alan_gibson6

I can't comment on the ease of tilting telephotos, nor on relative

qualities, because I don't use such long lenses.

<p>

Howard: what format are you using? Ellis comments that the i.c. of

the 270T is only 160mm, which means you wouldn't be able to tilt it

at all on 5x4! Even on 2.25 sq, it would only give you about 8

degrees, which is hardly enough to get the ground in Scheimpflug.

Tilting any lens about the rear node will tilt the plane of focus

without moving the image. An ordinary lens has this point in the

lens, so a physical tilt on the camera has this effect. A telephoto

lens has the rear node somewhat in front of the lens, so to tilt

about the rear node will involve a tilt and a shift and a bellows

movement.

I'm not convinced that there would be much difference between 2

inversions of the tank every 30 seconds compared to 4 inversions

every minute. The total agitation is the same, just more spread out.

If anything, I suppose the fourth inversion of the 4-every-minute

might have less effect than the first, so this regime might give a

little less overall agitation, giving lower contrast and slower speed.

<p>

When I try a new film/developer, I usually test it with my own regime

(which is 5 inversions every 30 seconds for 35mm). It's bad enough

keeping notes of different temperatures etc, I can't keep track of

agitation regimes as well.

I don't know if it is the best one, but a very good book is "The

Variable Contrast Printing Manual", Steve Anchell, Focal Press, 1997.

It sounds as if your first camera had dust inside it, which was

attracted to the film. You should clean the dust from your camera. An

antistatic brush over the loaded film might also help.

<p>

Some people here use readyloads. I read and followed the advice on

storing holders in plastic bags, brushing out before loading them,

and brushing the film after loading.

<p>

However, I discovered how to really reduce the problem: don't lean

over the holders when I load them! I suspect much of the dust came

from clothes, beard and hair. I now load by holding the film and

holder in front of me, and I also ensure the surfaces are also

horizontal, encouraging any falling dust to fall off.

<p>

Another tip that also reduced problems for me: I used to extract film

from the packet by sliding it out from the back of the polythene bag.

This created static, attracting dust to the film. Now I remove all

the film, in the cardboard folder, from the bag, and lift each single

sheet off the pack.

You can get some idea of the field of a lens in a camera shop by

holding a sheet of paper in one hand, the lens in the other, casting

an image on the paper. Use the shop window as the "subject". You

should easily see the light fall-off at the edge of the image circle,

and may also see a fall in definition. If the lens only covers, say

2.25" square, you will easily see that it doesn't cover 5x4. I

suspect that a 75mm lens won't do 5x4.

<p>

A flat field lens can indeed be used for general work, the "flat

field" just means that a flat object will make a flat image. However,

it may be optimised for close-up work, in which case it would make a

good enlarger lens.

<p>

Regarding Andrea's original question: do you know the format of the

MP 4? The lens is unlikely to cover a larger film, because repro

cameras don't usually have movements.

It sounds as if it is aimed at photographic education (learning and

teaching), rather than the actual process of photography. Maybe not

of interest to me (being neither educator nor student), but don't let

that stop you.

FWIW, I rate it at EI 800, developed in T-Max dev for 9.5m at 24 deg

C. Very clean, sharp grain, which does wonders for reducing the

effect of skin "blemishes". Possibly because of the grain, it doesn't

seem to work well with woolen clothing, or finely-patterned fabrics.

I was curious to see any answers to this. Probably everybody has been

stunned into silence.

<p>

Going by diagonals, a 200mm on 20x12" would cover 112 degrees, and is

equivalent to 55mm on 5x4", or 15mm on 35mm. It is possible, but I

suspect there is too little demand for such a lens to be commercially

viable. But, of course, the results would be wonderful.

<p>

A standard text is Sidney F. Ray, "Applied Photographics", Focal

Press. This gives good detail about the theory of lens types,

aberrations and how they are corrected (or traded-off), materials,

lens types, and uses. The second edition is 1994 (maybe there is a

more recent edition), and doesn't mention the more recent optics,

such as the Schneider Super-Angulon XL 47mm for 5x4". Scale this lens

up four times, and your needs may be fulfilled. If you can afford it,

perhaps Herr Schneider would make one for you.

<p>

Making your own lens is trivially simple. Take a 200mm magnifying

glass, restrict the aperture, and there you are. But your negative is

600mm across diagonals, and the quality of this optic would be

dreadful. You might be better off with a pinhole or zone plate.

<p>

Ray's book does not discuss the practical details of designing and

constructing a lens. Some of his references do. Grinding your own

lenses is possible: follow an astronomy trail, there are many books

on the subject. But astronomers use long focal-length (i.e. narrow-

field) lenses, which are much easier. To make a 200mm lens for 20x12"

that competes on quality with the "big boys" would need a powerful

computer and very good manufacturing techniques.

<p>

If you are serious about constructing your own lens, I suggest you

start with an easier one, say around 3000mm.

The formula is the first in the book: 1/f = 1/u + 1/v, where f =

focal length, u = lens-to-object, v = lens-to-film. Taking u+v=1829mm

(6 feet), then v = 378mm, and that's the bellows draw you need.

The Cadet is light and cheap, and can be easily carried in a

rucksack, and used in less-than-wonderful weather without bothering

too much about it. It's fairly rigid when the knobs are done up

tight, which can be easily done with gloves. As an example of high-

precision engineering, it ranks with a Trabant.

<p>

I use the wide-angle version, which can't use a 300mm lens. I can't

find the brochure, but I think you might have problems even with the

standard version racking a 300mm to focus at 6 feet.

>> Can anyone tell me how to size up the performance of a lens for

myself, as opposed to trusting what someone else thinks is good.

<p>

Use it. It's the only way. Sure, you can also get lens testing charts

if you are interested in objective tests, but subjective testing may

be more important.

<p>

IMHO, lens testing, whether subjective or objective, is most useful

when comparing lenses. Here, you might test the Ilex alongside

another lens that you already know, even if it is a different format.

Then you can directly compare sharpness, contrast, bokeh, or whatever

you are most interested in.

<p>

>> Subjectively, it seems to me that for some reason the lens is

sharp and performs better at f 8 than at f 16 or 22. In theory this

shouldn't be the case.

<p>

The lens may have been made for a hand-held camera, and optimised for

a relatively large aperture. In any case, if f/8 is sharper than

f/16, then accept that fact.

<p>

>> Sometimes this old lens seems sharp and at other times it seems

really bad.

<p>

If this happened to me, I would check that there wasn't anything

loose in the lens,and it wasn't fogging up in humidity. Then I would

check my own technique.

<p>

>> Also, how can you test a lens for circle of illumination?

<p>

Test it. Put it on a 10x8 camera, or use the 5x4 and shift the lens

or back or both to get maximum displacement, and photograph a brick

wall, or a series of lens charts, parallel to the lens and film. Look

at the negative or slide, and determine where the limit that is

acceptable to you lies.

<p>

>> Would shutter vibration be a factor, and how would you know you

had it if it was a problem?

<p>

It's usually only a factor when hand-held or on a flimsy tripod, and

the vibration should be very much lower than a 35mm SLR. Again, you

can do a practical test. With a tripod, photograph a lens chart at

different shutter speeds, varying the illumination of the chart to

get a constant aperture. If the negs with the faster speeds are

sharper than those of the slower speeds, then you have camera shake.

If I had to choose between two lenses, where one exactly covered my

negative, and the other other had a much larger image circle, and I

didn't need movements, I would suspect that the lens with the smaller

image circle MIGHT give higher quality, because there are always

trade-offs, and something would have to be sacrificed to get the

larger circle. Of course, that "something" might be price.

<p>

No, I don't think the manufacturers you refer to "direct lens

aberrations towards the outer most edges of the image circle". True,

it is possible, and a manufacturer could decide to trade-off edge

properties against on-axis properties, but such an effect would be

swamped by the trade-offs involved in increasing the image circle.

Besides, high quality lenses more usually have a goal of consistency

across the field.

http://www.photogs.com/bwworld/index.html has lots of articles on

printing, and B&W forums.

Yes, it sounds like a condeser problem. For even illumination,

assuming a point light source, the image of the lamp, through the

condensers, should fall on the lens. Because the 80mm lens is closer

to the negative than was the 135mm, the condition no longer holds.

<p>

Possible solutions/kludges are:

<p>

- Obtain a shorter focal-length condenser.

<p>

- Stay with the 135mm lens.

<p>

- Increase the distance between the lamp and the condenser.

<p>

- Turn the point light source into a diffuse source, for example by

putting tracing film between the lamp and the condenser. Beware of

excessive heat.

I agree with Jeff, and here's an anecdote about "DON'T underexpose

and DON'T overdevelop". My apologies if it is drifting somewhat from

the topic.

<p>

When I was even younger than I am now, I used to believe that I could

increase the effective speed of my film by stewing it for a long time

in developer. What I didn't fully appreciate was that the major

effect was to increase contrast. This raised the density of mid-tones

appreciably, and I used to judge "correct" exposure as that which

reproduced a grey card as grey on the negative. For some styles of

photograhy, this is not a terribly bad definition of EI (Effective

Index), although it is not the standard definition. However, I now

normally judge "correct" exposure (and development) to be that which

gives me good detail in whatever shadows I am interested.

<p>

Incidentally, the (dubious) definition of correct EI being defined as

reproducing a grey card as mid-grey on the negative seems to be

adopted by some manufacturers. Watch out for phrases like "you can

expose at EI 3200 if you don't care what happens to the shadows".

Sergio puts it well. Although the "overexposed" highlights will be

denser, this will be more than compensated for by the

"underdevelopment".

Jeff, thanks for pointing out that error. I was trying to give an

example when people might legitimately "overexpose", but my brain was

going faster than my fingers, and I left out some important words.

That paragraph should have read:

<p>

On that basis, if your subject has a contrast range of 8 stops, AND

you set your meter to 2 stops slower than your film's ISO, AND you

meter shadows and highlights, AND you calculate the mid-point, AND

you set your camera to that reading, you will capture all the tones.

Depending on your meter, you *might* get the same result by setting

the meter 1 or 2 stops slower than your film's ISO, and taking an

average reading.

<p>

Jeff also says: "DON'T underexpose and DON'T overdevelop." I only

partly agree with this. I do believe that developing for more than

normal is OK, when the intention is to increase contrast. In these

circumstances, the film might neeed a slighty increased EI to

compensate, at the shadow end of the characteristic curve. Adams

calls this "N+1", or whatever. But overdeveloping in order to

underexpose is only OK if we remember that we will also increase

contrast.

It has been said "there are no dumb questions, only dumb answers", so

here comes one.

<p>

He does this because he is a zone system fanatic. Or, at least, he

knows some of the underlying principles.

<p>

His subject is contrasty. He knows that a normal exposure and

development will yield a negative that is also contrasty, and will be

difficult to print. So he plans on developing less. This will reduce

the contrast on the negative: subject highlights that would have been

a dense black will be, say, a dark grey. But it also affects, to a

lesser extent, the other end of the characteristic curve: shadows

that would have been light grey will be slightly lighter, or totally

clear. By giving the extra exposure, he knows that he can raise the

tone of the shadows back where they would have been with normal

development.

<p>

The opposite also applies: increasing development ("pushing" the

film) gives increased contrast as well as requiring less exposure

(increasing the EI).

<p>

Of course, he has read Adams and BTZS, and has done extensive

testing, and knows how to adjust EI (Exposure Index) and development

to give a required CI (Contrast Index), while retaining Zone 0 at

density 0.1 above film-base-plus-fog.

<p>

On the other hand, perhaps he just knows a couple of rules of thumb.

If you get a good lens, there will be no distortion visible on

"ordinary" shots. 90, 75, 72, 58, 47, whatever you need to cover the

required angle.

<p>

But I suspect that what you call "distortion", I call "perspective".

If you make a print with a given lens, and then don't view the print

at the correct distance, your picture will have false perspective.

<p>

For example, use a 90mm lens, and enlarge x2. The "correct" viewing

distance is then 180mm. With a 47mm lens, enlarged x2, the correct

viewing distance is only 94mm. If you can't squint that close, but

hold the print 300mm from your eyes, you will get a false

perspective, and three-dimensional objects will appear "stretched"

away from the picture centre.

<p>

So if you don't want this effect, just work out the degree of

enlargement and the viewing distance (200-300mm for prints, more for

gallery walls), and choose your lens accordingly. Bear in mind that

we tend to look at pictures at a distance roughly equal to the

picture's diagonal, which is why "standard" lenses are equal to the

film's diagonal (because they don't give this false perspective).

<p>

So to be really picky, suppose you want to crop a 5x4 negative down

to 6x17 format. The usable part of the negative will be 5x1.77", and

the diagonal will be 5.3", or 134mm. So a 135mm lens will be the

"standard".

This topic keeps coming up, in various forums. I agree with Andy: the

correct exposure is the best exposure.

<p>

For merely "ok" results, people talk about B&W negative latitude. If

you meter a grey card, you will get good detail in shadows about 2

stops below that reading, and highlights about 6 stops above.

(Speaking very loosely, the film has more latitude to overexposure

than underexposure.) The exact numbers depend on the film and

development. On that basis, if your subject has a contrast range of 8

stops, AND you meter shadows and highlights, AND you calculate the

mid-point, AND you set your camera to that reading, you will capture

all the tones. Depending on your meter, you *might* get the same

result by setting the meter 1 or 2 stops slower than your film's ISO,

and taking an average reading.

>>I never used it for that purpose so I don't know how good

it is but it is at least an option.

<p>

Just for completeness, yes, it is excellent flash spotmeter.

Just calculating the f-stop is easy: it's the hole-to-film distance

divided by the diameter of the hole. A 1mm diameter hole, 200mm from

the film, is f/200. If your meter doesn't go this far, write down the

series 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45, 64, 90, 128,

181, 256... until you get there, and you can now work out the shutter

speed & aperture combinations.

<p>

Film manufacturers give you reciprocity failure compensations, which

you will need, but they may not go far enough. The great thing about

reciprocity failure is that it compensates for over-exposure. So if

you expose for 40 minutes when the correct exposure was 10 minutes,

the film won't be 2 stops over-exposed.

<p>

But instead of all this theory, you could just spend 10 minutes

knocking up a pinhole, make a few exposures, and see what happens.

If you have a choice of doing a movement with the camera, or later in

software, the camera choice will always give you better quality. This

applies whether you have "real" or "digital" film, and will always

apply.