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03-26-2008, 02:40 AM   #1
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New DA* and limiteds - FF capable?

I was reading the Official Pentax spec releases for the 35mm macro limited and noted the description - "Developed specifically for PENTAX digital SLRs". I took this to mean smaller glass, until I noted the same description was given for the DA*200, which has been shown to be a FF lens.

Looking back, older DAs (the ones that speak to this at least) say it differently: "The image circle in DA-series lenses is designed to perfectly match the 23.5mm x 15.7mm size of the CCD used in PENTAX digital SLRs to optimize camera performance."

I'm very curious as to whether or not this means Pentax is slowly upping the FF compatible lens count, or if there is nothing to be read into this wording. Anyone know if the 35 (or others) are FF compatible for example?


Kelly

03-26-2008, 02:58 AM   #2
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The common wisdom is that some DA have FF image circle, like DA 40Ltd, DA 70Ltd, DA* 200.

Even my DA 50-200mm kit lens seems to be FF.

There may be a stronger vignetting than usual (my DA 40Ltd has it in my film camera's VF) but this should be easy to fix automatically in lightroom.


The common wisdom also says that MTF (resolution) drops off more quickly outside the APS-C image circle than with a FA lens. However, AFAIK nobody has yet done a FF resolution test with any of the DAs.

I would volunteer to do one if my film body (P3N, MX stolen ) would allow me to manually control aperture w/o the aperture ring, or at least to know which one it used (film has no EXIF ).


BTW, the DA are called DA because they lack the aperture ring.
03-26-2008, 08:21 AM   #3
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QuoteOriginally posted by falconeye Quote
The common wisdom is that some DA have FF image circle, like DA 40Ltd, DA 70Ltd, DA* 200.

Even my DA 50-200mm kit lens seems to be FF.

There may be a stronger vignetting than usual (my DA 40Ltd has it in my film camera's VF) but this should be easy to fix automatically in lightroom.


The common wisdom also says that MTF (resolution) drops off more quickly outside the APS-C image circle than with a FA lens. However, AFAIK nobody has yet done a FF resolution test with any of the DAs.

I would volunteer to do one if my film body (P3N, MX stolen ) would allow me to manually control aperture w/o the aperture ring, or at least to know which one it used (film has no EXIF ).


BTW, the DA are called DA because they lack the aperture ring.

I for one would find it quite interesting to note the performance with a film body. My ulterior motives are at work. I do openly wish Pentax will one day embrace a FF sensor. The 08 lens roadmap has lots of interesting offers ahead though and no immediate guarantee of FF lens performance, and has me wondering if I should give up the requirment. Part of me says "enjoy them now, get them regardless of FF compatibility" but the money part of my brain has kept me on course thus far, not wanting to suddenly suffer the need to sell half my collection one day at a big discount if and when the FF sensor arrives.

I can see why Pentax wouldn't want to confuse anyone by stating DA lenses could perform on the original film frame (as they have no aperture ring, as you've pointed out and no current FF body to justify the notation) but the recent change in wording noted above makes me wonder if there is an intent to the provision of FF ability on some of the lenses.

With the smaller size of the 12-24 and 10-17, I'm betting there are some of the older DAs that would _not_ perform on a 35mm frame at all, even badly. OTOH, in the 'normal' range, pancakes have been common for years and perhaps reusing existing designs wasn't an issue regardless of future FF sensor plans. But now, with the DA* telephotos a big savings could have been realised in size and material by having glass specific to APS-C. Thats where I start to get my hopes up that there is method to the madness, that Pentax themselves are leaving the door open for a future full sensor (as much as they currently may shrug it off).

Anyways, if anyone would find it interesting to note said performance, I'd be happy to hear of it, even just for curiosities sake.

Sorry to here your MX was stolen, btw. My psychic premonition just told me the person who did its dog was flattened by a bus and they are wondering of Karma had anything to do with it
03-26-2008, 10:03 AM   #4
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QuoteOriginally posted by thePiRaTE!! Quote
I for one would find it quite interesting to note the performance with a film body. My ulterior motives are at work. I do openly wish Pentax will one day embrace a FF sensor. The 08 lens roadmap has lots of interesting offers ahead though and no immediate guarantee of FF lens performance, and has me wondering if I should give up the requirment. Part of me says "enjoy them now, get them regardless of FF compatibility" but the money part of my brain has kept me on course thus far, not wanting to suddenly suffer the need to sell half my collection one day at a big discount if and when the FF sensor arrives.

I can see why Pentax wouldn't want to confuse anyone by stating DA lenses could perform on the original film frame (as they have no aperture ring, as you've pointed out and no current FF body to justify the notation) but the recent change in wording noted above makes me wonder if there is an intent to the provision of FF ability on some of the lenses.

With the smaller size of the 12-24 and 10-17, I'm betting there are some of the older DAs that would _not_ perform on a 35mm frame at all, even badly. OTOH, in the 'normal' range, pancakes have been common for years and perhaps reusing existing designs wasn't an issue regardless of future FF sensor plans. But now, with the DA* telephotos a big savings could have been realised in size and material by having glass specific to APS-C. Thats where I start to get my hopes up that there is method to the madness, that Pentax themselves are leaving the door open for a future full sensor (as much as they currently may shrug it off).

Anyways, if anyone would find it interesting to note said performance, I'd be happy to hear of it, even just for curiosities sake.

Sorry to here your MX was stolen, btw. My psychic premonition just told me the person who did its dog was flattened by a bus and they are wondering of Karma had anything to do with it
Consider this from Pentax's perspective. Some of the DA lenses will work on film bodies. But there will be a cost. There very likely will be issues with corner sharpness, distortion at the edges, etc.

In this day of pixel peeping and 400% magnification, can you imagine the howls of outrage that will happen if Pentax ever said a DA lens was useable on full frame and pixel peepers saw there was corner softness?

We have all seen enough beating of breasts and self immolation on different fora over the "failings" of all the various camera brands. So it's far easier for Pentax to assert that the DA lenses are for digital only. And if you choose to use a DA lens on a film body, that was your decision & it is your problem if you don't like the results. At least this is what I would do if I were in the marketing department.

If Pentax ever came out with full frame body, they will also likely include an option that lets you use the 1.5x crop factor of the existing DA lenses. This will let you continue to use the sweet spot of the lens.

If you see anyone in your neighbourhood street corner trying to sell you a super-clean AE1 + kit for a cheap price, it's mine. It was stolen when my house was broken into last year.

03-26-2008, 10:09 AM   #5
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QuoteOriginally posted by falconeye Quote
BTW, the DA are called DA because they lack the aperture ring.
DA is digital optimized, and they have no aperture ring. FF lenses with no aperture ring are FA-J.
03-26-2008, 10:14 AM   #6
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QuoteOriginally posted by tranq78 Quote

If Pentax ever came out with full frame body, they will also likely include an option that lets you use the 1.5x crop factor of the existing DA lenses. This will let you continue to use the sweet spot of the lens.
Does Canon or Nikon do this with their bodies? It is an interesting thought...have a menu setting that essentially turns the FF sensor into and APS sized one by shutting down pixels. Or better yet, have it sense the lens on the body and shrink the effective sensor size accordingly. You'd lose resolution but if you're at 20+mp FF, likely wouldn't make that big of a difference.
03-26-2008, 10:36 AM   #7
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QuoteOriginally posted by thePiRaTE!! Quote
But now, with the DA* telephotos a big savings could have been realised in size and material by having glass specific to APS-C.

Sorry to here your MX was stolen, btw. My psychic premonition just told me the person who did its dog was flattened by a bus and they are wondering of Karma had anything to do with it
I believe that image circles (43mm for FF) don't matter anymore as soon as focal lengths exceed them by a large enough factor.


My MX got stolen in '86. I'm over it now No, I'm not. I made a Manhattan police officer hunt the thief with me but he gave up too easily. Actually, can you imagine that the thief managed to crowl all the first floor of an otherwise empty cafe hiding underneath the tables and grabbed my MX sitting on a chair at the wall opposite to the stairs? He really wanted my MX!

Last edited by falconeye; 03-26-2008 at 11:07 AM. Reason: added a verb ;)
03-26-2008, 10:53 AM   #8
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QuoteOriginally posted by tranq78 Quote
...In this day of pixel peeping and 400% magnification, can you imagine the howls of outrage that will happen if Pentax ever said a DA lens was useable on full frame and pixel peepers saw there was corner softness?...

...If you see anyone in your neighbourhood street corner trying to sell you a super-clean AE1 + kit for a cheap price, it's mine. It was stolen when my house was broken into last year.

I certainly can imagine it! I did empathize with Pentax vagueness in current literature. I wouldn't expect them to let us know until they had a product that could take advantage. But yet, my curiousity on those mysterious edges is piqued!

I theorize that Pentax are building FF compatible lenses with good edge performance in the newest line-up, quietly building-up lenses useable when and if they decide a FF sensor is feasible.

I'll keep my eyes peeled for your kit!


QuoteOriginally posted by falconeye Quote
I believe that image circles (43mm for FF) don't anymore as soon as focal lengths exceed them by a large enough factor.

I'm not sure I fully understand. Do you mean that the DA*teles are as small as they need to be already? This would shoot a hole in my theory... kinda Couldn't they realize a size savings as they have with smaller, faster wides for APS-C?

03-26-2008, 10:57 AM   #9
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QuoteOriginally posted by nostatic Quote
Does Canon or Nikon do this with their bodies? It is an interesting thought...have a menu setting that essentially turns the FF sensor into and APS sized one by shutting down pixels. Or better yet, have it sense the lens on the body and shrink the effective sensor size accordingly. You'd lose resolution but if you're at 20+mp FF, likely wouldn't make that big of a difference.
The new Nikon D3 does have this feature: allowing switching between FF and APS-C. However, I wouldn't want to have a 20MP+ FF camera, the effectiveness of such camera is questionable. The reason the D3 is so well-received is because of its low MP. That would effectively translate to much bigger photosites: higher dynamic range and extremely well-controlled high iso noise.

As for the possible softness of the current DA on FF camera, my thought is exactly the same. Nevertheless, Pentax would most likely to go with Nikon approach to main the backward compatibility. Though if the future DA* 300 is confirmed to be an FF lens as well, I guess Pentax is paving way to its future K1D. I always look forward to the day Pentax release its 1st FF, that's why I always hesitate to get too deep in with any DA lens (shift of FOV and strong vignettin/softness).
03-26-2008, 11:05 AM   #10
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QuoteOriginally posted by thePiRaTE!! Quote
I'm not sure I fully understand.
You can't because no verb



QuoteOriginally posted by thePiRaTE!! Quote
Couldn't they realize a size savings as they have with smaller, faster wides for APS-C?
Look.

A 300mm f/4.0 needs an aperture d of, well guess, d=f/4 and with f=300mm you get d=75mm.
A 200mm f/2.8 needs an aperture d of, well guess, d=f/2.8 and with f=200mm you get d=71mm.
Which, btw. explains why both have 77mm filter diameter, and cost and weight about the same.


No image circle involved. It's overwhelmingly simple which is why we all got math teached in school

Now, when the image circle starts to be in the order of aperture d or focal length f (rather than being significantly smaller) you start to make a lens which is bigger and more expensive than the above minimum parameters would require. Which is why my argument does not apply to zoom, normal, or wide angle.


What I forgot to say also...

This implies another thing... APS-C or even FF sensors only record a fraction of the light captured by a fast and long tele in the first place. So, with fast long glass (which is expensive like hell anyway) you better use a digital MF.

Last edited by falconeye; 03-26-2008 at 11:15 AM.
03-26-2008, 05:19 PM   #11
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Ok, thanks for the explanation. So basically, no matter the sensor size (unless larger) a 300mm lens must have a minimum diameter to account for its aperture making the superflous image circle just left over math instead of denoting future FF compatiblity intent.

This helps, but it still leaves the door open to the possibility of the larger sensor... assuming edge performance is up to par. Of that I still can only hope to know.
03-26-2008, 07:46 PM   #12
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As some have commented, large image circles are harder to meet with short lenses.

Also, when you talk about "smaller glass" while again this might apply to short focal length lenses, a 200mm F2.8 needs to be 77 mm in diameter to get the front end of the lesns big enough to let the light in.

Remember f-stop = focal lenght / diameter and therefore 200 / 77 = 2.72 As a result, there will not be that much reduction in "glass" on a telephoto DA lens because physics says it has to be that big regardless of the image circle.
03-26-2008, 07:57 PM   #13
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QuoteOriginally posted by Lowell Goudge Quote
Remember f-stop = focal lenght / diameter and therefore 200 / 77 = 2.72 As a result, there will not be that much reduction in "glass" on a telephoto DA lens because physics says it has to be that big regardless of the image circle.
Lowell, I generally highly esteem your postings.
But in this particular case, why did you repeat more or less exactly what I had written in the previous post? (never mind, just curious)
03-27-2008, 03:21 AM   #14
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Instead of all this theorizing, wouldn't it be easier to just mount the DA lenses on a film body and see the result. I'll try out the following lenses on the weekend and post the results:

SA 18-55, SA 50-200, DA70

and I'll do the same with DA*50-135 when it arrives, and DA*16-50 when it comes back from CR Kennedy. All my other lenses are full frame.
03-27-2008, 03:37 AM   #15
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Ah! No need to test DA70 it seems:

Also, I should note that the 70 works fine with film cameras, without vignetting or loss of resolution.

Pentax | SMCP-DA 70mm f/2.4 Autofocus Lens | 21620 | B&H Photo
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