Lunt 80mm DSII illumination problem.

[johnnyt123]

Hi.

I am having trouble evenly illuminating the solar disc with my Lunt 80mm DSII
There is good detail only in the upper half of the field of view.
And if I try to tune the bottom half then the upper half completely blows out.

I bought this scope maybe 3 years ago and have hardly used it.
And the other day I brought it out to image and was very disappointed with the performance.

Does any one in how to address this problem because quite frankly I would rather throw it out than have to live with the problem.

Regards.

John.

[AstroJunk]

Check the blue glass of your blocking filter. It's on the scope side of the diagonal.

Lunt scopes have a very bizarre issue of this piece of glass becoming covered in gunk that will spoil your view. Fortunately there is a fix, so have a look and if it is cloudy, then look here: http://www.iceinspace.com.au/forum/showthread.php?t=144429

[Strawb]

This is cleanable but it does take a while . I used brasso( silvo) on mine and it cleaned up ok. I did query lunt and they sent me a couple of replacements ( which I since gave away) so you can always give them a shout too

[AstroJunk]

The popular household cleaning product CLR dissolves off it in just a few mins. as discovered by IIS'er Star Catcher

[tempestwizz]

I have a 60mm Lunt with the double stack add on. I find the tuning quite tricky, and honestly have not mastered it yet.
If the blue filter is not your issue, remove the double stack section and use it as a single stack version for a while. You will find it is much easier to get even illumination. Once you regain some confidence in the scope set replace the double stack when you have a good single stack image, and then experiment with the double stack tuner and see what affects you get.
I'm thinking that they need to be tuned to almost the same pass and with just a slight offset. I'm thinking that they way they achieve the narrow pass and can generate artifacts which can interfere and cause the poroblems you describe. I'm thinking it's almost impossible to get a full frame double stacked image evenly illuminated and suitable for imaging. Ok for visual, as you can look at different parts, but the camera is unforgiving.
I'm awaiting a replacement blue filter for my system also, but that's not the cause of the uneven illuminations.

Cheers Briab

[johnnyt123]

Thanks for your responses.

I will have a look at the blue filter and see if it is the problem and I might also give Lunt a quick message about the matter.

Regards.

John

[Merlin66]

Tuning a double stack is a two (or three - see later) process.
To achieve maximum transmission at the narrower DS bandwidth (0.5A ) firstly remove the front etalon....
Tune the other to achieve maximum contrast and visible surface detail. Once this is achieved do'nt touch it again...it is on band.
Add the second etalon and adjust it to give the brightest image - at this point it will also be on-band.
If all goes well, there surface features, active areas, filaments and spicule forest should be visible across the FOV.
There's one more thing that can be done to improve the uniformity of the FOV and that is rotating the front etalon (without changing the tuning) relative to the other etalon. Use a small piece of masking tape at the edge to monitor the rotation, a quarter of a turn should improve things, but trials will quickly confirm any improvement.
You can also check that the blocking filter diagonal is not contributing to the problem. It can also be rotated in angular position relative to the OTA to see if there is any change in the FOV.
Hope this helps.
Ken

[johnnyt123]

So I examined the b1800 blocking filter and this is what I found on the blue filter.

I gather that this may be the source of my problem....

Regards.
John.

[johnnyt123]

You can see the smear of this greasy material.

My question is how to remove it all wiht damaging the filter.

[Merlin66]

Copy Lunt for a replacement.
You could remove and try the CLR cleaning as per message #4

[AstroJunk]

There is a little dab of silicon on the locking ring to keep it secure in transport, but it offers no real resistance, just scrape it off. Spin that locking ring off and the blue disc can be tipped out of its holder.

CLR is the only stuff that will dissolve that gunk. Place it in a glass of undiluted CLR, leave it for 15 mins then rub it off gently with a paper towel. Rinse and repeat until you are happy it's all gone.

If you have some latex gloves, use them when putting it back in the holder - it's a little bit fiddly and easy to get a fingerprint on the disk! I didn't both re-siliconing the locking ring on mine.

Easy as that.

[johnnyt123]

Hi again..

I spoke to Sirius Optics the vendor from whom i purchased the scope originally and despite having been sold, the new owner kindly offerred to contact Lunt on my behalf and seek a replacement filter.
So fingers crossed that this happens soon.

Thanks all for your help. I just thougt it was always my lack of processing skills, but when i realised that even visual observation was laboursome i thought something might be wrong.

Thanks once again

John