Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
09-13-2007, 07:34 AM   #16
Senior Member




Join Date: Jan 2007
Location: Carradale, Scotland
Posts: 289
wrong, wrong, wrong

QuoteOriginally posted by stewart_photo Quote

However, disregarding that (and keeping this very simple so as to not overwhelm you with too much info), there are slight differences between a digital and film lens when it comes to how well they focus on that sensor or film plain. Film lenses were designed to focus on a point where film is located in a film camera, which several millimeters behind the point where digital sensors are located today in digital cameras. Hyprid lenses (those supposedly optimized for both film and digital) split the difference and focus at a point midway between a digital sensor and the old film location. The new digital lenses give up on film entirely and focus solely on the location of digital sensors today.

Of course, you're not going to see any of this in your images because it's only a matter of millimeters, with any minor focusing differences well within the depth of field of a particular lens and camera combination. Someone running tests with a focusing chart using a very narrow depth of field might notice it, but it very seldom matters in the real world.

stewart
Do not try to understand this, this is completely WRONG

The register distance for your Samsung will be exactly the same as the register distance for a lens designed for 35mm in the same Pentax mount. That's why you can use lenses designed for 35 mm on your Samsung, or your Pentax digital camera. Apologies to Stewart but he has it completely wrong.

09-13-2007, 07:47 AM   #17
Veteran Member
pcarfan's Avatar

Join Date: Sep 2007
Location: Dayton, Ohio
Photos: Gallery | Albums
Posts: 2,960
I've seen this and another post of yours, and to me the answers given sounds very complicated, even though I fully understand what's going on. It's difficult to explain, but I'll try in terms of what I understand to how you percieve it.

First, consider this. There is no difference in whether the lens was made for 35mm film camera or a digital SLR (as related to this issue). It does'nt matter whether it is a 50mm lens made for a digital camera or a 50 mm lens made for a film camera, it will behave exactly the same. Lens is not the issue. It's the sensor/film.

Take ANY 50mm lens (obviously they have to be compatible, but again try to keep it simple and ignore such factors) and put it in a film camera and you'll capture a 50mm view, put that same lens in a K10D then you'll capture a 50*1.5 or a 75mm view. That's all there is to it. Lens is the same, but the view you capture is magnified by a factor of 1.5 in the K10D as compared to a film camera.

Does this help ?

So, your experiment to demonstrate this should be set up this way. Take a shot with a 50mm lens in the K10D, and then compare it to a shot taken at 75mm with a film camera from the same exact position, the pictures will be identical.

Last edited by pcarfan; 09-13-2007 at 10:58 AM.
09-13-2007, 09:57 AM   #18
Veteran Member
mattdm's Avatar

Join Date: Feb 2007
Location: Boston, MA
Photos: Gallery
Posts: 2,964
QuoteOriginally posted by pcarfan Quote
So, your experiment to demonstrate this should be set up this way. Take a shot with a 50mm lens in a digital camera, and then compare it to a shot taken at 75mm with a film camera from the same exact position, the pictures will be identical.
Of course this is a bit oversimplified -- "identical" is too strong. They will have a very similar field of view, but won't necessarily be exactly the same in other ways.
09-16-2007, 01:30 PM   #19
Veteran Member




Join Date: Jun 2007
Location: Owego, NY
Posts: 976
QuoteOriginally posted by mattdm Quote
Of course this is a bit oversimplified -- "identical" is too strong. They will have a very similar field of view, but won't necessarily be exactly the same in other ways.
Correct. For example, DOF (depth of field) is the same for a given focal length lens regardless of sensor size. The end result is that a shot taken with a 50mm lens with 1.5x crop factor and one with a 75mm lens and 1x crop factor (film or Canon FF) will have the same field of view, but differences in terms of what is in focus. The DOF will be greater for the 50mm 1.5x shot.

This is a well known phenomenon in amateur/semi-professional filmmaking. DV camcorders have much smaller sensors than film cameras, and as a result, much greater DOF. It is generally agreed that while there are many aspects to the "film look" for moviemaking, one of the most important is a narrow DOF, which camcorders just simply cannot replicate without crazy hacks. (If you do some searching, you'll see that movie filmmakers have made adapters that basically project the image of the scene onto ground glass which is then filmed by the camcorder, as opposed to directly filmed, in order to emulate the DOF of film.)

09-16-2007, 07:44 PM   #20
Veteran Member
pcarfan's Avatar

Join Date: Sep 2007
Location: Dayton, Ohio
Photos: Gallery | Albums
Posts: 2,960
QuoteOriginally posted by Entropy Quote
Correct. For example, DOF (depth of field) is the same for a given focal length lens regardless of sensor size. The end result is that a shot taken with a 50mm lens with 1.5x crop factor and one with a 75mm lens and 1x crop factor (film or Canon FF) will have the same field of view, but differences in terms of what is in focus. The DOF will be greater for the 50mm 1.5x shot.........
This luminous landscape article contradicts you

DOF2

I know it's commonly accepted to zoom in to reduce DOF, but it's sort of abmiguous.....

The images are however not identical like I said as the perspective will be different. My response was only getting to the initial posters frame of thinking and explaining how it needs to change with a similar but corrected viewpoint and a corrected experiment similar to his. Which IMO makes it easier to understand. The key is simplicity.

Last edited by pcarfan; 09-16-2007 at 08:00 PM.
09-16-2007, 08:36 PM   #21
Veteran Member
mattdm's Avatar

Join Date: Feb 2007
Location: Boston, MA
Photos: Gallery
Posts: 2,964
QuoteOriginally posted by pcarfan Quote
This luminous landscape article contradicts you

DOF2
Actually, it's agreeing, but just wording the argument differently. Note, from the article (emphasis mine): "In fact, if the subject image size remains the same, then at any given aperture all lenses will give the same depth of field." But in the case of a smaller sensor, the subject's image size only appears to be the same because when you view the result, you're usually enlarging it to the same size as the full-frame image.
09-17-2007, 07:46 AM   #22
Veteran Member
pcarfan's Avatar

Join Date: Sep 2007
Location: Dayton, Ohio
Photos: Gallery | Albums
Posts: 2,960
QuoteOriginally posted by mattdm Quote
Actually, it's agreeing, but just wording the argument differently. Note, from the article (emphasis mine): "In fact, if the subject image size remains the same, then at any given aperture all lenses will give the same depth of field." But in the case of a smaller sensor, the subject's image size only appears to be the same because when you view the result, you're usually enlarging it to the same size as the full-frame image.

Agreeing to what ? The question is, given the same frame of view (subject image size), does the DOF change with the focal length of the lens used?

Given the same frame of view (subject image size) the DOF change with the focal length of the lens or no ?

I don't even know why you mention "But in the case of a smaller sensor, the subject's image size only appears to be the same because when you view the result, you're usually enlarging it to the same size as the full-frame image", as even though it's true it has no relevance to whether the focal length matters for DOF ????? What am I missing?????

Last edited by pcarfan; 09-17-2007 at 10:49 AM.
09-17-2007, 03:47 PM   #23
Veteran Member




Join Date: Jun 2007
Location: Owego, NY
Posts: 976
QuoteOriginally posted by pcarfan Quote
Agreeing to what ? The question is, given the same frame of view (subject image size), does the DOF change with the focal length of the lens used?

Given the same frame of view (subject image size) the DOF change with the focal length of the lens or no ?

I don't even know why you mention "But in the case of a smaller sensor, the subject's image size only appears to be the same because when you view the result, you're usually enlarging it to the same size as the full-frame image", as even though it's true it has no relevance to whether the focal length matters for DOF ????? What am I missing?????
Subject image size = size of subject on sensor (regardless of sensor size)

i.e. for a given focal length, subject image size remains constant, but the percentage of the sensor covered by that image depends on sensor size.

As an extreme example - It's nearly impossible to get the "subject in focus, background out of focus" effect with point-and-shoots because the actual lens focal length is so short (in order to achieve a particular field of view on a tiny sensor)

Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, circle, d-xenon, dslr, equivalent, film, fl, length, lens, mz-5n, photography
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
What can a first generation DSLR and a 40 yr old lens do? Lowell Goudge Photographic Technique 4 10-09-2010 07:43 AM
Question Site favicon strangeness emr Site Suggestions and Help 3 10-30-2009 03:30 PM
DSLR Lens Design David Pentax SLR Lens Discussion 14 08-04-2009 03:32 PM
old m lens on dslr Barry_S Pentax DSLR Discussion 8 12-27-2008 12:43 AM
Using an M lens on DSLR tux08902 Pentax SLR Lens Discussion 3 08-28-2008 02:28 AM



All times are GMT -7. The time now is 10:43 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