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Forum: Pentax SLR Lens Discussion
01-13-2013, 09:26 PM
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This can easily be explained by focal length alone.
I found an interesting article on DOF and pupil magnification here:
The DOF equations
a quote from the above article:
"Apart from the DOF, the pupil magnification affects quantities such as the depth of focus, the effective aperture (in relation to exposure) and the field of view, For faraway subjects the pupil magnification has no significant influence on these quantities; it becomes important for image magnifications greater than, say, 0.1. In the very macro regime the impact of a nonunitary P is substantial."
in other words, when you start attaching extension rings, bellows or reverse mounting a lens, pupil magnification becomes relevant.
Unless you do a lot of close macro work it's not likely to play any significance.
my 2 cents
CAK
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Forum: Pentax SLR Lens Discussion
01-13-2013, 04:11 PM
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Can you show us a practical application for pupil magnification?
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Forum: Pentax SLR Lens Discussion
01-13-2013, 12:46 PM
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I have prepared yet another comparison sketch for everyone's amusement. This one shows The DOF region with a 50mm lens @f4.0 on a full frame camera, and when that lens is swapped onto an APS-C camera that stepping back by approximately 50% will yield a similar sized object on your plane of focus. However your background will be narrower and the foreground will be broader. Also the DOF will be increased so in order to achieve a "similar" DOF you will need to open the aperture to f2.8.
Again I am only using the data obtained from the DOF calculator as a baseline for comparing the effective DOF regions created by a given lens on various formats of sensors. The actual specific depth of field distances is not really relevant, it is the relationships of the regions that I am trying to depict.
Sincerely,
C. A. Kirk
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Forum: Pentax SLR Lens Discussion
01-13-2013, 12:27 PM
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According to Wikipedia:
The pupil magnification of an optical system is the ratio of the diameter of the exit pupil to the diameter of the entrance pupil. The pupil magnification is used in calculations of the effective f-number, which affects a number of important elements related to optics, such as exposure, diffraction, and depth of field. For all symmetric lenses, and for many conventional photographic lenses, the pupils appear the same size and so the pupil magnification is approximately 1.
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Forum: Pentax SLR Lens Discussion
01-12-2013, 08:08 PM
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I don't use these charts when I shoot anyway, they are far too anal for me. I usually just stop the lens down and if I like what I see I push the button.
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Forum: Pentax SLR Lens Discussion
01-12-2013, 07:44 PM
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Depth of Field is a rather subjective topic to begin with as a person's visual acuity will vary so much between individuals. I was just using the Cambridge charts as a baseline for observing the differences in DOF from format to format.
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Forum: Pentax SLR Lens Discussion
01-12-2013, 07:05 PM
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My next step was to then go to the Depth of Field Calculator at: "cambridge in colour (dot) com" to look up specific DOF data regarding an average lens, lets say a 50mm @ f4.0 (I chose f4.0 because the difference between sensor formats was more dramatic than say f1.4 for the purpose of the diagrams I was drawing.
My first sketch shows Depth of Field for a 50mm lens @f4.0 focused at 20ft. if on a full frame sensor (36x24mm)
My second sketch shows the the same 50mm lens @f4.0 focused at 20ft. on an APS-C (24x16mm) sensor:
The following sketch shows that in order to obtain a similar image, with both similar field of view as well as depth of field, without changing vantage point that you will have to change both the lens and aperture.
Again, the data depicted in my sketches was obtained from the DOF calculator found at: A Flexible Depth of Field Calculator
I hope some of you find my sketches helpful
Sincerely,
Christopher A Kirk
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Forum: Pentax SLR Lens Discussion
01-12-2013, 06:33 PM
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Hello people,
Although I have been a forum member for a while, I don't post very often, but because this has been such a fascinating discussion I thought I might chime in.
At first when discussing DOF from a given lens I wasn't grasping the concept that it could be different given different camera formats. After reading up a little regarding circles of confusion I decided to create some visual aids to help comprehend what's going on when a given lens is swapped between camera/sensor formats.
Utilizing my CAD background I came up with the following sketches:
I just a simple guy, so visualizing things with sketches helps. I hope my sketches are useful to others
other sketches to follow.
CAK
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Forum: Film Processing, Scanning, and Darkroom
01-14-2011, 02:52 PM
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Abstract:
I bought an FS2710 about 12 years ago at Fry's Electronics for about $600. It is a very tedious unit to use. Although there is a holder for a strip of six 35mm negatives you have to slide a ring around the ONE image that you are going to scan. (so scanning a strip of six images takes six individual operations.)
It also needs a SCSI adapter to plug into so for me that means keeping an older computer operational in order to use the scanner. (I don't have any extra slots in my current desktop)
It does come with a 35mm slide adapter though I have never used it.
I have been using Vuescan software to operate the scanner (since the accompanying canon software was really weak) and it does produce decent 2700dpi results.
http://c-a-kirk.com/Friends/The-Ball-Family/1998-Yosemite/1998-Yosemite-10-o...Mj9Nj-X3-1.jpg
As far as comparing it to the Minolta Dimage... I can't, because I have never used it. I have seen numerous people on this forum praising the Minolta while I Have not seen anyone with anything to say about the CannoScan 2710. It works for me for now, but it is very tedious to use.
Sincerely,
Chris Kirk
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Forum: Pentax DSLR Discussion
08-20-2010, 12:37 PM
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hmm... My first camera was a Kodak Instamatic that I got when I was around ten or eleven. (1970 or so) I used it to supplement the family album and pictures taken by dad and his Polaroid SX-70.
Later, when I wanted learn something about photography (& as an excuse to transfer out of choir) I took Mr. Runyon's Photography class in Jr. High. Here I used an Ansco Memar with a Bertram Chronostar hand held light meter. The Ansco wasn't even technically a rangefinder as you had to set focus by manually guesstimating with the front lens ring. For my sixteenth birthday dad bought me a Spotmitic-F (I still use one now)
Digital came in 2002 with a Nikon CoolPix 5700 which is now broken and I never really liked anyway. Serious digital came in 2007 when I bought a K10D.
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Forum: Film SLRs and Compact Film Cameras
07-31-2010, 05:38 PM
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I was always a plus-x / tri-x kind of guy back in the late 70's early 80's.
After a long spell of not doing anything photographically I got back into photography digitally (K10D) and then later nostalgia set in and I picked up a spotmatic-f like the one I had way back when. Only this time I sought after fine grain films like Panatomic-X... (What do you mean they stopped making it in the late 80's!!!)...
To make a long story short I found several bulk rolls on eek-bay that were apparently stored well.
These are from my first attempts with pan-x developed in hc110 dilution-H I believe. (This batch of film was expired in 1986)
On the other hand here are a couple of the more modern Ilford Pan-F+ also developed in hc110
I think I'm having more fun with the Pan-X. However, I believe the Illford will work for me when I run out of the panatomic. I'm quite satisfied with fuji acros 100 but I don't have any scans to show right now.
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Forum: Film SLRs and Compact Film Cameras
05-17-2010, 03:45 PM
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Hi there knowledgeable Pentax Forums members,
I recently purchased an MZ-S and so far I am really enjoying this camera. However, I have searched high and low for either the cs-105/cs-130 cable switch or the much coveted TS-110 timer switch to no avail.
The problem seems to be the oddball connector used for this camera (and the 645nii) only. It appears to be a "mini xlr" (also known as "Tini Q-G") connector type. There seems to be a multitude of variations among this connector family. Can somebody help me out with the correct part number and where I can order it so I might splice it onto the end of a generic timer switch in place of the tip ring sleeve stereo style plug that seems to be the standard now?
Thank you so much for any help that all of you can offer.
Sincerely,
Christopher A Kirk
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Forum: Pentax DSLR Discussion
02-04-2010, 01:55 PM
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Hello every one, I haven't posted to this wonderful site in quite a while but I thought I'd chime in on this one even though my desire in a dslr will probably be deemed silly.
I would like a dslr that would offer intercahangeable sensors.
Although you have a lot more lattitude in iso(asa) of a sensor by adjusting the gain of the output than with film by pushing/pulling any sensor or film tends to operate best at their native iso(asa).
So give me a camera that comes with a stock sensor that has an average resolution for every day stuff, but then allow me to swap it out for a sensor with a smaller number of big honking sensor sites that'll give supurb high iso (asa) performance. Conversely, another option might be a sensor with a slew of tiny ssensor sites for supurb resolution. Maybe you could throw in another option with no bayer filter for better b&w performance. (much like choosing between pan-x, plus-x or tri-x depending on conditions/desired effects that we did back in the old days except to greater extreems.)
Like I said, my idea is silly, if not simply overly complicated / expensive to accomplish.
but look who wrote it, "cak" is not to be trusted.
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Forum: Lens Clubs
01-09-2009, 12:45 AM
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Thank you Asahiflex. I like that last one too, especially the colors I got as the sun was starting to go down.
I havn't had any of my Takumars long enough to really get to know them yet, but I really prefer the way they feel over my more modern lenses. I haven't seen to much CA with the 400 but I have had a lot of PF with it in contrasty scenes. I don't know if that's the ccd in my k10 or the lens itself. I've read in places where a lens that experienced bad PF on the k1od's ccd was all but eliminated by attaching the same lens to a k20d with its more modern cmos sensor. (something to do with the micro lens on the photo cells and the distance between them, it's mostly "Greek" to me)
Anyway, I seem to like the 400, It's really all I could afford in that department I got it for about 250 US on ebay.
Again, thanks for the kind words.
Chris
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Forum: Lens Clubs
01-09-2009, 12:04 AM
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Hello people,
This will be my third post, I'm still quite new here.
This thread is probably the one that most motivated me to join in PentaxForums. I must say that the images here are among the most amazing that I have seen. I only hope that my humble attempts can stand up with some of the great shots I have seen here.
These shots were taken at a little spot here in the east county of San Diego called Mt. Helix. The first shot is looking over the shipyards and Coronado, the city of San Diego is off screen to the right.
Super-Multi-Coated TAKUMAR 400/5.6
This next one is looking east towards the Laguna mountains After a recent storm that gave our So. Cal. mountains some rare snow that was gone within days.
Super-Multi-Coated TAKUMAR 400/5.6
To the south is Mt. Magil
Super-Multi-Coated TAKUMAR 400/5.6
A eucalyptus tree
Super-Multi-Coated TAKUMAR 28/3.5
The top of Mt. Helix is an amphitheater that was built in the 1920's.
these were all taken with the 28/3.5
Oh yes, these were all taken on my K10D,
I hope you all enjoy these as much as I did taking them!
Sincerely,
Christopher A. Kirk
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Forum: Film SLRs and Compact Film Cameras
01-07-2009, 10:26 PM
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I know it's ancient, but its what I have.
Is there any body out there that is familiar with this relic who might be able to advise how to obtain decent results with this old dedicated film scanner?
I have recently started developing my own film again and just looking at the negatives I feel I could obtain respectable results if I had the space and funds to set up a traditional wet darkroom. (space is my key limitation) However the scans seem to start out flat, and post processing for wider tonal range just isn't quite doing it for me.
I'm expecting the problem(s) are mostly user error. Attempting to learn how to use the film scanner, the vuescan software, Lightroom 2, CS4 all at once is making for a very large learning curve. But I'd like to start at the begging: Am I scanning my negatives properly to begin with, and can I improve my results much without having to spend a grand + on a coolscan 5000?
I posted a couple of samples in my "Salutations from San Diego" thread in the "welcomes and introductions" forum.
Thanks for any advice that might be available,
Christopher A. Kirk
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Forum: Welcomes and Introductions
01-06-2009, 10:55 PM
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Greetings and Salutations All,
It's about time I introduce myself, I have been lurking here since about the last part of '07 when I bought my K10d. (for my cousin's wedding) Since then I have gleaned a great deal of useful information from this site. A necessity since (photographically speaking) I'm new to this digital stuff. I got into photography pretty heavily back in junior high school (oh so long ago) and for my 16th birthday my dad bought me my first SLR, a brand new Spotmatic-F. Since High school however photography became more of just a hobby and eventually I lost what little equipment I had including that beloved Spotmatic-F. In the past decade I tried to get back into taking pictures so I bought a n**** n70 but for some reason it just didn't feel the same and I lost interest again. But when my cousin announced her wedding (and after recovering from angioplasty) I decided to give it another go. I pickup up the K10D and it just felt right!! I really love this camera but there's a bit of a learning curve for this digital stuff. I still like film. Black and white specifically. In fact I seem to be obsessed! So obsessed that I sought after a replacement for that beloved Spot-F and as many Takumars as I can afford.
So to conclude this rather lengthy introduction I thought i would include a couple of my latest endeavors in photography:
Tri-x film developed in hc110 dilution E (that part worked pretty well)
scanned with a POS CanoScan FS2710 (about 10 years old and a royal pain)
this one is ilford pan-f+ in hc110 dilution H
Sincerely,
Christopher A. Kirk (hence the handle "cak")
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