Zooms and Optical Specifications

When one looks at a lens for a DSLR and the focal lengths are specified as 18-

200mm, how does this convert to a numbered factor such as "10x optical" or "6x

optical" as specified for P&S cameras?

 

For DX lenses?

 

For FF lenses?

 

Ray

200/18 = 11.1... so it's 11x zoom.

Also, Ray, the 10X or 6X or whatever number is sometimes pointless. For instance a

70-300 zoom is about a 4.3X zoom, and an 18-70 is about 3.9X, but they're different

focal lengths. On P&S cameras, even though they are often very high "x" numbers, they

RARELY go as wide in perspective as an 18-xxx lens does. So... there's more to the spec

than just the "x" number.

 

ALSO... keep in mind that a really high X does not mean it's better than a lower one. For

instance, the 18-200 11.1X zoom is a really nice lens for many purposes, but it's not

"better" than a 17-55 f2.8 zoom (within the focal length they both share of course). In fact

the 17-55, even though it's only a 3.2X zoom, is WAY better.

 

So... there's much to learn. Not sure if you understood all that.

The 18-200 is an 11x zoom. The zoom factor is determined by dividing the longest focal length by the shortest one (regardless of format). P&S cameras use 135 format "equivalences" as a marketing trick to make their lenses appear longer and imply something about the optics that is not true; regrettably this is also done with DX lenses. P&S cameras also make a distinction between "optical" zoom and "digital" zoom, the latter being simply in-camera cropping that is again intended to fool consumers into believing they are getting something miraculous out of their camera's tiny sensors.

Thanks all for such a speedy response !

 

Yes, Peter, I understood all that. It was just "one of those things" that has never occurred to me and that a buddy of mine asked, I couldn't answer him and I felt stupid that I didn't know the answer (and yes, felt stupid asking the question here!).

 

Regarding the 18-200mm vs 17-55mm (and other focal lengths), definitely yes, clear as a bell!!

 

Thks again - I'll be falling asleep a bit smarter tonight -

 

Ray

<I>P&S cameras use 135 format "equivalences" as a marketing trick to make their lenses appear longer and imply something about the optics that is not true; regrettably this is also done with DX lenses. </I>

 

<P>Actually, DX lenses are <B>not</B> labelled by their 135 format

equivalences. An 18-200mm DX lens gives the same field of view on

a DX format DSLR as an 18-200mm lens for an old film camera would

(if such a lens existed).

 

<P>Also, I'm not sure what you think the P&S manufacturers are

implying about the optics that isn't true. The main misleading

aspect may be the maximum apertures, which may look normal, but

for some super-zooms are actually small enough that at the long

end of the zoom the image will be substantially softened by

diffraction.

Hi Radford ...

 

Hmmmmm ... I suppose that one - actually, the MAIN aspect - of all discussions about lenses and cameras that REALLY bother me is the following:

I do weddings with MF equipment (Pentax 645N) and related peripheral equipment - lenses, flash, brackets, filters, etc .... For many reasons I feel the need to convert to digital. The only digital camera I own is the Konica-Minolta Z5 and the 8x10's that I produce from this camera are simply incredible. I've never used this camera professionally, it's my fun, vacation, birthday party, etc ... camera.

 

After many weeks of research, I had selected the D200 and just when I'm ready to buy, the D300 gets announced and so I'm waiting for hands-on reviews to see if this camera's specifications are all they're touted to be by the proponents. OK, here's the nagging doubt ... I read about certain lenses, the primo lenses like the DX 17-55mm f2.8 having certain "flaws" ... WHAT ???? If my Minolta Z5 can produce stunning 8x10's at $650 CDN - lens included - why should there be problems with a $1,560 CDN (plus tax) lens - camera not inlcuded ????

 

This keeps going through my mind as I get ready to blow thousands of dollars to convert to digital. What's wrong with my thinking ???

 

Ray

For Radford:

 

"Actually, DX lenses are not labelled by their 135 format equivalences."

 

No they are not labeled that way, but the 135 "equivalent" shows up all the time in marketing literature and in EXIF data. A more useful measurement would be horizontal (not diagonal) FOV.

 

"Also, I'm not sure what you think the P&S manufacturers are implying about the optics that isn't true."

 

Mostly the relative quality attainable from a given focal length and its DOF isolation. These tiny lenses are full of CA and they suffer from the design limitations of really small lenses. If someone thinks they will get a shallow DOF using a P&S camera because it has a lens with an "equivalent" focal length of a say 90mm, they are in for a rude awakening. The Nikon Coolpix 4800 states that its longest focal length is 300mm "equivalent" with a maximum aperture of f/4.4, which sounds extraordinary when stated in those terms. However, here's a shot taken at 170mm @ f/5.6 with my D200: http://photos.imageevent.com/tonybeach/recentfavorites/large/AWB_2588.jpg and the Coolpix would never produce an image like that.

 

For Raymond:

 

"If my Minolta Z5 can produce stunning 8x10's at $650 CDN - lens included - why should there be problems with a $1,560 CDN (plus tax) lens - camera not included ????

 

This keeps going through my mind as I get ready to blow thousands of dollars to convert to digital. What's wrong with my thinking ???"

 

I'm not sure what complaints are being said about the Nikkor 17-55/2.8, you can find someone griping about anything on the internet. The biggest complaint I hear about that lens is that it is a DX lens and will someday be obsolescent -- and that's not going to happen any time soon (or possibly ever). The lens has a well deserved very good reputation and any complaints are a measure of its relative quality compared to expensive pro lenses that will put whatever is in front of your Minolta Z5 in the dirt.

 

As for making the move to a DSLR, I would say the water is warm so jump on in. If you can wait, then by all means wait for the D300; if there is some reason you need a DSLR before December, $1300 is a fair price for a D200 today (it will be less tomorrow, and less next month).

Hi Raymond ...

 

Supposedly, some digital camera lenses are designed to better work with a digital sensor (an array of tiny lenses in front of a Bayer pattern in front of the actual pixel) better than the chemical layers of film. The light rays from the lens are supposed to hit the pixel lenses at a better angle or something like that.

 

I think that might be what you are thinking of.

 

If you want to convert to digital, wouldn't it be cheaper to get a digital back for your system?

Anthony, $1300 for a D200? Where? A few months ago, the street price (new) was about $1350, but for some reason they've climbed back to $1500. Even at KEH, used prices for LN- condition aren't much less than that.

For Tom:

 

"If you want to convert to digital, wouldn't it be cheaper to get a digital back for your system?"

 

I haven't looked into the prices on these recently, but they do tend to be expensive. There are advantages and disadvantages. One of the advantages of a smaller format is smaller gear, smaller files, better high ISO performance (medium format backs often top out at ISO 400), and generally faster lenses.

 

"$1300 for a D200? Where?"

 

I got one last month for that much (including shipping) from Cameta Cameras. I know of someone else who is a regular contributer to this forum who also got the same deal at about the same time from the same seller.

Heck a factory demo with 1 year warranty just went at auction for $1210. Too bad I bought my second body 2 months ago. Had I known the D300 was coming, I might have waited and kept using my D70 as a second body. But I know there are shots I would have missed too.

 

As for Raymond, he said he had already decided on a D200 just before the D300 announcement. If I were he, I'd get on a few waiting lists for the D300 right away.

 

An alternative is to get the D200 now and resell it later when the D300 is in hand. Consider the difference in price as a rental fee.

 

It all really depends on one's time frame and budget.

ANTHONY: I guess you're right, you can always find somebody griping about something on the Internet. I suppose that Ferrari and Lamborghini owners have complaints of their own !! Still, it seems to me that when you've got the "crème de la crème", owners of these lenses - like the 17-55mm f2.8 - should be praising more than complaining and maybe they are and I'm only picking up on the negatives however small they are. Then again, if no one was looking for improvements, we'd still be shooting with Brownie cameras !

 

TOM: Digital back ... OUCH !! I've been waiting for Pentax to develop a digital back for the 645N or 645N-II ... they haven't and digital backs for other cameras are going for around $20k or and so way overpriced compared to Canon or Nikon alternatives in my opinion. And no, Tom, no pressing need for going digital ... I just have to make it happen within the next year or so. For once - YEAH - I'm sitting at the beginning of a new product! And so can wait and see the hands-on reviews from the likes of Thom Hogan, Ken Rockwell, DPreview, owners on this forum and the Nikonians site, etc ... Working something out with the camera store regarding buying a D200 with an option for a D300 ... interesting. I think someone worked a deal similar to this ... can't remember where I picked this up. If I remember correctly, it semed to be one sweet deal ... buy the D200, commit to the D300 purchase, and get full-price refund on the D200 when the D300 becomes available !!!

 

Many thanks again for all your info and suggestions.

 

Ray

"Still, it seems to me that when you've got the "crème de la crème", owners of these lenses - like the 17-55mm f2.8 - should be praising more than complaining and maybe they are and I'm only picking up on the negatives however small they are."

 

Raymond - see http://en.wikipedia.org/wiki/Self-handicapping Some are destined to complain on internet forums about minute technical specifications, while those who are happy are too busy taking photos. Many of the most famous photographers just take whatever camera is handed to them and make great images, through timing, lighting, composition, etc. Not that technicals don't matter, but it's no substitute for talent.