John

26 minutes ago, chiltonstar said:

But presumably, despite the excellent optical quality, they are not able to beat the laws of diffraction though? 65mm is 65mm........

Chris

I'm sure that is true.

I've not really changed my observing approach. I tend to cycle round the scopes that I own giving each a session. The 12 inch dob has had more use than the others over the past 2 weeks because the skies were dark and the Virgo / Coma galaxy fields were presented well.

Alt-azimith mounts without attached technology are my usual preference and I've not changed that either.

So no difference other than more clear nights than I would normally hope for during March and April

Sounds very nice Doug

Clouds here though

Hi Andrew,

Very nice to hear from you and I'm glad you still have some involvement with astronomy.

Hope the family is keeping safe and well too.

Best regards,

John

5 minutes ago, Pete Presland said:

No not really, but in the right direction. Certainly better than the Jupiter and Saturn for the foreseeable future.

True - last year we had both a major dust storm on Mars and it was so low it was bouncing along the rooftops here.

4 minutes ago, Pete Presland said:

According to Calsky it transits at 43.239 degrees at opposition on the 13th October.

In Pisces I think. So not really near the zenith. Better than last years opposition though.

Just now, Waddensky said:

It's all about airmass. When an object is low above the horizon, you have to observe through much more atmosphere then when an object is near the zenith, causing scattering and absorption and turbulence.

Unfortunately, observing near zenith is nearly impossible with horizontal mounts like dobsons, so there is a "golden mean" somewhere.

Tracking more challenging with a dob when pointing towards the zenith but it is possible to observe there. M51 is up there currently and I've observed that quite a few times with my 12 inch dob over the past few weeks.

2 minutes ago, Pete Presland said:

certainly looking forward to seeing Mars up nearer there later in the year.

Will Mars actually be anywhere near the zenith this year ? - I thought it would still be pretty low down.

As you near the horizon you get both additional disturbance from looking though more atmosphere and also a thing called atmospheric extinction - a dimming effect.

The higher up in the sky the better, especially when trying for stuff that is challenging.

Nice sketch Ade.

Just a bit too cloudy here to make observing worthwhile unfortunately.

Where does the objective sit within that apparently long dew shield Mike ?

Is it at the bottom end or somewhat up it like the DL is ?

Very, very very fine scope I think Mike - many congratulations

Takahashi triple layer packaging is the business as well - other brands should take note !

The use of an ED glass element (you only need one element to be ED) in the objective, if done well, corrects much of the CA and that correction is then in the optical system and will benefit optical elements further down the optical chain eg: eyepieces, whether they use ED glass or not. There are circumstances where an eyepiece will add a little CA of it's own eg: at the edges of a very wide field of view or if a non-achromatic eyepiece such as a Huygens is used in a reasonably fast scope.

It is the combination of an ED glass with other glass types in the objective of the scope, rather than the ED glass itself which is important. The optical figure, coatings, objective cell, lens spacing all make a difference to the final result as well.

The different types of ED glass have different Abbe numbers and refractive indexes which indicate the potential they have, when combined with suitable mating elements (very important that last bit) to produce a corrected image for the eyepiece optics to handle. Some brands now are choosing not to disclose the glass types used saying that their products should be judged by their actual performance.

Many quality eyepieces have used ED glass types for many years without promoting the fact. Some brands have chosen to make this a selling point though.

This whole topic is the subject of long and sometimes heated discussion on other forums !

Hi Ken,

I don't recall that there is any objective tilt adjustment on the ED80. Or the ED100 an ED120 for that matter.

When I had ED80's (a while ago) I had to shim the end of the scope tube with insulation tape or similar to impart tilt to the objective / objective cell as needed.

The focuser alignment with the optical axis is adjusted in the same way.

It is crude I'm afraid.

In fairness I found that the ED100 I owned and my current ED120 have not needed any collimation adjustment but for some reason the ED80's (I have had 2 of them) both did

That is good news !

I had a similar result when I requested that a light in a nearby school car park was partially masked to keep it's light off my house and garden. It took a couple of letters copied to my local councillor but they did take action eventually.

Contrast and background darkness can be improved by applying magnification so hyper wide eyepieces allow that while retaining wide true fields.

In terms of pure light transmission, reports from folks who use really big aperture scopes under really dark skies have shown that the very best are the Zeiss ZAO orthos followed by the (as Mark says) Baader Classic Ortho 10mm (the 18mm is pretty good as well) then followed by Delos, XW's Ethos etc, etc. The Morpheus is probably a good choice as well but I have not used those personally.

Here is the website that covers the reports I am referring to:

http://www.faintfuzzies.com/

Well worth browsing though their reports.

1 minute ago, Setaarius said:

I mean some eyepieces can cut weaker structures in DSO and the object becomes flat, homogeneous, and some eyepieces cut out weak objects completely and then in one eyepiece it is visible, in the other one not or in one directly, and in the other with averted vision.

That sounds like you want the highest light transmission then ?

When you say cutting out DSO detail do you mean in terms of reduced light transmission or in terms of not having a wide enough view ?

Personally I use Ethos eyepieces myself with my 12 inch F/5.3 but it sounds like you are not so keen on those ?

Just about to get clouded over here. Nice while it lasted today, though

The more northernmost spot group seems to have subtly changed it's form over the past hour. A couple of the smaller spots seem less distinct now than they were - paler ?

Just been having a look with my Tak 100 and the Lunt HW. Seems to be 7 or so small spots broadly in two groups but associated with each other. Set in an area  of complex faculae - like a mass of pale spaghetti vaguely centered around the two groups of spots.

Seeing is variable here. Some nice, sharp, moments at 125x but then things go hazy and I need to back off the magnification to regain a sharp view. So nice to have a zoom eyepiece for this - you can instantly react as the seeing varies.

Worth keeping an eye on and worth setting the scope up for

The view of Izar the other night with my Tak FC-100DL at 281x was very like the 200mm Aberrator image. Really tight stars and a big gap.

Great report Stu !

I have a rather old copy of the Broadhurst Clarkson and Fuller catalogue (bookalogue as they called it) which dates to around the time that the little Tal 65 became available over there. Dudley Fuller says in there that he rarely recommends scopes of less than 3 inches aperture but he was delighted to make an exception for the Tal Alkor becuse it has exquisite optical quality, excellent design and is over-engineered in a way that you just don't find in the average scope of this aperture.

Your experiences confirm Dudley's views I think

1 hour ago, Stardaze said:

What's your preferred tool of choice for collimating John? Wondering whether a laser is better Han a Cheshire for the secondary?

I use a simple cheshire eyepiece. I have had a few laser collimators and still have one. Having got so used to the cheshire view now that is by far my most often used tool. My secondary rarely needs adjustment and the primary just the occasional tweak so it's not a challenging scope to maintain.

I put together this simple set of eyepieces a couple of years back expressly for travel and outreach (not that I've been able to do any for the past 6 weeks or so !) the aim being to have good optical performance, robustness, ease of viewing (ie: comfortable eye relief etc), not much to cart about and relatively low cost. I can carry them all in my coat pockets.

I've been pretty pleased at the way that these have performed for their cost (around £50 or less per item). I've found myself using them for my own sessions quite often as well. The coverage is from 30mm / 70 degrees AFoV to 3.2mm. The zoom + barlow combination gives a very useful 9.5mm - 3.2mm zoom. They get well used as you can see from the markings on their barrels !

Anyone else have a similar set for similar reasons ?

My 12 inch F/5.3 is stored in a corner of the dining room which is about 3 metres from where it is used, on the patio. I prefer to observe standing up and had the base of my dob "made to measure" so that I could do that.