Focus position of 294MC much further back than canon 1000D

[gerardsheldon]

Can anyone please tell me why the focus position for the 294MC is much further back than the canon 1000D.   

They have been used in prime focus positions (without any other lens like comma corrector). The 294MC does have an IR/UV filter.  I just can't work it out.  

[ONIKKINEN]

The flange distance for a DSLR is 44mm+ t-ring so around 55mm, while with the 294 it will be (i think) 17.5mm + the thickness of whatever nosepiece you put on it (few mm more).

So nothing is wrong here, the sensor of a DSLR just sits much further back from the connection to the scope than a dedicated astro cam.

[StevieDvd]

The have different back focus positions so need the focuser racked in/out more. When using a recuder, for example, you would note the back-focus needed and may have to add spacers for different cameras. A few use 55mm as it's standard for most DSLR but thoer cameras lke the 294 based ones would need spacers.

Does that asnwer the question or have I missing something?

 

[gerardsheldon]

Thanks.  i just did some approximate measurements and it does look like the sensors are in the same place.  I didn't realise how deep the sensor is in the Canon camera.