QHY8L spacing

[jambouk]

No idea why I am finding it so hard to get my head around spacing, but I am.

Anyway, I want to use a QHY8L at different times with both a Skywatcher 0.85x reducer on an ED80, and on a Celestron 0.63x reducer on a standard C11.

1. What is the distance from the chip inside the QHY8L (presume letter "A" in my illustration) and point "B"?

2. For the 0.85x Skywatcher reducer, what is the optimal distance from "A" to the reducer (presume point "C")?

3. For the 0.63x Celestron reducer, what is the optimal distance from "A" to the reducer (presume point "C")?

4. Where on the Skywatcher 0.85x reducer do I measure back to the sensor, from "1" or "2"?

5. Where on the Celesron 0.63x reducer do I measure back to the sensor, from "3" or "4"?

Thanks for ANY clarification

James

[PhotoGav]

Hi, I can answer regarding the Skywatcher questions as I have just spent three months imaging with the incorrect spacing and have learned the hard way!!! So,

1. Don't know, but that should be easy to find out by reading the QHY8 spec sheet.

2. 55mm

3. Don't know, but again, check the manual.

4. From '1'.

5. Don't know, but I would guess '3'.

Good luck!

[PhotoGav]

Just checked the QHY8L manual and the answer to q1 is 20.2mm, so for the skywatcher reducer you have 34.8mm of space to fill...

[jambouk]

I hadn't seen that version of the manual, but since found it online. You are a star. In fact I think the answer to Q1 I was asking is 10mm, as the 20mm includes the odd shaped aluminium housing the IR filter which isn't part of the spacing length when using the "centre and tilf adjustment ring" which I seem to need.

I am really grateful for this!

The questions about the reducers are based on the fact the optics inside the Skywatcher reducer are well away from point "1", but the optics in the Celestron one are flush with point "4"... seems odd.

I am getting there It seems I already have the correct spacers then for the Skywatcher reducer, just need to work things out for the Celestron one now.

James

[PhotoGav]

My pleasure. Yes, it's a mine field and doesn't really make any sense when looking at the objects in question, you just have to believe what you read in the manuals!!

I had an extra 5mm of spacer in my imaging train with the ed80 and the stars in the corners of the field were significantly elongated, so spacing really does make a huge difference...

[jambouk]

In fact, I think I've got 5mm too much on my ED80 set up, because the 32mm spacer doesn't screw all the way into the reducer and leaves a 5mm gap! I'll have to find a shorter spacer!

I think I've also cracked the Celestron issue; 110mm from sensor to the flange. I can achieve that with my current adapters and bits and bobs. Bonus!

JD

[jambouk]

Skywatcher excess 5mm issue solved. I just removed the "centre and tilt adjustment ring" and screwed the T2-T48 spacer directly onto the IR filter housing, and that gives me 45-46mm, plus the 10mm inside the camera, so 55-56mm

At last!

Thank goodness fr SGL.

James

[PhotoGav]

Hooray!

[lensman57]

You need to be careful with Mead/Celestron F0.63X reducers. I believe the original design called for 110~115mm of back focus but I have read that in later designs they changed this to 55~56mm of back focus, the reason for this change was apparently to allow the camera to clear the bottom of the Fork/Mount as it pointed near to the Zenith. So you have to find out which version you have.

A.G

[jambouk]

Thank's, i'll email FLO and check. They must be fed up of me by now

James

[jambouk]

Hi James

The celestron reducers are not 55mm, this is the spacing for most ( not all) reducers and flatteners used with refractor Telescopes ( and for many coma correctors used with Newtonian Telescopes)

105 to 110 is correct for the Celestron f6.3 reducer James

Regards

martin

[russellhq]

Just checked the QHY8L manual and the answer to q1 is 20.2mm, so for the skywatcher reducer you have 34.8mm of space to fill...

That's the mechanical distance. The camera also has an optical window, which I'm sure I've read is 3mm thick. So would roughly add 1mm to the optical path length.

[lensman57]

That's the mechanical distance. The camera also has an optical window, which I'm sure I've read is 3mm thick. So would roughly add 1mm to the optical path length.

You may have to check on that Russell as I have read that Atik for example give the backfocus distance inclusive of the optical window.

A.G