Forgot Password
Pentax Camera Forums Home

Show Printable Version Search this Thread
04-18-2010, 05:56 AM   #1
Veteran Member

Join Date: Dec 2009
Location: Ontario
Posts: 550
How much of a difference between 2.8 and 3.5

I have somewhat of a dilemma now. I have two 135mm prime lenses. One a no name Beck and another Takumar one. Now I find the Takumar produces sharper and more vibrant colours compared to the Beck one. However, my real question is how much of a difference will there be between a F2.8 (Beck) and F3.5 (Takumar)? I have I will have DOF difference with the Beck being shallower. However will the F2.8 be that much better in low light conditions? It seems to me that it is less than 1 stop and that could easily be fixed with ISO or shutter speed.

Thanks for the insight and comments

04-18-2010, 05:59 AM   #2
Veteran Member

Join Date: Apr 2009
Photos: Gallery
Posts: 489
2/3 stop........................
04-18-2010, 06:42 AM   #3
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,742
there won't be much difference in DOF either...if I were you I would stick to the takumar...there are alot of users here that love that lens, and use it in low light.
04-18-2010, 06:49 AM   #4
Veteran Member

Join Date: Mar 2007
Location: Nove Zamky, Slovakia
Photos: Gallery | Albums
Posts: 7,181
as Cosmo pointed out it's 2/3 of stop.

Now that means shooting at ISO 640 instead of 400 or 1250 insted of 800 or accept 2/3 of stop less in shutter speed if you don't want to bump the ISO up. This affects 2 things: 1- motion blur as speed produced by f3.5 at acceptable ISO (to you of course) may not be fast enough to freeze the motion. 2-lens/camera shake blur, where again the shutter speed you get may not bee fast enough to prevent shake blur.
Minnd you in dim light 2/3 of stop can make huge difference with 135mm. While f2.8 would give you lets say 1/125 shutter speed f3.5 in thee same conditions and settings would only produce 1/80 which at 135mm is notablee difference.

oh and one more thing. When trying M135/3.5 I found out that f3.5 is just dark enough to render micro prism collar of my focusing screen nearly useles...while not the best, it's still usable at f2.8

04-18-2010, 07:17 AM   #5

A tricky question. Two different lenses, probably with two entirely different optical formula, both at wide open . . . . .

I think we need sample pics to tell you, really.
04-18-2010, 08:39 AM   #6
Veteran Member
Mike Cash's Avatar

Join Date: Jan 2007
Location: Japan
Photos: Gallery
Posts: 6,952
You said it yourself.....a "no-name" Beck (I've never heard of it) and a "Takumar"....still loved, respected, used and coveted around the world almost four decades after they went out of production.

Does the f2.8 and f3.5 bit really even enter into the question?

But just for the technical bit, the difference between f2.8 and f4 is one stop, so f3.5 is less than one stop difference. Not enough to be a factor in making a choice.
04-18-2010, 08:50 AM   #7
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,399
In terms of stops it is about 1/2 to 2/3 but this means 50 to 60% increase in shutter speed wide open. while SR and high iso can help some, freezingthe subject needs shutter speed.
04-18-2010, 08:57 AM   #8

Join Date: Oct 2007
Location: Savannah, U.S./Baguio City, P.H.
Posts: 5,979
sell both and buy a takumar 135 2.5

04-18-2010, 11:18 AM   #9
Veteran Member
Tuner571's Avatar

Join Date: Mar 2008
Location: Ohio
Photos: Gallery | Albums
Posts: 1,550
Really I don't think that there is much of a difference. I mean your shutter speed is going to change and you depth of field might increase slightly, but not by much. If I were you I would sell both and pick up the takumar 135 f/2.5 myself, it really is a great lens to use.
04-18-2010, 02:49 PM   #10
Veteran Member
RioRico's Avatar

Join Date: Jun 2008
Location: Limbo, California
Posts: 11,264
As mentioned above, the fractional f-stop difference is trivial except in low light, when it's minor. The Takumar is worth far more, produces better results, etc. The no-name Beck can be useful if you're shooting in hazardous places and you don't care if the lens is damaged or trashed. If the f-stop difference were greater, if the Beck were a f/2 for instance, then it would be worth keeping for situations where speed is more important than image quality, like blackmail.

But it all depends on what you want to shoot, and from how far away, and what else you want the lens to do, if anything. Sell both and buy a Takumar 135/2.5, or almost any 100/2.8 or f/2 macro, or...

It depends on the light you shoot in. For low-light, faster is better. For daylight, slower is often sharper. My GOLD STANDARDS in that range are an Enna Tele-Ennalyt 135/3.5 and especially the Jupiter-11 135/4, both with astounding optics. (Less than US$90 for the pair.) Some people rob minimarts to pay for a 200/2.8 beast; my light little Tele-Takumar 200/5.6 cost US$29 and is tack-sharp throughout its range. And 'pods are handy.

So it's all a matter of where you shoot and when and how hazardously, and how much glass you want to carry, and how much cash you want to drop, etc. I'll repeat my mantra -- Ask yourself: Where do I want to go? What will get me there? How much am I willing to spend to be happy?
04-18-2010, 02:55 PM   #11
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
Note that while mathematially, f/3.5 might be 2/3 of a stop slower, the actual labeling of the stops is rarely mathematically correct. On lenses that can do f/2.8 or better, f/3.5 is simply how Pentax labels the half stop between 2.8 and 4. So I wouldn't assume a lens that is labeled f/3.5 is actually any more than half a stop slower.

I have the M135/3.5 and use it all the time in low light (for concerts, primarily). While sure, I wouldn't mind if it were half a stop faster, that's *trivial* to make up in shutter speed and/or ISO, and it's so much smaller and lighter than any of the f/2.8 lenses that I'm really not overly tempted by them. The Takumar probably doesn't have that going for it, of course, but if you find it a better lens, that's all that matters.
04-18-2010, 03:42 PM   #12
twitch's Avatar

Join Date: Nov 2009
Posts: 4,571
Another difference is 10mm in aperture. That 10mm will give you a greater possible blur of background.
04-19-2010, 12:43 AM   #13
Veteran Member

Join Date: Oct 2008
Location: Sweden
Posts: 359
Forget about the difference in speed, keep the Takumar.
To sell both and get a K135mm F2.5 is not a bad idea if you can cope with its size.

Kind regards
04-19-2010, 09:26 PM   #14
Veteran Member

Join Date: Dec 2009
Location: Ontario
Posts: 550
Original Poster
I would love to buy a 2.5 but they aren't easy to come by and I'm guessing they aren't that cheap. I will post some sample pictures from the two lenses in a couple of days. But I'm probably going to sell the Beck along with my film camera body. Could probably be easier to sell them as a package then separately. Thanks all for the help for now.
04-19-2010, 10:20 PM   #15
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 4,844
I think the best 135mm f3.5 option is the Pentax-M. Depending on what Takumar version you have, you can possibly sell the Takumar and get the Pentax-M for the same price. The Pentax-M is a much more convenient size.

For f2.8 and a small budget, I still like the Vivitar made by Komine. These are very cheap and common. You can find one of these for less than $30 shipped.

The SMC Pentax 135mm f2.5 is really a great lens. The extra speed may not be worth the extra cost, and it is bigger. The Super-Multi-Coated Takumar 135mm f2.5 model 43812 is the same formula and is actually a bit lighter. Model 43802 or Super-Takumar f2.5 versions are not far behind in quality and are sometimes sold at decent prices.

The Takumar Bayonet 135mm f2.5 is not a bad lens if you can find one for $20. At $75, it's a bad lens.

  • 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!
beck, f2.8, k-mount, pentax lens, slr lens, takumar
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Similar Threads
Thread Thread Starter Forum Replies Last Post
Difference philippe Pentax SLR Lens Discussion 6 02-03-2010 10:22 AM
What's the difference Dxn2 Troubleshooting and Beginner Help 6 12-26-2009 06:55 PM
FA vs. F? What's the difference? PentaxForums-User Pentax SLR Lens Discussion 3 12-23-2009 08:37 AM
Difference between PZ-1 and PZ-1P Stevopedia Pentax Film SLR Discussion 9 11-04-2008 11:57 AM
And the Difference is ? Jesus Photographic Technique 15 09-26-2007 02:13 PM

All times are GMT -7. The time now is 07:01 PM. | See also:, 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?
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]