I'm not sure how the SW/Olivon would fare on an f/5 scope. I can get 171x on the Moon with a 7mm ortho' and a 3x Barlow. I got a good 150x on Jupiter although I also took that to 171x and 166x for a short while. Jupiter's weird though and conditions are really important. I thought the ST80 did as well as the 102mm Skymax with Jupiter. I am not sure what it would be like with Saturn, probably good at 150x. I think 150 - 160x would be the limit for most planetary but you could push it easily to around 180x for lunar viewing. I got 199.9x once on the Moon accidentally by putting the wrong eyepiece in, it didn't look that bad, in fact it was quite sharp, if a little darker. The yellow tint from the Semi-Apo was much more apparent though lol!

 

I’ve done some more daylight testing with the TSO 0.5x reducer. This time with 15mm Celestron Omni and Kellner EP’s, a 17mm Celestron Plossl (the ‘Baadertron’), a 20mm TeleVue Plossl, and finally a 19mm TeleVue Panoptic. The reducer’s thread is still showing no signs of wear and threaded into all of the tested eyepieces easily.



Both 15mm eyepieces give 66.6x on the 90mm Omegon MightyMak (f/11.1) for a TFOV of 0.75° (45 arc minutes). I’ve used 50° for the AFOV value of the Celestron eyepieces as I don’t totally believe their figure of 52°. With the focuser, if my calculations are correct, they both give 33.3x for a 1.5° TFOV. The Omni didn’t seem to struggle with this even though now the MightyMak is essentially f/5.5. The relatively wide angled Kellner showed a tiny bit of vignetting but it also seemed to deal with it well.



The 17mm ‘Baadertron’ gives 29.4x for a 1.7° (1°, 42') TFOV with the reducer increasing its TFOV from 0.85 (51 arc minutes). Again, it seems to deal with this well as far as I can tell in a daylight test.



The 20mm TV Plossl has a 17.1mm field stop and gives exactly 25x for a 2° TFOV with the reducer. There was a hint of vignetting but I can’t see it as being problematical.



The 19mm TV Panoptic has a 21.3mm field stop. It will give 26.3x with the reducer for a 2.58° (2°,34‘,48”) TFOV. There was some noticeable vignetting, which was expected, but not as intrusive as I thought it would be. The 19mm TV Panoptic continues to surprise me. It’s probably my most used eyepiece on every scope I have.

 

Hey Ray -

You might be able to find this on the web. But while it's as complete as you could possibly imagine, there's one minor problem:



It weighs in at 701MB!

It's rather like downloading the entire Encyclopedia Britannica - Aardvark to Zygote. But it was(is?) free.

I hope you're feeling better -

Dave

 

Or this: http://ap-i.net/avl/en/start

 

Virtual Moon Atlas is best found here:

https://sourceforge.net/projects/virtualmoon/

That is one excellent program, Mak. If I were ever lost on the Moon, VMA is the one I'd consult!

Dave

 

Yeah, it's excellent. I'm a tad dubious about downloading anything from sourceforge though. I don't think uBlock Origin will even open sourceforge pages by default. Depends if you like OpenCandy or not I suppose lol.

 

Then I take it you don't suggest people get Stellarium?! That is also a SF download.

Personally, I've never had any issue with SF, and trust them. They also have the very best free software-programs for astronomy-folks like us. It's always a pleasure to me to take a nice stroll through their astro-section to find any new one's that have been added.

Whenever I download something from the other sites, I almost always get a bug riding with it. Though I screen everything with Kastersky's anti-virus (consider the tops) and Malwarebytes (free-version - EXCELLENT!), somethings manage to get by as they can be programmed not to "hatch" until they detect they are in a system. Then no-fun-time begins. The last one crawled in by my visiting CloudyNights - browser redirect to a hard-core XXX-site - which Malwarebytes finally killed - but these things are getting more sophisticated in the ways they are designed to elude the usual scanning people do & use. This is where heuristic-analysis comes into play.

Now I'm using a 3-way to: approach, find, and kill. Kaspersky, Malwarebytes, and Spybot Search & Destroy. As well as Malwarebytes Anti-Exploit (MBAE). Both Malwarebytes are free - just remember to update and run daily. Or more often if you do a lot of strolling about! Spybot S & D is free also. Kaspersky's will cost you.

I also keep two complete copies of my hard-drive on external HD's. I believe those who rely on "The Cloud" will be in for a very rude awakening.

Dave

 

Yeah but you can also get Stellarium from its own homepage.

http://www.stellarium.org/en_GB/

I think Sourceforge were OK once but they went over to the dark side. Maybe things have improved but their downloads were getting a bad reputation for all sorts of wrappers and PUP's.

Kaspersky's a dependable AV. I use Panda, the Basque Country's finest lol. Although half the time I'm in Ubuntu so I don't need an AV with that. I do have some browser hardening though.

MBAM has now upgraded to #3 and has MBAE included. I don't use it anymore and I've uninstalled the standalone MBAE as it will only be available as freeware now as a perpetual beta.

I remember Spybot S&D, although I don't use that anymore either. I still run an on-demand SUPERAntispyware, which I've run on various computers for nearly ten years. Some have questioned its efficacy now Nick has sold it but it does find tracking cookies lol.

http://www.superantispyware.com/

I've used SpywareBlaster for about as long as SAS.

http://www.brightfort.com/spywareblaster.html

Finally I regularly make a Macrium image.

http://www.macrium.com/reflectfree.aspx

 

It's probably worth looking at other makes, but the ST80 is almost legendary as an inexpensive good achromatic doublet. Synta are really good at mass producing these. I doubt you'd get the same quality for any other scope that costs less than most TeleVue eyepieces do. They've done the same with reflectors (Newtonians, Mak's and SCT's). I wish I'd have bought the 90mm Orion Apex instead of the MightyMak.



The chocolate teapot came back more broke than when I sent it back to Germany. I've decided to write it off as a loss, for my own sanity.


The Moon book (paperback) looks like it will be good, not necessarily with Vegemite though lol.



The Astrozap looks like it could work. Although I'll put the Skymax on a taller mount!

I got first light with the TSO/GSO reducer on a twilight Venus with the MightyMak. I got 12.5x, 4 arc minutes TFOV and a 7.27mm exit pupil on a 40mm Plossl. I could still see the phase (with a #56 filter).

 

Actually, Ray, I rather draw a blank when I think (or try to) of other small, fast refractors. I know there are some - but the ST80 is by light-years the most popular one. Most every other is an APO - for 10X the price. People have allowed themselves to be convinced that a little blue around bright objects is as disasterous as the asteroid that polished off the Dinosaurs.

The ST80 is the most popular. And I'd have to guess this is an earned standing. I, for one, am quite happy with mine. Happy enough to have gone for a Crayford 10:1 Dual-Focuser / Visual-back that cost more than the scope itself.

Dave

 

Retail therapy definitely works!

 

I’ve been reading North’s ‘Observing the Moon’ and he has some interesting views on what he calls secondary spectrum problems (CA) in short tube refractors. He’s obviously a very clever boffin-type chap so he could be right about much of this. Amongst other things, like stopping down the aperture (so that’s what the little lens cap is for! lol) and minus cyan filters, he discusses using an inexpensive short achromatic Barlow. He postulates that the Barlow’s yellow-green light focus is furthest from the lens and will generate a negative secondary spectrum that can counteract the positive secondary spectrum of the telescope objective. This would be more effective in reducing CA than using an achromatic Barlow or amplifier according to North. Which is great news if you have a cheap Barlow I suppose.



I’m not so sure how this applies to lunar viewing with approximate 0.5mm exit pupils but it could work for Messier Objects with less expensive eyepieces. A lot of medium priced Plossls and other eyepieces don’t always work well in fast scopes of f/5 and under. Celestron recommend that their Omni series are not used in anything below f/6. I’m guessing this doesn’t apply to Plossl makes like TeleVue which are designed to work in quite fast scopes, hence the expensive retail price. With my 8mm TV Plossl I can get 50x for a TFOV of exactly one arc minute and a 1.6mm exit pupil on the ST80. 50x is about the best balance of magnification detail and decent exit pupil for most DSO’s I find. Much lower and you don’t see the detail and higher the target can be too dark. The upshot of all this is that if my sums are correct, I can get a TFOV of not much under one arc degree (00:56:15) at 53.3x for a 1.5mm exit pupil with a combination of a Celestron Omni 15mm Plossl and an achromatic Barlow. Most Messier Objects can be comfortably viewed within one arc degree. The 8mm TV Plossl only has a field stop of 6.5mm. I don’t have any figures for the 15mm Omni but it has to be twice that at least. The 2x Barlow has effectively doubled the ST80 focal ratio to f/10 and alleviated a lot of chromatic aberration at the same time. Just a few thoughts.


M41 as imagined by Stellarium seen through a 15mm Plossl with a 2x Barlow.

 

For ~

'This would be more effective in reducing CA than using an achromatic Barlow or amplifier according to North. Which is great news if you have a cheap Barlow I suppose.'

(above) read ~

'This would be more effective in reducing CA than using an apochromatic Barlow or amplifier according to North. Which is great news if you have a cheap Barlow I suppose.'

 

To be honest Ray, I'm pretty sure the X-Cel 2x is an apo'.



Both of the Celestron Barlows above are achromatic.

The 2.5x TS Optics is a bit of an enigma as some say it's an apo' and others claim it's only an ED glass doublet. It's almost certainly a rebranded GSO.

http://www.gs-telescope.com/content.asp?id=121

It does state quite clearly that it's a three element Barlow on the housing. Which is usually indicative that it is an apochromatic. I would classify it as such anyway.

 

Well that's some good news about your hand Ray. You should be just in time for some early spring viewing. I'm pretty sure Saturn rises early in late February. It will be low though. Between 05:00 - 06:30 here, a tad higher than Antares, at just under 15°.



The X-Cel 2x will double the focal length of the ST80, technically making it 800mm and increasing it to f/10. I don't know about cancelling out any green-yellow aberration. Green light is around 510 nm and yellow light around 570 nm. I would have supposed a good apo' Barlow was corrected for this. Hence why North recommends an inexpensive achro'.

You could be in luck: http://agenaastro.com/celestron-1-25-universal-t-adapter-2x-barlow-93640.html