how to test enlarging lens? (apo-componon 4.5/90)

[chris77]

hello forum.

i have just bought a schneider kreuznach apo componon hm 4.5/90 for just abought 380 $.
the lens seems to be in good shape, no scratches, very few dust, no cleaning marks.
i am about to use it for big enlargements in b&w (using liquid emulsion).

tried to set up a test yesterday, challenging my componon-s 100mm.
i am using vg photo paper to run the tests of different "sections".
but it seems that as long as i am not using a laser-tool to align the vertical head (durst m800) with the wall its
pretty impossible to get decent results in the corners (or it becomes a bit of a lottery)
the grain focuser i am using only works in the center of the projection.

so what i did, align the enlarger as good as i could, focus in the center, stop down and print a sample paper from one of the corners. results are really not blowing my mind. the componon-s is almost as sharp in the corners. maybe thanks to being stopped down to 8.5 instead of 5.6??

any ideas how to test this lens for lets say 30-40 x enlargements?

i measured the distances to all 4 corners of the projection. but as sharp as it is in the center, i have not succeeded to get the corners right, the depth of field is too narrow closing this lens only 2 stops (1.5 stops actually)..
if its not a good example i can still return it, so... what do you think is the best i can do using simple tools and of course a glass carrier, negs are 6x7.

any help appreciated.
nice weekend to you all.

chris

 

[ic-racer]

You need to align the negative to the lens very carefully. Use a glass carrier. You need an enlarging focuser that can visualize the corners. I don't think you will detect any difference between the two lenses enlarging 6x6cm negatives or 35mm. The 90 APO will probably be sharper at the edges than the 100 doing 30 to 40x from 6x9cm format. Realize that at 40x enlargement, the relative aperture is so small that diffraction will spoil enlargements from both lenses. For example at 5.6 on the barrel, the aperture is around f250.

 

[chris77]

well. thanks for your quick answer.
obviously i cannot expect a "big gain" in what i am trying to do, stepping up to the 90 apo.

i was expecting better rendition and sharpness in the corners (especially going as big as 30-40 x) and less light falloff. but obviously i expected too much and my results are not only due to improper alignement..

 

[RobC]

I would suggest you have bought the wrong lens. The optimum performance of that lens is at around 6X enlargement. It should perform well upto 12X enlargement after which it will start to degrade.

All enlarging lenses have optimum enlargement factors. I'm not sure there is any lens which is optimised for 40X enlargement. However a Rodaon-G 105 is optimised for 20X enlargement and 40X is at the extreme end of its capabilities.

A lens optimised for 6X enlargment and maybe range of 2X-12X could well shows signs of vignetting due to closeness of lens to film when trying 40X enlargement which it wasn't designed for.

Just becasue its an APO doesn't mean it will work well at any enlargement factor.

 

[Neal]

Dear Chris,

First, a plug for the Versalab Parallel laser alignment tool. I find its ease of use makes me much more likely to tune in my enlarger than other methods I've tried and it has done more to improve my prints than any other purchase I've made. I know it's not cheap but an inexpensive lens with good alignment is far better than an expensive lens with things out of whack. Next, look for negatives that will allow for comparisons other than sharpness. Distortion shouldn't be a big issue with a decent enlarging lens but an advantage might be found. My uneducated guess is that the ability of a lens to focus all colors to the same plane is of less value when not printing slides. My assumption is that you are printing b&w and if that is the case, you might try making your comparison with color negatives.

Good luck

 

[Bob Carnie]

You should not consider depth of field when using enlarger lenses

In a perfect aligned/ glass carrier set up a apo lens or any enlarging lens is perfectly fine at wide open.
I will suggest there is some Depth of Focus , but I only close done two fstops to get better time.

 

[Bob Carnie]

I use a 90 mm apo rodenstock with medium format and do get great edge to edge sharpness at 30 x30 print size.

 

[RobC]

You should not consider depth of field when using enlarger lenses

In a perfect aligned/ glass carrier set up a apo lens or any enlarging lens is perfectly fine at wide open.
I will suggest there is some Depth of Focus , but I only close done two fstops to get better time.

Have you got that the wrong way round Bob?

The depth of field at the negative (not print) is around 0.082mm with a 90mm lens @ F5.6 with effective aperture F218 for 40X enlargement.
Theoretically you will get 8 lp/mm in the print assuming everything is perfect which it isn't likely to be. And assuming the software I'm using is correct.

 

[Bob Carnie]

The depth of field is considered at the lens camera stage, I sure I don't need to explain as the aperture is closed down the light is force to come into the camera at a more narrow
angle which creates a longer depth of acceptable focus as we close down, all things considered if we focus one third of the way into the area of the scene we want to hold sharp. the lower the apeture the greater possibility.
APO enlarging lenses as I know them are manufactured to focus on a single plane. this does not allow for the above depth of field theory which is very important in image capture. this term is not applied for enlarging.

Now I will not argue that closing down will possibly help( maybe on edges?? but I have never seen a difference, when I focus and enlarger I use wide open to get the crispest grain I can achieve and closing down does not give added sharpness IMO. I basically close down to get a good time for printing.
I use a laser alignment tool and glass carriers and normally or in most cases the lens I am using is slightly larger than normal. Also centering the bulb, lens , negative and easel blades have a huge impact on sharpness and edge definition.

I always set my easel first, by finding the center position, then I place the negative into direct center.. I never set the negative first and then move the easel to fit.

Have you got that the wrong way round Bob?

The depth of field at the negative (not print) is around 0.082mm with a 90mm lens @ F5.6 with effective aperture F218 for 40X enlargement.
Theoretically you will get 8 lp/mm in the print assuming everything is perfect which it isn't likely to be. And assuming the software I'm using is correct.

 

[gorbas]

Anybody having experience with using taking, normal focal lenght lens for gigantic (lets say - 20X>) enlargements? Hasselblad had one accessory mount with blank (camera/enlarger) end for this purpose?

 

[M Carter]

Anybody having experience with using taking, normal focal lenght lens for gigantic (lets say - 20X>) enlargements? Hasselblad had one accessory mount with blank (camera/enlarger) end for this purpose?

I'd love to hear about this as well...

 

[RobC]

I think it would require using a macro lens for best results. Try it and see.

Bear in mind that taking lenses aren't usually designed to be flat field. If they were, they would work better as enlarging lenses (if they can focus close enough like a macro lens can)

 

[semi-ambivalent]

Dear Chris,

First, a plug for the Versalab Parallel laser alignment tool.

Plug #2.
(Beseler 23CII XL. Built like a Checker Cab and about as straight. This device fixed that. Well worth the price if you're chasing that perfect print.)

s-a

 

[ic-racer]

I try not to use DOField or DOFocus with enlargers. Optical formulas, when used with enlargers, are 100% identical to view cameras if you consider the bellows to be extending from the lens board downward to the enlarging easel. In which case the light comes in from the subject (negative) through the lens to the paper. In that case the DOField is indeed up at the negative. The other theoretical way to look at it is to fix one side of the lens as a perfect plane and let all deviations of focus fall on the other 'plane' (which may not be so flat). In that case we can use a glass negative carrier as our reference plane and ascribe all focal discrepancy (flatness of field and non-parallelism) to deviations observed at the baseboard. In that case you might consider it as Bob pointed out with DOField at the baseboard. But I'd not criticize anyone for mentioning it one way or the other.

 

[chris77]

after another night of test runs..

good morning to you..

did some more tests on 25x enlargement from 6x7 negative.

1. as others have mentioned, the alignement of negative glass carrier and lens is crucial, while the alignement of the enlarger head (vertical) with the wall is a bit less important.

2. the apo componon 90 will show grain throughout the image in 25x enlargement.
although grain is definitely sharper and better defined in the center!
still working on even better alignement (using a meter and water level), one of these laser tools would come in handy here..


thanks so far for all the good input.
interesting stuff..

more tests to come.
also the comparison between this excellent schneider lens and the mamiya sekor z 110mm taking lens..

 

[RobC]

thats why I mention DoF at the negative. Until you realise how narrow it is you don't understand why alignment is so critical and using glass neg carriers keeps the neg in a very narrow plane which is required for optimum results, as is having the lens truly perpendicular to the negative. Margin for error at the print surface is much greater but that is not a reason not to get that as good as possible too.

 

[chris77]

thats why I mention DoF at the negative. Until you realise how narrow it is you don't understand why alignment is so critical and using glass neg carriers keeps the neg in a very narrow plane which is required for optimum results, as is having the lens truly perpendicular to the negative. Margin for error at the print surface is much greater but that is not a reason not to get that as good as possible too.

rob, what would you say, is the dof at the negative affected by the aperture of the lens? and if so, would the effect on the print be big enough to be measured? especially in a very big enlargement (25x or more).

 

[RobC]

Think of an enlarger as a macro camera because that is what it is. Study the maths and behaviour of macro photography as you approach and pass 1:1 magnification. The physics/maths changes once you get into 1:1+n territory or rather the normal simplified formula that is used to calculate DoF is not applicable. The full on correct formula is required.

Download PreDesigner software and study it. It will tell you the numbers once you get your head around it. There is an android app version too but the desktop version is more useable.


http://www.winlens.de/index.php?id=70

http://www.opticalsoftware.net/index.php/downloads/android_lens_calculator

 

[RobC]

rob, what would you say, is the dof at the negative affected by the aperture of the lens? and if so, would the effect on the print be big enough to be measured? especially in a very big enlargement (25x or more).

Aperture markings on lenses are the ratio of the aperture diameter to the focal length focusssed at infinity. When enlarging you are not focusssed at infinity, you are focussed well into the macro range. i.e. greater than 1:1 magnification. That means lens extension is great which makes the effective aperture much smaller. In the example I gave above that puts your print approx 3.5 meters from the lens. You must have high ceilings.

At effective aperture of F218 diffraction is very great which means useable DoF is very narrow before image sharpness degrades greatly. Simplified DoF formula no longer works. Full on correct formula is required. Or just use the software I gave link for to see what actual theoretical numbers are. If the red lines in lens Systems graph do not cross in the Orthometar lens type then you probably have settings wrong.

There is a bug in the desktop version for windows. When you first open the software you must maximise the window as the first thing you do. Otherwise flipping from Systems to Depth of Focus tabs doesn't work properly. I have reported this bug ages ago.

having said all that, the best you can do is make negative perfectly flat by using glass carriers and make lens perfectly perpendicular to negative.

To answer your question more directly using the software and my example above, if you close down from 5.6 to F11 the effective CoC in the print becomes 0.58mm and the lp/mm becomes only 4 which is low resolution and therefore will be visible to the human eye. So it is counter intuitive to assume that closing down the aperture will make things better. It does increase DoF at the negative BUT it also has a negative and undesirable effect at the print. This I would suggest is why Bob says he sees no benefit in closing down smaller than F5.6 and I would suggest you aim to use F5.6. If closing down more than that improves things then may indicate that your film is not flat or your lens is not perpendicular to the film.

All this assumes everything is setup perfectly which for most of us it isn't. As soon as something is out of whack in the system it can make a very big negative effect at large magnifications.

 

[Bob Carnie]

Ok so I have a practical question as I really cannot compete with Rob C on the theory..


So I put my 6 x7 negative in the enlarger , set up a 30 x40 magnification on the easel, I am using glass carrier and assume that I know how to laser align the negative stage, lens stage, and baseboard.

I focus at wide open for grain sharpness and make a test of the image....

I then stop down two stops and make a second test image..

Which one is sharper???

 

[chris77]

DoF markings on lenses are the ratio of the aperture diameter to the focal length focusssed at infinity. When enlarging you are not focusssed at infinity, you are focussed well into the macro range. i.e. greater than 1:1 magnification. That means lens extension is great which makes the effective aperture much smaller. In the example I gave above that puts your print approx 3.5 meters from the lens. You must have high ceilings.

At effective aperture of F218 diffraction is very great which means useable DoF is very narrow before image sharpness degrades greatly. Simplified DoF formula no longer works. Full on correct formula is required. Or just use the software I gave link for to see what actual theoretical numbers are. If the red lines in lens Systems graph do not cross in the Orthometar lens type then you probably have settings wrong.

There is a bug in the desktop version for windows. When you first open the software you must maximise the window as the first thing you do. Otherwise flipping from Systems to Depth of Focus tabs doesn't work properly. I have reported this bug ages ago.

having said all that, the best you can do is make negative perfectly flat by using glass carriers and make lens perfectly perpendicular to negative.

To answer your question more directly using the software and my example above, if you close down from 5.6 to F11 the effective CoC in the print becomes 0.58mm and the lp/mm becomes only 4 which is low resolution and therefore will be visible to the human eye. So it is counter intuitive to assume that closing down the aperture will make things better. It does increase DoF at the negative BUT it also has a negative and undesirable effect at the print. This I would suggest is why Bob says he sees no benefit in closing down smaller than F5.6 and I would suggest you aim to use F5.6. If closing down more than that improves things then may indicate that your film is not flat or your lens is not perpendicular to the film.

All this assumes everything is setup perfectly which for most of us it isn't. As soon as something is out of whack in the system it can make a very big negative effect at large magnifications.

that is a fine answer to my question.
thank you very much for taking the time to explain it so well and for the links.

 

[RalphLambrecht]

could it be the taking lens?How do the corners compare to the center in the negative on the light table with a loupe?The corners may not be as sharp as the center to begin with.You can't expect it to get sharper in the enlargement.

 

[chris77]

Ok so I have a practical question as I really cannot compete with Rob C on the theory..


So I put my 6 x7 negative in the enlarger , set up a 30 x40 magnification on the easel, I am using glass carrier and assume that I know how to laser align the negative stage, lens stage, and baseboard.

I focus at wide open for grain sharpness and make a test of the image....

I then stop down two stops and make a second test image..

Which one is sharper???

i guess that depends on the lens you are using..
the schneider apo 90 is supposed to be sharpest around 5.6

given that everything is perfectly aligned.
can it be done?
i believe so, thats why i have been spending half of the afternoon with my 3 best friends.
level, meter, and screwdriver..

 

[Bob Carnie]

Any Enlarging Lens.

 

[kobaltus]

The schneider apo 90 sharpest aperture is 8.