Help with Skywatcher Esprit 100 and flattener

[Stuart1971]

1 hour ago, teoria_del_big_bang said:

@Juicy6 Out of interest what is the thing ringed in red below?

Steve

That looks like a heater ring for the sensor glass, to stop frosting....ASI made them for there early ASI1600 and other cameras....the thing you have ringed in red, it the power connector....the heater sits flat on the front of the camera, it’s very thin... 👍😀

Edited August 3, 2020 by Stuart1971

[Juicy6]

5 hours ago, teoria_del_big_bang said:

@Juicy6 Out of interest what is the thing ringed in red below?

Steve

Anti dew heater - https://astronomy-imaging-camera.com/product/anti-dew-heater

[Grierson]

On 02/08/2020 at 18:07, teoria_del_big_bang said:

..................................    But still do not forget to correct for the thickness of the filters as this could add up to 1 mm if they were 3 mm thick. ...................................

Could I ask a naive question. Assuming the filters are inside a filter wheel, as in this case, and the width has wheel has already been included why is it necessary to include the thickness of the filters in the calculation? Thanks - John   

[Grierson]

 X

Edited August 4, 2020 by Grierson
Sorry - Double take!

[teoria_del_big_bang]

46 minutes ago, Grierson said:

Could I ask a naive question. Assuming the filters are inside a filter wheel, as in this case, and the width has wheel has already been included why is it necessary to include the thickness of the filters in the calculation? Thanks - John   

Because the glass in the filter refracts the light path and alters the focal point. So add 1/3 of the thickness of the glass of the filter.

Thanks to @andrew s for the drawing.

I took the drawing from this thread but the thread is a little confusing as it talks about adding 1/3 of the filter thickness and also subtracting it but as it pushes the focal point further back then you definitely must add it.

do-filters-add-to-back-focus

 

Steve

Edited August 4, 2020 by teoria_del_big_bang

[Grierson]

Steve, many thanks. Very helpful. John.