alec_myers

December 3, 2009

Alec, good luck at f/256 !

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Ho ho... please, don't burst my bubble of optimism about this!

December 3, 2009

Im aware many labs (including Walmart labs) will be going dry printing in the future, using Dye Sub for the process.

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Ink-jet I think - nobody has got the cost of dye-sub down low enough, as far as I see. Check out the Fuji Frontier DL410, based on Epson inkjet technology.

RA-4 is still cheapest per print, by a wide margin, but you need big volumes to make it worthwhile. I wouldn't write it off in roll format for a while yet.

December 3, 2009

Does loss of detail at the smallest aperture relate to the (reduced) amount of light that gets through the lens?

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Loss of detail due to diffraction: it's a wave effect, and can only be understood by thinking about the effect of the lens on the electromagnetic radiation (light) that hits it. The lens performs a transform (a fourier transform) on the waves so that the intensity of the electromagnetic field (in the plane of the lens) varies across the aperture according to the spatial frequency of the incoming wave.

The highest spatial frequencies, that represent the sharp edges and tiny details in the image, pass through the outermost edges of the lens.

When you close down the aperture you filter out the highest frequencies and lose the sharpness in the image. It's very similar to turning down the "treble" tone control on a hi-fi.

December 2, 2009

Matt,

you'll have a bit more DoF on the DX body. It's pretty much hair-splitting, though.

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I think that's true... I certainly don't fuss for the difference in DoF between the Canons with the 1.3 crop factor and the full frame 5D. I have however bought a LF camera for some fun, and I'm looking forward to examining the DoF issues on 5x7 format. However since I'm going to be making contact prints and not enlargements I know I'll get at least some of the DoF back because my acceptable circle-of-confusion can be quite large.

December 2, 2009

all other things like lens, aperture, and distances being equal

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With great respect to Matt, this is the sort of thing I mean - you can't keep all other things equal. You can't, for instance, keep the subject magnification at the sensor the same, and also keep the framing the same. There are too many possible things that can be "kept the same", some of which have to change.

December 2, 2009

This is a perennial question to which lots of people have different answers. Essentially DoF depends on a lot of different factors like magnifcation, aperture, focal length, object distance, what size circle of confusion you pick, sensor size.

When you ask if DoF depends on sensor size it really depends which of the other factors you change, and which you keep the same in your "comparison".

Some people like to keep the focal length and aperture the same, and think about it as though a smaller sensor is just a chunk taken out of the middle of a larger sensor. "Not so", say others - "you have use a different focal length to get the same image, a longer focal length on a larger sensor, and that changes the DoF. "

Then there are those people who say keep the same lens, but move closer to the subject so it fills the same proportion of the frame. That means the subject distance changes.

I'm sure there are other ways to look at it too, and each of these comparisons - each as valid as any other, each with their "this is the only correct way to look at it" champions - will give a different answer to your question.

One thing is true though, which is that DoF is a woolly number because it depends entirely on your subjective judgement about how much out-of-focus is still acceptably in-focus. And between a FF and DX sensor there is not a great deal of difference so that you would be hard pushed to spot the difference in DoF between two photos with different sensors, regardless of which of the possible different comparisons you think is the most correct.

December 2, 2009

Diffraction effects which rob pictures of their sharpness at small apertures depend on the absolute size (in mm or inches) rather than the f-number. As Scott says, with large format cameras the focal lengths of typical lenses tend to be much longer for a given angle of view therefore you can stop down to a much smaller f-number to get the same size physical aperture (and therefore equally acceptable diffraction effects) as with, say, 35mm photography.

Stopping down to very small apertures helps to make up for the decreased Depth of Field that the long focal length lenses involved in LF bring.

December 2, 2009

Wait..no one answered. What should my Proof Setup be while editing?

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Speaking for myself, I didn't answer this because I didn't understand what you're asking.

Do I convert to sRGB before saving?

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It depends what you are going to do with the saved file. If you're saving a jpeg for web display, probably. If you're saving your edits to a master copy of an image, probably not.

December 2, 2009

Please check that link ... it comes up with a 404 error for me - and I'd like to read it.

Oh wait - is it this:

<a href="http://www.earthboundlight.com/phototips/color-management-feeling-lost.html">http://www.earthboundlight.com/phototips/color-management-feeling-lost.html</a>

December 1, 2009

You could always take a regular b/w negative on a half-plate, which I think works out at about 5x7, and then contact-print a positive onto another glass plate.

December 1, 2009

Thanks everyone. One last thing...Is is best to use a calibrating kit from a company like Pantone or from the company from which I get most of my prints made?

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You need something like a Pantone Huey. I'm surprised to hear that the people who supply photographic prints also make monitor calibration systems?

December 1, 2009

even churches in the U.K. are not properties owned by the public

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If we're on the subject of the UK, then here what constitutes "in public" or "in a public place" is entirely different from "on publicly owned property". You have no expectation of privacy at a wedding in a church, or while in a shopping centre, or even at a ticket-only event - or anywhere you might reasonably expect to be seen by other members of the public, regardless of who owns the property. Incidentally, by law, wedding ceremonies must be open to the public so that anyone who wishes can attend and raise an objection to the union. The celebration can be as private as you wish - but the marriage ceremony must be open-doors.

December 1, 2009

Firstly calibrate your screen - profiling devices are cheap.

Secondly read up on this site: <a href="http://regex.info/blog/photo-tech/color-spaces-page1">http://regex.info/blog/photo-tech/color-spaces-page1</a>

Thirdly, accept that whatever you do to the image you have no control over the calibration or lack of it of the system that the image is viewed on, nor with which program it's viewed. So the bottom line is "you can't." Just something to live with.

December 1, 2009

The maximum aperture does, if the light is low.

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OK, so that's not actually true. Firstly the AF system doesn't focus at the focal plane of the lens, it focuses behind the lens using a system of secondary mirrors and lenses. A wider aperture means that the cone of light from a point on the subject illuminates more of the AF sensors (the f/2.8 sensors are only lit when the cone of light is as wide as an f/2.8 lens gives you) but it doesn't illuminate them any more brightly. So there's no benefit to the AF system to using (for instance an f/1.4 lens over a f/2.8 lens. There is is extra light entering the lens but as far as the optical path to the AF sensors is concerned all of that extra light is wasted.

That's why the AF performance of Canon cameras is quoted down to a particular EV number (-1, say) without reference to the aperture of the lens. The specs say things like "cross type for f/4 and faster" but that's because of the angle of the light coming from opposite edges of the aperture (the angle of the light cone of a point on the subject) is important - not the brightness. The sensors sensitive to contrast in the 'cross' direction are only illuminated at all when the angle of light entering the mirror box comes from the edges of an aperture that's f/4 or bigger.

However, it is very much true to say that if you stop the lens down to f/5.6 or f/8 then no light will hit the AF sensors at all except some of the ones for the centre point, which are positioned to read very narrow light cones such as you get from telephoto lenses with extension tubes, even at max aperture. Even then the AF is less accurate because that cone of light is very narrow.

AF in DSLRs works somewhat like a rangefinder camera where the camera measures the best registration between two secondary images formed through opposite sides (left/right - and for 'cross-type' sensors, top/bottom too) of the lens aperture.

Although the focused image at the sensor plane gets brighter as the aperture widens this doesn't apply to the amount of light hitting the AF sensors, which are not in the main sensor plane.

November 30, 2009

Well Tara, after reading Rob's post and Raymond's post, you should now be coming to see why it's best not to ask what is essentially a question of law on a photographer's forum. And if you do, remember that the answers come from people who are wholly unqualified.

Also bear in mind that the vehemence with which a point of view is stated and the strength of language used to express it bears no relationship to the correctness of the answer.

November 30, 2009

Bengt: You are absolutely right, focal length won't make any difference to the DoF for a typical portrait with a sensible lens. But like all rules-of-thumb, I think it's good to be clear that it doesn't always work.

November 28, 2009

With a given magnification the f-number alone decide DOF.

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This is approximately true, but only where you are far from the hyperfocal distance. If you compare two lenses you will see this "rule" breaks down: if you increase the focal distance at the same f-number the wider lens will get to its hyperfocal distance before the other, at which point that lens will have an infinite DoF and the other not. Ergo DoF does depend very much on the lens' focal length, as well as f-number.

November 26, 2009

The published formulae for D-76 and D-76R are not the same as the Kodak commercial product. For instance if you make up the published formulae by mixing the powders and adding them to liquid all at once the result doesn't dissolve (I've tried it) - the metol has be dissolved before the sulphite. The Kodak product is quite happy to go into solution in a single go.

I'd agree you're better off using it as John suggests.

November 24, 2009

I would ask them what their budget is; having raised the issue themselves and pointed out that they have one they can hardly refuse to tell you.

Then you can decide what you're prepared to offer for that budget. Fewer photos, perhaps.

I totally agree that you save the discount for the second and subsequent jobs; otherwise they have a great incentive to pick someone else next time and play the same game on them.

November 24, 2009

All digital cameras have dead pixels, sometimes hundreds, but they get masked out by the camera (copied from the pixel next door). Sounds like they haven't set the dead pixel mask right, but it wouldn't be considered a fault with the camera.

November 23, 2009

Russ,

You're absolutely right. They're not negatives at all, they're original-film positives. Very sloppy nomenclature on my part.

Apologies for jumping at your post.

November 22, 2009

Doremus,

here are the results for a scrap piece of film (positive image) split in four. From the left:

<ol>

<li>un-toned</li>

<li>selenium toned without bleach/redev</li>

<li>bleach in ferricyanide/chloride, redev HC110, tone</li>

<li>bleach in ferrcyanice/bromide, redev HC110, tone</li>

</ol>

All the toning was in 1+19 selenium toner until completion (no further visible change, approx 10 mins)

There may be some colour difference between 2 and 3/4, but not much visible between 3 and 4.

I'll keep experimenting and post here if I find anything useful.<div></div>

November 22, 2009

Doremus,

Thanks. Actually I think I don't really care what people think of me as long as they have something interesting to say!

The reversal process doesn't use a rehalogenating bleach (oxidiser) just an acidified permanganate followed by a metabisulphate bath to remove the silver. Here's a scan of my notebook with the different colours. Top left is the raw silver, top right is the dark colour I rather liked from the selenium, the bottom left is the more sepia-like selenium that I don't care for so much and bottom right is a true two-step sepia tone (halogenation bleach, then thiourea bath).

I've tried some different film stock too. I get a much more earthy red result with HP5+. I'm also trying different formulations for the first developer.

I do like your idea about inserting a rehalogenation/redevelopment step before the selenium toner. I'll try that out and see if it makes any differences.<div></div>

November 21, 2009

You probably know, but while citric acid is used by the catering industry (it's what makes lemon juice acidic) so is acetic acid, as it's the majority component of vinegar.

November 21, 2009

Unless you are going to printing color, why are you trying to achieve a certain color?

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I'm developing the film to positive (develop, bleach, clear, fog, redevelop) as the final product - but that's not particularly relevant. Please be assured that I *do* actually want to tone the negative. (It's soooo frustrating when you ask a question for a particular reason and most of the replies assume you must be an idiot, wasting your time, and/or doing completely the wrong thing.)

Tim - thanks.

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