camera change

[bruno]

Hi All  I have just changed cameras from DSLR to a zwo 533, the question?  on the 533 I got the back focus to the required 58mm then when on the scope (80mmrefractor) I had to adjust the scope focuser to 55mm to get an image.

But with the camera (44mm)& the 0.85 reducer (35mm)  I only had to adjust the focuser to 19mm?

there was no FR on the 533, but it would take it to the same backfocus if i put it on.

 

Thanks in Anticipation Bruno 

[david_taurus83]

Hi Bruno. I'm not quite sure what exactly your asking?? You mention you have a 0.85 reducer so I'm guessing this is the Skywatcher ED80 you have? The 533 should come with all the adapters you need to get the required 55mm back spacing required for that reducer. The 16.5mm M48/M42 adapter, the 21mm M42 spacer and the 11mm female M42 spacer and the camera with 6.5mm from shoulder to sensor all add up to the required 55mm. It should be the same as using a DSLR (44mm) and T ring (11mm).

[bruno]

Hi David

With the 533 + filter holder + reducer i get an overall length of 70mm to achieve this I got rid of the reducer and replaced it with just a 2mm extension piece of 22mm giving me the 58 mm i need.

the question is why then do i have to bring the focuser on the scope another 54 mm?, Also if i put my f/reducer on my DLSR which has a back focus of 44mm i only have to adjust the focuser on the scope 19mm?

Hope that explains it a bit clearer.

 

[Budgie1]

Where are you measuring the back focus from & too?

Most of the common makes of DSLR have a 55mm back focus, this is from the rear of the flattener/reducer lens to the front of the camera sensor. Attaching a standard T-adaptor between the DSLR & the flattener/reducer achieves the required distance.

As David has said, ZWO include spacers with their cameras to cater for this distance. If you're filter holder is the ZWO Filter Draw, they conveniently make this 21mm thick so it can replace the 21mm spacer supplied with the camera.

[bruno]

Im measuring from the where the f/reducer buts up the the scope focuser back to the 533 sensor, just  checked the lens is only 10mm inside the reducer body & i been measuring the whole body upto the focuser (my bad).

still why did i have to wind out my focuser another 54mm when i had the correct b/focuser to get an image, i'd have thought that once yo got your b/focus on your camera you would'nt have to wind out much.

[alacant]

40 minutes ago, bruno said:

you would'nt have to wind out much.

Think where the dslr sensor was positioned when in focus with the ff. Your 533 sensor with the ff needs to be at that same distance. 

Now look at how far buried in the camera the dslr sensor is: 44mm. In the 533 it's only 6mm.

Any good? Worse?!

Cheers and HTH

 

Edited April 5, 2021 by alacant

[bruno]

Now understand it a bit better, only need to wind 17mm now with the ff on, got two decent images the other night thanks for all your imputs