First light for Ethos and UHC filter

[Astronut]

It looked promising earlier tonight and I'd had a long lie-in until early this afternoon and planned not to sleep as I have to be up anyway at 4am. It turned out to be a very brief session until the damn clouds rolled in again. The neighbour had his house extension lights on so no real chance to get dark apapted. Despite this and the brief time I had, I managed to test the 2" Astronomik UHC filter for the first time with the Pentax XW 30.

M42 was quite low down in the most light polluted part of my sky (towards the town centre) but it was an obvious target. I first looked without the filter and could make out the usual nebulosity fanning out either side of the trapezium.

Fitted the filter and looked again. I was pleasantly surprised that most of the stars in the field were still easily visible although they were definately dimmer but not nearly as much as I expected based on the reports I've read about UHC filters. They had a blue-green tint to them and stars toward the edge of field had the same blue-green tint plus some red on the outer edges. It looked a little like chromatic aberration but I suspect this could be due to coma at the edge of field. The sky background was quite a bit darker and the nebula stood out quite well despite it being low down in the light polluted murk. I could definately see more nebula. Roll on next winter when it's closer to the meridian after the neighbours have gone to bed.

The snow clouds from the NNW were threatening to roll in so I targetted the double cluster with the Pentax. I still had the filter attached but it still looked rather good despite the blue-green tint and dimming. I removed the filter and took the view in for a couple of minutes (for later comparsion with the Ethos). Then I fitted the Ethos. Oh no, I couldn't get focus with the standard Skywatcher crayford focuser (slight panic attack). I had to pull the eyepiece out of the tube by about 3/8" so I get just enough inward travel from fully racked out to achieve focus.

I have a Moonlite focuser on the way from Steve@FLO and this has a lower profile but with 1/2" inch extra tube travel and with the extra 3/8" added to the height with the compression ring I think I'll be OK. If not, I'll have to get an extra spacer.

Both clusters were still nicely framed but I had over twice the magnification with not much reduction (30-40%) in the FOV and a darker background. Very very nice and the clusters looked rather good. I could detect some coma at the field edge but not much (a Paracorr would sort this out). The FOV seemed very flat (compared to the Pentax XW which has slight field curvature towards the edge) and the stars seemed nicely focused right to the edge (taking the edge of field coma into account). I couldn't detect any false tint either. The view looked colour neutral to me as it does in the Pentax but I really would have liked more time to compare. I've heard some Naglers can give a yellowish tint but I couldn't see this in the Ethos. This is a very wide field and I had to roll my eye around it to take it all in - luvly jubly

I moved on to one of my favourite open clusters M37. This is a beautiful cluster in the Pentax with the stars sprinkled like fine gold and silver dust in a bit of a v-formation. In the Ethos, it's obviously more than twice as big but still with plenty of background sky surrounding it and that fine dust resolves into many many stars. I wish I could have got a longer look at it but the clouds rolled over and I had to pack it in

I'm really looking forward to taking in some globular clusters with this amazing eyepiece

I've recently confirmed I have mild astigmatism in both eyes (+0.5 dioptres) and this shows up when I'm using the Pentax XW 30mm. I tried using my glasses for the first time with the Pentax tonight and it makes a difference to focusing. With my glasses I no longer see the short lines perpendicular to each other either side of focus so from now on I'll use my glasses with the Pentax. It has long eye relief so I can still easily see the whole field with the eye guard fully down. The Pentax gives me quite a large exit pupil (6mm) so I suspect this is why my astigmatism shows up. The Ethos gives me a smaller exit pupil of 2.6mm and to my relief I didn't see any signs of the astigmatism when focusing the Ethos. It's a great relief I don't have to wear my glasses with the Ethos which has a shorter eye relief (15mm) than the Pentax (20mm) because with them on it's impossible to see the whole field.

I wish I'd had more time so I could give a more detailed report and review. Maybe next weekend (how long have I been saying that to myself? ) Damn this UK weather.

[jarbi]

Hi,

Thanks for your nice and detailed report ! I can feel your pain when you needed to stop too early... It happens here as well, Belgium is not any better than UK I think.

Back to the topic, the Ethos gives really stunning wide views. Feels like falling into the sky :shock:. You can be sure the Moonlite will sort out the focusing issue, I use it with the lowest profile and longest drawtube. The only exception not reachig focus is using the 5x Powermate, I need a short 2" extension tube there.

cheers,

Janos

[Astronut]

The Moonlite I have on order (not here yet - wot's 'appened to it) has the standard drawtube so I think I may need a spacer between the tube and the focuser body. I'll compare it to the standard focuser if and when it arrives. I'm planning to get a 2x Powermate soon so I hope that won't give the same problems as your 5x Powermate.

[lunator]

AN

Nice report.

I'm looking forward to reading a full report on the Ethos

Rgds

Ian

[Astronut]

Moonlite's arrived and I fitted it today. The holes in the tube didn't quite line up with the tapped holes drilled in the curved base adaptor from the universal installation kit supplied so I had to use a round file to slightly elongate them. Apart from that minor hitch and having to remove both mirrors before filing, fitting was a breeze. Re-collimation took quite a while though - I'm a bit [removed word] about collimation

It's as smooth as a really smooth thing and even though I've only used the half-inch spacer I have an extra 10mm outward travel so that should sort out the Ethos focussing problem

I'm really glad I opted for the compression rings too - makes a big difference; weighty eyepieces are securely gripped with confidence without marking the barrels.

Will post some piccies in a new thread after my final modification (for now) is completed - flocking the tube.

And then maybe, just maybe I'll get a clear night and a chance to use all this new gear.

[PhilM]

That's a really nice report to read. I have a similar small astigmatism, it only really shows up in my my 40mm Paragon and only really on brighter stars. I'm gradually increasing my number of televue eyepieces and will be giving the dioptrix system a try. I've read reports that even with shorter focal length eyepieces people are saying it has increased the amount of detail they can detect in planetary observations for example. It would be interesting to find out if it did have an impact on the ethos.

Glad the moonlite seems to be sorting the focus issue,

Phil.

[Astronut]

That's a really nice report to read. I have a similar small astigmatism, it only really shows up in my my 40mm Paragon and only really on brighter stars. I'm gradually increasing my number of televue eyepieces and will be giving the dioptrix system a try. I've read reports that even with shorter focal length eyepieces people are saying it has increased the amount of detail they can detect in planetary observations for example. It would be interesting to find out if it did have an impact on the ethos.

Glad the moonlite seems to be sorting the focus issue,

Phil.

I've probably read the same reports on the Dioptrx. I think their astigmatism was a bit more severe than mine though which means it can show up with shorter FL eyepieces. So far I haven't noticed it with the Ethos (with the brief time I've looked through it) but if and when I get chance to use it more I'll have more time to check and re-check if my astigmatism shows up. If it does then I might consider getting a Dioptrx lens. I'm reluctant to get one at this stage though.

[James]

With higher powers the dioptrix often becomes unnecessary, especially when the astigmatism isn't that severe as the exit pupil from the eyepiece is much smaller so the 'faulty' curve of the eye isn't such an issue. Once I get down to about 5mm focal length I can use my left eye again (astigmatic to the tune of -2.75) which is great as its considerably more light sensitive than my right eye. Of course going shorter than 5mm on my 10" f/4.7 isn't always possible.

James