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Forum: Pentax KP 9 Hours Ago  
Setting the lowest "preferred" ISO
Posted By photoptimist
Replies: 13
Views: 412
The reluctance of a digital camera to go to the lowest ISO in P-mode may related to highlight preservation (as others have noted).

One key difference between print film and digital cameras is how they handle over-exposed areas. Print films can often handle many stops of overexposure while still capturing some of the detail in the brightest areas. Digital camera sensors tend to clip anything that is too bright which means no detail will be visible in the over-exposed regions..

Yes, an ISO 100 image might be a tiny bit less noisy but it may come at a cost of rendering nice fluffy clouds are featureless white blobs.
Forum: Pentax KP 2 Days Ago  
KP Bulb Mode Processing Times (Overly Long?)
Posted By photoptimist
Replies: 4
Views: 330
That's almost certainly due to using "slow shutter speed noise reduction." That setting takes a second picture with the shutter closed to get a dark frame image of the sensor's noise pattern that the camera then subtracts from the actual image. The second noise reduction shot takes as much time as the first shot so that's why a 2 minute exposure required another two minutes of processing.

You can change the setting but you might want to test the results before using it on an important image. Without that extra processing, the images will be noisier.

If you are doing a lot of bulb work under relatively controlled conditions, you can take your own slow shutter speed noise reduction images -- just take a complete black shot (no light, lens cap on, etc.) with the slow shutter speed you've been using. Save that "dark frame" and subtract it in post. Note that the "dark frame" depends on the shutter time and the temperatures inside the camera. You might need to take a few dark frames during your photoshoot to get the best results.
Forum: Pentax Medium Format 3 Days Ago  
Are my 135 and 200mm lenses really getting infinity? have big doubts.
Posted By photoptimist
Replies: 10
Views: 674
If the flange focal distance (lens-mount to film-plane distance) is off by ∆, then the image magnification when the lens is supposedly at ∞ will be m = ∆/f. The distance from the film plane l to the focus point on the subject would be f*(2 + m + 1/m).

For ∆ = 2 mm, I'd expect the 135 mm lens to focus at about 9.4 meters and the 200 mm lens to focus at about 20.4 meters.

For ∆ = 2.6 mm, I'd expect the 135 mm lens to focus at about 7.3 meters and the 200 mm lens to focus at about 15.8 meters.

So maybe the adapter is off by 2mm and the 200mm lens is off by an additional 0.6mm

Some complicating issues:

1. The exact distance of adjustment of the helicoid is not easy to calculate because it is a function of the lens design. With some true telephoto lens designs (used to make the lens and helicoid more compact), the helicoid moves less than would be expected compared to the thin lens formula.

2. It is really hard to judge the center of focus near infinity because the hyper-focal effect biases the depth of field toward infinity. Although some use a one-third / two-thirds split between the front and back depth of field that is only correct if the center of focus is exactly one half the hyper-focal distance. If the lens is set to the hyperfocal distance then everything from 1/2 the hyperfocal distance to infinity is "in focus." Compounding this issue is that atmospheric disturbances and haze make distant objects fuzzier than they should be. Stars at the zenith make a good "infinity" target but unless the lens can focus past infinity, it's hard to tell whether the non-zero size of the stars is caused by atmospheric effects, aberrations in the lens, or a lens that cannot get to infinity focus.

Overall, it seems the adaptor is certainly damaged, defective, designed wrong. It's also possible that the camera body is not quite right, either.
Forum: Pentax Medium Format 3 Days Ago  
Is it time to ditch the SD card concept?
Posted By photoptimist
Replies: 121
Views: 6,669
Removable memory reduces risks of data loss -- if the camera breaks, is lost, has a data corruption event, or gets stolen, then less data is lost if the photographer uses removable cards and swaps with some frequency.

Removable memory enables higher-volume workflows -- a card swap lets the photographer keep shooting while an assistant downloads the card(s) and begins post processing.

Removable memory enables less down time for shooting -- even with USB C, swapping cards is faster than connecting the camera and waiting while it downloads.

The added cost of removable memory is negligible in the grand scheme -- is anyone really going to tie-break between two high-spec cameras and buy the model with no card slot because the slot-less camera is $30 cheaper?
Forum: Troubleshooting and Beginner Help 4 Days Ago  
Confused by different types of RAW file
Posted By photoptimist
Replies: 9
Views: 521
TL;DNR: It is likely that your viewing program understands DNG better than it understands PEF and is using the in-camera image settings stored in EXIF to generate a viewable image.

Background: DNG is a more standardized RAW format. PEF is a Pentax-specific RAW format. Each camera maker has their own proprietary RAW format which may include some features not readily available with DNG. Both DNG and PEF store the RAW, unprocessed sensor data.

Most of the in-camera image settings (white balance, color processing, sharpness, contrast, etc.) have absolutely no effect on the RAW sensor data stored in a PEF or DNG file. However, those in-camera image settings are used to create any JPEG image associated with the picture such as the thumbnail and the JPG twin if you use RAW+JPG. Moreover, the in-camera image settings are stored in the EXIF data. Many viewing and editing programs will use those in-camera image settings if the program knows how to unpack the RAW file. To unpack the file, your software needs updated code or configuration files to know how to handle your camera's files. Different software makers are better (or worse) at creating updates for every new camera model and sometimes users don't update their software often enough.

Note: You will never ever actually see the RAW file outside of some very technical image data processing programs. If you actually tried to look at the RAW data, it would be very muted, very green, and composed of a checkboard pattern of black-to-red, black-to-blue, and black-to-green speckles. Moreover, unless you had a 14-bit per color channel monitor, any viewing of the RAW file would required a contrast adjustment that pulls up the shadows and would make the image look even more muted.

Under almost all circumstances, viewing a RAW file requires processing the RAW pixels into something the monitor can display and which corrects for technical peculiarities of the camera sensor. Thus, viewing a RAW file entails interpreting the colors which requires using at least some of the data in EXIF.
Forum: Troubleshooting and Beginner Help 6 Days Ago  
Uploading raw files to Amazon Photos
Posted By photoptimist
Replies: 17
Views: 712
Hmmm... Sounds like Amazon does not want you to store big files.

1. See what happens if you rename the .DNG file to be .HEIC. Does it come back the same size and still open properly if you rename it back to .DNG?

2. See what happens if you make changes to the EXIF data so Amazon's systems don't know it's size or the model of camera. (And does downloading the file and reverting the EXIF settings work?)

3. Create a clever workflow to split a DNG into 4 panels (and a second workflow to remerge them).

4. Perhaps the larger issue is that a free service is worth every penny.

P.S. I would not use Amazon or (any free service) as your only back-up of an image. "The Cloud" seems like the perfect "truth in advertising" name for these services because clouds often evaporate into thin air.
Forum: Troubleshooting and Beginner Help 09-17-2022, 08:32 AM  
DA SCM 300MM fr lens- auto focus not working?
Posted By photoptimist
Replies: 6
Views: 404
Define "stopped working":
* no movement at all,
* hunts unsuccessfully,
* error messages,
* consistently out-of-focus,
* does not work in live view, etc.
Forum: General Photography 09-14-2022, 12:43 PM  
Good perspective don't come easy!
Posted By photoptimist
Replies: 12
Views: 732
Some genres of photography do get to adjust the composition in almost any way they want. Product photographers are masters at this art form. And certainly a big part of photographing people (for fashion & art) is in posing them in carefully selected surroundings with carefully selected props and carefully positioned lighting.

It's landscape photographers who are forced to live with inconveniently arranged clouds, poorly spaced layers in rock walls, trees that aren't perfectly full all the way round, and a sun that sometimes would be sooo much better if it would be willing to set to the north sometime (besides above the Arctic circle).

Even the drawing/painting people need to learn to respect the physical geometry of perspective unless they want to dance off into the worlds of Escher, Dali, and Cubism.

Of course, if it were all so very easy, it would not be worth doing!
Forum: General Photography 09-14-2022, 04:47 AM  
Good perspective don't come easy!
Posted By photoptimist
Replies: 12
Views: 732

At issue is the classification of photographs into works of fiction and works of non-fiction.

Some images are so heavily edited that no one would confuse them with reality. But others are more sublte and could mislead the viewer into thinking that is what that place/person/city looks like. Personally, I'd say that photographer's do have a right to use Photoshop in any way they choose but that failure to disclose editing would be unethical. Photographs are food for thought and undisclosed edits are like a food maker not disclosing the artificial colors and flavors they used in the ingredients.

Maybe all photographs should be double-sided: one side of the print shows the photographer's final edits and the backside shows the unedited scene.
Forum: General Photography 09-13-2022, 01:22 PM  
Good perspective don't come easy!
Posted By photoptimist
Replies: 12
Views: 732
Ah, life in the world of photography!

On an outing with another couple to a rural park in the foothills of the local mountains, I took photographs and another person painted. I was forced to live with the existing placements of a particular rustic farm house, dusty trees, hazy mountains, sky, and lighting as they were on that day at that time. She rearranged and rescaled the object, changed the perspective, and adjusted the light as she composed a scene on canvas with bright acrylics.

I captured "reality" as it was in it's lackluster banality. She captured the emotional essence of an old farm building in the foothills.

Photography (especially landscape photography) has the challenge that nature and physics control most of the particulars of the image. Sure, clever composition, good lens choice, perfect timing, and luck in the lighting-lottery provide some control, but not as much control as is enjoyed by practitioners of the synthetic arts like painting that are not so constrained by reality.
Forum: Pentax K-1 & K-1 II 09-13-2022, 06:29 AM  
K1II Pixel Shift vs GFX100: who wins? (geek post warning)
Posted By photoptimist
Replies: 37
Views: 1,757
Hmmmm.. It might be a bit trickier than it seems.

If you are comparing K-1 Pixel shift to the GFX100 by pixel peeping, then the acceptable circle of confusion and DoF depends on the properties of the sensor:

In the red and blue channels of a Bayer sensor image, the acceptable circle of confusion would be tied to twice the pixel spacing of the sensor. In the green channel, the acceptable circle of confusion would be tied to square-root-of-two (1.414) times the pixel spacing of the sensor.

For a pixel shift image, the acceptable circle of confusion would be tied to one times the pixel spacing of the sensor.

If you are comparing K-1 Pixel shift to the GFX100 by making prints of a certain modest size, then the circle of confusion and DoF depend on human visual acuity and how the print is viewed. That circle of confusion on the print then relates back to a circular of confusion on the sensor through the ratio of the sensor format size to the print size.
Forum: Pentax K-1 & K-1 II 09-12-2022, 12:09 PM  
K1II Pixel Shift vs GFX100: who wins? (geek post warning)
Posted By photoptimist
Replies: 37
Views: 1,757
The equating of a 36MPix pixelshift image to a 144 MPix Bayer filter image isn't totally wrong.

A 144 MPix Bayer filter RAW image only has 36 MPix of red channel data and 36 MPix of red channel data. Both of these channels have to upsampled (that's what demosaicing does) to fill in all the missing data in red and blue. A 144 MPix Bayer filter RAW image only has 72 MPix of green data that is also upsampled.

36MPix pixelshift image upsampled to 144 MPix would have the same resolution in red and blue as a 144 MPix single shot Bayer filter image but the upsampled pixelshift image would be a bit softer in the green channel than the 144 MPix camera image. The 144 MPix single shot Bayer filter image might suffer from some aliasing artifacts while the pixelshift image might suffer from subject movement or light nonuniformity artifacts.

That's why I said "it's complicated"

For subject matter that is totally motionless and lit with a stable light source (not an inconsequential prerequisite), pixelshift image will compare favorably with Bayer filter images of nearly double the sensor pixel count.
Forum: General Photography 09-12-2022, 10:26 AM  
Thinking Mirrorless?
Posted By photoptimist
Replies: 14
Views: 1,083
The problem for Kodak was that they had become a photographic film, photographic paper, and photochemical manufacturing and distribution company. Sure, they understood a huge amount about the end goal of film -- the faithfully recorded and beautifully presented photograph -- but the company was 99% invested in a particular means of creating photographs -- the photochemical process.

The shift to digital meant that demand for almost all of Kodak's consumable photographic supplies would disappear. All those sophisticated Kodak factories, huge warehouses, and associated jobs go, too. It's not surprising that the executives, managers, and workers at Kodak who had spent a lifetime creating a photochemical powerhouse failed to embrace an invention that would see the demolition of their life's work.
Forum: Pentax K-1 & K-1 II 09-12-2022, 08:16 AM  
K1II Pixel Shift vs GFX100: who wins? (geek post warning)
Posted By photoptimist
Replies: 37
Views: 1,757
"It's complicated"

The Bayer color filter array on the K-1 and the GFX100 means that these cameras resolve different numbers of megapixels in the different color bands. With a Bayer filter, 1/4 of the pixels see the red channel, 1/4 of them see blue, and 1/2 of them see green.

Or to put it another way, 3/4 of the sensor is blind to details in red, 3/4 of the sensor is blind to to details in blue, and 1/2 the sensor is blind to to details in green. Putting a sharp lens in front of the Bayer color filter array sensor (that lacks an antialiasing filter) means that tiny details in red have a 75% chance of being lost!

In single shot mode, a K-1 resolves 9 Mpix in red, 9 MPix in blue, and 18 MPix in green.

In single shot mode, a GFX100 resolves 25.4 Mpix in red, 25.4 MPix in blue, and 50.8 MPix in green.

Pixel shift mode carefully shifts the sensor in a square pattern of 1-pixel increments so that every pixel in the image is sampled in red and blue and is sampled twice in green. This mode fully measures all the pixels in all the colors.

Thus in pixel shift mode, a K-1 resolves 36 Mpix in red, 36 MPix in blue, and 36 MPix in green (with better DR from average two samples).

For images with a lot of detail in the red or blue channel, K-1PS mode would beat GFX100. For images with a lot of detail in the green channel, the GFX100 would probably beat K-1PS mode.
Forum: Canon, Nikon, Sony, and Other Camera Brands 09-03-2022, 02:39 PM  
Folding Camera Club
Posted By photoptimist
Replies: 2
Views: 222
Sounds great! I have got my father-in-law's old Kodak Retina but not had the time to put a roll of through it.

(I assume that anyone whose "folding camera" is one of those new folding smart phones would be dunked in stop batch and ejected! ;) )
Forum: Digital Processing, Software, and Printing 09-03-2022, 06:55 AM  
Black & white conversion, what is right?
Posted By photoptimist
Replies: 24
Views: 1,151
A couple more thoughts:

Perceptual brightness: Perhaps another approach is to think about the human eye's perceptions of intensity or brightness. The mathematical definition of intensity as the average or R, G, and B gives equal weight to the three channels but does the human eye perceive a 100% red patch as being as bright as a 100% green patch? And doesn't a 100% blue patch seem "darker" than a 100% green patch? How do patches of pure yellow, cyan, and magenta compare to each other? How much does one have to dim a yellow patch to have the same visual brightness as a 100% green or a 100% red patch?

B/W images of a MacBeth color checker: It might be useful/interesting to look at monochrome images (film or various digital monochrome treatments) of a color checker target ( macbeth color checker "black and white film" - Google Search ). These could show how different B&W processes vary in how they record the specific pigments of the color checker.
Forum: Digital Processing, Software, and Printing 09-02-2022, 04:35 AM  
Black & white conversion, what is right?
Posted By photoptimist
Replies: 24
Views: 1,151
To do it "right" you would need to pick a specific black and white film and then adjust the red, green, and blue levels to match that film's color response. Orthochromatic B&W films are not sensitive to reds while panchromatic B&W films are.

There's also the subtle issue of white balance: do you want a monochrome image of the subject as it was lit or as it would have appeared on B&W film without any color-correcting filters for the type of light source?
Forum: Photographic Industry and Professionals 08-31-2022, 11:28 AM  
Viltrox Says Canon has Demanded They Stop Selling RF-Mount Lenses
Posted By photoptimist
Replies: 113
Views: 3,710
In today's smaller (maybe-shrinking) market for standalone cameras, it's not surprising that a company like Canon would want to (maybe need to) ensure that it gets a cut of the revenues for every Canon-compatible lens or accessory.

One unintended effect of the short flange distances of mirrorless cameras is that it makes life much easier for third party lens makers. For most optical designs, there's plenty of room between the last element and the flange of today's mirrorless cameras. That makes it easy to design what-ever mount-specific tidbits that marry the optics to whatever body. A third-party lens maker can have much better economies of scale than Canon's in-house lens design and manufacturing operations if the 3rd party can instantly release versions of every new lens that can fit almost every mirrorless camera.

However, the body makers need lots of revenues to cover R&D on their very sophisticated electronics and firmware in their cameras. Body makers also need ongoing revenues from lens and accessory sales to pay for firmware updates and development of the next body.

As the camera industry consolidates, the camera makers may be forced to block 3rd parties to ensure their survival.

Sadly, tough times sometimes mandate tough tactics.
Forum: Pentax SLR Lens Discussion 08-28-2022, 05:13 AM  
Inputting the wrong focal length on older lenses
Posted By photoptimist
Replies: 7
Views: 488
The focal length setting controls the sensitivity of the SR system because the sensor motion needed to correct for camera shake is proportional to focal length.

That means if put in a slightly too-large value for the focal length, SR will slightly over-correct and your images won't be as shake-free as they could be. Likewise, if put in a slightly too-small value for the focal length, SR will slightly under-correct and your images won't be as shake-free as they could be.

The effects of slight over-corrections or under-corrections would only be noticeable at shutter speeds slower than about 1/focal_length.

In the case of inputting 28mm with a 24mm lens, the over-correction is only about 17%. If your experience with SR is that it removes say 3 or 4 stops of camera shake, a 17% over-correction would mean you'd get only about 2 or 2.5 stops of shake removal.

Now if you had accidentally used 200 mm as the focal length with your 24 mm lens, you might get some really shaky images. (Any input focal length that is MORE than twice the actual focal length will amplify the shake.) Even in that case of using 200 with a 24, you'd probably not notice any difference if the shutter speed was fast (e.g., faster than 1/200 second).
Forum: General Photography 08-27-2022, 05:17 PM  
Macro decision coming up, a question before I do it
Posted By photoptimist
Replies: 17
Views: 839
There's little difference in depth of field between the two focal lengths for macro magnifications. The whole "wide angles have deeper depth of field than telephotos" rule only applies to lower magnifications.

That said, a shorter focal length does encompass more of the (blurry) background behind the subject so the look can be quite different. Shots with the 50 will have more background objects than shots with the 100.

Another big issue with macro focal lengths is that it's a lot easier to get to high magnifications with a short focal length. A 50mm macro set for 1:1 and with 50mm of added extension tubes or bellows gets to 2X magnification. A 100mm macro set for 1:1 needs 100mm of extension tubes or bellows added to get to 2X magnification. High magnification macro (>3X) usually involves shorter focal length macro lenses to keep the camera-lens distance reasonable.
Forum: Pentax Medium Format 08-27-2022, 04:59 AM  
AF problems with Pentax 645z
Posted By photoptimist
Replies: 5
Views: 403
A couple of generic suggestions for how this could happen:

Dirt on the AF sensor lens: The AF sensor sits under the floor of the mirror box and has a lens that looks up into the mirror assembly. Dirt such as hair, threads, etc. on that lens will cause unreliable AF. That AF sensor lens can be cleaned with air (e.g., a little bulb blower) when the mirror is up for main sensor cleaning .

Loose mount: Any looseness or play in the lens mount (of the camera or the lens) can cause significant random shifts in the plane of focus. For example, if 55mm lens on a 645Z focused to 5 meters will shift to focusing at about 4.6 meters with just a 50 micron (the breadth of a human hair) shift of the lens-sensor distance.
Forum: Pentax SLR Lens Discussion 08-20-2022, 04:09 PM  
What is your forever lens?
Posted By photoptimist
Replies: 121
Views: 5,684
Gosh... I'd have to pick some sort of super-zoom even if they are big, slow, and not so sharp.

There are too many scenes that demand an ultrawide focal length, too many scenes that demand a telephoto, and too many scenes in between to settle for anything less than a good range of focal lengths.

I had a 28-200 on my last film camera (OM-4Ti), a 28-200 equivalent on my first digital camera (Minolta Dimage), and an 18-200 on my first Pentax camera (K10D), so I'd have to pick something like that for this challenge.

Can someone please please please make a 12-300?
Forum: Pentax SLR Lens Discussion 08-20-2022, 04:40 AM  
Suggestions for Testing a Bunch of Teleconverters for Resolution
Posted By photoptimist
Replies: 12
Views: 571
What a wonderful idea!

You've already got a good handle on what to do. A few ideas:

1) Use pixelshift: PS provides a more rigorous test of the resolution of the lens and also avoids the color moire issues created by a high-resolution B&W target with a Bayer filter sensor.

2) Thoughts on lens selection: Every teleconverter has a design value for the location of the nodal point of the exit pupil of the mounted lens. Lenses that have a much shorter exit pupil (e.g., compact wide-angle lenses) or much longer exit pupil distance (some telephoto lenses and many telescopes). Pentax' own recommendations for compatible lenses with it's DA 1.4X AW (HD PENTAX-DA AF REAR CONVERTER 1.4X AW / Converter / AF Lens Adapter / K-mount Lenses / Lenses / Products | RICOH IMAGING) list a number of lens that may fail to focus even with contrast AF -- a sure sign that not all teleconverters work with all lenses. Your instinct to use the A 135 is probably good but you might try some of the other lenses in your bag to see if some just happen to be very sharp on the teleconverter.

3) Max aperture and vignetting test: The location and diameter of the front element of a teleconverter determines that maximum aperture it can handle (e.g., a teleconverter with small front element will clip the wide cone of light coming from a wide-open f/1.4 lens. The overall design of the teleconverter determines how much it vignettes, too. Pentax recommendations note that some lenses don't work at apertures larger than f/2.4 on the DA 1.4X AW. Shooting a uniformly lit target at a range of apertures (with reciprocal shutter speed) can detect these effects as dimming of the corners and under exposure at larger apertures.

4) An "extra credit" astrophotography shot. Bright infinitesimal pinpoints against a deep black background provide a stringent test for all sorts of aberrations. Any fat tails in the point spread function will be much more visible in an astrophotograph.

5) Extra credit stacking: As long as you've got your set-up in place, you might try stacking two teleconverters. OK, 8 teleconverters create 36 possible pairs (or 72 if you test A-in-front-of-B and B-in-front-of-A) so that's too much! But maybe you could test a few of the best teleconverters with stacking.

Have fun!
Forum: Pentax Medium Format 08-15-2022, 07:22 AM  
Dirty P67 55-100
Posted By photoptimist
Replies: 2
Views: 278
That is almost certainly dirt on your sensor (not the lens) as seen with the lens stopped all the way down.

Two tests to try:

1) Test another known-good lens with the aperture stopped down as small as possible (f/22 or smaller). I'd bet you'll get a picture with the same pattern of spots and threads although they might be fuzzier and fainter depending on the exact aperture and subject matter.

2) It's possible that the aperture mechanism on your P67 55-100 is malfunctioning -- stopping down more than it should. You can test that by looking into the lens while shooting at a large aperture (e.g., f/4.5 and then maybe f/8) and watching to see if the aperture iris inside the lens stays open or closes down smaller than it should.
Forum: Pentax SLR Lens Discussion 08-12-2022, 09:15 AM  
Turning K-3/3 into street camera :)
Posted By photoptimist
Replies: 28
Views: 1,381
The 21 versus 40 is a personal choice that depends on your tastes in FoV (21 gets more of the background and has more depth of field) and your personal comfort in approaching the subject (40 lets you be a bit further from people and provides more subject separation).

Your 20-40 gives you a unique opportunity to try both focal lengths before your buy another lens. If you go out and shoot a bunch of street shots, zooming as you see fit, you can see which focal lengths you use most. You might naturally tend to use the 20 end or the 40 end or discover that you gravitate toward the middle and should buy something like a 28. Another test is to set the zoom at some focal length and tape it down and then spend some time shooting to see which focal gets more keepers and has less frustrating lost opportunities.

Either approach will help you find a prime focal length that works for you (or discover you can't live without the zoom).

Good luck!
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