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“LUNT FC100DL”


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  • Fedele changed the title to “LUNT FC100DL”

A Daystar Quark chromosphere would go quite nicely with the F/9 focal ratio of the DL. You could also get the Quark combo instead and use a 3-5X barlow to reach the appropriate ~F/30 advised for the Quark.

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I also think a Quark could be a better bet, other options are going to involve significant irreversible modifications to the Takahashi which would not go down well if resold.  A budget achromat would be perfectly suitable for this monochromatic application.  High end refractors don't necessarily have the best correction for H-alpha.     🙂  

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using LUNT parts needs modifcations?

If so, FC100DL remain for WL (and in the future for Daystar yes), but for now i will choose another OTA to use with LUNT parts. For Knw i want to go from large fields to HR, with no power needs

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7 minutes ago, newbie alert said:

Can't see why your using a premium scope to capture 1 wavelength,  a lunt is basically a achromat.. you don't need premium correction for a single wavelength 

Maybe it is the quality of the lens figure that he is after ?

 

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41 minutes ago, Ricochet said:

I'm sure Solarscope can help you. You want double stacked 100mm etalons, a blocking filter and a custom adaptor to fit the etalons to the front of your Tak.

https://solarscope.co.uk/filter-systems/

I've no idea how much that all costs though.

Hmm. The Solarscope DS 100mm filters are almost £30k in the EU!! Much less in the UK.
Apart from the incredible price, I don’t think the Tak FC-100s are robust enough for two external 100mm filters (which can also be sourced from Lunt for about £15k.) 

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1 hour ago, newbie alert said:

Can't see why your using a premium scope to capture 1 wavelength,  a lunt is basically a achromat.. you don't need premium correction for a single wavelength 

It’s not just about chromatic abberation, good correction of spherical abberation makes a big difference to the detail seen. That said, and ED100 would likely be just as good.

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Avoid the Coronado - Meade has just been bought by Orion, and they are reassessing the whole business. There is very patchy support for Coronado products at the moment.  
Lunt LS80 would be nice - though still pricey, particularly double stacked. Lunt has now moved to using modular ED refractors for their scopes which can also be used at night. Might be a few old model dedicated solar LS80s still available at stores. The etalons themselves haven’t changed.
There’s also the interesting new Baader/Solar Spectrum Sundancer, which has just been released. 
Best piece of advice is to do your homework - solar scopes/etalons are very variable in quality, so one option might be to buy secondhand, when you can actually test the etalon first. Quarks in particular can be poor. Definitely not a decision to be rushed.

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1 hour ago, Stu said:

It’s not just about chromatic abberation, good correction of spherical abberation makes a big difference to the detail seen. That said, and ED100 would likely be just as good.

How do you get chromatic aberration on a HA wavelength.. it's not broadband

 

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2 hours ago, John said:

Maybe it is the quality of the lens figure that he is after ?

 

Seeing will affect the final image or visual aspect rather than the lens quality.. after all ha is at the red end of the spectrum so the green/ blue isn't even there

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Spherical aberration is colour/wavelength independent.
Optical surface roughness is also colour independent.

iStar offer h-alpha specific achromats. World class solar imagers use iStar H-a objectives.
I find my 150/10 iStar H-alpha objective a real improvement over my Celestron 150/8.
Even with a 1.125x GPC, to produce f/10, the Celestron was inferior in H-alpha to the iStar.

Larger H-alpha refractors tend to be used at high magnifications. Both for imaging and visual.
Putting high demands on optical quality in the entire optical train.
An APO may have poor correction in the deep red.

The iStar H-alpha objective provides high quality mono images of the sun in white light with a wedge.
Its close-up moon images are also of very high quality when the seeing allows.

This is just another option. Rather than modifying a premium APO. Where originality is highly valued.
You will still need one [or two] H-alpha etalons, a D-ERF and blocking filters.
Plus a sturdy mounting to handle the long and heavy instrument.

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58 minutes ago, newbie alert said:

How do you get chromatic aberration on a HA wavelength.. it's not broadband

 

Please read what I said. Not CA, SA.

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When I decided to increase my Lunt 50mm aperture to a 80mm Frankenscope, I chose to use
the ED80 as an objective. (As "belt & braces" an 80mm Baader D-ERF too!). I did "research"
quite a few Ronchi (not raunchy!) PICS of achromat frac performance on a certain DE forum,
and decided that spherical aberration at HA might be a bit "uncertain" re. some achromats.
Aside from "Achromat Purple", most seemed to be best corrected (spherically) for Green? 🤔

Aside: In light of above, I may have to take back everything I said! lol. But worth a read!?!? 😉
https://interferometrie.blogspot.com/2017/06/3-short-achromats-bresser-ar102xs.html
 

Edited by Macavity
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11 hours ago, newbie alert said:

How do you get chromatic aberration on a HA wavelength.. it's not broadband

 

Spherochromatism means that a scope which is well corrected for SA in green or blue could have terrible spherical aberration in deep red light.

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3 hours ago, Peter Drew said:

Or vice versa which is why some achromats can be ideal for Ha work.  Some users re-space the lens components to optimise the effect.     🙂 

True, although I'd be surprised if an objective was optimised for deep red as standard given that it's practically invisible to the eye in low light. The re-spacing thing is interesting - I've heard of people doing it to try and improve performance of cheap optics but didn't know it worked for an application like this.

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It also begs the question, if there’s no benefit in Ha, why has Lunt moved to expensive ED doublets and triplets as base scopes for its entire range? The answer’s obviously because more people are attracted by a ‘do it all’ package than separate scopes for night and day, but I’m surprised Lunt hasn’t at least retained some of the cheaper, non-ED dedicated solar scopes in its range for the many people who already have an ED night scope, and don’t want a second.  
I use a TV85 (ED doublet) for solar and its excellent - never thought whether it’s particularly well corrected for hydrogen alpha though. 
Meanwhile Coronado SMIII “70mm” solar scopes use a fast and cheap achromat. Presumably pretty unpleasant for night astronomy, but corrected to perform well in deep red.

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