From: Mark Gaffney <markgaffney@me.com>

Date: May 19, 2010 9:12:14 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Tarantula nebula..NGC 6744.. Jupiter

Milton, 

I don`t know if this would be of interest to the group but the topic was started here, so heck! 

The distance of the Nikon DSLR in chain with it`s necessary minimum of extenders & the CRG from the scope back is about 12 cms ( I guess the chip is in the middle of the camera body). 

I presume you mean I should be measuring the Scorpion or guide camera`s distance from it`s front (the chip is somewhat inside of this) to the centre of the barrel of the OAG (a little beyond the prism) whilst it`s in the guide port? If so that`s about 12 cms with my longest nosepiece & Mogg extender.

With the DSLR focused on the sign on the land object (at about 80 metres) & the Scorpion with it`s extender/ nosepiece seated square in the guide port I`m getting an image of something..at one end of rotation of the arm.. (perhaps the tarp on the tent in front of the big metal box). 

I`m guessing the Mogg extenders & the Meade ones I`m using for the DSLR may be designed to do this?

It`s a little difficult identifying & getting this object in focus because of the bright sunlight..(though I had a piece of board shielding the lap-top). 

Night-time is difficult because you`re partially blind even using a torch but daylight has it`s difficulties too doing this rather elaborate set-up. 

This morning (as usual) I was having problems with the Nikon F-mount adapter & also the C-mount ring inside the Scorpion coming loose necessitating a search for tools.

Doing this properly in the dark- achieving focus & right exposure given these parameters are different to infinity,( & not tripping over or dislodging some cable or another) would take a great deal of practise & patience.. You are to be admired for your own mastery of the process!

Mark.

On 20/05/2010, at 6:40 AM, Milton Aupperle wrote:

Mark;

On 19-May-10, at 2:03 PM, Mark Gaffney wrote:

Hi Milton, 

I may be a bit stupid  but I can`t get my head around how exactly to do this measurement? 

Why don't READ that "Using the CROAG"  document I sent you several months which has pictures in it that shows how to do this on the first page?

All I can think is to measure how far apart the two cameras are on my shipping container.

You don't do that.

You measure the distance from the telescope end of the OAG (that's the part attaches to the back of the Telescope / or Focal reducer) to the front of the CCD in each camera.

If the CCD's in both cameras are exactly the same distance to the front of the OAG, they are parfocal, which means both will be in focus at the same time. That's unlikely and you may need to add or remove extenders and then slide the Guide camera in or out of the holder to get them both in focus.

Once you have the distances so they are close, you'll need to fine tune it a little bit to get sharp focus with both cameras and that's where your 80 meter sign comes in.

Milton Aupperle