From: Mark Gaffney <markgaffney@mac.com>

Date: May 1, 2008 11:44:05 AM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Re: Jupiter..

Hi Alan, As I wrote to Milton I think the image of Jupiter I was getting disappeared below .5 second. Probably my scientific method isn`t that great but I often find that keeping all the exigencies of imaging, alignment and focusing etc together is confusing and I`ve lost track of exactly why this happened! The finder on the C10-NGT has only 2 plastic screws and I obviously pushed one of them too far expecting more than it was capable of. The C10 has other problems such as the eyepiece and finder often locating themselves out of reach on top of the scope for certain objects. I`ll have to get myself one of those adjustable astronomical chairs! I`m finding here in the south, at this time of year I have to get out directly after dinner for the best, most obvious alignment stars (Canopus, Sirius etc.) and then the scopes` have dew all over them (even with a tarp) by the time Jupiter has risen. I generally like to catch some sleep earlier on and observe in the early hours of the morning so as not to disturb the other members of the household! Mark.

On 02/05/2008, at 3:15 AM, Alan Friedman wrote:

Hi Mark - 

As Milton has said, there are many problems going to a shutter as long as a half second. I sometimes use a long shutter (133ms), but when I do I always focus using the fastest shutter that provides an on screen image - even if the gain must be pushed beyond what I would choose for capture. Slowing the shutter brings compromises the real-time advantage to imaging with a streaming camera - at .5 second, accurate focusing would be very difficult.

At the focal length I work at - 7.5 to 11 meters, I don't find the finder scope very helpful as a tool to locate the image on the chip. The three screws and crosshairs are not really capable of sub arc minute accuracy. I do use it to locate the image in the visual field, then center it carefully and hope my tracking is good enough to keep it in view as a swap the camera for the eyepiece.

best,

Alan

On May 1, 2008, at 12:06 PM, Mark Gaffney wrote:

Dear Perry, My brother suggested plastic tipped metal screws as being
the go he thought, because the plastic on! es are just so obviously 
flimsy. The finder probably needs something softer on it`s surface
than metal. I just haven`t been near a nuts and bolts or hardware shop
to look yet! Mark.
On 01/05/2008, at 11:14 PM, hpholcomb wrote:

> Mark,
>
> I find that I have to realign the 7X50 finder on my VMC200L
> catadioptric more frequently that I'd like to.
>
> To minimize realigning effort, I replaced the small thumbscrews and
> Allen-head setscrews with something similar to "Bob's Knobs". Got
> them at Lowe's. Turns out that the rear set of set screws needed more
> length anyway for easier adjustment. I'm not going back to the
> others!!
>
> Perry