Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
02-03-2009, 10:46 AM   #16
Pentaxian
audiobomber's Avatar

Join Date: May 2008
Location: Sudbury, Ontario
Photos: Albums
Posts: 6,631
QuoteOriginally posted by alohadave Quote
I just recently upgraded to the 55-300 and it's the same speed as the 50-200
Not really. The 55-300 is F4.5 at 200mm, where the 50-200 is F5.6.


Last edited by audiobomber; 02-03-2009 at 11:52 AM.
02-03-2009, 11:48 AM   #17
Veteran Member
awo425's Avatar

Join Date: Jan 2008
Location: NYC, USA
Posts: 481
You can get used Pentax SMC F70-210 4/5.6 for $115 from the market section of this forum. It is for sale in the post "300+ lenses ..."
It is one helluva lens for the price, sharp wide open and better then Pentax DA 50-200. AF is noisy, but fast and IQ is great.
For macro I would look for a separate MF lens, or even a reverse focusing ring and Pentax 50mm prime lens.
I think decent lens in 70-210 range is more important in a kit then a macro.
02-03-2009, 12:11 PM   #18
Veteran Member
alohadave's Avatar

Join Date: Jan 2008
Location: Quincy, MA
Photos: Gallery | Albums
Posts: 2,024
QuoteOriginally posted by audiobomber Quote
Not really. The 55-300 is F4.5 at 200mm, where the 50-200 is F5.6.
1/2 a stop difference. Close enough.
02-03-2009, 12:18 PM   #19
Pentaxian
audiobomber's Avatar

Join Date: May 2008
Location: Sudbury, Ontario
Photos: Albums
Posts: 6,631
QuoteOriginally posted by alohadave Quote
1/2 a stop difference. Close enough.
2/3 of a stop.

02-03-2009, 05:08 PM   #20
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
QuoteOriginally posted by audiobomber Quote
2/3 of a stop.
If you do the math, yes, it might work out about that way in theory. But Pentax uses f/4.5 to represent the half stop between f/4 and f/5.6 - you can see that by going into Av mode with your camera set to use half stops and flipping through the choices. Of course, those numbers are also only approximate on a variable aperture zoom, but unless you've actually measured the exposures, the default conclusion from the specs would be that the 55-300 is 1/2 a stop faster at that focal length. And I assume there are also focal lengths where there is no difference at all. So the "average" improvement in speed would have to be *less* than half a stop.
02-03-2009, 06:57 PM   #21
Pentaxian
audiobomber's Avatar

Join Date: May 2008
Location: Sudbury, Ontario
Photos: Albums
Posts: 6,631
QuoteOriginally posted by Marc Sabatella Quote
If you do the math, yes, it might work out about that way in theory. But Pentax uses f/4.5 to represent the half stop between f/4 and f/5.6 - you can see that by going into Av mode with your camera set to use half stops and flipping through the choices.
My camera is set for 1/3 stops and it shows 4.0, 4.5, 5.0 and 5.6. Why would you set the camera for half-stops if you're trying to determine thirds?

I see what you're mean though. The 55-300 changes to F4.5 at about 120 and reports that nominal aperture until it changes to F5.6 at 210, so it's not actually F4.5 at 200mm, even though it says it is. So would that mean that the aperture has infinite stop positions in between the actual f-stops?

Last edited by audiobomber; 02-03-2009 at 07:14 PM.
02-03-2009, 08:04 PM   #22
Pentaxian
Nick Siebers's Avatar

Join Date: Jun 2008
Location: Madison, WI
Photos: Gallery | Albums
Posts: 2,139
I have a Tamron Adaptall 70-150mm zoom that does 1:2.5 macro. I think you can get one, and a PK adaptall mount, for under $100. Then later you can get a 90mm Adaptall macro that is almost as good as anything out there.
02-03-2009, 08:26 PM   #23
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
QuoteOriginally posted by audiobomber Quote
My camera is set for 1/3 stops and it shows 4.0, 4.5, 5.0 and 5.6.
Weird. My camera is set for half stops and shows 4.0, 4.5, 5.6. So I guess they use 4.5 as both the 1/2 stop and the 1/3 stop.

QuoteQuote:
So would that mean that the aperture has infinite stop positions in between the actual f-stops?
I don't know how it works for apertures that are not wide open, but that seems plausible. Wide open, simple math - size of opening divided by focal length, or something to that effect - would seem to suggest the actual maximum aperture does change continuously with focal length. But then, that doesn't explain constant aperture zooms. I haven't yet been sufficiently fascinated by the issue to read enough to begin to understand...

02-03-2009, 08:52 PM   #24
Site Supporter
sabarrett's Avatar

Join Date: Jan 2008
Location: Michigan
Photos: Gallery
Posts: 252
So... to the OP... Are you thoroughly confused now? (grin)
02-04-2009, 09:02 AM   #25
Pentaxian
reeftool's Avatar

Join Date: Dec 2007
Location: Upstate New York
Photos: Gallery | Albums
Posts: 8,009
I have the Sigma 70-300. It came with the package deal I got when I bought my camera. While I have got some very nice shots from it, I find it very soft abovve 200mm unless its bright sunlight and I'm shooting at f/11 or f/16. I would wait a few weeks and save a little more and get the Pentax 55-300. Another option is to look for used deals on Ebay or a dealer like KEH.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
k-mount, lens, pentax lens, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
2nd lens for a k-m (k2000) rotorhead Troubleshooting and Beginner Help 2 12-03-2009 06:37 PM
What macro lens do you suggest? Dynasty Pentax SLR Lens Discussion 13 11-22-2009 05:03 AM
good 2nd lens to purchase summatusmentis Troubleshooting and Beginner Help 24 04-13-2009 02:32 PM
Looking for advice on a 2nd lens Techno~ Pentax SLR Lens Discussion 19 09-13-2007 07:27 AM
Which 2nd hand lens? Darius4522 Pentax SLR Lens Discussion 8 03-22-2007 01:34 PM



All times are GMT -7. The time now is 05:39 PM. | See also: NikonForums.com, part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top