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04-07-2013, 11:46 AM   #1
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Film-era lenses on FF cameras

Two of my film-era lenses donít seem to perform as well on cropped digital cameras as they do on film cameras: the Super-Takumar 24mm f3.5 and the SMC Pentax 85mm f1.8*.

Will these two film-era primes perform better on a FF digital camera than a cropped camera? Technically, I can understand that film era wide- angle lenses may not be optimized for flat digital sensors (compared to the way film picks up images). But does this mean the Takumar 24mm is not going to perform any better on a FF camera?

Perhaps more importantly, some people say that many old Pentax primes are not ďgood enoughĒ to cope fully with the resolving power of a digital FF digital camera. Is this true or is it an urban myth? (Iím not even sure I know what ďout-resolvingĒ means!)

Itís entirely likely that some film-era primes will handle FF digital better than others, including the 85mm f1.8 versus the 85mm f2, but Iíve got no evidence for this.

Any views, experiences, or links about using film-era Pentax lenses on FF digital, and the type of lenses that cope best, would be most welcome.

Many thanks

*The Takumar 24mm produced wonderful Spotmatic images Ė images Iíve never been able to repeat on my digital Pentaxes, even allowing for the different cropped focal length. The 85mm f1.8 is often rated as a far superior lens to the M85mm f2 on film cameras, but Iíve used both on digital and canít see a noticeable difference. (Unlike the big difference between the stellar K28mm f3.5 and the M28mm f2.8).

04-07-2013, 11:53 AM   #2
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Digital sensors are more sensitive to aberrations, plus we tend to pixel peep more these days, which in my opinion is what's the root cause of most complains about lenses. As you would expect, the FF image quality will probably be the same (or worse if there's vignetting and edge distortion) since the FF sensor would see everything that the APS-C sensor does, and then some.

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04-07-2013, 12:13 PM - 1 Like   #3
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Since there is no Pentax FF digital the only evidence that can be pointed to is that derived from Canon shooters using Takumars on their cameras. And the Taks seem quite popular there though I think mostly for video. And also because they have been quite cheap compared to modern Canon glass.

Part of the problem is comparing film, printed on 8x10 perhaps to digital which is often blown up on screen to ridiculous sizes. So a print from your 24mm from film may look just fine but when a digital shot is examined carefully on the screen the flaws start to be more evident. And I think that will get worse with FF digital.

QuoteOriginally posted by utak Quote
Iím not even sure I know what ďout-resolvingĒ means!
Generally what is meant is that the sensor is capable of recording detail that the lens is not capable of showing. So on film when using a cheap lens the quality of the shot is limited by the lens, but if you use a really good lens then the image is limited by the film. Same thing on digital, as the sensors have gotten better the limit has moved from the sensor to the lens. So that poor lenses are no longer capable of producing all the detail that the sensor is capable of recording. For a long time this has not mattered, but as sensors have gotten better and included more pixels the balance seems to have shifted. I think we are at a point now that the sensor is as good as our good lenses. A FF 36mp next generation sensor will likely be so good that only pro quality lenses will be able to keep up to it.

IMHO the best of the film era primes will continue to hold their own going forward, but aberrations and flaws will be more evident and not all of those primes will be able to keep up. In the Takumar era wide angle and extreme telephoto lenses were not as good as modern lenses so I would think that the 35mm to 150mm range top quality lenses will be fine, those outside that range will likely not be as good as a modern lens.

Another factor is the coatings used, these have improved considerably over the years and have been altered again to work better with digital.

And finally, I have seen postulated that digital lenses work better with sensors because the sensor treats light at different angles differently, but film does not. So the design of a digital lens has to take this into account. I've not seen that in my own experience but I've no reason to doubt it either.
04-07-2013, 12:55 PM   #4
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if you're looking at photozone numbers, and test lenses, you'll find that the CA numbers are just as important as the MTF numbers. Especially when the CA gets to be over 1 pixel. Chromatic Aberation and purple fringing affect digital in a way that seems much worse than they did in film. Having just purchased a Sigma 8-16 with flourite elements that minimize CA (and purple fringing) at this point I'm wondering if any current glass that does not employ this type of design will be relevant in a few years. If you look at the numbers on photozone you'll see at that the Sigma 8-16 has better control of chromatic aberration than the DA 15 f4 or 14 2.8. I guess as a guy with a pile of lenses, my concern is that at some point, everything we now use will be pretty much obsolete. That being said if you're pixel peeping an image, you're probably doing the same thing as you'd be doing if you blew a picture up to 49 inches wide and then examined it with a magnifying glass. On some of our older lenses the fringing makes images unusable, especially if used with the Pentax 1.7 converter, which blows the CA and fringing up a further 70%

Just from a general observational view point I think the MTF wars are just about over and CA control will be the thing of the future. As for sensor out resolving lenses, you will be able to tell that has happened when increases in sensor density no longer produce increases in MTF numbers. So far every addition in MP in the same size sensor has brought an increase in resolution, as defined by MTF. The pay-offs are falling into the famous law of diminshing returns, in that in the last round of APS-c going from 16-24 MP has only brought about a 10-12 % increase in MTF scores, despite the 50% bigger file size. Similarly you can achieve another 10% improvement by going to a 24 MP full frame sensor. So we are getting to the bottom end of the MTF curve, and are probably getting close to flat lining. But new sensors are still getting more resolution out of old lenses, so we haven't flat lined yet. There's still a benefit to more MP and larger sensor sizes using older lenses, even though it isn't what it once was. And new lenses are making it less and less worthwhile investing in old glass if you're talking about maximizing performance...

That being said, my favourite lens at the moment is an A-400mm lens that has to be 25 years old. At some point someone will make a better new one, but I'm guessing I won't want to pay for it. I suspect the decision that older lenses don't suit your needs will be made on a case by case basis, and I'm doubting that anyone is going to find fault with current lenses if the final file size is under 2500 pixels. At that point you've reduced imperfections by half and they'd have to be really glaring imperfections to make a difference.

If you're just talking about taking great pictures that will be printed at 200 DPI or less, As in a 22 inch wide print on a K-5 I'm not sure the difference would be even noticeable. We have had noticeable purple fringing on some of our 30 inch prints, and it isn't pretty. But that is with an image taken with the DA 10-17 which is marketed as a fun lens, not a serious piece of glass. You'd be hard pressed to find even really old glass with as poor CA characteristis as it has.

04-07-2013, 01:40 PM   #5
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QuoteOriginally posted by Adam Quote
Digital sensors are more sensitive to aberrations, plus we tend to pixel peep more these days, which in my opinion is what's the root cause of most complains about lenses.
In the end he goes into detail about this matter, saying the same things as you do.
Chromatic aberrations
04-08-2013, 02:26 AM   #6
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Original Poster
Many thanks for these replies; they are very helpful.

The photos I sell commercially are nearly always printed under 30 inches , so generally Iím not a pixel peeper unless Iím cropping, and Iíve got some good results from budget zooms (e.g. Tamron 70-300mm at f8 or so), not just top of the range new Pentax primes. So using my FF compatible lenses on FF (if that ever happens) should not be too much of an issue.

One lesson Iíve learned here is that if old lenses handle CA well on film then they are likely to handle it well on FF digital. Also, FF will expose the edges more and this will be particularly noticeable with older wide angles that donít have good corner to corner resolution, and lenses without good coatings.

Most of my work involves taking photos of brick buildings, against bright skies, with trees/branches and some dark shadowy areas. The perfect scenario for CA/purple fringing, and corner to corner issues. This is an issue that will be exacerbated by FF. Iíve invested in Pentax glass because I really like the colors/contrast, and Iím grateful for the lens reviews on this forum that help me avoid lenses prone to CA (and I do actually have the DA10-17mm - for fun!). So I seem to be on the right track.

The other reason for posting this thread, is that Iíd sat down to write a review of the K85mm f1.8, as itís quite a rare lens, with relatively few reviews. The problem is that Iím not sure how to rate this lens. Itís clearly a top rated lens from the film era, but it is not so universally admired/valued on digital (including me),especially compared to fast 50s/55s on cropped sensors. On reflection, I think that for this specific lens, itís the focal length on FF that would confirm its legendary status, not only its optical performance.

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