ZWO EFW mini thickness

[Pitch Black Skies]

I've just received a second hand ZWO EAF mini. I did a little Google search to see how to achieve backfocus.

ZWO state the thickness of the mini EFW as 20mm.

I have measured it out of curiosity and have found it to be actually 21mm. That creates a problem for backfocus.

With a T2-T2 adapter included, it should give a back focus of 56mm as they state, with the 1mm extra to allow for a filter's glass. However, you will find it gives an actual backfocus of 57mm. That's an extra 1mm that shouldn't be there.

I'm not sure if it will make a huge difference to images but I'm really surprised how they could have gotten something like this wrong.  Please tell I'm missing something here. Is the Mini 1mm thicker than their other EFWs?

As a quick measurement, it might seem like 20mm but there is a lip on the backplate which must be accounted for too. See pictures attached.

 

Quick measurement ⬇️

 

Real measurement including the backplate lip ⬇️

 

The backplate lip ⬇️

Edited June 20, 2022 by Pitch Black Skies

[symmetal]

It's a different design from mine which is about 4 years old where the backplate extends the full width. I measured the thickness and it reads 19.95 to 19.98mm on my calipers.

Mine looks the same as the photos on FLO's site so yours maybe an earlier version which is now updated. 🤔

FLO's picture

Alan

Edited June 20, 2022 by symmetal

[Pitch Black Skies]

Thanks Alan,

It seems I must have an older version. I think the buyer said it was about 5 years old.

I hope the extra 1mm won't cause difficulties for me. That would be a right pain.

Edit: it probably isn't that bad actually. I could swap the 11mm spacer for a 10mm one. They should be fairly handy to come by.

Alan 

Edited June 20, 2022 by Pitch Black Skies

[michael.h.f.wilkinson]

I have both the mini and the full size EFW, and both come to 20 mm give or take a gnat's whisker. It almost looks like the back plate isn't screwed on the right way round, as the screws do not seem to be recessed properly. Might that be the cause of the problem? If so, that is easily fixed

[Pitch Black Skies]

I hope you're right, I'll take another look now.

[Pitch Black Skies]

Ah sh..ugar

It was on backwards 🤦😆😆😆

Edited June 20, 2022 by Pitch Black Skies

[michael.h.f.wilkinson]

6 minutes ago, Pitch Black Skies said:

Ah sh..ugar

It was on backwards 🤦😆😆😆

All's well that ends well

[Richard_]

These are the types of problems I prefer to have. It's always best to realise you're being a plonker than there being a real problem  (I say this from experience!) 

[symmetal]

Mounting the cover backwards would allow extra thick filters to be used I suppose, which the previous owner may have had, or else they needed an extra mm to get the backfocus right. 😁

Glad it's all OK. 🙂

Alan