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Forum: Monthly Photo Contests 10-08-2023, 07:00 PM  
Brussels Jazz Marathon
Posted By JohnI
Replies: 4
Views: 55
I stumbled on the Jazz Marathon while in Brussels for business. The main stage was set up in the city's Grand Place in front of the gothic-styled town hall, built in the 15th century.
Forum: Monthly Photo Contests 09-08-2023, 08:17 AM  
Why pedal?
Posted By JohnI
Replies: 12
Views: 42
Machilipatnam, India, May 2011
Forum: Monthly Photo Contests 05-10-2023, 08:27 AM  
Sailing ship mast reflected
Posted By JohnI
Replies: 51
Views: 367
Love the contrast between different eras of technology!
Forum: Monthly Photo Contests 05-05-2023, 05:47 PM  
Fenętre troglodytique - Vouvray
Posted By JohnI
Replies: 22
Views: 164
Troglodyte in France refers to people who live in caves, especially those along the Loire River. Many cave dwellings have a front entrance that looks just like an ordinary house, or only part of the residence is actually in the cave.
Forum: Monthly Photo Contests 04-25-2023, 02:24 PM  
Bottom of the Bean
Posted By JohnI
Replies: 11
Views: 132
The official name of Chicago's famous sculpture is Cloudgate. I'm in this photo in at least six places - possibly more!
Forum: Post Your Photos! 04-25-2023, 10:42 AM  
Nature a bug, all I need is a bug
Posted By JohnI
Replies: 10
Views: 566
Looks like a Northern Flicker (Colaptes auratus). Seems they're the only woodpecker relative that sometimes hops on the ground searching for food! See https://en.wikipedia.org/wiki/Northern_flicker This is a common bird in Wisconsin where I grew up.
Forum: Winners' Showcase 03-08-2023, 01:19 PM  
March, 2023 Third Place: Tetons and Trees
Posted By JohnI
Replies: 36
Views: 223
Converted from color image with modified yellow filter in Photoshop CS5.
Forum: Post Your Photos! 02-28-2023, 12:45 PM  
Nature Camellia - Double Blooms
Posted By JohnI
Replies: 16
Views: 494
Nice shot! I like the slightly mottled lighting. It looks like the "Pink Perfection" cultivar. We have a bush in front of our house in southern California, and it is as large now as it was in 1983 when we bought the house ... it must be at least 60 years old! I've seen double and even triple back-to-back blooms, and have taken many beautiful pix with my Pentaxes over the years.
Forum: Winners' Showcase 08-16-2022, 11:40 AM  
July, 2022 Winner: Vacation
Posted By JohnI
Replies: 77
Views: 537
I would like to nominate this photo
Forum: Monthly Photo Contests 08-16-2022, 11:40 AM  
vacation
Posted By JohnI
Replies: 37
Views: 417
I would like to nominate this photo
Forum: Monthly Photo Contests 08-15-2022, 03:42 PM  
Sunset over Nazareth
Posted By JohnI
Replies: 4
Views: 90
Took this from Mount Precipice while on a tour of Israel in 2015. The large building in the center foreground, with the dark conical roof, is the Church of the Annunciation.
Forum: Monthly Photo Contests 06-02-2022, 10:45 AM  
Tate Britain Gallery ("Old Tate"), London
Posted By JohnI
Replies: 23
Views: 213
Gotta love those spiral staircases! This one was modern and sleek, but rather bland without some photoshopping.
Forum: Pentax SLR Lens Discussion 02-22-2022, 11:25 AM  
Recommended lenses for astro and planetary photography
Posted By JohnI
Replies: 19
Views: 6,525
I've gotten good astrophoto results from this now-discontinued lens. Needs to be stopped down a bit for good star images. The attached shot of the heart of the Milky Way (Scutum-Sagittarius-Scorpius) on my K5 was 250 seconds at f2.2. From DNG camera raw file. Camera mounted on an iOptron SkyTracker. Location: Puako on the Big Island.
Forum: Monthly Photo Contests 01-04-2022, 03:00 PM  
Fogbow, seen from a cruise ship in Alaska
Posted By JohnI
Replies: 5
Views: 206
On deck 9 of our cruise ship, we were just above the low-level fog. Rainbow colors are faintly visible.
Forum: Post Your Photos! 12-14-2021, 07:09 PM  
Pets Who's that?
Posted By JohnI
Replies: 4
Views: 762
Looks like a tribble!
Forum: Photographic Industry and Professionals 12-08-2021, 12:41 PM  
Chromatic Aberration Corrective Coating
Posted By JohnI
Replies: 9
Views: 697
I looked at the phys.org article and found it quite interesting. However, I'm wondering about the mathematical dependence of the "delay effect" on wavelength, and I suspect that it may be proportional or inversely proportional to wavelength. That is the effect you get with a diffractive optical surface, often called a "DOE" (diffractive optical element) or "kinoform" by optical designers. You can use a DOE to cancel out the chromatic aberration of a single refractive lens element, but the cancellation can be perfect at only two wavelengths, because the dependence of glass's refractive index on wavelength is decidedly nonlinear. This leaves a residual chromatic aberration known as secondary color ... the bane of any long F.L. refractive system ... which also occurs with an ordinary achromat comprising crown and flint glasses. The ED glasses (fluorocrowns, generally) have a different nonlinearity that can produce less secondary color when combined with more ordinary glasses, and that's why they're used in most long F.L. telephotos. I know that Canon has experimented with incorporating DOEs in their lenses, though I don't know if any current production lenses use them.
I agree with Bob256 that the physical structure of the coating in the article would make it very prone to clogging with contaminants, so anything like that in a photographic lens would be used on a sealed internal surface, which I think is what Canon did for DOEs as well. BTW, DOEs are routinely used in infrared systems, as the elements are often fabricated with single-point diamond turning (basically a super-precise lathe), and most IR materials are machinable that way.
Forum: General Photography 11-23-2021, 10:40 AM  
Macro lens vs reverse ring
Posted By JohnI
Replies: 26
Views: 1,328
I bought one of these manual focus macro lenses a number of years ago, after reading a glowing review in Popular Photography. I think I paid <$50. I use it primarily for flowers, where the 1:2 maximum magnification really isn't a limitation. Without autofocus, it's not the best for insects, though I have gotten some good shots of spiders and praying mantises with it. For flowers, autofocus is almost superfluous. The attached photo of a rose is a 1200x900 pixel crop from a 6MP K100D image; the macro magnification was probably about 1:5.
Forum: Troubleshooting and Beginner Help 08-11-2021, 09:48 AM  
Polarizer Filter = More Vivid Colors?
Posted By JohnI
Replies: 43
Views: 2,808
Skylight from a clear sky is partially polarized (and blue) due to Rayleigh scattering. The polarization fraction (i.e, percentage of the light that is polarized) depends on the angle between the viewing direction and the direction of the sunlight, and is maximized at 90 degrees from the sun. When you shoot with a narrow-angle (telephoto) lens, this observer-to-subject-to-sun angle is relatively constant across the entire photo, and you can get uniform sky darkening with a polarizer. With a wide-angle lens, the observer-to-subject-to-sun angle can vary a lot, and you'll generally see a dark blue band running across the frame, often at a funky-looking angle. If you've got the sun directly behind you, the dark band of maximum polarization will be approximately parallel to the horizon and more "natural looking," which is shown nicely in Richard L's photo of the church. Here are some nice references: Blue Sky and Rayleigh Scattering The polarization of the sky
And if want to get more technical: Rayleigh sky model - Wikipedia
Forum: Monthly Photo Contests 06-01-2021, 11:23 PM  
Architecture photo entry
Posted By JohnI
Replies: 14
Views: 372
New Munich synagogue
Forum: Post Your Photos! 12-15-2020, 09:49 AM  
2021 Pentax Lens Tournament 60-250 f/4 Zoom!
Posted By JohnI
Replies: 0
Views: 161
SMC Pentax-DA* 60-250mm F4 ED [IF] SDM Reviews - DA Zoom Lenses - Pentax Lens Reviews & Lens Database

I love this lens! It's particularly good for photographing stained glass windows.
My copy is very sharp, even wide open and even at 250mm, and the FL range makes it handy in a wide variety of situations.
Forum: Photo Critique 10-26-2019, 05:53 PM  
Night Light trails attempt
Posted By JohnI
Replies: 25
Views: 1,253
Looks like more traffic would have helped the photo. Here in the Los Angeles area, that would not have been a problem!
Forum: Photographic Technique 05-18-2017, 03:28 PM  
Macro lens for macro photography (K10D body)
Posted By JohnI
Replies: 19
Views: 2,244
I also have the manual focus Vivitar 100mm f/3.5 that is also sold under other brand names, as mentioned previously by tryphon4. Although it is a very inexpensive lens, it's quite sharp, and I've used it for many of the flower photos on my website. I bought it because of a favorable review in Popular Photography. I appreciate the long working distance that a 100mm lens gives me.
Forum: Monthly Photo Contests 12-18-2012, 12:46 PM  
Snowy Austrian Forest
Posted By JohnI
Replies: 0
Views: 504
Taken 1 Dec 2012 just west of the Austrian town of Eben, south of Salzburg. Snowfall the previous night amounted to about an inch.
Forum: Monthly Photo Contests 01-12-2012, 12:49 AM  
Yellowstone River - June 2010
Posted By JohnI
Replies: 0
Views: 634
Taken from the north side - I forget which overlook - in the early evening when the canyon was already in shadow. Color boosted in Photoshop CS5.
Forum: Monthly Photo Contests 11-30-2011, 01:41 PM  
San Joaquin River Delta
Posted By JohnI
Replies: 1
Views: 991
Original shot taken from a Southwest Airlines flight just west of Stockton, CA. "Enhanced" in Photoshop CS5.
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