Some enlarging questions

NDP_2010

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I am new to the world of film printing and have done some black and whites.

I am curious with a few questions.

What is the advanatage of stopping down an enlarging lens? Is there any advanatage in having a fast enlarging lens?

I also have a few questions about exposure time.

I noticed that i left a few pictures enlarging for too long and the contrast was quite low and the picture was very dark. I tried a shorter time and the picture had much more contrast.

If i enlarge for a short period of time, does this mean highlight details will not be captured? If i have a picture where the forground is quite dark, can i ever effectively recapture these details while keeping the picture relatively contrasty or is it impossible as the picture was not taken correctly.

Thanks.
 

Marek Warunkiewicz

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Hi, here are some answers...

***What is the advantage of stopping down an enlarging lens?***

Better sharpness from edge to edge. Most lenses have a sweet spot of sharpness/acutance etc around 2 or 3 stops down from the most wide aperture.

***Is there any advantage in having a fast enlarging lens?***

Yes there is. basically it concerns the point above and printing speed. When you have a 2.8 lens and stop down two stops you get 5.6. Assume your time to get a good print is 12 seconds at 5.6. If you had a 5.6 lens and you stopped it down to 11, your time would be 48 seconds. It's all about the exposure time.

The ***dark contrast print*** question has more to do with your negative and contrast filter. To really answer that question we would need to know the paper used, time(s) of exposure of the different prints, developer and time in developer, the contrast filter used (if any) and ideally a scan of the negative prints.

You can capture a wide range of tones in a negative, it's all about the exposure and development (Zone system).

Marek
 

RalphLambrecht

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I see another advantage in using a 'fast' enlarging lens. Even if you enlarge at the 2-3 stops down from wide open, a wide-open lens will make it easier to accurately focus the image on the base board before you stop it down and enlarge to get the most out of the lens.
 

RalphLambrecht

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It's hard to answer this one without knowing what your printing method exactly is, but I can offer two articles, which may help you:

http://www.waybeyondmonochrome.com/WBM2/TOC_files/TimingExposureEd2.pdf

http://www.waybeyondmonochrome.com/WBM2/TOC_files/BasicPrintingEd2.pdf
 

Ian C

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In answer to your first question, there are several reasons to use a smaller aperture on an enlarging lens.

1. Lenses can be slightly sharper closed 1 or 2 stops. Thus an f/2.8 lens might be slightly sharper closed down to f/4 or f/5.6 (any difference is likely to be small).

2. If you want to give some parts of the print more or less than the basic overall exposure—called printing in and dodging—it’s useful to use a smaller aperture to give you sufficient time to perform these operations.

3. Composition and gross focusing of the projection is most easily done with the aperture fully open for the brightest, most easily seen image. But when you fine tune the focus with a grain focuser the image may be uncomfortably bright for your darkroom-adjusted vision. By closing down to the working aperture you’ll find grain focusing the dimmer image more comfortable to your eye and the grain is more easily resolved with the lens stopped down 1 or more stops.

4. In some cases, if you have no glass negative carrier and the negative isn’t as flat as you’d like, closing the lens may increase depth of focus at the negative sufficiently to give a slightly sharper print.

5. Though not a problem with modern lenses, older lenses sometimes had a defect called spherical aberration. Such a lens might be focused wide open, but would change focus as the aperture was closed down to make the exposure. That’s why darkroom workers were often cautioned to refine the focus after stopping down to the working aperture to compensate for focus shift due to possible spherical aberration in the lens.

The advantages of a fast lens are:

1. Brighter, more easily seen image for faster composition and gross focusing.

2. Potentially faster printing time. For example, an f/2.8 lens closed 2 stops at f/5.6 will print in half the time of an f/4 lens closed 2 stops at f/8.

For the second question, longer exposures don’t generally result in reduced contrast. I suggest checking carefully for light leaks prior to the lens. Some enlargers spill light from around the negative carrier or elsewhere striking the wall near the enlarger and bouncing back to the paper. This is exacerbated by the greater reflectance of a white or light colored wall close to the enlarger.

It’s likely not much of a problem with a large aperture as the total exposure time is so short that the spill light has little effect. But with a small aperture the printing time is much longer. It’s possible that such a long printing time will allow the spill light to “flash” the paper. If so, then the contrast will be reduced. That might explain your observation.
 

Bob Carnie

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I think a lot of expectations of improved sharpness by closing down is highly overrated.

An APO enlarging lens is designed be sharp at open apetures.
We in fact focus on the grain , with a grain focuser, do we not.

Can anyone here say that the grain gets sharper as you close down an Apo lens.
I for one have never seen this effect when using glass carriers in my darkroom. The grain is sharp, my print is sharp.

I am only stating what I see every time I focus, if anyone here can explain to me the theory of closing down improving grain sharpness, I am open to here it.
 

Bob Carnie

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I should add , the theory should also be backed up with actual prints showing better sharpness when one is using an aligned enlarger, good optics, image centered to the neg, condensor and bulb. Also I would expect a glass carrier.
 

fotch

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I think what it means that if something is not perfectly aligned, or parallel, the slight increase in depth of field will help in edge to edge sharpness. Not everyone has top of the line equipment nor the skills and patience to get the enlarger, lens board, easel, etc., into perfect alignment.
 

Bob Carnie

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To my knowledge we are not talking depth of field , rather depth of focus , which with an Apo enlarging lens there is extremely little or none.

 

fotch

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Bob Carnie said:
To my knowledge we are not talking depth of field , rather depth of focus , which with an Apo enlarging lens there is extremely little or none.
Click to expand...

Bob, I will admit this is way over my pay grade, however, in what the OP asked "advantage of stopping down an enlarging lens?", so,how is either different? Both depth of field and depth of focus are strongly dependent on changes in aperture, are they not?

The APO lens is not the average enlarger lens so I am not sure how that fits in to the answer for the original question.
 

RalphLambrecht

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As with taking lenses, stopping down an enlarging lens will improve image quality and cut down on lens aberrations. This is especially true and visible in the image the further you get away from the image center.

I find it easier to use the grain focuser with a wide open enlarger lens, because I can more easily see the 'snap' in and out of focus.

Depth of field (at the baseboard) and depth of focus (at the negative stage) are in a geometrical relationship with each other (see attached illustration).
 

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ic-racer

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The optimal aperture for any lens is not some nebulous guess at how many stops down to go. The published MTF curves and light fall off curves tell all.
The DOF is related to aperture size and magnification and acceptable size of circles of confusion. It is independent of lens design or construction or focal length.
 

Bob Carnie

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On a very practical level. Visually looking at prints

With all good things in place , like I suggested above.

Focus on grain with paper under grain scope.

make a print wide open , make a print two stop downs adjust time.

Do not re focus between.

Look at the prints.. If someone here can honestly say they say the one print is sharper than the other I will eat my shorts.
 

RalphLambrecht

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Bob

You should be able to see at least a difference in edge sharpness from wide-open to a couple of stops down. If you can't, you must have some wonderful lenses. Try the test with a picture of a resolution target and you should see it.

I don't have a lot of enlarging-lens MTFs, but I have attached one for a Rodenstock Rogonar-S. One can clearly see the performance difference between f/2.8 and f/5.6.

Regardless of this evidence, I'm not holding you to your promise. I don't think it's healthy.
 

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Bob Carnie

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I shop at Victoria Secrets

 

Bob Carnie

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I should add that for each format I am using a longer lens.
ie

35 - 80mm
6x6 ,6x7 - 90mm
6x9 - 105mm
4x5 -150 and 180mm

I am still convinced that sharp grain at wide open will not be sharper grain at 2 stops down.

There are a lot of factors that contribute to edge defects, but if you do all the good things your edges are sharp wide open. At least in my darkroom
 

RalphLambrecht

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Bob Carnie said:
... I am still convinced that sharp grain at wide open will not be sharper grain at 2 stops down.

There are a lot of factors that contribute to edge defects, but if you do all the good things your edges are sharp wide open. At least in my darkroom
Click to expand...

Bob

I already provided evidence to the contrary. All lenses suffer from aberrations to some extend. Enlarging lenses not excluded. Some of these aberration effects are reduced when the lens is stopped down.

Maybe your lenses suffer from a focus shift when stopping them down, offsetting the effect?
 

Ian Grant

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For many years I'd have agreed with Ralph, and that's how the lenses I used behaved in the 60's and early 70's.

However at some point I had to use a Rokkor lens wide open for some 20x16 prints and was amazed that the grain was sharp from the edges/corners through to the center. My Schneider Componon's are the same.

There may be a slight difference but unless you're printing Technical Pan (or similar) it's difficult to spot. Modern enlarger lenses have excellent flat field optimisation so should perform well wide open.

Ian
 

Bob Carnie

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It should be pointed out that I am only referring to grain sharpness within the print. I do understand falloff , abberations at the edge,of large prints can be problematic.

I too close down the lens, mainly for optimum printing times,

but if we are talking about focusing on a nose of a subject, being grain sharp then printing wide open, then closing down without refocusing and adjusting time, and then telling me the nose is sharper of a subject on the second print , I will start making the stew of my shorts.

Its really simple make two prints,
 

ic-racer

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Bob Carnie said:
I should add that for each format I am using a longer lens.
ie
Click to expand...

Yes this holds true by the MTF charts. When looking at the MTF charts, only go out to 50% on the X axis. Same with the light falloff chart; only go out to 50%. Then it is evident that larger apertures will be OK in this case because you are only using the center of the image circle. But, as I indicated earlier you really need to look at the MTF cart of the lens in question rather than making generalizations. For example, the Rogonar-S MTF chart posted earlier shows different characteristics than the Schneider lenses I use.

Also, a little clarification and explanation of MTF charts. We know from physics that the lens will have the least diffraction wide open. And it can be that the 'Line Pair Per Millimeter' readings on the center of the field will be greatest when wide open. However, the contrast of those line pairs will be suffering. This is one of the reasons for going with the MTF chart as it takes into consideration the contrast. So, that is why we see the center of the Rogonar-S lens produce a better MTF when stopped down but that characteristic should not be applied to all enlarging lenses. (See below).
 
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ic-racer

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Just to show that you shouldn't generalize comments about enlarging lenses, here is the MTF of a lens I use. It shows the following:
1) Wicked sharp in the center even when wide open f4 (probably better coated than the Rogonar S and smaller lens elements)
2) Sharper at the corners at F8 than F5.6 BUT...
3) If you only use the center of the lens (ie use it for a smaller format negative) it will be better overall at the wider aperture (what Bob is saying).


The 3 graphs across are F4, F5.6 and F8 in that order.
 

Ian Grant

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It's like the diffraction issue at small apertures.

Actual reality in final images doesn't match the theory or even tests because the criteria in practice aren't an optical bench.

That doesn't mean either is wrong rather that it's possible to get great prints or images when theory is chasing it's own tail.

It's about knowing your own equipment and not going by spurious tests.

Ian
 

RalphLambrecht

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I agree with this and your and Bob's comment about using longer lenses (that definitely helps, because you are trimming off the problematic part of the MTF), but I have one question:

You said, you're using this type of lens. But, this is a f=45mm lens and, therefore, not a 'longer' lens even for 35mm. What 'smaller format negative' are you using this lens for?
 
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