Go Back   Steve's Digicams Forums > Digicam Help > Newbie Help

Reply
 
Thread Tools Search this Thread
Old Oct 28, 2005, 10:09 PM   #1
Senior Member
 
fofa's Avatar
 
Join Date: Oct 2005
Posts: 547
Default

OK, I am not sure if this more of a rant than a question. Has to do with telephoto length and the results. Did some searches, here, on the net, etc. Still not sure I understand, but what I think I have figured out is the current digicam nX optical zoom factor is more a selling point than an actual measure of the telephoto results. I guess because I base any telephoto results on the 35mm equivalent 50MM lens. Less than that is wide angle, more than that is telephoto (for the most part). Since I have been looking at the current crop of UltraZooms, and their 35mm equivalent, this has brought up the question. Example, take the Panasonic FZx series with their 12X optical lens. Since I have not been able to find a conversion chart (I guess because it depends on the sensor size) of 35mm equivalent to nX zoom I'll explain this way. It is stated it has a 35mm equivalent of 35 - 420MM. So in my feeble mind (which I think is wrong now) 420MM = 12X. In my mind the 35 side didn't come into play because that is wide angle, not zoom. But when I was looking at the new Samsung Pro815 with it's 15X optical zoom, it's 35mm equivalent is stated as 28 - 420MM. Humm my brain says, how can a 12X and a 15X have then same 420MM top end. Some thing is fishy here. I would have expected the 15X to be like 525MM or something like that. So it would appear the Samsung will have the same telephoto capability, but a wider angle on it's lens. But I was expecting more telephoto with that 15X. Then I ran across this "It's important to realize that a 3x optical zoom on one digital camera may not give the same magnification as another with a 3x zoom. The Nikon 5400 has a 4x zoom, which when fully zoomed has a 116mm equivalent focal length. But Nikon 5200, which has a 3x zoom, has a 115mm equivalent focal length. Not much difference yet one is a 3x digicam and the other is 4x."
So now I am not sure how to look at these. Does this mean there maybe a 10X out there that has the 420MM 35mm equivalent? I mean, what does it all mean? Is there no standard? Maybe because I was thinking zoom = telephoto, but I know there are wide angle zooms. So don't let my bad use of the zoom word throw you. Since nX is a magnification factor, I would think it would be from a normal (50MM lens), and not from some wide angle reference since my eyes don't do wide angle. Magnification is what I get when I look through a magnifying glass, microscope, binoculers, etc.
:?
fofa is offline   Reply With Quote
Sponsored Links
Old Oct 29, 2005, 12:01 AM   #2
Senior Member
 
Join Date: Oct 2002
Posts: 544
Default

The "X" factor is simply a ratio of the widest and longest range of a lens... it's really kind of meaningless. For example, a 28-280 mm lens is a 10X zoom, but so is a 37-370 mm one. Most point and shoot cameras don't have a very good wide angle capability simply because the sensors are too small. This results in a cropped center section of a captured image.

The 35mm equivalency is just a way of providing a standard for all (almost) cameras.

In the wonderful world of DSLR lenses, the "X" numbers are rarely used. Instead, they use the focal length(s) like 70-200mm or 17-85mm. The confusion in these cameras is the "crop factor" which is based on the size of the sensor compared to a 35mm frame. The ASP C sensor is smaller than the 35mm frame and the camera crops the center of the picture. This results (actually acts like) a 1.6X magnification of the field of view (in Canon cameras). This factor applies to both the wide and telephoto ends of all lenses used on that particular camera. Your 50 mm lens will act like an 80mm one. Full Frame cameras, the expensive end of the DSLR families, don't have a crop factor. This results in superior wide angle performance... the 50mm lens acts like a 50mm lens.
Wildman is offline   Reply With Quote
Old Oct 29, 2005, 8:44 AM   #3
Senior Member
 
rjseeney's Avatar
 
Join Date: Dec 2004
Location: Taylor Mill, Kentucky
Posts: 2,398
Default

You are correct in assuming 'x" factor is a marketing ploy. Wildman's explanation is correct.It is simply the longest focal length divided by the shortest focal length. As was said what is really important is actual focal length..you don't here this talked about when refering to DSLR lenses because for the most part, DSLR users don't care what the "X" factor is.
rjseeney is offline   Reply With Quote
Old Oct 29, 2005, 6:18 PM   #4
Senior Member
 
BillDrew's Avatar
 
Join Date: Jun 2002
Location: Hay River Township, WI
Posts: 2,512
Default

You answered your own question.

fofa wrote:
Quote:
...but what I think I have figured out is the current digicam nX optical zoom factor is more a selling point than an actual measure of the telephoto results. ...
BillDrew is offline   Reply With Quote
Old Oct 30, 2005, 6:36 AM   #5
Senior Member
 
Monza76's Avatar
 
Join Date: Jul 2004
Posts: 4,093
Default

It is all here now, just let me tie it all together.

1- 50mm (actually closer to 45mm in reality) is a standard lens in 35mm because the focal length is approximately equal to the diagonal of the negative. A 50mm lens will give a perspective similar to looking with the naked eye.

2- The nX is a magnification factor with binoculars and telescopes, an 8X21 pair of binoculars magnify the view 8 times (equivalent to a 400MM lens on a 35mm camera) and have 21mm objective lenses (note larger lenses means more light gathering, an 8X50 pair of equal quality would work much better in low light, this is analogous to the F number on camera lenses).

3- As Wildman already stated, the nX factor in camera zooms just refers to the ratio of longest focal length to shortest, so a 35-350mm (35mm equivalent) lens is referred to as a 10X zoom, so would a 42-420mm or a 28-280mmand a 28-84mm would be a 3X zoom. The only thing this factor tells you is the relative difference between widest and longest focal lengths.

I haven't added anything here, just put it all together. When buying a camera based on the focal length of the lens remember to determine if you want wide angle or telephoto as your primary mode. Do you like to take people shots at parties, group photos, interior shots or sweeping landscapes??, if you do you may need a zoom with a 24-28mm (35mm equivalent) wide end. If your pleasure comes from birds and other wildlife, sports events, concerts, or you enjoy tight portrait photography (the head and shoulders shot), then you are better served with a lens that extends well beyond 200mm (35mm equivalent of course).

That, of course, is the big drawing point for the DSLR, zoom ratios rarely go higher than 4X for these big lensesbut you can have 2 or3 lenses to cover a very large range of focal lengths.

Ira
Monza76 is offline   Reply With Quote
Old Nov 3, 2005, 6:08 AM   #6
Member
 
Join Date: Sep 2005
Posts: 41
Default

Does anyone else think it would be nice if people started to talk in terms of field of vision, in degrees. That would actually describe much more meaningfully the function of the lens.

Or are people in a few generations time going to have to learn that back in the twentieth century, most consumer cameras had these 35mm 'film' sensors, so that's why we use '35mm equivalent' measurements...
pterrr is offline   Reply With Quote
Old Nov 3, 2005, 9:22 AM   #7
Senior Member
 
Monza76's Avatar
 
Join Date: Jul 2004
Posts: 4,093
Default

pterrr there is still one fly in the ointment. Angle of view makes much more sense, but if you have a 35mm film camera (or full frame digital like a Canon D1 or 5D) your lenses would cover a larger angle of view then the same lenses would cover on an APS sensor sized camera (like a 20D or 350D). That would mean that there would still be a filter-factor to contend with. This system would work very well for fixed lens digicams and 4/3rd cameras (or any other camera system where all sensors are the samephysical dimensions)however because they do not have sensor size issues.

A great idea but not the answer yet.

Ira
Monza76 is offline   Reply With Quote
Old Nov 3, 2005, 10:36 AM   #8
Member
 
Join Date: Sep 2005
Posts: 41
Default

Monza76 wrote:
Quote:
This system would work very well for fixed lens digicams and 4/3rd cameras (or any other camera system where all sensors are the samephysical dimensions)however because they do not have sensor size issues.

A great idea but not the answer yet.

Ira
Of course you are right, and it was rather innaccurate for me to say it would "describe much more meaningfully the function of the lens" - it's really the lens/sensor combination that it describes.

Still, it is the norm when people talk about kit lenses on dSLRs, for instance, for them to refer to the 35mm eq. focal length. In cases where lenses are interchangeable, and usable on bodies with a range of sensor sizes, it seems logical to me that one might talk about the actual physical dimension of the lens, and it's FOV when used with a particular camera body. Essentially FOV can always, AFAICT, be used in place of '35mm eq.'
pterrr is offline   Reply With Quote
Old Nov 3, 2005, 12:52 PM   #9
Senior Member
 
Monza76's Avatar
 
Join Date: Jul 2004
Posts: 4,093
Default

pterrr I agree completely, Except for Canon, all of the other film SLR companies seem to have settled on the APS sensor, that means they just need a different set of view angles for the film cameras. Olympus (and any other 4/3 producers which may appear) have no worries about angle of view since the standard is actually based on sensor size (a wise choice I believe although some have referred to it as an evolutionary dead end).

35mm became an ad hoc standard because it was the most popular film format for so long. Digital sensor size has not settled on a "standard" yet. If that happens then all of this nonsense may be forgotten.

Ira
Monza76 is offline   Reply With Quote
Old Nov 3, 2005, 4:31 PM   #10
Senior Member
 
BillDrew's Avatar
 
Join Date: Jun 2002
Location: Hay River Township, WI
Posts: 2,512
Default

Field of viewis a good measure for any camera that does not allow changing the lens, i.e., everything but SLRs. That with the "rule of thumb" that your thumb at arms length covers about two degrees gives a much better idea of coverage than saying the lens is 300mm (equiv), and certianly more than the meaningless 12x zoom.
BillDrew is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 1:32 AM.