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Bolex f-stop compensation.


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#1 Morgan Peline

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Posted 05 July 2006 - 07:44 PM

Hi,

I'm just about to do some tests with a Bolex H16 tomorrow (because I have 100ft rolls of neg). Just checking if I remember rightly as I haven't used one in ages...Do I open up an extra 1/3 to 1/2 stop on what my meter says to account for the prism?

I know that it is probably somewhere on the forum, but it's just that it's very, very late! I'd forgotten how to load it as well...can you believe that?

Thanks a lot!
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#2 Clive Tobin

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Posted 05 July 2006 - 08:49 PM

...Do I open up an extra 1/3 to 1/2 stop on what my meter says to account for the prism?

...I'd forgotten how to load it as well...can you believe that?


Bolex's word is that 20-25% of the light is diverted to the viewing system. Assuming 20% is correct, this means setting your meter to about 1/80 second instead of the physical 1/60-1/65 at 24 FPS. Or if your meter assumes the exposure time is 1/50 this means opening up 2/3 stop or else setting the ASA 2 steps lower on the dial.

As far as loading goes, the instructions I wrote for our TTL time lapse motor assume that many Bolexes will be used for time lapse filming, by people who normally use other brands of camera. Therefore the TTL instruction manual gives the basic threading and operating instructions for the Bolex. This can be found under the Instruction Manuals page on my website www.tobincinemasystems.com . Cheers,
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#3 Tim Carroll

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Posted 05 July 2006 - 09:35 PM

Hi,

I'm just about to do some tests with a Bolex H16 tomorrow (because I have 100ft rolls of neg). Just checking if I remember rightly as I haven't used one in ages...Do I open up an extra 1/3 to 1/2 stop on what my meter says to account for the prism?

I know that it is probably somewhere on the forum, but it's just that it's very, very late! I'd forgotten how to load it as well...can you believe that?

Thanks a lot!


A couple of years ago I gave Tim Tyler a PDF of the Bolex EBM manual and he posted it in the "Manuals and Docs" section of this web forum. You can go there and download it for free. Prism compensation is covered in there as well as how to load the camera.

Cheers,
-Tim
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#4 markb

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Posted 06 July 2006 - 07:00 AM

if your lenses have "Bolex RX" written on them the the T-Stops are already corrected for the prism light loss.
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#5 Leo Anthony Vale

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Posted 06 July 2006 - 01:48 PM

if your lenses have "Bolex RX" written on them the the T-Stops are already corrected for the prism light loss.


---Cite your source.

I've yet to see a Bolex lens marked in T stops & the manual gives the effective shutter speed.

---LV

Edited by Leo A Vale, 06 July 2006 - 01:50 PM.

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#6 Clive Tobin

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Posted 06 July 2006 - 09:55 PM

if your lenses have "Bolex RX" written on them the the T-Stops are already corrected for the prism light loss.

Wrong. This has been covered ad nauseam.

Bolex states clearly in their literature that the Bolex LIGHT METER has "adapted" shutter speeds to compensate for prism loss, NOT the lens calibrations.
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#7 Nick Mulder

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Posted 07 July 2006 - 01:37 AM

---Cite your source.

I've yet to see a Bolex lens marked in T stops & the manual gives the effective shutter speed.

---LV



The Vario-Switar PTL 12.5-100 power zoom has both f and T stops

Edited by Nick Mulder, 07 July 2006 - 01:42 AM.

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#8 Leo Anthony Vale

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Posted 07 July 2006 - 11:51 AM

The Vario-Switar PTL 12.5-100 power zoom has both f and T stops


---Okay, & the Angie Rx zooms.

Any primes?

Could this be...OLD SAW WARNING...the exception that proves the rule?

---LV
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#9 Nick Mulder

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Posted 07 July 2006 - 04:28 PM

Could this be...OLD SAW WARNING...the exception that proves the rule?


Yep... I just happened to have it right next to me when I was reading the thread... tis all :P
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#10 Mike Rizos

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Posted 11 July 2006 - 05:04 PM

Here's a web site that adds to the confusion concerning Rx lenses. It contains a very good history of Bolex cameras and lenses, but I've come to believe that it must be wrong on the Rx lens issue.

http://www.bolexequi...mLensesMenu.htm
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#11 Boris Belay

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Posted 12 July 2006 - 07:08 PM

Yes, that info is definitely WRONG, as is a number of other things on that site (nice idea, but...).
The reference on the RX lens issue (correcting optical aberrations introduced by the prism, NOT its light-loss) as well as actual shutter speeds (real and corrected) is this site :
http://www.city-net.com/~fodder/bolex/

Note that the EBM (and EL) does not have the same shutter angle as the traditional H16RX, and so, a different shutter speed.
-B.

Here's a web site that adds to the confusion concerning Rx lenses. It contains a very good history of Bolex cameras and lenses, but I've come to believe that it must be wrong on the Rx lens issue.

http://www.bolexequi...mLensesMenu.htm


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#12 Clive Tobin

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Posted 12 July 2006 - 07:15 PM

Here's a web site that adds to the confusion concerning Rx lenses. It contains a very good history of Bolex cameras and lenses, but I've come to believe that it must be wrong on the Rx lens issue.

http://www.bolexequi...mLensesMenu.htm


What, misinformation published on the Internet? I've never heard of such a thing. :-)
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#13 markb

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Posted 13 July 2006 - 02:26 AM

I hate to take the wind out of anybodies sails but this is the reply i got from Bolex in Switzerland, if anyone should know they should.

this is what they say.

Dear Sir,

If the lenses are marked Bolex RX, they should be automatically calibrated
to the Bolex Reflex system.

Best regards.

Bolex International SA
Marc Ueter

www.bolex.ch (16mm and Super 16 Bolex equipments)


it's common sense. why would angenieux, switar, schneider etc make a lens with "Bolex RX" stamped on the side and then epect you to do the compensation?

i've always used the t-stops and never had any problems, and all my lenses have t-stops.
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#14 Leo Anthony Vale

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Posted 13 July 2006 - 02:29 PM

I hate to take the wind out of anybodies sails but this is the reply i got from Bolex in Switzerland, if anyone should know they should.

this is what they say.
it's common sense. why would angenieux, switar, schneider etc make a lens with "Bolex RX" stamped on the side and then epect you to do the compensation?

i've always used the t-stops and never had any problems, and all my lenses have t-stops.


"If the lenses are marked Bolex RX, they should be automatically calibrated
to the Bolex Reflex system."

Their reply doesn't say that the calibration is for exposure.

Read this page:

http://www.city-net....olex/truth.html

The calibrations the reply refered to are for focal shifts, not exposure shifts.

The rex manual states the actual shutter speed is 1/65th sec and the effective shutter speed is 1/80th sec.
So, YES, they expect you to compensate for the prism's light loss by adjusting the shutter setting on your light meter.

If your lens are actually calibrated in T-stops, they are zooms. Compare the maximum T-stop against a non-TX version. Is it any different?

---LV
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#15 markb

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Posted 14 July 2006 - 02:27 AM

"If the lenses are marked Bolex RX, they should be automatically calibrated
to the Bolex Reflex system."

Their reply doesn't say that the calibration is for exposure.

Read this page:

http://www.city-net....olex/truth.html

The calibrations the reply refered to are for focal shifts, not exposure shifts.

The rex manual states the actual shutter speed is 1/65th sec and the effective shutter speed is 1/80th sec.
So, YES, they expect you to compensate for the prism's light loss by adjusting the shutter setting on your light meter.

If your lens are actually calibrated in T-stops, they are zooms. Compare the maximum T-stop against a non-TX version. Is it any different?

---LV


you make your films your way i'll do it my way! some people can never admit when they are wrong!!!
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#16 markb

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Posted 14 July 2006 - 02:38 AM

just to clarify for the confused, this was the email i sent to bolex

----------------------------------------------------------------------------------------------------------------------------------------------

Dear Sir

please could you tell me if the T-Stop of a lens marked "Bolex RX" will have
be calibrated to take account of the light loss through the prism or do i
still need to increase the exposure?


-----------------------------------------------------------------------------------------------------------------------------------------------

this was the reply

--------------------------------------------------------------------------------------------------------------------------------------------------

If the lenses are marked Bolex RX, they should be automatically calibrated
to the Bolex Reflex system.

-------------------------------------------------------------------------------------------------------------------------------------------------

i don't think they could make it any clearer. if you are still unsure why not email Bolex and ask them?
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#17 Chris Keth

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Posted 14 July 2006 - 11:56 AM

Bolex's word is that 20-25% of the light is diverted to the viewing system. Assuming 20% is correct, this means setting your meter to about 1/80 second


This is what I always did in film school. I just figured out adjested shutter speeds and taped them to the camera body.


Bolex's word is that 20-25% of the light is diverted to the viewing system. Assuming 20% is correct, this means setting your meter to about 1/80 second


This is what I always did in film school. I just figured out adjested shutter speeds and taped them to the camera body.
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#18 Leo Anthony Vale

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Posted 14 July 2006 - 01:53 PM

If the lenses are marked Bolex RX, they should be automatically calibrated
to the Bolex Reflex system.

-----------------------------------------------------------------------------------------------------------------------------

i don't think they could make it any clearer. if you are still unsure why not email Bolex and ask them?


---I'm not unsure.

Yet Bolex says lenses longer than 50mm that are not RX can be used on a Rex.
There is no special RX version of The Kern 17-85/3.5. Nor the Berthiot 17-85/3.m and 12-120/3.3, both of which were marketed by Bolex for the Rex..

Explain. Show your math.

If your RX lenses are not zooms, they are not marked in T stops.

---LV
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#19 Chris Keth

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Posted 14 July 2006 - 10:17 PM

you make your films your way i'll do it my way! some people can never admit when they are wrong!!!



Don't be a douche. We're all about the rational argument here.
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