How to check digital back for problems?

[nightfire]

I'm about to receive a digital back for my Hasselblad V. Since I'm new to medium-format digital, what are the usual procedures to examine a back in detail for technical problems and issues after purchase? I already thought about checking for sensor scratches and hot pixels. What other tests should I do to ascertain myself that the back, as well as the entire back/body/lens combo, will the deliver the best performance possible? Thanks!

[Graham Mitchell]

Apart from the obvious sensor scratches and hot pixels, I would recommend you test all ports/interfaces as working, e.g. the firewire port.

[eddysmit]

Also the strobe connectors if it has them.
If you have it, you have to see if it is in focus and that you can correct it with shims.
See if the sensor is not off parallel.

[ondebanks]

First and most important, "RTFM" - make sure that you are familiar with everything it can do and how to do it.

Check that it mounts/dismounts positively on the camera.
Check that the batteries charge ok.
Check that both batteries and DC adapter power it ok.
Check that images write to card ok and can be deleted in-camera.
Check that it tethers to computer ok.
Check any other ports - video out, flash synch, serial in.
Check that all the menu settings and buttons do what they're supposed to - shoot at different ISOs, white balances, image review options...
Shoot at the shortest and longest exposures that the camera/back permits, and check that you get an image.
In the case of long exposures, check that the option to take & subtract internal dark frames works both on and off (if it has this option)
If it's some years old, don't be too surprised at seeing a few hot pixels at mid-range exposure times: CCDs "age" due to cosmic radiation damage and their dark/hot current can rise.
http://www.harvestimaging.com/pubdocs/130_2009_IISW_cosmicrays.pdf
Check the in-camera tiff/jpg processing (if it has it).

[eddysmit]

So I have to store my camera in 1cm thick lead box?

[ondebanks]

A 1cm thick lead box won't help much. These are not X-ray photons; they are much higher energy, mostly muon particles which managed to penetrate an entire atmosphere of air. They'll also go through metres of soil or concrete without significant attenuation.
http://snap.lbl.gov/ccdweb/groom.pdf

Keeping your camera down a deep mine would work, though  . This is where the astronomical neutrino & proton decay experiments are set up, to avoid cosmic ray noise:
http://en.wikipedia.org/wiki/Kamioka_Observatory

In the same vein, I've read that Kodak used keep their stocks of fresh TMAX-P3200 down a salt mine, to prevent it fogging prematurely from radiation.
http://photo.net/film-and-processing-forum/00NHDE

Here's another link on radiation damage in CCDs, and the column defects it can produce (in addition to the hot pixels):
http://www.narrowbandimaging.com/block_column_page.htm

The universe is a hostile place. On terra firma, we are actually shielded from the vast majority of the nasty radiation. Few people have any inking how fortunate they are to have airmass=1.0 above their heads at all times...

Ray

[Dick Roadnight]

Check that it mounts/dismounts positively on the camera.

Are there not light seals on the digiback that need inspection and checking by doing a long exposure in bright sunlight with the lens cap on?

[shutay]

Don't forget a dust check shot as well. I.e., is it clean? Do you know how to clean your IR filter? Procedures and materials? Any dust with "halos" around them? Fungus???

[tbosley]

Hi,
A few items I've learnt from previous backs:

*If your back uses removable media- find out which ones you have will work/ purchase those known to work with your system asap.  Format and read memory with PC.  Also gives you a chance to also work with PP apps.
Nothing like taking back out only to find the media does not work well with back!


*Check the firmware and see if manufacturer has a more recent version.  Follow-up with the process to upgrade the firmware if necessary.

Some SW automatically uploads the newer firmware once connected.

*Check PC/Mac connectivity.  This will allow to sort through both SW and HW issues....

*Do what I call the "Alpha infinity tests" to see if your finder/back is out of alignment.

[nkbitsch]

I'm not the creater of this thread, but thanks for the great tips, and advices.

[nightfire]

Thanks for the very helpful input. I'm currently building a checklist... and waiting for the back...

Regarding the back/sensor alignment tests: what would be the best procedure for this? I read an essay by Joseph Holmes in which he recommended to focus on a prominent object far away, and compare the sharpness of shots at the widest aperture with the object in center, as well as in each of the four corners. Is this how it's usually done?

Regarding hot pixels: how many hot pixels are tolerable? In the DSLR world, the current dealer attitude seems to be that a few hot pixels per sensor are not to be considered a defect (and therefore would not constitute a reason for return/warranty repair), but rather are the inevitable consequence of high pixel density and the manufacturing process. How is the situation with MF digital backs, i.e. should I accept a hot pixel, or return the item?

[eddysmit]

May we know what back you are buying?
I just did the alignment tests with my Imacon Ixpress.
The chance that it is correct right on is small I think.
The shim that was provided with my back is 20µm.
To get it aligned correct, I had to add 17µm.
That is 2 pieces of paper  
Believe me, 15 or 20µm didn't work. It was out of focus.

I wonder if every back is aligned to the max?
The difference of 1µm is huge. I couldn't believe it myself.
My Ixpress has a lot of hot pix at 200ISO. However the software detects them and they don't show up in the picture.

Be sure that your camera is in top condition!!!!!!
If the mirror system is worn out, or the dampers aren't perfect, you will never get stable results!
I had this problem with my Mamiya 645 PRO.

[nightfire]

May we know what back you are buying?
I just did the alignment tests with my Imacon Ixpress.
The chance that it is correct right on is small I think.

The back would be a P45+.
How did you do your alignment tests?

[eddysmit]

I took some pictures from my screen, that had a testpicture on it.
Make sure that your camera and the screen are perfect vertical and aligned. Check if the center and all the corners are in focus (or the same out of focus) A brik wall also can do the trick.
Then I made a pile of books. A very thick one in the middle and some books closer to the lens and the other further.
Focus on the middle one, and see if that book is allso in focus on your screen.
If the further books are in focus, you have to add an extra shim. (could be 1 , 2 maybe 15µm extra, it takes time to find it out)
That's how I did it. Sure Hasselblad has sophisticated tools to do this...
I hope you understand my school English  ...