AP CCDT67 spacing

[emyliano2000]

Hello guys. 

I'm after some help for the spacing of the CCDT67 on my RC6. 

I've been looking online for some answers and I found the manual and a topic on cloudy nights about it but I'm wondering if I'm doing it right. 

The manual says that in order to have a reduction of 0.67x, the spacing needs to be 85mm.

I tried that and the stars on the edges and in the corners look horrible. I tried more than 85 with the same results. 

The camera that I'm using it with is a qhy163m with a 4/3 inch sensor. 

The guy on cloudy nights was saying that he got the best results with a reduction of 0.75x 

Using the formula given in the manual, I worked out that the distance from the sensor should be 76.25mm {(305-76.25)/305=0.75

Because the CCDT67 takes up 16mm of the distance and the sensor in 6.5mm deep, I could barely make up the 53.75mm (sx filterwheel, OAG and a few small spacers) needed to get the 0.75x reduction. 

Is this the right way to do it? 

Now, with my 4/3 inch (33.87mm) sensor and a reduction of 0.75x, following the manual, I should have a fully illuminated circle of 33mm. 

Would my stars be better now or should I try to get a 33.87mm fully illuminated circle? Are the star shapes on the edges and corners guided by the fully illuminated circle? 

The guy on cloudy nights posted a photo shot with an APS-C sensor and 0.75x reduction. Here's the link. 

https://www.astrobin.com/237518/?nc=user

Emil

 

Edited October 22, 2020 by emyliano2000