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Forum: General Talk 6 Hours Ago  
Your latest acquisition
Posted By photoptimist
Replies: 10,948
Views: 746,160
Perhaps you can convince her to put you on a diet of short lenses.

One new small lens each week and a short stack of SMUs would clearly be healthy moderation!
Forum: General Photography 1 Day Ago  
Are these striations actually on the feathers?
Posted By photoptimist
Replies: 13
Views: 566
Great image!

The light and dark striations on the brown portion of the feather look natural. They chevon naturally at the center of the feather, are present even in OOF areas, and aren't affected by imperfections in the feather.

The colored striation in the white tips of the feather look like classic aliasing artifacts.
Forum: Pentax K-1 2 Days Ago  
Mirror Slap / Shutter Shock on K-1
Posted By photoptimist
Replies: 21
Views: 846
Interesting!

I wonder if it's not just the low mass of the DFA 28-105 but also some internal elements of the lens that are prone to vibration. If mirror shock causes the AF group of elements or one of the zoom-groups of elements to move laterally even a tiny amount, it could induce a significant shift it the image.
Forum: Pentax KP 2 Days Ago  
Questionable battery life
Posted By photoptimist
Replies: 2
Views: 203
The CIPA rating is for room temperature. Chemistry and thermodynamics are in control of this issue, not Pentax.

The only way to prolong the life of a battery in cold weather is to keep it warm.

You might consider building your own external insulated battery pack that powers the camera via the AC adapter port or a dummy battery. I'm sure other cold-weather, time-lapse photographer have had this problem and that the internet would have some instructions for such a battery pack.
Forum: Pentax Medium Format 3 Days Ago  
TLR woes
Posted By photoptimist
Replies: 9
Views: 517
Yipes!

This looks like the effects of a flipped lens element. Is there a chance someone took apart the lens and reassembled it with one of the elements reversed?
Forum: Pentax K-1 3 Days Ago  
Mirror Slap / Shutter Shock on K-1
Posted By photoptimist
Replies: 21
Views: 846
1) ES would be a little noisier because the image will contain a very faint ghost of whatever the sensor was exposed to before the electronic reset. I've not tested it but would expect it to be most noticeable in night photography where you might see a very faint ghost of moving lights from before the intended exposure time.

2) There's nothing in menus. Whether some clever soul could create a firmware hack is another issue.

3) Adjustment probably can't help because it's inherent to the basic physics of the system -- the camera body pushes on the mirror to move it and the mirror pushes back on the body (Newton's 3rd law). The lighter and more compact the mass of the body, the greater the body's motion in response to the mirror's push-back. In theory, one can build shock-free mirror mechanisms with a clever counterweight that moves in the opposite direction of the mirror but that adds a lot of cost, complexity, weight, bulk, power draw, and noise.

P.S. One trick I've used to mechanically stabilize a camera is to bolt a small tripod to the bottom even for hand-held shots. The mass of the tripod suspended below the camera significantly dampens camera vibration. It may look silly and be a bit awkward but it might be worth a try. Call it a poor-man's steady cam.
Forum: Pentax K-5 3 Days Ago  
What size screw for K-5 Tripod?
Posted By photoptimist
Replies: 3
Views: 261
Technically, the typical tripod mount screw is 1/4-20 UNC (that's 1/4" diameter screw with 20 threads per inch of the UNC thread design which is the coarse thread variant of the Unified Thread Standard). It's the most common thread for 1/4" screws so it's easy to find.

Most of the tripod heads I've seen have about 3/16" of screw length protruding from the head plate.
Forum: Pentax News and Rumors 4 Days Ago  
Latest Pentax patent for a "Tilting Sensor"
Posted By photoptimist
Replies: 51
Views: 4,939
Good point! At a 5 tilt, on-sensor PDAF would suffer back-out in the center at f/11. Off-axis, the on-sensor PDAF black-out would be a function of the exit pupil distance used when designing the sensor versus the actual exit pupil distance of the specific lens.
Forum: Pentax News and Rumors 5 Days Ago  
Latest Pentax patent for a "Tilting Sensor"
Posted By photoptimist
Replies: 51
Views: 4,939
Exactly! Unless Pentax replicates the sensor-tilter on the focus screen, too, the only way to see the effects of sensor tilt is in live view.

On-sensor PDAF might still work if the sensor tilt is fairly small angle. A bit of math shows that even a 2-5 tilt angle of the sensor delivers a huge amount of tilt-effect to the image without creating excessively larger incidence angles or too much light fall-off across the sensor.
Forum: General Photography 11-08-2017, 10:40 AM  
New Reflex Film SLR
Posted By photoptimist
Replies: 69
Views: 1,501
Yes, creating one prototype for the can and another for the worms does present some risks when if comes time to stuff the one in the other. People used to the digital world think nothing of cramming another megabyte of stuff into a file, app, or computer. But physical things take physical space and the properties of optics place inconvenient constraints on where stuff must be put.

Kickstarter is a bit of a Wild West in terms of whether any given funded project actually comes to fruition. But without Kickstarter, these kinds of products would never ever be built -- a non-zero chance of success is better than a zero-chance that comes from never even trying.

I wish them luck although agree that they will need it!
Forum: General Photography 11-08-2017, 08:38 AM  
New Reflex Film SLR
Posted By photoptimist
Replies: 69
Views: 1,501
This concept seems like a great idea for people who want to give film a try without risking getting a dud body off eBay that needs a CLA, new light seals, or is just not repairable. Given that film gives no immediate feedback until the roll is developed, some people will surely be willing to pay more to get a new film camera body that they can trust.

The daylight interchangeable film backs seem like a very nice feature in this era of digital where one can change ISO, saturation, color/B&W at the flick of a switch. It's easy to imagine a day of film shooting in which one might want to swap between low or high ISO film, try slide vs. print film, or try color versus B&W on a scene.

Sure, this camera is not as old-school as resurrecting a classic body from a bygone era, but it certainly offers a cool opportunity to try different films and try different old lenses.
Forum: Photographic Industry and Professionals 11-07-2017, 05:19 PM  
Nikon selling -16,1% DSLRs, -15,5% lenses, -18,5% compacts this FY18/3
Posted By photoptimist
Replies: 30
Views: 1,233
The CIPA figures through Sept 2017 (http://www.cipa.jp/stats/documents/e/d-201709_e.pdf) show compact cameras actually growing faster than ILCs, DSLRs shrinking a few % year-on-year, and mirrorless growing very quickly but still lagging DSLRs.
Forum: General Photography 11-07-2017, 04:07 PM  
New Reflex Film SLR
Posted By photoptimist
Replies: 69
Views: 1,501
Great sleuthing!

So instead of "stop-down" metering, one could say the camera offers "open-up" focusing and framing.
Forum: General Photography 11-07-2017, 12:08 PM  
New Reflex Film SLR
Posted By photoptimist
Replies: 69
Views: 1,501
Yes, perhaps every lens plate has the required mechanical tidbits to link the DoF button to the aperture of the lens. And then there's an electromechanical actuator in the body that actuates the DoF button from inside when the shutter fires.
Forum: Photographic Technique 11-07-2017, 09:56 AM  
Landscape Stitched perspective and larger (flat sensor)
Posted By photoptimist
Replies: 6
Views: 439
There's really no right way to mush the 3-D world on to a 2-D image.

The human eyeball is much more like a fisheye projection both in the design of the retina and the way the eyeball and head scan the scene. But then the brain takes al the eyeball data and tends to do a conversion to rectilinear.

Imagine standing in the middle of a city block of 5-story buildings. On the one hand, visually, the buildings at each end of the street are smaller and less distinct with vanishing points going in both directions. That creates a fisheye version of the world.

Yet the mind sees all the road lines, fence lines, rows of windows, and rooflines as perfectly parallel with the buildings up and down the street being equally tall.

One can de-fish the image to make straight parallel lines stay straight parallel lines but then the objects at the ends and corners are stretched and distorted.
Forum: General Photography 11-07-2017, 09:41 AM  
New Reflex Film SLR
Posted By photoptimist
Replies: 69
Views: 1,501
Looking at the pictures, there's no evidence of any aperture coupling or actuation at all. And it doesn't look the interchangeable lens plate or mirror box have room for any levers and aperture motors.

Thus, it seems like it uses manual stop-down focus & Av metering.

EDIT: Hmmm... there's a DoF preview button so maybe there must be an aperture actuator in there someplace......
Forum: Pentax News and Rumors 11-07-2017, 07:29 AM  
Latest Pentax patent for a "Tilting Sensor"
Posted By photoptimist
Replies: 51
Views: 4,939
Actually, pure tilt isn't so bad -- the rays from the center of the lens to the center of the sensor are still nice and perpendicular to the sensor. It's really no different than attempting to AF a brick wall at an angle.

On the other hand, any shift of the exit pupil beyond a few mm (the exact number depends on the lens aperture and PDAF aperture) is wholly incompatible with both DSLR and on-sensor PDAF because it blacks-out one half of the phase contrast system.

CDAF should work all right with both tilt and shift although it might be a bit slower or hunt a bit more because any advanced analysis of the blur to predict the required AF motion would be confounded by the strange behavior of blur circles in a T/S lens relative to a normal lens.

There's also the issue that when these T/S lenses were originally designed there was no cost effective way to have a mechanical drive train that could connect the camera body AF motor to the tilted/shifted focus assembly.
Forum: Photographic Industry and Professionals 11-07-2017, 07:02 AM  
Nikon selling -16,1% DSLRs, -15,5% lenses, -18,5% compacts this FY18/3
Posted By photoptimist
Replies: 30
Views: 1,233
The gross margins on top tier photo stuff may be high and yet it does not seem like Nikon, Canon, Sony, etc. are all that profitable. All that overpaid gross margin is either going to cover losses on the low-end equipment or it's being spent on R&D, marketing, professional services, etc.
Forum: Photographic Industry and Professionals 11-07-2017, 05:34 AM  
Nikon selling -16,1% DSLRs, -15,5% lenses, -18,5% compacts this FY18/3
Posted By photoptimist
Replies: 30
Views: 1,233
This in not surprising.

Standalone cameras now only sell to people who can afford to buy two cameras: a smartphone first and then a second standalone one. And because a standalone camera only makes sense if it is markedly better than the person's first camera (the smartphone), the second camera has to be a pretty good one.

The good news is that it will force camera makers to only make good cameras because nobody is going to buy a camera that isn't an upgrade from a smartphone.
Forum: Photographic Technique 11-06-2017, 05:43 PM  
Landscape Stitched perspective and larger (flat sensor)
Posted By photoptimist
Replies: 6
Views: 439
With a long focal length lens for the tiles and a modest total swing of the panohead, it's not hard to stay rectilinear which is to say that you are replicating what a wider lens would do on a larger format camera. Brenizer method photos tend to do this. If all the straight lines in the scene remain straight lines in the final image, then the stitch is rectilinear and equivalent to a wider angle on a larger format camera.

But as the total swing of the head grows large (say like over 120 and certainly if the pano tries of cover 180), then the stitch is likely to end up being equiangular (each pixel covers the same angle of the scene) which actually ends up using more of the resolution of more of the frames but it does cause distortions in which parallel lines converge.
Forum: General Photography 11-06-2017, 01:15 PM  
The Perfect Camera
Posted By photoptimist
Replies: 29
Views: 1,040
The list of design conflicts is pretty good.

What is interesting is that there are some very strong design considerations that push cameras to be mid-sized:

Cameras can be too small:
1) poor DR imposed by the physics of light (the photon flux in scenes of everyday life)
2) poor subject isolation (DoF) for lenses of practical aperture
3) poor physical ergonomics

Cameras can be too large:
1) the camera body and lenses (especially telephoto lenses) become unwieldy
2) the cost of silicon (or film) becomes prohibitive

Thus, camera makers and camera buyers are likely to gravitate to cameras of a certain middle size. There's a sweet spot around 35 mm FF in that most camera bodies and lenses in that format fit in the human hand and use a sensor of about the size and sensitivity of the human retina. In turn, the volume of production of those mid-size cameras drives a lot of development of component technologies (sensors, AF, mounts, meters, etc.), lenses, and accessories scaled to suit mid-size cameras. This makes these mid-size formats even more attractive to everyone.

Of course, that's not to say there won't be people that opt for tiny or huge cameras as their "perfect camera."
Forum: Pentax Film SLR Discussion 11-06-2017, 10:02 AM  
Asahi Pentar K - Value? (Yes, PentaR)
Posted By photoptimist
Replies: 19
Views: 838
Nice find!

Rare objects really have no set value -- it's all a matter of finding that special buyer who really values the item and has the money to pay. You could say the price all depends on whether copies of the object are rarer than the buyers of the object.

That said if a "bad condition" copy sold for $1000, a good condition copy might sell for much more (or it might sell for less if the richest collector of this item already bought one for $1000 and doesn't need another one).

It really is priceless in the sense of being with out a price.
Forum: Pentax News and Rumors 11-06-2017, 07:30 AM  
Latest Pentax patent for a "Tilting Sensor"
Posted By photoptimist
Replies: 51
Views: 4,939
Yes, image circle size issues are a major challenge for tilting lenses because tilting the lens causes the image circle to move laterally across the sensor.

In contrast, a nice feature of a tilting sensor is that it can be designed to ALWAYS stay within the image circle of the lens. If the default location of the sensor is all the way forward at the focal register plane (the plane of focus if the lens is set for infinity), then tilting the sensor backwards will bring parts of the foreground into focus but the sensor will stay in the cone of the image circle.
Forum: Pentax News and Rumors 11-05-2017, 07:49 PM  
Latest Pentax patent for a "Tilting Sensor"
Posted By photoptimist
Replies: 51
Views: 4,939
Exactly right.

What's confusing about IBIS is that the system does correct for pitch and yaw tilting motions of the camera and lens but it only corrects the lateral shifting of the image across the sensor created by tilt but does not correct for any change in the plane of focus.

The Scheimpflug principle effects of tilting the sensor could be pretty useful for wide angle lenses.

Even a modest 1 mm tilt of the sensor would provide a powerful tilting of the plane of focus for architectural photography. A 24 mm lens with a 1 mm sensor tilt could have infinity focus at the top of the frame and about a 0.6 meter foreground focus at the bottom of the frame.

The effect weakens rapidly with longer focal lengths. A 50 mm lens with a 1 mm sensor tilt could have infinity focus at the top of the frame and a 2.6 meter foreground focus at the bottom of the frame. A 100 mm lens with a 1 mm sensor tilt could have infinity focus at the top of the frame and a 10 meter foreground focus at the bottom of the frame.
Forum: General Photography 11-05-2017, 09:54 AM  
Macro versus Telephoto lenses for long distance shooting
Posted By photoptimist
Replies: 12
Views: 421
That may be true.

How about a 10,000 lightyear test target? An image of the night sky will provide a decent estimate of the Point spread function - Wikipedia of the lens which can be used to estimate resolution.
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