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

[Bob Carnie]

why? please explain

The schneider apo 90 sharpest aperture is 8.

 

[RobC]

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 can't answer that. I'd say 5.6 should be about as good as it gets but if you try 10 supposedly identical lenses one of them will likely out perform the other 9. One may be best at f8 and another at f11 and another at f5.6.

When it comes down to your real world practical evaluation you find which performs best in your system.

You can use software all you like to understand the theoretical side of it but practical tests always trump theory.

 

[Bob Carnie]

Rob

All I can rely on is real world practical evaluation and I have found that once its focused its not getting any sharper by stopping down. If you are
grain sharp on the paper - and if the print looks grain sharp - this is all I can hope for.

I think workers just need to do this simple test, (mind you without a glass carrier to stop any negative movement which would flaw the test), so use glass and a good grain scope , my observations after a few prints verify's my opinion.

Now when we are talking about different lenses I am not a lens designer nor am I well qualified to discuss this on a theoretical basis.( I basically am a simple printmaker making prints for others) to date I have been gainfully employed doing this for 39 years.
I can imagine there is a real reason why some lenses are indeed better than others. But from a practical layman point of view , Depth of Field is not a relevant issue in real world enlarging printing. IMHO of course.

I do appreciate your points though.
I did find a nice jump in quality when I went to a APO rodagon over a regular rodagan. This was a visual improvement and I cannot
give a reason for this.
I have also found that a 90 Apo give me much better edge sharpness than an 80 Apo, but I can figure out that the extra coverage is pushing
the light into the sweet spot of a given lens if there is such a thing.. That too I can see but not give the theory behind.

Bob

I can't answer that. I'd say 5.6 should be about as good as it gets but if you try 10 supposedly identical lenses one of them will likely out perform the other 9. One may be best at f8 and another at f11 and another at f5.6.

When it comes down to your real world practical evaluation you find which performs best in your system.

You can use software all you like to understand the theoretical side of it but practical tests always trump theory.

 

[chris77]

Rob

All I can rely on is real world practical evaluation and I have found that once its focused its not getting any sharper by stopping down. If you are
grain sharp on the paper - and if the print looks grain sharp - this is all I can hope for.

I think workers just need to do this simple test, (mind you without a glass carrier to stop any negative movement which would flaw the test), so use glass and a good grain scope , my observations after a few prints verify's my opinion.

Now when we are talking about different lenses I am not a lens designer nor am I well qualified to discuss this on a theoretical basis.( I basically am a simple printmaker making prints for others) to date I have been gainfully employed doing this for 39 years.
I can imagine there is a real reason why some lenses are indeed better than others. But from a practical layman point of view , Depth of Field is not a relevant issue in real world enlarging printing. IMHO of course.

I do appreciate your points though.

Bob

Very interesting input, bob. thanks!
always good to hear from pros, and i am saying this because in the professinal life real world experience rules over everything else (once a certain understanding is there).

but out of my perspective, trying to do very big enlarging from 6x7, my question would be the opposite.
do i loose sharpness stopping down?
thinking stopping down as last resort to balance out tiny imperfections in alignement..

 

[RobC]

Bob, as you pointed out, you use a lens of a bit longer focal length than is required. This is good policy as most lens MTF charts show falloff of performance towards the corners of coverage. By using the slightly longer focal length you take the lowest performing part of the lens out of the equation.

But for people like me who who don't have high ceilings or low counter top height, this is not always possible so we're stuck with using the standard focal lengths unless we move to horizontal enlarging but that may not be possible either.

Stopping down seems to lift the performance up. But the sweet spot is usually obtained by F5.6 or F8. Maybe F11 or higher for longer focal length lenses.

 

[Bob Carnie]

You are taking a real chance by thinking that stopping down on a mural size print is going to take out imperfections

You will not lose sharpness by stopping down and I really doubt you will be helped with alignment out of whack.

I will give you an example of a predicament I am currently in.

I am taking a 35mm strip 6 frames up to 40 inches on the long side, I need to use my 11 x14 enlarger due to the length of the film( will not fit in Omega)
I am finding the max I can get is about 40 inches but I am getting lens fall off at one end due to the lens I am using.. no matter what I do
the last frame is lighter( I can fix this by darkening that frame) but its also slightly soft.
I do not have any more height to raise the head and use a longer lens which would then give me proper coverage.
I am screwed so to speak, and I may actually have to cut the joice in the ceiling to raise the head..
I have made a print and for 95% of the people it looks ok, but I know its wrong and a compromise..


I kind of think you may be in this boat as well until you figure out how to make sure your alignment issues are ok... Yes you will be able to make an art
print. most people may thing one edge out of focus is cool and you are special.. but from a nit picking viewpoint we both knows this sucks.

Very interesting input, bob. thanks!
always good to hear from pros, and i am saying this because in the professinal life real world experience rules over everything else (once a certain understanding is there).

but out of my perspective, trying to do very big enlarging from 6x7, my question would be the opposite.
do i loose sharpness stopping down?
thinking stopping down as last resort to balance out tiny imperfections in alignement..

 

[chris77]

You are taking a real chance by thinking that stopping down on a mural size print is going to take out imperfections

You will not lose sharpness by stopping down and I really doubt you will be helped with alignment out of whack.

I will give you an example of a predicament I am currently in.

I am taking a 35mm strip 6 frames up to 40 inches on the long side, I need to use my 11 x14 enlarger due to the length of the film( will not fit in Omega)
I am finding the max I can get is about 40 inches but I am getting lens fall off at one end due to the lens I am using.. no matter what I do
the last frame is lighter( I can fix this by darkening that frame) but its also slightly soft.
I do not have any more height to raise the head and use a longer lens which would then give me proper coverage.
I am screwed so to speak, and I may actually have to cut the joice in the ceiling to raise the head..
I have made a print and for 95% of the people it looks ok, but I know its wrong and a compromise..


I kind of think you may be in this boat as well until you figure out how to make sure your alignment issues are ok... Yes you will be able to make an art
print. most people may thing one edge out of focus is cool and you are special.. but from a nit picking viewpoint we both knows this sucks.

sure we do. do you think i would spend the whole weekend aligning planes?
i am a perfectionist wihout a laser tool.
so i am working with what i have got in order to see if i can get there.
grain sharpness in all for corners of a 25x enlargement. thats 1.8x1.5 meters.

meanwhile training my eye to get perfect focus from 3 meters distance. funny how well it works with some training, given a very sharp neg with written word, or other high contrast structure..

so i dont want to stop down to save me from aligning.. no way, and its clear to me it wouldnt work anyway..
cant find sharpness where there is none ...

 

[RobC]

At 25X enlargement you should be fine at F8 or even F11 at a push. At 40X everything becomes a lot more critical.

So you may be worrying about something that is not a real world problem.

If print is sharp in center and equi sharp in all four but not as sharp as center then its likely a lens issue.

I just checked the MTF for the current apo hm componon 90 and at F4.5 there is significant falloff of performance towards the corners. They don't show charts for f5.6 but they do for F8 by which time the performance has been lifted up. So it may just be that your particular lens sweet spot is F8 as suggested by kobaltus.

 

[Bob Carnie]

Too bad your not in Toronto , I would lend you my laser tool ..

Also for fine focus , have someone man the lens knob , the other at your paper looking for grain.. if you practice enough it takes about 15 seconds to nail the grain.. I would not want to be
trying to do this alone or with out grain focus. We do this all the time on the Omegas.

All my Durst mural enlargers had a motor hand grip to focus which made it very easy.

For my 11 x14 Devere , I focus easily at paper stage as the knobs are right there.

sure we do. do you think i would spend the whole weekend aligning planes?
i am a perfectionist wihout a laser tool.
so i am working with what i have got in order to see if i can get there.
grain sharpness in all for corners of a 25x enlargement. thats 1.8x1.5 meters.

meanwhile training my eye to get perfect focus from 3 meters distance. funny how well it works with some training, given a very sharp neg with written word, or other high contrast structure..

so i dont want to stop down to save me from aligning.. no way, and its clear to me it wouldnt work anyway..
cant find sharpness where there is none ...

 

[blindpig]

Bob I had a similar problem(back in the day),was trapped and couldn't find the extension needed for clients print enlargement so finally resorted to a 45 degree first surface mirror beneath the lens which in my case gave me the length needed for a longer lens(required flipping the negative over to compensate for the image reversal caused by the mirror) but saved the job for me.
Just a thought(of course it introduces another alignment problem.But it's" no hill for a stepper",LOL!).
Don

 

[Bob Carnie]

Well we all know Drew invented photography, I believe Mustafa is moving to California to work with him.

Nice summation on lens design.. I have always found lens flare and surrounding object flare to be a real bummer for sharp type in images and in the mural rooms I cut my teeth in we were
very aware of this lesser known evil


QUOTE=Michael R 1974;1953766342]It just depends on how well corrected the lens is wide open. Assuming alignment is not an issue and you don't need depth of field/depth of focus, the performance of any lens (taking, enlarging, whatever) is always a balancing act between correction for optical aberrations, and diffraction. When you stop down any lens, some aberrations (if present) are lessened, but diffraction (bad) increases, so it's a trade-off. If a lens is fully corrected for aberrations wide open, it is said to be "diffraction limited", meaning that stopping down will only result in more diffraction and won't improve any other characteristics. However in practice very few lenses are diffraction limited at their widest apertures (even Apo-whatevers), so strictly from an optical performance perspective they usually have an optimal aperture somewhere smaller than wide open. Go wider than the "optimal" aperture and aberrations more than offset the improvement from reduced diffraction. Stop down further than the optimal aperture and diffraction more than offsets the improvement from reduced aberrations. As an example, for Apo-Rodagon enlarging lenses, I think Rodenstock indicates closing down one stop from wide open maxes out performance, while for their non-Apo lenses it is two stops. I don't think most current apochromatic lenses are true apo.

Note this is a generalized explanation and doesn't address things like optimal magnification range.

On the other hand, depending on the case, magnification etc. there is no guarantee what can be measured on an optical bench will be noticeable to you in the print (unless you're Drew Wiley). So if you see absolutely no differences between wide open and closed down a stop (even at the edges/corners), ignore all this and just make prints.[/QUOTE]

 

[cowanw]

It just depends on how well corrected the lens is wide open. Assuming alignment is not an issue, you don't need depth of field/depth of focus, and focus is perfect, the performance of any lens (taking, enlarging, whatever) is always a balancing act between correction for optical aberrations, and diffraction.

As an example, I got it in my head that I wanted to try a 300 mm lens on my 8x10 enlarger, and started with a 300 Congo Tessar, which I got cheaply.
As a f4.5 I thought it would be nice and bright to focus with, but found that wide open the image (at such close distances, compared to it being a taking lens) the image was so soft that focusing was only possible as guesswork. Nevertheless the lens stopped down to f8 functioned dramatically better. In the meantime I have also acquired a Companon and a Rodagon for comparison and they both are sharp wide open as one would expect at enlarging distances.
I asked the lenses and they spoke!

 

[Bob Carnie]

Don
No room in my darkroom for this solution... Marco B who is a member here has a setup at Gallery 44 that may work, I donated a 5x7 enlarger to them and not sure if its up or not, this may be my solution locally without cutting into floor joice.

Bob

Bob I had a similar problem(back in the day),was trapped and couldn't find the extension needed for clients print enlargement so finally resorted to a 45 degree first surface mirror beneath the lens which in my case gave me the length needed for a longer lens(required flipping the negative over to compensate for the image reversal caused by the mirror) but saved the job for me.
Just a thought(of course it introduces another alignment problem.But it's" no hill for a stepper",LOL!).
Don

 

[RobC]

But from a practical layman point of view , Depth of Field is not a relevant issue in real world enlarging printing. IMHO of course.

I only intoroduced DoF into the discussion so that the OP understands why alignment is so important. Once you know alignment and film flatness is key to sharp prints, particularly at large magnifications, then I agree that any consideration of DoF is not necessary because its trumped by alignment which takes care of it.

BUT when you are working at the absolute limits of what a lens is capable of (large magnifications) then using the software is handy to tell you what the theoretical limits are and that you are wasting your time trying to go beyond them.

 

[cowanw]

Not quite germane to the topic but tilting the easel for perspective correction/distortion may be a reason for stopping down.

 

[Bob Carnie]

I just got pm'd to state the situation I am in with the magnification of the strip of film

I am about to tackle this problem and will post the variables here so all can see, I will also list the weapons(lenses) I have at my disposal to work with as well the maximum height I am allowed by the enlarger.

I would like to wait until I am ready to redo this image as it requires quite a set up of trays, I am printing silver next two weeks so I will post the exact predicament. And maybe a better lens focal length may show itself.

I currently have 150, 180 , 240, 300 and 360mm lenses for this enlarger so you would think I was covered.

 

[MattKing]

Is there a 6x7 camera system that uses a focal plane shutter for which a macro lens was made?

Could the Mamiya RB67 140mm macro lens be adapted for the purpose?

 

[RobC]

Is there a 6x7 camera system that uses a focal plane shutter for which a macro lens was made?

Could the Mamiya RB67 140mm macro lens be adapted for the purpose?

If you can mount it to the enlarger lensboard then it will work. How well it will work is another question. And how easy it is to focus could also be an issue since you have lens to film focus and lens focus to deal with but not insurmounatable I would have thought.

try it and let us know how you get on.


Just remember that enalrging lenses are designed and highly corrected for flat field so will likely always out perform camera taking lenses used for enlarging. Is it really worth the hassle. You're very unlikely to discover a magic bullet.

 

[MattKing]

If you can mount it to the enlarger lensboard then it will work. How well it will work is another question. And how easy it is to focus could also be an issue since you have lens to film focus and lens focus to deal with but not insurmounatable I would have thought.

try it and let us know how you get on.


Just remember that enalrging lenses are designed and highly corrected for flat field so will likely always out perform camera taking lenses used for enlarging. Is it really worth the hassle. You're very unlikely to discover a magic bullet.

The RB67 lenses depend on the camera's bellows for focusing, so they should be suitable. I just don't know how one would deal with the built in leaf shutters.

 

[RobC]

you can tell I'm not an RB67 user then

 

[ic-racer]

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???

At magnifying to 30x40, even with the lens wide-open, your effective aperture is so small, that any additional stopping down may lead to mush. One can use mathematics to calculate the actual projected size of the Airy disks (caused by diffraction) at various apertures and magnifications, but an experienced projection printer can just use his-or-her eyes to determine what is best.

 

[ic-racer]

Since both diffraction and de-focus can wreak havoc in projection printing, the view-camera focusing method of Hansma can be adapted to the enlarger.
Focus the enlarger by moving the head on the column; this is like focusing the view camera with the rear standard. Focus on the center of the image and note where the column is. Then focus on any other part of the negative that may be out of plane or affected by curvature. Do this without touching the focus knob, by moving the enlarger head. Then set the head to the point exactly half-way between the extremes. This will optimize your depth of field at any aperture.

If you want, you can actually calculate the aperture to get it all in focus based on the focus spread (based on view camera focus equation of Hansma).

N = 20/(1+M) * square root of 'dv'

N = Aperture number
20 = user dependent constant (circle of confusion 0.15mm for me)
M = magnification
'dv' = millimeters of focal depth measured on the enlarger column (between your high focus and low focus points).

 

[chris77]

some results..

well. another night of testing.

to make it short, differences are subtle, and without a high precision alignement tool i wont be able to get more out of it.
distance between durst m800 (negative plane) and wall: 2.5 meters.

the sekor z 110mm taking lens: pretty sharp with good sharpness in the corners, very little light fallof @ f8
but somehow the image doesnt look right. as if it was compressed in a way. also while focussing wide open there was a kind of "halo". when i look at the test strips it looks "congested". dont know how to explain better.
maybe the 110mm is not suitable.

componon-s 100mm: image 10% bigger so difficult to tell if its really less sharp, i doubt it. image quality is improved, image looks "steadier" @ f11, equal field throughout the image.

apo componon 90mm: image is again 10%bigger, but resolution and sharpness are at least equal to componon s (a bit sharper). contrasts are improved to my eye @ f8
@f11 even sharper! beats the componon-s, not by a lot though..

conclusion. i guess it needs even better alignement. i did what is possible without precision tools. measured the four corners of negative stage to the lens stage. would need a caliper gauge to get more precise.
controlled these measurements with a water level, looking very good, and took care to get the whole enlarger in good alignement with the wall (which is not 100% straight but shouldnt matter)

so thats it from me. not very scientific i guess.
i am actually somewhat surprised to not see more difference between the two componons.
maybe i will do one more test tonight, and this time move the enlarger forward to balance the focal difference.
should give better results..

 

[RobC]

Just don't forget that you are using those componons way outside of their design range so there is no reason to expect one to be much better than the other.

If you ever see a Rodagon-G 105 up for sale then grab it. It won't be cheap and they are almost as rare as rocking horse pooh.

 

[chris77]

Just don't forget that you are using those componons way outside of their design range so there is no reason to expect one to be much better than the other.

If you ever see a Rodagon-G 105 up for sale then grab it. It won't be cheap and they are almost as rare as rocking horse pooh.

hmm.. well, i guess you are right. 25x is relly the limit (even for the apo 90 (0.25 - 0.04))
maybe tonight i will go easy on them
15x should be a whole different story then ...