Portra 400 Pushed 2 Stops

Donald Qualls · Feb 26, 2022

Matt Hall said:
I do not have a lens/shutter that I can use to flash the sheets and I KNOW that I cannot be accurate to 1/30 sec using the dark slide. I will need to attenuate the light source by at least 7 stops to get the time out to 4 seconds where I can be accurate enough to even consider using the dark slide. At least I have a starting point.

Here's a possibility on this front: you can get a 4x5 camera with working shutter (you don't need or want the lens for this, so it doesn't matter what the glass is) for a fairly modest price -- I see them around $100 every so often on eBay, and I'm not looking hard because I already have a Speed Graphic and two Graphic View (an original and a II) -- a lightweight field camera would be welcome, but I haven't the money to shop seriously at present. You only need a shutter that works and a light tight bellows to use the setup for flashing film. Ansel used to use a dome mounted on the same lens he was using for the images to do preflashing in the field when he determined it was needed -- but your setup with a white-lit surface, combined with removing the glass from the shutter, would give you the same effect with good evenness and (depending on your light setup) fine control of the light intensity and color.

Light Capture · Feb 26, 2022

Matt Hall said:
Well, I just picked up my film and there are a bunch of notes on the envelope from the lab. I didn't tell them I was doing a test strip exposed to straight white light. They got a little freaked out when most of my frames were either completely dark or clear. I think they assumed they had processed it wrong. Kinda funny actually!

So the results have surprised me a bit. I thought that the correct flash point of just reaching readable density would be around the 5 to 10 second area. I wasn't even close! I can clearly see density in the 1/30 sec. exposure for the 2 stop push and 1/15 sec. for the one stop push using a loop and the naked eye. I thought it would be easy to flash the 4x5 sheets since the time would be in seconds since I will have to do it manually using the dark slide. Now with the correct time at 1/30 - 1/15 sec. I am left with a problem. I do not have a lens/shutter that I can use to flash the sheets and I KNOW that I cannot be accurate to 1/30 sec using the dark slide. I will need to attenuate the light source by at least 7 stops to get the time out to 4 seconds where I can be accurate enough to even consider using the dark slide. At least I have a starting point.

I guess I should have mentioned that I am using a German Equatorial Mount with dual axis drive for my exposures. You can see the camera I built for this in the following string here on Photrio:

https://www.photrio.com/forum/threads/aero-ektar-12-inch-f-2-5-4x5-astro-camera.189944/

I will also be using a 400mm f/5 guide scope with a 2-inch eyepiece for tracking using an illuminated reticle to help keep the entire system trained on one point in the sky with no errors. I'm trying to get some detail in the gaseous region around Orion, including some of the H-alpha emission areas (think Horsehead nebula) and such. That is the reason for the extended exposure times I need. Not too many photons from those distant objects reach us here on Earth. My favorite film for astrophotography was the Fujichrome Provia 1600 which was a 400 speed film made for pushing 2 stops in processing. Bright points like the heads of comets, etc. would get burned up, but for the most part it rendered some great images with surprising tonal ranges. Shadow detail was also excellent. But, as we all know, all these great films are gone. You can go back to my Feb. 16 post in this string to see one of my favorite shots.

I would recommend using white balance filter over the lens focused to infinity. Makes things easier and more predictable on different formats and lenses. Drawback is that there will be some fall-off. If important that would need to be tested.
It could be done in two ways. With light table in front of the lens covering whole negative or with lens pointing to the white wall and pointing strobe to the wall.
This would probably mean repeating the pre-flashing test.

Other way is doing it the same way as your test and build an opaque box with combination of ND filters to the front to reach 7 stops.

We very often forget that our eye's and ear's response is logarithmic. Double the amount of light (1 stop) is needed for appreciable increase in density.
Same as hearing someone talk few hundreds of meters away. You can hear it far away but can't really understand what is being said until you come closer.

Portra 400 Pushed 2 Stops

Donald Qualls

Light Capture

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