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

Reply
 
Thread Tools Search this Thread
Old Oct 30, 2005, 6:18 PM   #1
Senior Member
 
fofa's Avatar
 
Join Date: Oct 2005
Posts: 547
Default

Ok another question. As I bounce back and forth between an ultrazoom and dslr, and researching each, I was looking at the Pentax *ist DS (smaller size) and the fact it can use "older" lenses. Figured I might be able to save money if I could get a couple older lenses like off eBay. So just looking I ran across some 70-200 MM lenses (figured I could always get a 2X converter to push it out to 400). And all these looked to be about 2 times the length of the 50MM lens physically (hard to tell by a picture, so just a guess). Then I ran into this Sigma 28-200MM lens that looks about the same length as a 50MM lens. WOW would that be nice. But I keep thinking how do they put 200MM in a short lens like that? You must really be giving up something. Can you shorten the physical size of a lens but still give it a long focal length, and still take quality photos?
Thanks again.
fofa is offline   Reply With Quote
Sponsored Links
Old Oct 31, 2005, 1:49 AM   #2
Senior Member
 
Join Date: Aug 2002
Posts: 851
Default

New lenses are designed by computer, so they can optimize factors like physical lens size vs aperature vs focal length.

The 28-200 you mention may look small, but along side a 50 f1.8, you would realize that it really is quite a bit bigger. It is also, most likely, shown at it's shortest focal length. At it's longest focal length, the front element extends out, so the lens increases in length about 2.5 times (maybe even a bit more). The lens is also quite slow. Typical 28-200 lenses have an aperature range of f3.5 at 28mm, to f5.6 at 200mm.

Some of the *older* lenses may not be nearly as good as some of the newer lenses, so do your homework before purchasing an older lens. Putting a 2x teleconverter on any lens, will also cost you about one f stop in speed, across the board.

Some of todays new compact zoom lenses are suprisingly good. As always it depends upon what you expect to get out of the lens.

Declan
amazingthailand is offline   Reply With Quote
Old Oct 31, 2005, 6:06 AM   #3
Senior Member
 
terry@softreq.com's Avatar
 
Join Date: Jun 2004
Posts: 2,539
Default

True that older lenses may not be as good as new ones, but I'd take a hard look at some older very fast primes!

lol.



Terry


terry@softreq.com is offline   Reply With Quote
Old Oct 31, 2005, 7:54 AM   #4
Moderator
 
Join Date: Aug 2004
Posts: 8,529
Default

Quote:
But I keep thinking how do they put 200MM in a short lens like that? You must really be giving up something. Can you shorten the physical size of a lens but still give it a long focal length, and still take quality photos?
What you will typically find is that lenses like this have a very small maximum aperture and often variable - i.e. it may have a max aperture of 3.5 at it's shortest length but 5.6 or 6.3 at the maximum zoom. That's the big compromise. Also 2x TCs will reduce your aperture by TWO stops - i.e. a lens that is 4.0 will become 8.0 with a 2x TC and you'll also see a noticeable drop-off in quality and focus speed. In general it is recommended to only use 2x TCs with high quality lenses. Also, I know Canon's non-professional cameras (300D, 350D, 20D) lose autofocus ability on anly lense over 5.6 / 6.3 aperture. So, if you have a lens that has a max aperture of 5.6 and put on a 2x TC, you will not be able to autofocus (without taping pins to keep lens from reporting aperture to the camera). I'm not sure if Pentax has similar issues.

As for old vs new lenses - I suggest researching each lens on a case by case basis. Look for valued advice from resources you trust before buying any lens.


JohnG is offline   Reply With Quote
Old Oct 31, 2005, 3:53 PM   #5
Senior Member
 
Monza76's Avatar
 
Join Date: Jul 2004
Posts: 4,093
Default

The Pentax *istDS is a good choice especially if you don't mind manual focus. There are some great SMC Pentax A -series lenses out there that offer every feature, except autofocus, for a great price used. Just stay away from third party lenses designed for P series Ricoh cameras, they can get stuck on the DS.

I would stick with fast primes and zooms labelled SMC Pentax A, or SMC Pentax M if you don't mind loosing exposure automation. All autofocus designed for Pentax should work regardless of manufacturer (except the old Pentax ME-F lens). Note that the A series lenses are very well built, offer faster apertures than most of the later lenses, and are relatively cheap on ebay.

BTW remember an excellent SMC Pentax A 70-210mm f4 lens (fixed aperture) will be a 105-315mm on a *istDS (or D, DL or DS2). Hardly any need for a teleconverter.

Check out Bojidar Dimitrov's site for info on Pentax cameras, lenses and accessories. http://www.bdimitrov.de/kmp/

Good luck

Ira



Monza76 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 4:42 PM.