David Cortner Lunt 60 mods

[Bob Yoesle]

David Cortner appears to have made some successful modifications to his Lunt 60 using 90 and 152 mm objectives. His blog showing his stunning images (one of which appears in this months Sky & Telescope) and the instruments can be found starting on this page:

http://www.davidcortner.com/slowblog/20120717s.php

[colinsk]

That is a great shot. I can't find any spherical aberrations in the image. Has anyone who takes images looked? The LS60 might just be a good candidate for modding.

[swisswalter]

Hi Bob

thanks for digging out and sharing. That seems to be a great mod

[marktownley]

Cool fish! Thanks for that Bob!

[Merlin66]

This is based on Vijo's successful Ls60 mod, details in his thread.
It's great to see others being able to replicate the success.
Well done dave.

[colinbm]

Gee, that's really getting up close & personal
Col

[Photonist]

The original thread where the ”Lunt LS60 code” was cracked successfully is here, a few threads below http://solarchat.natca.net/index.php/en ... &start=120

Great that the thread have been useful to someone

Viljo

[davidcortner]

Whoa, thanks for the kudos. And thanks for the key insights that helped me get that scope and its successor working quickly. Don't mean to seem ungrateful -- I would've said something earlier but I haven't checked in here in a while. For anyone who wants more details, start here:

http://www.davidcortner.com/slowblog/20120817s.php

and page forward and back. I'm dealing with some electronics issues at the moment and now with the Sun passing south of the trees that border the backyard, I'm getting my G11 out of storage and tuned up for portable duty. See you on the wire! dc

[davidcortner]

A quick followup here in case anyone's following this example closely. While imaging today, I noticed that the 75mm Lunt ERF has cracked. Whether due to heating or to rough handling is an open question. It's a clean split very nearly through the diameter; the two pieces are hanging together, barely out of plane with each other, and still work surprisingly well, but something needs to be done differently. Either the mounting for the filter was too primitive, or asking a 75mm sub-diameter filter to handle the flux from a 152mm objective was asking too much. dc

[colinsk]

That is a shame. If you replace it please send the pieces to Ken or someone so we can get a spectral curve.

[Bob Yoesle]

My understanding is that the Lunt ERF’s are an RG type of glass - i.e. similar to the DayStar ERF’s (blocks UV) with additional dielectric coatings for IR (similar to the Baader ERF’s). So theoretically, if the dielectric side faced the objective little heat would have been transmitted or absorbed, even if placed nearer to the focus as your diagram indicates. So this is very puzzling. Perhaps contacting Lunt directly might help to discover the reason for the failure.

[davidcortner]

Yeah... that was my understanding as well, so, within reason, I figured I could pour quite a lot of energy on it. Where I had it placed, the 152mm objective should be producing about 400% of the intensity of full, unfocussed sunlight, which didn't seem obviously excessive. The filter was not hot to the touch like the old two-piece Lumicon ERF quickly got. There *were* some physical shocks to the whole outfit while working out hardware bugs and the rig rattled around some during transportation until I found the right packing scheme. Maybe I just didn't work out the cell well enough to protect the filter mechanically. Anyway. I've ordered some optical cement and my plan is to attach the two ERF pieces to a clear filter. The two halves were slightly out of plane in their broken, unsupported state and I think that rather neatly explains the odd degradation of images produced during the last few sessions. But with the halves supported on a polished glass substrate (a clear filter by any other name) and gently set back together (think shards of dielectric pottery), the reflection from the front surface looks literally flawless. It gives me hope that I can get back to where this is nowhere near the limiting factor in my image quality without dumping a lot of cash into a fix. If I am wrong, I'll make sure to ask where to send the pieces so y'all can measure them and put the data to good use. Cheers.

[andreahaku]

Hi David,

I just modified a 152/900 like yours with PST pieces. I used a 75mm Baader D-ERF and fitted it at the end of the 3" focuser tube. It's perfect and works perfectly. I used it for more than two hours yesterday and didn't have any single problem.

The focuser was completely out at its maximum (10cm).

Don't know what's the difference between the Baader D-ERF and the Lunt ERF but sincerely I don't think that it cracked for the heat. I think it's more likely due to the "physical shocks" you're reporting.

I wish that you'll be able to solve the problem and fix it as I really like your images and have been following you when taking my decision to buy the 152 or not

I just published a couple of images made with it (HA and White Light) in the "This is Solarchat" section. You'll find more in my blog. I hope you like it.

Clear Skies,
Andrea

[peter drew]

I'd just like to add that I've made several mods with internal ERF's of Baader and red glass in scopes up to 220mm aperture with no problems (yet).

[davidcortner]

Thanks, Andrea and Drew. Your experiences are very encouraging. If I end up replacing rather than repairing the ERF (as seems likely, eventually), I'll conisder seriously the Baader D-ERF in as large an aperture as I can afford and will make or have made a much better cell for it.

[andreahaku]

Ciao David,

as you can see from Stephen review of the Lunt 152 here:

http://solarastronomy.org/reviews/LUNT% ... review.pdf

Lunt has gone with the same solution.

At page 8 there's a picture clearly showing that Lunt has places the ERF in front of the focuser quite near to the very end of the tube length. If Lunt has gone for that solution, than we can be sure that is a safe position. We can ask Stephen or any other people owing it, to tell us how much "inside" is the ERF and how wide is it.

Andrea

[Bob Yoesle]

FYI - Lunt now offers custom machine work, which might be the way to go for making a cell for their ERF:

http://luntsolarsystems.com/blog/lunt-engineering

I have had great work done for me by Telescope Service of Germany for mounting my Baader D-ERF 110 in a custom cell:

http://www.cloudynights.com/ubbthreads/ ... PHPSESSID=

BTW, I will be using this sub-aperture D-ERF when I eventually get my 150 scope put together:

http://solarchat.natca.net/index.php/en ... do-etalons

[andreahaku]

I had my original cell made by TS as well for my D-ERF and they did a great job.

I posted a couple pictures long ago here:
http://solarchat.natca.net/index.php/en ... t-mod#7756

It took them 3 weeks to do it