My flattener doesn't really flatten?

[White Rabbit]

Hi guys.

I've just purchased a SBIG STF8300m ccd and I'm having problems getting the my flattener to do it's job.

My set up is as follows.
Orion Premium 102 refractor 714mm f7
WO Flat 4 0.8 reducer this reducer is meant for refractors of up to 1000mm so my scope should be right in the sweet spot. Details of the flattener here http://www.williamoptics.com/accessories/flattener4_features.php

The ccd specs are here https://www.sbig.com/products/cameras/stf/stf-8300m/. I cant find the focus distance form chip to lense as I suspect that to be the problem but I dont know how to work it out.

can anyone help with the maths or is this sort of thing more trial and error. I have a spacer set that I might try and place in between the camera and flatter and see if that works.

Thanks
Sandy

[whzzz28]

Hi White Rabbit.

The backfocus is critical to making the flattener work.
According to WO you need a Lens-to-chip distance of : 66-86mm
The SBIG camera without filters has a backfocus distance of 17.5mm (according to SBIG).

Filters will add 1-2mm so not work considering, but your filter wheel will add distance. Not sure what wheel you have but if you look on the manufacturer's website they normally give you either the back focus distance or dimensions of the wheel.
Don't forget to factor in the adapters, they can be 5-10mm as well (if there are any).

So you need to make up at least 48.5mm between the flattener and the camera.
Your wheel will be about 15-20mm so 30mm roughly of extension is probably needed.

Something like: http://www.astroshop.com.au/products/details.asp?id=MAS-005G would work.

The WO unit gives you a large range to work with so maybe go with 35mm for safety, up to you.

[White Rabbit]

Awesome, thanks for the detailed response. I have a spacer set already so I'll experiment with them when I get some clear weather.

Thanks
Sandy

[TR]

This may help. I have a first generation camera, and used this. I found this on the old SBIG site before it was revamped. I believe the new cameras have the same measurements.

Terry

[White Rabbit]

Thanks Terry a picture speaks a thousand words.