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02-29-2012, 01:10 AM   #376
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QuoteOriginally posted by Clavius Quote
I've read through the entire thread, and there's nothing that proves the heat/expansion-theory wrong.

And even if that theory was proven wrong, then it still doesn't neseccarily mean Pentax chose white for other reasons then preventing heat/expansion. Cameramakers aren't automatically aware of solid evidence presented in this forum.
I'll refer you to Nikon to explain your theory .. they must surely be interested to know they got it wrong all these years.

Of course there is nothing I have read or seen that says that there is NOT some expansion, no matter how minor, due to direct sunlight but if there is then it is likely that the expansion stays within acceptable tolerances with regard to optical distortion. If you can't see the distortion because it is so minor then it can be disregarded, as Nikon, Sigma etc. seem to have done.

I wonder why stargazing telescopes are white ? Moon-burn perhaps ? Sorry, not that funny

02-29-2012, 03:25 AM   #377
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And the reason solar collectors are black, and not white is?

Let me answer for you: it's all about the infra-red absorption/reflection characteristics, rather than the visible light ones. This is not to say that all blacks are the same in either light, or all whites, but rather their radiant heat performance depends on what their surfaces are made of. The US paint study referred to was rather limited in that it obviously only applied to automotive finishes, and I might say that the clear coat finish that most cars have (which is the thing that gives them the shine that older cars were never able to match, no matter how hard you polished) is the first reflecting surface that any sort of light encounters, so it isn't necessarily going to prove anything about the paint underneath, unless you strip it off before the test. Perhaps someone's done this, too - I couldn't say. I will say this, however, that if you want to see the effects of differential expansion and contraction, the next time you look at a Tarmac road, have a look at the effect of white opaque markings on the surface. This rather dramatically illustrates the effect that materials of a different colour and composition can have on structural integrity, when exposed to heat.

Aside from all that, given the size of this lens, the colour of the camera on the end of it is almost irrelevant. My black K-5 is pretty much dominated by the silver colour of my FA*80-200, or even the cream colour of my somewhat smaller F*300!

I suggest we wait and what its optical performance is like, before we start worrying about its thermal or decorative performance.
02-29-2012, 04:03 AM   #378
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That dark-painted surfaces get hotter than white-painted is so obvious that I don't know why it's discussed at all. I have a white house and we have a very dark-painted cabin, and I can tell you the color makes a huge difference to temperature, something I can see clearly when I paint either of them, or if they get wet (btw. we also have white wooden garden chars and tables, and I've often wished they were dark - then they would dry much quicker after a rain).
02-29-2012, 04:12 AM   #379
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QuoteOriginally posted by gazonk Quote
(btw. we also have white wooden garden chars and tables, and I've often wished they were dark - then they would dry much quicker after a rain).
Well, we have black garden chairs, and I can tell you the downside: When it's hot in the summer... And you're wearing short pants... And you sit down on them: AUCH!

02-29-2012, 04:40 AM   #380
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QuoteOriginally posted by Frogfish Quote
a US Govt study no less stated there was no difference between white and black painted cars in regards to heat absorbtion.
IIRC what was in the thread, we agreed that this was due to windows being the main factor for heat absorption in cars. And then matte vs. glossy would play a big rôle too. E.g., military matte vehicles get hot enough in the sunshine to cook eggs. It is done actually
02-29-2012, 04:41 AM   #381
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QuoteOriginally posted by Clavius Quote
Well, we have black garden chairs, and I can tell you the downside: When it's hot in the summer... And you're wearing short pants... And you sit down on them: AUCH!
Hehe I guess the best compromise is light brown ones (we have some of them, too). Maybe Sigma got it right with their ugly military-colored 200-500/2.8
02-29-2012, 05:58 AM   #382
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QuoteOriginally posted by RobA_Oz Quote
I suggest we wait and what its optical performance is like, before we start worrying about its thermal or decorative performance.

The voice of reason....I Totally agree.

Thank you.
02-29-2012, 06:59 AM   #383
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I thought seriously about this scope. I think it would of been a good spotting scope. Excellent dig-scoping.
If Pentax could make this with AF in the price of 3.5K-4.5K it would be in the hunt. But the dog they are showing is a joke.

Kowa 500mm f/5.6 FL Telephoto Lens/Scope TP556 B&H Photo Video

http://www.kowa-prominar.ne.jp/pro/lens/img/feature/telephoto_graph.jpg


Last edited by garyk; 02-29-2012 at 07:28 AM.
02-29-2012, 08:53 AM   #384
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QuoteOriginally posted by garyk Quote
If Pentax could make this with AF in the price of 3.5K-4.5K it would be in the hunt. But the dog they are showing is a joke.
Far too expensive for a 90mm. The similiarly specced 100mm Pentax PF-100ED is well below $2k. And the higher specced 110mm Sigma 500/4.5 with AF and twice #lens elements is almost in your price range too ($5k).

The 560mm F5.6 obviously is a 100mm. The most expensive glass is 150mm (600/4 etc.).
02-29-2012, 09:51 AM   #385
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QuoteOriginally posted by thibs Quote
Geez guys, stop moaning. An affordable long tele is good news for Pentax users.
If they go out right now with a 300/2.8, it wouldn't sell (but forums, I know).

They need to build momentum, and that's what Ricoh does. If I ever buy such a lens, it will be a DA, not a DA*. No way I could afford a DA* Tele.
A long focal length lens is as long as its focal length : 560 mm

A telephoto lens is shorter than the focal length. This is probably what Pentax means by "design used in astronomy"... the lens will be really long, longer than most other lenses in this range.
02-29-2012, 11:00 AM   #386
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QuoteOriginally posted by zapp Quote
A long focal length lens is as long as its focal length : 560 mm

A telephoto lens is shorter than the focal length. This is probably what Pentax means by "design used in astronomy"... the lens will be really long, longer than most other lenses in this range.
That's certainly the impression from the prototype, if truly coming from an astronomical basis, how about not a zoom but inbuilt Barlow.
02-29-2012, 02:11 PM   #387
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QuoteOriginally posted by Col Quote
That's certainly the impression from the prototype, if truly coming from an astronomical basis, how about not a zoom but inbuilt Barlow.
Barlow lens may also be adjustable. It works like variable focal length TC. Actually each photographic TC is a variation of Barlow lens design.
Long focal length optical design may produce very clean high resolution IQ. Let’s remember old long Tacumars with a fewer lens elements, but exceptional sharpness. 1.4X-2X built in adjustable Barlow lens/group may not compromise IQ too much, adding kind of limited zoom option.
There is a quote from Wikipedia:
Teleconverters are variations on Barlow lens that have been adapted for photographic use. It increases the effective focal length of a photographic lens it is attached to, making it a telephoto lens. A true telephoto lens uses a configuration similar to a Barlow lens to obtain a shorter tube length for a given focal length.
02-29-2012, 07:05 PM   #388
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QuoteOriginally posted by jpzk Quote
It seems like a concensus is building around the 560/5.6 to be a "consumer grade"
(budget) lens.

Maybe it won't be as IQ'd as a Sigma 500/4.5 but I am still hoping that it will be nearly or just as good as my DA*300/4.

A 500mm lens has been in my "wants" and "needs" for a while and perhaps this new Pentax 560mm will fit the bill, who knows?
One thing is certain: let's wait and see reviews once it has been tested out in the field.

JP


Actually, one should not make too much emphasis on the lack of star (*) designation. Although star lenses are usually among the best, the name do not neccessarily designate optical quality but the use of certain exotic glasses in the construction (after a formual no one has been able to decipher). Many optics don't need the type of glass that warrant the star designation in order to achieve superb optical performance due to their construction. They may still be among the best lenses the world has seen. Eg the Limiteds are not star lenses. The FA645 120/4 macro is a stellar lens - some says it is the sharpest telephoto ever made for MF - no star; other says the FA645 35/3.5 is the best wide angle for MF - not a star lens either. There are several non-star lenses for the 67 system too thats fantastic.
As you say; lets see how it performs before making judgements.
03-01-2012, 02:02 AM   #389
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QuoteOriginally posted by Frogfish Quote
It would also help if you read through the thread properly instead of jumping in the middle ... then you'd know what I was referring to. I did mention, but it seems you chose not to bother reading through the thread again, already that the links were in this thread (or the other main 560mm thread) on this very subject, whereby a US Govt study no less stated there was no difference between white and black painted cars in regards to heat absorbtion. Nikon seem to have understood this.
Sure I jumped in the middle, I've only been lurking through the both threads looking for nice little tidbits on the new 560. The plain fact is that black objects absorbs heat better than white objects. I suggest you look up the concept of albedo. As for that US Government study that you pointed out, please provide a link so we can take a look at it.

As for Nikon and Sigma's black lenses, have you ever considered that perhaps they use a different method of combating the heat? White makes a great way of reflecting heat. SIlver moreso. Space probes and satellites take advantage of this.

As it turns out, black is better for re-radiating that absorbed heat too (the concept is called emissivity). What does this prove? That the issue of white vs. black and heat is more complicated than most people think.

White lenses may not heat up as fast, but black lenses probably lose that heat faster (once there's some shade or a good breeze).

Frogfish, I am only asking for proof. You have provided none as far as lenses are concerned. Proof would be a technical paper from Nikon or Canon explaining this, or some scientifically minded person performing well thought out experiments with actual lenses (and not cars). Something along those lines, not an an analogy (black vs. white cars) that may not apply because it's cars vs. lenses. It also depends on the testing methodology used and the exact circumstances.

EDIT: You know what, enough of this prattling on the merits of black vs. white, let's get back to how much this dang lens will cost, and when it'll be available for purchase...

Last edited by HawaiianOnline; 03-01-2012 at 02:03 AM. Reason: Added clarification
03-01-2012, 03:03 PM   #390
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Long telephoto lenses can be focused past infinity in order to compensate for thermal expansion/contraction so temperature of the lens is an issue....

Last edited by Pål Jensen; 03-01-2012 at 03:41 PM.
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