KAF-16200 on FSQ85

[andrewluck]

Here's a flat from a Moravian G3-16200 mounted on my Takahashi FSQ85. Illumination appears to be down about 20% in the corners.

CCD parameters calculated in Pixinsight look similar to the specifications (this is a grade 2 sensor). If anyone is interested I can post the calibration frames used.

 

Andrew

Edited July 6, 2016 by andrewluck

[MattJenko]

2" filters?

[ChrisLX200]

Yes it has to be 2" filters with this big sensor. Drop-off seems reasonable and easily corrected with flats. I've seen very few results with this new camera so would be interested to hear how you get on with it

ChrisH

[andrewluck]

Yes, 2" filters in an external wheel.

Main driver was the move to mono. However, as my main interest is large dark nebulae the increase in area will be very welcome.

Y axis guider runaway at the moment that I need to fix before I can get any pictures

Andrew

[ollypenrice]

27x34mm is pretty big. I wonder if the FSQ85 will give distortion free stars at this size? Both Yves Van den Broek and I found that it was nowhere near covering the 11000 chip without distortion. I know Tak claim it will cover 35mm format but - well - I think it may be a rather wild claim.

Are your filters 2 inch mounted or unmounted? We use both in our dual rig. The vignetting is certainly more severe with the mounted set but both are workable on the full frame Kodaks and FSQ106.

Olly

[andrewluck]

Only some images of the sky will confirm, one way or the other. I'll post here as soon as I have some.

Sensor size is 27 x 21.6 so the diagonal is 34.6mm rather than the KAI-11000's 43.6 so it's considerably smaller.

Filters are mounted.

Andrew

Edited July 9, 2016 by andrewluck

[ollypenrice]

2 hours ago, andrewluck said:

Only some images of the sky will confirm, one way or the other. I'll post here as soon as I have some.

Sensor size is 27 x 21.6 so the diagonal is 34.6mm rather than the KAI-11000's 43.6 so it's considerably smaller.

Filters are mounted.

Andrew

Ah, I misread the chip dimensions. My apologies.

Olly

[andrewluck]

No problem.

Andrew

[andrewluck]

Initial results indicate that this camera is a little large for the FSQ85 but Takahashi claim a 44mm imaging circle and we're well inside this. I will make some enquiries as to whether this is typical. From the specification:

"gives an almost homogeneous flat field of 44mm diameter. At prime focus, at the edge of field (22mm from the optical axis), stars remain pinpoints, including on pixels of 7µ width. "

The focuser is well racked out and the image appears to shift a few pixels when the auto focus routine is running. The FWHM plot indicates I have a little sag so I'll need to order an extension tube.

Andrew

 

Edited July 23, 2016 by andrewluck

[ollypenrice]

As I said above, I think Takahashi are overly optimistic in the flat field claims they make for the FSQ85. There does seem to variability from instrument to instrument, too. I used mine with a 15mm sqyuare chip and had excellent results but I think Takahshi should be brought to book over their field size claims. This has been much discussed on here.

Olly

[andrewluck]

Looks like I have some tilt to remove and also the focus could use some work as although I'm focussing on a star at the centre of the frame the best focus is offset towards the top of the image. Looks like Takahashi Europe are prepared to work with me to help fix this as I'm the first person that they're aware of trying this combination.

Just need some clear skies for the test images.

Andrew

[andrewluck]

Still working through the issues with Takahashi Europe so this is just to give a feeling for the image area covered by this combination. This has been resized to 40% of the original uncropped frame.

(R 210 minutes; G 140 minutes; B 140 minutes; all bin 1x1)

Andrew

 

[andrewluck]

Does anyone have any experience of tilt issues in the CAA for the FSQ85?

Andrew

[Barry-Wilson]

Yes, I have.

Without reducer at F5.3 I have a flat field.  With reducer I get 3 perfect corners and my top left corner (as viewed on my monitor) has a small amount of tilt.  Endlessly tweaking the 3 grub screws on the reducer has never fully removed it but has reduced it to a small fraction of a small tilt!

I have replaced the grub screws in the reducer, drilling out the holes and replacing with larger diameter caphead screws: this helped deliver more control to the adjustments. I have removed the CAA and examined it but not been able to make any adjustment with it.  My top-left tilt is small and not readily noticeable except by me.  My last tweaking gave an almost perfect field until I decided to rotate the ccd for framing and back came the small amount of tilt.

I have taken the plunge and bought the 3" FT focuser with tak adapter from Starlight but not had it delivered yet.  I am hoping that this will deliver perfect results!

[andrewluck]

Thanks Barry. Useful information.

I have what appears to be a lot of tilt and Takahashi want to take a look at it. Investigating flights to Strasbourg at the moment!

This is despite adjusting the focuser tension and purchasing an additional M72 adapter so the focuser is only racked out 10mm.

Have you run the Pixinsight WavefrontEstimation script? If you do, I'd be interested to see the results (especially without the reducer). I've knocked the relevant bits of the test I ran into a pdf report.

 

Test report.pdf

[andrewluck]

I flew to Strasbourg last week and took the train down to Colmar to meet with Richard Galli at Optique Unterlinden. Richard speaks excellent English and I was made to feel very welcome while they looked at my Baby-Q.

As I've previously indicated, Takahashi recommend that the focuser be extended no more than 15mm and to achieve this I'd purchased a 37mm long 72mm extension tube. With hindsight, this was a mistake and I should have bought an 87mm tube and replaced the 50mm tube with it. More on this later.

With the telescope on a table, pressing on the tube and focuser revealed that there was some free movement in the focuser tube. This I removed by tightening the tension screws slightly.

Images were still showing a large amount of tilt and running the Wavefront Estimation script in Pixinsight on a set of defocused star images showed some coma and astigmatism. The report I generated is in the post above. I highly recommend running this script to check the performance of any new refractor to ensure yourself that it meets specification. Based upon my experience, the results are very accurate.

At this point I was unable to determine the cause of the tilt and took the telescope to France. Once on the optical bench a tiny mis-collimation was evident and the front lens was slightly loose in it's cell. Apparently this is a fairly common problem. Both problems were corrected by reseating the cell in the tube and tightening the locking ring. Collimation is set at the factory by using small pieces of tape under the front cell but the adjustment was so small it was not necessary to replace these.

I also took my extension tubes and these were checked on a measurement table with a dial gauge. This is where my main problem was. While each component was accurately machined there is always a small tolerance which in this case was under 0.04mm error in orthogonality. However, when screwed together, in my case these errors added to create a total error of >0.07mm or >70 microns. Their mechanical engineer decided that the likely cause of the issue was the Takahashi 50mm extension and they replaced this FOC. This reduced the total error to <0.04mm.

Test images since I returned home show that there is some small residual tilt in the Y axis that is possibly in the camera and I have some thin tape to shim the camera on it's adapter. Wavefront Estimator shows a much improved PSF image and much better aberration figures.

So, to summarise the recommendations:

1: Use Pixinsight's Wavefront Estimator to determine optical quality and collimation

2: Use the minimum number of extensions and adapters that you can arrange

3: Use a tilt adjuster in the image chain (or be prepared to shim components as required)

4: Do not assume machined components will have insignificant errors in them

There is some residual field curvature. The recommendation here is to either focus on an off centre star or focus on a centred star and then offset the focus about 10 microns. This will result in slightly larger stars but much reduced distortion in the corners. This will only help when you have everything else aligned though.

Takahashi Japan attended the recent Paris astronomy show and indicated that they are aware of the filed curvature issue and have a new flattener on the drawing board that will correct this issue.

 

[whipdry]

Thanks for the update.

On 08/12/2016 at 22:12, andrewluck said:

Takahashi Japan attended the recent Paris astronomy show and indicated that they are aware of the filed curvature issue and have a new flattener on the drawing board that will correct this issue.

Did they indicate if this would be an exernal (add on) flattener or a change from the existing rear elements of the Baby Q ?

 

Peter

[andrewluck]

My impression was that this will be an additional flattener.

Andrew

[ollypenrice]

It's good to see Takahashi doing something about the issue. Hope you get sorted.

Olly

[astrocatinfo]

Thanks for all your words on this experience. As an owner of a Baby Q I'm a bit disapointed to know that it's not as "perfect" and "premium product" as I payed for it...

Bad news for Takahashi. Next time I will maybe better pay less for another quadruplet that can perform as well as Takas.

[andrewluck]

I'm not sure that such an instrument exists and certainly not cheaper than the FSQ85 imo. Takahashi Europe are now quoting a 40mm imaging circle on their website which is closer to reality than the 44 that was originally claimed but when you get close to this the overwhelming issue is tilt in what you hang off the back. Once this is sorted then a small defocus will round out the stars in the corners. I'm not there with mine yet but AstroBruiser is getting pretty close with his judging from the results he sent me recently.

There's certainly a case for using an FSQ106 when you get to this size and resolution of sensor. You'll be operating a close further from the edge of the specification.

Andrew

[WanderingEye]

On 08/12/2016 at 22:12, andrewluck said:

I flew to Strasbourg last week and took the train down to Colmar to meet with Richard Galli at Optique Unterlinden. Richard speaks excellent English and I was made to feel very welcome while they looked at my Baby-Q.

As I've previously indicated, Takahashi recommend that the focuser be extended no more than 15mm and to achieve this I'd purchased a 37mm long 72mm extension tube. With hindsight, this was a mistake and I should have bought an 87mm tube and replaced the 50mm tube with it. More on this later.

With the telescope on a table, pressing on the tube and focuser revealed that there was some free movement in the focuser tube. This I removed by tightening the tension screws slightly.

Images were still showing a large amount of tilt and running the Wavefront Estimation script in Pixinsight on a set of defocused star images showed some coma and astigmatism. The report I generated is in the post above. I highly recommend running this script to check the performance of any new refractor to ensure yourself that it meets specification. Based upon my experience, the results are very accurate.

At this point I was unable to determine the cause of the tilt and took the telescope to France. Once on the optical bench a tiny mis-collimation was evident and the front lens was slightly loose in it's cell. Apparently this is a fairly common problem. Both problems were corrected by reseating the cell in the tube and tightening the locking ring. Collimation is set at the factory by using small pieces of tape under the front cell but the adjustment was so small it was not necessary to replace these.

I also took my extension tubes and these were checked on a measurement table with a dial gauge. This is where my main problem was. While each component was accurately machined there is always a small tolerance which in this case was under 0.04mm error in orthogonality. However, when screwed together, in my case these errors added to create a total error of >0.07mm or >70 microns. Their mechanical engineer decided that the likely cause of the issue was the Takahashi 50mm extension and they replaced this FOC. This reduced the total error to <0.04mm.

Test images since I returned home show that there is some small residual tilt in the Y axis that is possibly in the camera and I have some thin tape to shim the camera on it's adapter. Wavefront Estimator shows a much improved PSF image and much better aberration figures.

So, to summarise the recommendations:

1: Use Pixinsight's Wavefront Estimator to determine optical quality and collimation

2: Use the minimum number of extensions and adapters that you can arrange

3: Use a tilt adjuster in the image chain (or be prepared to shim components as required)

4: Do not assume machined components will have insignificant errors in them

There is some residual field curvature. The recommendation here is to either focus on an off centre star or focus on a centred star and then offset the focus about 10 microns. This will result in slightly larger stars but much reduced distortion in the corners. This will only help when you have everything else aligned though.

Takahashi Japan attended the recent Paris astronomy show and indicated that they are aware of the filed curvature issue and have a new flattener on the drawing board that will correct this issue.

 

I realise  this is an old thread, but just wondered if you could help, I have one of these scopes and the focuser is solid with no flex, but when closing right up there is a time gap at the top and not at the bottom, where the focus tube meets the green housing, so it seems that it’s slightly out of line, would these two screws be able to adjust that if I loosen the back one slightly and tighten the front slightly to take out the tube tilt..

see picture

 

[andrewluck]

If there's no flex then tightening the tension screws won't fix anything.

That looks like a pretty big gap to me and I wonder if the black ring has been cross-threaded on the focuser tube.

Andrew

[WanderingEye]

5 minutes ago, andrewluck said:

If there's no flex then tightening the tension screws won't fix anything.

That looks like a pretty big gap to me and I wonder if the black ring has been cross-threaded on the focuser tube.

Andrew

Ok, many thanks

sorted now.... I think....