durst for any given format/lens. Use the 240 top and bottom.

4x5, stick to a 150mm until you are very familiar with the unit.
You do not mention which model it is, I assume it is a Componon?
Use the 240 on top and the 200 on the bottom, curved side facing each other.

What other formats do you plan on shooting and printing on the 138?

Hi Allen

I have the combination pages for the condensors, I haven't been able to use it fully yet, I have only been testing it out, I got it of Ebay for my Birthday present which isn't until October, but these LF enlargers are few and far between in Australia, so I snapped it up. I am going to pull it apart and refurbish it between now and October, it will be just ike getting a new one.

I only plan to process 4x5 and 5x7 on it, I have a Durst c35 for the 35mm and 6x6 negs. The lens in question is a 210mm Rodenstock Gerogon lens, The unit came with 3lenses and their boards.
Regards
David

[Greg Blank]

And you understand all that right? If so how many good pictures do you make per year? ;)


I am not sure anyone really answered you correctly

Oops ! Forgot to post the useful formulae in order to be comprehensive ! :D

- for a desired magnification M, if the enlarger lens has a focal length f, the total distance D between the negative and the enlarger board is :
D = f . (M + (1/M) +2)

example : I need M=2 in order to get a 8x10" print from a 4x5" negative, if f=210mm, then D = 210x(2 + .5 +2 ) = 945 mm

- for a given fixed distance D between the board and the negative, D should be bigger than 4f (otherwise no sharp focus can be found), and the two possibilities for focusing are given by
x = (1/2) . (D (+ or -) SQRT(D^2-4.f.D))
where x is the distance between the lens and the negative; the corresponding magnification ratio is M = (D-x)/x

Example : take D = 900 mm and f = 210 mm ; the two focusing possibilities are x1=334 mm ; M1 = 1.7 and the (useless) other solution is x2=566mm ; m1 = 1/1.7 = .59

[David Woods]

And you understand all that right? If so how many good pictures do you make per year? ;)

Greg

How many pictures I am happy with, or other people find acceptable?

David