21 replies to this topic

[lorenzo italy]

On the afternoon of Saturday 14 May I managed to cut out half an hour to try out the triple stack photography of the Sun.
I also had more time available, but the half hour is the time that the sky remained clear ...
By now the setup is tested, the only unknown is the tuning of the DS Coronado module, the only one that has the greatest possibility of regulation. In fact, the Lunt has the etalon always fixed in the same position, and the Quark also has the temperature regulation in the most optimal position.

 

main telescope: Lunt H-alpha 60mm
double stack module: Coronado SMII 60mm
triple stack module: Daystar Combo Quark chromosphere

ZWO ASI178mm camera with GSO 0.5 reducer
footage from 30 seconds at 16fps processed with Autostakkert3, Astrosurface and Paint Shop pro

 

Lorenzo

 

[bigdob24]

Looks like you have all 3 working well, nice capture.

[hopskipson]

Stunning!

[MalVeauX]

Sweet contrast Lorenzo!

 

Very best,

[Look at the sky 101]

One word  , Wow. 

[PhotonJohn]

Beautiful image Lorenzo.

[BYoesle]

Hi Lorenzo,

 

That's a nice image!

 

However, there does seem to be a bit of contrast or brightness gradient radially from the center to the edge. This might be explained if the Combo Quark had no telecentric employed (or a non-optimized telecentric) to normalize the axial rays across the etalon - was this possibly the case?

 

The other possibility is that narrowing the bandpass via double/triple stacking will reduce the size of the Jacquinot ("sweet") spot, and the internal etalon is particularly sensitive to this via the collimator lens optics... perhaps a combination of both effects is at work?

 

Can or have you done a DS v TS comparison with changing only the exposure to normalize prominence brightness, and using identical processing? I would be particularly interested in close images of the solar limb with a prominence, as well as close up images of filaments and active regions...

 

Looks very promising!

[peterm]

Very nice indeed. There is a lot of detail in that image. Bravo!

[Averton]

We wish to go with Johann - wow. 

[lorenzo italy]

Thanks to all for the appreciations.

 

 

Hi Lorenzo,

 

That's a nice image!

 

However, there does seem to be a bit of contrast or brightness gradient radially from the center to the edge. This might be explained if the Combo Quark had no telecentric employed (or a non-optimized telecentric) to normalize the axial rays across the etalon - was this possibly the case?

 

The other possibility is that narrowing the bandpass via double/triple stacking will reduce the size of the Jacquinot ("sweet") spot, and the internal etalon is particularly sensitive to this via the collimator lens optics... perhaps a combination of both effects is at work?

 

Can or have you done a DS v TS comparison with changing only the exposure to normalize prominence brightness, and using identical processing? I would be particularly interested in close images of the solar limb with a prominence, as well as close up images of filaments and active regions...

 

Looks very promising!

 

Hi Bob,
you are right about the triple stack image. I don't use any Barlow or telecentric before Combo Quark, because I can't get a useful focus. So the Quark works at f8.3, which is very far from the optimal value. But still some improvements to the image bring it anyway.
Here are three more photos I took this morning.
This time I was able to use the focal length of the Lunt (500mm) without any reducer. I don't know how, but I was able to find an optimal point for the triple stack image even at this focal length. The Sun in TS seems more like a ball of wool, the image is so soft and blurry (but I like it anyway). Blame for the turbulence and the fact that I had to use slow shutter speeds to avoid raising the gain too much.

 

-- single stack   gain 42 exp 0.006
-- double stack  gain 42 exp 0.029
-- triple stack     gain 99 exp 0.289

 

I used the same processing in Autostakkert3 for all three images, adding only 25 frames.
In Astrosurface I made a passage with the same wavelets for SS and DS, slightly more incisive for TS.
I hope they can be useful to you.

 

Lorenzo

 

single stack

 

[lorenzo italy]

double stack

 

[lorenzo italy]

triple stack

 

[philmor56]

Wonderful study there Lorenzo!

 

I'm not seeing the gradient in these shots, pretty well flat to the edge. 

You're right about the TS being kind of "wooly" though.

There's always something new to try and improve on. It's what keeps us doing this!

 

Well done. 

 

Cheers

[BYoesle]

Hi Lorenzo,

 

Those are some great pics and processing examples. I also appreciate the larger image scale. 

 

Definite increases in contrast from single through triple stack, and unfortunately obvious decreases in image quality. I would attribute this to the increased length of exposures required. The Quark is not providing it's narrowest bandpass due to the lack of telecentric use, and it also has significant internal non-removable blocking and likely the least transmission of the three etalons in the system.

 

Judicious use of gain would be helpful to shorten the exposure time and degradation from seeing effects - at 60 mm you do not seem to have enough light to pull off triple stacking very well and need all the image brightness you can get.

 

Stacking etalons requires taking steps to maximize transmission. If you want to seriously pursue triple stacking further, here's what I would consider:

 

Get a second 60 mm non-richview tuned front etalon for triple stacking (Lunt 60, or original SM60). The SMII and SMIII richview etalon's ERF is integral to the filters operation and should not be removed as described below. (Note: the SMIII double stacked telescopes have both a richview and non-richview etalon - both of which are also tilt-tuned - but these do not seem to be currently available as separate items).

 

You can remove the RG630 ERF from this non-richview 60 mm etalon - your current SMII and internal etalon already have this ERF as well, so it's completely safe to remove them from the new front etalon for double or triple stacking use. This etalon with the removed ERF would be the second of the three etalons in series.

 

Alternatively, you could sell the SMII and get two non-richview 60 etalons. After removing both the ERF's, use a 75 mm Baader DERF ahead of both. This will require a fabricated DERF cell to fit the forwardmost 60 mm filter's case. It will take some finessing to optimize tilts to handle the retro-reflections between the etalons. This will optimize the front etalon double stack. The internal etalon/ERF will now be the third and final etalon in the system. You might also see if a circular polarizing filter could help if internal/external reflections prove problematic - but then again this filter significantly impacts image brightness.

 

Lastly, you'll now have to use the Lunt blocking filter (the Quark served as both an etalon and blocking filter). The Lunt BF's transmission can be improved by replacing the BG38 forward blue filter with a 1.25 inch thread-on KG3 UV/IR blocking filter.

 

Thanks again for your efforts and pictures. 

 

Now when the weather improves I may have to give triple etalon stacking a try. Getting three of them to play well with each other is the main issue... 

[lorenzo italy]

Thanks Bob for the precise and useful tips to improve my equipment.
I had thought about replacing the blue filter of the bf Lunt too, but given the triple stack I use now, it would not make sense.
Also all the variations of the etalon modules you described, which are useful for improving the detail view in TS, are out of my reach for now.
It is already a lot if I have managed to reach these levels.
The only improvement, if you can call it that, could be the removal of the small erf that is on the Quark's nose.
I believe that in TS it is not needed, if not to make the image darker.
My only doubt is that if I take it off what will I find underneath? Directly the etalon?
In this case I wouldn't do it since I don't want to expose it to air. Or you could replace it with a softer filter, like a simple uv / ir cut, which I think lets in more light. But then I would have the doubt when I use the Quark alone with the 127mm refractor. In this case I mount a 35nm Baader h-alpha filter before the diagonal. I don't know if that would be enough as a protection since I would take the little erf out of the Quark's nose 

 

Lorenzo

 

 

 

[BYoesle]

Hi Lorenzo,

 

I have no direct experience with the Quark Combo, but this filter is either a sort of sub-diameter ERF or a blocking filter component. Perhaps someone will chime in as to what this filter might be. It looks easily removable for TS use. All you'd need to do is have another 1.25 inch threaded adapter to the main Quark body.

 

If you do remove it I'd only image with it to see what happens and avoid any possibility of IR/UV getting through, although you could use a UV/IR blocking filter to help in this regard. If it is a trim filter, the preceding etalons will likely prevent any leakage of side harmonics.

 

The Quark etalon will not be exposed if you remove this filter. Typically the very thin mica etalon is sandwiched between two optical windows, and additional blockers and trimmers are placed on either side of the etalon as seen here:

 

 

If removing this filter makes the image way too bright, using the Lunt BF after the Quark might just tame it enough for practical use. But given how less bright the image is with TSing, I doubt this will be the case.

[ch-viladrich]

Excellent Lorenzo. Thanks for sharing !

 

Bob advices are very wise

 

In particular, you could push the gain much higher, and increase the duration of the videos. For FD images, you can go easily to 120 s video duration (even 180 s). Then, you will be able to decrease exposure time (maybe 0.1 s in TS and 0.02 s in DS) while increasing gain value. An the end of the day, you will keep the same percentage of images in your stack.

[torsinadoc]

Fantastic examples!

[lorenzo italy]

Thanks Bob and Christian for the valuable advice.

 

Fantastic examples!

 

Thanks Alan.

 

Lorenzo

[R Botero]

Great shots Lorenzo and the comparison of SS vs DS vs TS is excellent!  Great thread.

 

Roberto

[hopskipson]

Really nice images Lorenzo!  I tried triple-stacking for a while but the results were not half as good as what you have here. Have you tried using a 2x telecentric or Powermate if you have one? Might be worth the try to narrow the Quark.  You could then add a 0.5x reducer to get the same FOV.

[lorenzo italy]

Great shots Lorenzo and the comparison of SS vs DS vs TS is excellent!  Great thread.

 

Roberto

Thanks Roberto.

 

 

Really nice images Lorenzo!  I tried triple-stacking for a while but the results were not half as good as what you have here. Have you tried using a 2x telecentric or Powermate if you have one? Might be worth the try to narrow the Quark.  You could then add a 0.5x reducer to get the same FOV.

Thanks James,

I have to say that I was lucky to find three etalons from different manufacturers that still work well used in the TS. I have a telecentric, but it's 3x. I tried to put my achromatic 2x Barlow TV, but I couldn't focus. Next time I'll try with an extension ... Anyway, I'm already satisfied like this, I didn't think myself either.