Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
05-24-2016, 10:30 AM - 12 Likes   #1
Pentaxian
normhead's Avatar

Join Date: Jun 2007
Location: Near Algonquin Park
Photos: Gallery | Albums
Posts: 35,931
Understanding folks saying a TC doesn't ad more detail.

There would seem to be a lot of confusion around this issue.

My first series of images went as follows... taken at about 40 feet, with not a lot of detail in the test subject.
DA*200


DA*200 plus 1.4


DA*200 plus 1.7


DA*200 plus stacked TC


* it should be noted, there are slight but insignificant increases in detail when viewing these images as pixel peepers, but when reduce to the same size they are really insignificant.

The biggest difference would be smoother and smoother bokeh in the back ground, not more detail on the test subject.

You could reasonably look at these images and say, well, the TC doesn't really add anything to the image. to understand how TC's work this is a critical point. The problem with this as an illustration was, there was no detail in this image the DA*200 couldn't resolve, at this distance. So adding a TC added nothing.

You can see this in the old comparison on the site years ago where someone compared a K-01 image with a D800 image and found them to be about equal. The simple fact is if the K-01 can resolve all the detail, then the D800 can't really add anything. So you can see how it would be quite possible to assume that both extra resolution and using a TC doesn't increase detail, after some testing.

For a higher res image to be better than a lower res image, there has to be detail in the high res image that the low res image can't resolve. This is not true in every image, so there are cases where neither a higher resolution sensor or TC do not increase IQ. The above images being a case in point.

But what if I back up to 60 feet, and use a target with finer detail than the DA*200 and K-3 combination can resolve from that distance.


Then both the 1.4 and 1.7 TCs produce increasing level of detail not available in the original image.
HD DA 1.4 TC


F 1.7x AF adapter


- note- these are 1:1 crops of these images, reducing the image size of larger image can mean the gain in detail is lost in the image reduction.

The TCs allow us to capture detail not available in the DA*200 image by itself. I believe the confusion in this area is because, using an inappropriate target, it is possible to do a series of tests where the TC's don't really add anything new. However it is also possible to do a series of tests where TCs add a considerable amount of detail. And those would be in that zone after which the original lens and sensor combo is able to resolve visible detail in a scene, and in the zone where the TC is able to resolve more detail, before getting beyond that to where neither lens or lens and TC combo can resolve available detail. After getting a TC perhaps the first thing to realize is, in some cases it is just a framing aid. In other cases you can bring out more detail. It's all about understanding the circumstances where these things might happen.

Another situation where the TC won't add anything would be where there is some very fine detail that can't be resolved by the original lens, but that can't be resolved by the TC either. I'm sure I could fine tune the above test, so that both th DA*200 and the DA*200 plus the 1.4 didn't do a decent job of defining the bar code, but the 1.7 did. A TC is kind of like a higher resolution camera. You might not get any benefit from it, in a given image, but, on a subject filling less than half the frame, you won't get any less. But you might get more.


Last edited by normhead; 05-24-2016 at 01:08 PM.
05-24-2016, 10:40 AM - 1 Like   #2
Pentaxian
D1N0's Avatar

Join Date: May 2012
Location: ---
Photos: Gallery
Posts: 6,277
When your lens greatly outresolves your sensor a good TC could give you mere detail.
05-24-2016, 10:48 AM   #3
Pentaxian




Join Date: Feb 2015
Photos: Gallery | Albums
Posts: 7,914
Yes, this makes sense to me. If the image falling on the sensor plane out-resolve the sensor because the subject is too small or because the subject details are too small for the sensor resolving power, then adding a TC can add resolving power. So, the lower the pixel density of the sensor the more benefit from the TC... because glass is analog... and digital sensors are sampling what comes out of the lens. Typically, the spectrum of optical signal out of a lens (even a bad lens) if infinite (with some gradual loss of contrast for higher details but the signal is never zero), while out of a digital sensor past nyquist the signal is mathematically zero (there cannot be any image detail finer than the pixel spacing). In other words, the TC is even more interesting with digital. The reason why people have a bad experience with TC is that they crop the image with TC by the same amount as without TC.... while they should be cropping at least as wide as the TC enlargement to get any benefit from the TC. In fact, the whole point of using a TC is not to crop.
05-24-2016, 10:50 AM   #4
Site Supporter
Site Supporter
jatrax's Avatar

Join Date: May 2010
Location: Washington Cascades
Photos: Gallery | Albums
Posts: 12,316
Thank you Norm for an excellent explanation!

I think at least some of the negativity toward TCs is a remnant from the days when many got a cheap TC when they bought their film camera. Sales people loved to sell them. But the quality of some of those cheap 2x TCs was so bad that while they technically worked they reduced the image quality noticeably. I certainly felt that way, until I got the HD 1.4x RC and that changed my mind. I needed to move from "TCs are bad" to "bad TCs are bad".

05-24-2016, 10:55 AM - 1 Like   #5
Pentaxian
Na Horuk's Avatar

Join Date: Feb 2012
Location: Slovenia, probably
Photos: Gallery | Albums
Posts: 11,183
Hm, I should have been more clear in the other thread. The detail is still from the lens, the TC just magnifies it. This magnification can make things that the sensor wouldn't capture, big enough for the sensor to capture.
So, good clarification in this thread. With a good lens and good TC, the image can benefit.
QuoteOriginally posted by jatrax Quote
I think at least some of the negativity toward TCs is a remnant from the days when many got a cheap TC when they bought their film camera.
And this is definitely part of the problem. There are still many cheap TCs available online
05-24-2016, 11:37 AM   #6
Pentaxian
Tjompen1968's Avatar

Join Date: May 2012
Location: Norrköping, Sweden
Photos: Gallery | Albums
Posts: 1,428
Looking at the images with the 1.7 I wonder if the 1.7 is a TC per say since it has changed the DOF in the image. Any idea to why this happens?
05-24-2016, 11:43 AM   #7
Pentaxian
normhead's Avatar

Join Date: Jun 2007
Location: Near Algonquin Park
Photos: Gallery | Albums
Posts: 35,931
Original Poster
QuoteQuote:
So, good clarification in this thread. With a good lens and good TC, the image can benefit.
It's like a high resolution camera. Conditions may not favour the extra resolution coming into play, and you can yawn and say ho hum, but when conditions are right, it can give you something you'd never get any other way.

---------- Post added 05-24-16 at 02:44 PM ----------

QuoteOriginally posted by Tjompen1968 Quote
Looking at the images with the 1.7 I wonder if the 1.7 is a TC per say since it has changed the DOF in the image. Any idea to why this happens?

Longer FL means less DoF from the same distance, as far as I know. The fact that it is achieved with a TC makes no difference.

If you back the lens with the TC so you get the same field of view you got without it, then you would get similar DoF. But in essence you aren't taking the same picture if you don't change position.

Last edited by normhead; 05-24-2016 at 11:48 AM.
05-24-2016, 11:50 AM   #8
Pentaxian




Join Date: Feb 2015
Photos: Gallery | Albums
Posts: 7,914
QuoteOriginally posted by Tjompen1968 Quote
Looking at the images with the 1.7 I wonder if the 1.7 is a TC per say since it has changed the DOF in the image. Any idea to why this happens?
If aperture is the same and distance is the same, then DoF is reduced by the TC.

05-24-2016, 12:05 PM   #9
Otis Memorial Pentaxian
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 37,256
QuoteOriginally posted by Tjompen1968 Quote
Looking at the images with the 1.7 I wonder if the 1.7 is a TC per say since it has changed the DOF in the image. Any idea to why this happens?
Relative aperture is decreased 1 stop for the 1.4x converter and 1.5 stops for the 1.7x. DOF will follow the actual focal length/aperture (lens + converter) per the normal rules.

Edit: DOF (perception of acceptable sharpness) may be affected by overall detail captured. Normalizing magnification of the images also affects DOF.


Steve

Last edited by stevebrot; 05-24-2016 at 01:03 PM.
05-24-2016, 12:09 PM   #10
Pentaxian
Tjompen1968's Avatar

Join Date: May 2012
Location: Norrköping, Sweden
Photos: Gallery | Albums
Posts: 1,428
Does it count that the aperture goes from 4 to 5.6 on a f/4 lens when using a 1.4 TC?

(EDIT: The answer was posted before I got it posted....)

As I have understood it and what I see when putting the 16-50 on the K-1 is that with the TC it has "cropped" the image circle and enlarged it to fit almost a FF sensor. I.e it removes the vignette (almost all). I then thought that it really looks the same as if only cropping the image. Well, my thinking is that since there is the same distance, no shift in perspective, the DOF should stay the same since I am only "cropping" the optical image circle.

That is why I am asking. And I would like to understand where my thinking is flawed if so.
05-24-2016, 01:44 PM   #11
Senior Member




Join Date: Nov 2011
Location: Hampshire UK
Posts: 287
QuoteOriginally posted by normhead Quote
I'm not sure what you're saying here.
That when cropping you can see more detail when using a good enough teleconverter/lens combination than with the lens alone. I said 'in the middle bit' because the edges may be vignetted, and the lens resolution may be less, in which case you might not see any improvement at all. But in the image centre, you will - and I do, with my DA* 300 mm + 1.4TC + K-3 combination.
05-24-2016, 01:46 PM   #12
Pentaxian




Join Date: Jan 2016
Location: Fulton County, Illinois
Posts: 3,630
A number of the responders have examined technical aspects of this question beyond my ability (without my studying up), but I look at it this way. The TC can't invent details not "seen" by the main lens, but by magnifying it could make apparent details the main lens transmits that might not be evident using the main lens alone.

A crappy TC or one ill-matched to the main lens could of course degrade detail. I didn't think of TCs needing to match a lens until some lens company started selling TCs for particular lenses, calling them "matched multipliers." I didn't know if that was hype or reality.

Considering that we could think of the TC-plus-main-lens as a single system, however, one might wonder whether a really good TC could could coax more detail out of marginal quality lens. Or looking at it another way, could that good TC ever, perhaps in certain conditions, seem to correct for some liability of the mediocre lens so that the image improved. It seems unlikely.... but I would hesitate to say "impossible."
05-24-2016, 02:21 PM - 1 Like   #13
Site Supporter
Site Supporter
newmikey's Avatar

Join Date: May 2007
Posts: 1,904
Another aspect of a TC is metering (and one of the reasons I think a TC can still be useful). If you take an image with a lens without TC, and crop a portion out of the image, the meter will still have assessed the whole scene visible (or captured by the sensor). We all know the meter can be "fooled" by large portions of extremely dark or light background (such as sky).

With a TC, the previously cropped portion of the image is now enlarged to fill the whole sensor image and the metering will only assess the crop area, therefore less likely to be "fooled" by portions of the image you didn't want to capture to begin with. Metering will therefore be more precise, or correct, for the captured FOV.

So, with other words, while a TC will always degrade image sharpness of the "naked" lens (better TC's only slightly so), the exposure will be better which may still result in a better image overall. The fact that you are also able to better assess composition through the viewfinder also helps a bit. All in all, an excellent lens with a very good TC will deliver a good image with barely perceptible degradation of detail resolution but improved exposure accuracy. Stick a good lens on a bad TC things go south very quickly and a mediocre lens will likewise not result in acceptable sharpness and IQ.

I've found that sticking to a 1.4/1.5X TC and using an excellent lens with it can certainly be beneficial. I have just purchased a Kenko Pz-AF 2x off eBay but I expect that performance to be nothing to write home about even on my DA*50-135 or the Sigma 85mm/f1.4 - time will tell but if nothing else, it may sometimes get me the shot I'm after where a crop just wouldn't do.
05-24-2016, 03:12 PM   #14
Pentaxian




Join Date: Jul 2009
Location: Tromsø, Norway
Photos: Albums
Posts: 1,032
As always, it depends. On both the lens, the TC and the camera.

I have one TC that effectively reduces the images to 0,1 perceived Mp when its in focus. I don't know why I haven't thrown it in the garbage yet.
I have two other TCs that work excellent single or stacked.
05-24-2016, 03:18 PM   #15
Pentaxian
D1N0's Avatar

Join Date: May 2012
Location: ---
Photos: Gallery
Posts: 6,277
QuoteOriginally posted by Simen1 Quote
As always, it depends. On both the lens, the TC and the camera.

I have one TC that effectively reduces the images to 0,1 perceived Mp when its in focus. I don't know why I haven't thrown it in the garbage yet.
I have two other TCs that work excellent single or stacked.
Just take out the lens, then you can use it as an extension tube for macro.
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!
conditions, da*200, detail, dof, image, images, k-mount, pentax lens, res, resolution, series, slr lens, target, tc, tcs
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Idiot doesn't Know the Difference Between a Tripod and a Minigun Winder General Talk 23 11-21-2015 08:28 AM
on my old *ist DS photo preview doesn't work any more antoniomontag Troubleshooting and Beginner Help 5 01-13-2015 11:02 PM
Nature Who doesn't love a pelican slowpez Post Your Photos! 7 12-26-2014 02:24 PM
Pentax-F 50/1.7 doesn't show as A when using A-type teleconverter asharpe Pentax SLR Lens Discussion 8 10-31-2014 02:52 AM
Error for-sale ad doesn't show price Aegon Site Suggestions and Help 4 04-29-2011 07:43 AM



All times are GMT -7. The time now is 04:07 PM. | 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