I have a couple of questions about batteries in the TL120. I recently
tried to purchase some of the silver oxide replacements for the ones
that came with the camera but my local supplier said he is not getting
any more of the silver oxide ones. No reason given. But he did have
the appropriate battery as an alkaline battery.

Has anyone had experience with the life from alkaline batteries? Any
worse?

Second question. Has anyone experimented with the TL120 on very long
exposures - star trails etc.? I am wondering how long I could hold the
shutter open, given that the mechanical shutter is tied in to the
battery and will only operate on 1/30th of a second without a battery.

regards,

Harry Calderbank

Harry Calderbank wrote:

>
>
> I have a couple of questions about batteries in the TL120. I recently
> tried to purchase some of the silver oxide replacements for the ones
> that came with the camera but my local supplier said he is not getting
> any more of the silver oxide ones. No reason given. But he did have
> the appropriate battery as an alkaline battery.
>
> Has anyone had experience with the life from alkaline batteries? Any
> worse?

Can't help you with this right now. I'll try to find the data
sheets for the two different chemistries and see how they compare
for this size cell.

>
> Second question. Has anyone experimented with the TL120 on very long
> exposures - star trails etc.? I am wondering how long I could hold the
> shutter open, given that the mechanical shutter is tied in to the
> battery and will only operate on 1/30th of a second without a battery.
>

I have done several measurements on the camera starting with
http://tech.groups.yahoo.com/group/MF3D-group/message/301
and most recently with
http://tech.groups.yahoo.com/group/MF3D-group/message/1663

My conclusion (based on the shutter drawing 28ma) is that the
batteries should easily cover six or seven hour exposures.
Please let us know if you find something different!

John Thurston
Juneau, Alaska

--- In MF3D-group@yahoogroups.com, John Thurston wrote:

> My conclusion (based on the shutter drawing 28ma) is that the
> batteries should easily cover six or seven hour exposures.
> Please let us know if you find something different!
>
> John Thurston
> Juneau, Alaska
>

Many thanks John. I must have missed (or forgotten) your ealier
posts on the subject. I'll look forward to any findings on the
silver oxide vs. alkaline. Given that the batteries only cost a few
dollars each it will be worth a few experimental exposures. Might
have to wait a while for a clear starry night. There's a growing
moon to contend with at the moment. I let you know the results.

regards,

Harry

Harry Calderbank wrote:

>
>
> I have a couple of questions about batteries in the TL120. ...
> Has anyone had experience with the life from alkaline batteries? Any
> worse?

I can't answer your question from practical experience. Maybe
someone else can. Until they do, though, I'll offer some
information taken from product literature.

The capacity of the different chemistries is hard to peg. The
Silver oxide (Energizer 357/SR44
http://data.energizer.com/PDFs/357-303.pdf )
is listed with a capacity of 150mah

Alkaline (Energizer A76/LR44
http://data.energizer.com/PDFs/a76.pdf )
is also listed at 150mah

Zinc Air (Energizer 675/PR44
http://data.energizer.com/PDFs/675.pdf )
is listed at 635mah

The problem is that the each chemistry has a different nominal
voltage, discharge curve and specified cut-off voltage. The SR44
starts at 1.55v and is considered depleted when it reaches 1.2v.
The LR44 starts at 1.5v and isn't considered depleted until it
reaches .9v. The PR44 starts at 1.4v and is also measured down
to .9v.

So you see, it's hard to compare especially when we don't know
the characteristics of the TL120 shutter and meter. We don't
know how many volts they must see to continue to work as
expected, nor do we know how their power consumption varies with
voltage. It still haven't built that power supply I said I was
gonna build so I could figure this stuff out.

My wild guess is that the SR44 will last 30% longer than the
LR44. This is a GUESS based on several minutes staring at the
discharge curves provided by Energizer. I also expect that each
manufacturer's batteries will be a bit different.

If I were going to go do some back-country work with my TL120 and
expect its batteries to do many long exposures, I'd try to build
a battery pack for it. I'd make a little battery box to screw on
the bottom of the camera and protrude into the battery
compartment. It would carry some rechargeable, high-capacity
batteries and have space in it for an iron-filled hand-warmer
(http://www.heatmax.com/HotHands/index.htm) for use in cold
weather. You may not need this, but if it is ever dark and clear
enough in Alaska to see stars, it is also pretty cold. They
kinda go together.

John Thurston
Juneau, Alaska