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Forum: Pentax Lens Articles
07-07-2008, 02:50 PM
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Hi everybody,
I would like to open up a thread dedicated to one topic:
DA lens on Full Frame: a sticky test shots thread.
This thread shall be dedicated to test shots of a DA lens mounted to a full frame body (e.g., a film camera body). By test shot, I mean shots dedicated to evaluate the performance. Shots of ordinary subjects aren't suitable to this task, normally, and should not be posted. So, these are the rules:
- K mount lens dedicated to the APS-C form factor is used.
- Image is taken full frame 36mm x 24mm.
- Lens hood was removed.
- And ideally, no filter is mounted.
- The aperture used is specified (note that film cameras don't record EXIF...).
- Sample image shows the entire field of view.
- Sample image(s) show(s) corner, border and center performance at 10MP-100% (multiple crops, or single not-resized image).
- The subject is such that resolution and vignetting at the borders can be compared to the center.
The idea behind this thread is obvious: To compile enough data to assess the spectrum of available lenses for a forthcoming full frame DSLR in K mount.
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Table of results as obtained in this thread (updated regularly):SMC Pentax-DA primes...
SMC Pentax-DA zooms...
- DA 10-17mm F3.5-4.5 Fish-Eye ED [IF]: FE, see #59, #61, #94. 10mm: heavy vignette / 14mm: almost no vignette / 17mm ++ (Reps, froeschle, Gooshin)
- DA 12-24mm F4 ED AL [IF]: - (below 16mm, xitek.com), o (at 18mm, architorture), + (at 20mm, architorture), ++ (at 24mm, architorture)
- DA 16-45mm F4: - (below 21mm, Nesster)
- DA* 16-50mm F2.8 ED AL [IF] SDM: - (xitek.com)
- DA 17-70mm F4 AL [IF] SDM: - (KjetilH)
- DA 18-55mm F3.5-5.6 AL: - (at 18mm, Spongefingers; below 23mm, xitek.com)
- DA 18-55mm F3.5-5.6 AL II: missing
- DA 18-250mm F3.5-6.3 ED AL [IF]: - (xitek.com)
- DA 50-200mm ED: -
- DA* 50-135mm F2.8 ED [IF] SDM: - (elho_cid)
- DA* 60-250mm F4 ED [IF] SDM: ++ (officially rated "designed for FF" by Pentax patent US7489452) probably good on full frame but evaluation still missing; the rating is +++ with a baffle modification, + without)
- DA 55-300mm F4-5.8 ED: 0 (+, ++ at tele end, viking79)
Sigma K mount DC...
- Sigma 18-200mm f/3.5-6.3 DC: -
- Sigma 10-20mm f/4-5.6 DC: - (below 14mm, Gooshin)
- ...
Tamron K mount Di-II...
Overall rating scale:
+++: no significant difference between APS-C and FF corners
++: difference but usable at full aperture with a small loss in corner IQ only
+: usable staring at f/4~f/5.6, with no or a small loss in corner IQ only
o: usable at f/11 or with big loss in corner IQ only
-: not usable
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Forum: Lens Clubs
10-17-2010, 07:55 AM
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Lens Fetish?
So far only topless :lol:
So, how about a totally nude, full shave, wide open photo ? :cool:
(disclaimer, may be illegal in the US, watch at your own risk! :rolleyes:)
"Zeiss Distagon Torture* 18"
A Zeiss Distagon T* 3,5/18 which I photographed this year at Photokina in Cologne. 13 elements in 11 groups. Some image processing. E.g., I added traces of the schematic drawing from the technical document after making it transparent (no scaling involved -- the Zeiss drawing has correct scales!).
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Forum: Pentax Lens Articles
10-02-2018, 04:29 PM
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Thanks for sticking the thread.
Note that I no longer regularly visit this forum so won't keep links alive if somebody moved the pages around ...
P.S.
This thread now lives for 10 years and never went havoc, or died. Probably never happened anywhere else in the internet ;)
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Forum: Pentax DSLR Discussion
01-29-2010, 09:33 AM
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You are right.
And this thread should close because new posts only add new confusion to the topic.
And while you are right, Marc, Graystar does have a point as well. Which he would have found treated if he would have cared to read through the thread ...
Like you said, Marc, equivalence is a mapping of one sensor size properties to another in such a way that the resulting images are independent of sensor size ("look the same").
This projects a set of all possible images for one sensor size onto the set of all possible images for another.
And for all images which have been mapped it turns out the the effect of sensor size is zero (including effects like noise or diffraction; and assuming perfect glass). Therefore, you are correct, Marc.
But as a matter of fact, too, the following is true: The set of all images for APS-C, when equivalence-mapped into the set of all images for FF, only spawns a subset within this set. There ARE images which have no equivalent images for APS-C (Because the sensor's total full well capacity could have been made larger and because there are no equivalent lenses for glass like 50mm/1.4).
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Forum: Pentax DSLR Discussion
09-24-2009, 04:53 PM
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No need to make a distinction between noise and DoF (this is what this thread was started for). You need a 20mm f/1.2 APS-C to match the FA31.
And I pointed out above that there are other reasons in favour of FF than noise. The lack of wide aperture wide angles is just one of them. So, you are right.
I have this lens and it is amazing. However, on film make sure not to have people in the edges (or to shoot portrait orientation) because otherwise, they will look reeeeeaaaally faaaaaaaaaaaat :)
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Forum: Pentax DSLR Discussion
09-24-2009, 07:46 AM
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The focal length of a lens is printed on the lens. It cannot miraculously change ;)
The FoV with a given sensor and given focal length always is the same, of course. The FoV is larger with a larger sensor of course, but this larger FoV will not be (fully) usable with a DX lens due to vignetting (black corners) and/or corner softness.
Read:
- FX lens = image circle >= 43mm
- DX lens = image circle >= 29mm but < 43mm
(image circle = diameter of usable area of image when projected onto the focal plane)
There is no other difference between DX and FX lenses.
Note that all Pentax FA lenses are like FX and most DA lenses are DX. Some DA lenses are FX though.
Therefore, the Nikon firmware allows to crop the usable middle area from an image taken with a DX lens.
The black borders will lead to bad exposure meter readings. The Nikon firmware may or may not be able to compensate for this effect.
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Forum: Pentax DSLR Discussion
09-24-2009, 05:13 AM
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As I strive for utmost precision in the FF debate, let me add this to this simple statement (I know that you are aware of it):
You are right as far as the noise debate is concerned. But there are two more subtle advantages with FF:
- You may have a tad more dynamic range at the lowest ISO setting (anti noise debate ;) )
- As you stop down on FF for a fully equivalent image, you may have a tad less distortion coming from classical optics aberrations (diffraction is the same).
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Forum: Pentax DSLR Discussion
09-23-2009, 06:28 PM
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This in turn, my friend, isn't true either. Read the thread. Marc said to use f/5.6 and increased ISO (I agree). However, "your" f4 lens on FF is bigger and therefore, gathers more light.
Marc, you're right. But it is possible to follow a different path of reasoning where you end up using the same ISO (and underexposing by 1 stop).
I believe that 24X36NOW followed that path which led to the confusion. I replied above to explain how both paths of reasoning are equivalent.
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Forum: Pentax DSLR Discussion
09-10-2009, 07:48 AM
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Great explaination, thanks!
Add to it the legacy of the registration (or mount hole) diameter. As studied in another thread, the PK mount is limited to f/1.2, some other SLR mounts to f/1.1 and some range finder mounts to f/0.95.
So, a PK mount 50/1.4 is possible while a 30mm/1.0 isn't. The excellent PK mount 30/1.4 from Sigma may be as good as it gets.
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Forum: Pentax DSLR Discussion
09-09-2009, 01:32 PM
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It isn't above ISO800. It is at every ISO if ISO is kept constant, i.e., if lens size is allowed to change.
Then, the noise advantage is 2log(1.53)/log(2) or 1.23 stops. Independent of the day ;)
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Forum: Pentax DSLR Discussion
09-07-2009, 03:39 AM
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My post #145 was too long to have been noticed. Let me repeat the relevant sentence:
The larger sensor has an advantage for low ISO dynamic range.
(allowing longer exposure at the same physical aperture or a wider physical aperture (same f-stop), so that more photons overall can be collected before the sensor is "full").
We all have been looking at the wrong end of the ISO range:
- At the high ISO end, the advantage entirely comes from the bigger lenses able to collect more photons (this thread).
- But at the low ISO end, the advantage entirely comes from the bigger sensor which is able to collect more photons before overflow.
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Forum: Pentax DSLR Discussion
09-02-2009, 05:17 PM
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I nice collection of good questions.
1. Correct. And the cost of long tele lenses roughly increases with physical diameter to the power of 2.5.
2. This is the correct way to look at it. Lens availability. I once checked that for the Pentax system, the DoF/noise advantage of MF vs. FF is little because of a more limited choice of MF lenses.
3. Mistaken, yes. Cf. post #33.
BUT, and this is missing from my post #33, FF at ISO100 performs like APS-C at ISO50 (with a lens big enough) and ISO50 may not be available for APS-C. But D700 starts at ISO200, so equal again ;)
4. Theoretically, yes. Practically, no.
E.g., the Olympus Zuiko ED 35-100/2.0 is almost twice as expensive as the equivalent DA*50-135/2.8 for APS-C which in turn is more expensive than the A 70-210/4.0 for FF ever was.
Which is why I keep saying that the cheapest SLR system was FourThirds in the past, is APS-C now and will be FF in the future. Simply because glass stays expensive while the cost of electronics keeps going down.
5. Yes, there are technical limits for how large a lens can become in practice. For microscopes and mirror-less systems, this limit seems to be about f/0.7. For SLR about f/1.1-f/1.2. But the real point how large a lens can become and still stay sharp.
The best lenses (I know one) have their sharpest f-stop at f/2.8, excellent lenses at f/4 and good lenses at f/5.6. A majority of consumer zooms performs best at f/8. So, even with big money, f/2.8 seems to be the limit for maintaining full resolution.
So, if an f/2.8 lens is already used for FF, then APS-C will most likely not be able to catch up, neither in resolution (at f/2.0) nor in light (at f/2.8).
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Forum: Pentax DSLR Discussion
09-01-2009, 01:56 PM
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YOur 5D takes "better" pictures (less noise and less DoF) if you use a lens with the same f-stop. But because of longer focal length, this same f-stop lens will be bigger (larger diameter), heavier and more expensive.
If you could find an equally big lens for the shorter focal required on APS-C, then your 5D wouldn't make better images anymore. If you can find and afford it.
Or as I prefer to say: FF may provide more options.
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Forum: Pentax DSLR Discussion
09-01-2009, 11:52 AM
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This is just another side of the same medal we have been talking about in the other thread.
Let me jump straight to conclusion now:
Two cameras taking images with
- same distance to subject
- same field of view
- equal diameter lens (same lens aperture in mm, possibly different f-stops)
- same shutter speed
- same quantum efficiency (same CMOS process)
will produce identical (i.e., indistinguishable!) results when considering the following aspects:
- image composition
- noise
- dynamic range
- depth of field
- resolution limited by diffraction
To be explicit: the sensor size doesn't come into play here!
Additionally, cost is mostly determined by weight of glass and would be almost independent of sensor size too (same size of lenses, same weight, same cost).
Where sensor size comes into play is here:
- possible number of pixels
- possible resolution as limited by classical optics for a given cost
(a 50-135/2.8 APS-C 100 lp/mm zoom may be harder to build than a 75-200/4 FF 67 lp/mm zoom)
So, when comparing FF with APS-C, available lenses (and their diameters in mm) and their cost must be compared. Not the sensor sizes.
It is the availability of bigger glass which gives FF a head (like 75-200/2.8 for FF but no 50-135/2.0 for APS-C). And the inavailability is not marketing (only). It is partly due to technical obstacles which would make such offers expensive. Like FourThirds already is more expensive than APS-C now, when including the cost of glass.
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Forum: Pentax DSLR Discussion
07-15-2008, 12:07 PM
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Dear Pentaxians,
we have heard many comments about wrong focusing because the AF sensors appear to be larger than one would naively think.
The following is an official Pentax drawing about their size and positioning for the 11 sensor Safox system. Please, use to your advantage.
Pentax Safox sensor layout 
Source: I accidentally found this info in the German Pentax *ist film camera booklet on their German website (PDF):
http://www.pentax.de/downloads/photo/de/PENTAX%20%20_star_ist/Slim-Jim-ist-GER.pdf.
It officially applies to the Pentax *ist film camera only. But I guess, it applies to all current Pentax DSLRs as well.
This is the text which goes with the drawing: "Wie aus der Skizze hervorgeht, sind die CCD-Sensoren in unterschiedlicher Form angeordnet." (As shown by the drawing, the CCD sensors are layed out in varying shape.)
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Forum: Pentax K-1 & K-1 II
03-17-2016, 08:39 AM
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Let me cite a paragraph from that site where they pretend to quote an engineer:
I am sorry to say so, but that is utterly nonsense and I have a hard time to believe an engineer actually said so. The sensor features a full digital readout and the specific daughterboard Pentax has developed has no effect on the noise the sensor captures (assuming a minimum technical standard). Pentax marketing is counting on less educated readers. But that always fires back in this internet age. Didn't they learn a thing or two over the last couple of years?
Therefore, I must say information spread by Pentax about the sensor cannot be regarded reliable information anymore.
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Forum: Photographic Industry and Professionals
12-30-2019, 05:37 PM
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Just a clarification ... I posted the link because I thought my fellow Pentaxians may find it entertaining. I am a bit confused about all the negativity. The opinions expressed (by Chris) weren’t meant to be taken too seriously.
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Forum: Photographic Industry and Professionals
12-30-2019, 03:56 AM
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Hi friends,
I don’t know anybody noticed ... over there at dpr, new years resolutions were posted but not for Pentax :( As Jordan pointed out today, it was by mistake.
Here is an unlisted! youtube video from dpr tv about new years resolutions for Pentax, narrated by Chris. Enjoy :)
->
Youtu.be
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src="https://www.youtube.com/embed/e6QSl5zgXMY?controls=1" allowfullscreen>
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Forum: Photographic Industry and Professionals
01-18-2020, 05:49 AM
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So, we Pentaxians are like the archetypical wife ... whatever you say, you just cannot win :D
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Forum: Photographic Industry and Professionals
01-19-2020, 03:40 AM
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So then I am sorry. Certainly not intended.
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Forum: Pentax Lens Articles
10-14-2012, 02:37 PM
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Forum: Pentax Lens Articles
12-17-2011, 12:32 PM
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Thanks beholder3, that's exactly the kind of content I was hoping for. Great and thank you very much! :)
The corner shading is vignetting as the loss of light isn't 100%. I've seen some of it too but not as strong. And vignetting was kind of normal for a FF zoom if remember the old days correctly :)
In order to judge the vignetting you showcase, I'd like to know what image area you scanned (some film cameras expose more than 24x36mm), at which aperture and focal distance you shot (shorter distances could be worse) and what gradation your film emulsion was (some hard gradation films can make a little vignetting look like shading).
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Forum: Pentax Lens Articles
12-10-2009, 02:29 PM
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Having the FA*300/4.5, I just need the time to run a roll of film to repeat my test ;)
I got the impression that the DA* has a subtle advantage in center resolution over the FA*, so all in all, both lenses may be good choices for full frame. Not to forget the DA* 60-250 ...
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Forum: Pentax Lens Articles
12-09-2009, 06:26 PM
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I added an entry about the D FA Macro 100mm F2.8 WR in the opening post.
This is the first new lens released by Pentax being specified full frame officially by Pentax. Even the DA* 55mm f/1.4 was not specified as such by Pentax.
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Forum: Pentax Lens Articles
02-07-2009, 04:34 PM
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As our friend whatever7 has pointed out, there are a number of shots with DA lenses on film present in the following thread on xitek.com:
Pentax½ºÆ¬»úÉí+DA¾µÍ·¾ãÀÖ²¿ - ÎÞ¼ÉÂÛ̳
I haven't seen much information we haven't covered yet. But then, I don't speak Chinese ;)
The first post quotes some focal lengths for some zooms where the black circles disappear.
Like: 18-55 bad <23mm.
It says DA* 16-50 full black circle, 12-24mm bad <16mm, and 18-250 full black circle.
I updated my OP accordingly.
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