gnomus

Another very happy Mesu owner here. My only concern about it for your situation is that I am not sure how "mobile" it can be - even in the two section form. It is a substantial piece of kit. Of course set-up/tear-down can be done and, as we have heard, there are people doing it. It might be a good idea to try to see one in the flesh so that you know what you are letting yourself in for. (The same goes for an EQ8 of course). If I was looking for a mobile set up, I think I would be considering one of the Avalon mounts, but I have no idea how suitable these are for use with large Newtonians.

We have a winner!!!!

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.

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.

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'?

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.

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.....

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.

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."

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.

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).

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?

... or 'very drunk' perhaps?

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.

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?

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?