Enlarging lenses and neutral density filtersgreenspun.com : LUSENET : Large format photography : One Thread
Having just read Ctein's book Post Exposure, I have begun to think about enlarger lens sharpness. My Schneider 150mm/5.6 Componon-S lens has, according to Ctein, its best sharpness at f/8 or f/11. Even with f/11 on my Saunders 4550 XLG enlarger, the exposure times are very short in the few seconds range. I would like to keep my times around 10-20 seconds. Often this means using f/22 on my favorite negs. The light on this enlarger must be quite bright. My enlarger does not have any filter drawers above or below the lens, or ability to use gels. I have the VCCE head and NOT a color head.
My question is whether it would be advisable to use a screw-on neutral density filter on the lens to achieve a one or two stop reduction in light so that I can use f/11, but still have longer times for my exposures as noted above. Is this just trying to guild the lily? And would this just be adding in problems by adding something into the light path below the lens and therefore offset any gains in sharpness by trying to stay at the so-called optimal aperture?
Thanks for any comments!
-- Scott Jones (email@example.com), December 13, 2001
I'm not familiar with the VCCE head, but on my 4500 II w. Dichoric head there's a knob that, when turned, gives you about two stops less light - it's used for burning in.
Does the VCCE head not come with this feature? If so, you could expose at f11, and with the knob turned, effectively be exposing at f/22. If not, then sorry I wasted your time :-)
I've also read/heard that the last thing you want to do is put a filter in front of the lens when enlarging....
-- Ken Miller (firstname.lastname@example.org), December 13, 2001.
I read Ctein's book and had the same idea you did -- and the same concerns that I might be doing more harm than good. I nonetheless bought a two-stop ND filter that I screw into the front filter thread on my 135 mm el-Nikkor. The prints I have made using the filter look very sharp and contrasty at all enlargement sizes up to 16 X 20, which is as big as I can go in my darkroom.
What I have not bothered to do, however, is to make comparison prints with and without the filter, so I can make no claims that using the optimum aperture with the filter produces a result superior to that to be obtained with a smaller aperture and no filter. I can say that putting the ND filter on the front of the lens produced no obviously disasterous effects.
-- David Mark (email@example.com), December 14, 2001.
I'm also considering using below the lens filtration. According to Steve Anchell in his book (The Variable Control Print Manual), after testing, he could find no discernable difference between using filters above or below the lens. Kodak Wratten neutral density filters are at least as high quality as VC printing filters, so that which applies to the latter should also apply to the former.
You might look up his book and try his testing methodology. For that matter, it would also make sense to try his test on whether there's a discernable difference between printing at f11 and f22. Theoretically, there's a difference. But, can one see it in the print for the typical enlargements that you use?
In selecting enlarging lens apertures, Rudolf Kinslake (Lenses in Photography), a well known authority on lenses, suggests that the linear aperture should be no less than 1 percent of the lens to paper distance. The linear aperture is Focal_Length/f-stop. This would imply that f22 on a 150mm lense would be appropriate for lens to paper distances up to about 27 inches. Again, try testing to see if it really makes a difference in practice.
-- neil poulsen (firstname.lastname@example.org), December 14, 2001.
One thing you probably should check before you get too concerned is that _your_ lens works the same as Ctein's. There's always some positional uncertainty (slop) when you build something and your lens may be amazing and sharpest at 5.6 or you may have to stop down to f16 to get to the sharpest point. There's also the issue of making sure that your enlarger is aligned and properly damped from vibration and everything.
Second, you may want to look into getting some kind of regulated dimmer for your head. With a lot of lights (and I'm not sure about the one you have, someone else can hopefully give you a definite answer), if you reduce the voltage to the bulb you can 1) make the light dimmer 2) reduce aging of the bulb (hugely) and 3) make the bulb last much longer. It may give you longer printing times with larger apertures and increase how long your equipment works.
-- Nathaniel Paust (email@example.com), December 14, 2001.
Be careful when using a dimmer. You might change the color temperature of the light emitted by your enlarger. This may impact on your images, due to the sensitivity of enlarging paper, especially VC, to different parts of the color spectrum. It may work fine. Also, check with Saunders to see if this will have an adverse impact the enlarger's transformer.
-- Dave Karp (firstname.lastname@example.org), December 14, 2001.
Is there a possibility of installing a neutral density gel filter above the negative somewhere? This would eliminate the concern over filters below the lens.
-- David Rose (DERose1@msn.com), December 14, 2001.
You know after reading all of this, I made a test in my darkroom of one 8x10 print with fine detail that I normally print at 16 seconds at f/22 with my 150mm enlarging lens at full frame. I made equivalent prints at all the f/stops from 5.6 to 32. I then randomly shuffled them and examined under magnification. Amazingly f/22 looked the best. The only really noticeable difference was f/5.6 looked bad. All the rest looked very similar if not identical.
Is all this sharpness testing stuff just way over the top for real life prints? I am very fastidious and exacting in my processes and approach to things and it seems that real life results just may not need this degree of attention to detail. What do you think?
-- Scott Jones (email@example.com), December 14, 2001.
It might be. Depends on the degree of enlargement and your entire system actually. Ctein was basically saying that an enlarging lens that is at its best at wider apertures will resolve more (less losses to diffraction). However, if your lens/film combination was good enough to give you about 50-60 lpmm on the neg, and you were enlarging 2X, it is highly unlikely that you will notice the differences in an 8x10 print - an enlarging lens set at f/16 should still be capable of resolving the necessary information. Might show up at higher enlargements since the demand for resolution gets larger there. If your best print appeared at f/22, it is also likely that your negative is sagging in the carrier (I'm assuming you are using glassless). Thus, the small aperture helps to provide depth of focus and resolves things more uniformly across the entire negative, rather than the smaller apertures that resolve some parts very well and have some parts subtly out of focus).
IMHO, a lot of Ctein's concerns apply more for MF and 35mm folks whose enlargement ratios are much greater. Having said all that, I think it is a good idea to work at the aperture the enlarging lens is best at and try to adjust other settings to give you the exposure imes you like working with (to facilitate dodging and burning etc). I don't know much about your enlarger but the easiest way to reduce light output might be the following. Expose a sheet of film completely to light and develop it (you can figure out how much density you would like to develop it to - each 0.3 density unit reduces the light by a stop). Place this somewhere above the negative, preferably taped to the head (but push comes to shove, you can even try above the carrier. I would avoid placing things in the optical path, simply because it is another thing you will have to keep scrupulously clean. Out of the optical path, it is less of a concern. OTHO, if you're getting the results you want, that allow you to express your photographic intention, why bother with all this? If the final print looks good, that is all that counts.
Good luck, DJ
-- N Dhananjay (firstname.lastname@example.org), December 14, 2001.