Effect of megapixels on print size

[Big Mike]

But implying that the 8mp camera will by default do worse, is quite simply not true. Given equal setups (same tripod, same lens, things like that) mega pixel count has no bearing whatsoever on how clear a photo will be. Sensor size on the other hand does.

I don't think he is implying that at all. Given equal set ups...you are correct, but he is saying that the set up that you use is more important that the number of MP you are recording...and possibly the size of the sensor (within reason).

So when someone asks how big of a print (acceptable quality) they can make...it depends on the file size (MP count), noise levels (Sensor size) and sharpness (technique, lens, software etc.).

That's how I see it anyway.

 

[voodoocat]

I'd put megapixel count lowest on the list of factors required for a good large print. Sensor size and sharpness (lens and tripod) are far more important.

 

[Jeff Canes]

I'd put megapixel count lowest on the list of factors required for a good large print. Sensor size and sharpness (lens and tripod) are far more important.

Ditto, but of those I would but the lens as the most important

 

[DocFrankenstein]

How big are you gonna print?

I've done 13*19 prints from the rebel.

How did they look?

They looked really good. I upsized them in the photoshop, so that you can't see individual pixels... etc... But it's nice and sharp

Of course, if you look at it from 8 cm and get really anal.... You could say that the detail is "smooth" or something...

But the rebel produces 3000 by 2000 file... 19 inches...

3000/19=157 dpi

If you consider that most of the color magazines print at 75 dpi and I think the maximum is 150 DPI...

You should be ok with the rebel sensor. Just don't shoot with 24-300 zoom

 

[voodoocat]

If you consider that most of the color magazines print at 75 dpi and I think the maximum is 150 DPI...

where'd you get that # from?
Magazines print between 200-399 dpi for the most part. Digital and 35mm usually doesn't get printed higher than maybe a half page in magazines. For full page prints the quality magazines require medium format and larger.

 

[DocFrankenstein]

If you consider that most of the color magazines print at 75 dpi and I think the maximum is 150 DPI...

where'd you get that # from?
Magazines print between 200-399 dpi for the most part. Digital and 35mm usually doesn't get printed higher than maybe a half page in magazines. For full page prints the quality magazines require medium format and larger.

I may be wrong, but I remember seeing figures of that order somewhere on luminous landscape and an offset printing book I read 2 years ago.

I can't find any quotes. Again... I may be wrong, but I do remember the 150 DPI for "quality glossy magazines" from some professional book about printing.

But it may be 300 dpi too...

Most of the physiology books claim that the human eye by itself can't distinguish detail finer than .1 mm.

It doesn't make sense to print at more than 230? LPI or something like that...

And considering the viewing distance for 13*19 poster... I think 157 DPI is adequate. IMHO

 

[Digital Matt]

I don't understand why you'd even compare the two like that. It's apples to oranges.

I could also say an 8mp 1/200s at ISO 100 will look better than a 6.3mp 4s at ISO 800. But it doesn't prove that the 8mp camera is cleaner or sharper. I don't get what you're trying to prove. Are you trying to justify your 6.3mp purchase?!?

I made a comparison to illustrate the fact that resolution does not = sharpness, and that getting large prints is not solely dependant on megapixels. I never said, or implied that an 8mp camera will default to worse. As Big Mike and others said, megapixels are really not the most important thing, and I'd hate to see someone buy a large mp camera and automatically expect to get good enlargements.

As far as 75 DPI, be careful when you say DPI. There are two terms involved in printing. Dots per inch, and LINES per inch. Printers use lines per inch, and DPI. 75 LPI is 150 PPI. Pixels are for your screen. 75 LPI, or 150 DPI may be fine for newspapers, but high res photo prints are done at 150 LPI, 300 PPI, and no less, when quality is a must. My 20x30s from my Rebel print at 200 DPI and look good, but you are viewing them typically from a few feet away. All of our prints at work ( I work for a photo digital photo studio) are done at 300 PPI.

 

[jadin]

I made a comparison to illustrate the fact that resolution does not = sharpness, and that getting large prints is not solely dependant on megapixels. I never said, or implied that an 8mp camera will default to worse. As Big Mike and others said, megapixels are really not the most important thing, and I'd hate to see someone buy a large mp camera and automatically expect to get good enlargements.

Roger that. To me it sounded like you trying to imply that the 6mp would be automatically better, which wouldn't add up. Looks like we're both arguing for the same thing.

 

[TomRussell]

sorry to resurrect an old subject but..

i've personally seen 20x30 prints (off true photographic stuff) made from a 3 megapixel camera. that look absolutely amazing. Obviously the image was resampled upwards so the final print is at about 150-300 dpi, but that doesn't change the fact that the image that was there in the beginning was from a 3 megapixel camera.

Once you reach above 8x10/8x12, the ball game changes - resolution doesn't come into it so much. You don't eye something that large close up with a magnifying glass, if you do, sure you'll see a loss of clarity, but you don't normally look at something like that up close - it's to be viewed from, say, a pace back while the photo is hanging on a wall. There, a 3 or 4 megapixel camera, so long as you resample the image upwards, can look absolutely stellar.

If you've got a good picture, print it.

You have no excuses.

 

[hlasso]

...
You should be ok with the rebel sensor. Just don't shoot with 24-300 zoom

Interesting...

I just bought a Canon Digital Rebel and attached it my Canon 75-300 USM lens. I can clearly see that shots with this lens are less sharp than those with the one enclosed with the camera.

Is this due to the lens (too slow) or something else?

Should I shoot a higher speeds? (e.g. 1/480 with 300mm focal length)

I'm about to shoot some portraits of my family and friends, so I'd use a 135mm or so focal length, but I also want to print the pictures in a reasonable size... Am I missing something?

 

[Big Mike]

...
You should be ok with the rebel sensor. Just don't shoot with 24-300 zoom

Interesting...

I just bought a Canon Digital Rebel and attached it my Canon 75-300 USM lens. I can clearly see that shots with this lens are less sharp than those with the one enclosed with the camera.

Is this due to the lens (too slow) or something else?

Should I shoot a higher speeds? (e.g. 1/480 with 300mm focal length)

I'm about to shoot some portraits of my family and friends, so I'd use a 135mm or so focal length, but I also want to print the pictures in a reasonable size... Am I missing something?

I think that lens is known for being a little soft...especially at full zoom.

If you are shooting hand held...you should keep the shutter speed (denominator) close to or over the focal length. I think the 1.6 crop factor applies for this rule of thumb. So when shooting at full zoom, you would want the shutter speed to be 1/500. To get that speed in less than bright sun light you will probably have to jack up the ISO because opening up the aperture will not be enough. A nice fast lens would help too.

To get around this, you can use a tripod & remote release (or self timer). This is always a good idea if you want to make enlargements anyway.

 

[voodoocat]

The crop factor shouldn't have an effect on the 1/focal length rule. The image isn't being magnified any more than a 300mm so you would still go with 1/300 as a safe handheld shutter speed.

 

[DocFrankenstein]

The crop factor shouldn't have an effect on the 1/focal length rule. The image isn't being magnified any more than a 300mm so you would still go with 1/300 as a safe handheld shutter speed.

If you want to make a print of the same size, then you have to multipy by 1.6

Interesting...

I just bought a Canon Digital Rebel and attached it my Canon 75-300 USM lens. I can clearly see that shots with this lens are less sharp than those with the one enclosed with the camera.

18-55 you mean?

Is this due to the lens (too slow) or something else?

It's a "cheap" consumer lens. It's not designed to give sharp pictures or to focus quickly.

Should I shoot a higher speeds? (e.g. 1/480 with 300mm focal length)

I think 1/300th would be ok if you hold your cam steady.

I'm about to shoot some portraits of my family and friends, so I'd use a 135mm or so focal length, but I also want to print the pictures in a reasonable size... Am I missing something?

It's only sharp when you stop it down to f/8, but then you'd lose the bokeh. If you open it up all the way, you have an OK bokeh, but you lose the sharpness...

You need a better lens. Try 50/1.8... it's a good lens and costs 70 bucks. Good for portraits too.

Then you'll see the difference between a good lens and a bad lens

 

[voodoocat]

The crop factor shouldn't have an effect on the 1/focal length rule. The image isn't being magnified any more than a 300mm so you would still go with 1/300 as a safe handheld shutter speed.

If you want to make a print of the same size, then you have to multipy by 1.6

I was talking about the rule for getting a sharp photo without the aid of a tripod or stabilizing device. The focal length never changes with the crop factor so it's the same exact magnification regardless of film format. A 300 lens would require ~1/300 shutterspeed when shooting handheld.

 

[DocFrankenstein]

I was talking about the rule for getting a sharp photo without the aid of a tripod or stabilizing device. The focal length never changes with the crop factor so it's the same exact magnification regardless of film format. A 300 lens would require ~1/300 shutterspeed when shooting handheld.

Would you like to extend this rule to small sensor digicams?

For example: Canon S1 IS has a sensor of around 3*3 mm. The lens built into the camera has focal length from around 4.5 mm to 38mm or something like that, which is an equivalent to 300mm at the telephoto end. If applied the same terminology as DSLR, it has a crop factor of (let's say) 10...

Now, by your rule, I should consistently be getting sharp pictures handheld at 1/30th of a second, even though the equivalent focal length for full frame is 300 mm.

Good luck with that!

Therefore, you'd have to multiply the focal length of the lens by 1.6...