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Summer Triangle Challenge

Field Flattener/Focal Reducer

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I have an Altair Starwave 115 f/7 ED Triplet, and 294c Pro Tec camera.

I find that I am getting coma, almost certainly due to the 17.47 x 12.86 size sensor. Not bad, but enough to want it gone.

As such I need field flattener (coma corrector), and it would be useful to combine this with a 0.8x Focal Reducer.

What, if any, are you using, with a similar camera/scope combination.

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You could try the one below - you may need to play with the spacing but it says it works for telescopes with focal ratios of f5.5 to f8, so should work with yours. This is both a flattener and a 0.8x reducer, which sounds like exactly what you want. 


I personally use a Hotech 1x flattener (which says it works for telescopes with focal ratios in the range f5 to f8) and that works well on my William Optics 81 GT IV. 

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Thanks Ian, I will look at that option.

It does seem quite cheap for an optic?

Having spent £1200 on a scope, the optics of which have proved to be very good, I am a bit wary of putting cheap glass in- line. But maybe the optical qualtity is fine.

A bit like when I spent over £3k on a 5d MklV, I have only ever used L series lenses with it.

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This has been recommended as a good match for the 115. The only problem is it would seem that there is a six week supply delay, so I will have to look at alternatives.


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If you want the best - then get Riccardi x0.75 FF/FR

This one would suit your scope:


but is out of stock (maybe you can find it somewhere in stock)

There is larger version (and more expensive), that you don't really need over smaller one - but is in stock:


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I looked the Ricarrdi, which was in stock at APM in Germany, but could not be 100% sure that it would be a good match for the Altair 115 ED Triplet and 294c combination. Non dedicated flatteners, can be problematical, either working well, or not so well. The Ricarrdi would have been an expensive experiment if it was not suitable, as probably not returnable. The Altair/Planostar is designed, and guaranteed to match the 115, but is out of stock, with no availability date in sight. Apparently there is a shortage of ED glass. So, it was back to tried and trusted FLO to see what options they had.  Although the Altair 115/294c combo is an untested set up with a WO Flattener,  a WO option was suggested. Given FLO's 30 day returns policy, and following helpful discussions with Dave, and Grant at FLO, I have ordered the WO unit.

Having looked at the back spacing requirements etc, I am fairly confident it will do the job nicely. 🙂

From back in my earlier imaging days (pre 2014), it was nice to find that upon my return to Astro imaging, FLO's customer service/support is still as good,  as it always was.👍

I will of course feed back my finding to FLO.


Edited by centroid
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5 minutes ago, centroid said:

I looked the Ricarrdi, which was in stock at APM in Germany, but could not be 100% sure that it would be a good match for the Altair 115 ED Triplet and 294c combination.

Although you decided to go with another unit - maybe some will find this valuable.

Two seem to be a good match - here is spot diagram of such setup:



At 21mm away from optical axis, vignetting is 3% and RMS spot is 7µm. Airy disk diameter is 8.7µm

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It does look good Vlaiv, but it would have been a £360 gamble, which made me  decide otherwise, albeit it might well have been fine.

If the WO unit matches well, and produces a good result, then I will be more than happy. I have had WO gear in the past, and was happy with the optical performance.

Its nice being able to try the WO optic on my setup, in the knowledge that if  it doesn't perform, I can return it, thanks to FLO's excellent customer support policy.

That said, I am fairly confident that it will do the job, and produce the desired result.

According to Mark Ludes, the APM CEO, the Planostar is a "Chinese" copy of their Ricarrdi design.

The Altair Planostar was the obvious choice, as it is matched to my scope, and guaranteed as such. However, there is no stock in the UK, or in Europe, and nobody can predict when there will be.

Edited by centroid
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Ordered from FLO yesterday, and arrived this morning 🙂

It certainly looks, and feels like WO quality, as I remember it.

No clear skies here this weekend, or in the forecast ☹️

Edited by centroid
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