[aurele]

To illustrate the impact of sensor size : Imagine a picture in the grey area. Every rectangle is a different sensor size.
So if you mount a 70mm on a camera to shoot the same subject, from the same place, you'll see a different thing in the viewfinder.



Simply said the yellow rectangle corresponding to a 1/3" sensor is like cropping a lot the picture.

Hence why everyone say this : a focal lengt don't change whenever it's on a FF or APS-C or anything else, BUT the field of view (what you see) will be different depending on the format

Attached Images

 

---

Last edited by aurele; 12-04-2017 at 12:50 PM.

[VoiceOfReason]

But an indicated 70mm on a K1 DFA lens when put on a K3 will not yield 70mm but a higher, narrower focal length. Hence, my looking for an APSC specific lens.

Nope, all a FF lens does is give a larger image circle. A great for instance is a DA 50 f/1.8 (APSC lens) has exactly the same FoV on your camera as an FA 50 f/1.8, which is a full frame lens. A 12-24 mm Sigma lens is a FF lens and it will show exactly the same FoV on your camera as the Pentax DA 12-24, which is an APSC lens. If you put them on both on a K1 the Pentax version will vignette badly, the Sigma one will not.

[pschlute]

But an indicated 70mm on a K1 DFA lens when put on a K3 will not yield 70mm but a higher, narrower focal length. Hence, my looking for an APSC specific lens

Afraid that is incorrect. 70mm is 70mm whether it is mounted on a FF camera; an APS-c sized sensor; or an old cardboard box with a piece of unexposed film in it. Any FF designed lens can be used on an aps-c sensor and will give a magnification and FOV identical to an aps-c specific lens of the same focal length.

[kjphilippona]

You do have to watch for bad copies of that lens though, more than most lenses. Where ever you buy it if you do, be prepared to exchange it if your first copy isn't up to scratch. Everyone with a good copy seems to be just thrilled with it.

i purchased one of those used from The Photographer's Marketplace
and even with +10 on the fine focus on my K3 and K-1, it doesn't start getting sharp until f4. Stupid thing is ok on my K-50. I would recommend the DA*50-135, gave my copy and K5II to my daughter, she uses it to shoot weddings Its been converted to screwdrive so focus is much faster and takes beautiful sharp pictures!

[mohb]

for some praise of the Sigma, well worth getting if you can find a copy http://https://www.pentaxforums.com/forums/130-lens-sample-photo-archive/196...es-thread.html

[mikesbike]

I highly recommend the DA* 50-135mm f/2.8 for its fine IQ, WR, excellent handling (it does not change its length during focusing or zooming), and compact size for the APS-C equivalent of a FF setup of 75-200mm f/2.8 at half the weight. I use mine frequently in lower-light and/or for faster-moving subjects, even at wide-open aperture with good sharpness of detail. IQ runs from good to excellent through its range. I also have the fine DA* 200mm f/2.8 for when I need the extra reach. This system works fine for my needs. It would match perfectly with a 17-50mm f/2.8 lens.

[UncleVanya]

But an indicated 70mm on a K1 DFA lens when put on a K3 will not yield 70mm but a higher, narrower focal length. Hence, my looking for an APSC specific lens.

The APSC lenses on an APSC camera look just the same on that APSC camera as the Full Frame lenses of the same focal length.

Here's an example:

Take any focal length lens, let's use 15mm. Put the DA 15 on the K-3 - take a shot. Then the DFA 15-30 - take a shot. The scene will be rendered with the same basic magnification, height and width - there could be minor differences due to liberties taken with actual focal length vs. labeled focal length or the zoom design vs. a prime but substantially similar results will be had. Put the two lenses on a K-1 - set in full frame mode. The DA 15 will fail to fully cover the sensor and parts will be blacked out outside of the APSC area due to the lens lacking coverage there. The DFA 15 will show the same central portion as the DA 15, but will cover the entire sensor giving a wider result to the image. This only occurs because 1) the sensor is larger, and 2) the lens is able to cover the entire sensor optically.

So it is true that a FF lens on a FF camera gives a wider view at the same focal length, but it is NOT true that a FF lens on an APSC camera gives any different view than an APSC lens of the same focal length. You can get wider by going FF if the lens and sensor are both larger, but you don't get narrower because the lens is FF on APSC - you get narrower with both APSC and FF lenses on APSC because the sensor is smaller.


Imagine you built your house with 1 window per room and they faced towards a distant mountain chain. In one room you gave yourself a wide tall window in the other you gave yourself a narrow short window. If you took the storm windows off the big window and put them on the small window you don't see anything different than if you use the right size storm window. The lens on a camera is the storm window in this analogy. Put the small storm window up on the big window and you have to cover part of the window with wood to get it to fit. This blacks out a lot of the view. But the reverse is not noticed even if it may be less efficient in terms of weight and cost.

[mikesbike]

you get narrower with both APSC and FF lenses on APSC because the sensor is smaller.

Exactly. But you do still get narrower. So the resulting image from the DA* 50-135mm f/2.8 on the K-3 or KP is akin to that of the DFA 70-200mm f/2.8 on the K-1. While going to a FF 70-200mm f/2.8 lens would of course get you more reach, since it goes out to 200mm FL, and with the smaller APS-C sensor will present a narrower FOV akin to 300mm on FF, it also loses some range at the short end- 70mm instead of 50mm. The DA* 50-135mm f/2.8 would seem to be a more ideal matchup to the 17-50mm f/2.8 zoom lens, unless longer reach is what is mainly needed.

[Rondec]

The focal length is the focal length. The DA lenses will look the same on a K3 as the DFA lenses at the same focal lengths -- albeit the DA lenses will have more vignetting than the DFA lenses. An APS-C sensor is just smaller than a full frame sensor and so it "crops" the image as compared to full frame. But I wouldn't worry about that unless you are shooting both formats. I think the whole equivalence thing was most useful for old film photographers in the early 2000s who were switching from film to APS-C digital SLRs and were trying to figure out how to get similar framing to what they were used to on 35mm. Well, and I guess camera companies sold it as a way of giving more length to your lenses (which it doesn't).

But if you like 135mm on your K3 than you should look for a lens that covers that focal length and don't worry about the whole DA/DFA/FA thing.

[audiobomber]

I am very happy with my Tamron 70-200mm f2.8, especially for the price. Like many of my lenses, screw noise can be a concern. Image quality is great. Unfortunately, due to the size of this lens, I rarely carry it. Even though it is smallish for a 70-200 f2.8, it is a very large lens compared to a 17-50 f2.8. I passed on the lovely 50-135mm due to widespread reports of SDM failure.

I would consider getting a 100mm or 135mm prime as a mid-length telephoto to mate with a 17-50.

[normhead]

I would consider getting a 100mm or 135mm prime as a mid-length telephoto to mate with a 17-50.

I really liked my DFA 100 macro with the 1.4 TC at the zoo the other day.

With the TC....


Without....


But most were taken with my DA*200... some with the DA*200 and TC, Getting to 200/280 with TC is important for most wildlife work.

[jddwoods]

The 50-135 is a bunch of primes, even at 2.8. Left on K20 in 2010, right on K3II last month. Same client, same 50-135, both at 2.8.

You definitely got some really nice pictures with the DA* 50-135. its on my wish list. What you also have here is a good apples to apples comparison of the K20 to the K-3II using the same lens and the same subject. Do you see a big difference in image quality with the same lens on an older body compared to a newer one? I ask this because I am on the fence regarding upgrading my K-5 to something newer such as a KP. I already have a K-3 and I really see a difference in image quality to my 65 year old eyes only in heavy crops with a sharp lens. Maybe dropping $900 to $1000 on a new body may not give me the return on investment that I could get with a lens upgrade. The DA* 11-18 is on my radar screen followed by the DA*50-135.

[gm4life]

If you are talking 35mm FOV eq. the D FA * 70-200 F 2.8 is sure a GREAT performer and is TACK sharp wide open, I love this lens on a crop - effectively gives me a 100-300mm which is great for telephoto landscape situations, wildlife, sporting events (I rarely attend) or low light performances etc. Hell - it would be great for wedding or portraits too at the wide end. It isn't an inexpensive lens by far the most expensive single item in my kit - BUT it delivers the goods. I thought about the crop 60-250 and 50-135 but I wanted more reach that the 50-135 and F 2.8 as well - so the D FA * 70-200 it is! Plus if I ever decide to cave and go FF my two most expensive pieces of glass will be designed for FF or fully FF compatible per Pentax - which is ONE great way to dive into FF. I am MORE than content with my crop kit due to size of the lenses the extra reach and cost/benefit perspective. If I was to go FF I am afraid the 31/43/77 would find a way into the bag along with the 15-30. Talk about away to piss away another 5 grand - no thank you!

I will patiently wait for the 11-18 DA HD * F2.8 and whatever crop body comes next and call it good. If the D FA * 85mm ever comes out and isn't outrageously expensive I might consider it as well. As it would convert to a nice classic 135mm prime in 35mm terms. That would really cover all the remaining "gaps" in my focal range between those two. Not that I have any large gaps NOW but I do suffer from LBA.

---------- Post added 12-11-17 at 09:59 PM ----------

I really liked my DFA 100 macro with the 1.4 TC at the zoo the other day.

With the TC....


Without....


But most were taken with my DA*200... some with the DA*200 and TC, Getting to 200/280 with TC is important for most wildlife work.

Awesome. Just awesome... Great photos and thanks for sharing!

[jddwoods]

My eyes are two years older than yours but I had new lenses put in both eyes about 11 years ago ( cataract surgery) so I may have an advantage! Right now, all my work is with a pair of K3IIs. I'm happy, my customers are happy. Plenty of resolution and I shoot a lot of low light in theater.

As for seeing an an image quality difference, no. I'd buy the lens. Get a used one from UsedPhotoPro.com or KEH.com, both offer 6 month warranties. My lenses haven't change in a long time but I've been through lots of bodies, I put a lot of wear on them.

Thanks, this is very helpful. My end of year bonus came through and I decided to keep my K-5 and K-3 going without a body upgrade but went for a new lens, the price on the DA* 300 dropped low enough that I could not pass it up. My Telephoto kit is now complete.

[derelict]

Here's something for you to do to prove this to yourself. Take your 135mm lens and go shoot an object across a field with it. Now, go grab a lens that is designed for APSC, but 135mm falls within the range of it if a zoom, set it at 135mm, and take a pic of the same thing. Your images will have exactly the same FoV.

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.