[Simen1]

When people say D-FA (or DA lenses for that matter) are digitally optimized, what exactly does that mean in technical terms?

Where can i find good image comparisons between "identical" lenses with and without digital optimization? I want to see how much this optimization matters in real photos.

[max_pyne]

hm the only lens coming to mind would be FA* 300 F4.5 and DA* 300 F4? not sure about that one, but i think i read somewhere something about it... or was it the FA* 200 F2.8 vs. DA* 200 F2.8, someone will know. :-)

[Na Horuk]

Where can i find good image comparisons between "identical" lenses with and without digital optimization?

Well, they wouldn't be identical anymore, then.
What it should mean:
-lens has been optimized so the angle of incidence of light hits the sensor at an angle that the sensor can detect well (film doesn't care what angle)
-lens has mutlicoatings that prevent as much reflections from the back element as possible (digital sensor is shiny and can cause ghosting between sensor and back of lens - film doesn't do this)
-lens uses multicoatings that allow higher resolution (modern digital sensors are more demanding than many types of film use to be)
-lens uses coatings and element shape that reduce purple fringing (for some reason, PF is a bigger problem with digital sensors than with film)
-lens only projects image circle large enough for the sensor, and not any bigger. If the image circle is significantly bigger, that could lead to a loss in contrast overall. This point only stands because most digital cameras were APSC not that long ago, but now many cameras are FF (same size senor as 35mm film), so this point is no longer as relevant. And many Pentax DA lenses, even though they were built for APSC, actually project an image circle big enough for FF (search for thread "DA lenses on full frame")
-lens has shorter focus throw, for faster AF. Lenses used to have a longer focus throw, so that precise MF was possible. With modern designs, MF is not really taken into consideration (lenses often don't have distance scales, and even fewer have DoF scales)
-lens has auto-aperture, lens ID, etc. (not a big deal anymore, has been around for a while even in film days). This one often means the lens has no aperture ring at all, which means that many older SLR cameras cannot use it properly (They rely on you manually setting the aperture on the ring and the camera itself cannot do that, like more modern SLR and all DSLR cameras do)

But! There is no guarantee any lens actually has these characteristics. I don't think the term "optimized for digital" is legally defined, so they can slap that sticker on anything.
Pentax actually has a couple of lenses that have a long lineage, running some decades long (and we can only speculate what changes, adjustments, tweaks were made in the optics throughout this time). Examples are FA 35mm f2 and DA 35mm f2.4 or F 100mm macro, FA, DFA 100mm macro, or FA 50mm f1.7 and DA 50mm f1.8. The DA lenses have no aperture ring, no distance scales, a short focus throw, more modern lens coatings,.. Can you tell the difference? And is it any bigger than, let's say A 50mm f1.7 going to F 50mm f1.7? Basically, during every new lens lineup generation, the marketing department needs to SAY something about them. And since we are all using digital cameras, its a good idea to emphasize that the lenses were made with digital in mind. And they had to be, because who shoots film anymore? Very few people.
Are they all fully optimized for digital, in every single way? Probably not. Are the problems that some film era lenses exhibit on digital sensors any fewer on the optimized versions? Probably yes. Are all film era lenses inferior to their modern "digitally optimized" descendants? Probably not. Are all film era lenses bad, useless on digital sensors? Definitely not.

Basically, for this kind of stuff, it really depends on the specific lens design and construction. Pentax M 50mm 1.7 is probably not quite as sharp and doesn't have as nice bokeh as DA 50mm f1.8, but its made of all metal and has distance scales. Its not a bad lens, has very few optical weaknesses. Depends what your priorities and uses are. Some people prefer metal, others plastic. Some want a mellow film look to their photos, others want a modern saturated high contrast look. So ask for the specific lens that you are interested in. Do research for the lineage of the lens you want to buy.

[Simen1]

-lens has been optimized so the angle of incidence of light hits the sensor at an angle that the sensor can detect well (film doesn't care what angle)

I have to disagree. Film _is_ angle dependent, but not as much as digital (at least from decade old CCD based DSLRs). Modern CMOS sensors with 3-4-5 micron pixel pitch and micro lenses have low angle dependency. (chief ray angle)

-lens has mutlicoatings that prevent as much reflections from the back element as possible (digital sensor is shiny and can cause ghosting between sensor and back of lens - film doesn't do this)

I have to disagree again. Film is quite reflective too. Take a look if you forgot.

-lens uses multicoatings that allow higher resolution (modern digital sensors are more demanding than many types of film use to be)

I agree, that makes sense.

-lens uses coatings and element shape that reduce purple fringing (for some reason, PF is a bigger problem with digital sensors than with film)

That makes sense too. Maybe because of different sensitivities for purple? Or maybe because people more often pixel peeps on digital?

-lens only projects image circle large enough for the sensor, and not any bigger. If the image circle is significantly bigger, that could lead to a loss in contrast overall. This point only stands because most digital cameras were APSC not that long ago, but now many cameras are FF (same size senor as 35mm film), so this point is no longer as relevant. And many Pentax DA lenses, even though they were built for APSC, actually project an image circle big enough for FF (search for thread "DA lenses on full frame")

Makes sense too. The lower contrasts probably originates from stray light reflected of the area around the active sensor area.

-lens has shorter focus throw, for faster AF. Lenses used to have a longer focus throw, so that precise MF was possible. With modern designs, MF is not really taken into consideration (lenses often don't have distance scales, and even fewer have DoF scales)

I think that is an AF vs MF optimization, not digital vs film optimization. Ignoring the AF film period i will agree that the two optimizations correlate.

-lens has auto-aperture, lens ID, etc. (not a big deal anymore, has been around for a while even in film days). This one often means the lens has no aperture ring at all, which means that many older SLR cameras cannot use it properly (They rely on you manually setting the aperture on the ring and the camera itself cannot do that, like more modern SLR and all DSLR cameras do)

Yes. Lens ID, focal length and so on helps the camera focusing, adjust shake reduction and so on.

[markkuk]

Optimizing for digital also means taking into account the thickness of the filter stack in front of the sensor, film cameras don't have 2mm of glass in front of the light sensitive surface. See LensRentals.com - The Glass in the Path: Sensor Stacks and Adapted Lenses

[Digitalis]

hm the only lens coming to mind would be FA* 300 F4.5 and DA* 300 F4? not sure about that one, but i think i read somewhere something about it... or was it the FA* 200 F2.8 vs. DA* 200 F2.8,

aren't you forgetting the DA40mm f/2.8 Vs M40mm f/2.8, DA 50mm f/1.8 Vs M/K/A 50mm f/1.7

[Wolfeye]

I think the OP is referring to the F-DA class of lenses, not F or FA on D. Isn't the new 24-70 the only lens in that class?

I doubt there's any real degradation in shooting one of these new lenses with film.

[pete-tarmigan]

I think the OP is referring to the F-DA class of lenses, not F or FA on D. Isn't the new 24-70 the only lens in that class?

D FA 50mm f2.8 Macro
D FA 100mm f2.8 Macro
D FA 100mm f2.8 Macro WR
D FA* 70-200mm f2.8
D FA 150-450mm f4.5-5.6

Pentax D FA Prime Lenses - Reviews and Specifications - SLR and Interchangeable Lenses - Pentax Lens Reviews & Lens Database
Pentax D FA Zoom Lenses - Reviews and Specifications - SLR and Interchangeable Lenses - Pentax Lens Reviews & Lens Database

[Na Horuk]

I have to disagree.

Sensible points,
Film is shiny, but its not reflective in the same way, I guess. Or we just didn't make a big deal of that kind of ghosting/loss of contrast in the past. And yeah, I did some film photography, but I didn't develop film myself, and I didn't do any film equivalent of pixel peeping. If features were recognizable, that was good enough.

The lower contrasts probably originates from stray light reflected of the area around the active sensor area.

Yep. Many lenses now have a lens baffle at the back, which limits light as much as possible.

Anyway, seems like you already know what digital optimization is / can be.

[normhead]

What ever digital optimization is, apparently forum members don't approve at least for the 50. Hard to believe given how ugly those old FAs are.



According to forum users, Pentax ruined this lens making it digital.... either that or the people who rated the FA were a lot less discriminating.

The DFA 100 fares much better... (and still looks better.)

[vonBaloney]

I have to disagree again. Film is quite reflective too. Take a look if you forgot.

The backing is, but the light doesn't hit that side. The emulsion side is quite dull and non-reflective. Certainly there are many lenses with internal reflection problems that only occur on digital. If they'd been like that on film, they never would have been made...

[romay]

That makes sense too. Maybe because of different sensitivities for purple? Or maybe because people more often pixel peeps on digital?

No, it's because because digital sensors are more sensitive to UV and IR. Film era lenses were never corrected outside the visible spectrum. If you use them on digital the uncorrected UV/IR image becomes visible as fringe. If the fringe is mostly purple, it's the uncorrected UV image. If it's mostly red, there's also some IR in it. You can mitigate it by agressively using UV/IR cut filters on your lens. That's also the best way to tame the 43mm ltd.

[bdery]

From an optical designer's perspective, Na Horuk is spot on.

I have to disagree. Film _is_ angle dependent, but not as much as digital (at least from decade old CCD based DSLRs). Modern CMOS sensors with 3-4-5 micron pixel pitch and micro lenses have low angle dependency. (chief ray angle)

Micro lenses have helped a lot, and film is not free from angle dependence, but is is much less dependent than digital sensors. A telecentric design helps a lot with digital. And I mean a LOT.

I have to disagree again. Film is quite reflective too. Take a look if you forgot.

It doesn't have to be non-reflective to be "less reflective".

[vonBaloney]

No, it's because because digital sensors are more sensitive to UV and IR. Film era lenses were never corrected outside the visible spectrum. If you use them on digital the uncorrected UV/IR image becomes visible as fringe. If the fringe is mostly purple, it's the uncorrected UV image. If it's mostly red, there's also some IR in it. You can mitigate it by agressively using UV/IR cut filters on your lens. That's also the best way to tame the 43mm ltd.

I have heard some claim that, but the sensor already has a UV filter on it. In any case, I've yet to find a filter that has a positive effect on fringing. If it does decrease it, it is doing so by lowering sharpness along with it (which naturally blurs the lines where fringing occurs, i.e. a crappy filter will get rid of fringing, but will also lose resolution), OR often it makes it even worse or creates a fringe where there is none with no filter...

[romay]

Well, I was talking ab out UV/IR cut filters. I doubt you tried any of those yet as they are hard to obtain and expensive
Even an expensive off-the shelf UV filter does not block the UV spectrum that is responsible for fringing with older lenses, you need a special filter with a more narrow passband.
And yes, of course the sensor has an UV filter, but no filter is 100% effective. Ever tried UV photography? It's quite possible even with an unmodified camera / lens. A lot of people think you need special lenses and your sensor filter removed, but that's far from the truth. If you use long enough exposure times in combination with the right filters, you can get pretty nice pictures in the UV range (and then you'll notice that UV pictures are exactly the same color as PF).
You don't need a lot of UV to hit the sensor either. UV is inherently higher energy than the rest of the spectrum, which makes things worse. The UV photons hit the sensor so hard that often the charge spills over to the neighboring pixels, creating some sort of bleeding which also worsens the PF.