Alternative to the Coronado/ Lunt IFT (mini-erf)???

Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...
User avatar
swisswalter
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 17951
Joined: Thu Feb 06, 2014 4:28 am
Location: Switzerland
Contact:

Re: Alternative to the Coronado/ Lunt IFT (mini-erf)???

Post by swisswalter » Fri Apr 26, 2013 8:36 pm

Hi Bob

thank you for the informations and the plots
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)

User avatar
Bob Yoesle
Almost There...
Almost There...
Posts: 534
Joined: Thu Mar 08, 2012 7:24 pm

Re: Alternative to the Coronado/ Lunt IFT (mini-erf)???

Post by Bob Yoesle » Sat Apr 27, 2013 3:07 pm

For much higher transmission and image contrast from your CaK PST mod the only filter from the whole CaK PST that is important is the very front one that is closest to the objective, use this with a baader k-line in conjunction with a solar wedge with no ND filtration to act as an ERF, you will find this an improvement on the already excellent results you get. This is of course for imaging and not visual.

Thanks Mark! May give that a try.

Sounds like the "Holy Grail" - an ITF which can be used safely for Ha and CaK!!!


There appears to be a problem. In my first report atmospheric conditions were poor and I just did a quick check to see if an image made it through at 394 nm, and didn't attempt use at 656 nm.

Yesterday conditions were better -- but the filter appears to produce significant astigmatism, and detail is considerably diminished compared to without the filter. I again did not check at 656 nm -- I assume the same problem would be evident.

Here's an image without the filter:





Here's and image with the filter (best focus obtainable):





Both images are identically processed. Assuming the substrate is of high quality and suitably flat, I thought perhaps the filter might be being impinged by the mounting ring. When I attempted to loosen the retaining ring, it was too tight to loosen and I didn't want to risk damaging the filter or the mounting/retaining ring without the proper tool.

I have written to Mr. Winchester on the issue, and asked if I should return the filter for inspection, or if there is a tool he could send me on loan to see if it indeed is a mechanical entrapment issue, or an optical substrate issue.

I will keep you posted.

Bob B)
Diagonally parked in a parallel universe.

Curiosity is the father of knowledge; uncertainty is the mother of wisdom.

Goldendale Observatory

Dark-Sky Defenders

User avatar
swisswalter
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 17951
Joined: Thu Feb 06, 2014 4:28 am
Location: Switzerland
Contact:

Re: Alternative to the Coronado/ Lunt IFT (mini-erf)???

Post by swisswalter » Sat Apr 27, 2013 5:31 pm

Hi Bob

thanks for sharing that. A huge difference
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)

colinsk
Almost There...
Almost There...
Posts: 507
Joined: Sat Mar 10, 2012 9:30 pm

Re: Alternative to the Coronado/ Lunt IFT (mini-erf)???

Post by colinsk » Sun Apr 28, 2013 3:08 am

Thank you Bob.
Thank you, Here are some references I have collected.



Etalon Article Part I

Etalon Article Part II

Solar Patents of interest

Bratislav
The Sun?
The Sun?
Posts: 8
Joined: Wed Apr 24, 2013 11:48 am

Re: Alternative to the Coronado/ Lunt IFT (mini-erf)???

Post by Bratislav » Mon Apr 29, 2013 1:14 am

Bob,

it is nearly impossible to introduce astigmatism to a thin plano parallel plate. One would need to bend it to breaking point and even then transmissive astigmatism would be negligible.
I'm afraid it looks like Omega used a poorly polished/figured substrate.
Using the ERF that far from focus is always going to test the optical quality quite severely.

Bratislav

User avatar
Merlin66
Librarian
Librarian
Posts: 3254
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Contact:

Re: Alternative to the Coronado/ Lunt IFT (mini-erf)???

Post by Merlin66 » Tue Apr 30, 2013 8:19 am

OK, managed to get a few minutes with the single stacked SM60/ED80 to check out the ITF options...unfortunately the seening (and clouds) interfered with the final test...may be soon.
DMK21..
The "comparison master" was the BF10 and this needed a 1/1000s exposure for the surface detail..not much in the way of proms...no surprises...
The next up was the Oliver UV-IR/Kg3 filter...very noticeably brighter screen image..
ended up with a 1/5000 exposure and even this picked up the filaprom above 1173. I was impressed....
Unfortunately the cloud built up before the Omega Bod Ha could be trialled properly..
IMHO the UV-IT/KG3 looked VERY good and certainly, at this stage a very good alternative to set-ups which have an up-front ERF...
I'll process and upload the limited images I got, but so far Oliver wins!!
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

User avatar
Merlin66
Librarian
Librarian
Posts: 3254
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Contact:

Re: Alternative to the Coronado/ Lunt IFT (mini-erf)???

Post by Merlin66 » Thu May 02, 2013 5:48 am

Another day, another opportunity...
Seeing was very poor but while out visually with the D-ERF, 102PST mod I was impressed by the large prom.. :ohmy:
I don't usually image with the 102PST but...
Set up the DMK21 gain=280, gamma=195.
Each image below has been processed exactly the same through Registax 5.1 (I will have to go back and do them again - I think there is more detail to pull out)
This was just to compare the available ITF "replacement" filters.
#1 - Std BF10, exp 1/120



#2 - Baader 35nm Ha filter, exp 1/1429



#3 - Oliver's UV-IR/KG3 filter, exp 1/909



#4 - A combination of the Baader and the UV-IR/KG3, exp 1/909


As you see all the "alternatives" need a much reduced exposure. The Baader only 1/1429sec!!
The UV-IR actually seemed to be better, with a 1/909sec exposure
and there was little difference noted with the combo.
I'm not sure these trial prove much...but I certainly will be doing more work with the UV-IR/KG3.
Feedback welcome...
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

User avatar
DSobserver
Almost There...
Almost There...
Posts: 550
Joined: Sun Feb 19, 2012 2:36 pm
Location: FRANCE

Re: Alternative to the Coronado/ Lunt IFT (mini-erf)???

Post by DSobserver » Thu May 02, 2013 5:53 am

It seems that I missed something : is Baader 35nm Ha filter ok to replace the ITF or is it only for photo?

User avatar
Merlin66
Librarian
Librarian
Posts: 3254
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Contact:

Re: Alternative to the Coronado/ Lunt IFT (mini-erf)???

Post by Merlin66 » Thu May 02, 2013 6:05 am

See the original first message in the thread:
http://solarchat.solarastronomy.org/ind ... t-mini-erf

There are two issues:
1. Finding a replacement ITF ("mini-erf") for the basic PST which has no up front ERF.
2. Finding a replacement for the ITF in the Coronado/ Lunt blocking filters (which are used with either a red or ERF filter up front.

The Baader I've only tested visually and imaging wise with an up front ERF. (#2 above)
I don't have a PST configured (yet) to test it for option #1.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

User avatar
swisswalter
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 17951
Joined: Thu Feb 06, 2014 4:28 am
Location: Switzerland
Contact:

Re: Alternative to the Coronado/ Lunt IFT (mini-erf)???

Post by swisswalter » Thu May 02, 2013 10:04 am

Hi Ken

thank you very much for that comparison. The oliver/baader combo is great
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest