Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
08-31-2010, 05:13 PM   #31
Pentaxian
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,796
" no 200mm lens is going to be as sharp as the various shorter options for the same subject magnification"

E.G FA31mm f/1.8 / FA*85mm f/1.4

08-31-2010, 05:28 PM   #32
Veteran Member
omega leader's Avatar

Join Date: Jan 2008
Location: Niagara Region, Ontario Canada
Photos: Gallery
Posts: 417
Original Poster
QuoteOriginally posted by Digitalis Quote
" no 200mm lens is going to be as sharp as the various shorter options for the same subject magnification"

E.G FA31mm f/1.8 / FA*85mm f/1.4
Digitalis,

Explain this to me. Is this due to atmospheric variations (more air in the way) or is there some basic scientific principle I'm missing.

Why can't a 200mm lens doing 60 line pairs resolve the same as a 50mm lens doing 60 line pairs? Or is it is simply that typically the further you vary from a simple lens the complexity of creating that same resolving power increases?

The only other reason I can think of is the corresponding decrease in depth of field and acceptable sharpness so it appears at though a shorter lens will have more resolving power?

Help, don't leave me hanging.
08-31-2010, 05:47 PM   #33
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
Note Digitalis was actually quoting me on that statement - not sure if he was agreeing or suggesting that those two lenses might be counterexamples.

Anyhow, it's not that it's *impossible* for a longer lens to outresolve a shorter one. It's just that they rarely do. Look at MTF numbers on Photozone, look at Yoshihiko's resolution numbers, do tests with whatever lenses you have lying around - the trend is pretty consistent. Unless you're comparing an absolutely amazing 200mm lens again a really terrible 50mm lens (for instance), the 50mm is going to win. The DA*200 in particular does quite well for a 200mm prime - but not as well as pretty much any shorter lens. It's *peak* MTF according to Photozone is 2074/2036 (center/edge), and it doesn't reach that until f/5.6. Whereas the FA50 will easily beat both of those numbers at f/5.6, and it's peak for the center is considerably higher, shooting at f/4.

Of course, I'm not saying that the differences are particularly significant, or even that one should really care about them for portraits. But given that one of the stated reasons for starting this quest was better edge sharpness, I thought I'd point out that this really isn't going to happen by going to a longer focal length.

Note I am talking abut the same subject magnification, because that's what's relevant here (full body portrait). It does *not* follow that you're better off shooting wildlife with your favorite 50mm lens and then cropping. It *does* follow that you'd get better shots with the 50 than with your 200 if you were shooting the 50 from close enough to get the the same subject magnification.
08-31-2010, 05:55 PM   #34
Veteran Member
Pentaxor's Avatar

Join Date: May 2009
Location: Vancouver, B.C.
Photos: Gallery
Posts: 6,513
if he wants a 200mm lens with great resolving power, he might want to get the A*200/4 macro. but then again, it is hard to find and can be really pricey.

08-31-2010, 06:13 PM   #35
Pentaxian
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,796
Marc sabatella is correct, there aren't many 200mm lenses that can match a 50mm f/1.4 prime . The only two that I own that come close is the Canon EF 200mm f/1.8L and the Pentax FA*200mm f/4 ED Macro - and both of these lenses have been discontinued for some time.

There isn't any real equivalent to the 200mm f/1.8 In Pentax K mount. The FA*200mm f/4 Is basically impossible to find These days...because it is one hell of a lens. However you might be lucky and find a 135mm f/1.8 which is probably just as good optically speaking.

In regards to your DOF concerns I hope you have considered your subject to background ratio. Moving your subject further away or closer to the background has more impact that the aperture of your lens.
09-01-2010, 08:04 AM   #36
Veteran Member
omega leader's Avatar

Join Date: Jan 2008
Location: Niagara Region, Ontario Canada
Photos: Gallery
Posts: 417
Original Poster
Digitalis,

The Depth of Field is independent of focal length.

For a 1.7m tall subject, a 300mm 2.8 at 11.9m gives 0.17m DOF, while a 200mm 2.8 at 7.9m also gives 0.17m DOF.

If you shot the same with a 14mm 2.8 at 0.6m you would also get 0.17m DOF.

Each of these would have the same subject matter the same size in the image and have the same DOF, only the angle of view would be different.
09-01-2010, 08:21 AM   #37
Veteran Member
Pentaxor's Avatar

Join Date: May 2009
Location: Vancouver, B.C.
Photos: Gallery
Posts: 6,513
QuoteOriginally posted by omega leader Quote
Digitalis,

The Depth of Field is independent of focal length.

For a 1.7m tall subject, a 300mm 2.8 at 11.9m gives 0.17m DOF, while a 200mm 2.8 at 7.9m also gives 0.17m DOF.

If you shot the same with a 14mm 2.8 at 0.6m you would also get 0.17m DOF.

Each of these would have the same subject matter the same size in the image and have the same DOF, only the angle of view would be different.
any luck on the lens that you are looking for?
09-01-2010, 08:48 AM   #38
Veteran Member
omega leader's Avatar

Join Date: Jan 2008
Location: Niagara Region, Ontario Canada
Photos: Gallery
Posts: 417
Original Poster
Yeah Pentaxor,

I spoke with a local shop and they have a Tamron 70-200mm that I'm going to rent for the long weekend. They also have the Pentax 200mm and will allow me to put the rental fee towards the purchase of either.

I figure a first hand look is the best way to go. And they have both in stock.

09-01-2010, 11:40 AM   #39
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
QuoteOriginally posted by omega leader Quote
The Depth of Field is independent of focal length.
Assuming you adjust distance to subject to keep subject magnification the same, yes. I know you realize that, but didn't want others to be confused.

QuoteQuote:
For a 1.7m tall subject, a 300mm 2.8 at 11.9m gives 0.17m DOF, while a 200mm 2.8 at 7.9m also gives 0.17m DOF.

However, because your distance to subject has changed, so has the camera-to-background distance, and the ratio of that to subject distance. This can very much affect the appearance of the out of focus areas, as you're changing both the *amount* of background as well as *how* out of focus it is. There might be an actual focal-length-dependent component to this as well; I'm not sure. But the upshot is, while actual DOF might be the same, the degree of background blur you get will be different, and it usually works out such that the background is more blurred with longer focal lengths even when keeping the subject magnification and hence DOF constant.
09-01-2010, 05:40 PM   #40
Pentaxian
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,796
"The Depth of Field is independent of focal length."

I'm more aware of that than others on this forum.

Subject/background ratios are very important in portraiture, almost as important as lighting ratios. If your subject is far enough away from your background you can isolate them more effectively, giving the illusion that an even faster lens has been used. I understand your need to reduce the amount of background in the image. At the same focus distance a 14mm lens is going to have much more background visible than a 77mm lens would have more when compared to a 300mm lens...the trick is to find the balance.

I'm assuming these are on location portraits?
09-02-2010, 01:59 PM   #41
Pentaxian
RonHendriks1966's Avatar

Join Date: Jan 2009
Photos: Gallery
Posts: 8,714
To be honest I think it is stupit to make portraits with real long lenses. I use the DA40mm, DA*55mm, FA*85mm and DA*50-135mm for it. But on the other hand their your pictures and that's all that matters.

I did some portraits with a Sigma 170-500mm lens.

This one at 430mm and flash on wireless trigger:


This one at 500mm, also flash wireless.


So anything is possible. Bye a lens and enjoy it.
09-02-2010, 02:26 PM   #42
Pentaxian




Join Date: Jul 2009
Location: Seattle
Posts: 7,103
A full body shot I assume would mean that there is head room in the frame? I mean, there will be space around the subject and at that shallow DOF you want, who cares if a lens is soft on the corners wide open? It will a be blurry in that area anyway if I envision your shot correctly.
09-02-2010, 10:22 PM   #43
Ash
Community Manager
Loyal Site Supporter
Ash's Avatar

Join Date: Mar 2007
Location: Toowoomba, Queensland
Photos: Gallery | Albums
Posts: 22,695
Well Ron, you've shown here with these portraits how much the 400+ mm focal lengths flatten out perspective - the second one shows an extraordinarily widened face, to the point where it is quite unnatural. But what detail in the portraits.
09-03-2010, 12:34 AM   #44
Pentaxian
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,796
here is a full length portrait example from my FA31mm f/1.8 -


ISO 100 1/60th @f/4 with wireless AF540FGZ polariser used.

I will say that there are some benefits to using telephoto lenses over 100mm for portraiture. For instance I was doing some portraits that had to include the building that my subject was standing in front of, the only way to get this was by either running the risk of standing in the middle of the street and risk getting hit by a car, or use a longer lens to get the shot, (I ended up using a 300mm f/2.8 lens). One practical concern with using longer lenses is for portraiture is whether your wireless triggering system has the range required. All optical triggering systems from major camera manufacturers have the range of a thrown Doberman , so some sort of RF triggering system is required. Personally I use Pocket wizards for off camera strobes, and Elinchrom skyports for professional monobloc heads for on location work - because the biggest problem I have with cheaper triggers is that they can be unreliable and I cannot waste time trying to fiddle and figure out why things aren't working. It gives the wrong impression when you are spending more time fiddling with your gear than Photographing your subjects.

My 1,000th post WooT!

Last edited by Digitalis; 09-03-2010 at 01:27 AM.
09-03-2010, 05:54 AM   #45
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,400
QuoteOriginally posted by Digitalis Quote
here is a full length portrait example from my FA31mm f/1.8 -


ISO 100 1/60th @f/4 with wireless AF540FGZ polariser used.
so if you are using a 31mm for full length, why all the interest in 200mm, is it for background isolation only?
QuoteQuote:
I will say that there are some benefits to using telephoto lenses over 100mm for portraiture. For instance I was doing some portraits that had to include the building that my subject was standing in front of, the only way to get this was by either running the risk of standing in the middle of the street and risk getting hit by a car, or use a longer lens to get the shot, (I ended up using a 300mm f/2.8 lens).
I don't get it? using a longer lens will include less of the building if you want full body for the subject, as opposed to mioving out, and going longer, surely this is a case for moving in and going wider isn't it?
QuoteQuote:
One practical concern with using longer lenses is for portraiture is whether your wireless triggering system has the range required. All optical triggering systems from major camera manufacturers have the range of a thrown Doberman , so some sort of RF triggering system is required. Personally I use Pocket wizards for off camera strobes, and Elinchrom skyports for professional monobloc heads for on location work - because the biggest problem I have with cheaper triggers is that they can be unreliable and I cannot waste time trying to fiddle and figure out why things aren't working. It gives the wrong impression when you are spending more time fiddling with your gear than Photographing your subjects.
I can't argue there, but have you tried an extender on the camera mounted flash, like a better beamer? My limited understanding of the flash communication is that it is one way, from the body mounted flash to the remote ones
QuoteQuote:
My 1,000th post WooT!
contrat's
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!
f2.8, k-mount, lens, pentax, pentax lens, performance, portraits, slr lens, tamron
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Help for new long lasting lens danpinoy Ask B&H Photo! 2 08-25-2010 08:44 AM
Best choice for a long, prime portrait lens? m88k Pentax SLR Lens Discussion 23 08-11-2010 03:13 PM
How long should a lens repair take? CX15 Pentax SLR Lens Discussion 2 02-02-2010 07:26 AM
Cheap long lens usapatriot Pentax SLR Lens Discussion 29 07-28-2009 11:55 AM
Pentax 110 Slr Lens 50mm F2.8 Portrait Lens danahauk Pentax SLR Lens Discussion 2 12-19-2007 08:18 AM



All times are GMT -7. The time now is 03:23 AM. | See also: NikonForums.com, CanonForums.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