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Old 20-03-2013, 04:50 PM
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rmuhlack (Richard)
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Megapixels and print sizes ??

Like many others here I am considering progressing from a DSLR to a cooled CCD at some point. Obviously there are many factors to consider - image scale, QE, read noise, dark noise, well depth etc.

For me (and perhaps others here too...?) another factor apart from those above is the suitability of images produced for printing, as I would not only like to produce quality images to display on the web, but also to print and frame for display in my house and as gifts to family/friends etc.

My local photo lab prints at 300dpi, and I take it that this is pretty standard. My understanding is that to produce a print with no image quality loss, the maximum enlargement I can make is [pixel width of sensor]/300 x [pixel height of sensor]/300. For my 400D which is 3888 x 2592 pixels, that translates to approx 12 x 8 inches.

If that is correct, does that mean that for a QHY8/SXVR-M25C (~3115 x 2025) or KAF6303 (~3066x2044) the max size is 10x6", or for the SXVR-H694 (~2750x2200) the max size is 9x7" or for the QSI540 (2048x2048) the max size is 6.8x6.8".

Am I missing something here, or is it really about spending serious coin to only produce A5 sized images? Or is it simply that images from these cameras are not intended for producing hard copy prints, rather they are for on-screen viewing only (where obviously they look spectacular)...?

Is this an area where the humble DSLR still has an edge over their more expensive counterparts?


Last edited by rmuhlack; 20-03-2013 at 05:00 PM. Reason: typo
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Old 20-03-2013, 04:56 PM
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MrB (Simon)
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Not necessarily.
The 300dpi is their highest print resolution, but they can probably make it bigger(lower resolution).
The quality of the print depends on how closely it will be viewed.
For example, I recently had a poster printed for work, the poster was 2.4 x 2.4 metres and done at a print resolution of approx 50dpi(approx two pixels per millimetre). The poster was on display at the back wall of a trade stand at a conference and approx 3 metres away from passers-by. At this distance the 'pixels' were not noticable.
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Old 20-03-2013, 05:07 PM
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Octane (Humayun)
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You have to take viewing distance into account, too.

You can probably get away with 150 ppi and still have a decent print.

H
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Old 20-03-2013, 08:26 PM
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naskies (Dave)
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Acceptable print sizes involves much more than just megapixel count. It's the same idea that a higher megapixel camera isn't necessarily better than a lower megapixel camera - it depends upon the quality of the pixels too.

A better way to think of it is in terms of "signal to noise", like with capturing images. Signal is the picture you want to show - colours, shapes, edges, fine detail, etc. Noise is anything that detracts from that - pixellation, thermal noise, grain, abnormal transitions, etc. Longer viewing distances effectively minimise the "noise".

If you have properly sampled stars (e.g. 1''/px in 2'' seeing) with accurate tracking, then even if you enlarge the image by a *HUGE* factor it won't look pixellated. On the other hand, an image scale of 4''/px in 2'' seeing will give you square stars - which looks horrible very quickly upon enlargement.

Another factor to consider is that a CCD images' pixels are usually higher quality than for a DSLR - 16 bits for most CCDs vs 12 bits for most DSLRs. If you shoot with a mono CCD, the resolution will be much higher compared to a Bayer matrix too.

On an aesthetic level, your subject matter influences your maximum reasonable print sizes too. That's why night scape images often look spectacular, even though at the pixel level the stars are distorted, the image is noisy, etc. On the other hand, a close-up image of a single nebula requires a lot of stacking and photon capture to get the same "wow" effect.

Short answer: if an image looks spectacular on screen, it'll look spectacular in print if you use quality materials and a good print process
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Old 20-03-2013, 08:45 PM
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rmuhlack (Richard)
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Thanks everyone
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Old 20-03-2013, 09:50 PM
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Andy01 (Andy)
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I'm a professional studio portrait photographer. I regularly take the 12mb files from the d700 from its native 34 MB much bigger sizes in Photoshop.

The standard size @ 300 dpi is approx 12x16" but that's no real gauge of the quality of an interpolated print up sized in PS. I regularly sell clients prints up 24x30" or even 30x40" from these files and they still look fantastic!

Yes it's subjective and probably depends on the quality of the file and detail you're looking for, but unless you want to line your walls with your image, you'll probably be just fine with most of the CCD's out there.

Disclaimer: I've recently purchased an SBIG 8300c and when I get my head fully around it, I'll share my experiences with print sizes!

Cheers
Andy
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