Jump to content

Banner.jpg.b89429c566825f6ab32bcafbada449c9.jpg

New William Optics GT-81 Triplet Refractor

FLO

Recommended Posts

FLO

FLO

Posted
  • Author
Posted
This seem to be cheap for a triplet?

I know what you mean, our thoughts on affordable triplet refractors are well known so we have been watching this model very carefully, particularly after reading about some of the mixed results some members have experienced with other similar spec refractors.

We know precisely where the optic is sourced (but cannot say). We first saw a mock-up (body only) back in February. Since then two have been here in the UK being tested. Both were very very nice indeed. If William Optics can consistently deliver the same performance then the GT-81 Triplet is going to be HUGE!

William Optics have an excellent reputation for their CNC machined telescope bodys and 'most' of their lens cells have been very good indeed. It also features the new upgraded DDG focuser. We have high hopes but however it turns out you will have our full support, including the option of a no-fuss refund within 30-days if not happy ;)

HTH,

Steve

Link to comment
Share on other sites
  • Replies 131
  • Created
  • Last Reply
FLO

FLO

Posted
  • Author
Posted
Can someone tell me what the advantages are of a triplet over an ED skywatcher frac then?

The third element provides enhanced false-colour correction.

When light travels through a lens it is bent, the more it is bent the more likely the glass will act as a prism and separate white light into its components. The affect is referred to as 'colour fringing' or 'chromatic aberration' and is seen as a thin bright cyan or magenta fringe of colour around the edge of bright objects.

The cheapest way to reduce colour fringing is to make the tube longer so the light isn't bent as much. (I really cannot understand why some long-tube achromats command such a high price!). Alternatively you can throw money at the problem - you can use a more exotic low-dispersion glass. The Skywatcher Evostar 80ED and its stable-mates are good examples of doublet (two lens elements) refractors that employ a low-dispersion glass element for reduced colour fringing.

A better albeit more expensive solution is to use a third element for enhanced colour correction - a triplet. But triplets are considerably more difficult to manufacture to a high standard, hence the high price. If you are imaging then the extra cost is more easy to justify. Also, triplets often produce more field curvature so imagers usually use them together with a 'field flattener' or combined 'reducer/flattener'.

When a telescope has achieved a high level of colour correction it is referred to as an Apochromat or APO. Some (usually those who have spent a considerable sum on a triplet) will say you need at least three elements to achieve true apochromatic performance. What is or isn't truly apochromatic has been the subject of many forum 'discussions'. Reading them is like watching someone dance on the head of a pin!

Normally, below £1000, we recommend a good doublet with low dispersion glass but this new triplet from William Optics might prove to be an exception...

HTH,

Steve

Link to comment
Share on other sites
Rossco72

Rossco72

Posted
Posted

However, Is the benefit of triplets only really realised when doing one shot color?

For narrowband mono does the same level of correction become so important?

I don't know the answers but I am interested to hear from those who might...

Cheers

Link to comment
Share on other sites
Ant

Ant

Posted
Posted

For narrowband imaging an Achro is all you really need. The exotic elements required for things like the ED80 or the third element for a full triplet APO bring all light to focus at the same point...

But if you are only looking at a small part of it then this isn't an issue. The only thing that I've found is that using Ha, OIII and SII parfocal filters with my ED80 is that a small amount of refocus is need when changing between the filters.

CA isn't an issue in narrow band.

Cheers

Ant

Link to comment
Share on other sites
FLO

FLO

Posted
  • Author
Posted
However, Is the benefit of triplets only really realised when doing one shot color?

The reduced colour fringing is noticeable visually, though whether it is worth the increase in cost depends on the individual. Some observers are very intolerant of false colour whereas others really aren't bothered. Colour fringing can also affect edge definition (or more precisely 'acutence') because if an edge has a fringe then it cannot be well defined.

For narrowband mono does the same level of correction become so important?
It is not as important because narrowband filters only transmit the narrow band of light that is of interest, not the chromatic abberation. You can achieve excellent results with a good quality achromat. Although, a quality ED doublet or triplet is normally manufactured to a higher tolerance than a more affordable achromat. But, for the price of an apochromat you can buy a larger/faster achromat... Decisions, decisions...

I just know that at some point someone is going to post a 'yes but' response, and they will probably be right. I am attempting to explain things in a way that will not confuse the beginners here on SGL, or myself :)

HTH,

Steve

EDIT: Posted before seeing Ant's response ;):D

Link to comment
Share on other sites
Whippy

Whippy

Posted
Posted

I believe the issues with achromats (especially the faster ones) and narrowband imaging are more to do with other abberations such as spherical abberation (SA). I would imagine if something like the Vixen Polaris or TAL100 were a bit faster, they would make decent narrowband imaging scopes.

Saying that though, with the ED's and these triplets coming through at these kinds of prices, why would you bother? This scope does look very tasty!

Tony..

Link to comment
Share on other sites
shaunster

shaunster

Posted
Posted
However, Is the benefit of triplets only really realised when doing one shot color?

Also tri-colour mono imaging usign RGB filters, the more expensive triplet refractors tend to control the blue channel a lot better

Link to comment
Share on other sites
andrew63

andrew63

Posted
Posted

I was thinking along the same lines. Skywatcher ED and clones have had the field for good budget scopes pretty much to themselves - they will need to respond as triplets are the flavour of the month!

The WO looks good, but sometimes wonder if a touch of style over substance with this company...

Andrew

Link to comment
Share on other sites
Deneb

Deneb

Posted
Posted
When can we expect to see and hear of peoples first experiences with the new scope and how it performs with the competition...is it all too good to be true?

When I receive mine :hello2:, when will they arrive ? me thinks FLO will make that annoucement nearer to the time.

Nadeem.

Link to comment
Share on other sites
Keiran

Keiran

Posted
Posted
Also tri-colour mono imaging usign RGB filters, the more expensive triplet refractors tend to control the blue channel a lot better

I know that you have a problem in the blue channel with your zs70 as does nadeem with is megrez 72, but your using a CCD and when imaging with a DSLR I dont seem to get the probelm... I am interested to know just what difference i would see between a smei and a triplet?

Link to comment
Share on other sites
ronin

ronin

Posted
Posted

Don't worry too much about the colour, at night it is dark.

Does make you wonder if they may poduce it in alternative colours at some time.

The GW link implies they have it in stock, doesn't seem to say about a wait time.

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.