Happy New Year to "Tech Tips" readers! Before we get started this time, just a brief reminder that this column is not intended to be brand-specific. Please feel free to submit technical questions regardless of the photographic equipment involved.

In your October column, you gave an expected total duration for time exposures for a Canon 1DMkII. Could you let us know what we can expect with a 20D and the BP511A? And - I've experienced the camera running low on juice during a long exposure; it wrote the file to the card just before shutting down. However, what if I had been using long exposure noise reduction and the camera runs out of juice during the second, dark-frame subtraction exposure? Does it (1) lose the image, (2) write the first exposure, (3) subtract the partial dark-frame from the first exposure and write the result, or (4) do something I'm not creative enough to imagine?

Canon Inc. has not published a comparable figure for maximum bulb exposure time on a single BP-511A with the EOS 20D. However, according to the Product Development Center, the correct specification is approximately 3 hours at room temperature (68F/20C). This duration can be doubled by using two fully-charged BP-511A battery packs with optional Battery Grip BG-E2, and it can be extended indefinitely by using AC Adapter ACK-E2. At 32F/0C, battery life is reduced by approximately 25 percent.

In the scenario you describe (power loss during long exposure noise reduction processing), the image is lost. This is because the data is not released from the camera's buffer memory (which requires power) until the long exposure noise reduction processing is complete.

Generally speaking, shorter exposures result in fewer problems with noise reduction. This is one of the reasons for the popularity of multiple consecutive exposures for astrophotography, together with increased dynamic range. For more info, check this Canon article on the Web.

I seem to have lost the product information or manual that came with my battery charger or the battery, I can no longer remember which. I have been all over your Web site, but have had trouble locating an owner's manual or other product information to download. I would greatly appreciate a url to any site where I can download the information. Also, I would be hugely appreciative of advice on how to store my three batteries (NP-E3) when not in use to maintain maximize life. Should they be stored charged or discharged, and should they be periodically recharged, even if not used? Thank you for any help you can give.

Canon posts electronic versions of its camera and software manuals, but not for accessories like Ni-MH Charger NC-E2 and Ni-MH Battery Pack NP-E3. If you are a USA resident, I would suggest that you contact our Customer Support Center at 1-800-828-4040 for further assistance. They should be able to help you obtain printed copies of the instructions for these products.

For maximum battery life, the NP-E3, like most other rechargeable battery packs, should be discharged prior to long-term storage. This can be done safely with the Refresh button on the NC-E2 charger, but it can also be done by using the NP-E3 with your compatible EOS SLR until the battery pack can no longer power the camera. If you are not planning to use your NP-E3 battery packs for a long time, they should be charged and discharged at least once every six months.

Are you able to say what Canon's reasoning is behind putting mirror lock-up in so deep in the menu system? In the old days all we did was push a lever. My FTb couldn't have been easier. And I know that my Canon New F-1 didn't need it due to their good engineering of the mirror. I never missed having it. But if a camera needs it, and my 5D clearly does, what's their reason for not making it a simple switch on the body like in the old days?

There are two separate issues here: (1) Physical differences between older and newer cameras; (2) control layout and menu design.

On point 1, cameras like the FTb were mechanically controlled, and as a result, mirror lock was mechanical. By way of comparison, today's digital cameras are electronically controlled, as we all know. Overall, this is clearly a good thing for many reasons, relating not only to digital capture but also to camera functions such as shutter speed and aperture control in terms of the ability to select and control intermediate settings precisely. But along with all the technological advances come a few trade-offs, including the loss of mechanical mirror control. There are a lot of technical reasons why this had to happen, and I don't have the time to get into the subject deeply, but the gist of it is that the camera's CPU has to know what's going on with the mirror in order to control the rest of the camera properly. As a result, even though mirror movement is carried out with a mechanical spring, the whole mechanism is electronically controlled and therefore consumes power. Speaking specifically about EOS cameras, the bottom line is that the reflex mirror cannot be locked up indefinitely using our current design. Power consumption is one of the reasons, but not the only reason, why mirror lock is limited to a maximum of 30 seconds with our cameras. Is there any possibility that our engineers will redesign this function to extend or eliminate the 30-second limit? Your guess is as good as mine, but frankly I'm not expecting any imminent changes in this regard.

Be that as it may, point 2 is another issue for Canon's R&D to consider. All I can tell you is that customer feedback requesting the accessibility of mirror lock to be improved has definitely been forwarded to our engineers. Now the ball is in their court, so to speak. In the meantime, there are some workarounds, such as the ability to register and quickly recall groups of custom function settings with the EOS-1 class DSLRs, and the C mode on the EOS 5D.

I am getting very confusing information from your tech support people on the maximum capacity SD card which will work in my 1Ds Mark II. I have a 4GB Transcend SD card formatted for FAT32, which works perfectly in my two computers, reading and writing. Yet when I try to format it my 1Ds Mark II, I get a message that says try another SD card, cannot format. The camera formats 1GB SD cards fine. Your tech support people said in their e-mail to me that "Any card with a capacity up to 2048GB that adheres to the Type I or Type II CompactFlash and SD card standards, and is formatted with either a 16 bit (cards up to 2GB) or 32 bit (for cards larger than 2GB) file addressing system, should work in your camera." That appears impossible to me, since it would mean an SD card of over 2 trillion bytes would work, but my 4GB card does not. I note that the recent firmware for this camera suggests that you can use a CF card of 8GB and an SD 2GB card to install the firmware update. Am I to understand from this that an SD card over 2GB capacity will not work in my camera? I am thoroughly confused and frustrated because the manual says nothing about limits on capacity and I fully understand that I must have a Fat32 format to use over 2gb. Can you please help me? Thanks.

The e-mail response you received from Canon U.S.A., Inc.'s Tech Support Center was correct. The fact that your particular SD card is not working with your EOS-1Ds Mark II is most likely due to a firmware issue between the camera and that card. My suggestion is that you try other brands of SD cards, although the Transcend brand appears to be the only option currently available with a capacity higher than 2GB in SD format.

On your other point, it's important to understand that the maximum capacity of the FAT32 standard (i.e., 2048GB) is not the same as the maximum capacity for either CF or SD cards. Those specifications are determined by the organizations that govern the standards for those cards:

http://www.sdcard.org/

http://www.compactflash.org/

Currently, the SD Card Association says that 8GB SD cards are "on the way," and the CFA says the CompactFlash specification can support capacities up to 137GB, even though the maximum capacity of currently available CF cards is approximately 16GB.

Thanks for reading "Tech Tips"! That's it for now. See you in February!

You are invited to submit questions about photo equipment, imaging technology, or photo industry trends that may have a bearing on your work or interests. I cannot promise to answer everything, but I pledge to do my best to address the issues that concern you. (Please use the e-mail link provided at the end of this article.)