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02-07-2012, 04:51 PM   #76
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You know, some telescopes are in fact refractive; and I doubt a 560mm reflex would be f/5.6. All I know of are f/8 or something like that.
It is reasonable to believe they used their experience with their refractors in order to improve long distance performance, affordability (i.e. good results without the use of exotic lenses) or whatever.
And it is irrelevant if reflectors are better for astronomy; this is a photographic lens.
Just my 2 cents.

02-07-2012, 04:51 PM   #77
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Lets hope not. 5.6 seems fast for a mirror.
02-07-2012, 05:23 PM   #78
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QuoteOriginally posted by m8o Quote
"Sharp, well-defined images — particularly with distant subjects — thanks to the adoption of optics used in astronomical telescopes"

... sure sounds like a Mirror lens to me. [!] Are there any excellent optics used in astronomical telescopes that are not mirror base in the last century?
Amateur astronomers rank photo tele lenses highest, refractive scopes second and reflective scopes (mirrors) last. So, Pentax making refrence to astronomical telescopes is not a good sign. Astronomical telescopes have too few lens elements to really compete with photo tele lenses.

Sure, the difference is minimized by small nominal apertures (around f/8 refractive, f/11 reflective) where scopes are almost diffraction limited only. But photo tele lenses can be sharper at wider nominal apertures, at f/5.6 and below; requiring more lens elements, 10 or more.

I would be very disappointed to learn the DA 560 f/5.6 is crippled, with only 4-8 lens elements and no or only one ED element. Such a lens can be replaced by a DA* 300 with a sensor with small enough pixel pitch.
02-07-2012, 06:08 PM - 1 Like   #79
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Pentax telescopes using ED telephoto lenses


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QuoteQuote:
The optics of this scope are based on the classic Petzval design, with a doublet objective in front and a 2-element corrector before the focuser. The front lens of the doublet objective is made of SD (super-low dispersion) glass, and the front lens of the corrector is made of ED (extra-low dispersion) glass. The aperture is 105mm and the focal length is a short 670mm (F/6.38).
With the heavy-duty focuser and 4-element optical layout this scope was designed especially for imaging. According to the specifications provided by Pentax this telescope is capable of providing an 86 mm image circle with the ability to support heavy equipment like large format film cameras or big CCD cameras. One thing to consider, because of the corrector lenses and the big focuser, is that balancing this scope can be tricky as it is very BACK HEAVY.
Pentax 105SDP Refractor - Review

Pentax uses APO SD & ED glass in their telescopes.








Last edited by jogiba; 02-07-2012 at 06:24 PM.
02-07-2012, 06:20 PM - 1 Like   #80
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I'm hoping they're just using 'astronomical' as a marketing word to get people excited, rather than as a real, technical term. I.e. someone in the Marketing group heard that Pentax had some telescopes and asked if telescopes use lenses, and when they heard yes, bam, a marketing ploy was born.
02-07-2012, 06:30 PM   #81
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Pentax SD250 3,000mm F12

02-07-2012, 07:50 PM   #82
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well this is why we love Pentax . me personally cant wait for that wide zoom that they are planing for us !
02-07-2012, 07:51 PM   #83
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Good to learn. ...3,000 F/12? I'll hand-hold it! [j/k]

Ok, back to this 550mm. Just seen a pic of it. It''s beautiful and obviously not a mirror lens!

Next thing to worry about ... hope it has a focus limiter. I can't tell you how many BIFs I miss because my Sigma 300/2.8 doesn't have one; 'specially when a TC is mounted. There's a switch on the bottom, but that could just be a MF/AF switch.

02-07-2012, 08:08 PM   #84
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QuoteOriginally posted by m8o Quote
Good to learn. ...3,000 F/12? I'll hand-hold it! [j/k]

Ok, back to this 550mm. Just seen a pic of it. It''s beautiful and obviously not a mirror lens!

Next thing to worry about ... hope it has a focus limiter. I can't tell you how many BIFs I miss because my Sigma 300/2.8 doesn't have one; 'specially when a TC is mounted. There's a switch on the bottom, but that could just be a MF/AF switch.
If there's just one switch, I'm guessing MF/AF. Can you share where you saw the picture?

Thanks for sharing either way, helps to firm up my LBA.
02-07-2012, 08:12 PM   #85
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QuoteOriginally posted by ElJamoquio Quote
If there's just one switch, I'm guessing MF/AF. Can you share where you saw the picture?

Thanks for sharing either way, helps to firm up my LBA.
I want to see a picture please too!! and again its amazing how every time I get angry with Pentax they come up with a lens road map that make me crave and inspired again. fantastic lens choices
02-07-2012, 08:12 PM   #86
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Just saw it on the other thread. Looks like there's two switches, if you look closely? I'm gusesing that rear 'black knurling' is for a polarizer?

02-07-2012, 08:36 PM   #87
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That is a smashing looking piece.
02-07-2012, 08:39 PM   #88
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Thats a Nice piece of lens, certainly looks exciting!! Maybe it has AF/MF and a focus limiter. Yes, colar would be for rotation of a polariser.
02-07-2012, 09:52 PM   #89
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White color Pentax lenses...Good.
02-07-2012, 09:53 PM   #90
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I was just speculating that Pentax modified the old M67 400mm f4 lens and added optics equivalent to a 1.4 TC to make it a 560mm f5.6. A comparison of the lines of the M67 400mm f4 lens with the photo of the DA 560mm f5.6 shows similar lines the the 560 showing a longer rear end towards the mount. Perhaps this is to accommodate the autofocus mechanism and the 1.4TC optics?
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