Re: Variable aperture zoom question
Sac> I'm standing by to be corrected. Sac> Mafud Sac> [EMAIL PROTECTED] Sac> [EMAIL PROTECTED] Mafud, the correction is simple ;) do you have a variable aperture zoom? try it yourself. Point a variable aperture zoom toward a evenly lit wall, set ~YOURSELF~ an aperture (e.g. f/8), and see the corresponding shutter speed change as you zoom in and out. JUST DO IT Good light, Frantisek Vlcek - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Variable aperture zoom question
Kent suggested: >Well that is correct except at the widest >setting. If you have a 28-80/4-5.6 lens >and >set the aperture manually at F4 and zoom from >28 to 80mm you will end up at >F5.6 even if the >ring says F4. This is because at the >widest setting the aperture >ring is not >involved in the actual diaphragm function. >The insides of the lens >barrel is what >determines the aperture in that case. It's >actually easy to see the >effect. If you sit at >28mm and change the ring from 4 to 5.6 the >shutter value will >change. If you move up to >around 80mm and switch it between 4 and 5.6 >the shutter >value will not vary at all. I don't agree. My experience with the F 70-210/4-5.6 on my -5n is that at 70mm, the aperture values shown on the ring correspond to the actual value fed to the meter. At 210mm, each value is a whole stop slower - i.e. f/4 on the ring shows as f/5.6 in the viewfinder; f/32 as f/45. At an intermediate length, say 150mm, the difference is more like half a stop - f/8 becomes f/9.5. Since I seldom use anything but TTL metering, this doesn't matter to me, but for purely manual flash, I'd need to compensate for it. I think Mike's original question was "does f/8 on the ring of a variable-aperture 28-80 still mean f/8 at 50mm?" Well, if all Pentax v-a zooms work like mine, the answer is no. Hope that's some help, Clive. - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Variable aperture zoom question (on topic shurely)
Thank you John, when I wrote my response I did not include any facts as I felt that would have been inappropriate . Take two examples: FA28-70/4, and FA80-320/4.5-5.6 (I have these so can speak with confidence). When the 28-70 is set to 70, the iris is fully open giving f/4 (the opening is 17.5mm diameter). Zoom the lens to 28mm and the iris gradually closes, noticeably as you zoom between 35mm and 28mm. When you do this you become aware that the lens could (in theory) be a variable aperture f/2 ish to f/4. With the 80-320, at 80mm the iris diameter is 80/4.5 = 17.8mm. If you applied this iris to the 320mm end the effective aperture would be f/18, so the lens's aperture mechanism is connected to the zoom mechanism to close the iris as you zoom wider. The maximum aperture at the wide end is limited by optical performance rather than geometry. In any case, with the 80-320 set to minimum aperture (f/32 at 80mm), the viewfinder indicates a change to f/38 as the lens is zoomed to 320mm. Regards Jim Brooks > -- > > Date: Thu, 06 Dec 2001 20:09:05 -0600 > From: John Mustarde <[EMAIL PROTECTED]> > Subject: Re: Variable aperture zoom question (on topic shurely) > > On Thu, 06 Dec 2001 10:13:26 GMT, you wrote: > >>"[EMAIL PROTECTED]" wrote: >> >>"I'll say this and no more: when you ~manually~ set the aperture, the >>"variable aperture" becomes a "preset" (by you) aperture. Nothing you do >>while zooming will (can) change the aperture until (you) change it to a >>different setting. **And it does not matter whether you set it wide open or >>close it down all the way. The aperture CANNOT (does not) change until you >>change it-period." >> >> >>Er... simply, **this** (is) ~wrong~ -period. >>Regards >>Jim Brooks > > How right you are, Jim. Selecting F8 at the aperture ring will give > F11 at the tele end of a variable aperture zoom, assuming the zoom > varies by a whole stop. > > Of course, one might not notice this difference in the viewfinder of a > Super Program or other camera that reads in full stops, if the > variable aperture zoom varies by only one stop; but one would > certainly notice the exposure difference in the resulting slides if > one used the same selected Tv and aperture ring Av at the tele end as > at the wide end. > > I don't know if the aperture blades actually close during zooming (I > think not) so someone could argue that "the aperture really doesn't > change" but in fact, as the word aperture is commonly used in an > exposure and DOF connotation by photographers, the aperture actually > does change, even if it is only the "relative" aperture as stated in > F-stops rather than the physical diameter of the iris opening. > > In other words, selecting F8 at the aperture ring will give F11 at the > tele end of a variable aperture zoom, assuming the zoom is one which > the manufacturer says has a nominal one-stop variation such as the > very common f4-f5.6. > > I don't think angels dancing on the end of a pin can confuse the > difference between F8 and F11, but I'm sure someone will try to say > that F8 ~actually is~ F11 in *all* circumstances, and if I were only a > ~good~ *professional* photographer I would know that by heart, or else > I should be out taking photos instead of testing variable aperture > zoom aperture behavior. > > Here's how I did the test: I took out a couple of cameras, variable > aperture zooms, and fixed aperture zooms. Then I set the aperture to > F8 on every zoom. Then I set each lens to its widest setting. Then I > took a reading using center weight of a light, evenly illuminated, > wide wall, using each lens on each camera. Then I set each lens to its > longest setting, and repeated the tests. > > In every case, the proper exposure for the fixed aperture zoom was the > same whether at wide or long end; the proper exposure for the variable > aperture lens was one stop different at the long end than at the wide > end. > > So, in my small sample test, the variable aperture zoom varies the > effective aperture when zooming from wide to tele, despite the fact > that the desired aperture is fixed on the aperture ring. > > And the PZ1p and MZ-7 actually display this difference in the > viewfinder. Selecting F8 at the aperture ring shows a value of F8 in > the viewfinder when zoomed to the wide end; when zoomed to the long > end, the value in the viewfinder gradually migrates to F11. > > In other words, as I zoomed to the long end I could see the exposure > bar graph descending and the aperture readout changing from f8 to f9.5 > and
Re: Variable aperture zoom question (on topic shurely)
On Thu, 06 Dec 2001 10:13:26 GMT, you wrote: >"[EMAIL PROTECTED]" wrote: > >"I'll say this and no more: when you ~manually~ set the aperture, the >"variable aperture" becomes a "preset" (by you) aperture. Nothing you do >while zooming will (can) change the aperture until (you) change it to a >different setting. **And it does not matter whether you set it wide open or >close it down all the way. The aperture CANNOT (does not) change until you >change it-period." > > >Er... simply, **this** (is) ~wrong~ -period. >Regards >Jim Brooks How right you are, Jim. Selecting F8 at the aperture ring will give F11 at the tele end of a variable aperture zoom, assuming the zoom varies by a whole stop. Of course, one might not notice this difference in the viewfinder of a Super Program or other camera that reads in full stops, if the variable aperture zoom varies by only one stop; but one would certainly notice the exposure difference in the resulting slides if one used the same selected Tv and aperture ring Av at the tele end as at the wide end. I don't know if the aperture blades actually close during zooming (I think not) so someone could argue that "the aperture really doesn't change" but in fact, as the word aperture is commonly used in an exposure and DOF connotation by photographers, the aperture actually does change, even if it is only the "relative" aperture as stated in F-stops rather than the physical diameter of the iris opening. In other words, selecting F8 at the aperture ring will give F11 at the tele end of a variable aperture zoom, assuming the zoom is one which the manufacturer says has a nominal one-stop variation such as the very common f4-f5.6. I don't think angels dancing on the end of a pin can confuse the difference between F8 and F11, but I'm sure someone will try to say that F8 ~actually is~ F11 in *all* circumstances, and if I were only a ~good~ *professional* photographer I would know that by heart, or else I should be out taking photos instead of testing variable aperture zoom aperture behavior. Here's how I did the test: I took out a couple of cameras, variable aperture zooms, and fixed aperture zooms. Then I set the aperture to F8 on every zoom. Then I set each lens to its widest setting. Then I took a reading using center weight of a light, evenly illuminated, wide wall, using each lens on each camera. Then I set each lens to its longest setting, and repeated the tests. In every case, the proper exposure for the fixed aperture zoom was the same whether at wide or long end; the proper exposure for the variable aperture lens was one stop different at the long end than at the wide end. So, in my small sample test, the variable aperture zoom varies the effective aperture when zooming from wide to tele, despite the fact that the desired aperture is fixed on the aperture ring. And the PZ1p and MZ-7 actually display this difference in the viewfinder. Selecting F8 at the aperture ring shows a value of F8 in the viewfinder when zoomed to the wide end; when zoomed to the long end, the value in the viewfinder gradually migrates to F11. In other words, as I zoomed to the long end I could see the exposure bar graph descending and the aperture readout changing from f8 to f9.5 and finally to f11. Lenses tested: variable aperture zooms: F 70-210/4-5.6; FA 28-105/4-5.6 (original Power Zoom version); Vivitar 28-105/2.8-3.8 (manual focus); Fixed aperture zooms: F 24-50/4; 35-70/2.8 (old original AF for the ME-F). Cameras: PZ1p; MZ-7 I'd like someone with a constant aperture zoom that goes to 100mm or longer try this same test, and let me know the results. And someone else with a variable aperture zoom with a manufacturer's stated nominal variation of more than one f-stop range (say, 100-500/f4.5-7.3) conduct a small test to see if the effective aperture varies by the same amount as the stated range of variability of the zoom. In conclusion, if anyone thinks their variable aperture zoom fixed at F8 on the aperture ring will shoot at F8 when zoomed to tele, they should keep their camera on autopilot, or meter again and adjust shutter speed downward at the tele end, or just leave the shutterspeed alone and trust the wide exposure latitude of print film, lest they suffer from underexposed negs. -- John Mustarde - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Variable aperture zoom question
In a message dated 12/6/01 12:49:19 PM Eastern Standard Time, [EMAIL PROTECTED] writes: > Well that is correct except at the widest setting. If you have a 28-80/4-5.6 > lens and set the aperture manually at F4 and zoom from 28 to 80mm you will > end up at F5.6 even if the ring says F4." You're saying that a lens at f/4 ~migrates~ to f/5.6 in what is a no eletronic situation. The "A" setting closes (opens?) a circuit. Of the "A" the les is a manul lens. You must then explin how this "phantom" migration happens. > setting the aperture ring is not involved in > the actual diaphragm function." Yup. > The insides of the lens barrel is what determines the aperture in that case. > It's actually easy to see the effect. If you sit at 28mm and change the ring > from 4 to 5.6 the shutter value will change." Goes without saying. > and switch it between 4 and 5.6 the shutter > value will not vary at all." Only if the one-stop movement does not interfere with the amount of light, though theoretically it should. > that's because the amount of light is not changing because the barrel of the > lens housing is already stopping the amount of light to around F5.6 anyway." > OK, twisted, but OK. > > constant aperture zooms that are opened up at the short end." Zoomed to 80mm? That's the LONG end. > design of a constant aperture zoom is nothing more than > opening up the front element and lens barrel so that the diaphragm is not > vignetted by the barrel at the long end." OK > Kent Gittings > _ > -Original Message- > > Subject: Re: Variable aperture zoom question > > In a message dated 12/5/01 4:19:36 PM Eastern Standard Time, > [EMAIL PROTECTED] writes: > > That's precisely the point - that because the zoom lens is variable > > aperture, I cannot be guaranteed that the amount of light admitted through > > the lens will be constant over the zoom range of the lens. > IF you use a PK/A variable aperture lens with the lens in any position other than "A", the aperture WILL NOT change, withthe exception of using TTL flash in the aperture AE mode. The way you decribe it, ~you're~ setting the aperture yourself. It won't change no matter how you zoom (with the one TTL flash exception noted). > I'll say this and no more: when you ~manually~ set the aperture, the > "variable aperture" becomes a "preset" (by you) aperture. Nothing you do > while zooming will (can) change the aperture until (you) change it to a > different setting. > Specifically: when an "A" lens is not on "A," the lens becomes either > semi-manual? (aperture only) or full manual (aperture and shutter on manual > setting). > **And it does not matter whether you set it wide open or close it down all > the way. The aperture CANNOT (does not) change until you change it-period. > > Mafud > [EMAIL PROTECTED] > [EMAIL PROTECTED] - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
RE: Variable aperture zoom question
Well that is correct except at the widest setting. If you have a 28-80/4-5.6 lens and set the aperture manually at F4 and zoom from 28 to 80mm you will end up at F5.6 even if the ring says F4. This is because at the widest setting the aperture ring is not involved in the actual diaphragm function. The insides of the lens barrel is what determines the aperture in that case. It's actually easy to see the effect. If you sit at 28mm and change the ring from 4 to 5.6 the shutter value will change. If you move up to around 80mm and switch it between 4 and 5.6 the shutter value will not vary at all. that's because the amount of light is not changing because the barrel of the lens housing is already stopping the amount of light to around F5.6 anyway. >From a different perspective you could say that these are actually F5.6 constant aperture zooms that are opened up at the short end. Often times the design of a constant aperture zoom is nothing more than opening up the front element and lens barrel so that the diaphragm is not vignetted by the barrel at the long end. Kent Gittings -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of [EMAIL PROTECTED] Sent: Wednesday, December 05, 2001 7:51 PM To: [EMAIL PROTECTED] Subject: Re: Variable aperture zoom question In a message dated 12/5/01 4:19:36 PM Eastern Standard Time, [EMAIL PROTECTED] writes: > That's precisely the point - that because the zoom lens is variable > aperture, I cannot be guaranteed that the amount of light admitted through > the lens will be constant over the zoom range of the lens. > > I *thought* this phenomena applied to variable aperture zooms only when set > wide open. I'm trying to determine if this applies to *all* aperture > settings of the lens. > I'll say this and no more: when you ~manually~ set the aperture, the "variable aperture" becomes a "preset" (by you) aperture. Nothing you do while zooming will (can) change the aperture until (you) change it to a different setting. Specifically: when an "A" lens is not on "A," the lens becomes either semi-manual? (aperture only) or full manual (aperture and shutter on manual setting). **And it does not matter whether you set it wide open or close it down all the way. The aperture CANNOT (does not) change until you change it-period. Mafud [EMAIL PROTECTED] [EMAIL PROTECTED] - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org . ** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. This footnote also confirms that this email message has been swept by MIMEsweeper for the presence of computer viruses. www.mimesweeper.com ** - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
RE: Variable aperture zoom question
If it did there would be no real need for the aperture ring because it
wouldn't be accurate at all. From experience this only happens at the
wide-open setting due to the movement of the focusing group in the barrel.
When stopped down one stop it no longer varies the amount of light because
this was caused by the angle of the focusing group as it approached the
front of the lens and changed its subtended angle in relation to the front
of the lens opening. Once the diaphragm is stopped down its travel doesn't
change its relationship to the aperture opening caused by this so it no
longer varies.
Kent Gittings
-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]On Behalf Of Michael Nosal
Sent: Wednesday, December 05, 2001 4:25 PM
To: [EMAIL PROTECTED]
Subject: Re: Variable aperture zoom question
At 03:36 PM 12/5/01 EST, Mafud wrote:
>In a message dated 12/5/01 12:03:46 PM Eastern Standard Time,
>[EMAIL PROTECTED] writes:
>
>> "The replies to my original query seem to agree with what I was told -
that a
>> variable aperture zoom lens will vary the amount of light admitted as you
>> zoom in and out, no matter what I set the aperture ring to."
>>
>Not true. The variable aperture function happens only with PK/A lens in the
>"A" position. Your question specifically stated: "when ~I~ set the
aperture".
>**Otherwise, you could not choose your apertures for lighting or depth of
>field.
>
That's precisely the point - that because the zoom lens is variable
aperture, I cannot be guaranteed that the amount of light admitted through
the lens will be constant over the zoom range of the lens.
I *thought* this phenomena applied to variable aperture zooms only when set
wide open. I'm trying to determine if this applies to *all* aperture
settings of the lens.
Depth of field is *usually* desired in relative amounts ("more depth of
field" or "less depth of field" than it is in absolute amounts ("I want 3.5m
of acceptable focus") so having an effective aperture change of about 1 stop
probably won't screw up your desired depth of field. But it will mess up
your exposures.
>Remember: other than setting depth of field, the aperture has little to do
>with flash photography (assuming you lights/strobes are capable of
producing
>f/22 [f/32 for medium, f/45 for large format] lighting).
>
Aperture has everything to do with flash photography. I cannot adjust the
shutterspeed more than 1 stop. Too slow and I get camera shake, too fast and
it won't sync with the flashes. 1/60th, or 1/100th are my choices (on a
ZX-7).
Adjusting studio strobes can be tricky - sometimes your strobes only adjust
1 stop up or down, sometimes you can adjust in .1 stop increments. Sometimes
you cannot physically move the lights to adjust their intensity.
Film speed is also fixed - 100 or 160.
That leaves adjusting the aperture to match your lighting.
Except that a variable zoom lens can give a perfect exposure at 50mm,
overexposed at 35mm and underexposed at 80mm, even though the aperture ring
is set to f8 the entire time.
>Though you didn't say so, on PENTAX camera bodies with the "AE" function,
>~if~ your shutter is set on manual, and your lens is on "A," you're in
>shutter priority mode. But it seems you're describing manual studio
>operation, both shutter and aperture being ~set by you~. If so, and since
you
>didn't mention using a light meter, the presumption is you're using the
>camera meter. In such a studio situation, what you describe is full manual
>operation.
>That is: you've manually set the camera to "X" speed (or slower), then set
>the aperture for depth of field. In that situation, zooming only frames
your
>subject (again, depending on the power of your lighting).
This is metered with a handheld meter, full manual mode on the camera.
Now, it *MIGHT* be possible, for the camera to adjust for this effect. If I
set the aperture on the BODY, and I use a FA lens, the camera could detect
the focal length of the zoom, and compensate automatically when closing down
the aperture.
That is, if the lens does truly let less light in at the tele end than it
does at the wide end, then the camera could close down the aperture a little
bit less, to maintain consistent exposure.
Anybody know of any systems that do this?
--Mike
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Re: Variable aperture zoom question
I believe that when using Pentax cameras that allow you to set the aperture at the camera body, such as PZ-1P or ZX-7 and leaving the lens set at "A", the aperture will remain fixed as you zoom the variable aperture lens. Send your FREE holiday greetings online! http://greetings.yahoo.com - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Variable aperture zoom question (on topic shurely)
"[EMAIL PROTECTED]" wrote: "I'll say this and no more: when you ~manually~ set the aperture, the "variable aperture" becomes a "preset" (by you) aperture. Nothing you do while zooming will (can) change the aperture until (you) change it to a different setting. **And it does not matter whether you set it wide open or close it down all the way. The aperture CANNOT (does not) change until you change it-period." Er... simply, **this** (is) ~wrong~ -period. Regards Jim Brooks - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Variable aperture zoom question
In a message dated 12/5/01 8:46:30 PM Eastern Standard Time, [EMAIL PROTECTED] writes: > So I think you're wrong here, but it'spossible that I'm misunderstanding > what you're trying to say. > > chris > What I've said is: the physical aperture does not change. What happens in the viewfinder I'm not clear since I don't own nor have I used all models of PENTAX SLR cameras, and since there have been more than a few issued I don't know about, there might be a change (in the viewfinder). But does the aperture itself change as you contend? Do this: look at the aperture as you zoom. Does the aperture change? Or does any PENTAX camera act differently? PENTAX exposure modes: Programmed AE: lens on "A": shutter dial on "A" (Auto): camera automatically selects the most appropriate combination of shutter speed and aperture, changing them simultaneously... Aperture Priority AE: lens on any f: number: when the aperture is set manually, the shutter speed is automatically adjusted by built-in electronic circuitry according to the subject's brightness to provide appropriate exposure... Shutter Priority AE, the shutter speed is set manually and the aperture value is automatically controlled according to subject brightness... Metered Manual: lens on any aperture, shutter dial on "M (manual) The combination of shutter speed and aperture is completely up to you. PENTAX flash modes: TTL auto flash: When connected with a PENTAX dedicated TTL Auto flash unit, the metering cell inside the mirror box will detect the light hitting the film plane and automatically control the flash output. If you use a TTL flash unit, and set the camera in the Aperture-priority AE mode, ~you can choose any aperture in the flash range, thereby achieving great control over depth of field~... Here is the ~ONLY~ instance shooting ~TTL~ flash where the camera will adjust the aperture: Programmed Auto Flash: ~If~ you use a PENTAX dedicated TTL flash unit with the camera in the Programmed AE or shutter priority AE mode, the camera will automatically select the proper aperture and automatically control flash output. But remember, the question was: "If I set the aperture"? And my response(s) fit that condition: "If ~I~ set the aperture"? Meaning? Setting the aperture yourself on a PENTAX body obviates both the programmed auto flash or shutter priority modes. Mafud [EMAIL PROTECTED] [EMAIL PROTECTED] - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Variable aperture zoom question
> I'll say this and no more: when you ~manually~ set the aperture, > the "variable aperture" becomes a "preset" (by you) aperture. > Nothing you do while zooming will (can) change the aperture > until (you) change it to a different setting. [snip] And it does > not matter whether you set it wide open or close it down all the > way. The aperture CANNOT (does not) change until you change > it-period. No. In a constant-aperture zoom, the diaphragm opening is either effectively opened wider or closed down narrower as one zooms to longer and shorter focal lengths - this extra engineering is necessary to try to maintain a constant aperture. Since the aperture of a lens, in f-stops, is equal to focal length divided by iris opening, longer focal lengths require wider openings and shorter lengths require smaller openings to maintain the same ratio. However, in a variable-aperture zoom, the designer simply lets the iris opening stay fixed during focal length changes (or sometimes only partially compensates for focal length changes). If the diaphragm opening is fixed at a certain size, as an example, then zooming to a longer focal length will result in a larger f-stop ratio (i.e., a smaller aperture), while zooming to a shorter focal length will result in a smaller f-stop ratio (i.e., a larger aperture), even if the aperture ring is untouched by the photographer. Therefore, despite the statement that "the aperture CANNOT (does not) change until you change it", the aperture (as an f-stop ratio) DOES change as you zoom in a variable-aperture zoom (although it does NOT in a fixed-aperture zoom, but only because the designer compensated for zooming by employing a correspondingly "opposite" diaphragm change). You said "I'll say this and no more" - Well, I will say no more on this myself, but I'll bet that you can't - . Fred - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Variable aperture zoom question
On Wed, 5 Dec 2001 [EMAIL PROTECTED] wrote: > I'll say this and no more: when you ~manually~ set the aperture, the > "variable aperture" becomes a "preset" (by you) aperture. Nothing you do > while zooming will (can) change the aperture until (you) change it to a > different setting. [snip] > **And it does not matter whether you set it wide open or close it down all > the way. The aperture CANNOT (does not) change until you change it-period. I don't think this is true. If you take a variable-aperture zoom lens, like the 28-80/3.5-5.6 and set the aperture ring to "3.5", then the camera's LCD shows f3.5 at the 28mm setting. But as you zoom in, *without touching the aperture ring*, the real aperture (as shown on the LCD) will gradually change until it's at f5.6 at 80mm... even though the lens has been set manually to f3.5. So I think you're wrong here, but it's possible that I'm misunderstanding what you're trying to say. chris - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Variable aperture zoom question
At 03:36 PM 12/5/01 EST, Mafud wrote:
>In a message dated 12/5/01 12:03:46 PM Eastern Standard Time,
>[EMAIL PROTECTED] writes:
>
>> "The replies to my original query seem to agree with what I was told - that a
>> variable aperture zoom lens will vary the amount of light admitted as you
>> zoom in and out, no matter what I set the aperture ring to."
>>
>Not true. The variable aperture function happens only with PK/A lens in the
>"A" position. Your question specifically stated: "when ~I~ set the aperture".
>**Otherwise, you could not choose your apertures for lighting or depth of
>field.
>
That's precisely the point - that because the zoom lens is variable
aperture, I cannot be guaranteed that the amount of light admitted through
the lens will be constant over the zoom range of the lens.
I *thought* this phenomena applied to variable aperture zooms only when set
wide open. I'm trying to determine if this applies to *all* aperture
settings of the lens.
Depth of field is *usually* desired in relative amounts ("more depth of
field" or "less depth of field" than it is in absolute amounts ("I want 3.5m
of acceptable focus") so having an effective aperture change of about 1 stop
probably won't screw up your desired depth of field. But it will mess up
your exposures.
>Remember: other than setting depth of field, the aperture has little to do
>with flash photography (assuming you lights/strobes are capable of producing
>f/22 [f/32 for medium, f/45 for large format] lighting).
>
Aperture has everything to do with flash photography. I cannot adjust the
shutterspeed more than 1 stop. Too slow and I get camera shake, too fast and
it won't sync with the flashes. 1/60th, or 1/100th are my choices (on a ZX-7).
Adjusting studio strobes can be tricky - sometimes your strobes only adjust
1 stop up or down, sometimes you can adjust in .1 stop increments. Sometimes
you cannot physically move the lights to adjust their intensity.
Film speed is also fixed - 100 or 160.
That leaves adjusting the aperture to match your lighting.
Except that a variable zoom lens can give a perfect exposure at 50mm,
overexposed at 35mm and underexposed at 80mm, even though the aperture ring
is set to f8 the entire time.
>Though you didn't say so, on PENTAX camera bodies with the "AE" function,
>~if~ your shutter is set on manual, and your lens is on "A," you're in
>shutter priority mode. But it seems you're describing manual studio
>operation, both shutter and aperture being ~set by you~. If so, and since you
>didn't mention using a light meter, the presumption is you're using the
>camera meter. In such a studio situation, what you describe is full manual
>operation.
>That is: you've manually set the camera to "X" speed (or slower), then set
>the aperture for depth of field. In that situation, zooming only frames your
>subject (again, depending on the power of your lighting).
This is metered with a handheld meter, full manual mode on the camera.
Now, it *MIGHT* be possible, for the camera to adjust for this effect. If I
set the aperture on the BODY, and I use a FA lens, the camera could detect
the focal length of the zoom, and compensate automatically when closing down
the aperture.
That is, if the lens does truly let less light in at the tele end than it
does at the wide end, then the camera could close down the aperture a little
bit less, to maintain consistent exposure.
Anybody know of any systems that do this?
--Mike
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Re: Variable aperture zoom question
In a message dated 12/5/01 8:53:28 AM Eastern Standard Time, [EMAIL PROTECTED] writes: > Subj:Re: Variable aperture zoom question > > (Hi, > > Fred wrote: > > > > Mike: > > > > > Suppose I have a variable aperture zoom lens, say 28-80mm > > > f3.5-f5.6 If I set the zoom at 28mm, and set the aperture wide > > > open, it should be f3.5. If I then zoom to 80mm, the effective > > > aperture goes down to f5.6, right? And if I zoom to 50mm, the > > > aperture will be somewhere in between, say f4 maybe. > > > > Right. > > Right. > > > > Now suppose I set my zoom to 50mm @ f8. > > That's not an easy task. The aperture markings usually correspond to > the widest aperture. So, if you set the focal length to 50 and the > perture ring to where "8" is marked, you will have f/8 @ 28 and > something like f/13.5 @ 80 mm. > > > > If I zoom out to 28mm, will the effective aperture stay at f8? > > > If I zoom in to 80mm, will the effective aperture stay at f8? > > > Nope, in both cases (although my understanding is that the relative > differences in aperture at different focal lengths diminish as one moves > away from "wide open"). > > If you did manage to set exactly f/8 @ 50 mm, the answer is no to both > questions. > > > In any event, if you're using TTL metering (which most of us use most of > the time), then the exposure recommendation should automatically compensate > for the variable aperture problem. > > This is, fo course, correct and the most important thing. The trouble > with the variable apertures comes in play when you use manual flash, > studio flash, etc.) > > Cheers, > Boz _ Pardon me if I misunderstand the gist of you response: the operative question asked by Mike was : "if I set"... Are you (anyone) now suggesting that setting the aperture manually, somehow changes the aperture as you zoom? How? ***Taking the aperture ring off "A" makes it a ~manual~ lens, or are you (anyone) saying that somehow, the camera/lens changes what is a (preset) aperture anyway? How? Mafud [EMAIL PROTECTED] [EMAIL PROTECTED] - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Variable aperture zoom question
At 10:14 AM 12/5/01 +0100, Boz wrote: >Hi, >That's not an easy task. The aperture markings usually correspond to >the widest aperture. So, if you set the focal length to 50 and the >aperture ring to where "8" is marked, you will have f/8 @ 28 and >something like f/13.5 @ 80 mm. >The trouble with the variable apertures comes in play when you >use manual flash, studio flash, etc. > >Cheers, >Boz Okay, so using a variable aperture zoom is fairly hit or miss when metering manually. So a fixed aperture zoom is what is required if one wants to be certain about matching exposure to your metering, correct? Will I be able to set f8 on a fixed aperture zoom and know it is going to be f8 if I zoom in or out? (My choices among Pentax autofocus are rather limited - the wicked expensive 28-70/f2.8 or the very inexpensive 28-70/f4) --Mike - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
RE: Variable aperture zoom question
My F zoom lenses appear to have a second mark (a green dot) on the aperture (not there on the primes) which would appear to align with the lower of the two f settings. My guess would be this is the real f stop for the opposite and of the range... e.g. an F 70-210 1:4-1:5.6 Main orange f stop mark is at f4 when the green dot is next to f 5.6. The orange mark is showing the f stop for 70mm and the green dot is showing it for 200mm. So it would follow that when the lens is zoomed in between those two focal lengths that the aperture would be somewhere in-between the two. Unless I am missing something this *must* be the case... I would say in order to get f8 you need use the lens like a prime (at one or other end of it's zoom range), and set the f8 against the corresponding mark for whichever end of the range you are using. Perhaps somebody else has a more definitive answer, as this is certainly only my best guess. Regards, /\/\ick... - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Variable aperture zoom question
Mike: > Suppose I have a variable aperture zoom lens, say 28-80mm > f3.5-f5.6 If I set the zoom at 28mm, and set the aperture wide > open, it should be f3.5. If I then zoom to 80mm, the effective > aperture goes down to f5.6, right? And if I zoom to 50mm, the > aperture will be somewhere in between, say f4 maybe. Right. > Now suppose I set my zoom to 50mm @ f8. > If I zoom out to 28mm, will the effective aperture stay at f8? > If I zoom in to 80mm, will the effective aperture stay at f8? Nope, in both cases (although my understanding is that the relative differences in aperture at different focal lengths diminish as one moves away from "wide open"). > In other words, how can I tell if I'll really get f8 when I set > it to f8? You can't, exactly (although at f/8 you'd probably be close enough if you were using print film). That's one reason why many of us Pentax dinosaurs prefer sticking to the ol' constant aperture zooms. The fact that, in general (with some exceptions, of course), most (typically older, often MF) constant aperture zooms are better built than most (typically newer, often AF) variable aperture zooms, is another reason for the dinosaurs amongst us. But I digress... In any event, if you're using TTL metering (which most of us use most of the time), then the exposure recommendation should automatically compensate for the variable aperture problem. Fred - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
