Posts Made By: Kevin Barker

James
Congratulations.

I think you will find collimation very easy to sort out.

I have owned the 6 inch f -12 and it took one half turn of a push or pull screw to collimate after rough alignment with my eye looking down the tube. The scope stayed aligned for the year and a half I owned it. I was very impressed with the optical quality. I sold it because of the strain on my mount and because of a lack of portability.

Certainly sharper and with more contrast than the run of the mill achromats of shorter focal ratio. I was surprised how good the scope was with respect to star clusters. And as for double stars the performance was remarkable.

Best wishes

Kevin

James
D&G did make and offer an ED doublet 5.1 inches in aperture a few years ago. f ratio f-9.5

I understand it did not perform as a true apochromat and was difficult to fabricate.

I have yet to hear from an owner. I am familiar with Zeiss AS short flint lenses, owning two which I have made into optical tubes. AS63/840 and AS80/840. Rather than the crown element being special they use a special flint glass. They have excellent contrast at longer f ratios and colour correction significantly better than achromats of the same focal length.

I believe the AS 110/1650 and 130/1950 both had excellent levels of colour correction for visual use.

Best wishes

Kevin

Mark
I fortunately have two fluorite scopes that are triplets and the performance is excellent. I am sure the best synthetic fluorite(FLP53 etc) glasses have similar performance.

For purely visual use I am sure a doublet with fluorite or the best synthetic fluorite can deliver virtually everything that a triplet can but for film photographic uses the triplet may be superior.

I have an old 80 mm semi apo doublet with short flint glass that I have compared with more modern ED doublets and it shows a little more false colour but possibly superior planetary views.

I am sure the quality of manufacture and choice of glass in a doublet can lead to outstanding performance. Longer focus achromats if well made can also deliver excellent performance, one only needs to look through a Zeiss Telementor to realise this.

I believe that the notion Fluorite is not all that durable is more of a fear than reality. Most Fluorite scopes have the fluorite element at the rear of a doublet or sandwiched in a triplet. ED glasses can also be very fragile.

Also Tak FS series scopes have hard coated fluorite lenses which resist the elements.
Best wishes

Kevin

William
I think I can answer this question. I have owned a D&G an 6 inch f -12. And currently own a Zeiss APQ 130 an f 7.7 triplet apochromat like the AP.

While the D&G will have excellent smooth optics and a lovely star test the amount of residual chromatic aberration for a 5 inch at f 10 will mean low contrast markings will be harder to see in this scope compared to an apo. The AP will reveal sharper more well defined planetary images.

It will still do a tremendous job but in terms of image contrast on fine planetary detail it will be slightly less impressive than an AP 130.
My brother has recently sold his 5 inch f 15 D&G after acquiring a 715 Maksutov. His scope was fairly close to the point where secondary colour does not hurt the fine detail to the extent of a shorter focus achromat.

I have recently built an AS 80 f 10.5 short flint achromat of a high quality which has significantly less false colour than a standard achromat. It is effectively like an f -15 3.1 inch achromat. I have tested it beside an ED doublet (semi)apochromat and it holds up well, possibly being better at rendering fine detail on planets than an ED. Using this as an example and knowing how good D&G achromats are I would say an f 20 or 25 D&G 5 inch doublet would approach the apo performance in terms of planetary detail seen at the eyepiece. In short if you get to a focal length 4 -5 times the aperture in inches false colour starts to be barely visible and a non issue with respect to performance.
Deep sky and double performance would match an apo at f 15 with a 5 inch D&G, possibly f-12.

5 inch D&G's are excellent and vastly superior to the average short focus Chinese mass produced scopes. They are a much better value at less than 1500 US in an ota than the $5000 or so for an AP.

One last point, I am convinced long focus doublet achromat's have the potential to approach or even out perform short focus triplet apo's for visual use. A bit like the argument for planetary eyepieces and how monocentrics and orthoscopics seem to be the best. Less glass and potentially superior polish etc.

Best wishes

Kevin

Todd

50 mm then consider a 2" Meade or Tele vue plossl.

11 mm if you are on a budget consider a 10.5 mm Meade plossl or a 11 mm Tele vue plossl. 50 degree filed is wide and nicely defined. Eye relief is O.K. Contrast very good.
Plossl's work well at f 6.
Or perhaps a UO orthoscopic, 45 degree field and sharp optics.
A 10 mm TV radian is another choice but expensive.

Any 11 mm eyepiece at 2" with a 65 degree field worth its salt will be expensive. I reckon the Tele vue will out perform most fo them in terms of contrast.

Best wishes
Kevin

Brian
The lens is hard coated I assume. I would clean it if it is impairing the view. Although oblique light can make matters look worse than they are when looking at coatings and the lens surface.

Pollen or insects landing on the lens can cause small hard shiny marks. I have had mosquitoes that have literally died on the lens and stuck to the damn thing. Perhaps wood or coal smoke is another source of this problem.

Using an alcohol based cleaner sparingly and carefully e.g. isopropyl/distilled water 70/30 and good quality lens tissue should not damage the lens in any way.

Kim
Congratulations on this investment.
I found the fringe killer unnecessary with my wee AS80/840 too. With and without it in good seeing there was no advantage.
This AS150/2250 sounds wonderful. I bet in very good seeing the scope could cope with very high magnifications on doubles. Perhaps 500-600?

Your 40 mm orthoscopic might work well with this long focus telescope.

Best wishes

Kevin Barker

Nils
I have binoviewed with 80 mm, 100 mm and 130 mm telescopes all high quality refractors. The binoviewer I have used is a Baader Mark V(w/1.7X glaspath) which although it has a lot of glass has very well coated optics.

I tend to use a 12 inch Newtonian with a single eye for deeper sky viewing and use the binoviewer for brighter views in the refractors.

The eyepieces I have sets of are 32mm TV Plossls, 13 mm T6 Naglers, 10 mm TV Radians and 11 mm TV Plossl's. All have a mass about the same with the exception of the low mass 11 mm TV Plossl's.

Nebula and galaxies are slightly fainter in the bino viewer. Although the extra comfort is a fair compromise. I tend to think that the 130 mm is a better aperture for binoviewing as compared to a 100 mm. Especially for planets. This is not just the extra light collection it is also the comfort of the exit pupil which gets less than .8 mm at say 170 X with a 100 mm scope and starts to be a tad difficult to align.

I do see an improvement in detail of low contrast features discernible with two eyes in good seeing on planets.

I find the 13 mm T6 naglers very nice with just enough eye relief to enjoy the extra wide view.

I have used cheaper binoviewers in friends telescopes but noticed lower contrast and reflections which were annoying.

Another annoying thing about binoviewers is the ipd and focus varies a lot from observer to observer. It can be time consuming when others are sharing the views to keep adjusting.

I await Jupiter next year with the 130 mm and Baader set up.

best wishes

Kevin B

Paul

There has been quite a bit of stuff on ebay.de lately. Several AS objectives in the past fortnight and bits and pieces here and there.

I think one reason why things are so slow on astromart is the very weak US dollar. A lot of Zeiss stuff seems to be in European countries where a stronger Euro affects folks offering gear to a US web site.

Regards

Kevin

Kim
I have for several years read indirect references to the supposed fact that prisms are preferred.

It could well be an "urban myth" amongst Zeiss owners perhaps it is a fact but no where have I read anywhere a technical reference from say a Zeiss information leaflet!!

What Roland discusses below is of some interest to me.
As is what Markus refers to.

Another perhaps "urban myth" is the discussion about oil leakage and the effects on star tests. Again it was talk but no real quantitative info.

As Markus suggests the answers may be known by Mr Baader and his optical staff. Or as Paul suggests Dr Lalk

Perhaps we should ask them for an answer.

best wishes

Kevin