Red #25a

I have some questions, with possibly obvious answers:

 

I just started using a Red 25A Hoya filter with a 50mm Pentax. I had read on

another forum that some adjustments were necessary when using the filter. This

was actually about HIE film. I�m using Tri-X 400, but I did so with the �HIE�

advice�I didn�t keep a log of my shots� The HIE advice was to go 3 stops

up/or down�I forgot which, so I did both. The conditions were right before a

storm with really cloudy skies, and were just pictures of a house. I bracketed

through 36 shots, trying normal exposures, then overexposures/3-stops up (this

is called step-up, right?) and underexposures/ 3 stops down (step down?). Some

came out correctly exposed�with just normal looking clouds�now I know there was no �

dramatic effect due to the sky's grayness.

 

There were some ridiculously dramatic images�what I think is called the

�moonlight effect�, a really dark sky and lighted clouds, but with a

(underexposed) silhouette of the house. Is there any compromise here�the

moonlight effect in the sky with a correct exp of the house? Is this where

dodging or burning come into play, with printing, or something else?

 

Also, when adjusting the exposure, I have a TTL meter�do I take the reading WITH

the red filter on and adjust? Or do I take the normal no-filter reading, then

put the filter on to adjust to what the no-filter conditions suggest? Any other

basic know-how with the filter would be greatly appreciated.

 

Thanks!

Since the camera meters through the lens, mount the filter on the lens, set the exposure according to the meter, and bracket up or down a stop or two. You should get good exposures even without bracketing. With the 25A the blues in the sky will be very dark, and the white clouds should be white. I am sure someone on this net has an example for you to see.

Rosemary, with TTL metering it is metering "Through The Lens" (including anything stuck in front of the lens such as a filter), so you actually don't need to compensate for the filter at all. It never hurts to bracket a little bit though -- maybe a stop up and a stop down -- because your meter can certainly be fooled, and also there is no such thing as a right or wrong exposure...more like interpretations of a scene, so one of your brackets may be actually more interesting than the meter reading.

 

Hope that helps!

you take the meter reading on an SLR camera with a built in meter (I assume that is what you are calling TTL....Thru the Lens) with the filter on. That is the correct exposure........well, as correct as any other you would take and just believe the meter.

 

a Red #25a filter is a color contrast filter for black and white film. It transmits it's own color (ie lightens it in the print) and absorbs it's complimentary color (darkens it in the print). So a red 25a will lighten red and darken cyan (blue and green) in the print.

 

Thats ALL it does

 

The reason the HEI info says to bracket so much, is because you don't know how much near infrared energy is in the scene....and neither does the meter, really. It has nothing to do with the red filter itself. And, it has no bearing on using the filter with Tri-X.

 

Your moonlight looking ones are probably the underexposed ones......and no.....by normal means you can't get the house and "moonlight" to both be light in the same pic. Actually you could get the same effect with out the filter.......just underexpose the film.

<br><br>most films today are panchromatic today, Tri-X definitely is........which you will need to know when you look at <a href="http://www.crime-scene-investigator.net/filters1.html"><u>this black and white contrast filter page</u></a>....hope it helps

Red #25 filter at work...

Whether the through lens meter compensates correctly may depend on the meter and what kind of cells it uses. Modern meters should do fine as they are, but some of the older ones are not really completely panchromatic. I have found that the CDs cells on my Nikon F do not fully compensate, and it's helpful to add one more stop of compensation to what the meter indicates. The Konica T3 has a similar characteristic. I usually take the meter reading and then open it up one stop more.

CDS cells have a higher red sensitivity than silicon and other modern cells. CDS cells do have some infrared response, but I'm not sure how accurately they react. I know the meter needle in my SRT will jump slightly when I point an infrared remote at the lens. I've noted this on old Konicas, Minolta SRT's, and Canons.

Run some tests with the film you plan to use.

I use EV 15 for the sunny normal scene value with TRI-X (ASA 400)(EV 17 without filter). Which is two spots for the the 25 red filter. I feel that Red 25 is about 2.5 (or maybe a little towards 2.0) stops when using TRI-X 400.