Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
01-02-2018, 09:28 AM   #31
Emperor and Senpai
Loyal Site Supporter
VoiceOfReason's Avatar

Join Date: Jun 2010
Location: Mishawaka IN area
Photos: Albums
Posts: 5,975
QuoteOriginally posted by derelict Quote
So, explain this to me then. K3 mounted on a tripod and not moved a cm between shots.
Tamron 17- 50 @50


Zenit 50mm


The FoV is obviously different. The FF 50mm prime is giving me a completely different photo (closer to 75mm in FoV) than the APSC specific lens set at 50mm. This is what I am talking about and why I am looking for an APSC specific lens. I want an equivalent lens to the Tamron in terms of focal length. If the Tamron tops out at 50, I want the next lens to start out at a true APSC 70mm, not jump up to around 100mm. That is a chasm. I am looking for a 2 APSC lens kit. The primes I use when I am shooting film. The zooms on the K3 will be for everything else.

So, I am contemplating a Sigma 70- 200/ 2.8 EX DG. The reviews section does not show whether it is APSC specific or FF. They show that people are using it on the K1 and on K7/ 5/ 3 bodies. Does anyone know? I am guessing that this lens on my K3 is going to be closer to a 100- 300 instead of a true 70- 200.
Looks like a bad case of focus breathing. Now go take the same lenses and take a picture of something 100 feet away at the same focal length.

01-02-2018, 09:29 AM   #32
Emperor and Senpai
Loyal Site Supporter
VoiceOfReason's Avatar

Join Date: Jun 2010
Location: Mishawaka IN area
Photos: Albums
Posts: 5,975
Focus Breathing (Focal length variation with focus distance)- Bob Atkins Photography explains it some.
01-02-2018, 04:38 PM   #33
Loyal Site Supporter
Loyal Site Supporter
UncleVanya's Avatar

Join Date: Jul 2014
Photos: Gallery | Albums
Posts: 16,980
Focus breathing. Unrelated to the apsc and full frame status of the lenses.
01-03-2018, 07:32 AM   #34
Veteran Member
derelict's Avatar

Join Date: Jul 2011
Location: NoVa
Posts: 525
Original Poster
So, here is a question: why did Pentax bother with the 50-135 then? If the 50-135 is the APSC equivalent of a 70-200 FF, but it does not matter, why create a whole new lens? Why not just crank out more 70-200s?

01-03-2018, 08:17 AM   #35
Emperor and Senpai
Loyal Site Supporter
VoiceOfReason's Avatar

Join Date: Jun 2010
Location: Mishawaka IN area
Photos: Albums
Posts: 5,975
QuoteOriginally posted by derelict Quote
So, here is a question: why did Pentax bother with the 50-135 then? If the 50-135 is the APSC equivalent of a 70-200 FF, but it does not matter, why create a whole new lens? Why not just crank out more 70-200s?
Because the 50-135 has the same FoV on APSC as the 70-200 does on FF.

Here's an easy way to test this yourself. Take your 50mm prime and put it on an APSC camera, then go to some place like your downtown area. Focus down a road and take a pic with that lens on an APSC camera. Now, keep the tripod in teh same spot, but swap your APSC camera for a full frame one, put the lens back on, and again, take a pic down the road. Make sure your focus point for both is a ways away, a couple hundred feet at least. Now compare the shots and you will see that the APSC has a narrower FoV than the FF one does, and that's because the light coming through the lens hits a sensor with a smaller area.

You could even put a medium format camera in the mix to prove this. Take a 645z and put the 55 MM lens on it. Take a pic from a tripod in a filed. Now wake a K1 and use an adapter to put the 645 55 mm lens on it, set ti on the same tripod focused across the same field aimed at teh same spot and take a picture with it. Now do the same with a K3. Now compare all three. The 645z will have a wider Fov than the K1, which will in turn have a wide FoV than the K3, and if you really want to have fun throw a Q in there for a still narrower FoV. If I can get my hands on a 645-K adapter I could demonstrate this next time it is clear and nice enough outside.

What you seem to be missing is that the MM on a lens is just that, the focal length of a lens. heres another good demo for you. If you have access to a K1 and a K3 or other Pentax APSC camera then get something like the DA*55 or the DA* 200 or DA*300. Take a pic of the same subject with both cameras at the same distance. Those lenses were made for APSC originally. You could also do the reverse and take an FA 50 or pretty well anyone's (Sigma, Tamron, or Pentax) 70-200, and take an image of the same object at the same distance at 70 and at 200 with the K1 and the K3. You will notice that on every single shot the FoV on the APSC will be narrower. This is not a function of the lenses, but a function of the sensor sizes themselves. The only thing that "equivalence" is good for is figuring the FoV between cameras. That's it. Heck, throw the K1 in crop mode and you get an APSC FoV no matter what lens.

The only thing that you have to watch for on an APSC only lens is that the image circle is smaller and will cause severe vignetting on FF in some cases because the hole that the light goes through is smaller than the diagonal measure of a FF camera. That's it.
01-03-2018, 08:25 AM - 1 Like   #36
Loyal Site Supporter
Loyal Site Supporter
pschlute's Avatar

Join Date: Mar 2007
Location: Surrey, UK
Photos: Gallery
Posts: 4,339
QuoteOriginally posted by derelict Quote
So, here is a question: why did Pentax bother with the 50-135 then? If the 50-135 is the APSC equivalent of a 70-200 FF, but it does not matter, why create a whole new lens? Why not just crank out more 70-200s?
I think you are getting confused between how the FOV changes between two different camera formats , 35mm film or FF digital versus aps-c digital. It is the format that causes the change in the FOV and not whether the lens was designed for a specific format.

If you put a 70-200 lens on an aps-c camera you will get a FOV that looks like how a 105-300 would look on 35mm/FF. Now many folks would find that FL range a bit on the long side so they created a 50-135. Now when you mount that on a aps-c camera it has the FOV of how a 75-200 would look on 35mm/FF.

But the point of this thread is that either 50-135 or 70-200 when mounted on the same body will still show the same focal length and FOV . On your K3 both lenses at say 100mm will give the same magnification and FOV. It cannot change, except at close focus where focus breathing may affect it. But this does not apply to all lenses.

Last edited by pschlute; 01-03-2018 at 08:34 AM.
01-03-2018, 08:40 AM   #37
Loyal Site Supporter
Loyal Site Supporter
UncleVanya's Avatar

Join Date: Jul 2014
Photos: Gallery | Albums
Posts: 16,980
QuoteOriginally posted by derelict Quote
So, here is a question: why did Pentax bother with the 50-135 then? If the 50-135 is the APSC equivalent of a 70-200 FF, but it does not matter, why create a whole new lens? Why not just crank out more 70-200s?
I'm sorry but you have a fundamental misunderstanding of the role sensors and lenses have on field of view.

The lens focal length determines the field of view on a specific sensor size. There are exceptions related to the type of lens (fisheye vs rectilinear) but generally speaking the same focal length s the same field of view on a camera with the same sensor.

Different size sensors give different results. A full frame sensor has more surface area, and if a lens provides a wide enough image circle that lens will show a wider field of view when used on the larger sensor. A lens that doesn't cover the sensor adequately will have very poor performance or even deep black outside the intended coverage area.

Imagine this: You have an 8x10 view camera. You mount a 300mm lens, which on an 8x10 camera is a normal perspective lens NOT a telephoto. Imagine you then mask off the glass plate with black paper to only leave an opening the size of a 35mm negative. If you expose film using that and then enlarge it you will see the same telephoto perspective you expect a 300mm to give on 35mm film. If you then changed the lens and mounted a 300mm designed for 35mm to your 8x10 camera, the image would be virtually the same in the masked off section. If then you removed the paper mask, you would see that the 35mm lens did not cover the 8x10 ground glass, and thus wouldn't work as a lens for the 8x10 since it wouldn't cover the frame fully.

The 50-135 isn't able to cover the full 35mm frame in the same way as the example above.

However... If we put a 50-135 on an apsc camera and a different 50-135 that covered full frame on the same camera we would see the same image coverage and framing with both lenses. If those same lenses were placed on a full frame camera, the apsc lens would have blacked out part of the frame, and the full frame would now show a wider perspective than before. The original shots made on the crop camera would look more telephoto.

The 70-200 mounted on a full frame gives the same rough perspective as a 50-135 mounted on a crop sensor.
01-03-2018, 05:39 PM - 1 Like   #38
Senior Member




Join Date: May 2014
Location: Delta, British Columbia
Posts: 132
I made some quick graphics to maybe help explain a bit how the image circle created from a lens works with different sensor formats.

Attached Images
     

Last edited by cgchang; 01-03-2018 at 06:45 PM.
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!
crop, fa, ff, flickr, head, k-mount, k3, kit, lens, norm, pentax lens, range, slr lens, tc, time
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Help choose a lens in the 70-200 range Tonycog Pentax SLR Lens Discussion 34 12-12-2016 08:46 AM
IQ of FF vs APS-C primes on APS-C bodies lightbox Pentax SLR Lens Discussion 26 11-10-2016 06:50 PM
Does the gap between 17-50 and 70-200 cause you problems on your APS-C Pentax? BigMackCam General Photography 19 09-06-2016 09:54 PM
Lens tests on K-1 : 15-30, 24-70, 70-200, 31, 43, 77, 100 Macro, 28-70 and 80-200 Mistral75 Pentax SLR Lens Discussion 14 06-28-2016 11:46 AM
When is an APS-C lens not really an APS-C? lightbox Pentax SLR Lens Discussion 17 03-27-2015 07:45 PM



All times are GMT -7. The time now is 05:53 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