GazOC

I've got the APM 13mm,  the Myriad 3.5 and the 5mm. They look very similar, given the crossover in sizes between the two ranges I'd be surprised if they aren't fundamentally the same eyepieces.

Ah! You're right, John. It's 3.5mm I was getting confused with 

I've been waiting for this one, fits nicely inbetween the 5.5 and the 9.

http://apm-telescopes-englisch.shopgate.com/item/333634313036

On 23/10/2020 at 01:54, John said:

It's somewhere between FPL-51 and FPL-53 in terms of potential for CA control but remember that the glass used in the mating element plus the figure and polish of the lenses is equally important.

 

Not much chance of forgetting it, John. You can pretty much guarantee that someone will make that comment every time a thread is started about glass types 😉

I've had my ED120 and ED100 on an AZ4 with stainless steel legs and an extension tube. 

The damping down time on the 120 was borderline what I'm willing to put up with but the ED100 was fine. I think upgrading the Skywatcher ally tripod is very worthwhile even with the bit of weight the steel tripod adds 

Hi all,

I was looking at dipping my toes back into a bit of lunar/ planetary imaging and was dead set on getting a ZWO ASI 290MC camera but then saw this from QHY. Does anyone have any experience or views on it?

https://www.modernastronomy.com/shop/cameras/lunar-planetary/qhy-lunar-planetary/qhy5iii462c-planetary-and-nir-imaging-camera/

It seems an attractive option with the far IR sensitivity as I definitely want to go down the OSC route for planetary but would also like the advantages mono gives for lunar imaging.

3 hours ago, Nair al Saif said:

The evostar was it an achro or an ed and why was it better?

It was the achromat. I didn't have them both side by side but I'm pretty sure I had them at the same Jupiter opposition (it was ~15 years ago so I can't be sure). 

The 127 gave clearly better views of Jupiter than the 120 and I've always regarded the planet as the acid test for refractors.

Ironically, given the question, I sold the 127 when I bought an ED120 which rendered the achromat a bit redundant

I've owned a Skywatcher 120 and a clone of the Bresser 127, the latter was by far the better scope.

Result!

I'd upgrade the Celestron, I'd prefer to have the  thinner 80mm tube over the 100mm that the ED80 uses 

I'd go for the ST102 for the reasons mentioned above, it would be the perfect compliment to the 127 Mak. 

The ED80 is undoubtedly optically superior to the ST102 (as it should be given the relative prices) there's no beating the extra aperture for DSO observing.

11 hours ago, mikeDnight said:

Here goes:  There's another thing to consider also and that's the amplification factor of the secondary mirror. I seem to remember from years back that an F2 primary with a 5X amplifying secondary, creating a F10 system, doesn't amplify the heat errors by 5X, but by 25X. (5X^2). So thermal equilibrium is much more difficult to achieve in a catadioptric system using an amplifying secondary, or even with an open Cassegrain design. What puzzles me though, is that a Maksutov always seems to perform better, presenting sharper stars and higher definition than a SCT. Why? I have no idea! Perhaps it's that awful Schmidt corrector plate that's responsible for those cotton wool star images and drunken planetary views?? 

I'm working on being more sensitive. How am I doing?👍👎

The reason I've read is that, while in an ideal world there's no reason a Mak/Cass should outperform a SCT, it's easier to accurately mass produce the Mak corrector than it is the SCT corrector so the customer is more likely to get better quality optics.

(Disclaimer: I am not a telescope manufacturer) 😉

@John I tried to find one but couldn't but if you can locate a similar diagram for an ED doublet or an achromat it may show the idea more clearly 

Depending on how the designer has chosen to set up scope the focus point for the wavelength at the blue end of spectrum will be further apart from the on the vertical scale  from where the red/ green wavelengths come to focus than it is the example above. This is the CA you see at the eyepiece 

It's sounds like you're sold on the refractor and planets despite the pros and cons probably weighing in favour of the Cass being the more versatile scope overall?

If that's the case then go with the 'frac 👍

I've used a HEQ5 for lunar/ planetary imaging with a 180mm Mak and it's more than capable.

I like the look of that, John 

18 minutes ago, John said:

There is the Feathertouch for the Lunt HA scopes. Could that be adapted ?:

https://www.firstlightoptics.com/specialist-focusers-borg-tele-vue-lunt-gso-rc/feathertouch-125-dual-speed-focuser-for-lunt-50mm-solar-telescopes.html

I think Moonlite might have something similar ?

Ouch! It's worth 3 times more than the scope 😉

Does anyone make a 1.25" only Crayford or R&P focuser? I'm guessing not but it could be an option for people who wanted to move away from the stock focuser without wanting the extra weight of a 2" focuser on the back of the scope?

I'm very sceptical of the baffle tube being the problem, it's very carefully tapered in width from top to bottom 

That's not to say it can't be wrong, just that the designers have given that part a fair bit of time and effort 

Are the gold 150mm Maks not full aperture but have oversized mirrors in the later black diamond models?

I only ask as this was supposed to be the case with the 180mm model and, from the model I measured, the gold model also had an oversized primary the same size as the black diamond version 

@Mr Spock  Has anyone measured a Skywatcher 150mm primary or effective aperture? They don't seem to get mentioned as much as the 127 or 180 for some reason

1 hour ago, JamesF said:

I've just had a quick look at my (blue Skywatcher) 127 Mak.  I reckon the clear aperture of the corrector alone is no more than 118mm.  119mm at the very most.

James

I've taken the corrector out my blue Mak and made a couple of *very quick* measurements. 

The clear aperture of the front of the corrector seems to be 127mm, the back of the corrector is harder to measure but the ID of the cell is 133-134mm with a ~3mm lip all around near the corrector so somewhere very near 127mm.

I wish I'd have measured the primary when I had the thing stripped a few weeks ago as that is often given as the reason for the restricted aperture but haven't got the stomach to attempt that job again 

Or a "Skymax Pro 190" and chucked an extra 50 quid on the price 😉

2 minutes ago, John said:

Thanks Gaz - I'm glad I was not imagining it !

So I wonder just what Synta / Skywatcher did actually change to increase the effective aperture ?. Maybe nothing and the tales of the 180's operating at less than 180mm are myths ?

 

 

The mirror is oversized and there's lot of space in between the mirror and the tube so I can't see that being the problem

To me, that leaves the baffle coming out of the primary (realistically the secondary baffle isn't going to knock off 10mm from the effective aperture) as the only possible culprit but  whoever designed that part has made sure it tapers in as it gets closer to the secondary. 

Just MHO but I'd be surprised if Skywatcher redesigned the scope to give it an extra 10mm aperture and then said nothing about it ? 🤷

1 hour ago, John said:

I've seen a thread somewhere on the original gold tube 180 which showed that it has a primary the same diameter as the more up to date one that @Captain Magenta took apart recently. Is there some other modification that would increase the effective aperture such as a re-designed secondary baffle ?

 

That'll be me 😉

The mirror is 200mm. It could be that that baffle coming out of the primary is cutting out light but it looks very carefully graduated in width as it approaches the primary

Someone has put a lot of thought into the width of the baffle at any given point. That's not to say they've not just got it wrong but they've not just stuck a tube on and hoped it's correct