Tuesday, November 29, 2011

Something That Was Never Possible in Film SLRs

I can upgrade the firmware in my Pentax K10D.  I have reason to believe that even though I am using SD cards in it, it will (and certainly after the firmware upgrades) support SDHC, so that I can put as much as 32 GB of RAM inside.  Right now, the 2 GB SD card lets me take more than 300 pictures at 10 megapixels.  The AmazonBasics SDHC Class 10 16 GB Secure Digital Card that I just ordered should let me take an entire European vacation without changing the card.

Not that I am planning to do that, but then I can switch the 2 GB SD card into the Soundfly SD and make it a bit more compact sitting on the console.  Also, because this is a class 10 SDHC card, it should store pictures considerably faster than the existing SD card--something that matters when you are taking long time exposures for astrophotography.  A 30 second exposure takes many, many seconds to complete.  I am not sure if this is because of the time to write to the card, or because it is doing some complicated operations on the data before it starts to write.  I figure that it can't hurt.


  1. On the completion time, it'd be processing.

    The data written to the card will be 10mp worth (exact size depending on settings, whether it's RAW or JPEG, etc.), which takes the same amount of time whether it's a snapshot or a 5 minute pinhole exposure or astrophotography.

    Long exposures should be nothing more than letting the sensor accumulate light for a longer period.

    (Which reminds me, I should look into a new DSLR - my K100D is showing its age.

    I don't care about more megapixels, but newer sensors are simply better.)

  2. I suspected that the long time was doing some sort of compression, but I am a bit unclear exactly what. This is not a cumulative collection of frames; it is data being gathered from an array of sensors. I am hard pressed to see why it takes so much longer. It is not like summing thousands of frames.

  3. The Pentax K-5 16.3 MP is on sale at Amazon.

  4. Perhaps its doing dark frame subtraction? That's where it takes a second image with the shutter closed, then subtracts that from the original capture, so that chip imperfections are cancelled out.

  5. No question that it has to do dark frame subtraction, but why would that take longer with a 30 second exposure than a one second exposure?

  6. I subscribe to the philosophy of shooting on smaller cards. That way if one goes bad, the camera gets stolen, card gets lost, etc. then I have not lost my entire week's vacation photos. Just my 2 cents

  7. Marc Cote: That's more a call to frequently copy/upload/whatever your pictures and other irreplaceable data. I suspect your system still allows for plenty of failure modes.

    I myself am utterly paranoid about backups and restores (been playing this game since 1978 (sic) and a thorough multi-target backup system saved my data when the May 22nd Joplin tornado hit) and buy 16 GB cards since they're cheap enough and you never know when you might need to take a lot of pictures or video, use them for some sort of backup kludge or to carry a lot of data in a tiny package, etc. etc.

  8. Dark frame subtraction generally is done by taking a second exposure (with the shutter closed) of exactly the same length as the shutter-open exposure. The idea behind the same-length exposure is that "hot" pixels in a digital camera are not an all-or-nothing proposition; rather, the "hot" pixels "heat up" slowly over time. Thus, by taking a dark frame of the same length as the light frame, your "hot" pixels will end up with approximately the same light levels as they acquired during the light frame, which means that you'll get the most accurate results possible after subtracting the dark frame from the light frame.

  9. By the way, on most cameras, the long dark-frame exposure is an option that can be turned off. On the Nikon D700 (the first one that I found an article about with a quick Google search) the menu option is called "Long Exp. NR", short for "Long Exposure Noise Reduction". If it's on, the 30-second exposure will be followed by the camera shooting a 30-second dark frame. If the option is turned off, the camera will still do dark-frame subtraction on any shots longer than N seconds (for some value of N), but it will take a single split-second frame to figure out the hot pixels. The results will be decent, but not as good as shooting a dark frame of the same exposure length as the light frame.

    So if you're shooting a 4-hour exposure (to get star trails, for example) you might want to look for the option and turn it off. But if you're shooting 30-second exposures, I would recommend leaving the option on, to improve the quality of your results.

    And either way, a faster SD card isn't going to noticeably improve your processing time. Now, if you were doing sports shooting (where you're trying to shoot as many frames per second as physically possible) then a faster SD card would be VERY noticeable.

  10. I meant processing, not as processing a collection of frames, but on the theory that it might need to do more processing on the sensor data for a long exposure.

    On thinking about it again, that isn't a very compelling explanation, from what little I know of how camera sensors work for long exposures.

    So it's puzzling that it would take any longer at all...

    (I wasn't aware, for instance, that any cameras did automatic dark frame capture, but then a) I don't do astrophotography and b) I buy *cheap* DSLRs - a D700 body costs more than my car is worth.)