There are a ton of possibilities.

Provide a link to Cambridge in Colour - http://www.cambridgeincolour.com

Then prepare a lecture on whatever aspect of photography people need to work on. It could be article on Black and White conversion - http://www.cambridgeincolour.com/tutorials/color-black-white.htm - or it could be something else. The idea is to give people something they can take away which with practice will make them a better photographer.

There are so many resources, and having a club night to learn a new skill is a great way to get people up and going.

I've used the iPhone for artsy images - not because it was my first choice. Sometimes it is the tool I have at hand, and it is at least sufficient to frame an image that captures part of what I want to convey.

For people starting in street photography it is a useful tool to overcome the problem of fear of taking candid photographs of strangers. Feeling more relaxed, and less visible is a great way to begin. You can concentrate on framing and timing. The big DSLR draws a lot of unwelcome attention, and it makes the street a more intimidating space. A Sony A7 series camera with a 50mm lens would probably be a great street camera. I have used my D800 and it is tougher to use because of the size. (I love doing night with my infrared converted D7000 with an infrared flash. That is a stealthy camera.)

Composition is the art of rendering an image in a way that is sympathetic to brain states. It is a way to induce or trigger a change of state in the viewer to feel an emotion, instinct or composite of several emotions or instincts that through their similarities and complementary qualities are deemed to be one or more of: powerful, beautiful, disturbing, sympathetic, horrific, compelling or nuanced.

Poor compositions are noisy and confused. They leave the viewer cold, bored and possibly irritated. They are trite at best, and insipid at their worst.

How to compose is an exercise in learning about this, and discovering through study, play and practice what is effective. To that end learning about what makes effective composition through the application of various 'rules' is useful. They are the starting point - not the end point. The aim is to know the rules and to be aware of them when composing an image. It is not to be bound to them dogmatically, but to have an awareness that images that subscribe to them work on people in a reasonably coherent fashion. They are paints in our palette which we can choose to use or not to realise our vision.

I am going to be the exception to the rule. I owned this lens before it went swimming on a canoe trip ... thankfully it was insured as was the D3x it was mounted on.

While it a good general purpose f2.8 24-70 zoom, it is not as robust a lens for weather as my primes. I also prefer primes, so that was a mark against it for me - not for others. For me, a 24 tilt-shift, my 50 and my 105 cover the territory, and for street, the 50 is less obtrusive, and the tilt-shift enables me to appear to be shooting at something other than the subject. For landscape the above primes really do it, (and I carried those three on my 80km hike at Killarney last summer.)

If I were an event photographer I would love this lens. It's strengths are versatility, very good IQ, and at f2.8 a quite reasonable speed.

You really have to look at what and how you shoot to determine if it is what you need.

With the D810 on the market, the price for a quality second hand D800/E has dropped enough that you may be able to keep the motorcycle. (Sorry about the wife and child though.)

see http://www.ebay.com/itm/NIKON-D800-36-3MP-DIGITAL-SLR-CAMERA-BODY-USED-/291307206482?pt=Digital_Cameras&hash=item43d3433752

If you are willing to be patient, and watch and wait you will find what you want at a good price.

I think I have seen that book, and they were gorgeous.

The trick would be to time-share that kind of camera system. Four people could pool resources to do it. Besides, I expect that some of the medium format crowd are old large format shooters, and would be extremely tempted. (That and I would rather look like a dentist having a midlife crisis with a camera, than an executive having a midlife crisis with a Porsche.)

I did not know that Ansel Adams did those shots. I learn something new every day.

I just loved by 8"x10" film camera, and want something similar in the digital domain. I can't go backpacking with the 8"x10" because it is just too much to carry, even for two people with the camping gear. I think 4"x5" is another story, and of course no I don't contemplate carrying a cooling system as that would just blowout the load even more than my 8"x10" film camera.

FYI, Spectral instruments already has a 112 mp 95 x 95 mm sensor that comes in at around the $100K mark. It is broad spectrum sensor without a bayer array - i.e. strict monochrome, but you can use filters to choose what part of the spectrum to shoot.

see http://www.specinst.com/BrochuresDatasheets/1110S%20KT%20brochure_AH_web.pdf

http://www.digitalcameraworld.com/2012/05/18/112-megapixel-camera-captures-starry-skies-during-the-day/

And yes it has enough dynamic range to capture starry skies in daylight - with a cooling unit taking the temperature down to -100C. (Since shooting stars in the day is not really my thing, if I got a mere 18 f-stops of DR I would be more than satisfied, since that would mean a lighter rig.)

Provided the pixel pitch is not so small that the camera is not resolving any more real detail due to diffraction limitation, and the lens being used is capable of resolving a high enough number of lines per millimetre (LPM), and a good tripod is used and/or good hand hold technique with a high enough shutter speed is used to prevent unintentional blur. As you see there are a lot of factors that can lower the real resolution.

I personally would welcome a large format sensor (4"x 5") with say 120 mp. The pixel pitch would be around 10 microns which should grant a massive dynamic range potential before going to such extremes as cooling systems. As someone who love landscape photography, that sensor on a view camera with full movements would have me over the moon. (I would never need to use a graduated neutral density filter again, because I expect that 18 f-stops should be realizable without cooling, and probably in excess of 20 with cooling.)

I am about to turn 56, and I hope by the time I hit 65 and retire I will be able to set myself up with this system. (I am budgeting $100K for it, and putting aside money in a dedicated account each year.)

No argument that an 800 mm prime would be welcome, but even with that puppy, cropping will be required more often than you might like.

Yes there is more to a camera than MP - no question. But for birders and wildlife shooters pixel density permits a level of cropping that is often a requirement due to the size of the subjects and the fear radius that inhibits getting close enough to not need to crop.

Actually your D7100 may very well look slightly better if you were using the same very sharp prime lens on each camera. Why? Because you are cropping out that small section, and the APS-C sensor (24mp) on the D7100 would have a significantly higher pixel density than the D810. Let's assume you were using a Zeiss Otus 55 or 85 mm lens for the shot, and you were shooting at no more than F5.6 so as to not hit diffraction limitation. Also, you better be using a tripod, and a fast enough shutter speed to freeze any blur from wind. Assuming all of the above, the increase in pixel density would reward you with a higher resolution image.

In situations where significant cropping is likely, the D7100 will offer more resolution because of its pixel density, but the differences become pretty small if you don't control all the other factors that can decrease your resolution. If I were a bird or wildlife photographer, the D7100 would be my go-to camera.

The sample shots show how much cropping can be done on a D800 using the 105 f2.8 macro lens while walking across a street.

D800 - minor crop for perspective - almost full frame reduced to 1/4 mp

(Download)

Significant crop around right light and window

(Download)

Crop on document in window

Pixel density limits the utility of additional pixels due to diffraction.

I expect that full frame 36mp, APS-C 16mp and Medium format at around 60 to 80 mp is really about the limit. In most cases the sensor is out resolving the lens with the exception of the very best lenses at between f4 and F8 (max).

Now give me a 4" x 5" 120 mp sensor and a great viewing camera to mount it on, and I will be over the moon. (There is a scientific back by the way that comes in at around that size and capture 22 f-stops of DR.) A mere $100K or so.

I like the proportionality. I has a lovely textural and layered feel that is geometrically interesting.

The mood it creates for me is one of solidity and tranquility. I would happily hang it in my home.

That said: It is one hell of a lot of money, and even if I was as rich as Bill Gates, I am not sure I could justify it. So much of the monetary value of art is artificial. My view is simple: If I love the work and it fits within my budget I will buy it.

I like this work, quite a lot. There are other photographs I prefer, and they don't clock in at that price.

Phase One makes a great entry level CMOS medium format back. They sell for a mere 35K - which means most of my students have several.

If you are asking seriously, the answer is a big "it depends". It depends upon your style of photography and which lens set offers you what you are most interested in. Both produce excellent cameras - one may be a better match for you than the other.

I have taken some great shots with mine.

It has an effective focal length of 75 mm on your D7100, and should make a superb portrait lens.