Ovoids with Mesu and Tak FSQ 85

[gnomus]

Late to this thread, but I was worried about my fsq106ed (new Q) and oval stars!

I decided to make a proper test using CCD inspector!

The advice is to take 10 or so 20 sec sub's..taken from a fairly rich field devoid of globular's and nebula...unguided .....stack them together in CCD inspector and then look at the curvature n tilt.

The logic being that guiding etc will distort the stars.

This should eradicate the sensor and the focuser tilt as being the cause of oval stars which it did for me, though I did also use a DTI to measure all sorts of movement, including the Captains wheel effect, which turned out to be negligible.

Aside from this, there are a set of grub screws on the side of the focuser that you can adjust to just stiffen up the focuser (on the 106 at least). Though friend of mine has loads of wobble on his FSQ 106 and has not been able to remove it by this means.

Frustrating issue with Taks !

Ray

Takahashi state:

As on the FSQ-106ED, the built-in field flattener, perfectly [my emphasis] designed and manufactured, 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 [my emphasis again] ...

My view is that if the scope does not function as promised then it should be returned.  

[ollypenrice]

You shouldn't have to focus on the one third lines with this scope.

Having been absolutely delighted by mine (which is now Sara's) I have often extolled its virtures but both Steves have had issues and this is not good. It's a great shame. My subsequent Tak experiences (using my own very second hand FSQ106N and Tom's similar instrument) have also been entirely positive (not that this proves anything. I just mention it.)

At the resolution available on here I find it hard to tell whether or not the corners are worse in the 5 min subs. What do you think, Gnomus?

Olly

PS I had my first Mesu nightmare last night but it turned out to be my fault. I had somehow managed to reverse the sign in the encoder steps setup menu. (Or it might have been the cat. I bet she did it!) The Mesu continues to 'just work' in a way that seems to be beyond the powers of much of the kit we use, as Steve Steppenwolf says.

And, further to Sara's point, this thread would be a good port of call for anyone reading here.  http://stargazerslounge.com/topic/256544-a-couple-of-star71-wips-m45-m31/

Edited November 9, 2015 by ollypenrice

[gnomus]

You shouldn't have to focus on the one third lines with this scope.

Having been absolutely delighted by mine (which is now Sara's) I have often extolled its virtures but both Steves have had issues and this is not good. It's a great shame. My subsequent Tak experiences (using my own very second hand FSQ106N and Tom's similar instrument) have also been entirely positive (not that this proves anything. I just mention it.)

At the resolution available on here I find it hard to tell whether or not the corners are worse in the 5 min subs. What do you think, Gnomus?

Olly

PS I had my first Mesu nightmare last night but it turned out to be my fault. I had somehow managed to reverse the sign in the encoder steps setup menu. (Or it might have been the cat. I bet she did it!) The Mesu continues to 'just work' in a way that seems to be beyond the powers of much of the kit we use, as Steve Steppenwolf says.

Thanks Olly.  I have taken a crop from the same region of the 5 second and 300 second exposure and upscaled it a little.  I hope this helps.  There are clearly less stars on the 5 second image.  On the 300 second image the stars are brighter and a bit more 'swollen'.  Nevertheless, the ovoids look to be identical in proportion.  I've circled a few just to give an idea.  What do you think?

[ollypenrice]

Yup, that excludes PA conclusively.

I'm really sorry you're having this hassle.

Olly

PS I'd send that crop to the supplier.

Edited November 9, 2015 by ollypenrice

[gnomus]

Yup, that excludes PA conclusively.

I'm really sorry you're having this hassle.

Olly

PS I'd send that crop to the supplier.

Already done. The supplier is getting a new FSQ85 in for me.

No need to be sorry ..... although ..... on reflection .... this is all your fault!!!!

I hope the new one works....

[Starlight 1]

That good new Gnomus,had been reading post and Olly check out one of my sub on my 106 just to see if Qc is in all Tak.

[ollypenrice]

That good new Gnomus,had been reading post and Olly check out one of my sub on my 106 just to see if Qc is in all Tak.

I did so and thought it perfect. However the corrected circle on the 106 is so big that you can't find a camera to test its potential. A good thing for all our wallets, I dare say...

I'm glad you'g getting a new one to try, Gnomus.

Olly

[strutsinaction]

...

The result is that I have ovoids present in at least 3 of the four corners of all images.  To my mind the worst affected area in all images is the bottom right corner.

...

Just an idea. Maybe rotate your camera 90 degrees and repeat the test. If it's always the same bottom right hand corner that shows the most distortion then would that indicate sensor tilt?

I've been taking a closer look at some of my earlier images taken with the FSQ85. Coincidentally, I have elongated stars in the bottom right hand corner, more so that the other 3 corners. The other corners show some elongation but in different directions - radial I believe. This does not appear to be a PA issue. E-mail sent to Mr King for advice!

Regards

John

[gnomus]

Just an idea. Maybe rotate your camera 90 degrees and repeat the test. If it's always the same bottom right hand corner that shows the most distortion then would that indicate sensor tilt?

I've been taking a closer look at some of my earlier images taken with the FSQ85. Coincidentally, I have elongated stars in the bottom right hand corner, more so that the other 3 corners. The other corners show some elongation but in different directions - radial I believe. This does not appear to be a PA issue. E-mail sent to Mr King for advice!

Regards

John

I had perfectly acceptably (I suppose nothing is perfect) round stars with the same camera on my ED80.  I've spent enough time on this particular scope and it is going back.  I hope that I had a bad copy, but you and I are not the only people who have had radial distortion is our corners.  Are you using a KAF 8300 sensor?  

[strutsinaction]

... Are you using a KAF 8300 sensor?  

No, I use a QSI690 (which was returned to QSI to get the Sony Glow fixed). Hoping I don't have to return my Tak!

Regards

John

[gnomus]

No, I use a QSI690 (which was returned to QSI to get the Sony Glow fixed). Hoping I don't have to return my Tak!

Regards

John

I believe that that chip is physically smaller than the Kodak, correct?  Whether or not you return your Tak is, of course, a matter for you.  Are you happy with what it is doing in your corners?  Have you tried the 5 second pointing at the zenith test?

Edited November 9, 2015 by gnomus

[strutsinaction]

I believe that that chip is physically smaller than the Kodak, correct?  Whether or not you return your Tak is, of course, a matter for you.  Are you happy with what it is doing in your corners?  Have you tried the 5 second pointing at the zenith test?

Yes, smaller chip and, yes, I was happy until I started reading your thread and started pixel peeping 

I will try the zenith test the next time it's clear.

Regards

John

[gnomus]

Yes, smaller chip and, yes, I was happy until I started reading your thread and started pixel peeping 

 ......

John

Oh dear. I really am sorry.

[Owmuchonomy]

I feel for you Gnomus.  I have virtually the same issue with my refractor which it is claimed produces a flat field even on a full frame sensor and it has at last been picked up by the supplier after me sending very similar corner crops and other data.  My findings point to (and my gut feeling is that) the likelihood the collimation is slightly out as Olly says above.  However, mine was almost a third of the price of yours.  I wish you good luck and I will follow your plight.

[gnomus]

A rather strange development. Having said that he would get me a new FSQ 85, the supplier has now reneged on this. He tells me that Takahashi have examined my FITS files and determined that I have a very slight tilt somewhere in my set up. This is of the order of 0.02mm. The supplier tells me that this is somethng that Takahashi may not be able to correct (they could correct a larger error).

The supplier could not tell me how a sensor tilt could give rise to a radial distortion pattern.

He went on to tell me that the problem was exaggerated by my having a camera with such a small sensor pixel size. I suggested that my sensor pixel size was not especially small at 5.4 microns and that there were many cameras with smaller pixel sizes than this. "In which case they would show the problem more", was the response. It was suggested to me that I should have a pixel size of 7 or even 9 microns. When I pointed out that I had made it clear from the outset that I intended to use an Atik 383L with the scope, he responded that it was I who had decided to purchase the scope despite having this camera.

I said that it seemed unlikley that we were going to be able to resolve the matter and I said that I wished to return the scope for a refund. The retailer refused to take the scope back and refund me. He did offer to send the scope to Takahashi so that they could issue me with a "certificate" confirming that there was nothing optically amiss. I am now having to consider the best way forward.

Has anyone been in this situation before? Any advice? Am I right to assume that I would not get radial distortion if this was a tilt somehere in the imaging chain?

[DanL]

Might be clutching at straws but when and how did you buy the scope? From what I've read it, if it was an online transaction then distance selling regs say you have 14 days to tell them you want to return goods even if it's not faulty and no obligation to provide a reason for returning it.

Otherwise it would be dependent on the suppliers good will return policy or item is faulty or doesn't do what it is supposed to do - which seems to be in dispute.

https://www.gov.uk/accepting-returns-and-giving-refunds

If you're not eligible for a refund I would be tempted to have Tak re-certify it. They might find and correct something when taking a closer look at it.

[gnomus]

I think you will find that the Sale of Goods Act affords consumers considerably more protection than this, especially in cases where the item is not of satisfactory quality, as described (pinpoints out to 22 mm from optical centre) and/or not fit for purpose. The worst case scenario is the County Court, but I would prefer to avoid that (although I have found with people who have not paid me that it is effective). What I found most disappointing was the supplier's attitude.

Edited November 10, 2015 by gnomus

[ollypenrice]

Good grief, you are resolving at 2.47 arcseconds per pixel which is positively coarse, so the claim that your pixels are too small is risible. The UK 'sweet spot' is often estimated as being at 2.0 arcsecs per pixel and you are well above that. Imaging down to 0.6 is commonplace. I did it for two years on a full format camera. Many of my friends ask why I put up with 1.8"P/P on the TEC140/ full fformat outfit and I say, 'because it's nice and tolerant and relaxing to do.' So your  pixels are on the big side, not the small side, and you'd have plenty of imagers to confirm this.

On top of that your chip diagonal measures 22.5mm for a claimed imaging circle of 44mm so you are using a tad over half the full circle. So you have a forgiving pixel size and are using a chip which exploits about half the light cone. Reality check, you should not even be taxing the optics in the slightest. Sara can prove that a Baby Q can cover this chip easily.

However, the tilt remains a possibility. The fact that it wasn't there on the ED80 may not be proof of the chip's orthogonality because the Baby Q has a faster F ratio and so greater depth of field.

And I do suspect that, while it may not be perfect, you might have a very hard time beating the Baby Q once you get into long colour exposures...

As for that stuff about pixel scale, it's bunkum.

Olly

Edited November 10, 2015 by ollypenrice

[steppenwolf]

The fact that it wasn't there on the ED80 may not be proof of the chip's orthogonality because the Baby Q has a faster F ratio and so greater depth of field.

I believe that Olly meant 'less' depth of field here? However, I do agree with Olly completely that you have a well optimised system with regard to the sampling -  you are comfortably in the right area in my opinion as well - hang it, I bought the same 'scope  BECAUSE it was a good match to the 8300 chip!

I am sorry to hear that the supplier has had a change of mind as I am not sure where that leaves you except perhaps checking out the tilt that I suggested earlier on in this thread but as for the pixel size being too small, although I was told something similar, I am far from convinced.

[gnomus]

During the phone call the retailer kept repeating that the tilt was only 0.02 mm (he must have said this about a dozen times) and that this amount of tilt would be difficult to eliminate - it being so small.  My response to him was that I was looking at an image that had ovoids that encroached almost to the centre of my images and that this was unacceptable to me.

Would 'tilt' give me the radial pattern that I am seeing - the ovoids go in different directions in each corner?  The retailer said I only had tilt in one axis (I think the Y axis, but I'm awaiting the report from Tak).

[sharkmelley]

That's a very disappointing result for you.  Is the supplier implying that Takahashi consider a tilt of 0.02mm be acceptable on the FSQ-85ED?  If that is the attitude of Takahashi then it is very disappointing for their future potential customers.  I would be very annoyed to pay that money for such a scope and find it has that tilt.

It is certainly the case that tilt can lead to the elongations in the directions you are seeing i.e. giving the appearance of a kind of field rotation in one or more corners.

So, if you keep the scope you will want to diagnose whether the tilt is in the scope itself (i.e. the optics and focuser) or in the adaptors/attachments or the camera sensor.  Unfortunately this is likely to be a laborious process.

Mark

[ollypenrice]

I believe that Olly meant 'less' depth of field here? However, I do agree with Olly completely that you have a well optimised system with regard to the sampling -  you are comfortably in the right area in my opinion as well - hang it, I bought the same 'scope  BECAUSE it was a good match to the 8300 chip!

I am sorry to hear that the supplier has had a change of mind as I am not sure where that leaves you except perhaps checking out the tilt that I suggested earlier on in this thread but as for the pixel size being too small, although I was told something similar, I am far from convinced.

Thanks, Steve, he did!  I've been out of bed for the large part of four days and it's beginning to show... The Baby Q is a good match with far smaller pixels. Note Horwig's post here. http://stargazerslounge.com/topic/255014-deeper-into-m31-from-les-granges/ I worked on this data so I know it's genuine and the pixels are far smaller than those of the 8300.

Olly

[gnomus]

Horwig's shot was taken with a 106 though if I'm not mistaken. Would anyone be able to let me have an FSQ 85 (no reducer) and 383L combo image/frame that I could send to my supplier to show him that ovals are not inevitable?

[michael.h.f.wilkinson]

I am no DSO imager, but I do now something of optics. My physics intuition would be that a slight tilt would result in a band of sharpness across the image, at right angles to the "slope". It almost looks like the optics have some cylindrical distortion, caused by some lack of collimation, perhaps.

[Zakalwe]

Did you buy it using a credit card for some or all of the purchase? If so, you are, depending on the timescale, protected under Section 75. You can make a claim directly to the card issuer without involving the supplier.