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02-12-2012, 01:09 AM   #256
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Right now, nobody knows for sure, but now that I've talked to the folks who went to CP+, they're under the impression that it collapses as well.

02-12-2012, 04:45 AM   #257
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Traditional tele lens vs. astro telescope design

Ok, the plot thickens that we are seeing a 4" telescope design here. The length (very long for a tele lens but normal for a scope) being the fifth hint or so.

So, I'd like to contribute a bit more insight about what to expect of such designs.

Let me assume for the best which seems to be an optical 4 element Petzval design plus maybe an additional LFF (Large Field Flattener). A Pentax scope of similiar specification is the Pentax 100 SDUF or Pentax 105 SDP. In this PDF, you'll find a scientific measurement of the resolution of this Pentax scope (German!). The Petzval design dates back to physicist Jozef Maximilián Petzval and was first used in 1841.

The best direct comparative tests of such a scope design and an advanced 10+ element photo tele lens design I could find was conducted by Samir Kharusi from Oman who has an amazing pool of devices

In the first test, he compares 140mm optics (as opposed to 100mm) using what appears to me being the 21 MP Canon 1DsmkIII FF camera.

In the second test, he compares 60mm optics (as opposed to 100mm) using the 10 MP Canon 40D APSC camera.

Note that in the first test, he uses a Petzval design plus additional Large Field Flattener. Also, he clearly misses exact focus sometimes with the tele lens.

Direct sources are here:
-> televue_canon
-> TV-60is


From this and other sources I conclude that a good scope design has the same excellent optical performance in the center and at infinity focus compared to a more complex photo tele lens design. However, it's performance drops off when approaching the edges or a closer focus. OTOH, contrast and clarity in the center seems to even outperform the more expensive 10+ element tele lens designs.


So, I think I can summarize the pro and cons of the forthcoming 560/5.6 already:


SUMMARY

IMHO (based on peliminary information as of today) the Pentax DA 560/5.6 is a tele prime lens at a good price point (sub $2000) which rivals the optical performance of much more expensive glass, near the center and at infinity focus, good enough to be used with a tele converter and with good clarity and contrast. OTOH, the lens is very long (and possibly heavy) and the performance will degrade towards the edges of the image field which makes it better suited for APS-C than full frame although it most likely would cover a medium format image circle. Or all in one: Be Different
02-12-2012, 04:55 AM   #258
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QuoteOriginally posted by derekkite Quote
That lens seems to be outstanding. Not to minimize your skill in handling it.
Thanks! This photo was also taken at F/4.5. I didn't have to crop it. I only cropped the sides off creating an 8x10 photo. The K-5 is great in lower light and it held feather detail without strong sunlight.




QuoteOriginally posted by ElJamoquio Quote
The Sigma 500mm is pretty nice. I would be purchasing one now if it wasn't for the 560 coming.
One thing you all will have to do is make sure your autofocus nails your subject with that 560mm. Autofocus is inexact especially with slower lenses. I struggle a bit with an F/4.5 lens. I almost always machine gun birds with my camera using two or three round bursts while I am concentrating on nailing it. A lot of times something in my brain will confirm that I nailed it because the action typically occurs so quickly.
02-12-2012, 05:16 AM   #259
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QuoteOriginally posted by traderdrew Quote
Autofocus is inexact especially with slower lenses.
I think it is more a question of light, contrast and shake. Of course, a faster and sharper lens helps with all three. The AF gets no good signal if it has to integrate over a long time (low light) while the lens shakes and maybe, the subject lacks contrast. This is why a tripod can help the AF.

02-12-2012, 05:41 AM   #260
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QuoteOriginally posted by falconeye Quote
I think it is more a question of light, contrast and shake. Of course, a faster and sharper lens helps with all three. The AF gets no good signal if it has to integrate over a long time (low light) while the lens shakes and maybe, the subject lacks contrast. This is why a tripod can help the AF.
I can't disagree with this. Autofocus improves in direct sunlight and direct sunlight usually helps contrast given the sunlight is not to strong. I always handhold this lens also and I suspected a monopod would help my autofocus issues. I have a monopod and I have been trying aquire a monopod head now but it is on backorder.
02-12-2012, 06:56 AM   #261
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QuoteOriginally posted by Fly Quote
All that I hope from this lens is: That it is reasonably priced. 2k to 2.5k. That it has no glaring optical faults, and that its minimum focus distance is within a couple feet of the DA 300.
That doesn't seem likely :

DA*300 : 140cm
Signa 500/4.5 : 400cm
Pentax DA 560/5.6 : ?
02-12-2012, 07:04 AM   #262
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QuoteOriginally posted by Frogfish Quote
... or

Honey look a rabbit behind us ........ smack !!
Haha, nice one

But in all seriousness we will have two cameras one with the 55-300 on it The 560 will be for those things I can't or won't get closer to (um Nice Kitty)

I saw a Bigma in-store today and it isn't that well.... BIG, considering the FL it covers.
02-12-2012, 08:00 AM   #263
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remember though that at the long end the bigma is only f6.3 i think

02-12-2012, 08:14 AM   #264
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QuoteOriginally posted by stormcloud Quote
remember though that at the long end the bigma is only f6.3 i think
They are talking about the Sigma 500/4,5, not the Sigma 50-500/4-6,3
02-12-2012, 08:30 AM   #265
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QuoteOriginally posted by falconeye Quote
IMHO (based on peliminary information as of today) the Pentax DA 560/5.6 is a tele prime lens at a good price point (sub $2000) which rivals the optical performance of much more expensive glass, near the center and at infinity focus, good enough to be used with a tele converter and with good clarity and contrast. OTOH, the lens is very long (and possibly heavy) and the performance will degrade towards the edges of the image field which makes it better suited for APS-C than full frame although it most likely would cover a medium format image circle. Or all in one: Be Different
Considering that my favorite 500mm pictures right now are actually cropped to 1500 mm or so, that might be a good tradeoff for me.
02-12-2012, 08:41 AM   #266
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QuoteOriginally posted by falconeye Quote
Let me assume for the best which seems to be an optical 4 element Petzval design plus maybe an additional LFF (Large Field Flattener). A Pentax scope of similiar specification is the Pentax 100 SDUF or Pentax 105 SDP. In this PDF, you'll find a scientific measurement of the resolution of this Pentax scope (German!). The Petzval design dates back to physicist Jozef Maximilián Petzval and was first used in 1841.

The best direct comparative tests of such a scope design and an advanced 10+ element photo tele lens design I could find was conducted by Samir Kharusi from Oman who has an amazing pool of devices
That's good to know.....thanks for posting!
02-12-2012, 08:44 AM   #267
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QuoteOriginally posted by Frogfish Quote
That doesn't seem likely :

DA*300 : 140cm
Signa 500/4.5 : 400cm
Pentax DA 560/5.6 : ?
The DA*300, if I recall correctly, focuses much closer than many of it's competitors.

Which would indicate the same might be true of the 560. Just looking at it's length you might assume that it focuses close; but without knowing what lenses, etc., it's using it's tough to tell.
02-12-2012, 09:34 AM   #268
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Traderdrew: Not to thread hijack here, but this is what I use with my long lenses on a monopod. Quite happy with is.

https://plus.google.com/u/0/photos/101688500536284805756/albums/5702776639091151265
02-12-2012, 09:42 AM   #269
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Minimum focus distance is not critical. 15 ft or so, or equivalent to the Sigma at 4 meters, or even up to 6 meters. 560 is long. Especially if the focus throw, weight and optics are compromised.
02-12-2012, 09:56 AM   #270
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QuoteOriginally posted by ElJamoquio Quote
The DA*300, if I recall correctly, focuses much closer than many of it's competitors.

Which would indicate the same might be true of the 560. Just looking at it's length you might assume that it focuses close; but without knowing what lenses, etc., it's using it's tough to tell.
But at 4m distance you have a horizontal FOV of 16.59cm, at 1,4m only 5.39cm, at 10m with 41.47cm a head probably still fills the frame... I guess not such an issue then...?
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