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Resolution - not New Year

keithht 8 2 United Kingdom
3 Jan 2013 12:39PM
Hi, last year I purchased a Sony SLT-A35, which in natural light situations is a very good camera, unfortunately recently I have discovered it is as useful in studio flash situations as a chocolate fireguard and as recently I have been offered studio space for free I need a camera that works in a studio flash environment, so I purchased a Canon EOS 550d which as it retains an optical viewfinder works very well in a studio environment. My question is this although the Sony has a 16mp sensor and the Canon an 18mp one when images are viewed and the file details are viewed although the pixel dimensions are correct for each camera both Windows image viewer and Photoshop give a separate resolution figure, in the case of the Sony it is invariable 350dpi and in the case of the Canon it is 72dpi - what is this referring to and does it have any important implications. Sorry about the rather rambling post but is their anyone out there who understands this...Cheers Keith Tomlinson

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JackAllTog Plus
9 5.0k 58 United Kingdom
3 Jan 2013 1:23PM
The dpi value is dots per inch and is usually used for printing(, or sometime for classifying displays though pixels per inch might be better)
Its really meaningless whilst editing on the PC as you are zooming in and out all the time.
I'd quess the Sony one is suggesting you print it out at 350dpi (quite high) whilst the Canon one is saying view this on a PC at 72 dpi/ppi.

Nice one on the studio, hope your getting good results with the canon.

Why does the SLT not work though - i don't understand?
puertouk 6 1.1k 17 United Kingdom
3 Jan 2013 1:49PM
The 72 dpi is for viewing on the internet or on a monitor. You normally set the dpi at 300 as a rule of thumb for printing.
keithh Plus
14 25.4k 33 Wallis And Futuna
3 Jan 2013 1:52PM
Not quite. PPI is Pixels per Inch when related to electronic viewing and DPI is Dots per Inch when used in printing. DPI is important - PPI very much less so in general.
keithht 8 2 United Kingdom
3 Jan 2013 2:30PM
Hi again, thanks for those responses I am aware of the significance of those DPI's in internet and printing situations but what puzzles me is that they are presented as parameters of the original jpeg files straight from the cameras themselves i.e. In Windows Photo Gallery if you display an image and then click on File, Properties, and Details you get a display that has several sections and in the section labelled Image you get:
Horizontal Resolution
Vertical Resolution

In the case of the Sony the vertical and horizontal is listed as 350dpi and in the case of the Canon they are listed as 72dpi looking at the Image Size menu in Photoshop the same figures appear and as I said originally these are not images I have manipulated in any way, why?....Cheers Keith Tomlinson
ChrisV Plus
11 2.1k 26 United Kingdom
3 Jan 2013 3:33PM
Why? It appears Sony and Canon are using different defaults. Resolution is a tricky thing, but you really only need to worry about it if you are specifying for an output device [even if that is merely the screen]. The 18mp of the Canon is always obviously going to give you more absolute resolution [which is the overall pixel dimensions of the captured image] than the Sony.

Printers that reproduce in dpi/lpi [newspapers/books/print adverts etc] will often ask for double the resolution in ppi to the screen they're using [eg 300ppi for 150dpi], but that is overkill and in practice you can get away with closer to 1:1 and other forms of printing [large format inkjet and dye sub] need less still.

To work out the size you can print to, just divide the total pixel height by the ppi required by the printer. If you have an image that is 5184 pixels in height [like your Canon] you will be able to make a print that is 34.56" tall at an output of 150ppi.

But I too am puzzled as to why you can't use the Sony for studio shots. Are you using strobe heads or continuous lighting? I would have thought you'd have to manually meter either for the first type and either should auto-meter for the second.

I've successfully shot with strobe flashes using various Canon and Nikon bodies and also Panasonic CSCs with EVFs - the manual settings would be roughly the same with each, to within 1 ev.
keithht 8 2 United Kingdom
3 Jan 2013 4:22PM
Hi ChrisV, thanks for taking the time to answer my question. I sent a private message to JackAllTog explaining the problem with the SLT. The problem only applies to the SLT-A35 and is due to the fact that the viewfinders are electronic and the view through them is linked to the exposure value being set by the aperture and shutter settings, darkening and lightening respective to the setting. Unfortunately the values you set in a typical studio flash situation probably something like f8/f11 @ 1/100th mean that the viewfinder is too dark to compose your picture. I say that the problem is unique to the A35 because on the A37 you can disable LiveView giving you a viewfinder image that is able to be seen.
ChrisV Plus
11 2.1k 26 United Kingdom
3 Jan 2013 5:18PM
That's something I hadn't thought of! Although in most of the studio situations I've been in I've often been after a shallower DoF than f11 [although with the FF cameras you do need to close down a bit more to get the same range you would with APSc]. They wouldn't of course darken the viewfinder unless you're hitting a DoF preview. Interesting - although I'm sure quite frustrating!

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