DOF depends on only one thing, the Scale Ratio, sometimes called the Magnification Ratio.

Scale Ratio is now many times your sensor size will fit into the subject size. Which is altered by how close you are to the subject and the size of your subject, your sensor size is a constant (obviously).

Putting a 50mm lens onto a Pentax Q will only alter how close you need to be to the subject to frame the same shot. If your framing the same shot on any camera with any focal length lens the DOF will be exactly the same with all combinations. Once the Scale Ratio is known the DOF can be read off a table such as this one.




Even the effect of aperture is Scale Ratio, this time how large the aperture is compared to the size of your sensor, as the aperture is (usually) smaller than the sensor or film it mitigates the effect of the lens Scale Ratio, you get a wider DOF with smaller apertures.

All the reviews of the Pentax Q mentioned the small sensor which put me off buying one, when the price came down I took the plunge, if I had listened to all the reviews, both magazine and on the Web I would have missed these shots.

http://www.flickr.com/photos/chris-judge/sets/72157631977076250/

Not one review mentioned it's image quality, none mentioned what a great advantage there is with a small sensor for long reach using manageable, cheap, lenses, or saw the wide depth of field as an asset.

At least with forum reviews you have some recourse by posting your comments, with magazines you have none. Like Smeggypants I haven't bought a photography magazine for years.

Just for you John I also took a shot with a Sigma 500mm mirror lens, meant to post it before - sorry




Not as good as the cheap Paragon 500mm refractor lens which cost just a few pounds on eBay a few years ago (less than £20 if memory serves).

Same processing on both, just re-size and a little High Pass sharpening at the same settings.

The first image from the K5-II certainly looks sharper, but that could just be a slight amount of camera shake on the second.

The K5-IIs should be sharp out of the camera and have more resolution, DXO doesn't measure resolution.

The Pentax referred to on some old Metz flashguns would have been the old Spotmatic with just a pair of sync contacts, it didn't matter what the trigger voltage was back then.

But it is true that any modern flash should have a low trigger voltage, but as it's so easy to check with a cheap voltmeter you can pick up for a fiver at most any filling station it's worth doing as a matter of course, I have plenty of old flashguns (Metz included) with trigger voltages in the 100 - 400V range which will blow the sync circuit of most any digital camera to kingdom come. Better safe than sorry is all I'm saying.

The reason why the (usually) -ve contact is in the groove of the hotshoe was so that you couldn't accidentally touch both sync contacts and get a shock.

I agree John, formatting a card in the device it's going to be used in is the only safe way to use cards. Formatting re-news the DCIM (Digital Camera Image Management) file in a camera, cards don't use the same formatting as hard drives they cannot see the whole memory map as they are paged memory, if an image tries to spread onto another memory page it will corrupt the card.

The data in the DCIM file prevents this, amongst other important things, such as not allowing a larger new file to overwrite a deleted file if there's not enough room for it which leads to 'orphan files' which will corrupt the new as well as the partially overwritten file. It also controls the beginning and end of each image/video file in playback.

If this is off topic (and it is), I apologise, but it's really important to know.

Thanks John

Another Pentax Q HDR taken tonight in Sheffield



Sheffield_04 by screwdriver1, on Flickr

Having seen how good the Q is at telephoto, I thought I would try the opposite, so I made a converter to fit a cheap set of bellows from a Q>D adapter, basically a thick washer, I used an old Takumar 55mm f2 for the lens







The reason I used a Q>D Type adapter is you can make the Q lens mount to M42mm lens mount distance below the 36.26mm (45.46mm - 9,2mm) with the bellows closed which means any 42mm lens will focus on infinity.

It's Winter here, but a few Lobelia flowers are still hanging on manfully

a few pics




The flower is 13mm across

Closer




Pop the flash up and back off a little




These are full frame, just re-sized for posting.

Pentax Q downsides

1) Initially price, £600 was way too much, not a problem now the price has come down.

2) Battery life is short (around 2 hours at the most) Fortunately it's a common battery and can be bought for around £3.00 each inc P&P (eBay, there are genuine suppliers on eBay, but 'caveat emptor' does apply). You'll need more than one extra. If you are using the standard 8.5mm lens with the hotshoe viewfinder you can turn off the rear LCD which greatly extends battery life.

3) It's not the fastest camera out there, if you apply any filters and/or effects it can be several seconds before it can take another picture, not a problem for me as I will use Photoshop if I want 'effects', but the front dial is a waste for me. On the same theme Pentax have enabled bracketed shots for HDR very well, it takes the bracketed shots very quickly (within a second for the 3 shots), but it takes around 4 seconds to store the images onto the card (shooting in Raw). Again not really a problem.

4) Lack of a good wide angle lens which is a function of the small sensor, apart from the 3.5mm fisheye the widest lens is the 5 - 15mm zoom which is the equivalent FOV of a 27.5mm to 82.5mm, not 'super' wide.

5) More of a technical one this, you can't use small apertures with lenses and adapters, the small sensor is prone to diffraction, as all small sensors are, f8 starts to show signs, f5.6 is fine.

Pentax Q Upsides.

There are lots,

1) Image quality is surprisingly one of them, it almost holds it's own against my K5 even in low light, it's not as good, but it's closer than you might think. I held off buying a Q because of all the who-ha about the small sensor, the first thing every review went on about. In practice it really isn't an issue, image quality is better than good and the 8.5mm kit lens is frankly superb.

2) Obviously size, it's the camera that's always with me, I can carry the whole kit of spare batteries, cards, lenses etc in a few pockets.

3) The opposite of 4 above is also true. You can get amazing telephoto shots with the Q and a lens adapter, the superb Pentax 300mm f4 becomes a superb 1650mm f4! A bird photographers dream come true and all with a small pocket-able kit. Very useable for Astro photography as well as terrestrial, Moon shots are easy, a 500mm lens will fill the frame with the Moon on a Q.

4) A street photographers ideal camera, the 'shutter sound' can be turned off and you have a pretty much totally silent camera, the small size also works here too as does the image quality, if street photography is your 'thing' (and after buying a Q it might well become your 'thing')your away.

All in all a very useful bit of kit, I would strongly suggest getting the twin lens kit as both the 8,5mm and the 5 - 15mm lenses are almost impossible to find at the moment.