[house]

It looks like lenses aren't exactly focused at the same place which can show a big difference at close distance. Depth of field blur can change if one lens is focused a little closer.[COLOR=Silver]

That was my first thought as well but considering how sharp the distant towers are in the center I don't think its the cause. The towers should be a bit defocused if the lens didnt reach infinity.

Still confused but I think Paul the Sunman had another set of images from the port showing poles without metal hats. The same behaviour could be noted there. My conclusion is that the 1530 must have monstrous field curvature at 21mm. Strange we havent heard about it though.

[Abbazz]

That was my first thought as well but considering how sharp the distant towers are in the center I don't think its the cause. The towers should be a bit defocused if the lens didnt reach infinity.

Still confused but I think Paul the Sunman had another set of images from the port showing poles without metal hats. The same behaviour could be noted there. My conclusion is that the 1530 must have monstrous field curvature at 21mm. Strange we havent heard about it though.

Others have noted the field curvature:

There’s also some field curvature mid-zoom, but it’s not unexpected in an ultra-wide zoom like this.

Tamron SP 15-30mm F/2.8 Di VC USD Canon-mount lens review

Of course, it is possible to mitigate it by focusing near the edge of the frame but here I wanted to show both lenses used in the same conditions and the D FA 21 is superior.

Please note that the difference of sharpness we are discussing here is hardly visible except at 100% and that the images were taken at f/5.6, which is not the aperture people usually use for landscape photography at infinity. At f/8-f/11, there won't be any difference.

There is absolutely no doubt that the 15-30mm is great and delivers stunning images. It's just that I find the D FA 21 a bit better and easier to use in all situations –which is perfectly normal considering that we are comparing a zoom to a top of the range prime lens. If only it had an aperture ring and better autofocus then it would be perfect...

Cheers!

Abbazz

[Ian Stuart Forsyth]

Field curvature is not always a bad thing. for a lot of my landscape and back ally. Focusing for field curvature for landscape can be tricky but once you know the profile of it and how your object fall within the frame you can make use of it

[Abbazz]

Field curvature is not always a bad thing. for a lot of my landscape and back ally. Focusing for field curvature for landscape can be tricky but once you know the profile of it and how your object fall within the frame you can make use of it

That's very true. Lots of Zeiss wide lenses have a sterling reputation for landscape photography yet exhibit lots of field curvature.

Cheers!

Abbazz

[house]

Field curvature is not always a bad thing. for a lot of my landscape and back ally. Focusing for field curvature for landscape can be tricky but once you know the profile of it and how your object fall within the frame you can make use of it

For sure there are, not so uncommon, scene configurations where field curvature helps. Field curvature really is a negative though and it imho makes no sense to play it down, despite most uwa's suffering from it. In my experience the dof behavior tends to become noticeable. It doesn't make visual sense (even if it should).

A flat field sharpness fall off looks natural. With uwa lenses the dof is deep enough to cover a lot. You just look at the shot and don't even consider the dof limitations. With field curvature you get inexplicable smeary horizon or edges that stand out.

Generally speaking even a large aperture shot (f1.8) at ~20mm looks great if dof is flat. See this cameralabs shot with the Z20. NikonZ20f1-8S_f1-8_70256 | Sample images taken with a Nikon ? | Flickr there are more in that album that could be of interest.

Some samples suggest the DFA21 has a very strong field curvature at f2.4 which makes sense with the design objectives. It must really flatten out dramatically as you stop down.

[Rondec]

It looks like lenses aren't exactly focused at the same place which can show a big difference at close distance. Depth of field blur can change if one lens is focused a little closer.

---------- Post added 29-01-22 at 18:14 ----------


Ricoh seeing people switch to Sony using their Pentrax glass, Ricoh probably want to secure their future camera business by making it harder to adapt Pentax lenses on foreign mirrorless cameras. Or unless Ricoh are planning to make their own mirrorless cameras with an adapter that works with KAF4.

I thought most brands had gotten away from mechanical aperture levers and Pentax was lagging in that respect. Sigma gave one of their reasons for not continuing to produce K mount lenses, as the fact that Pentax still used a mechanical lever -- obviously that wasn't the main reason, but they did mention it.

KAF 4 lenses should be easy to adapt to other brands lenses, if someone sits down and does the reverse engineering necessary to get them to work. There probably aren't enough KAF 4 lenses out there to make it worthwhile right now, but certainly it seems unlikely that Ricoh changed the aperture lever simply to make it hard to adapt their lenses to other mounts.

[house]

I thought most brands had gotten away from mechanical aperture levers and Pentax was lagging in that respect.

You can have aperture ring without aperture lever. See my 28mm shift. I don't think any of the Fuji, Sony etc lenses have levers?

It is peculiar how Pentax was about the only brand still producing aperture ringed lenses (Fa limiteds) then when everyone and their dog reintroduced the aperture ring Pentax stopped!

[sebberry]

I thought most brands had gotten away from mechanical aperture levers and Pentax was lagging in that respect. Sigma gave one of their reasons for not continuing to produce K mount lenses, as the fact that Pentax still used a mechanical lever -- obviously that wasn't the main reason, but they did mention it.

KAF 4 lenses should be easy to adapt to other brands lenses, if someone sits down and does the reverse engineering necessary to get them to work. There probably aren't enough KAF 4 lenses out there to make it worthwhile right now, but certainly it seems unlikely that Ricoh changed the aperture lever simply to make it hard to adapt their lenses to other mounts.

The 55-300 PLM uses an electromagnetic aperture - no lever there.

[acoufap]

You can have aperture ring without aperture lever. See my 28mm shift. I don't think any of the Fuji, Sony etc lenses have levers?

It is peculiar how Pentax was about the only brand still producing aperture ringed lenses (Fa limiteds) then when everyone and their dog reintroduced the aperture ring Pentax stopped!

Pentax' aperture lever works fully mechanical. Position is set by the fully mechanical aperture ring of Pentax lenses and only cameras that "understand" this physical position signal can work with this position representing aperture information. Aperture rings of other brands may work electronically and the signal is transmitted fully this way.

If a Pentax lens offers an A position, and the A position is set, the aperture value is transported via contacts - not via lever - to the camera. If the lens doesn't have an aperture lever and no special contacts to communicate with the camera, the aperture value can't be transported to the camera.

Your hint on the 28mm shift lens (this one? , f/3.5-32) seems interesting to me since the aperture value cannot be transmitted to camera bodies.

I don't know this kind of lenses but I guess if you set the aperture on this lens, the aperture stays closed according to the set value. Now metering can take place. Depending on the chosen aperture the viewfinder might show a very dark image when mirror is down - like if you choose the DOF lever (manually closing of aperture) when using more modern lenses..

If interested have a look at the PF story about K Mount evolution.

[house]

Pentax' aperture lever works fully mechanical. Position is set by the fully mechanical aperture ring of Pentax lenses and only cameras that "understand" this physical position signal can work with this position representing aperture information. Aperture rings of other brands may work electronically and the signal is transmitted fully this way.

If a Pentax lens offers an A position, and the A position is set, the aperture value is transported via contacts - not via lever - to the camera. If the lens doesn't have an aperture lever and no special contacts to communicate with the camera, the aperture value can't be transported to the camera.

Your hint on the 28mm shift lens (this one? , f/3.5-32) seems interesting to me since the aperture value cannot be transmitted to camera bodies.

I don't know this kind of lenses but I guess if you set the aperture on this lens, the aperture stays closed according to the set value. Now metering can take place. Depending on the chosen aperture the viewfinder might show a very dark image when mirror is down - like if you choose the DOF lever (manually closing of aperture) when using more modern lenses..

If interested have a look at the PF story about K Mount evolution.

Yes the 28 shift is a preset lens, with two aperture rings to allow you to shift quickly between wide open and selected aperture.

You describe well the various options for non levered lenses with aperture rings.

[gatorguy]

This thread has been enough impetus to trim down the lens collection a tad to clear space for the DFA21, will even be selling off my FA31. To the Marketplace in a day or two!

The new lens seems so impressive, even tho it definitely had no interest for me when first announced. A couple of forum members, Digitalis in particular, have changed my outlook.

[biz-engineer]

That D-FA 21 limited looks fantastic. I'm seeing some price drop, it's very tempting.

[repaap]

I'll propably sell also my 15-30 for this DFA 21...would be very hard to see my FA 31 to go thou. I do really like that lens. 15-30 is practical and very good, but it is also a bit boring, I do not really like it's bokeh, at all. (I'll buy 11-18 for my K-3III instead, it has that * and seems to be very nice lens. Some guys even use it witk K-1! and those pictures look nice too)

[normhead]

Field curvature is not always a bad thing. for a lot of my landscape and back ally. Focusing for field curvature for landscape can be tricky but once you know the profile of it and how your object fall within the frame you can make use of it

That's what I've always said.

Sometimes the fisheye distortion enhances the image.


DA 10-17 fisheye on a K-5 at 11 mm.
The distortion actually makes a more pleasing image.

[Durf]

This thread has been enough impetus to trim down the lens collection a tad to clear space for the DFA21, will even be selling off my FA31. To the Marketplace in a day or two!

The new lens seems so impressive, even tho it definitely had no interest for me when first announced. A couple of forum members, Digitalis in particular, have changed my outlook.

I doubt that you'll regret buying the 21mm! This 21mm is now my main landscape lens and almost always on my K1, replacing my much larger 24-70mm and IRIX 15mm. My kit is trimmed down to the 21mm, 43mm, 100mm macro WR. I can do most of my landscapes and nature photography with just these 3 lenses alone. My kit is MUCH LIGHTER now!

There's still room in my bag to toss in the 15mm IRIX if I know I'm going to need a super wide. But, I can also just use the 21mm to do a wide pano if needed. This 21mm is incredibly versatile and a great lens. I also have room to toss in the 70-210mm f4 if I know I might need a little reach and compression.

Moving forward, the 21, 43, and 100 have been working great for what I do and my back and knees thank me!