Need help with spacer for QSI camera & flattener

[Andy01]

Hi folks,

Having just aquired a nice new QSIwsg8 camera, I'm now trying to work out which spacer I need to use with my William optics FLT 110 and P-Flat4 flattener/reducer.

My SBIG ST8300c works well with a 35mm spacer between the camera and the flattener, I have several spacer rings of varying sizes but I can't seem to get the distance right to bring the QSI into anything resembling focus.

Any suggestions welcome please! :help:

Cheers
Andy

[Andy01]

According to William Optics, the flattener lens needs to be 55mm away from the chip on a DSLR with std T-Ring. The SBIG has 17.5mm backfocus so 55-17.5 = 37.5mm spacer. I found that a 35mm spacer worked well for me.

The QSI documentation says the wsg8 with t-mount adapter has 50.17 backfocus, so theoretically 55-50 = 5mm spacer?

It's difficult first time around because if it's not in focus you can't see any stars!

Andy

[algwat]

Not exactly what you need, but I have used various larger circlips that are about a 1mm width to space out small amounts in-between larger 50mm spacers. I have even put then in the front of a orion guide camera just sitting loose around the edge of the chip to get good focus and make other c-mount lenses stand off to the correct position. rgds, Alan

[Amaranthus]

Do you mean you are racked out completely with your focuser? Maybe try getting it working without the FF first, just as a sanity check?

[Andy01]

I tried the focusser in almost every position possible from fully in to fully out with a wide variety of spacers, t-rings and combinations of both.

As a sanity check, I put the SBIG back on instead and focussed and aligned a star in the centre and ran phd with my guidecam to guide the mount. This was to keep the star in frame so I could remount the QSI and swap and experiment with various rings.

Still couldn'd see anything, possibly the ccd's on the two cameras are located differently? I even tried aligning on the moon just to check if the QSI was generating a preview image but all I got was a big white out of focus image on the screen instead of a black one!

Cheers
Andy

[LewisM]

Try a Takahashi FSQ85... I need a 95mm spacer from the back of the CAA to the front of the FLI... Insane! All screwed, so no flex, but just insane.

[LewisM]

...but the images are worth it. One sharp little beastie :)

[algwat]

just another rough suggestion, some solid core thick copper wire wound around the threads at the appropriate point in the tube train becomes a variable spacing solution. rgds, Alan.

[HarryD]

Hi Andy

This is the reply I got from Bintel here in Sydney:

With the QSI camera the 2" nosepiece can be unscrewed and the adapter on the faceplate of the camera is T-thread.

I have a spacer kit from Orion that has a 5mm, 10mm and 25mm spacer ring.
With these you will have a couple of options:
75mm using the 25mm spacer or
85mm using the 25mm and 10mm spacer

There is also a variable t-ring spacer from Orion:
http://www.bintel.com.au/Astrophotography/Camera-Adapters---T-Rings/Orion-Variable-12-17mm-T-thread-Spacer-Ring/1733/productview.aspx (http://www.bintel.com.au/Astrophotography/Camera-Adapters---T-Rings/Orion-Variable-12-17mm-T-thread-Spacer-Ring/1733/productview.aspx)

This could be used to vary the spacing by very small increments if the reducer/flattener spacing is that critical - however it doesn't sound like it if the WO specs give 20mm latitude for spacing.

I have theses spacers on hand so I'll put one of each away for you.


Hope that helps you.

Greg

[Andy01]

Thanks Greg, That's exactly the same Orion spacer kit that I have so I'll keep trying...

Cheers

AC

[Paul Haese]

Don't worry about focusing the scope just yet. Your figures on a 5mm adapter are right. You need to ensure the flattener is at the correct back focus. Get an adapter made by Precise Parts at 5mm with the flattener thread at one end and the QSI thread at the other. It will focus then.

[gbeal]

I think all you need is the 5mm or so spacer to be honest.

The SBIG works, and it is "about" 17mm. The Flat4 is designed with the DSLR spacing in mind, so 44+/- and 10+/- for the T ring, about 55mm again +/-.

From the comments about, the QSI without the nose-piece is about 50mm back-focus, so the 5mm will suffice. If however the QSI has 5mm back-focus WITH the nose-piece then things change, but only by 50mm.

Assuming the 5mm spacer is what you need then the fine-tuning could be done easily with the Flat 4, it has adjustment between "66mm and 86mm". I usually use mine at about 76mm, the mid-point, but at least it can be fine-tuned to get the best star images at the corners.
Gary

[HarryD]

The QSI site gives a distance of 50.292mm for the 683wsg-8.

The WO site gives different distances for various telescopes eg for the FLT132 it's 71.5mm.

So 71.5mm - 50.292mm = 21.208mm.

For a FLT110 it's 73.5, so 23.208mm spacer.

If WO has recommended distances it would be wise to use their recommendation as a starting point.

[HarryD]

Just ordered a custom adaptor from Precise Parts for my WO FLT132

Custom adapter, WO AFR-IV Adjustable Flattener/0.8x Reducer to QSI 500/600 wsg with T-thread, L=21.2 mm

Cost US $138 delivered

Why muck around when spending this much money.

[Paul Haese]

Agreed. My recommendation was based on the former stated back focus of 55mm. Starting with the flattener/reducer back focus distance and then subtracting the QSI back focus distance will get you spot on for what adapter length you need.