150mm F10 PST mod, first impressions.

[peter drew]

In a nutshell, excellent. Today was the first with prolonged sunshine suitable for some serious testing. The seeing was variable and conditions were very windy. The best views were close to the good images posted on this forum and as good as the smaller aperture scopes that I have. I'm not an imager (yet), so my current goals are visual. The 150mm Istar objective appears to be plenty good enough for solar work, it is mounted in a 180mm o/d aluminium tube. A 110mm Baader D-ERF is mounted 600mm behind the objective, a PST body with a 15mm Coronado BF completes the rest.The scope was mounted on an EQ6 Pro. After i hour of constant exposure I removed the ERF which is mounted in a separate holder and loaded through a slot like a CD, the cell and the ERF were cool. I replaced the ERF, removed the complete PST assembly and focused the red beam on to my hand, no sensation of heat. By contrast, I caught the reflected beam from the ERF which focused about 400mm outside the tube on to a piece of wood, the wood started smouldering. I can't think of a more graphic way of demonstrating the effectiveness and importance of this unit. The objective, through which the beam passed was also cool. My only disappointment was the BF15, the image quality was fine and the field of view presented a full solar disk at 60X but the "sweet" spot did not seem any larger than that of the original BF5. It was neccessary to scroll round the image to see each feature at its best and the background was noticeably brighter. An annoying circular reflection covering half of the field was eliminated by rotating the BF which was interesting and worthy of further experiment. Overall I,m extreemly happy with the outcome for a little work and an outlay of less than £1500. I'll try and post some pictures of the instrument as soon as I've tidied it up a bit.

[poita]

Great stuff!

Are you still using the PST black box?

Interesting about the BF15 sweet spot, I wonder if that is the PST etalon or the BF causing it?
Have you tried a Lunt 1200 as an alternative?

[marktownley]

Excellent report Peter! Good to read! Keep us updated with your progress

[poita]

I doubt they are related, the Istar stuff from Starizona is drop shipped from the manufacturer I believe.

You can buy just the F15 6" objective (150mm/F15) for about $550, not a bad deal.

http://www.istar-optical.com/istar_031.htm

[Derek Klepp]

Thanks for the report Peter.I am thinking the 150mm /F15 would be very good for WL viewing also . Have you tried it with a wedge at all?

[swisswalter]

Hi Peter

great report. I'm looking forward to your further reporting and the pics

[peter drew]

Thanks for your combined interest. Today offered much better seeing and showed better the potential of this instrument. It easily supported 160X although wind buffeting restricted it to 60X for a comfortable view.The current active area erupted again around 12.30pm, rivers of molten gold appeared to flow from the centre of the large spot and stream towards one of the outlying spots. Retuning the etalon made it possible to exactly pinpoint the origins of the outflow, definitely from the spot itself. As the view is in 2D it's tempting to see this activity as flat on the solar surface whereas the truth is probably that it is an arching loop seen in plan view. The resolution of fine detail was outstanding and it's difficult to imagine how it could be significantly improved. I have a collection of 5 PST bodies two of which have had the complete internals removed to form a "stage 2" mod, to be honest, unless the original PST had focusing or astigmatism problems, I find little difference between modded and unmodded bodies. I actually like to retain the black box as a sort of homage to the original designer. Having swapped many of the available components, the best arrangement is currently an unmodded black box + mini ERF and Coronado BF15. This, however is just day 2.

[marktownley]

Thanks for the update Peter!

Glad the new toy is working as you would like.

[Carbon60]

Hi Peter,

You and I are following a parallel path since we're both developing a 150mm solarscope. I'm also using an ISTAR 150mm/f10 and I'm completely scratch-building the OTA from aluminium tube and bar sections. My ERF is 90mm and located within the OTA at the appropriate point.

I look forward to sharing some images once the finishing touches are in place. A quick test run the other week looked very promising, even though the lens was only clamped in place.

Regards

Stu.

[peter drew]

Hello Stu. Great to know someone else is working on the same project, makes things much more interesting. My main objective with telescope building is trying to achieve the best possible results for the least financial outlay I'm now confident that subdiameter ERF's are a viable proposition, this certainly keeps the cost down, from recent experiments I have concluded that provided that the ERF is positioned less than half the focal length from the objective, the reflected beam and therefore main heat, will be focused outside the telescope.Good luck with your endevours.
Peter.

[marktownley]

Welcome Stu! Looking forward to hearing how both these scopes develop

[poita]

Hey Stu, that setup you described is exactly what I am planning with the 90mm DERF, I'm hopeful we will end up with something very special!

[peter drew]

Poita. You will!

[Carbon60]

Can't wait for some decent spells of sunshine now, here in the NW of England.

My scope should be finished this weekend! Yahooo. It's surprising how long it has taken to scratch build this thing (started in December) and what with the holidays and so on.... I'll post some pictures of the various stages of build for anyone interested.

With regard to the scope, Ken (Merlin66) has a lot to answer for.... I read some notes about LADS and LASSes (Large Area Double Stacked and Large Area Single Stacked solarscopes) and was hooked....

Mark, thanks for the welcome.

Cheers

Stu.

[Carbon60]

Peter and Poita,

Any further progress?? I tried mine yesterday and was somewhat disappointed with internal reflections and relatively poor image quality. The detail on screen is extraordinary, but trying to get good image capture was difficult at best. Not sure why..... My Etalon seems to have a 'sweet-band' rather than 'sweet=spot'. I tried my stage 2 and then reverted to stage 1 mod, but there was no noticeable difference. Frustrating is not the word!!

I was hoping for some enlightenment.

Regards

Stu.

[marktownley]

[quote]Not sure why..... My Etalon seems to have a 'sweet-band' rather than 'sweet=spot'. I tried my stage 2 and then reverted to stage 1 mod, but there was no noticeable difference. Frustrating is not the word!!

I found with my external etalons, if they were not perfectly square with the optical axis then I got this sweet banding effect. Maybe a similar thing is happening with your setup regards the PST etalon?

[Carbon60]

Many thanks Mark.

I'll look into that. Everything has been precision machined, so all interfaces should be parallel, but it worth teaking to see if anything can be done to help.

As for the internal reflection, I was wondering if there might be a back reflection of the internal ERF coming off the rear of the objective lens and back down to the imager. Maybe further tilting of the ERF could work here. I'd be interested to hear from anyone with suggestions on how to cure this.

Still, the PST Etalon is the main priority.

Thanks again Mark.

Regards

Stu.

[peter drew]

Stu. My 150mm mod is also still a work in progress. I am using a BF15 but the extra field tends to exaggerate the sweet spot of the PST etalon which normally appears to cover the field of the original BF5. When using the BF15 it's necessary to scroll round the solar disk and centre the sweet spot on the area of interest, how this would affect imaging remains to be seen. There are some internal deflections but I find them to be minimised by retaining the mini ERF and also rotating the BF relative to it which seems to move the worst reflection somewhat out of the immediate field. I have an oversize main tube to which no baffles are fitted as backlighting from the PST etalon lights up the rear of them to a surprising degree, the tube will be flocked in due course. As far as performance is concerned, the visual image in the sweet spot area, on a good day, is not far short of the excellent images on this forum. I would love to have a side by side comparison with yours in the near future if possible.

[hunterknox]

There's something in the water in Lancashire for sure! Very impressive projects. I'm looking forward to seeing some pics!

[Carbon60]

Thanks for the reply Peter. I noticed things were worse when I removed the mini ERF too, so that will go back in place and I'll try rotating the BF to see if that will also help. I wonder if a polarising filter on the camera would help reduce any reflections?? I guess it could impact image quality (contrast) though.

Side-by-side comparison sounds like a plan.....I'll try out a few things first when I next get the chance and let you know how it goes.

Regards

Stu

[Carbon60]

Hi Hunterknox,

There's something in the water, for sure......

I remember from previous conversations that you had a sweetspot issue with your PST Etalon and didn't you fix it by adjusting the lens elements on the Etalon itself? Any insight here would be welcome.

Regards

Stu.

[hunterknox]

Hi Stu,

Sorry to disappoint but my etalon's OK actually. There is a sweet spot but it's tuning-dependent so if the tuning's right the sweet spot disappears - no need for any lens adjustment. My only other issue was with an internal reflection before I tilted the ERF. Once I'd fixed that tilting it was fine.

Tom

[colinsk]

I sold my PST. It had a tilt inside the etalon that gave a 1 lamda wave to every view. Inside the band the view was great. but the on band view was only 1/3 of the field of view.

[Carbon60]

A few tweaks (changed the tilt angle of the ERF in the OTA, rotated the BF and camera) reduced/eliminated the internal reflections and Newton's rings, so things look a lot better now than they did originally.

Here is one from a couple of weeks ago. I took this with a 2.5x TeleVue Barlow and processed it using Registax with flatfield and PixInsight (deconvolution).

Hopefully it uploads OK....first attempt.

Regards

Stu.

[marktownley]

Looks good to me Stu! B)

[swisswalter]

Hi Stuart

that is going to be great. On my monitor it is a tad dark