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09-25-2012, 04:58 PM   #1
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IBIS is the road block to Pentax FF...

While reading all of the interviews over Photokina, one item stuck out. One of the Pentax execs said that the DA lenses were not FF just larger to accommodate the movement the sensor's IBIS. This means that if Pentax does come out with a 24 Megapixel FF camera, it can not have IBIS as the sensor would go out of the image circle of even the best FA lens out there.
This is the conundrum for Pentax and why we are not seeing any hint of FF coming from their lips. They went the IBIS route with APC because it could be done with a slight increase in lens size while all the other FF and APC manufacturer's went with in lens stabilization. IBIS can not be done on FF so what is Pentax to do. Release a non-stabilized body to go with all the non-stabilized lenses. This has to be the crux of the problem and why of all the manufactures using Sony sensors, Pentax is the lone camera company with no FF.

09-25-2012, 05:17 PM   #2
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I'm pretty sure Sony has in-body stabilization in their FF models.
09-25-2012, 05:31 PM   #3
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Maybe the Sony mount is a little bigger, and the light can hit a bigger area?
No idea...
09-25-2012, 05:35 PM   #4
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QuoteOriginally posted by jeffshaddix Quote
I'm pretty sure Sony has in-body stabilization in their FF models.
But Sony has a full range of full frame alpha lenses. The DT lenses are crop sensor only.

09-25-2012, 05:36 PM   #5
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Considering I haven't heard of any problems with non-OS Sigma/Tamron lenses on Sony, I doubt the image circle is much larger than normal.
09-25-2012, 05:37 PM   #6
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QuoteOriginally posted by boriscleto Quote
But Sony has a full range of full frame alpha lenses.
And with a bigger image circle than FF...
09-25-2012, 05:45 PM   #7
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I haven't thought about it much but the sensor movement might just cause some vignetting. Users with shaky hands or the O-GPS1 astrotracer would see the problem most.
09-25-2012, 05:48 PM   #8
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It's plausible, but I'm not convinced this is the issue at all.

However, I do think it's possible that many of the "FF tested" DA lenses have a slightly smaller image circle than a typical FA lens. In other words, FA lenses would still work fine with SR.


Also, they may want people to buy the new FF lenses they're developing. But I really think the problem is time. It just takes ~1.5 years to develop a new camera. My guess is they were trying to fit a FF sensor in the K-5/K-7 body, but it somehow wouldn't fit. They were trying to cheat the timeline by not having to develop it all from scratch, and it didn't work out.

In other words, back in January, when they were getting all giddy and dropping these hints that they were developing a FF, they actually believed that they could shorten the normal time frame. Now they're having to accept that the development will take just as long as normal.



However, Sony makes it work somehow, so if the in-body SR is part of the problem, it will be interesting to hear about it later.

09-25-2012, 07:41 PM   #9
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That is why I am getting the K-30 to pair up with my K-5 now. The FP will help a lot with my macro stuff. The K-5 II and IIs are just stop gaps as you say. The K-30 has the best of the latest technology Pentax has to offer. I will wait for the K-3 or K-5 III to arrive with all the new bells and whistles before getting another top end model. It will be interesting to see just how they work out the future of the K line.
09-25-2012, 07:43 PM   #10
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Do Pentax FF lenses work on Sony FF cameras? Like how you can use an adapter to get it working on the NEX? Would that solve the question, since SR only requires a focal length to work?
09-25-2012, 08:38 PM   #11
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The point is, Pentax doesn't even have a modern FF lens lineup. The fact some DA lenses happen to cover 35mm format is accident, they definitely aren't FF lenses (considering corner sharpness, CA, vignetting, etc.). Any IBIS implications are secondary.

For them to come up with a FF camera, they need a real FF lens lineup first (since it wouldn't make sense to release a FF with a 24-200-ish rebadged Tamrom zoom). I don't see it happening in the foreseeable future. It took forever just to strengthen the DA line.
09-25-2012, 08:59 PM   #12
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QuoteOriginally posted by JinDesu Quote
Do Pentax FF lenses work on Sony FF cameras? Like how you can use an adapter to get it working on the NEX? Would that solve the question, since SR only requires a focal length to work?
Pentax's register distance is 45.46 mm and the Sony A-Mount is slightly shorter at 44.50 mm. So nobody makes an adapter since it would not focus at infinity.

The Sony E-mount is 46.1mm wide inside diameter which is wider than the Pentax at 45mm. The Alpha mount is much bigger than either the E-mount or the K-mount, but I don't know the exact number. I don't think it is as large as Canon at 56mm.

My guess is that the A-mount lenses projects a larger image circle, and the IBIS of the A900 is not as good as that of the K-5 or the Sony APS-C bodies which suggests Sony does not have as much room to move the sensor and keep it in the image circle. A900 only give you about 1-2 stops while APS-C systems give you 3-4 stops. Maybe the A99 is better.

I still think the reason invested in OIS (HD 90mm F/2.8 for 645D) is because they will use it on a Full Frame K-mount.

Maybe someone can come up with the technical specifications for the image circle size of the K-mount. A FF sensor requires a minimum of 43.3mm and to reduce vignetting you need more than that. Then the question is how much movement does IBIS require to provide 4 stops of stabilization?
09-25-2012, 09:26 PM   #13
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I'm too lazy to go look this up, but are all of the other full-frame sensors out there the same exact size, or do they vary like "APS-C" sensors which is really just a ballpark? If Pentax used a "90% size" FF sensor, could they get away with IBIS and still have compatibility with all those FF lenses out there? (DAs are another story.)
09-25-2012, 09:30 PM   #14
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QuoteOriginally posted by hcarvalhoalves Quote
The point is, Pentax doesn't even have a modern FF lens lineup.
I guess that depends on your definition of modern and of lineup. The FA Limiteds provide an excellent three prime lens lineup, no more or less than the quite successful Fuji X-Pro1 debuted with and has made do with for nine or so months. They're only now getting around to releasing a single zoom lens and have nothing longer than 60mm. In addition to the three FA Limiteds there are currently two DFA 100mm macro lenses, one DFA 50mm macro lens, and one FA 50mm lens. That rounds out as there being five different current DFA or FA prime lenses to choose from. On top of that there is a decent selection of current third party FF compatible lenses as well as lots of older Pentax lenses that would keep many early adopters well outfitted, be they zoom or prime shooters. Oh, and there's the FF compatible DA lenses you mentioned.

QuoteOriginally posted by hcarvalhoalves Quote
For them to come up with a FF camera, they need a real FF lens lineup first
I see this whole lack of FF lens options as being about the worst argument for there not being a Pentax FF camera. Besides, it's not as if they don't know how to make lenses. All that said, I expect that a when a FF camera is finally announced there will be at minimum a FF lens roadmap to go with it but likely at least a normal zoom to be released at the same time.
09-25-2012, 09:53 PM   #15
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QuoteOriginally posted by vonBaloney Quote
I'm too lazy to go look this up, but are all of the other full-frame sensors out there the same exact size, or do they vary like "APS-C" sensors which is really just a ballpark? If Pentax used a "90% size" FF sensor, could they get away with IBIS and still have compatibility with all those FF lenses out there? (DAs are another story.)
They are all 36x24mm.

APS-H (70%) was Canon's answer to exactly what you are suggesting, but without IBIS. Canon went to 70% APS-H for 2 reasons.

1. APS-H gave them the best performance (largest sensor) with their existing glass line-up.
2. APS-H was the largest sensor size that could be produced in a single mask at that time. FF required 3 separate masks. Now FF is produced in a single mask and that has reduced the cost significantly.

Canon has redesigned all of its film era glass to be digital friendly and handle high resolution FF sensors. The 31mm LTD already loses 1.09 stops to vignetting when used wide open on APS-C imagine how much it vignettes on a FF sensor wide open? I don't think there is much room to spare.

Vignetting

As a full format lens the 31mm f/1.8 enjoys a sweet spot advantage on Pentax APS-C DSLRs. Nonetheless vignetting can be quite obvious at wide-open aperture (1EV). The problem is gone by f/2.8.

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