Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
07-28-2010, 06:06 PM   #1
New Member




Join Date: Jul 2010
Location: Melbourne, VIC
Posts: 2
Which Zoom Lens? "Tamron AF 18-250mm", "Pentax-DA 18-250mm" or "Sigma 18-250mm"

Hi Guys,

I already have a "Pentax-DA 18-250mm F3.5-6.3" with my K7. I like this lens but there are some downfalls, sometimes it is very sluggish in focusing and drives me crazy. I was surfing the net for an alternative and I saw "Sigma 18-250mm DC OS HSM lens" which seems to be a good one, specially filter size, it's 72mm which causes in absorbing more light.
There is a Tamron as well, "Tamron AF 18-250 mm Di-II lens" but I guess I wont consider that one.
I have surfed the net but couldn't find any article comparing Pentax one against Sigma, so I was wondering whether anyone here has any idea which could help me to make a decision.
I have found review of those lenses in dpreview but it didnt help much

Sigma: Sigma launches 18-250mm DC OS HSM lens: Digital Photography Review

Pentax: Pentax-DA 18-250mm F3.5-6.3: Digital Photography Review

Tamron: Tamron AF 18-250 mm Di-II lens: Digital Photography Review

I should add that money is not an issue here (to that extent though )

Thanks for your help guys and have a good one.

07-28-2010, 07:58 PM   #2
hcc
Pentaxian
hcc's Avatar

Join Date: Nov 2009
Location: Brisbane, Australia
Photos: Gallery | Albums
Posts: 3,482
The Tamron 18-250mm is the brother of the Pentax DA18-250mm. Simply the DA18-250mm is a Tamron lens. Very little difference between these two lenses. If you already have the DA18-250mm, I would not consider to replace it by the Tamron 18-250mm.

The Sigma 18-250mm OS HSM is an newer more expensive lens. There have been some good user reports (see for example some threads in this Forum). But the lens Optical Stabilisation (OS) is redundant with the K-7 camera Image Stabilisation (IS). The lens OS and camera IS cannot work together: you must switch off the OS or the IS (*).

(*) On the pros and cons of OS vs IS, see the excellent article by slrgear.com: Image Stabilization Test: Olympus E-520 SLR Body - SLRgear.com!. Using an Olympus E520, www.slrgear.com compared the camera IS and the lens OS. The findings are clear: "The bottom line on the Olympus E-520's IS system is that it turned in a superb performance, very much on par with the best lens-based IS systems we've looked at".

Personally I have the DA18-250mm with a K-7. I considered the Sigma 18-250mm as an alternative to the DA18-250mm, but decided against because of the more expensive price, but also the HSM. I use my camera outdoor in rugged conditions and there have been still some concerns about the HSM robustness of some lenses.

In your place, I would keep the DA18-250mm. It is a great lens that you could complement with a series of prime lenses. For example, a fast prime for low-light conditions is definitely a great addition. (I bought the Nokton 58mm f1.4 and I am very pleased with it.)

Hope that the comment will help.

Last edited by hcc; 07-28-2010 at 09:18 PM. Reason: Typos
07-29-2010, 01:29 PM   #3
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
QuoteOriginally posted by hoomanshb Quote
I already have a "Pentax-DA 18-250mm F3.5-6.3" with my K7. I like this lens but there are some downfalls, sometimes it is very sluggish in focusing and drives me crazy. I was surfing the net for an alternative and I saw "Sigma 18-250mm DC OS HSM lens" which seems to be a good one, specially filter size, it's 72mm which causes in absorbing more light.
No, it doesn't. What matters is the maximum lens aperture, not the filter size. These two lenses are virtually identical in terms of maximum lens apertures.

Sluggish AF is mostly caused by not enough light or not choosing a contrasty enough subject to focus on. The only real difference between the two lenses you mention with be that the Pentax (and the identical Tamron) focuses using the camera motor, whereas the Sigma focuses with the lens HSM motor. That should help some in many cases, but when light or contrast is poor, all lenses will struggle.
07-29-2010, 11:40 PM   #4
New Member




Join Date: Jul 2010
Location: Melbourne, VIC
Posts: 2
Original Poster
Thanks for the replies.
Yes I have a few other lenses as well, a 105mm, a 50mm and a 10mm but a zoom lens for every day use is so good.
So Sigma lens uses its own HSM motor to focus, does it mean that it is quicker in normal light condition? And one more question bigger filter size has what advantages then?They could have made it smaller and made it cheaper. Is diaphragm in a particular stop, for example 2.8, in all lenses with all filter size the same?I thought diaphragm number is an portion of the amount of the light which comes into the lens and therefore a bigger filter size lens will be better in that?Isnt it?Please correct me if I m wrong?

07-30-2010, 09:50 AM   #5
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
QuoteOriginally posted by hoomanshb Quote
And one more question bigger filter size has what advantages then?They could have made it smaller and made it cheaper.
Might be cheaper to manufacturer with a smaller front element, but it's harder to *design* a lens with a smaller front element for a given maximum aperture.

It's possible the lens with the larger front element would have less vignetting, but I wouldn't assume that, either - I'd check tests like those on photozone.de

QuoteQuote:
Is diaphragm in a particular stop, for example 2.8, in all lenses with all filter size
the same?
Again, filter size has nothing to do with it. But the f-stop of an aperture opening by simple ratio: focal length : aperture diameter. That's why Pentax lenses always list it as a ratio: 1:2.8, etc.

So a 50 lens has a maximum f-stop of f/2.8 if the actual diameter of the aperture is 50/2.8 or around 18mm. But the size of the front element - which is what determines the filter size for the most part - might easily be different than that. And again, a bigger front element doesn't help if your actual aperture opening is only 18mm.
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!
af, di-ii, hsm, k-mount, lens, pentax, pentax lens, photography, review, sigma, slr lens, tamron
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
K-mount Experts: How to convert a "KAF2" lens to "KF"? panoguy Pentax SLR Lens Discussion 24 07-08-2010 05:20 PM
Sports "Highside Exit" took 1st Place in DPReview "Missed It by THAT much, Part 1" Challenge MRRiley Post Your Photos! 27 02-21-2010 08:26 PM
Pentax "A" lens and "F" 1.7X converter on K10d yyyzzz Pentax SLR Lens Discussion 4 07-09-2009 05:04 AM
"Hunger for a DA*50-135?" or "The DA*50-135 as a bird lens!" or "Iron age birds?" Douglas_of_Sweden Post Your Photos! 4 08-13-2008 06:09 AM
So where's the 60-250mm f/4 "buzz"? m8o Pentax News and Rumors 79 07-15-2008 10:06 PM



All times are GMT -7. The time now is 01:48 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