Wide angle EP advice for a 130mm F5 Newt

[cwis]

I've been reading lots on this and the more I read, the more questions....  

I've got the Skywatcher 130ps Newtonian on the AZ-GTI mount.  Initially I used the goto almost exclusively when observing, and purchased the following based on that mode of use:

Seben 24-8mm zoom (24mm while I centre target and zoom in to observe) and

OVL Nirvana 82 degree 4mm, for splitting doubles and planetary (amazing view of Jupiter the other week) etc.  I can do a goto and if the target isn't in the middle the wide angle means I can peer round the field stop, find it and centre it without changing EP.

I found using a mobile phone to move the scope about pretty much forced this mode of operation. If you want accurate goto, don't use the secondary encoders, don't move the scope manually - keep the clutches locked.  This kind of disrupted the "flow" as I kept having to look away from the eyepiece to zero in on a target with the phone, ruining my night vision on occasion, and you don't tend to tour about the sky either.

 

So I got myself an ESP32 microprocessor, an analog mini joystick and wrote in Micropython something that mimics a Sky-Safari connection to the Synscan software running on my mobile so I can use a tactile interface for navigating once I have set the initial goto. Testing it makes me want to do more manual navigation, and less goto though....

 

So now I would like a wide angle low powered eyepiece for star hopping, and enjoying the view! Something immersive, something to look at Andromeda with, if you want a specific target.  Up until now, edge sharpness wasn't really an issue but now I'm going to be looking at a vista, rather than a specific object, it suddenly is....

 Hence the reading, and these questions:

Pretty much the widest angle I can get is 68 degrees at 24mm due to the 1.25 inch focusser - right?

Can you still get hold of the Explore Scientific 68 degree 24mm? No one seems to have stock. 

Is the 24mm TV Panoptic worth the money in my circumstance, or will coma degrade the edges as much as the Explore Scientific with my F5 scope?  I don't think I can run to a coma corrector as well - that's more than my scope and mount combined!

Should I consider any other EP? Opinions welcome but be warned, there will be questions!

 

 

 

 

[Don Pensack]

Another eyepiece to consider is the APM 24mm Ultra Flat Field.

With a very flat field, coma will be minimal because not out of focus at the edge.

[cwis]

3 minutes ago, Don Pensack said:

Another eyepiece to consider is the APM 24mm Ultra Flat Field.

With a very flat field, coma will be minimal because not out of focus at the edge.

I can't find a stockist in the UK. Unless the Altair is the same? 8 lenses in 5 groups, 65 degrees - same spec? They look VERY different cosmetically though!

[Don Pensack]

You could buy from Germany.  But, the Altair Ultra flat is the same eyepiece with an external cosmetic change.

[John]

Here is the APM 24 UFF from APM in Germany:

https://www.apm-telescopes.de/en/binoculars/binocular-eyepieces/apm-ultra-flat-field-24mm-eyepiece-65-fov.html

A lower cost but still good alternative to the above and the ES 24 / 68 is the Maxvision 24mm 68. Out of production now but they do turn up pre-owned and for around £50 are a bargain.

I use a 24mm Panoptic myself and it's excellent but very pricey.

 

[cwis]

The APM/Altair seems like a fairly new design so I guess should perform well at its price point? The ES looks to have been about for nearly 10 years and is a similar cost...

I'd love to be able to justify a 24mm Pan but at my level in the game the extra money would probably be better spent on a sturdy tripod!

 

Many thanks for your wisdom gentlemen!

[cwis]

Just as an addendum, AltairAstro in the UK do next day delivery  - and I have just taken delivery of a shiny new 24mm UFF.  

First impressions - they need to get another photographer for their website - it looks a lot nicer in real life!  

 

[Louis D]

On 22/07/2020 at 09:20, cwis said:

Just as an addendum, AltairAstro in the UK do next day delivery  - and I have just taken delivery of a shiny new 24mm UFF.  

First impressions - they need to get another photographer for their website - it looks a lot nicer in real life!  

 

Definitely let us know what you think of it once you've had some time to evaluate it.  I've found it to be very usable with eyeglasses and mostly sharp across the field.

[cwis]

Right! FINALLY got  to pass some photons through the Altair last night!

I had a variety of targets last night, and a new way to navigate between them (picture attached).  Inside the quickly printed hot glued exterior is an ESP32 and an analog joystick.  The ESP32 was flashed to use Micropython just because  - I usually use the Arduino dev environment with them.

I threw together a script that looked for a SynScan* wireless network and connected to it, and then looked for a host listening on TCP port 11882 and connected to it.  One joystick enabled Az-Gti mount!

After aligning the mount (Polaris and Merak) I popped over to Epsilon Lyrae to see how the seeing was with a 4mm EP - it wasn't as good as expected - I could split the vertical double, but not the horizontal one. Then moved to Albireo and compared the Altair to the standard SW 25mm MA that came with my telescope, plus my Seben zoom on 24mm.

Conclusion: The zoom wasn't as sharp as either of the other two lenses anywhere apart from dead in the centre of the view. The SW appeared maybe slightly dimmer than the Altair, and the Altair showed the most colour of all of them. The SW was sharpish for maybe 50% of the field of view (50 degrees I think) whereas the Altair was sharp for 75% of the view (65 degrees so far more "usable" view).

The impression with the Altair was that of a nice star field - a vista, whereas the quick fall off of sharpness with the MA and the zoom concentrated your attention to the centre. 

Next I eyeballed Saturn and Jupiter, quickly before they moved over next door's house and got wobbly in the convection currents. All three EP showed me small (at around 25x mag!) planets - the MA and Altair having more contrast than the Seben. I might have been imagining it, but I THINK I saw slightly more detail on Jupiter (it really was very crisp!) with the Altair but the MA certainly wasn't bad. The Seben lost out really with lower contrast on these brighter targets.

Next Vega.  I use this star quite a bit with the  Alt-Az  - if I want to observe in its area of sky I'll do a goto there first and align before I move onwards. I'd noticed in the past there is a dim star next to Vega in the 25mm EP.  With the MA this star is very slightly clearer than the Altair - maybe better contrast? 

Finally a DSO.  Not really the conditions for DSO - back garden LP and my eyes didn't really get dark adjusted but I wanted to see what I could see - the Ring nebula. 

Initially I saw nothing, and then with averted vision I started to pick something out. Slowly it got clearer but didn't quite get bright enough for me to look at it directly. I think it looked circular and small but bigger than a star - not sure what I should be able to see with my scope - never looked before.

So my impressions view wise on the Altair - a crisp EP that does indeed seem to have a flat field of focus across a large percentage of its view. It's (very) slightly harder to use than the MA - eye position is a touch more important.

I tried with specs on and off - definitely off (for me) with the eye cup turned up - turning it down didn't allow me to get close enough to see the entire field with specs on. With it turned down specs off, I could get too close and blackouts etc occurred.  The spec says something like 29mm of eye relief but the eye lens is so recessed into the body of the EP that much of this is inaccessible.

In comparison to the MA it's more important to keep the eye centred on the  EP - I thought sometimes I could see coma half way to the edge of view but moving my eye slightly made the stars round again! It's probably at the point where the field stop is on the MA - narrower views are probably more forgiving in this respect.

In the hand this EP feels quality - all rubber grip and metal fittings, pictures online really don't do it justice. The eye lens really is a piece of work - huge and concave!

In summary then - a very nice EP. It's not sharp at the way to the edge on my scope, but I didn't expect it to be. It does deliver ease of use and comfort in use, a very pleasing vista of stars and a wide usable view.  I spent a lot of time last night just panning around with my new joystick control -  following satellites and wandering off to look at the view, which was exactly why I got this EP. It's not quite like putting your head in a bucket of stars, but it was so easy and pleasant to use that I kind of forgot that it and the telescope were there to a large degree, and just enjoyed, well, seeing....

[Don Pensack]

Yes, a 130mm f/5 has a very short focal length and a strongly curved focal plane.

Add coma from the f/5 mirror to that, and it's no wonder the edge deteriorates somewhat.

But, I'm glad it did as well as it did.

 

[cwis]

58 minutes ago, Don Pensack said:

Yes, a 130mm f/5 has a very short focal length and a strongly curved focal plane.

Add coma from the f/5 mirror to that, and it's no wonder the edge deteriorates somewhat.

But, I'm glad it did as well as it did.

 

It did very well - I'm really pleased. Thank you for the recommendation!

I'm glad I did my research first though - it was never going to be sharp right to the edge.

Rolling round the sky last night really started making me think about a big dobsonian. A nice lightbucket to pick out those M numbers. People always say buy a dob as a first scope, but I don't know whether I'd have got as much use out of one as I have with my Alt-az. Now, armed with a little knowledge however....