An apochromat is certainly not necessary, actually my preferred refractor for CaK imaging is a 80 mm f/11.3 TMB achromat. However a 115 mm achromat well corrected @393 nm would be too long, at least for my observing site. This apo is not only well corrected but also much more versatile.

Resuming this thread as I started calcium imaging with a 115mm f/7 Tecnosky triplet refractor. First results seem promising, the scope is better corrected than my previuos ones except the long focus TMB 80. If I am not wrong Peter Zetner obtained some very good images (better than mine) by using of ...

Great animation, Paul. I too experienced that kind of artifacts when wind or turbulence are strong. Sometimes I am able to get rid of the problem by selecting and stacking only few frames and/or adding some very large alignment poins in AS3! within the dark area.

Thanks for the detail. Unfortunately that Meade barlow is now difficult to find except in the used marked but I will try anyway. I tried yesterday to modify an airspaced meniscus Barlow but results were disappointing, no gain in contrast compared with the barlow in the original configuration. May be...

Interesting, thanks for sharing. It would be useful to know which brand is the Barlow you used because not all triplet barlows are equal. The spaced element of many triplets is a converging meniscus which is used mainly to correct the divergence of the marginal rays. However other triplets - some GS...

I think the graf you are showing for SCT spherochromatism in the blue end is way too exaggerated for optical engineers "blue" means the F line that is 486nm. At this wavelength SCs are still usable as one can see from the graph posted by Christian as well as in spot diagrams for SC. However CaK is ...

Absolutely fantastic, Stu.

Is there any tutorial for making animations with IMPPG ? Thks.

To my eyes negative 1 or zero seem the best, however I agree with Valery, send it back, no good.

Fine images, Mark. I too use my Quark to darken filaments through my Lunt-mod scope, my results depend much on finding the best matching tuning of both systems, not always easy to do.

Nice discs Alexandra. If the 100mm is the ED version it should be capable of doing much better than that in fine seeing conditions. I have it and in CaK or CaH is really fine at full aperture.

Getting f/30 by reducing the aperture will produce a faint image unless observed at the lowest possible magnification. Instead try to increase the f.l. with a good amplifier, there is no image degradation, I did it many times with my Quark and it works fine. Changing your yellow ERF with a D-ERF cou...

Quark's etalon needs a f/30 light cone to work properly, better around f/40, so increasing the f/ratio (possibly without reducing aperture) should produce better results. Try different setups and see which one works best.

Hi Roman If your Quark is exposed to sunlight while observing it may become too hot for tuning. For example my one needs only a modest heat input and works best at -5 position. Under the Sun it reaches tuning without any power supply and if connected to the mains the light remains orange. Try shield...

Superb CaK detail, Alexandra, did you take it at full aperture ?

Excellent images, very well processed.

Good result, granulation is evident. With a 0.5x focal reducer you can image the full disc.

Replacing the BF may help however incorrect tuning and poor seeing may also lead to obtain ill-defined images. Hope your new BF will improve things.

Thanks Alexandra, very kind

Thanks to all, this CaK device is indeed definitively more funny than my calcium Quark :D I noted that the filter is recommended up to 100mm aperture, I suppose an ERF is required for larger refractors but the 2" tube end has no thread for my blue CCD filter, is there any way to make an adaptation ?

Having used a Quark calcium for two years I eventually decided to try some CaK imaging. From the European Lunt dealer I found a good offer for a straight-through B600, which I preferred to the diagonal version as it has a shorter optical path (I have also a H-alpha BF1200 ST and indeed it is more ve...

Beautiful discs, Pedro, very sharp.

Nice images, Brian, I liked H-alpha in particular. WL and CaK appear quite dark on my screen, they could be improved by using of curves tool or a high pass filter. I tried to do so but some artifacts emerged at the top limb of the full disc. At full resolution CaK is impressive, very well resolved.

Your CaK discs are really super, Stu, very effective setup for this wavelength.

Thanks Alexandra, Stu.

Actually it does both jobs, cuts etalon harmonics and protects the etalon from excessive heat. Unfortunately this kind of filters are not designed specifically for solar observing and shall therefore be protected by using of some energy rejection device placed in front of them. Based on what occurre...