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Author Topic: Hasselblad CFV and Alpa TC  (Read 1770 times)
mmbma
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« on: June 19, 2013, 01:14:55 PM »
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I use a CFV 39 back with the Alpa Tc and I've been plagued by the purple color cast effect form the copal shutters. The issue has been identified by Alpa on their website but so far they have not provided a solution (other than a work around). Does anyone else use similar setup and have found a solution? Not sure if there's a later firmware from Hasselblad that address this issue.

Thanks

mmbma
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epines
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« Reply #1 on: June 19, 2013, 02:11:29 PM »
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Just to make sure -- you're aware of Phocus's "scene calibration" tool, right? Gets rid of all color casts, vignetting, etc. I'm happy to explain how to use it if you're not.
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carloalberto
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« Reply #2 on: June 21, 2013, 07:39:27 PM »
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>>Just to make sure -- you're aware of Phocus's "scene calibration" tool, right? Gets rid of all color casts, vignetting, etc. I'm happy to explain how to use it if you're not.>>

Yes please. I'd love a bit of help on this. Just got a CFV-50 and Phocus.
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neilwatson
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« Reply #3 on: June 21, 2013, 09:17:26 PM »
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Try this, as a test to narrow down what is happening.

Remove the sync cable between lens and digital back.  ( don't use a sync cable )
Use a simple wake up cable instead.
Set the digital back to xsyn mode.
Also set a 4 second shutter timeout on the digital back.

Compose picture.
Send wake up signal
Release lens shutter
Wait 4 seconds.
The digital back will write the digital file.

Then compare this picture with the picture your having problems with.

You will then know if it's a wake up / shutter timing issue.
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phoTOMgraphy
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« Reply #4 on: June 22, 2013, 05:42:23 AM »
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i've had similar problems with my h3d back on an arca rm3di.

do you see much more noise too?
then it's a wake up problem. the sync trigger comes when the shutter is almost fully open - so some light hits the sensor before the trigger is high.
and the back is in sort of a flushing mode at this time.
you may notice that the effect is heavier at shutter speeds of 1/30s and shorter. it seems hasselblad had in mind (at the time these back came out) that they would only be used in studio where you have longer exposure speeds. the longer the shutter speed, the lesser the affect.

see attached pdf from hasselblad.

like neil said, i use two cables - one cable release for the back and one for the copal shutter.
you can use a canon RS60-E3 cable release - less expensive than hasselblad's cable release ;-)

as long as you press the back's release it will expose. so you don't have to tweak the settings of the back to a specific time - 1/8 sec will do the job. just press the trigger and hold it - meanwhile press the copal trigger and release both when finished.
but it's a littlebit tricky when shooting lcc shots (3 hands are required ;-)   )

so i made myself a double cable release. this works fine.
see my post here: http://www.getdpi.com/forum/medium-format-systems-digital-backs/45196-selfmade-one-shot-cable-release.html

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thomasebruster.com
Arca Rm3di | RS90 | SK43 | RS28 | CFV-50
epines
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« Reply #5 on: June 22, 2013, 02:15:45 PM »
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For the original poster, the Scene Calibration tool should definitely get rid of that purple color cast. It's from the lens, not the shutter.

Here's my process, using an H3DII-39 back on an Arca Swiss 69 FC. Note: I believe Hasselblad changed a few things in the back between the H3D and H3DII, so settings / experience / process might differ slightly. And of course the CFV's settings and menu might differ. But hopefully the process is similar. It's actually simpler than it sounds.

- Compose and focus using ground glass if shooting to a card, or choose to compose and focus later if shooting tethered.

- Mount the back on the camera.

- Power up the back (by connecting via Firewire to an external battery or to a computer) before opening Phocus. On the back's menu, go to Settings > Camera > Body: FlashSync, Exposure Time: <1/8 sec.

- Open Phocus (or shoot to a card, if you don't want to shoot tethered).

- Connect sync port on lens to "In" port on back. Connect standard cable release to lens.

- Compose and focus using live view if shooting tethered. Include any camera movements (shift, rise, etc.)

- Shoot a few shots to finalize exposure and composition. At this point, you can choose to capture your scene-calibration shot before or after capturing your image. I typically capture the scene-calibration shot beforehand. All camera movements (and a center filter, if you have one) should be in place before shooting the scene-calibration shot.

- For the scene-calibration shot, here's a link to a demonstration on Hasselblad TV:
http://htv.hasselblad.com/video/scene-calibration-tool
And here's the Phocus user manual:
http://www.hasselblad.se/media/1901174/uk_phocus_manual_v6.pdf

- you'll need a frosted, translucent white plastic card to place in front of the lens. (Capture Integration sells a set of two (different sizes) for $20. It's a great little set.) You hold the plastic piece over the lens and shoot your same exposure, same f-stop. If you're shooting tethered, you can create the scene calibration now. If you're shooting to a card, you can create it later. Either way, in Phocus, under Adjust, go to the scene-calibration tool and click the Create button. Name the shot (I usually include the focal length, movements applied and shoot name. For example: 35_0_5down_BaerHome.) At this point you may have to place a check mark in the tool's header to make it active. Check both boxes within the tool: Remove cast and Equalize intensity. You should see any vignetting and color casts in your white capture disappear. If you shoot your actual image next, those adjustments should be applied to the image automatically. If you shot your image beforehand, copy those adjustments to the image (or, when viewing the image, select the scene calibration you just made from the scene-calibration tool's dropdown menu). You'll see any vignetting and color casts disappear. It works very well.

Hope that helps. Let me know if something's unclear.

ethan
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epines
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« Reply #6 on: June 22, 2013, 02:50:53 PM »
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One more thing -- if you're shooting a lot of shots in one spot, same camera settings, same lens, etc., you can just shoot a single scene-calibration shot at the start or at the finish of your shooting, then apply that scene calibration to all those shots in post.
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phoTOMgraphy
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« Reply #7 on: June 23, 2013, 05:44:49 AM »
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another one more thing - you can even use the scene calibration shot (when already neutralized) as a greycard to set the white balance.
works very well!  Grin


as i mentioned above - if it is a sync problem you should notice an increase of noise too. and the effect depends on the speed of the shutter.
in this case no lcc shot will do the job!

attached a comparison between h3d-back on arca and h3d-back on hasselblad body, showing the sync effect:
click on the thumbnails to clearly see the noise - it's terrible. the shutter speed was 1/60 as you can see in the filenames
« Last Edit: June 23, 2013, 05:49:29 AM by phoTOMgraphy » Logged

thomasebruster.com
Arca Rm3di | RS90 | SK43 | RS28 | CFV-50
alpenflex
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« Reply #8 on: June 23, 2013, 03:33:38 PM »
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I'm just a silent reader but I really do not understand why people here do not ask the manufacturers directly. When I had the same problem with my CFV-39 on my LF cam they were the only company mentioning the problem ( http://www.alpa.ch/en/news/2009/new-kid-on-the-block ) and I got an answer from ALPA in a split second by e-mail.

They recommended the manual triggering (two-shot-mode, auto-time-off set to 2-4 sec) with a handy Hasselblad release cord H ( http://www.hasselbladusa.com/products/lenses-and-accessories/h-system-accessories.aspx ) for little money or their full fledge one-shot-solution with their sync release ( http://www.alpa.ch/en/products/lenses/alpa-sync-solutions/alpa-sync-release.html ) which is much, much more convenient as it works with all exposure times independent of the auto-time-off... but comes at a price.

Scenen calibration is not compensating for color AND the strange noise in the shadows. The CFV-39 needs a wake-up. It's the sensor. The newer CFV-50 should be fine. Hope this helps.



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jotloob
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« Reply #9 on: June 29, 2013, 01:17:37 PM »
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The CFV-50 needs a wakeup signal as well . Use the same procedure as describe above .
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Jürgen
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