[Sideways]

What is the highest ISO people have enlarged successfully?

[little laker]

That's the more important question.

I've only ever blown up photo's that are shot at 200

[UnknownVT]

300ppi/dpi has long been held as the critical quality standard for prints -
although only a few years ago 200ppi/dpi had been touted as good quality (eg: "Popular Photography" still quotes this figure),
and I have used as low as about 160 ppi/dpi to produce many 10x8 that are closely scrutinized -
so sometimes it depends on the subject details too.

So taking that 300ppi/dpi as a critical "standard" -
one can then derive by the largest print one normally produces -

6"x4" = 1800x1200 =close enough to be ~2Mp
7"x5" = 2100x1500 = ~3Mp
10"x6.6" = 3008x2000 = ~6Mp of K100D
10"x8" = 3000x2400 = ~7Mp


Let's go to the other extreme of 160dpi/ppi -

6"x4" = 960x640 = ~0.6Mp
7"x5" = 1120x800 = ~1Mp
10"x8" = 1600x1280 = ~2Mp
16"x12" = 2560x1920 = ~5Mp
20"x16" = 3200x2560 = ~7Mp

or the largest "acceptable print" (using 160ppi/dpi) from -

2Mp (1600x1200) = ~10"x8"
3Mp (2048x1536) = ~13"x10"
5Mp (2592x1944) = ~16"x12"
6Mp (3008x2000) = ~19"x13" for K100D
7Mp (3072x2304) = ~20"x16"

The beauty of larger prints - larger than 10x8 - is that they are normally not held for viewing and not usually subject to "nose to paper" scrutiny - they are normally hung on walls in frames.....
so the lowly 150-160ppi/dpi becomes more than acceptable.

For critical work or smaller prints (say 7"x5") I would still tend to use 300ppi/dpi - but 10"x8" or larger one could drop the ppi/dpi.

Using the previous "standard" for quality of 200ppi/dpi - we get these -

6"x4" = 1200x800 = ~1Mp
7"x5" = 1400x1000 = ~<2Mp
10"x8" = 2000x1600 = ~3Mp
12"x10" = 2400x2000 = ~5Mp
15"x10" = 3008x2000 = 6Mp of K100D
16"x12" = 3200x2400 = ~7Mp

So generally if a camera is capable of producing 10"x8" prints at 300ppi/dpi -
which the K100D (3008x2000) can do - strictly speaking 10"x6.6" - as this is likely to be the biggest size that's handheld and subject to close scutiny -
any larger size are likely to be viewed at further distances so reguire less print pixel density - the K100D can probably get away with about 20"x13.3" at 150ppi/dpi for most display purposes, and even larger if the subject does not have any critical fine detail.

In fact most people can get by with a mere 2Mp for 6x4 (or just 3Mp if more 10"x8" are planned) -

but for people who want to be able to produce really good quality 10"x8" that's close to publication standards - then a 6Mp to 7Mp is a good choice......

Obviously as suggested more Mp also means one can crop and use smaller areas and still get good quality - but 6-8Mp is good enough for most of my needs.

[Lowell Goudge]

UnknownVT has an interesting point, but let's look at it a different way.

Hands up (figuratively) all those who think looking at your K10 or K100 shots full screen on your 22 inch 1680 x 1050 high res monitor is adequate?

Keep in mind that this is only 87 dpi !

I have seen 4 foot by 6 foot prints from 2 & 3 MP! Agreed you don't normally put your nose to the paper, but I always found that uncomfortable any way (my eyes don't focus that close).

The real issue as you print bigger and bigger is to resize and use interpolation to avoid making the pixle too large, this gives smooth images with enough sharpness to print big from small origonal files

[bt*ist]

Largest I've printed : 20x30inches onto canvas from my istDS. At ISO800, but with Noise Ninja used to reduce noise. It turned out very nicely, with noise really only visible in a slight bit of horizontal banding in the shadows.

[UnknownVT]

let's look at it a different way.

Hands up (figuratively) all those who think looking at your K10 or K100 shots full screen on your 22 inch 1680 x 1050 high res monitor is adequate?

Keep in mind that this is only 87 dpi !

I have seen 4 foot by 6 foot prints from 2 & 3 MP! Agreed you don't normally put your nose to the paper, but I always found that uncomfortable any way (my eyes don't focus that close).

The real issue as you print bigger and bigger is to resize and use interpolation to avoid making the pixle too large, this gives smooth images with enough sharpness to print big from small origonal files

There are many ways of viewing "photos" -

via TV (720x480 to 1920x1080)
via monitors/screens (640x480 to 1680x1050, 72dpi for Mac to 96dpi for PC)
newspapers (85 lpi ~ 85dpi)
glossy magazines (200lpi typical ~200dpi)
books (similar to magazines)
print to paper

As pointed out quality is dependent on viewing distance - that's why viewing on TV for example is OK - but walk right up to the screen and see the image "breaking down" - and think if that were a photo print - would it be acceptable - probably not.

It is similar for monitors/screens - but the pitch/dpi is finer so less complaints - but for a photo print held in the hand that kind of "resolution" dot-pitch probably would not be very acceptable - but viewed from a few feet away the image is fine....

Another really good example is newsprint - most of us have cut out photos from newspapers and been quite happy about it - now think if one's photo print quality was like that from our favorite photo lab..... that's another story - right?

Glossy magazines and fine print books do come closer to what we photo enthusiasts think of as "photographs"/print - but again if we get photo prints like the quality in magazines (and I am only talking about dot-pitch resolution and color gaumet, and not the artist quality of the shot) we probably would not be that satisfied with the photo lab.....

So we come back to our own photo prints -
either printing from our own home (and hopefully high quality) photo printer,
or from a professional lab (actually even the digital print stations at the typical Wlagreens, WalMarts of this world are very good)
- the quality becomes more "demanding"/critical.

Like I said for a number of years printing at 200ppi/dpi was the concensus standard which even "Popular Photography" magazine still quotes - but with rising megapixels - there seems to be a trend back toward 300ppi/dpi prints - as these are no longer stretching demands on modern digicams/dSLRs.

My own take is that on the largest handheld viewing photo size - normally 10"x8" - if one can print at the most demanding ppi/dpi - which is around 300ppi/dpi - that print would not be lacking even when examined at close scrutiny ie: "nose to paper" -
so (for me) correspondingly larger sizes - which requires correspondingly larger viewing distances would be acceptable at lower ppi/dpi-pitch.

I personally use about 150 ppi/dpi as my own minimum (which is about 20"x13.3" from my 6mp K100D) - since I know I can still walk up to a wall displayed print and squint, and I don't want a "newsprint" quality photo - of course YMMV.

However if someone wanted to produce a poster from one of my photos - who am I to argue - I'd be flattered
and more than accept if the reproduction pitch is going to be less than even 100 or even 72dpi......

Like I said YMMV.