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06-08-2011, 06:52 AM   #16
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You can estimate the size of the front element since the math to calculate that is :
focal length / max aperture = diameter front element, e.g.
300/F4 = 75, the DA*300 uses 77mm
200/F2.8 = 71,4, DA*200 uses 77mm
300/F2.8 = 107, 120-300 is 105 mm

06-08-2011, 07:09 AM   #17
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QuoteOriginally posted by andre-mz5 Quote
You can estimate the size of the front element since the math to calculate that is :
focal length / max aperture = diameter front element, e.g.
300/F4 = 75, the DA*300 uses 77mm
200/F2.8 = 71,4, DA*200 uses 77mm
300/F2.8 = 107, 120-300 is 105 mm
Thanks, didn't looked at it that way, but knowing it couldn't be large as a truck.

When I do combine some things (is that possible in lensdesign?) and look at the suggestion of Falk for a telelens Falk Lumo then he is ending up with a 90mm frontglass for his DFA*500mm/f5.6 lens that still works with a 1,4x TC.

So when using that same frontglass (did I now saved some R&D budget?) I calculate that I have to choose between having a 135-270mm/f3.0 lens when f2.8 is not possible (or have it a pitch darker at the long end, wich is more common then one thinks) or to make the lens shorter.

The other possible solution is to use a bigger front glas like 95mm for both.
06-08-2011, 07:37 AM   #18
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This is also a very interesting thread
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/146205-max-ape...mitations.html
06-09-2011, 07:18 AM   #19
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Is it limited interest in such a new lens? Or is it that we don't think there will be completely new lensdesigns from Pentax? Or is it just way to expensive to reach production? Or is it so new, that we don't want to burn our fingers on it?

06-09-2011, 09:42 AM   #20
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It is an interesting thread on an interesting lens. If Pentax did come out with this lens and a matching TC I will buy it. I would be a little more interested in a DA*135-300/f3.2 (or 4.0). Not reaching 300mm is a problem for wildlife photo.

Pentax needs a way to get beyond 300mm with high-quality lens or TC.
06-17-2011, 02:09 AM   #21
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Just to bring to everyones attention the threads coming out off the lens development survey: https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/146454-wich-le...r-d-money.htmlSince I'm going to try and summarice this survey after the weekend.
06-17-2011, 09:33 AM   #22
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Is it a lot difficult to make the current DA* 60-250 a f2.8 lens?
I think 60-250 is a pretty good range for APS-C?
06-18-2011, 02:33 AM   #23
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QuoteOriginally posted by LFLee Quote
Is it a lot difficult to make the current DA* 60-250 a f2.8 lens?
I think 60-250 is a pretty good range for APS-C?
Well lensdesign is not my expert, but making a 4x zoom is more difficult then making a 2x zoom. When you want to make it stand out on all apertures and zoompositions you probably be better off with designing a 2x zoom.

06-18-2011, 03:46 AM   #24
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I think a 150-300mm 2.8 with build in teleconverter (like the new Canon 200-400) would be an fantastic lens.
06-18-2011, 07:17 AM   #25
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QuoteOriginally posted by feverbeaver Quote
I think a 150-300mm 2.8 with build in teleconverter (like the new Canon 200-400) would be an fantastic lens.
Well maybe if you where asking for f4 that would be possible, but that is one expensive lens to design and built with that future. I'm curious at what pricetag that new Canon lens will be in shops. The Nikkor version, so without the extender, is costing 5749 euro, wich is 4,6x as expensive then the DA*60-250mm/f4 wich is currently the most expensive lens for Pentax. So my guess is that you are asking for something that is never going to be seen in Pentaxland in the near future (say 10 years).
06-22-2011, 08:28 PM   #26
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I think 135-270mm is possible but it will probably cost between 2000-3000. But it will be much smaller than Sigma's 120-300mm F2.8
06-22-2011, 08:30 PM   #27
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RonHendriks1966

I have read all your threads, then....I really wish you could buy Pentax...
06-23-2011, 01:29 AM   #28
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QuoteOriginally posted by henryjing Quote
I have read all your threads, then....I really wish you could buy Pentax...
Well that is just out of my reach. On the other hand we as usergroup can contribute to future succes of the Pentax brand, by using it, but also by buying it's products.
06-24-2011, 12:06 AM   #29
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Interesting, but i woudnt buy it.
07-30-2011, 02:35 AM   #30
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The multipurpose lens.

I thought of possible use for this lens again. I still think that this lens can be Pentax's answer to a lot of user demand:
  • 135-270mm/f2.8 for indoor and evening sports.
  • 189-378mm/f4 with a DA*1,4x TC for outdoor sports on big fields and some wildlife.
  • 270-540mm/f5.6 with a DA*2xTC for serious wildlife.
  • 378-756mm/f7,9 with a stack of DA*1,4xTC and DA*2xTC for long reach wildlife or even astro-work.
  • Since the lens is for APS-C you have to account in for size difference to full frame format (1,528x multiplying).

To have all these option for real in use all parts have to be of excellent image quality. Stacking TC's is giving offcourse compromises on image quality.
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