Vixen VMC110L F9.4 Maksutov as Solar Scope?

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Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by AndiesHandyHandies » Fri Mar 30, 2018 7:49 am

Hi,

I have a SH Lunt 110mm D-erf filter which would be suitable for this telescope.

Would the telescope work as a solar scope with a 3x Telecentric or tele-extender Barlow?

To give F28.2.

Andrew.

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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by Merlin66 » Sat Mar 31, 2018 2:41 am

The ERF. Would be OK, but what Ha filter system do you intend to use? Daystar???
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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by AndiesHandyHandies » Sat Mar 31, 2018 7:55 am

Hi

Will any 4 element 3x Telecentric or tele-extender work?

Under development 0.15nm H-alpha filters.

At the moment:

50nm red dichoric filter

0.15nm

Circular polariser

0.15nm

KG1


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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by Merlin66 » Sat Mar 31, 2018 8:14 am

Andrew,
I don’t think the filter combos you’re considering will get you the 0.1nm bandwidth required for effective Ha observing.
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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by AndiesHandyHandies » Sat Mar 31, 2018 2:52 pm

Hi

Should be 0.15nm.

Andrew.

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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by Merlin66 » Sun Apr 01, 2018 12:11 am

Ahhh
That makes more sense.
Which filters are to trialling? Omega Bob?
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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by marktownley » Sun Apr 01, 2018 9:16 am

These filters need to be in a collimated beam not a telecentric beam.

If they are omega filters I'll be perfectly honest I've never seen them work to a performance close to conventional etalon systems.
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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by AndiesHandyHandies » Mon Apr 09, 2018 9:14 am

Hi

All I really want to know is will this telescope work for a D-erf and a following 3X TC Barlow and a h-alpha etalon.

Will the corrector lens cause a problem like a Petzval or barlow in a refractor?

Andrew.

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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by Merlin66 » Mon Apr 09, 2018 9:22 am

All the major manufacturers of Petzval design refractors have said there’s no issue using them of solar observing ie with Herschel wedge.
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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by marktownley » Mon Apr 09, 2018 9:42 am

AndiesHandyHandies wrote:
Mon Apr 09, 2018 9:14 am
Hi

All I really want to know is will this telescope work for a D-erf and a following 3X TC Barlow and a h-alpha etalon.

Will the corrector lens cause a problem like a Petzval or barlow in a refractor?

Andrew.
Getting the right telecentric is key to the etalon performance. I think a Quark on the back would work quite well, even with the native 4.3x TC. Air spaced etalons and PST etalons give a very wide bandpass in telecentric. A daystar or solar spectrum would be the way forward. http://astrograph.net/epages/www_astrog ... ha_Filters
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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by AndiesHandyHandies » Mon Apr 09, 2018 4:36 pm

Hi

" For air spaced refractors this can take the form of a simple UV/IR cut or H-Alpha filter mounted internally. For oilled and Petzval refractors and any reflector, a front mounted energy rejection filter is required. The best of these are the Baader D-ERF types which will offer the best optical performance."

So not an optics problem as such. And Vixens optics would be protected.

Front D-erfs best for thermal control.

Andrew.

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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by marktownley » Mon Apr 09, 2018 9:17 pm

Yes, the optics would be protected by the ERF.
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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by AndiesHandyHandies » Sat Apr 21, 2018 8:06 am

Hi Mark

Why are Omega Bobs filters better in a collimated beam than after a telecentric barlow? The usual advice is that telecentric is better.

I have a PST so would this easily go with this scope for a mod? Its nearly F10 and plenty of rear focus, making it longer Fno, with the moving mirror focussing. Whilst the collimating lens will be fixed at the rear of the OTA, can it or the re-collimator be used to push the focal point back to +250mm OWHY, if the mirror focussing can get back that for for a near object. It might mean the collimated beam is slightly off parrallel.

I have bought a Beloptik 2" KG3 based on your comments and tried it on the PST. It seems to improve contrast on the darker features visually, no long IR?.
Hopefully extend the filter life as well.

Andrew

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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by marktownley » Tue Apr 24, 2018 5:22 am

Try the scope with the PST and see how you get on, I think the ability to focus the Vixen to get an working image through the PST will be key, the front collimating lens on the PST needs to be 200mm inside focus of the Vixen. How a filter performs in a collimated or telecentric beam is to do with the relative refractive indexes of the filter/etalon.
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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by AndiesHandyHandies » Tue Apr 24, 2018 6:43 am

Hi Mark,

Thank you for the reply and information.

So from experience we can stick with a collimator for Bobs filters?

Andrew.

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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by AndiesHandyHandies » Tue Apr 24, 2018 12:11 pm

Hi Mark,

For Bobs filters: "The effective index is close to 2.0."

Cheers. Andrew.

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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by marktownley » Tue Apr 24, 2018 2:08 pm

I've tried both collimated and telecentric with Bobs, I personally found collimated was better. However unless his filters have improved significantly I think all you will get is a blury proms and hazy large scale surface detail at best.
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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by AndiesHandyHandies » Wed May 02, 2018 10:26 pm

Hi

I cannot find transmission diagrams for the Lunt ERF.

Would I need a Beloptik KG3 filter as well for the far IR?

Andrew.

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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by marktownley » Wed May 02, 2018 11:00 pm

Lunt ERF is UV/IR coated RG630 glass. Yes, I would recommend a piece of KG3, not only for additional safety but also for thermal stability of the filters - not that they will crack but the heat will cause them to go offband - assuming we're talking about the bobs?

Compare the PST on the back of this scope to the Bobs, the Coronado will win hands down.
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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by AndiesHandyHandies » Thu May 03, 2018 8:08 am

Hi Mark,

Thats good to know. I will have to get a 1.25" Beloptic KG3 one as well to go in the short T2 terminated stub screwed in the back, to clear focus knob.

1. Bob forgot to send two replacement sets of H-Alphas when he split off the blocker which was causing excessive reflections. And he seems to have sent ones which are not seconds as coatings look perfect. May not have had 'New old Filters' stock. Plan is to compare them with ES 3x tele-centric, someone posted good pictures trying one, with my mates F30 collimated version. If they work OK then might try Baader TC if seems worthwhile. One filter and the blocker could be used for prominences and one as a continum filter on PST is last resort option.

2. PST mod. Do you know of short PST 50mm thread to T2 female adapter? There is the Swiss PST to 2" tube adapter which my mate could turn down. Using adaptor rings can be done with 3 I think.

3. Rusted original PST? I think from his handle, Ed Jones from CN, took a rusted PST objective apart and polished off the rusted coating. Is this worthwhile to get better brightness when replacing its function with 2" Beloptik KG3? Oliver says the KG3 is 1/20 wave, and he has mentioned annealing them up to 2", as Baader DERF. The PST is supposed to be safe with rusted coating but does it dim the image? Or I could find a 40mm F10 lens to replace. Is it a standard diameter?

I will end up with the PST and Vixen with best net result. And Vixen is a 'poor mans Questar' grab and go with its two ports.

Thanks. Andrew.

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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by AndiesHandyHandies » Thu May 03, 2018 11:22 am

Hi

I think my 1.25" 3x ES Tele-extender order failed due to CC expiry.

When using TC can you work at less than F30?

Would a 2x ES TC work for a smaller brighter image, which would just fill the field I calculate.

Andrew.

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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by marktownley » Thu May 03, 2018 11:29 am

1) Any chance you can point a link to the pic?

2) You can normally get SCT adapters to work, there is only minimal difference in thread pitch.

3) Wow! That is incredibly bad! The rust he took off is the ERF coating, so it will be brighter - but it's all the wavelengths you can't see that need to be concerned about. What do you need a PST objective for if you're putting the etalon on the back of another scope?
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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by marktownley » Thu May 03, 2018 11:30 am

AndiesHandyHandies wrote:
Thu May 03, 2018 11:22 am
Hi

I think my 1.25" 3x ES Tele-extender order failed due to CC expiry.

When using TC can you work at less than F30?

Would a 2x ES TC work for a smaller brighter image, which would just fill the field I calculate.

Andrew.
Simple answer - No.

I wouldn't waste you money buying telecentrics for a system that isn't going to work the way you think it is. Best to spend on adpaters and get the PST on the back of the Vixen.
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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by AndiesHandyHandies » Thu May 03, 2018 3:31 pm

Hi Mark,

I will give the PST a try then.

Thanks. Andrew.

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Re: Vixen VMC110L F9.4 Maksutov as Solar Scope?

Post by AndiesHandyHandies » Thu May 17, 2018 9:30 am

Hi,

Rodastro got the PST block mounted on the back of the Vixen.

Lunt 110mm derf just fits inside the dew cap. Taped on at the moment resting against felt circle on secondary cap.

We got the PST apart. The Gold tube and Etalon came off on one go. When we stripped of the rubber tuning ring and took out the screw for the tuning adjustment we found that a suspension C-ring spanner off his bike just fitted the slot and with that and double filter wrenches it parted from the tube. So tip is to remove the tuning rubber and screw and use a C-ring spanner to hold the etalon part.

Taking Mark T's tip on moving the collimator lens forward to save chopping tubes down Rod made a little holder for the collimator lens to slide down in the T2 stub on the back with the lens at the bottom.

Rod has a 42mm to 48mm low profile adapter ring and it screws in for about 3 threads to the different pitch in the PST etalon. There is a locking ring on the T2 stub. First try it locked against the tuning ring so he had to machine a spacer so that it would lock but leave the tuning ring free to turn.

First light this morning worked! Measuring the lens is just about 200mm from the focus. There is just enough room to set the PST focusser in the centre and still be able to focus with the Vixen. A little bit of luck virus.

There is a nice prominence at the moment 7 oclock for me on GEM mount. Best view with the PST was my 8mm Plossl and now its 25mm. More magnification looks fuzzy. 22.5mm on my Kunming Optics zoom was OK.

On the suns disk I can see details as well. There is a slightly brighter spot in the centre 50%. There seems to be a slightly off centre sweet spot as moving the prominence about it goes off-band to one side. How do you determine what makes a sweet spot off centre?

Try my new QHY camera next I suppose.

If I put a Beloptic KG3 in the focuser tube could I remove the PST ITF and get a brighter image? I assume the Lunt and KG3 would be safe enough.

I assume the limit on field is the 20mm aperture of the etalon and no real point in doing a Blocking Filter mod.

I have noticed that there seems to be some lack of clarity in posts about the difference between the ITF and Blocking filter. I suppose the different shape and sizes stops innapropriate replacements.

Andrew.

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