From: Mark Gaffney <markgaffney@mac.com>

Date: August 12, 2008 10:44:25 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Re: Unibrain camera etc.

Hi Milton, I guess I`ve got it a bit confused with fps rates. I notice the specs for the DBK 21AF04 say Sensitivity 0.5 1x at 1/30 sec. Does that mean the TIS camera has more than one exposure rate? How do the 2 compare ( Unibrain And TIS camera) as to maximum & minimum exposure times? Mark.

On Tuesday, August 12, 2008, at 07:09PM, "Milton Aupperle" <milton@outcastsoft.com> wrote:

--- In Astro_IIDC@yahoogroups.com, Mark Gaffney <markgaffney@...> wrote:

Mark;

I really don't know what your getting at here. CCD exposure time is

the inverse of the frame rate. The shorter the exposure the faster the

frame rate can be and the longer the exposure time the slower the

frame rate has to be.

The Unibrain cameras have a maximum exposure time of the CCD of 1

second. The longer the exposure the more light it captures and the

fainter it can see objects to guide with. If your guiding Magnitude 9

stars you need more ccd exposure time, if your guiding off a Mag 3

guide star you need a lot less exposure time. It all depends on the

aperture of the guide scope, the focal length your using, how

transparent and light polluted your skies are and how long your ccd

exposure time is.

What makes a good guide star is described in the Astro IIDC manual on

page 72. So you adjust the exposure time to try and get that sort of a

star, if possible.

And the frame rate isn't all that important for guiding. What is most

important is having a good strong star signal so that the guider can

lock onto it and differentiate it from the back ground.

Hope some of this helps.

Milton Aupperle

Hi Milton, I guess that`s what you do mean. It`s been a while since

I familiarised myself with this. I think I`ll try to rush through the

purchase of the Unibrain this pay. Mark. 

On Tuesday, August 12, 2008, at 03:49PM, "Mark Gaffney"

<markgaffney@...> wrote:

Hi Milton, Do you mean the above camera only has 1 second exposures

when taking pictures. Presumably it needs a live video stream to 

track objects for guiding? Forgive me my ineptitude in this matter. If

as you say this has been discussed previously could you direct me to

the relevant entries. I don`t think you`ve discussed it with me, have

you? By the time I`m able to make my purchases of a camera for guiding

etc. it may be just as well I put my money towards a Flea 2 camera

anyway. Mark.

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