[Ptitboul]

The equivalent (in terms of FOV and DOF) of the Sigma 10-20/3.5 for APS would be a 15-30/5.0 for FF that would probably have similar price and weight, but it does not exist.
But if one wants low price and weight, I think that the K-1 is not the best option.
If fully understand why the 15-30 proposed by Pentax opens at f/2.8, because it offers something that was not available on APS cameras.

Nevertheless, you can use the Sigma 10-20/3.5 in the range 15-20 on your K-1, and it will do the job almost as efficiently as a dedicated FF 15-20/5.0.

[stevebrot]

My impression was that the FOV in question was on APSC

That is the diagonal APS-C FOV for both focal lengths.

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.

Thanks for jogging the memory. I forgot about the Pentax-K 15/3.5 (rare beast!!!) and was unaware of the K 18/3.5 (apparently also very rare).

How about these:

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

Thanks for the heads up. I missed the "out" and will correct. I was thinking specifically of those, both of which require and adapter and mirror lock-up.


Steve

[UncleVanya]

That is the diagonal APS-C FOV for both focal lengths.

Too many flying topics. I realize you meant that - my point was you don't have to match 10mm on full frame and the 12-24 Sigma posted earlier is full frame and has a FOV wider than that - but it was mixed into the discussion with the 12-24 Pentax which confused things I think. Sorry about that.

[stevebrot]

The equivalent (in terms of FOV and DOF) of the Sigma 10-20/3.5 for APS would be a 15-30/5.0 for FF that would probably have similar price and weight, but it does not exist.

It sort of does exist and at a price point that reflects its image quality and a size/weight that reflects its maximum aperture.

Pentax HD PENTAX-D FA 15-30mm f/2.8 ED SDM WR Lens 21280 B&H

I believe the editors on this site are working on an in-depth review now that the lens is available on the market.


Steve

[truonganh]

if you can find a copy of Sigma 12-24mm F4.5-5.6 EX DG ASPH Lens for Pentax AF, it's a good choice.

[UncleVanya]

if you can find a copy of Sigma 12-24mm F4.5-5.6 EX DG ASPH Lens for Pentax AF, it's a good choice.

The link I posted earlier was to Sigma and they had a refurbished (or perhaps several) for $399.

[dakotapix]

If I've followed this discussion correctly, the OP asserted that the APS-C format had caught up with FF in the ultra-wide realm due to the availability of K-mount APS-C lenses with equal or greater FOV than those available for FF. Others demonstrated that there were equivalent lenses for FF, but the point still stands that APS-C has caught up on the basis of at least being able to match FOV.

One factor that I didn't see addressed directly (apologies if someone did) is the fact that for the same FOV, a FF lens is going to be working at a greater magnification, therefore may be able to perform better in the realm of sharpness, perhaps even with a less high quality lens.

I've taken two shots of a refrigerator magnet from the exact same location and same camera (K-1) mounted on a tripod. Distance was a little over 4 ft, aperture was f/5.6, 2 second timer, manual focus using live view at 16x magnification, target dead center in viewfinder. One lens was the DA Limited 15mm and the other was an A 24mm f/2.8 (same FOV as a 16mm APS-C lens). There's a little mismatch in the comparison, but the end results are quite different. Keeping in mind that the K-1 crop mode is a fairly good analog for the K-5 sensor, it's interesting to note that the 15mm lens seems to outresolve the sensor and that pixellation is definitely evident in the original file. Not the case for the 24mm lens. I'd be curious to see the results if anyone cared to try to duplicate the comparison using a K-3.

The 15 mm crop has been upsampled to display at the same size on your screen. YMMV.

Attached Images

View Picture EXIF

File Date

 

View Picture EXIF

File Date

 

[Adam]

Thanks for jogging the memory. I forgot about the Pentax-K 15/3.5 (rare beast!!!) and was unaware of the K 18/3.5 (apparently also very rare).

But to be fair, they are pretty bad by modern standards. And for the sake of transparency, I do own both 15mm's as well as the 18.

I think the best value for the money at the present time would be something like the Rokinon 24mm F1.4.

However, Pentax does have a handful of new FF primes on the roadmap, one of which is a wide-angle, and the other is a fisheye.

What Pentax needs in the short term, IMO, is an affordable 20mm, 24mm, and/or 28mm prime lineup such as those in Nikon's F1.8 series. These can deliver solid performance without breaking the bank.

[stevebrot]

What Pentax needs in the short term, IMO, is an affordable 20mm, 24mm, and/or 28mm prime such as those in Nikon's F1.8 series. These can deliver solid performance without breaking the bank.

I agree wholeheartedly. Although there is a dedicated group of ultra-wide enthusiasts on this site, it remains a niche market in my mind's eye. While it would be cool to see a D FA 15/4, the basics should be covered first and the Nikon lineup is a good example of how it should be done.


Steve

[Adam]

I agree wholeheartedly. Although there is a dedicated group of ultra-wide enthusiasts on this site, it remains a niche market in my mind's eye. While it would be cool to see a D FA 15/4, the basics should be covered first and the Nikon lineup is a good example of how it should be done.


Steve

Plus the 15-30mm covers that niche handsomely for the time being. People who really need it already have it

[UncleVanya]

Plus the 15-30mm covers that niche handsomely for the time being. People who really need it already have it

And in APSC the existing lineup already gives the nod to zooms going wider than primes. DA 15 is the widest prime, but the 10-17 and 12-24 both exist with wider FOV. I think you guys have it right, a 20 or 24 would be priority 1 since the 31 exists and is close to 28 already (albeit expensive). The 15-30 is there for really wide angle enthusiasts.

[Simen1]

I didn't see the Tamron Adaptall-2 SP 17mm f/3,5 in the thread, but that is a cheap FF alternative. Probably not as good as the Sigma 10-20 in crop mode, but I just thought it should be mentioned.

Anyway, try to use wide angle crop lenses in FF mode. Some of them don't need to be cropped all the way to 1,5x crop factor. Some will give decent results at crop factors in between 1,5 and 1,0. A circular "frame" can also be an advantage if the scene you are shooting is better viewed in another aspect ratio then 3:2. Personally I plan to use a Samyang 8mm f/3,5 CSII without the hood, in full frame mode on a full frame camera when I eventually get one. Irix 11mm f/4 and Samyang 12mm and Lowa 12mm looks quite interesting if I find the funds.

[LukeOB]

And possible future products

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

Is this a wishlist or something a little more definite? Would dearly like to see a dfa 14 2.8; or a 10-18 or similar - with a filter thread!!

[enoeske]

Is this a wishlist or something a little more definite? Would dearly like to see a dfa 14 2.8; or a 10-18 or similar - with a filter thread!!

Taken from the sticky

https://www.pentaxforums.com/forums/169-pentax-full-frame/313830-current-pent...w-picture.html

[northcoastgreg]

If I've followed this discussion correctly, the OP asserted that the APS-C format had caught up with FF in the ultra-wide realm due to the availability of K-mount APS-C lenses with equal or greater FOV than those available for FF.

I suspect the OP asserted a bit more than that. For a long time we've been hearing about the advantages of FF in terms of wide angle photography. Wide-angle lenses for FF tend to be cheaper (especially legacy WA's) and they will of course perform better (at least in terms of center sharpness). For example, you can purchase an old M 28 f3.5 for around $60. The closest you can come to that FOV on APS-C is the DA 21, which is considerably more expensive (used prices approach $300). Is the DA 21 a better lens? Yes. But on FF the M 28 will outresolve the DA 21 on APS-C.

Yet despite this seeming huge advantage for FF, right now (and at least for the immediate future) K-1 landscape photographers are really struggling to find viable wide angle solutions, especially once they wish to go wider than 28mm. If you wish for state of the art optics, there are only two options available, and both are heavy and expensive f2.8 zooms. And if you want filter rings on a lens wider than 24mm, there's really no credible options currently available. Hence the rather ironic situation for the K-Mount, where APS-C actually enjoys, at least in terms of options involving high-end modern optics, an advantage over FF.

One factor that I didn't see addressed directly (apologies if someone did) is the fact that for the same FOV, a FF lens is going to be working at a greater magnification, therefore may be able to perform better in the realm of sharpness, perhaps even with a less high quality lens.

Yes, that's true for the center of the image. But that's not necessarily true for the edges. I've been looking at some FF images taken with the FA 20-35, and while the center of the image is definitely sharper than what I could get with the DA-12-24 on APS-C, the edges are not as sharp. Outside the APS-C crop, the resolution of the FA 20-35 seems to fall off a cliff. If you're a landscape photographer, the primary reason you would migrate to FF would be for the added resolution. But if you can't improve resolution across the entire frame, what's the point?

What Pentax needs in the short term, IMO, is an affordable 20mm, 24mm, and/or 28mm prime lineup such as those in Nikon's F1.8 series. These can deliver solid performance without breaking the bank.

I would argue there's a greater need for a WA zoom with filter rings. An HD DFA 18-35 f4-5.6 with similar optical performance to the DFA 28-105 and filter rings could be sold at half the price (and perhaps half the weight) of the expensive and heavy DFA 15-30. Most landscape photographers need filter rings more than they need f2.8!