ED doublet or Budget Triplet?

[Thalestris24]

Hi

So it's that time of the year again (!) when I start thinking about getting a decent frac for imaging - especially as I've just had a winter fuel payment

But I'm torn between getting an ED with FPL-53 glass or a budget triplet with cheaper glass e.g. FPL-51 or Hoya FCD1 or FK61. It would seem the FPL-53 is superior but (without personal experience) it's hard to gauge what the difference would be in practice. I'm probably going to use it with a modded 1100d, and eventually also a cooled and debayered 550d, together with a filterwheel or drawyer. I suspect narrowband imaging won't be much different between ED and triplet - no colour correction to worry about, but what about sharpness?

As usual I'd be grateful for any thoughts and recommendations from experienced imagers

Many Thanks

Louise

ps I'm budget limited and can't afford a premium triplet but still want to get the best value I can 

[Davey-T]

I can highly recommend the WO Star71 Louise, nice flat field and round stars to the corners of an APSC sensor and no faffing about with reducer / flattener spacers, not a triplet and the old winter fuel allowance won't make much of a dent in the price, also nice and light for carting up and down stairs 

Dave

http://www.firstlightoptics.com/william-optics/william-optics-star-71-f49-5-element-refractor.html

[Thalestris24]

I can highly recommend the WO Star71 Louise, nice flat field and round stars to the corners of an APSC sensor and no faffing about with reducer / flattener spacers, not a triplet and the old winter fuel allowance won't make much of a dent in the price, also nice and light for carting up and down stairs 

Dave

http://www.firstlightoptics.com/william-optics/william-optics-star-71-f49-5-element-refractor.html

Hi Dave

Yeah, they are nice but I don't think they have sufficient back focus for a dslr + fw, which I mentioned I'll be using.

Thanks though

Louise

[Uranium235]

Hi Dave

Yeah, they are nice but I don't think they have sufficient back focus for a dslr + fw, which I mentioned I'll be using.

Thanks though

Louise

I think it will have the space to be honest, im about to take delivery of a quickchange system for the Star71 (by converting the filterwheel to an EOS bayonet fitting), so I can switch between the CCD and DSLR in just a couple of minutes, and with no threads to undo. So I will have a better idea of just how much focuser travel is left when the DSLR is on. Even if its tight, there are low profile M48-EOS adaptors you can buy which have an optical length of just 1mm.

[Davey-T]

Defo works with DSLR, I've used it with my 60Da, even comes with a T ring adapter, don't know about the filter wheel.

Dave

[Thalestris24]

Defo works with DSLR, I've used it with my 60Da, even comes with a T ring adapter, don't know about the filter wheel.

Dave

Yeah I know it's fine with a dslr but it has the standard 55mm back focus so I can't see how it can also work with a fw or filter drawer anymore than separate flatteners with 55mm spacing can.

Anyway, um, I was asking about differences between ED and budget triplets - anyone?

Louise

[Davey-T]

Just fitted my DSLR to the WOS71 and focussed on a distant street light (no stars)  and there's 14mm of focuser travel left.

What sort of aperture did you have in mind ? guess the ubiquitous SW ED 80 is the normal thing to go for plenty of great images taken with it but you may have to budget for the flattener.

Dave

[Thalestris24]

I think it will have the space to be honest, im about to take delivery of a quickchange system for the Star71 (by converting the filterwheel to an EOS bayonet fitting), so I can switch between the CCD and DSLR in just a couple of minutes, and with no threads to undo. So I will have a better idea of just how much focuser travel is left when the DSLR is on. Even if its tight, there are low profile M48-EOS adaptors you can buy which have an optical length of just 1mm.

quickchange system for the Star71? (curious though I can't really afford a Star 71 anyway...)

[ollypenrice]

I don't think this can be answered from principle. It is a case of, 'This specific scope versus that specific scope.' You can argue from theory till you're blue in the face but I'd be interested in looking at images taken with specific scopes and nothing else. I reckon a thorough trawl through 'what is being posted with what' is the only way you can answer this. The fact that earnest spec worshippers have not leapt in with their assertions about glass types is a bit of a relief, quite honestly, because I just don't believe it can be resolved that way.

Olly

[Thalestris24]

Just fitted my DSLR to the WOS71 and focussed on a distant street light (no stars)  and there's 14mm of focuser travel left.

What sort of aperture did you have in mind ? guess the ubiquitous SW ED 80 is the normal thing to go for plenty of great images taken with it but you may have to budget for the flattener.

Dave

Yeah but the flattener is still limited  to 55mm for correct spacing?

[Thalestris24]

I don't think this can be answered from principle. It is a case of, 'This specific scope versus that specific scope.' You can argue from theory till you're blue in the face but I'd be interested in looking at images taken with specific scopes and nothing else. I reckon a thorough trawl through 'what is being posted with what' is the only way you can answer this. The fact that earnest spec worshippers have not leapt in with their assertions about glass types is a bit of a relief, quite honestly, because I just don't believe it can be resolved that way.

Olly

Ok, thanks, Olly. I suppose a SW Equinox 80 + TS flattener might be a fairly good buy...

Louise

[Davey-T]

Could be a squeeze getting a filter wheel in any system that's only designed for 55mm DSLR back focus while still keeping the DSLR, I'd have thought a debayered DSLR would be easier with a NB filter in the T ring or a clip in.

Filter draws are min 15mm.

Dave

[Thalestris24]

Could be a squeeze getting a filter wheel in any system that's only designed for 55mm DSLR back focus while still keeping the DSLR, I'd have thought a debayered DSLR would be easier with a NB filter in the T ring or a clip in.

Filter draws are min 15mm.

Dave

Yes, but you can get flatteners with bigger spacing requirements e.g. the TS one which allows 115mm @ fl = 500mm so plenty of room for a fw.

Louise

[Davey-T]

Ok, thanks, Olly. I suppose a SW Equinox 80 + TS flattener might be a fairly good buy...

Louise

Only £165.00 less than a WOS71 and all that flattener / spacer faffing about

Equinox 80 does have FPL35 glass,  thought I'd just mention that for Olly  

Is that  the TS one that goes inside  a 2" focuser ?

Dave

[ronin]

I would opt for one of the budget triplets over the ED doublets. I suspect they are pretty good these days and argueing they are Chinese makes little use as the doublets will also be.

Even if the triplet is not perfect I have only ever read of ED doublets producing minimal CA not really no CA.

Problem of FPL-53 is manufacturers add it then push the glass to it's limits. You seem to get shorter scope not always a better one.

However as it reads you will have a filter wheel and that means not the full spectrum in one go so you will in effect lose the cause of CA, that being the 400nm to 750nm spectrum all going through at once. You may find the focus shifts between R and G and B a little on a doublet.

I assume that it has to be new ?

There is a WO Megrez 90 on ABSUK.

[Thalestris24]

Only £165.00 less than a WOS71 and all that flattener / spacer faffing about

Equinox 80 does have FPL35 glass,  thought I'd just mention that for Olly  

Dave

Yeah but, as explained, I need the extra spacing so needs must! Oh, the ota is only £525...

[Thalestris24]

I would opt for one of the budget triplets over the ED doublets. I suspect they are pretty good these days and argueing they are Chinese makes little use as the doublets will also be.

Even if the triplet is not perfect I have only ever read of ED doublets producing minimal CA not really no CA.

Problem of FPL-53 is manufacturers add it then push the glass to it's limits. You seem to get shorter scope not always a better one.

However as it reads you will have a filter wheel and that means not the full spectrum in one go so you will in effect lose the cause of CA, that being the 400nm to 750nm spectrum all going through at once. You may find the focus shifts between R and G and B a little on a doublet.

I assume that it has to be new ?

There is a WO Megrez 90 on ABSUK.

Yeah, I'd want a shiny new one and will also be using it with a colour dslr (no fw) so colour correction still important.

[John]

The WO Megrez 90 is an ED doublet that uses an FPL53 glass element. It's a very nice scope for visual but whether it's colour correction is good enough for imaging I don't know.

I think that the quality of the lens figure, polishing, coating and mounting is more important than the specific glass used although the match of the glass types in the 2 or 3 elements does matter. The ED glass types quoted are just one of the elements involved. The glass types used in the others matter as well.

[Davey-T]

I have a Revelation 100mm ED Doublet probably the same manufacturer as the Equinox scopes, certainly looks identical apart from the colour, CA is not really very noticeable in images but shows visually on bright objects.

Dave

[Thalestris24]

The WO Megrez 90 is an ED doublet that uses an FPL53 glass element. It's a very nice scope for visual but whether it's colour correction is good enough for imaging I don't know.

I think that the quality of the lens figure, polishing, coating and mounting is more important than the specific glass used although the match of the glass types in the 2 or 3 elements does matter. The ED glass types quoted are just one of the elements involved. The glass types used in the others matter as well.

Hi

Thanks. It's a shame manufacturers / sellers don't give full information. I suppose, as Olly said, one can only look at images made by particular scopes and make a comparison/judgement. I can't afford a high-end one so maybe can't expect perfection in my budget range.

Louise

[timwetherell]

I'm a purely visual observer but my experience is that FPL-53 does offer slight visual advantages (insomuch as one can generalise!) But those advantages really only become apparent at high magnifications and are subtle! 

I would have thought that in a shorter design of smallish aperture a triplet would probably win out because of the extra degrees of design freedom. Though I have no direct practical experience to back that up

[cs1cjc]

The Borg series are not cheap but the fully configured sets from FLO look to be good value.  The smallest fluorite Takahashi, http://www.takahashiuk.co.uk/Refracting-Telescopes/FS-60, is surprisingly affordable unless you want fripperies such as rings:-)

Although manufacturers provide no useful information, a number of independent testing houses are now publishing reports:

https://translate.googleusercontent.com/translate_c?depth=1&hl=en&ie=UTF8&prev=_t&rurl=translate.google.co.uk&sl=de&tl=en&u=http://r2.astro-foren.com/index.php/de/&usg=ALkJrhhaBn_6KuAdaZPsNPGfDaWfhRTKRQ

http://interferometrie.blogspot.co.uk/?view=flipcard

https://translate.googleusercontent.com/translate_c?depth=1&hl=en&ie=UTF8&prev=_t&rurl=translate.google.co.uk&sl=de&tl=en&u=http://r2.astro-foren.com/index.php/de/&usg=ALkJrhhaBn_6KuAdaZPsNPGfDaWfhRTKRQ

and see in particular: https://translate.googleusercontent.com/translate_c?depth=1&hl=en&ie=UTF8&prev=_t&rurl=translate.google.co.uk&sl=de&tl=en&u=http://r2.astro-foren.com/index.php/de/9-beitraege/01-aeltere-berichte-auf-rohr-aiax-de-alles-ueber-apos/195-a132-sechs-reisetaugliche-refraktoren-interstellarum-nr-73-dez-jan-2011-s48ff&usg=ALkJrhjShk3F1_MzQaf2Y4-95ipgClRgnQ

Colour (mainly blue in doublets!) in various objectives can clearly be seen here: http://www.teleskop-shop.at/testphotos/Refractor_color_test/Vega_testphotos_apochromats.jpg

[Davey-T]

Another option, with free reducer.

Dave

http://www.telescopehouse.com/telescopes/telescopes-by-brand/brand-explore-scientific/explore-scientific-ed-apo-80mm-f-6-carbon-fibre-1.html

[Thalestris24]

The Borg series are not cheap but the fully configured sets from FLO look to be good value.  The smallest fluorite Takahashi, http://www.takahashiuk.co.uk/Refracting-Telescopes/FS-60, is surprisingly affordable unless you want fripperies such as rings:-)

Although manufacturers provide no useful information, a number of independent testing houses are now publishing reports:

https://translate.googleusercontent.com/translate_c?depth=1&hl=en&ie=UTF8&prev=_t&rurl=translate.google.co.uk&sl=de&tl=en&u=http://r2.astro-foren.com/index.php/de/&usg=ALkJrhhaBn_6KuAdaZPsNPGfDaWfhRTKRQ

http://interferometrie.blogspot.co.uk/?view=flipcard

https://translate.googleusercontent.com/translate_c?depth=1&hl=en&ie=UTF8&prev=_t&rurl=translate.google.co.uk&sl=de&tl=en&u=http://r2.astro-foren.com/index.php/de/&usg=ALkJrhhaBn_6KuAdaZPsNPGfDaWfhRTKRQ

and see in particular: https://translate.googleusercontent.com/translate_c?depth=1&hl=en&ie=UTF8&prev=_t&rurl=translate.google.co.uk&sl=de&tl=en&u=http://r2.astro-foren.com/index.php/de/9-beitraege/01-aeltere-berichte-auf-rohr-aiax-de-alles-ueber-apos/195-a132-sechs-reisetaugliche-refraktoren-interstellarum-nr-73-dez-jan-2011-s48ff&usg=ALkJrhjShk3F1_MzQaf2Y4-95ipgClRgnQ

Colour (mainly blue in doublets!) in various objectives can clearly be seen here: http://www.teleskop-shop.at/testphotos/Refractor_color_test/Vega_testphotos_apochromats.jpg

Hi Chris

Thanks for that. I'm torn between the SW Equinox 80 and the TS Photoline 80 f6 triplet Apo. I've followed Olly's (always good) advice and looked through lots of images on Astrobin, lol. Both of the above scopes are within my budget (about £500-£600 for ota) and both seem to perform pretty well, and either would do the job for me, I think. Just need to make a decision! The TS scope does come with cnc rings... Plus Teleskop Express seem open to doing a deal with packaging a flattener and adapters. So that gives the TS scope the edge. As usual, I'm still open to suggestions, and will be sleeping on it, but will ask Teleskop Express for a quote .

Cheers

Louise

[Thalestris24]

Another option, with free reducer.

Dave

http://www.telescopehouse.com/telescopes/telescopes-by-brand/brand-explore-scientific/explore-scientific-ed-apo-80mm-f-6-carbon-fibre-1.html

Hi Dave

Yeah I'd seen that before but not especially keen on it. Thanks though!

Louise