gnomus

Have a look at the Astronomy Tools website - http://astronomy.tools/calculators/field_of_view/   

I quickly entered your scope and a 20mm eyepiece in visual mode.  Is this what you see?  Magnification is Focal Length of scope divided by focal length of eyepiece.  So I think your magnification is only in the mid-30s.  Try a shorter f/l eyepiece.  But be aware that your scope will have a magnification 'limit' at which the view will turn decidedly mushy.  Have a play on the site with different combinations.  

 

Regarding Vaseline, I know very little about these things, but I though I read somewhere that you had to be careful about using such things because of the propensity to pick up grit and similar detritus and for it to turn into a sort of grinding paste.

Ah OK.   I hadn't aprreciated that it was a triplet with a 3 element flattener - I just read the 6 element thing on the rim of the objective.  Sorry for wasting your time.

2 hours ago, DaveS said:

There are bench tests for optical alignment, but they're a bit specialised, Zygo interferometers etc. The optical elements can be parallel to each other, but if they're not centered then the stars will not be round. And if the elements are not correctly spaced there certainly will be errors, quite severe ones.

May I ask a really stupid question?  Why change the habit of a lifetime, I hear you ask?  I have just looked on the website and these are advertised as being 6 element flatfield scopes.  I had understood this to mean that - like the Takahash FSQ scopes are supposed to do (and the WO Star 71) - these already produced a flatfield image.  If so I am not sure what the spacers are doing.  Yes you may need a spacer in there so that the limited travel on the focuser allows you to achieve focus, but altering the spacing by small amounts will simply mean that the focuser ends up at different physical places, not that the chip to rear element distance has changed.

Have I lost my marbles?  It is possible.

I have seen a number of images from different Petzvals (I have had 3 x WO71s, for example).  Some of these seem to show the corner effect that you get when you don't have the spacing correct between flattener and sensor in a triplet.  Others seem to show the corner effect that you get when you have too much spacing between the flattener and sensor in a triplet.  

I wonder if these corner issues (that I also got on my FSQ 85) could be down to spacing between the various lens elements. If so, I have no idea what can be done about that.

Caveat: I have no idea what I am talking about, and I am one of the first to scoff when some internet loon starts spouting nonsense about my area of expertise.

4 hours ago, ollypenrice said:

Totally mad! 'Mad as the sea and wind when both contend which shall be mightier.'

Actually now that I think about it perhaps the word 'mad' is inappropriate.  If I present myself to the thought police will they give me a lighter sentence?  We need a new euphemism for 'stark raving bonkers' - can I suggest the word 'Astrodon'?

3 hours ago, Singlin said:

How about paying an extra couple of hundred quid for the seller to make sure or adjust the optics before shipping?

Would that necessarily give good results though?  I have no idea how optics are tested and adjusted - do they take them out into the field and do corner star tests?  Is there a bench test that can be done that will tell you if you can get round stars in the corners?  I hear it said that Petzvals can be prone to collimation errors.  But is it possible that a scope could have all of its elements perfectly parallel with one another, but for there still to be errors because the lens spacing within the scope is awry?  I would genuinely like to know.   

2 minutes ago, ollypenrice said:

F7? That's not.... 

Olly

No it isn't.  Are you mad?

I must say that I salute your patience.  I have had to return 3 scopes because I couldn't get decent stars in the corners.  I think I was lulled into a false sense of security by my ED80, which just 'worked'.  But I wonder if Olly might be on to somethng with his idea that we should demand a little less and pay a little more.  My next purchase is f/7.  I have fingers and toes crossed.....

On 28/11/2015 at 11:57, RobRob said:

Any news on getting this resolved???

Sorry I should have updated this ages ago.

I returned the scope for a full refund minus shipping costs (the retailer and Tak Europe were still insisting that there was nothing wrong with the scope).

Soon after I got a WO Star 71.  My first copy was duff (by which I mean seriously out of collimation - badminton shuttlecocks across the entire field).  This was replaced immediately by FLO (FLO were not the outfit that sold me the Tak).  The replacement scope was fine and gives me round stars in the corners. 

5 minutes ago, Gonzo said:

You must have some serious patience with astronomy, now that my system is up and running (minus the weather box), the weather forecast for the next week is utter Rubbish!!!!!!

I think the expression that gets used is 'character-building'.

Congratulations.  When I started following this thread last summer, I was in the process of building my completely manned (and womanned) observatory.  It is now built.  Nevertheless I am constantly tinkering with it.  I have nothing but admiration for those who have been able to set things up to work remotely.     

The latest advice (received today) from my Takahashi dealer (apparently endorsed by the importer) is:

"To assemble the components and expect them to work at this level is not realistic."  

FSQ85 offset focussing mentioned here (courtesy of sharkmelley):

https://groups.yahoo.com/neo/groups/UncensoredTakGroup/conversations/topics/59070

I'm going to try this next time I'm out imaging.

Regards

John

It will be good to know how you get on, but surely this should be unnecessary if we had a flat field, as promised.

It's good to know of this PI feature, but if you had read the whole therad you would have seen that we eliminated polar misalignment a few pages back.

If it's any consolation Steve I think my corner star elongation/distortion is worse than yours   See my latest image here:

http://stargazerslounge.com/topic/256830-ngc281-pacman-hoo/

Jury still out on this for me (at least, nothing from Mr King or Takahashi yet), although I have my suspicions that in my case it could be due to poor focussing.

Regards

John

It doesn't look out of focus to me John, but it does, as you say have that radial elongation effect.  Once I saw it in my images I kept imagining 'join-the-dots' type circles around the image (if only they were dots, eh?)

I don't know if they are worse than mine from the size of image you posted.  I assume these are from your QSI 690 which has a physically smaller size, so will be looking at a smaller part of the 44mm 'flat' circle than my sensor.  But I don't know what effect your smaller pixels would have on ovoid-osity (I think I may have invented that word).

I downloaded an evaluation version of CCD-Inspector.  It is pretty easy to use and it might help you to put some 'numbers' to what you are seeing.  However, I'm not sure that I am happy that I now know about this software - it might turn me into even more of a measurebator than I already am.  (That word by the way is I believe copyrighted to a certain Ken Rockwell.  I hope it causes no offence - but it is a perfect term for what can happen to some of us).

They can ask all they want, but you have no obligation to go to the retailer first or even at all. The law is clear- they are jointly and severally liable. This means that they are as liable, no more or no less, than the retailer. There is no "first point of call"- you have complete freedom to claim from the card issuer first if you so wish. If the card issuer takes this approach, then you might want to point the at case 86/08 on the Financial Ombudsman's website:

http://www.financial-ombudsman.org.uk/publications/ombudsman-news/86/86-consumer-credit.htm

"card provider refuses to consider claim under section 75 until consumer has first pursued the matter direct with the supplier:

complaint upheld

We were satisfied, from the evidence Miss V had provided, that the dinner service was not a matching set. So she had not been given what she had paid for with her credit card. Under section 75, she could seek redress from the supplier of either the goods or the credit.

We thought Miss V had taken reasonable steps to try to resolve matters with the supplier. Despite what the card provider appeared to believe, however, she was not obliged to have done this - or indeed to have returned the dinner service - before she could make a claim to the card provider.

We told the card provider that Miss V was not obliged to exhaust all possible avenues with the supplier before claiming under section 75. And we said we could see no reason why it should not pay the claim. The card provider argued that if it gave Miss V a refund then she would still have the dinner set, as well as getting her money back. It did not think this was fair." (emphasis mine)

Of course, you will be asked to prove your claim.

Yes, you could go down the Moneyclaim route. perhaps a written notification to the retailer might jog his/her conscience into action, especially if you remind them that the costs are claimable if you win. A S75 claim may be easier and faster.

OK Zakalwe I will think about that. If I go down the S75 route, does the scope go back to teh supplier or do the CC company own it?

My [removed word] can be replace with "very annoyed"!

... or 'very drunk' perhaps?

The card issuer may try and reject the claim if the retailer has rejected it.

If one was to make a claim under S75 and declined to offer the information that the retailer has supplied, but rather showed the maker's specifications and your finding showing those specs to be in doubt, then I would suspect that such a claim may be stronger. You are under no obligation to tell the card issuer that the retailer has rejected a claim, as the card issuer is jointly and severally liable. You are free to pursue a claim with the retailer or the card issuer.

An independent optician's report would nail it, but that would incur costs which the claimant would then have to pursue. The mention that the costs of such a test would be added to the S75 claim might also influence the card issuer to come to a sensible decision....

I had understood that if you go to the CC company they will ask why I have not approached the retailer. I may go down the CC route but it does seem unfair to me that the supplier can get away with this shoddy service. I know that there are costs involved in going to the Court but these are not too bad and at least I do understand this system, having used it before. Furthermore, Court costs can (and should) be added to the claim.

But - and just playing devils advocate here as I thoroughly sympathise - wouldn't that only apply if the item was faulty or misrepresented? What's the situation if Takahashi themselves say that it's within acceptable manufacturing tolerances?

Takahashi say that their scope will give 'pinpoints' out to 22 mm from optical centre. In the examples that I have posted do you see pinpoints at 12.5 mm from optical centre? Secondly, are you suggesting that if a company sells me a duff product, but then say that it is OK, I am just supposed to accept that?

Perhaps you are just teasing me, in which case I apologise for rising to the bait.

Thanks Zakalwe. I had thought about the CC company (I did use a card). I've never done that before though. Do they recoup the dough from the retailer?

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.

Thanks Michael. I am no expert, but it was telling that when I asked why one-axis tilt would cause the radial elongation (or cylindrical distortion as you put it) he didn't really have an answer.

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?

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).

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.

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?