[ZombieArmy]

Rear element diameter is no indication of image circle. Unofficial evaluation by Pentax Forums staff indicates two stars (out of three) for FF compatibility, meaning...

In the U.S. school system, A is first class, C second class/passing, and D barely passing. I can't see buying the DA if one wants a pancake for FF film or digital work.


Steve

To be fair the 40mm isn't a great 2.8 lens to begin with, I think most of my shooting is at f4 to f8 with it.

I'd think it would be an amazing light weight option for landscapes and around town city shots on ff.

[someasiancameraguy]

To be fair the 40mm isn't a great 2.8 lens to begin with, I think most of my shooting is at f4 to f8 with it.

I'd think it would be an amazing light weight option for landscapes and around town city shots on ff.

Which is exactly my use case. Something portable with decent IQ would be great.

[leekil]

Then you should get the M-series lens (no aperture ring on DA). FWIW, the DA versions, while similar, do not share optical design with the M-series.

Above diagrams lifted from The K-mount Page Web site: Pentax Normal Prime Lenses | The K-Mount Page

Looking at the back of the M40 and DA40, the exposed rear elements seems to be the exact same diameter, 9/16th of an inch. (Note that I used a tape measure rather than something that might be more precise, like calipers.) I guess it wouldn't be definite, but it's a good indication that the rear elements are probably the same, not differing as much as shown in the lens formulae above? How accurate of a lens formula does Pentax provide?

Viewing my photos on a full-frame with the DA40, they seem somewhat less sharp in the corners, but some of that is probably due to the composition, as the corners were not important to what I was photographing, and were in a different focal plane. And besides a possible different in the APS-C vs. FF formulation, maybe there is field curvature that might result in worse corners. I took some comparison photos under less-than-ideal conditions, I'll see what they might show.

[clackers]

The Corners of the DA or XS are always blurred because the lenses are made for APS-C.

I've used the XS on my K-1 and that's not true, pid.

[vector]

I found a near mint condition M40 in a local shop a month ago and picked it up. I haven't used it yet other than some quick indoors test shots. I guess I should put it on my K1 and get some outdoors test shots through the aperture range. Hard to get landscapes right now with our short winter days and working all day, but I'll see what I can do. I don't have a DA40 to compare against but its better than nothing.

[stevebrot]

I guess it wouldn't be definite, but it's a good indication that the rear elements are probably the same, not differing as much as shown in the lens formulae above? How accurate of a lens formula does Pentax provide?

As good as the catalog they were published in. In case it is not obvious, the two designs diagrams are not to scale with each other and are quite dissimilar.

Addendum: Different minimum focus distance is also a good indicator of design differences between similarly spec'ed lenses. The M 40/2.8 is 0.6m as compared to 0.4m for the DA lenses.


Steve

[stevebrot]

This is where I mention that there is an XR Rikenon 45mm f/2.8 pancake that is well regarded.




https://mannyquinto.wordpress.com/2012/01/03/xr_rikenon_45/


Steve

[ZombieArmy]

This is where I mention that there is an XR Rikenon 45mm f/2.8 pancake that is well regarded.




XR Rikenon 45mm f 2.8 | MCQuinto Photo Blog


Steve

I've been on and off looking for one of those for years. Can never find em for a decent price, it's always for some absurd amount.

Sorry but there's no way prices should match a 40 ltd and sometimes approach a 43...

[GUB]

There is also the Chinon 45mm f2.8 pancake. I recently acquired one but haven't done a comparison with my M40 or XS40. Sighhh --- give me a few days.
The thing is these pancakes are optimised for size not IQ - we shouldn't be too harsh on them. I can sense my M40 isn't quite up there with the M50 1.7 but I have noticed that it responds nicely in processing . In that other thread I linked to the XS was horrible on the corners on FF - enough so that it will be consigned to the K01.

[someasiancameraguy]

The simple fact is that if the DA 40 Ltd has similar levels of vignetting performance compared to the M 40, then there's no reason to get the M version. But if the vignetting performance is say 1-2 stops slower on the corners, maybe the M series will be better for film bodies where pixel peeping is less of a concern.

[aslyfox]

since the M 40 has been out of production

Description:
Also known as the "pancake," this is the smallest SLR lens that Pentax ever produced. It includes all the features of any other M lens.

In 2006, it was superseded by an even smaller DA version, but that version did not feature an aperture ring.

Read more at: SMC Pentax-M 40mm F2.8 Reviews - M Prime Lenses - Pentax Lens Reviews & Lens Database

at the least it is reasonable to believe that changes in SMC coatings ( not to mention HD for the Limited ) would have been improved since then but there is more noted:


- that the Limited has improved optics over the M

Description:
The SMC Pentax DA 40mm Limited is the successor to the original M 40mm "pancake" lens. It is slightly smaller and 20g lighter because it lacks an aperture ring, and features improved optics.. . .

Read more at: SMC Pentax-DA 40mm F2.8 Limited Reviews - DA Prime Lenses - Pentax Lens Reviews & Lens Database

and the XS

Description:
The SMC Pentax DA 40mm XS is based on the optical design of the SMC Pentax DA 40mm Limited . . ,

Read more at: SMC Pentax-DA 40mm F2.8 XS Reviews - DA XS Prime Lenses - Pentax Lens Reviews & Lens Database


the SMCversion of the Limited is out of production, but either the HD Limited and the XS is available new

[aslyfox]

There is also the Chinon 45mm f2.8 pancake.. . . .

. . . an XR Rikenon 45mm f/2.8 pancake that is well regarded.. . . .

any one know about this?

New Canon 40mm Pancake - A Threat to Pentax?
Full-Frame EF 40mm STM lens for under $200
By PF Staff in Articles and Tips on Jun 8, 2012

Read more at: New Canon 40mm Pancake - A Threat to Pentax? - Articles and Tips | PentaxForums.com

[GUB]

but there is more noted:


- that the Limited has improved optics over the M

Maybe for apsc but on full frame I found the falloff in the corners to be extreme.

[GUB]

I found one post saying that the Rikenon and the Chinon were the same without substantiation.

[Paul the Sunman]

The simple fact is that if the DA 40 Ltd has similar levels of vignetting performance compared to the M 40, then there's no reason to get the M version. But if the vignetting performance is say 1-2 stops slower on the corners, maybe the M series will be better for film bodies where pixel peeping is less of a concern.

I have over 800 photos taken with the SMC DA40 Limited on the K1. Looking back through them, I see there is strong vignetting wide open (f/2.8), though not unpleasingly for the images I took.

f/2.8 (strong vignetting)


Vignetting is much-reduced at f/3.2:

f/3.2 (little vignetting, but mushy corner)


and again at f/4, though the corners are very "muddy":

f/4 (extreme corner still mushy)


The extreme corners are improved at f/5.6. Though still not perfect at f/8, they are more than useable:

f/8 (good all round)


So, the usability of the DA40 Limited on the K1 depends on your usage. Stopped down to f/3.2 greatly reduces the vignetting, but still leaves messy extreme corners; the edges are fine. This is absolutely useable for portraits or other shots with a strong central focus. By f/8, although not perfect when pixel peeping, I would say "shoot away with impunity".