Forum: Pentax Q
06-03-2015, 07:29 PM
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Sorry, my answer was very short and my english very poor ...:o
I wanted to say that many elements are necessary to build a lens with large aperture or used on large sensors.
Q are abble to use less (good ED) elements in case of long focal lens as I show with my images and on the following diagram (#18 in the present thread) |
Forum: Pentax Q
06-03-2015, 12:42 PM
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Absolutely. But in case of "large" sensor only or large aperture (f/2.8 and more). For very small sensors, near the optical axis, very few aberations are to be corrected (f/6 is not wide open).
in addition of misaligned elements :)
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Forum: Pentax Q
06-03-2015, 09:32 AM
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:o
Not heavier than a bigma or so :) (3.814 kg without tripod)
But the ED80T-CF is not the worse ...
crop 50% (but not with PtxQ7) :
distance about 700m :eek:
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Forum: Pentax Q
05-12-2015, 10:19 AM
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Impressive !
And unexpected (for me) ...
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Forum: Pentax Q
05-03-2015, 09:42 PM
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excellent tip ! To be tested asap :)
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Forum: Pentax Q
05-03-2015, 09:40 PM
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+1
But what does it mean "At this magnification (over 70x)" ?
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Forum: Pentax Q
04-21-2015, 07:52 PM
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Yes, but it is not the same weight ...:(
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Forum: Pentax Q
04-19-2015, 06:04 AM
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Hello crewl1,
I don't think so. This reference ES is equivalent to the Meade model (used by PhenixJC). The main difference concerns the glass type : a sort of FPL51 for the Meade/ES, and the FPL53 for the Orion. FPL53 does not show any AC at all during observation and about 1 pixel using a Ptx Q7 (1.85µm).
The price in Europe has increased significantly during last weeks ... 1044 w/o VAT ... In 2011, the price was 780€ including VAT... http://eu.telescope.com/Orion-ED80T-CF-Triplet-Apochromatic-Refractor-Telescope/p/106820.uts |
Forum: Pentax Q
02-17-2015, 09:21 AM
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Forum: Pentax Q
02-12-2015, 04:08 AM
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Forum: Pentax Q
02-08-2015, 03:31 AM
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I will continue with pleasure :)
But remember, I ask to see, as St. Thomas :lol:
edit :
Nobody to correct my so poor frenglish ? You are very tolerant :)
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Forum: Pentax Q
02-08-2015, 03:05 AM
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it's a bit more complicated ...
I use, as many others, this formula as a guideline (theoretically for one simple lens) : f/D ~< 4.5µ
for color bayer sensor, where µ is the width (µm) of one photosite. In the case of Q7 (1.85µm), the smallest aperture to use to avoid diffraction is around 8. In fact, I use a 80mm diameter lens with a 480mm focal length and the results show no diffraction effect ... :)
The 05 toy lens 18mm/f8 seems to be consistent with this rule.
In fact, I ask to see some shots with the Tamy ... ---------- Post added 02-08-15 at 11:36 AM ----------
+1 as shown here .
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Forum: Pentax Q
02-07-2015, 09:25 AM
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I also have this point of view and I have nothing to sell. I also try to share my experience, anything else.
Sorry if I disturbed this thread.
:)
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Forum: Pentax Q
02-07-2015, 07:51 AM
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Thx for these new tests.
This focal range is very useful but not so impressive for me, considering sharpness is my first expectation. I prefer to keep my opinion until a 100% crop around the spring or the small letters, if you can do it.
The size (1036x777) may be delusive. ---------- Post added 02-07-15 at 04:01 PM ---------- My favorite target for testing is this picture, printed with a black& white laser printer at three line pairs per mm (the tightest lines), and placed at 6.5m from the lens.
It's easier to control all the conditions, particularly the turbulence. |
Forum: Pentax Q
01-31-2015, 06:49 AM
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Another contribution concerning the Q-T2 adapter, used to fix a telescope. I use the famous Orion ED80T-CF. That's a particularly sharp lense. Some examples already posted.
70m :
40m :
20m :
12m :
6m :
384 000 000m : |
Forum: Pentax Q
01-31-2015, 04:19 AM
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Hi Rafa !
Thanks for your comment.
Sure, but it's a special case of use : longer is the focal length, higher is the difficulty and narrower is the field of view. Shooting is obviously more complicated due to the vibrations ...
So DA300mm keeps a lot of advantages indeed.
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Forum: Pentax Q
01-29-2015, 11:48 PM
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and the equivalent setup with the combo PentaxQ-APO-ED-Triplet telescope (see the attached picture below).
The small number of lenses and the small size sensor limit the risk of aberration, and give an equivalent focal lenght as long as digiscopying.
Classical zoom lens or fixed focal lenght are good, but have many lens too. With APS-C or FF, it's OK. Not always with small photosites of the Q system. ---------- Post added 01-30-15 at 08:00 AM ---------- In fact, pictures are good proofs
Situation (~80m) :
Q7/ED80T-CF (reduce to 33%) :
Not the same target and not the same conditions (120m), but digiscoping is less sharp and shows more CA :
(more details here : http://www.chassimages.com/forum/index.php/topic,168569.msg4513404.html#msg4513404)
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Forum: Pentax Q
01-29-2015, 11:42 PM
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+1 ;)
+1 :lol:
In addition I have translated the scheme I used to explain my point of vue to convince JC.
First, the principle of digiscopying, with many lenses, often misaligned, and many resulting aberrations.
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Forum: Pentax Q
01-29-2015, 10:25 PM
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Hello Raf !
Thanks ---------- Post added 01-30-15 at 06:43 AM ---------- Hello Crewl1
I agree. But with an aperture of 6, 1/1000s is not so often used. On the other hand, electronic shutter is very very very slow (1/13s) : it's the great default of the Q/Q7/Q10/Q-S1 ... But you can even stop the move at 1/16000s (but with elongation or deformations due to rolling shutter).
Flash isn't really usable with the electronic shutter. But I use the ED80T-CF to shoot at 20~40m, flash is either not usable ;)
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Forum: Pentax Q
01-29-2015, 01:19 PM
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The crop factor of the Q sensor is 5,5x : it does not depend on the adapter ring. So the focal length is equivalent to 5.5x480mm= 2640mm (with a FF sensor).
The big advantage of the PentaxQ-K adaptor is the built-in mechanical shutter, as you say, to prevent rolling shutter in case of wind for example.
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Forum: Pentax Q
01-29-2015, 12:53 PM
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Hi Ken and Crewl1,
Bonsoir Phenix JC,
Yes, exactly : you need a K-T2 adapter ring in addition with the Pentax Q-K adapter.
I don't have the Pentax Q-K adapter, so I'm not sure, but I suppose it allows exposure up to 30sec, as a K mount lens. ---------- Post added 01-29-15 at 09:07 PM ----------
Hello Steve
Ken gived the answer: yes, it is a fix-focal lenght lense, no zoom at all.
The only advantage is a fantastic sharpness , near the theoretical possibilities of a 80mm diameter lens.
Many clones are avalaible around the world, for example :
in France : Lunette 80\/80
in Gremany : Teleskop-Express: TS Super Apo 80/480mm F/6 - Triplet FPL-53 - colour free
but only Orion delivers (via re-dealers in different states) the (not essential) carbon fiber model.
Be carefull, some clones are made of glass of second rank quality or are doublet (only two lenses), not triplet (three lenses). Only FPL-53 glass produces such CA-free pictures, IMO, combined with an aperture f/6. In astrophotography, it's not very distinguishable, but for wildlife photography, it's clearly a big difference. I had an Equinox ED80 before (FPL53 doublet), the color fringes were sometimes much more visible.
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Forum: Pentax Q
01-29-2015, 12:33 PM
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:o:D
Hi JC :cool:
Very happy to read you here ! I was impatient !
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Forum: Pentax Q
01-29-2015, 11:25 AM
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Sell it :D
I am very intrigued too :). My opinion was different but now ...
Because of the electronic shutter, it's very hard to shoot without a remote IR, a good tripod, no wind, and so on... : no birds fly, without mega-luck. Perhaps the Pentax Q-K adapter may improve the setup, but it is more expensive than Q/Q7...
Sorry :D
thank you for the interest.
I can continue to answer any question ... in my english... with my english ... something like that:D
A restless bird at 12m (2200mm eq focal lenght) |
Forum: Pentax Q
01-28-2015, 10:04 AM
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CA are due to the "afocal setup".
"Minus violet" or "fringe killer" filter may attenuate the CA, but it's not satisfaying IMO, and it's expensive.
The setup without ocular and without prime lense (the scope as a lens with t2 adapter) is much better. ---------- Post added 01-28-15 at 06:18 PM ----------
Yes, very very sharp. IMO, there is the same difference between bigma and DA300mm and between DA300mm and ED80T-CF :eek::D
I tried to explane that with the number of lens in a bigma or in afocal-setup (about 20 lens or more) and only three with a triplet apo-chromatic as in ED80T-CF.
I compared hand held 100-300mm panasonic zoom VR on (crop 100%)
and ed80t-cf on tripod (crop 100%) http://www.chassimages.com/forum/index.php/topic,217130.0/all.html
The focal lenght of the ED80T-CF is 480mm.
the equivalent (not resulting) FF focal lengh is around 2200mm on Q7, 2700mm on Q, and only 960mm on µ4/3.
The aperture is constant : 6, enough in most cases, due to a better transmission (only 3 lenses inside).
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Forum: Pentax Q
01-28-2015, 12:55 AM
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