Forgot Password
Pentax Camera Forums Home
 

Showing results 1 to 25 of 300 Search:
Forum: General Talk 05-30-2018, 06:45 PM  
The shocking truth about our Australian members. It's all a sham!!
Posted By wombat2go
Replies: 332
Views: 6,344
I am just a poor boy escaped that fake place
Simon & Garfunkel Lyrics - The Boxer

Men At Work - Land Down Under Lyrics | MetroLyrics
from a land down under
Where women glow and men plunder

Wandering around far too long
in hallowed places like the People's Republic of MeiGuo and the United States of ZhōngGuˇ

Oh yes, I am so happy to exit that fake place and join the real worlds
of brilliant politicians, enlightened populaces and splendidly altruistic medias

that i might just take the white Hoki R and go out among the blight and ignorance and run 20 red lights in their honor.
The Rolling Stones Lyrics - Far Away Eyes
...
And if you're downright disgusted
And life ain't worth a dime
...
Well, YOU KNOW what kind of eyes she got. ....
Forum: Pentax Medium Format 02-10-2018, 09:39 PM  
Home made 67II grip
Posted By wombat2go
Replies: 7
Views: 680
Here is how I made the grip for the RB67:
https://app.box.com/s/j8s76dmrtqgvkwekalmsx9hittdfa63q
https://app.box.com/s/9pfqhb9tlfkxen01pg8nv9zd6fugy7ho
That camera has recesses for locating spigots on each side of the 1/4 20 screw.
The L bracket was of welded steel and the hand grip was 6061 turned on the lathe.

The grip aids stability for hand held shots.
Also, it allows the camera to be hand carried out of the bag.
Forum: Photographic Industry and Professionals 11-24-2017, 08:36 PM  
Camera design problem at heart of Sony A7RIII sensor issues (raw cooking not enough)
Posted By wombat2go
Replies: 19
Views: 1,817
Hi P/O
I appreciate your comments and look forward learning about it and going out and taking some astro photos with my humble gear here.
My counterpoint
Nyquist & Shannon might disagree.
It is like saying you are going to hear your friend playing the drums in another state by phoning him every 2 seconds and hanging up after every second.

If it were possible that one pixel in a Bayer cell would be illuminated by a point source through a sharp 40mm lens,, with dark levels on all other pixels:
Firstly the level in that pixel will be attenuated by the Bayer filter, while other colors remain dark except for cross-talk.
Secondly the de mosaic will load the surrounding Bayer cells by ( let us say) linear interpolation.
Thirdly, the illuminated pixel will show little true color except its primary.
So we get a "smearing" which reduces the resolution to a level between the monochrome Nyquist and the Nyquist of the Bayer.
( My ref: Holst & Lomheim, who give detailed explanations about the Nyquist frequencies of the various arrays)

Today I looked at some wide angle astro images on inet . Most are blurred by being very low resolution jpgs.
Some (including Nasa) showed over exposed bright stars with aperture artifacts etc. I think they do this to show the point source stars.
Regards
Forum: Photographic Industry and Professionals 11-24-2017, 06:32 PM  
Camera design problem at heart of Sony A7RIII sensor issues (raw cooking not enough)
Posted By wombat2go
Replies: 19
Views: 1,817
Yes,
The Nyquist for monochrome is then about 46 arcsec and for Bayer cell is about 1.6 times that = 73 arc sec.

I used the diagonal out to the corner to get the 40mm AOV so my numbers were more conservative, using 80 arcsec for the Bayer.
Then FWHM of 3 pairs = 240 arc secs for smallest extended sources.
Forum: Photographic Industry and Professionals 11-24-2017, 05:39 PM  
Camera design problem at heart of Sony A7RIII sensor issues (raw cooking not enough)
Posted By wombat2go
Replies: 19
Views: 1,817
I read a bit about it today.
I am a bit interested to do some astro photos because there is a dedicated viewing area opened up on northern Michigan coast.
However I will wait till spring or so , not wanting to freeze out in the cold now.

The bare human eye resolves about 120 arcsec.
The Full Width Half Max (FWHM) of an extended source needs to be at least 3+ pixels for any sharpness from a camera.
- But I think there are not many extended sources out there ?

The A7R 111 has a Bayer Nyquist of about 60 line pair /millimetre
So putting the numbers together ( my calculations) , the A7R 111 with a 40 mm lens would need an extended source of about 270 arc sec for good resolution.

A pixel pair in the A7 R 111 is about 160 arcsec. So any point source ( provided the lens is not rolling down at 60+linepair/mm) will occupy maybe 2+ pixels.

I read the o/p's links a couple of times and i don't see how the very low roll off out to the Nyquist as shown by the authors, would cause their stars to disappear.
Maybe they have an unrecognised system problem like their post processing software or are using 8 bit monitors with low level images.
Forum: Photographic Industry and Professionals 11-24-2017, 09:02 AM  
Camera design problem at heart of Sony A7RIII sensor issues (raw cooking not enough)
Posted By wombat2go
Replies: 19
Views: 1,817
Quite extensively?

The Nyquist of the A7 111 is about 110 line pair per mm?
With Bayer it is about 60 / mm?

The graphs produced in the referenced report by a 3rd party, if accurately depicting the filter based on dark noise alone,
show a roll-off with shutter speeds at 30 seconds of approximately minus 0.8 dB/Octave.
That is 0.192 of a "stop" per octave of spatial resolution.

And what lenses and mounts and atmospherics are going to give 100+line pair/mm over 30 seconds on a 35mm camera?

I don't know anything about astro photography so I would be interested to hear about typical
resolution of high performance astro lenses and sensors.
Forum: Digital Processing, Software, and Printing 11-05-2017, 08:50 AM  
Question for Darktable (under Linux) users
Posted By wombat2go
Replies: 10
Views: 611
Hi Mack,

There are a huge range of operators for distortion on the command line using convert utility

The one you might need is -distort barrel "A, B, C" where the 3 coeffs are for 3rd, 2nd and 1st order radial distortions
If the radial coeffs are not avialble for your lens , you can find the coeffs by trials ( usually 3rd order is the main one)

Here are some examples of crazy overcorrections
original img: (XR Rikenon 1:3.5 28mm uncorrected
https://app.box.com/s/ievjf7xtl8y5ik7uglpjiwthdnqidd36

positive 3rd order radial overcorrection:
ZZ@localhost Barrel_Example]$ convert IMGP0206.JPG -distort Barrel "+0.5 +0.5 -0.5" My_barreledCrazy1.JPG
https://app.box.com/s/dk2wvaqsrx2j2bknsfh3tpa8w98swgis

negative 2rd order radial overcorrection:
ZZ@localhost Barrel_Example]$ convert IMGP0206.JPG -distort Barrel "-0.0 -0.5 -0.5" My_barreledCrazy2.JPG
https://app.box.com/s/91ghuz6hmg6mvnqtwsuanx9qnwp9fmfz
Forum: Pentax SLR Lens Discussion 11-01-2017, 07:26 PM  
How 'Bad' is DAL 18-55 vs Other Options?
Posted By wombat2go
Replies: 67
Views: 2,886
I have already commented on this thread that in my opinion the early 18~55 lens is not very good .
(Not even by my rather relaxed standards!)

Now I would respectfully comment with counterpoints to the "experts" about Weather Resistance on low cost K-lenses.
I used K and -M lenses on Pentax film and dslr cameras since 1979, that is 38 years.
The first K and M lenses I purchased years ago are a bit worn superficially but show no signs of water damage or corrosion.
I still use them.
I used these lenses in : rain, steel mills, zinc coating mills, tropical countries, surf beaches, and most relevantly, water skiing.
Some of my old lenses travelled maybe 400,000 air miles.
In water skiing the lenses and the Pentax K- mount cameras were subject to water spray and often deluge water,
then were stored in a wet bag usually.

So I would invite comments about why a Pentax K- amateur user would ever need a WR lens.
Forum: Photographic Industry and Professionals 11-01-2017, 04:58 PM  
Nikon firing nearly 10% of photo staff and shutting down DSLR lens / compact plant
Posted By wombat2go
Replies: 70
Views: 3,071
My opinion:
For most people, anything with interchangeable lenses is a crank handle gramophone.

Working with young people including engineers, Taipei, Osaka, Wuxi, Shanghai, Australia and various places in USA , with Pentax K-S1
I saw that they can switch the camera on,
but are knackered from there on ... Why all the numbers... Where is the picture...?

Meanwhile the young ladies with their own hand held devices are skillfully editing what they want in a few seconds.
Forum: Pentax K-1 11-01-2017, 12:44 PM  
Dynamic range test: K1 show 16ev of DR
Posted By wombat2go
Replies: 21
Views: 2,316
Sounds right and you will need a DisplayPort GPU with a 30 bit monitor to see the range smoothly. - in theory.
-Actually the old DVI 8 bit works well enough for me and I usually use that so I can watch the old video like British Pathe.
Forum: Pentax K-1 11-01-2017, 11:56 AM  
Dynamic range test: K1 show 16ev of DR
Posted By wombat2go
Replies: 21
Views: 2,316
The numbers in post #8 are in dimensionless ratio of (wanted_Pe) /(RMS(Total_Noise_Pe)

A SNR of 40 is 32 dB
Note that dB is a formal scientific unit (deci-Bel) and SNR [dB] =20log( (wanted_Pe) /(RMS(Total_Noise_Pe) )
Some time ago one of the "expert" camera reviewers apparently "invented" their own version of dB which would make comparisons meaningless.
Forum: Pentax K-1 11-01-2017, 09:14 AM  
Dynamic range test: K1 show 16ev of DR
Posted By wombat2go
Replies: 21
Views: 2,316
According to Holst & Lomheim:
SNR levels:
1 is industry standard used for defining system performance, because it is easy to measure.
10 is "good" image on a digital still camera and video
40 is producing "excellent" image.

On a camera array, the denominator (noise) consists of the square root of the sum of the following squares:
shot, floor, pattern, ADC, reset
Forum: Pentax SLR Lens Discussion 10-31-2017, 05:28 AM  
How 'Bad' is DAL 18-55 vs Other Options?
Posted By wombat2go
Replies: 67
Views: 2,886
Yes, that and the 1st generation DA 18~55 zooms here are probe to disconcerting "flare" when used into the sun.

I did this comparison in 2013 on same camera with one of the 18~55 lenses here and the much older SMC Pentax -M 1:2 50mm
18~55
https://app.box.com/s/xnir6j5sp99sdf05g6vs

1:2 50mm
https://app.box.com/s/izcv2q8akxhdh1ajxwuk
Forum: Pentax Film SLR Discussion 10-30-2017, 02:32 PM  
Analog Film versus Digital Photography
Posted By wombat2go
Replies: 66
Views: 3,651
Yes, This one is from a 1936 Zeiss Ikon Nettar: (posted before)
https://app.box.com/s/2vvkg62b2gt3lavig368
Forum: Travel, Events, and Groups 10-30-2017, 02:28 PM  
experiences traveling on airlines with cameras
Posted By wombat2go
Replies: 28
Views: 1,421
This year I obtained the TSA Precheck "KTN"
TSA Requires a Separate Screening of Cameras in Airports Now
"...Also, if you are enrolled in TSA’s PreCheck program, you won’t be required to remove cameras and other electronics from your bag...."
Forum: Travel, Events, and Groups 10-30-2017, 01:58 PM  
experiences traveling on airlines with cameras
Posted By wombat2go
Replies: 28
Views: 1,421
One time I carried an exhaust system for a racing motorcycle to Santiago de Chile.
Going through customs I had the thing wrapped around me like a big snake.
Went straight through the green exit, the inspector must have been a motorcycle guy, he just laughed and let it go!
Forum: Pentax Film SLR Discussion 10-30-2017, 01:48 PM  
Analog Film versus Digital Photography
Posted By wombat2go
Replies: 66
Views: 3,651
Here is a photo taken with the Pentax K_S1 and the XR Rikenon 1:3.5 28mm
It is a camera jpg of 3072 pixels wide, so the resolution is almost the same
as in the Fuji 35mm film photo of my post # 42 (65 cycle/mm)
https://app.box.com/s/joquvzcy7hwldyhja53kl7x6lehukr8v

Here is the RGB harmonic content of the digital camera vs cycle/mm
https://app.box.com/s/lvfx0nbohefby6q74qgzqd59yx9dgd5d
Forum: Pentax Film SLR Discussion 10-30-2017, 11:31 AM  
Analog Film versus Digital Photography
Posted By wombat2go
Replies: 66
Views: 3,651
I am still trying to get a feel for the margin between the film MTF curve and what is needed in typical hand held photos.

This photo was with the Ricoh KR-5, Fuji Superia 200 35mm and the SMC Pentax 1:2.8 40mm
The photo .tiff is of lettering on a sign so has lots of edges in it.
The Fuji film rolls off at approximately 40 per millimetre.
The scanner was set to a resolution corresponding to 62.5 lines /mm.

https://app.box.com/s/rrk6aeilqci7mj1wftzsr40vob83ktib

Here is the harmonic content in the photo:
The harmonics are in 16 bit format, so the high order ones are "blocky"
Next time I will put them in floating point.
https://app.box.com/s/7gdxro7wry7y5vxs1gpvkoib7s9gklg8
Forum: Pentax Film SLR Discussion 10-28-2017, 04:12 PM  
Analog Film versus Digital Photography
Posted By wombat2go
Replies: 66
Views: 3,651
I use Fuji Pro 400H C41 which is rated with a corner frequency at about 50 lines per mm, and Ektar 100 which is roughly 40/mm by the data sheets.
On the international 6x7 camera back (eg RH10) the frame width is 67.7mm.
Scan resolution needed for a Nyquist of 50/mm : 2 * (50 * 67.7) = 6770 pixels across.
That corresponds to a nearest scanner setting of 2400 pixels per inch on my PrimeFilm 120Pro.

Here is a scan of Ektar 100 using the vintage (1960's) Super Angulon 65mm on a (1953) 2x3 Graflex with 6x7 back.
(By the way I am finding this old lens difficult to use hand held)
https://app.box.com/s/9qrlw48oqngxx849v6tgrz4l0f129amc
I wanted to quantify how close the higher harmonics of these images are coming to the Modulation Transfer Function (MTF) rating of the film.

The image was converted into the frequency domain, then I extracted the amplitudes of harmonics.

After about the 700th harmonic, the level has tended to zero.
700th harmonic corresponds to a period of about 67 micrometer or 15 lines per millimetre.

So there seems to be reserve, meaning that a hand held photo like this needs a resolution safely below the MTF roll-off of the film and scanner.
Forum: Digital Processing, Software, and Printing 10-25-2017, 06:48 AM  
Darktable 2.0.7 under Linux Mint 18.2... a great Lightroom alternative
Posted By wombat2go
Replies: 44
Views: 2,980
If you have a GPU card, DT will run fast.
in the "gears" tab "core options" "activate OpenCL support" check on

Alternately, invoke DT in a terminal like this:
$ darktable -d opencl
Forum: Pentax Film SLR Discussion 10-24-2017, 05:23 AM  
Lenses to take to Paris
Posted By wombat2go
Replies: 24
Views: 1,602
Thanks, How it came to be, was that Peugeot and Renault cars were assembled in Australia after 1950.
My father was a dealer so my early memories were of our family cars being French!
And French cars were discussed at the dinner table!
I remember a Renault Dauphine for a while then a Peugeot 403 ( sedan like Columbo's)
Forum: General Talk 10-23-2017, 01:35 PM  
What is the best drill bit? (Sarcasm )
Posted By wombat2go
Replies: 279
Views: 8,586
Oh No ! he hasn't got a clone, has he?
Forum: Site Suggestions and Help 10-23-2017, 01:34 PM  
Question New title designations!
Posted By wombat2go
Replies: 86
Views: 3,401
I have started to be startled by the stars.
Forum: Pentax Film SLR Discussion 10-23-2017, 11:04 AM  
Lenses to take to Paris
Posted By wombat2go
Replies: 24
Views: 1,602
There is a Peugeot 403, released in 1955, coming toward camera on right of bus.
The Renault Dauphine going away on right of van came out in 1956.

But if that Mercedes on far left is a 220 , with factory fog lights and turn indicators above the headlamps, then it might be 1958.
Furthermore, I think that Simca Aronde behind the 'Benz is a 1958 90A by its mustache grill with no dome in the centre, and with turn indicators outboard.
Forum: General Talk 10-18-2017, 08:09 PM  
What is the best drill bit? (Sarcasm )
Posted By wombat2go
Replies: 279
Views: 8,586
Just a reminder,
We have to get on the grinder
And Adjust the angle of view,
To 118 plus/minus a few.
Search took 0.02 seconds | Showing results 1 to 25 of 300

 
Forum Jump


All times are GMT -7. The time now is 05:11 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top