question about zooms and cropping for close ups
Since I've been researching, I've concentrated on high zoom. This revelation finally hit me. Correct me if I'm wrong please.........

With resolution of 6-8MP and zoom of 5-6X I can still get a good close up by cropping. I can crop the pic to my desired close up & still get good image - how high does my resolution have to be? May be I don't have to concentrate so much on getting the maximum zooming camera (12-15X?).

Nikon D40 question - has 18-55mm lens - what zoom power is this comparable to - I don't know how to convert this number to something I am familiar with..

Comments (6)

The easy way to determine the acceptable quality maximum enlargement/crop for a certain camera is to make standard size prints, cutting the original file in halves in the Photoshop (or whatever you use to process), so that photo #1 is full size, #2 - half (equivalent to 2x size standard), #3 - quarter, etc. A very cheap, quick and exact way to measure it..


Comment #1

Wendysue wrote:.

With resolution of 6-8MP and zoom of 5-6X I can still get a goodclose up by cropping. I can crop the pic to my desired close up &still get good image.

I'll say "enlarge" rather than "crop" because I think it's important to keep in mind that that is what you are doing - enlarging the image, with all that that implies in terms of exposing flaws in the photo etc..

With that in mind (and leaving the question of resolution for later) - yes, you can get the equivalent of a longer lens by enlarging* if the image is good quality and especially good and sharp..

* But remember that the image will not have the characteristics of the longer lens - depth of field, perspective etc. A picture taken with a 100mm lens will still have "100mm character" even when enlarged. The same picture taken with a, say, 200mm lens will "look different"..

But if the image is less than perfect, and in particular, not perfectly sharp, then all you are doing is enlarging the flaws and the result will not look as good as the original uncropped image, or as good as a picture taken with the "right" length of lens..

So you can do what you say, but there are limits and it's no real substitute for a longer lens. In general I don't think you could say that you could go as far as 5 or 6x zoom via enlargement on a regular basis..

- how high does my resolution have to be? Maybe I don't have to concentrate so much on getting the maximum zoomingcamera (12-15X?).

As I said above, I don't think you'll find cropping/enlargement an adequate substitute for a longer lens. But anyway, resolution....

The resolution you need depends on the purpose and size of the image you want to produce..

If you are producing an image to be shown on a computer monitor, then 800-1024 pixels wide by whatever depth is the most you need. That is the limit of your monitor's resolution, anything more is wasted..

A 1024x768 image, for example, is about 768,000 pixels - that's less than 1 Megapixel. So in theory you could crop a 6-8MP image very heavily and not lose resolution. But noting as above - you are still enlarging the image and you may not get the best result..

A print, on the other hand, requires an absolute minimum of 200 dots per inch, and ideally closer to 300. At 250 dpi, for example, an 8x10 print requires 2,000 x 2,500 pixels - that's 5 megapixels. A 6x4 print, on the othe hand, needs only 1.5 Megapixels..

But you're not necessarily limited that much by the resolution of your camera. From the above you might assume that a 5MP camera can't produce prints bigger than 8x10. But you can - partly because you can go down to 200dpi if you need to , and partly because your photo editing software can interpolate - add new pixels - when you enlarge an image. This process isn't perfect of course - you can't add detail that wasn-t in the original image - but it can take you a long way - a surprisingly long way. I think there are people on these forums who have produced 16x20 or larger from 5MP originals..

Nikon D40 question - has 18-55mm lens - what zoom power is thiscomparable to - I don't know how to convert this number to somethingI am familiar with.

Depends on what it is you are "familiar with". Let's put it this way:.

Leaving aside for the moment a discussion of "crop factors" with digital compact cameras vs SLRs vs 35mm:.

Most compact cameras will express the zoom range as an "x" factor (eg 3x) whereas with SLRs like the D40, the zoom range of a lens is expressed in focal length - e.g. 18 mm to 55 mm..

You can only equate these if you know the actual focal length of the compact camera lens. This is usually inscribed on the front of the lens. But as a rough guide:.

The "base" or shortest length of a compact zoom will usually be around the 30-40 mm mark. So a "12X zoom" will probably be something like 30-360 mm..

In those terms, the D40 18-55 lens is 3x zoom. 18 x 3 = 55 (close enough).And the Nikon 18-200 zoom lens, for example, is (about) 11x zoom..

In short, as a VERY ROUGH guide, you could look at a compact camera, assume the base focal length is around 30mm, and use the zoom factor to understand ROUGHLY what sort of reach it has compared to an SLR lens..

BUT: All of that is leaving out the fact that lenses behave differently on compacts vs SLRs. I said above that the "base" focal length of a compact is probably around 30-40mm, but if you look at the front of the lens you will see a much smaller number - maybe 10mm or so. In other words, the front of that 12x zoom camera that I described as being roughly 30-360mm, will actually say something like "10-120 mm"..

Why is this so? Well let's get in to that later. For now, the first and simplest answer to your question is as I have put it above. If all you want is a rough guide to the comparison between a compact "12X zoom" camera and an SLR "18-55mm" lens then that is a starting point..

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window..

Comment #2

I'd go long with arrowman. If it will help I'll add that I do 32" x 24" from my _best_ 5 megapixel jpg's and they look OK but bear in mind that they hang on the wall and people don't get up close to them. For pictures that people go up close to I limit it to 20" x 16" but that is mainly because I got a few nice frames that size cheaply..

If you look at it from the end of the sequence, rather than from the beginning, you could argue that an A4 print needs about 1280 x 1760 for "everyday" quality (say 150 ppi) or 1650 x 2340 pixels for better (200 ppi) and even at "Exhibition" quality (the much quoted 300 ppi) we are still only talking about 2475 x 3504 pixels, or about the output from an 8 megapixel camera..

It might be an idea to select some of your typical photo's and crop out a bit those first two sizes and then print them to A4 and see what you make of them. The joy of digital photography is that we can experiment and churn out the result on the printer in minutes..

Regards, David.

PS BTW, when I started 9 or 10 years ago I had a top of the range camera that churned out 1024 x 768 pixels and I printed them at about 6" x 9" and they looked OK. Shows how theory and practice differ.....

Comment #3

Your D40 has a "Crop Factor" of 1.5; ie a 35mm film frame is 1.5 times larger than your camera's sensor..

(see ).

A 50mm lens gives a "normal" field of view for a full frame camera; divide by the crop factor to see what focal length is "normal" for your camera. This is 50mm/1.5= 33mm..

A lens has an effective magnification of it's focal length divided by the focal length for a "normal" image..

Your lens' minimum magnification is 18mm/33mm=.55xYour lens' maximum magnification is 55mm/33mm=1.67x.

Your len's overall zoom ratio is maximum/minimum = 3x..


Comment #4

Wendysue wrote:.

Nikon D40 question - has 18-55mm lens - what zoom power is thiscomparable to - I don't know how to convert this number to somethingI am familiar with.

Dave Martin wrote:.

Your lens' minimum magnification is 18mm/33mm=.55xYour lens' maximum magnification is 55mm/33mm=1.67x.

Your len's overall zoom ratio is maximum/minimum = 3x..

Just continuing Dave's very good explanation and relating it to your FZ8:.

50mm/6=8.33mmminimum magnification is 6mm/8.33mm=.72Xmaximum magnification is 72mm/8.33mm=8.64X.

Overall zoom ratio is 12X..

Comment #5

An 18-55mm lens on a 1.5 crop camera has a 3 times zoom 18 x 3 = 54mmAn 18-55 on a full frame camera still has a 3 x zoomAn 18-55mm on a 4/3rd (Olympus) camera still has a 3 x zoom.

The field of view will be different for each of those lenses (How telephoto they are) because the size of the "film" is different..

There is no need to establish a basemark of 50mm to describe the zoom ratio of any lens. Nikons 18-135 lens is still a 7.5 x zoom (7.5 x 18) even though most of the range is well past the 33mm unhelpfully referred to in the previous post. BUT to understand what you can SEE with that lens you need not only to know it's zoom ratio but also the size of the crop..

It is common for most manufacturers to give both the actual focal length of the lens AND the 35mm film equivalent which helps give some of us, using our experience, an idea of what the view will be like through that lens..

Long ago when 35mm film became popular (and before zoom lenses had been invented) someone determined that a 50mm lens should be described as a standard lens. This was loosely based on what the eye can see***. Anything that gave you a wider view is termed a wide-angle lens and anything that gave a longer view is termed a telephoto (with sub-species like moderate telephoto etc etc)..

That still remains the standard for describing lenses. Reviews on this site of asophisticated point & shoot may list among the Plus points that it boasts a true wide angle 28-xxx mm equivalent lens (Most point and shoots have a 38-xxx mm equivalent lens)..

So in 35mm terms the 18-55mm lens you mention is a 27-83mm lens. it will give a field of view from wider than most P & S cameras to less telephoto than other 3x zooms..

Hope that helps!.

***In fact the eye in a narrow sense can see 42mm but it does not stay still and focus on one central object but rather takes in a lot of detail very quickly by moving away from that central focus zone to explore more peripheral areas..

P.S. The longer the zoom ratio the more difficult it is to maintain high quality in the lens. It is for good reason that most pro zoom lenses are 3x zooms..

Chris Elliott.

*Nikon* D Eighty + Fifty - Other equipment in Profile.


Comment #6

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