[Timd]

While I know a full frame camera will have a wider FOV than a crop camera using the same focal length, and many were wanting a full frame Pentax for wide angle shots, I'm battling to get to terms with reality. Apart from the very expensive DFA 15-30 lens, the old wide angles are 28, 24 and 20mm, equivalent FOV to 18, 16 and 14 on an APC. Not very wide in my view.

I'm looking for an equivalent to the 10-20 lens that won't break the bank.

(I suppose you'll all say that to take advantage of the K1 sensor you'll need the DFA15-30; my point is crop has caught up to FF in the wide angle lenses)

(edit to correct equivalence reference)

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Last edited by Timd; 07-28-2016 at 08:25 AM.

[stevebrot]

...equivalent FOV to 18, 16 and 14. Not very wide in my view.

No, those focal lengths are equivalent to 28, 24, and 20mm. You can go shorter, but as with APS-C glass, distortion, vignette, poor corner performance, and high price are the trade-off. Assuming, of course, that you are not interested in a fisheye.

my point is crop has caught up to FF in the wide angle lenses)

Glad you made that clear.


Steve

(...spent much of the last decade searching for a compact and inexpensive 18mm prime equivalent to my Tamron 28/2.5...no success...)

[Timd]

No, those focal lengths are equivalent to 28, 24, and 20mm.

Well, you are correct if your frame of reference is full frame. My immediate past frame of reference is APC, so I disagree ...

[enoeske]

Well, you are correct if your frame of reference is full frame. My immediate past frame of reference is APC, so I disagree ...

Your choice of sensor doesn't effect the focal length of the lens. Those are 20mm, 24mm and 28mm lenses.

[Timd]

sigh. Yes, I know a lens focal length does not change. I'm looking for a FF lens for a K1 that gives the same FOV as my Sigma 10-20 gives on my k5, for a similar cost.

Put another way, there is no legacy lens with FOV on FF that the 10-20 has on the K5

[UncleVanya]

Your choice of sensor doesn't effect the focal length of the lens. Those are 20mm, 24mm and 28mm lenses.

That's why he said FOV.

And it is entirely correct to put any sensor as the frame of reference for discussion. Are you saying an 18mm lens on APSC isn't an 18mm lens? Of course not. Nor is he saying that a 28mm lens on FF isn't a 28mm.

The point which is being lost in people stirring up the mud is that he feels like wide angle - on Pentax - is easier to accomplish with APSC lenses like the 10-20mm from a cost vs. quality perspective.

I'm not the expert owning a K-3 and not having a K-1, but I think this is a valid question to pose and get feedback on. I do know that I have read that some of the ultrawide angles for APSC cover full frame over part of their range. But I'm not sure what level of IQ these have at those ranges or the exact ranges covered.

---------- Post added 07-28-16 at 12:01 PM ----------

Not a 10-20 but actually wider on FF than the 10-20 on APSC:
https://www.pentaxforums.com/forums/94-pentax-price-watch/326432-sigma-12-24m...furbished.html

[Imp]

No, those focal lengths are equivalent to 28, 24, and 20mm.

he said

FOV

[enoeske]

sigh. Yes, I know a lens focal length does not change. I'm looking for a FF lens for a K1 that gives the same FOV as my Sigma 10-20 gives on my k5, for a similar cost.

Put another way, there is no legacy lens with FOV on FF that the 10-20 has on the K5

If you are okay with primes instead of an all in 1 zoom (like the 15-30mm f/2.8), there are a few already

Samyang (Bower/Rokinon) 14mm f/2.8
Irix 15mm f/2.4
Laowa 15mm f/4
Zenatar 16mm f/2.8
Sigma 20mm f/1.8
Samyang (Bower/Rokinon) 24mm f/1.4
Sigma 24mm f/1.8

And possible future products

Laowa 12mm f/2.8
Pentax D FA 14mm f/2.8
Pentax D FA 10-18mm f/2.8
Pentax D FA 28mm f/2.8

[Interspieder]

[...]
I'm looking for an equivalent to the 10-20 lens that won't break the bank. [...]

Hey there,
the perfect equivalent would be
10mm*1,5= 15
20mm*1,5= 30

The perfect equivalent to your Sigma 10-20 would be a 15-30.

The problem at the moment is: Full-Frame by Pentax is pretty new. So the only available lenses are either the new 15-30 2.8 (which is bloody expensive for an enthusiast), 3rd Party-lenses (Samyang, Irix, Laowa etc), or old lenses.

I have myself a Sigma 8-16 and struggle to find a good equivalent on Full-Frame. There is the Samyang 14 2.8, the Irix 15 2.4, the Irix 11 4, the Pentax M 20 f4 etc.

In my opinion, there will be more lenses in the next time, for example by Tamron or Sigma (i hope at least). That would give us numerous new options..

[ChatMechant]

Well, that's one of the benefits of the aps-c system. lenses can be cheaper and smaller. Wide, modern ff zoom that's cheap?

[stevebrot]

Put another way, there is no legacy lens with FOV on FF that the 10-20 has on the K5

Why legacy? Yes, the traditional FF ultra-wide for SLR has been 20mm. Shorter lenses were made for the format, but not retrofocus and not compatible with the mirror being up[B] but are rare with many being non-retrofocus and unusable on SLRs without mirror lockup. The ongoing issues have been and continue to be designing to minimize barrel distortion, poor edge performance, and vignette. What's more, ultra-wides were considered to be a niche market and both pricing and production numbers reflected that.

If you want a zoom at a similar price/quality point with similar FOV, your point is well made. The Sigma 10-20/3.5 is a good performer at a moderate price and is fairly unique in both regards. The D FA 15-30/2.8 is in another league in both price and performance. If you can settle for a prime and mostly just want a FF lens at the wide end, I would suggest the Samyang 14/2.8 or Venus 15/4.

As I noted in my comment above, I have been looking for APS-C wide angle solutions for nearly a decade with only mixed success. For ultra-wide, I actually prefer a circular (fisheye) projection over rectilinear and if fishy doesn't cut it, a stitched image provides straight lines without the volumetric distortion common to all rectilinear ultra-wides in preferable IMHO.

In regards to APS-C, K-mount rectilinear lenses in the 10mm range, the current options offer reasonable quality and won't break the bank, though the choices are not extensive in those that are readily available:

• Sigma 10-20/3.5 $499
• Samyang 10/2.8 $399
• Tamron 10-24/3.5-4.5 $499

There are no premium K-mount offerings in this space. It is hard to tell how long both Sigma and Tamron will continue to offer their short APS-C zooms. If those lenses fall out of the lineup, the Samyang remains as the sole APS-C ultra-wide.


Steve

[UncleVanya]

There are no premium K-mount offerings in this space. It is hard to tell how long both Sigma and Tamron will continue to offer their short APS-C zooms. If those lenses fall out of the lineup, the Samyang remains as the sole APS-C ultra-wide.

Steve

Is the 12-24 Pentax not ultrawide? That's an 18mm FF equivalent. Not to mention the 10-17 Pentax... but that's a fisheye.

[stevebrot]

Is the 12-24 Pentax not ultrawide?

Good question. The OP drew the line at 10mm and FOV at infinity for that vs. 12mm is significantly different (110.5° vs. 100.5° diagonal). FWIW, I personally consider the 12-24 to be an ultra-wide. Whether the difference in FOV holds up at closer distances is hard to say. "Focus breathing" at the wide end of zoom range can be significant and is often skipped in lens reviews.


Steve

[UncleVanya]

Good question. The OP drew the line at 10mm and FOV at infinity for that vs. 12mm is significantly different (110.5° vs. 100.5° diagonal). FWIW, I personally consider the 12-24 to be an ultra-wide. Whether the difference in FOV holds up at closer distances is hard to say. "Focus breathing" at the wide end of zoom range can be significant and is often skipped in lens reviews.


Steve

My impression was that the FOV in question was on APSC - and there is a Sigma 12-24 that is Full Frame. I posted a link earlier. But I get your point about APSC lenses.

[lytrytyr]

the traditional FF ultra-wide for SLR has been 20mm. Shorter lenses were made for the format, but not retrofocus

Well, there's this:

SMC Pentax 15mm F3.5 Reviews - K Prime Lenses - Pentax Lens Reviews & Lens Database

and this:

SMC Pentax 18mm F3.5 Reviews - K Prime Lenses - Pentax Lens Reviews & Lens Database

for K-mount.

and not compatible with the mirror being up.

How about these:

https://www.cameraquest.com/VCSL1215.htm

I used to wonder about getting one to see if it would fit on a K-01,
but finally found a compact wide-angle solution with the 08 on a Q7.