5 replies to this topic

[LX200]

I am trying to help a buddy get set up in a nice Astro Photo rig... he is willing to spend some bucks.  He has decided on ZWO FF80 Refractor.

 

I am used to RASA and C8 Edge with focal reducer, so I am dealing with fixed back focus, so I am used to dealing with this stuff.... but...

 

I talked with High Point, and the guy there said back focus is not an issue with refractors, as you just adjust focus with focuser...   FF80 has flattener built in....

 

So he told me....

 

1. Put 48mm to 42mm adapter that comes with scope onto back of scope

2. Put 16mm spacer with 42mm threads on camera, this comes with camera

3. Connect

4. Get focus close by using manual focuser shooting through 2600 camera

5. Install ZWO EAF Electronic Focuser, should only need minor adjustments to focus now

 

Should be good to go.... adapter for ZWO EAF comes with EAF to connect to FF80

 

This sound right?  Measure twice... cut once... High Point is usually spot on, but since I am helping him out, don't want to give bad advice.

[John Berger]

I talked with High Point, and the guy there said back focus is not an issue with refractors, as you just adjust focus with focuser... 

this sounds misleading

 

he's confusing back focus with normal/front focus which are 2 different things

 

 

 

So he told me....

 

1. Put 48mm to 42mm adapter that comes with scope onto back of scope

2. Put 16mm spacer with 42mm threads on camera, this comes with camera

3. Connect

4. Get focus close by using manual focuser shooting through 2600 camera

5. Install ZWO EAF Electronic Focuser, should only need minor adjustments to focus now

 

that sounds strange too

 

you're right in saying the FF80 has a built-in flattener

 

but more than that, that refractor doesn't have back-focus requirements; you can use any back focus, up to, I think it's usually 4 inches for most petzvals; idk why the HPS guy is saying to use a 16mm spacer.

 

so as long as you have the right adapters, then you don't need to worry about spacing

 

idk the specific about the adapters you need or how the EAF connects, so I think someone else can clear that up.

Edited by John Berger, 25 June 2024 - 05:30 PM.

[hyiger]

I talked with High Point, and the guy there said back focus is not an issue with refractors, as you just adjust focus with focuser...   FF80 has flattener built in....

Not an accurate statement but I suppose close enough in this case. The FF80 is a Petzval refractor which means the flattener is fixed relative to the front objective. So back focus is irrelevant. However, this is only true of Petzval designs and not all refractors. You do need however enough spacers to achieve focus without fully racking the focuser out. 

 

Is this a mono or a color setup? 

 

If OSC, then my advice is to get a filter slider with an M42 male thread and M48 female thread like the one from Starizona or ZWO. The slider attaches directly to the camera. Then add enough M48 spacers between the slider and the scope until focuser is about 2/3's the way in. You don't want the focuser to stick out too much or the weight of the camera can introduce tilt.  

Edited by hyiger, 25 June 2024 - 05:44 PM.

[BlueMoon]

On my AT60EDP Petzval, I added a 30mm extension tube between the rotator on the telescope and the camera. My ASI183MM camera sensor needs to be about 55mm from the Petzval lens group. The AT60EDP has only about 20mm of drawtube movement (which is somewhat short) so the 30mm extension along with the thickness of the rotator insures I can reach focus using the drawtube normally. Hope this makes some sense. Cheers.

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Edited by BlueMoon, 25 June 2024 - 05:51 PM.

[John Berger]

oops, sorry, forgot about saying the focuser cannot stick out too much, because it's true, you can get tilt.

 

so you'll need spacers for that.

 

okay, I'm outta here before I mess up again 

Edited by John Berger, 25 June 2024 - 06:03 PM.

[michael8554]

The ZWO spec says there's no need to worry about Backfocus. Add what you like to the scope, it will give good images as long as you can focus.

 

So only add enough spacing to the rig to get focus.

Edited by michael8554, 26 June 2024 - 03:05 AM.