Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
11-27-2009, 06:56 PM   #31
Pentaxian




Join Date: Sep 2007
Location: Bay Village, Ohio USA
Posts: 1,047
We've had aperture-priority cameras for at least thirty years, from all manufacturers. I don't know of a single example of a camera that takes FL into account when calculating the shutter speed in Av mode, as the OP is asking for. It seems to me that this would be a complete re-definition of the meaning of aperture-priority, as it has been understood since the mid-seventies.

Now, perhaps he has a good idea, and perhaps some manufacturer will implement it, but would be a completely new exposure mode, so it is not fair to complain that Pentax has implemented it the way everyone understands Av. Av means, and has meant for thirty years or more, that you set the aperture and the camera picks the shutter speed.

Adding auto-ISO into the equation has muddied the waters more than enough. I think that with auto-ISO enabled, the camera may be trying to keep the shutter speed up, to avoid camera shake. In film days, of course, we couldn't change ISO on each frame.

11-27-2009, 10:29 PM   #32
Veteran Member
Eruditass's Avatar

Join Date: Jul 2009
Location: Pittsburgh, PA
Photos: Gallery | Albums
Posts: 2,206
Original Poster
QuoteOriginally posted by KungPOW Quote
Just want to point out that the previous respnces were also "real". It was you who negleted to tell us that you had the camera on Auto ISO. Good foe Mike to figure that out.

And yes, in auto ISO, my camera wants to stay at 1/100 regardless of the input lens length.

So, turn off auto ISO.

And M42 lenses do work better then M lenses in AV mode. M lenses only work wide open.
You mean when I mention it here?

https://www.pentaxforums.com/forums/825583-post14.html

And all the responses after that that failed to understand what I was asking, and instead explained things that were unnecessary?

Notice that I wasn't complaining about it being over or under exposed when changing the light coming into the sensor via aperture or environment.

Yes M42 lenses work better than M lenses in Av mode, but as I stated earlier, it is not as good as I have been led to believe. Thank you for explaining that they only work wide open, not that I mentioned it a couple times earlier in the thread when comparing M42 and M-series lenses..

By "real" I mean responding to the actual question I am asking. I have always known it is in auto-iso mode, though I may have not made it clear to the readers until post 14.

Last edited by Eruditass; 11-27-2009 at 10:41 PM.
11-27-2009, 10:31 PM   #33
Veteran Member
Eruditass's Avatar

Join Date: Jul 2009
Location: Pittsburgh, PA
Photos: Gallery | Albums
Posts: 2,206
Original Poster
QuoteOriginally posted by kuuan Quote
with selected aperture the camera in auto ISO and Av mode tries to get the shutter speed right and changes the ISO to achieve that. Actually this is what I would want the camera to do, can't see why this is a flaw.

If I do not want the ISO to change but the shutter speed, well, then better to fix the ISO and have the shutter speed will change..
Get what shutter speed? The shutter speed I selected? This is Av mode, not Tv mode, the camera is trying to get an arbitrary shutter speed.
11-27-2009, 10:33 PM   #34
Veteran Member
Eruditass's Avatar

Join Date: Jul 2009
Location: Pittsburgh, PA
Photos: Gallery | Albums
Posts: 2,206
Original Poster
QuoteOriginally posted by noblepa Quote
We've had aperture-priority cameras for at least thirty years, from all manufacturers. I don't know of a single example of a camera that takes FL into account when calculating the shutter speed in Av mode, as the OP is asking for. It seems to me that this would be a complete re-definition of the meaning of aperture-priority, as it has been understood since the mid-seventies.
Well, doh. Back then, in order to change the ISO you had to switch out the film or process in the dark room. Aperture-Priority ever since digital transmissions of focal length and the advent of automatic-iso has resulted in Aperture Priority taking into account focal length.
QuoteQuote:
Now, perhaps he has a good idea, and perhaps some manufacturer will implement it, but would be a completely new exposure mode, so it is not fair to complain that Pentax has implemented it the way everyone understands Av. Av means, and has meant for thirty years or more, that you set the aperture and the camera picks the shutter speed.
ALL manufactureres implement it on all lenses that transmit focal length. Now on lenses that don't transmit focal length, it seems to ignore the FL, even if we tell it what it is.
QuoteQuote:
Adding auto-ISO into the equation has muddied the waters more than enough. I think that with auto-ISO enabled, the camera may be trying to keep the shutter speed up, to avoid camera shake. In film days, of course, we couldn't change ISO on each frame.
In this case, the camera is trying to keep the shutter speed up to an random value that seems different on each camera, which is kinda dumb. All it takes to change this is like 2 register instructions... the focal length is already in the camera because it asks us for it when it turns on.


Last edited by Eruditass; 11-27-2009 at 11:17 PM.
11-28-2009, 01:10 AM   #35
Veteran Member
KungPOW's Avatar

Join Date: Nov 2007
Location: Vancouver, Canada
Photos: Gallery
Posts: 1,702
Good luck with your gear.
11-28-2009, 04:23 AM   #36
Pentaxian
Arjay Bee's Avatar

Join Date: Sep 2006
Location: Bamaga, QLD
Photos: Gallery | Albums
Posts: 3,057
Please explain for me the advantage of including the FL in the exposure algorithm?

I regularly use a range of m42 lenses, from 28mm to 360mm in AV mode or manual mode on my K20. I don't see the advantage of auto ISO as I prefer to make that decision for myself depending on situation.

Possibly somewhere above you have explained this but I didn't notice due to the heavy layer of static caused by your communication style.
11-28-2009, 04:38 AM   #37
Veteran Member
RuiC's Avatar

Join Date: Jan 2009
Location: Lisboa - The Grocery
Posts: 616
QuoteOriginally posted by Eruditass Quote
That defeats the purpose of Av mode...

It will just assign a shutter speed based on light. I want it to assign a shutter speed based on the FL I am using, using ISO to get there. Then when it gets there, it can lower the ISO if more light comes.

If I could assign the e-dial or +/- + e-dial to ISO it would be slightly better than M mode.
That is right procedure. There is no problem with your camera. I don't know ANY camera that sets the shutter based on the FL. Where have you seen that?

Rui
11-28-2009, 08:04 AM   #38
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,400
As a simple review of the OP and his issue / question, I believe the following is a summary.

The OP would like to have the focal length used as part of the exposure calculation, with auto ISO, Specifically that the target shutter speed is 1 / (FL x 1.5) such that the correct non stabalized shutter speed is selected for the focal length entered, as the target shutter speed when making an auto ISO adjustment .

If I consider this functionality a little further, the ideal solution (at least on my cameras which have dual thumb wheels) would be to let the camera pick what ever it wants, but assign ISO to one thumb wheel and shutter speed to the other.

In this way if you don't like the solution, then you can change it within the range allowed, for either ISO or shutter.

Aside from the fact that this is a change from what pentax has done on 100% of thier bodies to date, yes, I suppose it could be done, so why not put a letter / e-mail to pentax and propose it.

my own personal view is that it is far beyond minimum manual functionality that was intended on the pentax cameras, with legacy lenses, but there is nothing to loose in asking


Last edited by Lowell Goudge; 11-28-2009 at 08:19 AM.
11-28-2009, 10:41 AM   #39
Veteran Member
Eruditass's Avatar

Join Date: Jul 2009
Location: Pittsburgh, PA
Photos: Gallery | Albums
Posts: 2,206
Original Poster
QuoteOriginally posted by RuiC Quote
That is right procedure. There is no problem with your camera. I don't know ANY camera that sets the shutter based on the FL. Where have you seen that?

Rui
If you read the thread you'd realize that all DSLRs with auto ISO assign shutter speed based on FL. I wonder how many more times I will have to type the same thing in this thread.

But thanks for quoting the post where I explain everything quite clearly, and mention the benefits of being able to assign the e-dial to ISO. Everyone reading this thread appears to have missed that.

I did not think there was a problem with my camera, I was wondering if the implementation was the same on previous cameras - assignging an arbitrary shutter speed.

Last edited by Eruditass; 11-28-2009 at 10:51 AM.
11-28-2009, 10:41 AM   #40
Veteran Member
Eruditass's Avatar

Join Date: Jul 2009
Location: Pittsburgh, PA
Photos: Gallery | Albums
Posts: 2,206
Original Poster
QuoteOriginally posted by Arjay Bee Quote
Please explain for me the advantage of including the FL in the exposure algorithm?

I regularly use a range of m42 lenses, from 28mm to 360mm in AV mode or manual mode on my K20. I don't see the advantage of auto ISO as I prefer to make that decision for myself depending on situation.

Possibly somewhere above you have explained this but I didn't notice due to the heavy layer of static caused by your communication style.
Statement 1 depends on statement 2.5. Try to put 2 and 2 together.

Last edited by Eruditass; 11-28-2009 at 10:49 AM.
11-28-2009, 10:48 AM   #41
Veteran Member
Eruditass's Avatar

Join Date: Jul 2009
Location: Pittsburgh, PA
Photos: Gallery | Albums
Posts: 2,206
Original Poster
QuoteOriginally posted by Lowell Goudge Quote
As a simple review of the OP and his issue / question, I believe the following is a summary.

The OP would like to have the focal length used as part of the exposure calculation, with auto ISO, Specifically that the target shutter speed is 1 / (FL x 1.5) such that the correct non stabalized shutter speed is selected for the focal length entered, as the target shutter speed when making an auto ISO adjustment .
I would've thought this is every photographer's mind, but I guess not.
QuoteQuote:


If I consider this functionality a little further, the ideal solution (at least on my cameras which have dual thumb wheels) would be to let the camera pick what ever it wants, but assign ISO to one thumb wheel and shutter speed to the other.
As mentioned, I have asked for ISO to be assigned to the one e-dial in Av mode on the K-x. Right now a direct access button must be pushed first, but it shouldn't require it as the e-dial does nothing right now. This is how I have been doing exposures, btw.
QuoteQuote:
In this way if you don't like the solution, then you can change it within the range allowed, for either ISO or shutter.

Aside from the fact that this is a change from what pentax has done on 100% of thier bodies to date, yes, I suppose it could be done, so why not put a letter / e-mail to pentax and propose it.
Again, every DSLR uses FL to determine what shutter speed to aim for. It doesn't just pick a random value as it does with manual lenses
QuoteQuote:

my own personal view is that it is far beyond minimum manual functionality that was intended on the pentax cameras, with legacy lenses, but there is nothing to loose in asking
"far beyond minimum functionality"? That's an interesting use of terms. I guess its always good to be somewhat beyond the minimum, no?

I personally believe it's beyond what is expected with manual lenses, but was led to believe that it was implemented as such and had different expectations.

A better approach would have been to disable auto-ISO altogether with manual lenses. Don't include a feature if it isn't implemented correctly.

Last edited by Eruditass; 11-28-2009 at 12:24 PM.
11-28-2009, 11:52 AM   #42
Veteran Member
RuiC's Avatar

Join Date: Jan 2009
Location: Lisboa - The Grocery
Posts: 616
QuoteOriginally posted by Eruditass Quote
If you read the thread you'd realize that all DSLRs with auto ISO assign shutter speed based on FL. I wonder how many more times I will have to type the same thing in this thread.

But thanks for quoting the post where I explain everything quite clearly, and mention the benefits of being able to assign the e-dial to ISO. Everyone reading this thread appears to have missed that.

I did not think there was a problem with my camera, I was wondering if the implementation was the same on previous cameras - assignging an arbitrary shutter speed.
With film cameras when you have a fixed ISO there are only two variables to fix exposure: Shutter time and Aperture, no other variables. With DSLR cameras you have also the ISO setting variable. Exposure is NEVER dependent on FL. In any camera, be it at Av or Tv or M or whatever, you're setting exposure alone. And any camera sets exposure parameters based only on these 3 Variables, said shutter time, aperture and ISO. These are BASICS from Photography. Please tell me which camera/lens combo, name it please to see if I can understand, will enter FL in exposure settings. Or are you referring to variable aperture Zooms? With these of course the exposure values change because when you zoom in or out (changing FL value ) you are varying the Aperture automatically, so either Shutter time or ISO will change when in Av mode. When in Tv mode the changes would be in Aperture or ISO.

Much appreciated.
Rui
11-28-2009, 12:21 PM   #43
Veteran Member
Raybo's Avatar

Join Date: Dec 2007
Posts: 871
QuoteOriginally posted by RuiC Quote
With film cameras when you have a fixed ISO there are only two variables to fix exposure: Shutter time and Aperture, no other variables. With DSLR cameras you have also the ISO setting variable. Exposure is NEVER dependent on FL. In any camera, be it at Av or Tv or M or whatever, you're setting exposure alone. And any camera sets exposure parameters based only on these 3 Variables, said shutter time, aperture and ISO. These are BASICS from Photography. Please tell me which camera/lens combo, name it please to see if I can understand, will enter FL in exposure settings. Or are you referring to variable aperture Zooms? With these of course the exposure values change because when you zoom in or out (changing FL value ) you are varying the Aperture automatically, so either Shutter time or ISO will change when in Av mode. When in Tv mode the changes would be in Aperture or ISO.

Much appreciated.
Rui

I agree with RuiC.
11-28-2009, 12:36 PM   #44
Veteran Member
Eruditass's Avatar

Join Date: Jul 2009
Location: Pittsburgh, PA
Photos: Gallery | Albums
Posts: 2,206
Original Poster
QuoteOriginally posted by RuiC Quote
With film cameras when you have a fixed ISO there are only two variables to fix exposure: Shutter time and Aperture, no other variables. With DSLR cameras you have also the ISO setting variable. Exposure is NEVER dependent on FL. In any camera, be it at Av or Tv or M or whatever, you're setting exposure alone. And any camera sets exposure parameters based only on these 3 Variables, said shutter time, aperture and ISO. These are BASICS from Photography. Please tell me which camera/lens combo, name it please to see if I can understand, will enter FL in exposure settings. Or are you referring to variable aperture Zooms? With these of course the exposure values change because when you zoom in or out (changing FL value ) you are varying the Aperture automatically, so either Shutter time or ISO will change when in Av mode. When in Tv mode the changes would be in Aperture or ISO.

Much appreciated.
Rui
Wow... can you read? I will try to break it down for you.

I know how exposure works. Probably more than most people, down to the bits of light and logarithmic stops - I am a theory person.

Since on a DSLR, it has the ability to control ISO automatically, it intelligently selects a shutter speed based on the focal length for hand shake purposes, varying the ISO to obtain it (if in Av mode). In Sv and Pv mode, it also selects a shutter speed based on the focal length. The lens digitally communicates with the digital SLR to tell it which focal length the lens is at. This information is even stored into the EXIF data. The camera needs to know a goal of what shutter speed to select because today, there are 3 variables it can control by itself, when there only used to be 2. Since there is an extra variable, cameras now need to know what to aim at for one of the variables. This could be a shutter speed that will acceptably bypass handshaking, an aperture that has a max MTF, or an ISO that has an acceptable amount of noise.

The next part I am getting a little nit-picky about the camera communication, feel free to not read this if you do not understand how it works. No I am not referring to variable aperture zooms, because in no way does the camera really know the true aperture. It would actually be digitally impossible to communicate the exact aperture of a variable aperture zoom, you could only get it accurate to a certain precision. What is told, instead, is the fraction of light that will be received compared to wide open. The f/number you see in the camera on these digital lenses is fake and not even used to determine the final exposure. In fact, no lenses transmit their exact true f-number, just what fraction of light is expected to be received by the sensor or film. This is because aperture is a ratio of lengths that can never be exact, so they are approximate. Even if lenses could transmit the exact f-number, it would be absolutely pointless because each lens, through design or even manufacture tolerances, robs light a different amount before it gets to the sensor.

This doesn't matter to a camera because it doesn't need to know the aperture, it just needs to know the light it will receive. Thus, the 3 things that really determine exposure is the rate of light coming in (determined as a fraction of the light currently coming in), length of light coming in (shutter), and amplification of light (ISO).

So please don't explain the basics in my thread in a condescending matter, incorrectly assuming I don't know anything about photography. This isn't the beginner's corner.

Last edited by Eruditass; 11-28-2009 at 12:51 PM.
11-28-2009, 12:39 PM   #45
Veteran Member
Eruditass's Avatar

Join Date: Jul 2009
Location: Pittsburgh, PA
Photos: Gallery | Albums
Posts: 2,206
Original Poster
QuoteOriginally posted by Raybo Quote
I agree with RuiC.
You agree with him on what? The science of exposure that everyone does or should understand? or his incorrect assumptions about me?
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!
av, av mode, camera, dslr, fl, mode, mode and m42, photography, shutter
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
K-x Problem with manual mode and M42 lenses dude163 Pentax DSLR Discussion 10 08-11-2010 04:16 AM
How to achive Tv (Shutter priority mode) for K mount and M42 lenses? Sudhakar Pentax SLR Lens Discussion 12 06-03-2009 09:51 PM
For Sale - Sold: M42 / K / KA / FA Lenses Grab bag of Vintage to Current lenses. 50mm FA f/1.4 MikeDubU Sold Items 10 02-09-2009 12:45 PM
For Sale - Sold: SF1 Kit, ME w/50, 250/SL, K AF Lenses, M42 Lenses 247nino Sold Items 5 05-07-2008 04:28 PM
M-Mode Green Button M42 mount Confusion... MNCurt-K10D Pentax DSLR Discussion 12 02-08-2008 10:02 PM



All times are GMT -7. The time now is 07:38 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