[GUB]

OK I did this very quickly using lenscaps from an 18mm and a 24mm 110 lens as black discs. They are about 32mm and 26mm in diameter. The front element of a 110 70mm is about 46mm in diameter.
So;
Front element - 46mm – 1660 sqmm of glass
32mm diameter black disc – 800 sqmm (so half the light - 1stop)
26mm diameter black disc – 530 sqmm (2/3 the light – sort of ½ stop)

Original Q on AV no disc 1/320 sec

With 26mm – 1/15 sec - about 4.5 stops reduction.

With 32mm disc – no image

The disc sitting on the lens surface is not fully optically invisible.
The smaller disc can be seen as a small blob fully obscuring the centre of the image.

[photoptimist]

OK I did this very quickly using lenscaps from an 18mm and a 24mm 110 lens as black discs. They are about 32mm and 26mm in diameter. The front element of a 110 70mm is about 46mm in diameter.
So;
Front element - 46mm – 1660 sqmm of glass
32mm diameter black disc – 800 sqmm (so half the light - 1stop)
26mm diameter black disc – 530 sqmm (2/3 the light – sort of ½ stop)

Original Q on AV no disc 1/320 sec

With 26mm – 1/15 sec - about 4.5 stops reduction.

With 32mm disc – no image

The disc sitting on the lens surface is not fully optically invisible.
The smaller disc can be seen as a small blob fully obscuring the centre of the image.

Nice!

I'd bet that if you put the lens with the 32 mm disk on a 110 format camera, the image would have a very large blob fully obscuring the image circle of the Q (6.17 x 4.55 mm frame) but there would be some image in the edges and corners of the larger 110 format frame (13 mm × 17 mm).

[GUB]

Nice!

I'd bet that if you put the lens with the 32 mm disk on a 110 format camera, the image would have a very large blob fully obscuring the image circle of the Q (6.17 x 4.55 mm frame) but there would be some image in the edges and corners of the larger 110 format frame (13 mm × 17 mm).

Yes indeed I did that and you have it about right. And that is why I specified I was using the Original Q although I suspect it would still cover the later sensor. Of course the disc should in theory be invisible with just the image stopped down but it clearly doesn't work that way here just as it doesn't with a 28mm. Is there a simple explanation for that. Without checking further the disc is invisible on my 50mms and Takbayonet 135 as you would expect. I always thought with the 28s it was a function of retrofocus design.

[GUB]

OK here is what I think happens. The fact that something up against the front element vignettes rather than dims an image is due to the two factors:

The relative tiny size of the exit element (8mm) compared to the front element. (46mm)

And the relatively long physical length of the lens – about 50mm compared to about 35mm for a 50 1.7

This relatively confining exit combined with the length makes for a fairly strong parallax effect which is just about non existent for say a 50 1.7. So one side of the sensor is looking at the other side of the front element rather than all it. This (like a pinhole camera) means there is some degree of focus on the surface of the front element.

[desertscape]

The two main problems are chromatic and spherical aberrations.
The former was (for the most part) solved long time ago with the introduction of the so called achromatic lenses.
Spherical aberration is compensated, more or less, by the optical "tricks".

FYI- Spherical is corrected by 3 means; 1. Using an element with the opposite sign as the element that is causing the spherical. If a positive element (plano convex as an example) is causing the marginal rays to focus in front of the focal plane, adding a negative element will mostly compensate for it. 2. Bending the elements toward the diaphragm reduces both spherical and coma. 3. Using aspherical surfaces reduces spherical but in most cases does not completely eliminate it.

[ScooterMaxi Jim]

We have our own thread here, Alex, which has an extensive list of lenses and real reports.

As usual, this place provides accurate information versus 'what's out there'. I wouldn't trust B&H and Tony Northrup or whoever to get anything right.

As a generalization, any normal or tele DA prime works, but no DA zoom.

Even in the case of the zooms, they often work fine at the long end (my DA12-24 f4 is great from 17mm on, which becomes attractive to anyone who finds the DFA15-30 too expensive or big) or in the case of the DA*60-250, removing an inner baffle makes a real difference to vignetting.

Going full frame can be less expensive than APS-C owners think, especially with Pentax.

While it comes down to a matter of how much degradation a user is willing to accept, the official stance from Pentax and echoed on the guides at this site (including the zoom and prime listings posted last month) indicate that only the DA*200, 300 and 560 qualify as full frame in the DA range. You have APSc+ designations for a few others, such as the various 40s and the 50. As for the 50, it really quite clearly suffers in the corners. Even on APSc, the light fall-off performance is somewhat marginal at -.8 ev. It is a lens that does not get at all sharp in the corners until at least f/4 - on APSc. I'm fine with the limitations of this APSc lens, given the price point.

To say it is a good-performing full-frame lens on a semi-pro body such as the K-1, though, appears to be a questionable claim at best - no matter how often repeated. Most of the K-1 users here describe it as no more than "usable."

---------- Post added 12-20-2017 at 04:25 PM ----------

I had the Tokina 12-24 on Canon crop and full frame bodies. Yeah, the Pentax is a better lens due mainly to the superior coatings, but optical design is identical. While its true that the hard vignette disappears at 17 or 18mm on FF, the quality relating to sharpness, contrast and CA is especially low outside of the APSc image circle. A cheap 17mm full frame prime lens was a vast improvement. I'm not a fan of going to FF for the sake of it, especially when the optics fitted "work" but considerably fall short of what can be achieved in a proper APSc system.

[clackers]

While it comes down to a matter of how much degradation a user is willing to accept, the official stance from Pentax and echoed on the guides at this site (including the zoom and prime listings posted last month) indicate that only the DA*200, 300 and 560 qualify as full frame in the DA range.

As usual, James, you assert things instead of use the real data at places like Photozone, or the hundreds of photos your fellow members have actually taken on FF.

According to Photozone, the DA50 and FA50 actually vignette the same as the film era FA50 f1.4 and the newer DFA 50mm f2.8 Macro, and are superior to the FA31 Limited.

And according to DxO, better than the mighty Zeiss 55mm Otus f1.4 on a Nikon D500. Are you going to argue the $4000 Zeiss isn't really a full frame lens?

You can check out Rice High's findings here:

RiceHigh's Pentax Blog: Compatibility of DA Lenses on Full Frame

Our ratings, findings and real life shots going back nine years here:

DA lenses on Full Frame: Test Shots thread - PentaxForums.com

I spent a day with the K-1 shooting nothing but the plastic fantastics in FF mode to get shots that according to you, are apparently impossible ...

Autumn in the Dandenongs - PentaxForums.com

If you want to encourage consumerism and convince Pentaxians their much loved current lenses are no good, and they've got to spend more money, I can't condone that, I'm afraid.

---

Last edited by clackers; 12-20-2017 at 06:18 PM.

[ScooterMaxi Jim]

As usual, James, you assert things instead of use the real data at places like Photozone, or the hundreds of photos your fellow members have actually taken on FF.

According to Photozone, the DA50 and FA50 actually vignette the same as the film era FA50 f1.4 and the newer DFA 50mm f2.8 Macro, and are superior to the FA31 Limited.

And according to DxO, better than the mighty Zeiss 55mm Otus f1.4 on a Nikon D500. Are you going to argue the $4000 Zeiss isn't really a full frame lens?

You can check out Rice High's findings here:

RiceHigh's Pentax Blog: Compatibility of DA Lenses on Full Frame

Our ratings, findings and real life shots going back nine years here:

DA lenses on Full Frame: Test Shots thread - PentaxForums.com

I spent a day with the K-1 shooting nothing but the plastic fantastics in FF mode to get shots that according to you, are apparently impossible ...

Autumn in the Dandenongs - PentaxForums.com

If you want to encourage consumerism and convince Pentaxians their much loved current lenses are no good, and they've got to spend more money, I can't condone that, I'm afraid.

I'm not encouraging consumerism, but rather judicious use of hard-earned dollars based on appropriate mating of body to lens. You are the one encouraging purchase of the K-1 using lenses not strongly recommended by Pentax or the guides on this site (this would be fact based information). You easily could be accused of consumerism accompanied by poor judgment.

I've cited the -.8ev light loss on APSc - which is acceptable, but not good. You should cite the information for FF - which isn't going to be good at all. You should cite some fact somewhere, if that is the basis of your meme. Not that light fall off tells the whole story, especially regarding the CA-prone 12-24 design.

Finally, "as usual" is the personal argument taken most often when one has failed to be persuasive. I'll take it as a complement, though, as I do take pride in my consistency.

Sorry, but the photos you posted in your day with the K-1 simply are not convincing - at least to my eye. Whether processed for optimal effect or not, the quality simply falls short of what I would want to present in public. We all have different ideas of what is optically pleasing, so I'm sure you would find many of my images unacceptable optically, as well. We just see things very differently on this.

---------- Post added 12-20-2017 at 09:10 PM ----------

And according to DxO, better than the mighty Zeiss 55mm Otus f1.4 on a Nikon D500. Are you going to argue the $4000 Zeiss isn't really a full frame lens?

Don't follow you at all on this point. You realize you are making a claim about a pro FF lens mounted on a crop sensor body, right? We probably do agree that FF lenses do a good job of covering a crop sensor, especially that particular lens. Not all Nikon bodies with three numbers in the model name are FF, but they are pro class...

[clackers]

I've cited the -.8ev light loss on APSc - which is acceptable, but not good. .

(Laughs)

Did you think I was comparing those FF lenses on FF sensors?

It speaks a great deal about how evidence presented won't shift an attitude, when you don't even own a K-1.

So, let me explain.

Photozone measured the DA50 as having a 0.7 eV loss on APS-C ... Pentax SMC DA 50mm f/1.8 - Review / Test - Analysis

The DFA 50mm f2.8 Macro has a 0.7eV loss on APS-C. Pentax D FA 50mm f/2.8 macro - Review / Test Report - Analysis

The FA50 f1.4 has a 0.7eV loss on APS-C. Pentax SMC-FA 50mm f/1.4 - Review / Lab Test Report - Analysis & Verdict

I said the mighty Zeiss was tested on the D500 - not the D5. It's APS-C .. and guess what?

-0.8eV. Carl Zeiss Milvus 1.4/50 ZF.2 Nikon mounted on Nikon D500 : Tests and Reviews

You should cite the information for FF.

If you're hoping for a miracle, Jim forget it. None of these lenses will get better on FF - the Zeiss sinks to -1.6eV, according to DxO.

We all have different ideas of what is optically pleasing, so I'm sure you would find many of my images unacceptable optically, as well. We just see things very differently on this.

Are you actually objecting to the particular pictures of a fun day in a garden, James?

You don't seem to pay much attention to what others do, so here's where you can start your education, from your Pentax Forums colleagues ...

DA35 f2.4 - the Plastic Fantastic club - PentaxForums.com

Fantastic Fifty! The DA 50mm F/1.8 - PentaxForums.com

While you're criticizing these wonderful cheap lenses - glass to be proud of in the Pentax lineup - people are enjoying and using them. Even though I own the Sigma 35 Art and DA*55 (top two lenses in DxO's rating here ... guess what's at three and six? https://www.dxomark.com/best-lenses-for-the-24-mpix-pentax-k-3-recommended-primes-and-zooms/) , I reckon, more power to them!

BTW, the DA12-24 is regarded in that DxO list as *the* ultrawide zoom to have, and is in the Pentax Forum's official recommended gear guide. So, your opinion is ... just your opinion, I'm afraid.

[ScooterMaxi Jim]

Just trying to keep the focus on how particular lenses designed for crop perform on FF, but evidence presented by you strays elsewhere. Admittedly, the K-1 is different, a far-superior beast compared to a 5D.

I owned and heavily used that FF body for several years, and found the 12-24 design lacking for my needs. Consensus is pretty strong that as you go wider, the image quality adapting crop to FF deteriorates. Correspondingly on the long end, Pentax indicating that the 200, 300 and 560 primes are full-fledged FF capable of strong performance into the corners even wide open. Many other lenses perform quite well stopped down, including the DA 50, based on the images offered and various measurements - but only when stopped down. However, if you are forced to stop down to a greater extent, then you essentially lose the chief benefits of FF format. Comparing corner performance near wide open on my DA 50 with an old m50.f/1.4 on APSc - the old lens simply is far better with more natural transitions; the DA is very sharp in the middle, though. Then again, that old optic is better than the FF AF 50 f/1.4 from Canon, as well. These observations are based on what I find pleasing in the images, not relying on test measurements. Yeah, opinion.

Again, doubling down on me personally with comments such as "you can start your education" may provide some sort of gratification, but isn't persuasive evidence.

[UncleVanya]

Jim, I think the main point made was that apsc vignette numbers aren't very clear indications of performance on full frame. That was demonstrated in measured numbers.

Your observations of da 50 performance in general may in fact be relevant but the level of vignette doesn't seem worse than many lenses rated excellent on full frame.

[ScooterMaxi Jim]

The problem here is that the conversation relates specifically to crop lenses on full frame sensors. Citing DXO tests of Pentax crop lenses on crop sensors isn't proving anything in a scientific sense because there is no data on more than 50% of the sensor real estate. DXO has done no testing of lenses on the K-1 body, and no extrapolation is defensible.

If we must look at myth-busting data from tests such as Photozone and Lenstip, we discover that the corner performance in comparing the FA 35 with the DA 35 is vastly different - a far cry from claims often made that these two lenses are essentially similar and should perform very close to equally well. First of all, a half-stop difference makes them indisputably different optical designs. The slower DA should have a better hedge against vignette problems, but was ranked poorer than other crop comparables by Photozone regarding light fall off. The FA is ranked best in class in vignette measurements - again comparing with other FF lenses. Beyond that, we still don't know how they will compare on actual full frame sensors - but we have a real good hint...

[UncleVanya]

Even on APSc, the light fall-off performance is somewhat marginal at -.8 ev.

Jim - I wast trying to point out that the fall off performance data given was in response to this claim by you. The other data may or may not be relevant - I don't know personally but I do know that many other very well respected full frame lenses have worse fall off on even APSC than this. That said - that's not the only factor in lens selection.

[clackers]

Just trying to keep the focus on how particular lenses designed for crop perform on FF, but evidence presented by you strays elsewhere. Admittedly, the K-1 is different, a far-superior beast compared to a 5D. .

I have shot the DA35 and DA50 just fine on my Sony A7 as well, Scooter.

Any lens that vignettes badly on APS-C will vignette even worse on FF.

You can see that on the DxO results for the Zeiss first with the D500, then the D810.

I'd like to see your proof of anything different.

Again, doubling down on me personally with comments such as "you can start your education" may provide some sort of gratification, but isn't persuasive evidence...

Yet again, you're mistaken.

I'm not trying to win you over, Jim, I've already been thanked by PM for calling you out in this thread.

I had the Tokina 12-24 on Canon crop and full frame bodies. Yeah, the Pentax is a better lens due mainly to the superior coatings, but optical design is identical. While its true that the hard vignette disappears at 17 or 18mm on FF, the quality relating to sharpness, contrast and CA is especially low outside of the APSc image circle..

Again, a consistent theme for you, what is your proof?

Let us see your pictures backing your claim.

Here are mine on the K-1. Many people can't afford the DFA 15-30, the DA12-24 is one of their options, and they may already own one.

[ScooterMaxi Jim]

We probably have exhausted the subject...

But I would like to mention that folks with a K-1 can look to at least one real, FF UWA option that is generally available used or as a refurbished (how I got mine) - the Sigma 12-24. Even on crop, as indicated in the direct comparison here at PentaxForums, it is a better overall optic than the Pentax/Tokina. That is - if you get a good copy (I had to return the first sample which was considerably de-centered). The pricing now falls around $400 - a bargain. Having used both optical designs, I would agree with the assessment here.

Here's that direct comparison:
DA 12-24mm vs Sigma and Tamron 10-24mm Comparison Review - The Bottom Line | PentaxForums.com Reviews

It is worth pointing out that this review was based on a crop sensor. Obviously, as the only FF lens in the comparison, the Sigma would be that much better comparing them on the K-1, but few would think to bother for obvious reasons.