making a photography darkroom

[whisky-dave]

I was the one that mentioned it.

[whisky-dave]

Actually you should use both, especaily if the flash isn't mounted in the usual place. Light comes from the flash gun and the intensity of teh flash dimishes with teh inverse square law, hits the subject and travels back to the camera again obeying the inverse square law.

Flashes are usualy (apart from ring and dedicated macro which I couldn't afford (being at school) are built with the subject to flash distance of around 1 Metre to 5+ metres or so. When I used the GN it was for distances of about 1-6 inches, which means you've pretty much go to put them on manual. I also used manual when I was taking pictures of a baloon bursting.

have you ever seen one go below 30cm ?

quite a bit more. Didn;t have much succsess foudn the lighting too harsh and shadows were a problem too.

I only used the GN for 100 asa can;t remmebr altering it for difernt ASAs

That sounds right haven't done those calculating in this milenium.

Tomorrow I will teach him how to walk in a straight line, if I have the time. He is a bit of a waste of time coming up with crap he doesn;t understand and does even attempt to prove it.

[whisky-dave]

If you DO NOT know what GNs have to do with exposure for differing flash to subject distances there's no point in going further.

[dennis]

You claim your so called DoF mark on the camera is relevant to guide numbers so tell us why?

[dennis]

How does that improve over lensbaby?

[dennis]

Do you know what the bokeh of a typical mirror lens looks like?

[dennis]

I know how guide numbers work and the camera distance and hence his so called "DoF" mark is irrelevant. Its down to how far away the flash is and as you know on camera flash isn't very photogenic so you use an off camera flash and that can be at different distances to the camera.

I don't think WD is like that, I don't think he knows. All his answers are the sort of thing Rod comes up with after he has googled what the other poster has said.

I think he would be a terrible teacher of anything especially photography so i hope he doesn't really do it.

[dennis]

The distance to the camera is irrelevant.

Most flashes need a diffuser and filters when used that close as you don't want to stop the lens down to a pinhole, then the GN is useless.

I have used one below 30cm but it had variable power and few other useful features, it can even sync to the full speed of my camera even though its a focal plane shutter.

Ask a photographer to explain it to you.

[NY]

Ah, I thought I'd explained, Dennis.

WD was using the focal plane mark (what he calls the DoF mark) as a measuring point for measuring the flash to subject distance, as an alternative to measuring from the flash head to the subject.

The distance is needed for calculating the correct aperture - see Applications section of

f-number = GN/distance

Given that he was using very short distances, I'd have thought that flash head to subject would be the more correct thing to measure: beyond a couple of feet, the error of an inch or two between the two distances would be negligible.

The Wikipedia article says "The position of the camera is not relevant" which I take to mean that you could have the flash unit in a separate place to the camera (joined by extension flash lead to hot shoe) and the exposure would be the same no matter how far away the camera was - all that matters is where the flash unit is in relation to the subject.

I suppose this makes sense: if you illuminate a subject by a given set of lights, then you don't have to change the exposure if you move the camera closer or further away

[whisky-dave]

The mark is NOT relivent to GN. It is the place where the film or sensor is located. THE GN is a numberthat represents the power of teh light from the flash gun NOT the camera.

[whisky-dave]

Whats a lensbaby ?

[dennis]

Its a tool used by photographers.

At least one of which is a 2 element planar lens like the kickstarter.

[whisky-dave]

So is there a differnce between photographers and peole that take photos/snaps.

so you don't need a mirror lens for bokeh, I knew this in the mid 70s Bokeh isn't new.

[NY]

I never suggested that you did. I simply said that the bokeh of a mirror lens was characteristic - a doughnut shape on any bright highlight which is very out of focus, rather than a solid disc or solid polygon in the shape of the lens aperture that you'd get with a purely refractive lens.

[whisky-dave]

If you knoew a little about photography you'd have know that bokeh isn't new, and over 100 years old an nothing to do with mirror lenes, other than that mirror lenes made bokeh come back into the spotlight (sort of pun intented).

Which is why if you want to teach photography you do NOT start with a digital camera you can end with one of course.

[NY]

I'm puzzled. I haven't said anywhere that bokeh is new or that you only get it with mirror lenses or that you need a digital camera or a film camera to see its effects. Since it is basic optics, I'd expect it to have been known about since early photography if not before that going back to the days of the camera obscura. And since early cameras used larger negatives and therefore longer focal length lenses for the same field of view, it was probably more apparent on older cameras since a 50 mm *equivalent* lens on a large plate camera will have shallower depth of field than a 50 mm for a 35 mm camera at the same aperture. It is also possible that the shape of highlights and therefore the nature of the bokeh will have changed over the years as lens design has been refined.

It is a feature of all lenses that out of focus objects are rendered in a way that is characteristic of that lens. I've seen reviews and specimen photos of lenses for many years which show that some lenses give a "nicer" bokeh and others give a more intrusive bokeh. It so happens that mirror lenses give a very recognisable doughnut-shaped blur on highlights which (as far as I am aware) is not apparent on conventional refractive lenses - something that I referred to in passing a while ago in this thread.

To the best of my knowledge, a film camera and a digital camera with the same lens, the same size sensor and using the same aperture will give the same picture, in terms of depth of field and the amount and "look" of blur (bokeh). I can't see why you would learn more about bokeh with a film camera than a digital, but if you think differently, I'd be most interested to hear your reasoning.

In fact you don't even need a film/sensor to see it - it's visible on the ground glass focussing screen of an SLR (film/digital) even before you take a picture, though the graininess of the screen may obscure some of the detail which may only be visible in the finished slide/print/digital picture.

[dennis]

I didn't say that.

I knew before that I see you never did tell us what shape the bokeh of a mirror lens was. Mirror lenses predate digital too so its got nothing to do with your worthless digital is no good for teaching argument.

[whisky-dave]

Maybe is because you said "Mirror lenses also have very characteristic bokeh. But I won't make disparaging comments if people have to google to find out what bokeh is and what is characteristic about that of a mirror lens! "

Only those that have never done photography wouldn't know the above. Which is what makes photography differnt from deciding whether film or digital is best is irrelivant to photography that is the point.

Irrespective of film or digital media, and mirror lenes.

Yes adn this was not considered to be a good thing unless you wanted bokeh. I remmerb sports photographers not being 'keen' on it because iof it's distraction, it might have lokoed cool or arty but it was seen as a downside of a mirror lens rahter than an advantage.

Because people knew about this some 100 years before the digital camera existed. People that knew about photography rather than comparing film to digital would know about this.

[whisky-dave]

you didn't say what exactly. You didn't say it was a tool used by photographers.

Why wouuld I need to.

Yes I know.

I've never said that, which is why you're so confused here. I said film is better for teaching photography and I gave the reasons. The biggest is the distraction. give a student a digital camera and they go off shooting stuff without even considering the light or any other aspect of photography. If you ask a group of studetns what's needed for a good photograph I bet most will say a digital camera or a smart phone or instagram. They won;lt even consider the subject lighting or any other aspect of photography.

A similar thing is happening in schools in exams, we allow studetns to use calculators in exams, when schools do this while ther phone is their for being usedas a calculator yuo'll find the studetns on facebook during the exam.

Yes we know digital is best and it's far better to use a computer than a digital calculator, than a slide rule, than pencil and paper, in yuor head.

We all know how maths is best taught. Digital is better.

[dennis]

The only person comparing film to digital is you! Everyone else is comparing digital cameras to film cameras and saying they are the same as far as teaching photography goes. You on the other hand are saying they are different and digital is so different that its hard to teach photography with digital but still can't tell us why.