Spacer rings for DSLR imaging

[Carl]

Ok dumb question but i just went on to Peter Tans website and saw a heap of very thing spacer rings that you may need for improving image quality.
So exactly where do i place these in my image train when using a DSLR camera and field flattener?

Any diagrams on the web?

regards
carl

[gbeal]

Not dumb at all Carl, if you don't know ask, and anyone that tells you it is a dumb question is out of line. This is how we all learn, and especially on this forum.
Right, where was I? Oh yes.
Probably the spacers are not really applicable to your system.
In other systems, notably the cooled CCD cameras, they all seem to have a differing distance for the chip surface to front mounting surface. On my SX camera it is about 17.5mm, on the QHY8 for example it is about 21mm. Where this becomes an issue is with the likes of the Televue TRF2008 reducer I use. According to the manufacturers blurb it needs ~55-56mm from the chip surface to the rear of the reducer mounting. So in my case I need about 37.5mm of "spacers". I know I have one at 30mm, and another at 7.5mm so am sorted, but if I needed to make up a millimeter or two, these thin spacers are handy. Other times the advertised 55mm is just a guideline and you have to experiment with the scope and the flattener/reducer and see.
But in your case I would think your flattener would screw straight onto the T ring, which then mounts straight onto the camera, and you are off. Thee exists I suppose the ability to slip a spacer into the screw in section between the flattener and the T ring, to "extend" slightly the distance, but you would want to experiment to make sure it was dong a better job, not a worse one. Also, ensure there is enough thread holding Part A to Part B, the last thing you want in the dark is the camera falling off.
Gary

[gregbradley]

Flatteners and reducers have a specified metal back distance to work properly.

Metal back distance is the distance from the camera chip to the last edge of the metal frame of the reducer or flattener. It is something designed by the optical designer and is specified for that particular item.

So you have to find out what that distance is so you can get adapters set to make sure the flattener is that far away from the front surface of the imaging chip.

Unfortunately its not the same with various brands so if you have a few you end up with several adapters to match.

Greg.