Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
11-12-2014, 11:27 AM   #16
Site Supporter
Site Supporter
maxfield_photo's Avatar

Join Date: Mar 2011
Location: Cincinnati, OH
Posts: 1,216
Here are some shots from the DA* 60-250 on film from Falk Lumo's thread. Oddly enough, it vignettes at the telephoto end.

https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/31629-da-le...ml#post1747553

11-12-2014, 11:41 AM   #17
Veteran Member
cali92rs's Avatar

Join Date: May 2011
Location: Long Beach, CA
Posts: 3,354
QuoteOriginally posted by Lowell Goudge Quote
but every pentax camera since the A series could control the lens through the body

He doesn't say which film camera he is using. He could be using an ME or whatever for all we know.

---------- Post added 11-12-14 at 10:43 AM ----------

QuoteOriginally posted by aleonx3 Quote
Huh? every AF lens made recently are like that, not only in Pentax land...


Ummm, yea.
I don't see where I said Pentax was the only brand that didn't have aperture rings.
Maybe you can point out where I implied that.
11-12-2014, 11:46 AM   #18
Site Supporter
Site Supporter
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 17,869
QuoteOriginally posted by maxfield_photo Quote
Here are some shots from the DA* 60-250 on film from Falk Lumo's thread. Oddly enough, it vignettes at the telephoto end.

https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/31629-da-le...ml#post1747553
to me, it looks about 1 stop down at 80% of the frame, and 3 stops down right at the corner. this may be due to a shield at the back of the lens, like the rectangular ones pentax used to put on film lenses to limit stray light from entering the mirror box. if so, jjust remove the shield and you have a FF lens. anyone have a shot of the rear of the lens to confirm
11-12-2014, 12:09 PM   #19
Otis Memorial Pentaxian
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 42,007
QuoteOriginally posted by lytrytyr Quote
Misguided? Try figuring out a 3.8mm - 5.9mm zoom on a Q and a Q7!
Yes, misguided.

3.8mm - 5.9mm is what it is. Referencing it to the 24x36mm format is silly since very few Q users have an experience with the 35mm format. It would be better to label the lens as a wide zoom than 22-33mm FF equivalent. There is a stronger case to reference the Q's crop factor to APS-C. (Now does that sound dumb or what?)

As for the matter of aspect ratio when using degrees of arc, the same problem exists when using crop factor equivalence to 35mm FF.


Steve

---------- Post added 11-12-14 at 11:17 AM ----------

QuoteOriginally posted by narual Quote
Focal length is a mathematical formula
Ummmm...sort of. Focal length can, and traditionally is, measured directly on an optical bench.* It is a physical property of the lens and a measurement of its ability to refract light and focus light. That being said, focal length can be calculated as a design goal but is constrained by the refractive qualities of the materials to be used.


Steve

* I remember doing just that in physics lab...


Last edited by stevebrot; 11-12-2014 at 12:18 PM.
11-12-2014, 12:23 PM - 1 Like   #20
Veteran Member
aleonx3's Avatar

Join Date: Jul 2007
Location: Brampton, Ontario
Photos: Gallery | Albums
Posts: 3,996
QuoteOriginally posted by cali92rs Quote
He doesn't say which film camera he is using. He could be using an ME or whatever for all we know.

---------- Post added 11-12-14 at 10:43 AM ----------





Ummm, yea.
I don't see where I said Pentax was the only brand that didn't have aperture rings.
Maybe you can point out where I implied that.
Never mind.. I didn't read too much in it... not sure why I make that comment... LOL
11-12-2014, 12:32 PM   #21
Site Supporter
Site Supporter
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 17,869
QuoteOriginally posted by stevebrot Quote
Yes, misguided.

3.8mm - 5.9mm is what it is. Referencing it to the 24x36mm format is silly since very few Q users have an experience with the 35mm format. It would be better to label the lens as a wide zoom than 22-33mm FF equivalent. There is a stronger case to reference the Q's crop factor to APS-C. (Now does that sound dumb or what?)

As for the matter of aspect ratio when using degrees of arc, the same problem exists when using crop factor equivalence to 35mm FF.


Steve

---------- Post added 11-12-14 at 11:17 AM ----------



Ummmm...sort of. Focal length can, and traditionally is, measured directly on an optical bench.* It is a physical property of the lens and a measurement of its ability to refract light and focus light. That being said, focal length can be calculated as a design goal but is constrained by the refractive qualities of the materials to be used.


Steve

* I remember doing just that in physics lab...
steve, perhaps not your fault you are just last in line.

Start of rant
just to "focus" the discussion a little (yes pun intended) we also need to remind people that like focal length, F Stops are also a physical property of the lens, specifically focal length over diameter (of aperture or smallest part of the light path)

we either accept, like all other format shooters that focal length is focal length, or we simply throw it all away.

we don't label 645 or 6x7 lenses in 35mm equivalent, or visa versa, so why should we start now.
end of rant
11-12-2014, 12:39 PM   #22
Veteran Member




Join Date: Dec 2010
Location: Ontario
Photos: Gallery
Posts: 3,332
QuoteOriginally posted by stevebrot Quote
3.8mm - 5.9mm is what it is. Referencing it to the 24x36mm format is silly since very few Q users have an experience with the 35mm format. It would be better to label the lens as a wide zoom than 22-33mm FF equivalent. There is a stronger case to reference the Q's crop factor to APS-C. (Now does that sound dumb or what?)
It can be handy to have everything referenced back to a single standard for comparison between the many formats. The choice of standard is arbitrary, but 24x36mm is already well entrenched for this purpose whether we like it or not.

Degrees are great, but not what most people are used to. It's always nice when it's included in a lens description, horizontal, vertical, and diagonal angle of view on the intended format is ideal. It should also be given in radians, Celsius and Fahrenheit, just to see if anyone is paying attention.

11-12-2014, 12:47 PM   #23
Veteran Member
flaviopetrone's Avatar

Join Date: Aug 2014
Location: Reggio Emilia
Photos: Albums
Posts: 1,153
QuoteOriginally posted by BrianR Quote

Degrees are great, but not what most people are used to. It's always nice when it's included in a lens description, horizontal, vertical, and diagonal angle of view on the intended format is ideal. It should also be given in radians, Celsius and Fahrenheit, just to see if anyone is paying attention.

Yes, to make everything more complicated they could remove the focal length and just put the angle of view...
11-12-2014, 12:49 PM - 1 Like   #24
Veteran Member




Join Date: Dec 2007
Photos: Gallery
Posts: 8,237
QuoteOriginally posted by stevebrot Quote
Yes, misguided.

3.8mm - 5.9mm is what it is. Referencing it to the 24x36mm format is silly since very few Q users have an experience with the 35mm format. It would be better to label the lens as a wide zoom than 22-33mm FF equivalent.
I have to strongly disagree on a couple counts - first, it's likely that the Q users are mostly ILC customers already, probably still own or have owned aps-c, but possibly FF/film as well.

Second, forcing a new 'standard' based on Q format seems silly. Requiring buyers to learn what "3.8mm" really looks like for example compared to ap-sc, FF, film, another MILC, micro 4/3, etc. It's also likely they're already acclimated to 135mm reference from other formats they've used, which standardize to it.

It's best to do what we're doing now - state the real FL if you wish, but convert everything to a single standard for the sake of comparison so we know what FOV we're talking about. FF/135mm works perfectly fine as this standard.

Imagine the conversation otherwise:

Q: I want to buy this Q, but what FOV does this 3.8mm - 5.9mm lens give me?
A: It's a 3.8mm - 5.9mm lens, that's all you need to know.
Q: But... I want to know if it will be wide & long enough for what I want. What does it compare to?
A: It compares to a 3.8mm - 5.9mm lens. You're shooting Q, you don't need to convert to anything else, much less the odious "FF".
Q: Really, I just want to know what other lenses I might want to buy. Can you help?
A: No. This conversation is terminated.


Last edited by jsherman999; 11-12-2014 at 12:55 PM.
11-12-2014, 12:50 PM   #25
Otis Memorial Pentaxian
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 42,007
QuoteOriginally posted by BrianR Quote
Celsius and Fahrenheit, just to see if anyone is paying attention.
Kelvin too, to be complete


Steve

---------- Post added 11-12-14 at 11:54 AM ----------

QuoteOriginally posted by jsherman999 Quote
It's best to do what we're doing now - state the real FL if you wish, but convert everything to a single standard for the sake of comparison so we know what FOV we're talking about.
Why not just use the FOV? It is equally applicable to all formats (no notion of equivalence needed), is an established unit of measurement, and can easily be visualized by anyone having access to a protractor.*


Steve

* Required kit for all sixth graders.

Last edited by stevebrot; 11-12-2014 at 12:56 PM.
11-12-2014, 01:01 PM   #26
Veteran Member




Join Date: Dec 2007
Photos: Gallery
Posts: 8,237
QuoteOriginally posted by stevebrot Quote
Kelvin too, to be complete


Steve

---------- Post added 11-12-14 at 11:54 AM ----------



Why not just use the FOV? It is equally applicable to all formats (no notion of equivalence needed), is an established unit of measurement, and can easily be visualized by anyone having access to a protractor.*


Steve

* Required kit for all sixth graders.
How would it make things any easier, what would be gained?

You're still converting to something. (Serious question, what would be gained by doing that?)

Is "FF" that objectionable at this point that people can't even accept it as a standard that it's been adopted for for over a decade?
11-12-2014, 01:04 PM   #27
Otis Memorial Pentaxian
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 42,007
QuoteOriginally posted by stevebrot Quote
Why not just use the FOV?
Or just use common descriptive adjectives. That seems to work well for medium format and large format photographers (a dozen or more specific formats between both groups). That crowd has been able to work for the last 150 years without talking about crop factor or equivalence.*


Steve

* In all fairness, my copy of Simmon's "Using The View Camera" does include a discussion of and a table (p31) showing comparative angle of view for several different formats. The conclusion being "...the comparisons are useful as a place to begin thinking about how to find appropriate lenses for the kind of work you do."

---------- Post added 11-12-14 at 12:13 PM ----------


QuoteOriginally posted by jsherman999 Quote
Second, forcing a new 'standard' based on Q format seems silly.
Who suggested that?

QuoteOriginally posted by jsherman999 Quote
How would it make things any easier, what would be gained?

You're still converting to something. (Serious question, what would be gained by doing that?)
What would be gained? How about no more "real" focal length confusion such as has been expressed by the OP of this and several other similar threads in the last few weeks. As for conversion, the unit of measure for FOV (or Angle of View) is degrees of arc. No conversion needed. It works for all formats. The cool thing is that there is no longer any need to talk about equivalence. 45 degrees corner-to-corner is well, 45 degrees.

That being said, while using actual FOV may be good for calculation purposes, in practice I believe that descriptive text is more useful and intuitive:
  • Ultra long
  • Very long
  • Long
  • Normal
  • Moderate wide angle
  • Wide angle
  • Very wide angle
  • Ultra wide angle
These terms are currently in widespread use and reflect intended lens usage.


Steve

---------- Post added 11-12-14 at 12:30 PM ----------

QuoteOriginally posted by jsherman999 Quote
Is "FF" that objectionable at this point that people can't even accept it as a standard that it's been adopted for for over a decade?
Nope, no objection at all. After all, 8x10" has been an established standard for over a century. Oops Wrong FF...*


Steve

* There is a tradition of sorts in large format photography where camera format is stated as full, half, or quarter "plate" relative to 8x10" glass plate negatives.

Last edited by stevebrot; 11-12-2014 at 01:31 PM.
11-12-2014, 02:54 PM   #28
Site Supporter
Site Supporter
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 17,869
QuoteOriginally posted by jsherman999 Quote

It's best to do what we're doing now - state the real FL if you wish, but convert everything to a single standard for the sake of comparison so we know what FOV we're talking about.

Why not recreate the definition of "normal lens" with focal length equal to sensor diagonal as 1:1 with tele being greater than 1 and wide angle being less than 1. Then every one would talk the same ratio,

Oops. We can't do this because some lenses are used on many formats. How do you label the FA77 for example. It would have one number for film, one for APS-C and two for the Q at present (q and q10 are one size, q7 another)

Forget it all, state focal length and be on with it
11-12-2014, 03:03 PM   #29
Site Supporter
Site Supporter




Join Date: Sep 2013
Location: Australia
Photos: Gallery
Posts: 3,842
And to take it up a notch, not only crop factor and focal length but aperture as well
A Concise Explanation of How Crop Factor Affects Both Focal Length AND Aperture

Last edited by beachgardener; 11-12-2014 at 03:41 PM.
11-12-2014, 03:30 PM   #30
Veteran Member




Join Date: Jul 2010
Location: Cupertino, CA
Photos: Albums
Posts: 391
I am getting kind of eager for the OP to reply. I want to make sure he understands focal length better.
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!
35mm, 60-250mm, angle, answer, aperture, camera, conversion, crop, da, factor, ff, film camera, format, fov, frame, k-mount, length, lens, light, pentax, pentax camera, pentax lens, question, reviews, sensor, slr lens, steve
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
From Full-Frame Sony... to Pentax... to Full-Frame Canon Mr_Canuck Canon, Nikon, Sony, and Other Camera Brands 42 01-21-2014 12:50 AM
Full frame or no full frame.... Deedee Pentax K-3 & K-3 II 14 10-08-2013 05:39 AM
Full Frame vs Better Cropped Camera? RockvilleBob Photographic Industry and Professionals 37 02-17-2013 02:24 PM
Difference Between Full Frame (35mm) Sensor & Cropped (APS-C) Sensor richard balonglong Photographic Industry and Professionals 22 06-28-2012 02:20 AM
Full Frame Vs High Quality Cropped Body - Will Pentax Win/Survive in the Game? RiceHigh Pentax News and Rumors 219 05-18-2009 07:15 AM



All times are GMT -7. The time now is 05:05 AM. | 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