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02-09-2021, 10:34 AM - 1 Like   #181
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QuoteOriginally posted by biz-engineer Quote
I think I should do the same. Although I prefer to compare lenses before I would buy them. One of the thing I've noticed , while looking at many lenses, they all are sharp in the center and softer away from the center, even the very best ones. It looks like optics are such that flat lens performance would require proportionally very large elements or using lens machinery especially sized for processing larger lens elements. I can't prove it, but I guess the same machines are used for making lens elements for apsc , full frame or medium format lenses. As a result, the smaller formats benefit from getting the most accurate part of the lens making process, and the large format lens gets the borders of what the machine can do?
Getting good performance everywhere on a focal plane when also trying to achieve a low f/# requires glass nominally larger than the focal plane diameter and relatively telecentric imaging design. This implies a large throat (flange) and glass close to the detector. This is easier with mirrorless.

There are optical grinders and polishers sized all the way to large astronomical telescopes. I don't think curvature errors increase toward the glass edges (which may or may not be relevant only to focal plane edge performance. Rather, the actual need at low f/# and wide field is aspherical curvatures, significantly more expensive to grind and polish -- at least beyond the level of correction that diamond turning can achieve. And while we are making the perfect diffraction limited spot, we need to do it at multiple wavelengths using glasses (and possibly plastics) that are not available in every possible index of refraction and dispersion. The design has to be tolerant of thermal effects. The design has to be manufacture-able and affordable to the customer base.

One can see this principle in action on the Arsat 30/3.5 fisheye. Huge glass is needed for what is at maximum an 8.6-mm aperture. No matter how perfectly the glass was poured to spec, ground and polished to spec, and spaced to spec, there would be a limit to performance for a finite number of lenses with spherical curvature. The sharper 645 D-FA 25mm f/4 uses at least one aspheric to gain some improved resolution. At maximum, it only provides a 6.25-mm aperture. In both cases, for each point on the focal plane these tiny apertures are centered on corresponding points on the outer lens surface. So each path to any point on the focal plane has to have the same behavior, including the same light time-of-flight for all rays.

02-09-2021, 01:35 PM - 2 Likes   #182
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QuoteOriginally posted by barondla Quote
I've always thought star tests were one of the ultimate tests of lenses. Recently I read something here that has me confused. The earliest Pentax 6x7 lens is only a 4 element design and only decently sharp. It is rated much lower than the newer 200. However, 2 different reviews talk about how amazing the 4 element is for shooting the stars. One even discusses how the lens doesn't clip a color channel like most do. So here it seems a so so lens does well for astrophotography. I wouldn't have thought that possible.

Have you used this lens? Have you encountered the color channel clipping with other lenses?

Here's the link: S-M-C Takumar 6x7 / Super Takumar 6x7 200mm F4 Reviews - 67 Telephoto Primes - Pentax Lens Reviews & Lens Database.

Thanks,
barondla
This issue shows the subtlety of what makes a great lens, especially great one for astrophotography.

When we look at "good" astro photographs, the stars look to be of different sizes. Nearby bright stars appear to be larger balls and only the distant faint stars appear as tiny points. That's very intuitive to us because our own human eyes tend to see bright stars as "bigger" then faint stars.

In theory, however, the ultimate ultra-sharp lens would render all stars as almost infinitesimal points of light. With the perfect lens, even a physically large and nearby red giant star such as Betelgeuse (which is 764X the diameter of the sun and only 548 light years away) would be a pinprick only 0.2 microradians (1/25th arcseconds) across which is a very tiny fraction of a pixel on a 645Z with a 200mm lens. A perfectly sharp lens would concentrate all the light from a bright star such as Arcturus into a single pixel. For most color cameras, that would either be either a red, green, or blue pixel of a Bayer filter. A bright star would saturate that one color pixel and render the star as a single RGB dot regardless of the star's original color. If the camera has a low-pass filter designed to prevent these kinds of Bayer pattern artifacts, the star be spread over about 2x2 pixels and be white.

In real lenses, diffraction blurs the stars (as does atmospheric turbulence) but a diffraction-limited f/4 lens would still be too sharp to properly render the true colors of bright, nearby stars. With a perfect 200 mm f/4 lens, bright stars such as Betelgeuse would still render as white points a couple of pixels across.

What makes the best astro lenses are lenses that are pretty sharp but not too sharp. More importantly, they have perfectly circular point spread functions (PSF) that have a nice central peak (essential for rendering faint stars as a rich field of points rather than invisible blobs) and broad enough tails on the PSF to smear the bright stars into color-preserving balls. Most importantly, the best lenses have a uniform PSF across the field so that all stars have the identical shapes and sharpnesses.

The importance of a circular and uniform PSF carries over into other types of photography. Non-circular aberrations and non-uniform aberrations create noticeable center-to-corner variations in the appearance of the image. With non-circular aberrations and non-uniform aberrations, textures might be sharp in the center, fuzzy on some edges, and have strange smearing that differs across the image.


TL;DNR: Great lenses don't need to be perfectly sharp but they do need to be very uniform and have blur that are very circular.
02-09-2021, 06:18 PM - 1 Like   #183
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QuoteOriginally posted by photoptimist Quote
This issue shows the subtlety of what makes a great lens, especially great one for astrophotography.

When we look at "good" astro photographs, the stars look to be of different sizes. Nearby bright stars appear to be larger balls and only the distant faint stars appear as tiny points. That's very intuitive to us because our own human eyes tend to see bright stars as "bigger" then faint stars.

In theory, however, the ultimate ultra-sharp lens would render all stars as almost infinitesimal points of light. With the perfect lens, even a physically large and nearby red giant star such as Betelgeuse (which is 764X the diameter of the sun and only 548 light years away) would be a pinprick only 0.2 microradians (1/25th arcseconds) across which is a very tiny fraction of a pixel on a 645Z with a 200mm lens. A perfectly sharp lens would concentrate all the light from a bright star such as Arcturus into a single pixel. For most color cameras, that would either be either a red, green, or blue pixel of a Bayer filter. A bright star would saturate that one color pixel and render the star as a single RGB dot regardless of the star's original color. If the camera has a low-pass filter designed to prevent these kinds of Bayer pattern artifacts, the star be spread over about 2x2 pixels and be white.

In real lenses, diffraction blurs the stars (as does atmospheric turbulence) but a diffraction-limited f/4 lens would still be too sharp to properly render the true colors of bright, nearby stars. With a perfect 200 mm f/4 lens, bright stars such as Betelgeuse would still render as white points a couple of pixels across.

What makes the best astro lenses are lenses that are pretty sharp but not too sharp. More importantly, they have perfectly circular point spread functions (PSF) that have a nice central peak (essential for rendering faint stars as a rich field of points rather than invisible blobs) and broad enough tails on the PSF to smear the bright stars into color-preserving balls. Most importantly, the best lenses have a uniform PSF across the field so that all stars have the identical shapes and sharpnesses.

The importance of a circular and uniform PSF carries over into other types of photography. Non-circular aberrations and non-uniform aberrations create noticeable center-to-corner variations in the appearance of the image. With non-circular aberrations and non-uniform aberrations, textures might be sharp in the center, fuzzy on some edges, and have strange smearing that differs across the image.


TL;DNR: Great lenses don't need to be perfectly sharp but they do need to be very uniform and have blur that are very circular.
Fascinating, and your explanation makes perfect sense. Before reading the reviews, I was a little bummed to find my 6×7 was the 4 element. Now I'm looking forward to trying some astrophotos.

Thanks again for the explanation,
barondla
02-10-2021, 12:29 AM - 3 Likes   #184
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The different sizes of stars aren’t a distance effect. All stars are practically at infinity to camera lens. They have different sizes in the image because they have different brightness. The point-spread function of stars is never an infinitely small point. Brighter stars have brighter outer parts of the PSF so they appear bigger. The outer part of the PSF is not necessarily caused by diffraction. It can be caused by the atmosphere (scatter and turbulence, depending of the location and focal length), by the lens, or by scattering in the sensor or film (particularly worse on color reversals).

I don’t have experience on the 4-element 200mm lens. However, I had used the newer 200mm. It’s OK on 645z, provided that its lens elements are well aligned. Overall, all Pentax 67 lenses that I had used on 67 film are excellent, but poor on 645z. At least in astrophotography, film is much more forgiving to imperfect optics. These 67 lenses either were not designed to satisfy modern CMOS sensors, or their manufacturing accuracy does allow them to last long enough. The 200mm lens I tried had misaligned lenses and a tilted focal plane. This is easily visible on images of stars. Indeed, many 67 lenses I tried on 645z or FF DSLRs have such troubles, leading me to believe that they should stay with film. So far, among the about 20 various film lenses that I had tried on 645z, GFX50R, or FF, the only one that’s still acceptable (in terms of resolution only) is the Mamiya 645 300/2.8. Everything else failed.

02-19-2021, 03:19 PM   #185
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I should be getting the Fuji early March. Been doing and frying on it. Will get an adaptor and hold on to the 80 - 160, FA 200, A*300 and the FA 400... Considering which to hold on to as a back up, the Sony or the Z. Advice I have received is to keep the Sony.
02-20-2021, 03:48 AM - 1 Like   #186
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at the end of the day fuji gfx is overrated! (i'm a pentax 645z owner too...with all the newer digital 645 lenses + *300 and 45 in 67! i can use the 45 as a tilt/shift solution on my 645z! i'm using sony alpha like you do! and it's not a matter of money! but sony fullframe is great, especially my f2.8 400gm. and wih my cambo a can use all of my 645/67 lenses as a tilt/shift solution) so i think it makes no sense to change the system because the fuji lens-roadmap is not very special. as a "pro-company you NEED nativ tilt/shift lenses and a lot of fast lenses for sure!)

if i would like to use the best of the best, i'd use REAL medium format! a phase one xt...!

but in real life, i'm using only 30% of my cameras possibilities - despite i do fine art pigment prints up to dinA0! but the truth is, my mac pro late 2013 with 48gb ram is limitating!!!

so i'll never go up to 100mp because if you want to you can stitch pictures or shift a larger picture!

and you can lend such a monster if you want easy cheese! ;-)


QuoteOriginally posted by itshimitis Quote
I should be getting the Fuji early March. Been doing and frying on it. Will get an adaptor and hold on to the 80 - 160, FA 200, A*300 and the FA 400... Considering which to hold on to as a back up, the Sony or the Z. Advice I have received is to keep the Sony.
02-20-2021, 06:20 PM   #187
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QuoteOriginally posted by Foamberg Quote

but in real life, i'm using only 30% of my cameras possibilities - despite i do fine art pigment prints up to dinA0! but the truth is, my mac pro late 2013 with 48gb ram is limitating!!!
You need 128gb ram minumum and dedicated GPU if using something like On1 RAW, C1pro that can take advantage of a multi threaded and GPU acceleration.


Macpro 2013 uses what 2 8core Xeons and you can upgrade to 64gb max on them I think. Not sure on the GPU though.

02-21-2021, 03:40 PM   #188
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Was wondering why today's cameras still rely on external memory cards. If we look at the progress path of smart phones then eliminating the need for external sd cards on cameras seem to be a logical next step.

Hard wired internal memory would also be a lot faster, and has the potential to be more reliable as well.

Thoughts on this?
02-21-2021, 04:16 PM - 2 Likes   #189
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QuoteOriginally posted by TDvN57 Quote
Was wondering why today's cameras still rely on external memory cards. If we look at the progress path of smart phones then eliminating the need for external sd cards on cameras seem to be a logical next step.

Hard wired internal memory would also be a lot faster, and has the potential to be more reliable as well.

Thoughts on this?
Cards for me thanks. I can take my cards home with me and load them onto my desktop, and leave the cameras at work when I need to. But it could be nice to have some form of internal memory---would certainly solve the "forgot to put a card in the camera" problem, and the camera could write over to the card. Depending on the mp count, I'd say at least 256 if not 512 for internal memory.
02-21-2021, 07:50 PM - 1 Like   #190
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QuoteOriginally posted by texandrews Quote
Cards for me thanks. I can take my cards home with me and load them onto my desktop, and leave the cameras at work when I need to. But it could be nice to have some form of internal memory---would certainly solve the "forgot to put a card in the camera" problem, and the camera could write over to the card. Depending on the mp count, I'd say at least 256 if not 512 for internal memory.
You'd need 8TB in some cameras, especially with 16 bit RAW 102mp files. I've not long upgraded to a new Mac with 64GB RAM and 4TB SSD.
02-22-2021, 01:12 AM - 1 Like   #191
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QuoteOriginally posted by TDvN57 Quote
Was wondering why today's cameras still rely on external memory cards. If we look at the progress path of smart phones then eliminating the need for external sd cards on cameras seem to be a logical next step.

Hard wired internal memory would also be a lot faster, and has the potential to be more reliable as well.

Thoughts on this?
Hard wired memory isn't necessarily faster, and it's definitely *slower* when it comes to transferring to the computer. Heck, on the phone I run apps from the SD card, no speed difference.

Not only that, it's not even really a trend. It's mostly Apple doing it and it's exclusively for the cash...
02-22-2021, 08:03 AM - 2 Likes   #192
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QuoteOriginally posted by itshimitis Quote
You'd need 8TB in some cameras, especially with 16 bit RAW 102mp files. I've not long upgraded to a new Mac with 64GB RAM and 4TB SSD.
Those numbers seem extreme to me. 8TB in the camera? I think I get something like 2,000 images an a 256mb card with my Z. It's very unusual that i would go over 500 shots on a shoot with that camera...
02-22-2021, 08:16 AM - 3 Likes   #193
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QuoteOriginally posted by TDvN57 Quote
Was wondering why today's cameras still rely on external memory cards. If we look at the progress path of smart phones then eliminating the need for external sd cards on cameras seem to be a logical next step.

Hard wired internal memory would also be a lot faster, and has the potential to be more reliable as well.

Thoughts on this?
Here are five reasons cards are better:

Cards work everywhere: Most of my photography happens out of cell-phone range.

Cards are cheaper: Most cellular data plans have monthly data caps far below the number GB/month I'd need for photography. Worse, "data roaming charges" are excruciatingly expensive during foreign travel.

Cards have unlimited capacity: Any fixed-sized camera memory is going to be a problem on a heavy photoshoot -- high-resolution cameras can gather data much faster than cellular data can clear the buffer.

Cards are simpler: A card-less camera would require an internal digital asset management system (DAM) to track which images have been successfully transferred so the local copy can be deleted to free up precious buffer space. The photographer would have to totally trust the DAM and their cloud storage provider because glitches in either would mean loss of images. The camera's DAM also requires a user interface and some way to tell the photographer that they can't turn-off and pack-up the camera because it's still in the middle of moving files. That UI, including audible alerts, would also need to tell the photographer that they must put in a fresh battery in order to fully transfer all their images.

Cards take less battery in the field: With cards, the image is written once to flash memory where it is safe if the camera is turned off or runs out of battery power. With buffer+wireless, the camera has to write the image to internal flash memory (to make a power-safe local copy), then read that image from flash memory, and send it over the wireless link. That's three power-consuming tasks for wireless versus one task for the card.


That said, it would be really nice if camera makers offered some sort of modular system so a photographer could add an SSD, 5G cellular, or WiFi6 module to their system. The only remaining difficulty is in where to put the antennas required for high-speed wireless transfer so that the photographer's hands, head, or body don't block the signal.
02-22-2021, 01:35 PM   #194
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I am not sure that the suggestion was for wifi necessarily...? Wasn't the core suggestion for on-board storage of images on the camera? How we get them from the camera to a computer (cable, wifi, card transfer, etc.) is another question.
02-22-2021, 02:02 PM - 2 Likes   #195
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QuoteOriginally posted by Ed Hurst Quote
I am not sure that the suggestion was for wifi necessarily...? Wasn't the core suggestion for on-board storage of images on the camera? How we get them from the camera to a computer (cable, wifi, card transfer, etc.) is another question.
Indeed!

However, having the only copy of one's precious images (and your postings prove that your images are especially precious) stuck inside some chips inside the camera seems like a huge source of risk due to theft, robbery, electronic gremlins, gravitational misadventure, or the ocean's malicious tendency to throw salt water on anything within reach. Sure, Pentax makes very robust bodies (my K-5 survived a direct hit from the ocean), but.... who wants to press their luck. Main board damage or corrosion would render one's images inaccessible without heroic efforts and costs.

Thus, cards have the sixth advantage of being fairly independent of the camera body: Cards can be easily removed for safe keeping, have their own mechanical integrity as an added layer of protection from damage, and seem less prone to corrosion than the powered internals of the camera.
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