Today saw the launch of the Canon 5D mkII. This is something of a landmark camera for Canon as it follows up the massive success of the original 5D, which claims a full 2/3 of Canon's prosumer SLR sales. Big shoes to fill! So how does the new kid on the block stack up? Well here's the tech specs that matter: 21.1 megapixels full 1080p HD video recording at 30fps max ISO of 25600 (100-6400 expandable to 12800 and 25600) Digic 4 processor larger 3" screen with higher resolution New menus with quick control system 3.9 fps £2300 RRP Aside from the new 21.1MP sensor and the video recording (which I'll come back to later) the new headline feature is the 25600 max ISO. This indicates Canon's intention to tackle head-on the Nikon D3 and it's smooth usable high ISO images. The truth of the matter is, of course that ISO 25600 exhibits considerable noise - just as all the previous canon cameras have at their "extended" ISO settings. But the standard range of 100-6400 are all very usable now, even that top end 6400 ISO. Based on my limited testing at the product launch I'd say Canon are matching Nikon's high ISO performance and they're doing it with a 21.1MP sensor compared to the D3s 12.1MP. This is the news Canon owners wanted to hear. It seems like Canon has closed the technology gap created by Nikon's superb high ISO performance. So what about that HD video mode? Has Canon taken their eye off the ball with this feature? Do we really want our SLR cameras to be video cameras too? Well with the D90's 720p HD D-Movie function Nikon threw down the gauntlet and it seems Canon can't help but respond with their own 1080p video recording mode. This is bound to split people's opinions but those of you that do produce video should consider that this means you'll have a full HD camera with interchangeable lenses and far greater control over your depth of field than with a regular camcorder. This could create some very impressive videos in the right hands. There's even a mic input for connecting your shotgun mic. Most of the other features are "nice to have's". I liked the new menu system very much but the rest of the handling of the camera remains largely identical to the old 5D. The new screen is larger and more beautiful of course. And we have a small boost to the continuous shooting speed - not bad considering there are nearly twice as many pixels in a typical image now. So do I think this is a suitable successor to the 5D? Will it sell like the 5D did? These are the questions the Canon folks kept asking me at the press launch. I think the answers are yes and yes. The 5D mkII should be available to buy in November. Pre-orders are being taken now.

At last I'm home! I said yesterday that I was going to London for the Canon Autumn Collection 2008 press launch. Well it turns out it wasn't in London but Reigate, which I had assumed was in London. In fact it's just south of London but from where I stayed in Finchley the night before it might as well have been on a different planet! It took me longer to go from Finchley to Reigate than it did from Sandbach to Finchley. Curse you M25! Anyway the event went well but the day started with Phil Askey of dpreview.com posting all the juicy 5D details on his website before the event had even started. So there were no surprises at all for any attendees that were paying attention. Even so there were a couple of other new notable announcements today including the G10 and a couple of other new high end prosumer cameras, the SX1 IS and the SX10 IS. The only feature separating those latter two is the SX1's Digic 4 powered HD video mode. This was a shorter and more conservative affair than the previous couple of Canon launch events but all the main features were in place. Coffee and sausage butties on arrival - check. Short presentation starting with sales figures and ending with the big announcements - check. Hands-on demo area where we get to play with the new gear - check. They'd even laid on some birds of prey for us to take pictures of while trying out the new toys. Very nice. There were a smattering of other products including a new Digital IXUS (Digital ELPH for you americans) but this was the 5Ds day. Check my next blog post for my first impressions on the 5D mkII. Mainly the G10 has a 5x optical zoom that goes wide up to 28mm and the SX1 and SX10 have a long 20x optical zoom. Out of the two I liked the G10 more because all the manual features like ISO, exposure compensation and so-on are on nice dials on top of the camera. It's like going back to an old film camera! And it'll shoot RAW too.

At 9:30 tomorrow morning I'll be at Canon's head office in London for the launch of the Canon Autumn Collection 2008. You might think with the recent launch of the 50D that there wouldn't be anything exciting to see but there's a rumour going around that this might be where we see the announcement of the much discussed Canon 5D mkII. Remember the 5D was the first consumer level camera to have a full 35mm sized sensor and remains a favourite choice for amateurs and professionals alike. I myself have been using one since their launch. With that in mind and the recent advances made by Nikon with low noise, high ISO cameras the pressure is really on Canon to come up with something special. To follow along with me while I'm at the event just signup and follow me on twitter. I'll be twittering all the big news as it gets announced.

Like many of you I got the email today from Adobe saying that "something big is coming". This is the expected launch of Adobe Photoshop CS4 or PS.next, the latest version of our favourite photo editing package. Please note, though, that I have NO special knowledge about what features will be in CS4 but there have been a few sneak peaks. Some of the revealed features are:

• Photoshop CS4 will use your 3D accelerated GPU to really speed up moving around and zooming your images as you work.
• Photoshop CS4 can auto blend images shot at different focal lengths to merge them and give a greater depth of field. It literally finds the sharpest parts of each image and uses those to turn shallow depth of field macros into one complete image with a depth of field that would be unachievable using any modern lens.
• Context sensitive scaling - this adds the ability to scale an image without distorting the important subject areas.
• Photoshop CS4 adds the ability to stitch 360 degree panoramas.
• Lots of new 3D applications including the ability to map that 360 degree panorama onto the inside of a sphere and then paint directly on the sphere.

Any more than that I do not know. I'll see if I can get an interview with someone soon though..

Nathan recently wrote to me with a question:

Can you tell me what actually happens inside a DSLR camera when you change the ISO settings. For that matter what does it do in a film camera. Thanks. Nathan

Interesting question! Let's start with the film because that's what the digital version of ISO is trying to replicate. Film coatings are, as you know, sensitive to light. The more light that hits them the more the chemicals react. But the chemicals can be mixed in different ways so that they are more or less sensitive to light. So a film that is very very sensitive to light will go from unexposed to completely over-exposed much quicker than a less sensitive film. In film a higher ISO number means more sensitive film. More sensitive film means faster shutter speeds and better ability to get sharp shots in low light. Higher ISO also usually means grainier photos. The difference in grain between 100 ISO film and 400 ISO film is clearly visible. On some film cameras there is a dial that allows you to manually set the ISO. The idea is that you set the ISO to match the film you're using but some people use that creatively. On other cameras the ISO is set automatically by reading the metal stripes on the side of the film canister. Basically the ISO setting on a film camera is used together with a light meter reading to calculate shutter speed and aperture in order to get a correct exposure. All this stuff with chemicals and the sensitivity of the film is what a dSLR is trying to emulate with the digital sensor. However, there's just one sensor in your camera. You can't swap it out for a more sensitive one when you need more sensitivity. So what the camera does instead is to amplify the electrical signals that come out of the sensor. I'll explain how that works.. First of all you have to think of the sensor as a grid of dots or pixels. For the sake of simplicity forget about colour - just think in black and white. What each little pixel in your sensor does is catch photons. Photons are little parcels of light. Each pixel can hold a certain number of photons. Let's call that number 100. It's WAY larger than that but 100 is a nice simple number to work with. So in our simplified black and white world each pixel of the sensor can hold up to 100 photons before it can't hold any more. So when you're working at low ISO, with no signal amplification, light comes into your camera as photons and starts getting collected in the little sensor pixels. For a well exposed picture a bright spot might collect maybe 80 photons while a dark spot might collect only 20. That's fine because both are well within the number of photons our pixels can hold. So they send a signal back into the camera telling it how many pixels they collected during this exposure. So next the sun goes down, it's twilight and let's say it's only half as bright as it was. If we shoot again with the same settings we now get only 40 photons in that bright spot and 10 photons in that dark spot. But our sensor pixel can hold up to 100. 40 is less than half of 100 so our picture is going to come out dark and muddy. So if we amplify the signal by doubling it we get back to 80 photons for the bright spot and 20 photons for the dark spot. That gives us a nicely exposed shot again. Each stop of light you remove halves the brightness, in essence halving the number of photons being collected. So going from ISO 100 to 200 means amplifying the signal by 2x. Going from ISO 100 to ISO 400 means amplifying the signal by 4x and so on. More amplification means more grain. So that's the simple picture of how it works. Of course the world isn't so orderly and there are variations in how much light reaches a pixel. So two pixels that should be the same brightness might through random chance get a slightly different number of photons. Maybe one bright spot might get 81 photons while another gets 79. That's a small difference if you're not amplifying the signal. But those small differences make a huge difference if you're doubling or quadrupling the signal. That's why you see more grain on a high ISO picture.

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You'll no doubt remember that way back at the beginning of this year I did a review of the Drobo. I loved it and gave it top marks long before there was any hint of a sponsorship deal. Well I'm delighted to announce now that Drobo are sponsoring PhotoWalkthrough and you lucky people can get a $50 discount immediately if you buy a Drobo through the Drobostore and enter the coupon code "Photo". It's as simple as that. You can find out more about the discount and what Drobo actually is on our Drobo coupon code page or if you want to go back and see that Drobo video review again there's a Drobo video review page.

Yesterday we released Focus Ring episode 12; another show in the round-table discussion show all about photography. This was our largest panel ever featuring a few old favourite members plus two brand new members of the Photocast Network. It was one of our best ever shows. Don't miss it!

• "Focus Ring 12 - Wear a low cut blouse" - find it at www.photocastnetwork.com

If you're one of the many people who have been waiting for Podshow to announce their discount codes on the Nokia n810 Internet Tablet the wait is over and you can use our promo code - photowalkthrough - to get that massive 15% discount at either the US store - www.nokiausa.com/n810 or the UK store - btpodshow.com/n810. Find out more at our n810 coupon code page.