Zwo 533 spacer help

[Albir phil]

Hope this is in right topic place. I have a zwo 533 colour camera, got the usual supplied spacers I've read I need 55mm back focus yet when I use all the supplied spacers I still don't have 55mm as measured from the camera body. Is this measurement actually from the sensor which seems to be a few mm lower than the body of the camera, is this distance included in the 55mm🤔 help from anyone please 

[Budgie1]

The measurement is taken from the face of the sensor to the rear of the lens on the field flattener/reducer. 

On most ZWO ASI cameras, there is 6.5mm from the sensor face to the front face of the camera body. Add this to the 11mm, 16.5mm & 21mm spacers supplied makes your 55mm backfocus. 

If you're using filters in the imaging train then add an extra third of the thickness of the filter lens to your backspacing. So, if a filter is, say 3mm thick, you add another 1mm to your backspacing to compensate for it.  

[Elp]

In such circumstances it's always wise to consult the manufacturer product pages to find out all the information you need, they usually have technical drawings which show the dimensions you require. The 55mm measurement needed is from the bottom of the flattener thread (or telescope if it is a built in flattener type) to your camera sensor. In the case of most (not all) cooled zwo cameras, the distance from the front face of the camera to the sensor is 6.5mm, 17.5mm if you include the m42 female to m42 female coupler ring (as the ring is 11mm thick). You will get +/- from that 55mm due to manufacturing errors/acceptable tolerance.

Edited October 30, 2023 by Elp

[AstroMuni]

19 hours ago, Albir phil said:

Hope this is in right topic place. I have a zwo 533 colour camera, got the usual supplied spacers I've read I need 55mm back focus yet when I use all the supplied spacers I still don't have 55mm as measured from the camera body. Is this measurement actually from the sensor which seems to be a few mm lower than the body of the camera, is this distance included in the 55mm🤔 help from anyone please 

Hi, what other items do you have in the optical train? Note: that 55mm is from sensor. I dont have a filter wheel and use a Baader CC and I use the 21mm + 16.5mm + 11mm + a few spacers to get the right back focus. My UV/IR filter is inserted into the 11mm adapter using the provided T2 - 1.25" adapter. Good luck

Edited October 31, 2023 by AstroMuni

[michael8554]

It's implied in all the replies, but to be clear:

You only need 55mm Back Focus from a Coma Corrector or Field Flattener to the camera's sensor, not the camera's body.

And not all CCs and FFs have 55mm Back Focus - check the spec.

If you don't have a CC or FF you can attach the camera as close as possible to the focuser, to avoid focuser sag.

But far enough away from the focuser that infinity focus is possible of course !

The ZWO 533C Flange Distance is as Martin's image.

Michael

[Albir phil]

On 30/10/2023 at 15:26, Elp said:

In such circumstances it's always wise to consult the manufacturer product pages to find out all the information you need, they usually have technical drawings which show the dimensions you require. The 55mm measurement needed is from the bottom of the flattener thread (or telescope if it is a built in flattener type) to your camera sensor. In the case of most (not all) cooled zwo cameras, the distance from the front face of the camera to the sensor is 6.5mm, 17.5mm if you include the m42 female to m42 female coupler ring (as the ring is 11mm thick). You will get +/- from that 55mm due to manufacturing errors/acceptable tolerance.

Ok thanks a lot I guessed it was about 6.5 to 7 mm so as you say that makes up the diff , again thanks for the help 😃

[adyj1]

On 30/10/2023 at 14:26, Elp said:

In such circumstances it's always wise to consult the manufacturer product pages to find out all the information you need, they usually have technical drawings which show the dimensions you require. The 55mm measurement needed is from the bottom of the flattener thread (or telescope if it is a built in flattener type) to your camera sensor. In the case of most (not all) cooled zwo cameras, the distance from the front face of the camera to the sensor is 6.5mm, 17.5mm if you include the m42 female to m42 female coupler ring (as the ring is 11mm thick). You will get +/- from that 55mm due to manufacturing errors/acceptable tolerance.

Good advice - ZWO have an excellent resource for this:

The best solution of 55mm back focal length – ZWO ASI (astronomy-imaging-camera.com)

 

[michael8554]

That diagram and link is where the confusion starts and generates any number of posts.

The link says "Since most telescopes have a 55mm back focal length, " - really ?

ZWO should know better.

Michael

[StevieDvd]

24 minutes ago, michael8554 said:

That diagram and link is where the confusion starts and generates any number of posts.

The link says "Since most telescopes have a 55mm back focal length, " - really ?

ZWO should know better.

Michael

To be fair they also state "Please be noted that this tutorial only applies to 55mm back focal length. " 

[adyj1]

On 30/10/2023 at 13:54, Albir phil said:

I have a zwo 533 colour camera

Are you connecting it to a Field Flattener or a Coma Corrector? If so, which type and model do you have? 

[michael8554]

Hi Stevie

"To be fair they also state "Please be noted that this tutorial only applies to 55mm back focal length. " 

But IMO, without any mention of CC or FF, that's just as confusing.

Michael

 

[Bugdozer]

Can I be cheeky and express surprise that nobody has suggested "buy a different telescope" yet? 😉

[StevieDvd]

1 hour ago, michael8554 said:

Hi Stevie

"To be fair they also state "Please be noted that this tutorial only applies to 55mm back focal length. " 

But IMO, without any mention of CC or FF, that's just as confusing.

Michael

 

That's a valid point. I guess as they don't sell focal reducers they think it's the manufacturer of the reducer that  needs to mention that.  But we can't expect every reducer maker to know the settings for every camera can we.