swed80apo and/or wo 110 doublet

[tony]

i currently have a ed80apo, would adding or upgrading to a wo 110 doublet be a massive difference?

any advantages/disadvantages.

currently use ed80 for imaging with dslr, and soon atik 314.

[Chris]

I think the speed of the system is an important consideration for imaging, what f/ratio is the 110 compared to your 80? I've only got a 66 but its a pretty good performer when I'm at f/4.7. I guess another thing to consider is the weight?

[tony]

wo is f5.95, ed 80 is f7.5.

[Chris]

in that case I think it will make quite a bit if difference! faster and more aperture sounds like a good upgrade to me:)

[John]

The WO 110 doublet will show more chromatic aberration than the ED80 on account of i) it's larger aperture, ii) it's faster focal ratio and iii) it uses a FPL-51 glass element in the objective lens rather than the FPL-53 that the ED80 uses.

This won't make a huge difference for visual use and I'd pick the larger aperture scope for that but for imaging I understand that CA can become more of an issue.

I recall when the WO 110 doublet was launched some early adopters found the CA more than they expected. Perhaps they had expectations based on the excellent WO 110mm triplet though ?.

[tony]

The WO 110 doublet will show more chromatic aberration than the ED80 on account of i) it's larger aperture, ii) it's faster focal ratio and iii) it uses a FPL-51 glass element in the objective lens rather than the FPL-53 that the ED80 uses.

This won't make a huge difference for visual use and I'd pick the larger aperture scope for that but for imaging I understand that CA can become more of an issue.

I recall when the WO 110 doublet was launched some early adopters found the CA more than they expected. Perhaps they had expectations based on the excellent WO 110mm triplet though ?.

there are a lot of reviews for the ed80 and thats one of the reasons for buying it, also lots of images taken with said scope too. doesnt seem a lot around for the wo. i'm sticking with the ed80 anyway, just thought the wo may have been a worthy addition, or even an upgrade. must agree, the triplet is rather nice

[Chris]

oh I didn't realise that we where comparing different glasses, I've just looked on the WO site and they don't seem to mention FPL51 glass in the 110 spec? would this scope be considered semi-apo?

[John]

oh I didn't realise that we where comparing different glasses, I've just looked on the WO site and they don't seem to mention FPL51 glass in the 110 spec? would this scope be considered semi-apo?

The way things seem to work is that if they don't specify the type of ED glass used it's FPL-51 but where FPL-53 is used, they tend to mention it specifically (eg: the Megrez 90). To be fair, William Optics are not the only brand to use that approach.

That whole "is it an apo or not" thing is usually controversial so I'm not going to attempt to go there !

[Stu]

That sounds like it would make an interesting thread in its own right John. Is fpl-53 always better than fpl-51 in terms of colour correction, or its the figuring and matching of the lenses just as important?

Stu

[John]

That sounds like it would make an interesting thread in its own right John. Is fpl-53 always better than fpl-51 in terms of colour correction, or its the figuring and matching of the lenses just as important?

Stu

My (limited) understanding is that, as glass, FPL-53 has the potential to make an objective lens with better colour correction than FPL-51 because of it's dispersion / refraction characteristics. That said, there are many more factors that go into making a good objective lens, not least selecting the right type of glass for the other lens elements (the mating element in a doublet), figuring and polishing the lenses to a high standard, the coatings used, the machining of the objective lens cell, the spacing of the lens elements etc, etc.

I think it's entirely possible to make a mediocre objective lens using FPL-53 and a superb one using FPL-51. TAL have produced a 6 element apochromat (the Apolar 125) that shows excellent colour correction but does not use an "exotic" glass type at all.

I think I'd better stop there as it's a bit of a minefield !

[ollypenrice]

I wouldn't go for a large fast doublet for imaging. Even the Takahashi Sky 90 has some trouble controlling blue stars. A fast 110 doublet is going to to struggle even more.

Olly

[tony]

I wouldn't go for a large fast doublet for imaging. Even the Takahashi Sky 90 has some trouble controlling blue stars. A fast 110 doublet is going to to struggle even more.

Olly

so stick with the ed80?

[ollypenrice]

so stick with the ed80?

Probably. Do you have the reducer-flattener?

Olly

[tony]

Probably. Do you have the reducer-flattener?

Olly

not yet

[earth titan]

Stick with the ED80.

I've had experience of the effects of different glass on fast scopes for imaging and the CA is dramatic. Although a well made scope will always perform, my experience (although limited) is that for 'budget scopes' (anything less than a grand) FPL53 performs better than FPL51

Typed by me, using fumms...