michael.h.f.wilkinson

Another slight change, with an ES 17mm 92° EP replacing the Nagler 17T4 (leftmost EP, second row) The complete order of battle is: top row: Vixen LVW 42 mm, TV Nagler 31T5 "Panzerfaust", Nagler 22T4 (last T4 in the collection), UHC and H-beta filters, Orion Optics 2" Amici prism 2nd riw: ES 17mm 92°, TV Delos 14 mm, ES 12mm 92°, 2" dielectric star diagonal. 3rd row: Pentax XW 10 mm, TV Delos 8 mm, Pentax XW 7 mm 4th row: TV Delos 6 mm, Pentax XW 5 mm, Denkmeier filter-switch diagonal

Or as anti-tank grenade

Just received my Explore Scientific 17 mm 92° eyepiece. Veritable beast of an EP, and a worthy replacement for the Nagler 17T4. Very pleased indeed

The Askar has a much narrower field of view, and is too close to my Canon 200 mm F/2.8 L lens, the Samyang is much closer to the 100 mm, and much faster than the Askar. And then of course there is the Sigma 105 mm F/1.4. A real beast, but I am not sure it performs well at full aperture.

It is an EOS to T2 adapter from ZWO, which allows the use of their filter wheels with their cameras with the correct chip to flange distance

No idea, skies aren't cooperating

Here is a picture of my DIY solution

They seem to have a simple attachment to the tripod head using a 1/4" thread. That seems flimsy to me, as does the tripod. I use a much sturdier tripod, and use an M10 bolt as attachment directly to the tripod.

I have been using my Sigma 50-100 mm F/1.8 zoom for wide-field imaging, and whilst it works well enough on comets, using my Canon EOS 80D, the smaller pixels and longer exposure times I use for DSO imaging with the ASI183MM-Pro show up deficiencies. As I have a Canon 100 mm F/2.8 macro, I would like to use that instead. It doesn't have the tripod attachment, so I have cobbled together this using a pair of guide-scope rings. Now all I need are clear skies. I will be giving up a whole f-stop (and a bit), but hopefully the image quality will be better. Or perhaps I should get that Samyang 135 mm F/2.

For my APM 80 mm F/6 triplet (which is actaully a bit more demanding of eyepiece quality given it is faster than the TFC76), when not using the 2" diagonal (something I would really consider getting, it gives a FAR wider FOV), my set either consists of MaxVision 24 mm 68 deg (works like a Panoptic 24 at these focal) Vixen SLV 15, 9 and 5 mm if I want to travel light, or MaxVision 24 mm 68 deg Delos 14 mm Pentax XW 10, 7 and 5 If I do take the 2"diagonal, I replace the 24mm with the Nagler 22 mm T4, or even add the Nagler 31 mm T5 "Panzerfaust". These latter give awesome wide-field views.

Galaxy hunting is exactly what I have in mind for these EPs

Rather excited that I have been able to find a second-hand ES 17mm 92° EP for a very reasonable price. I love my 12mm, which replaced the Nagler 12T4. Now the Nagler 17T4 meets the same fate. The new EP should arrive on Friday.

Double stacking a Lunt Ca-K module (1 nm bandpass) with a Baader K-line filter (8 nm bandpass according to Baader) should not have any discernible effect on passband, but can reduce overall throughput. What does help a lot in imaging in Ca-K is the use of an ERF that transmits Ca-K, to reduce heat and therefore turbulence in the optical tube. I was lucky enough to get a second-hand Beloptik Tri-Band ERF (apparently, there are only six of these), which transmits bands around Ca-K, Solar Continuum and H-alpha, but I gather that Aries Instruments makes dual band ERFs. I really notice an improvement in sharpness if I install the ERF.

Cracking image!

Much depends on the exact shape of the passband. Double-stacking two H-alpha filters generally gives a 1.4x reduction of bandpass, as you would expect from Gaussian profiles. If however the bandpass has a roughly square profile, the resulting passband will not be much narrower. Much also depends on the centre transmission. If it is near 95% the result will be a maximum transmission of around 90% (0.95 squared). If it is much lower, the image will be much dimmed.

I was considering one of these filters until I got a bonus for working 25 years at the University of Groningen. That allowed me to go for the Lunt (one of the comparatively rare pieces of new kit I own). They are very pricey. I have heard of people double-stacking the K-line filter to get a narrower band. Would that help, do you think?

Nice images with great detail. Am I right in thinking the Baader K-line filter is wider in spectral transmission than the Lunt Ca-K modules?

Cheers Martin, I do not doubt I will do more of this kind of combined imaging

Just did some experiments by blending O-III into G and B bands and S-II and H-alpha into the R band of the RGB image in APP, then using hue and saturation components of the resulting image together with the H-alpha image as luminance channel to create a Ha-SII-OIII-RGB composite image. I still need to experiment more, but i quite like the result May have pushed saturation too far. I am thinking of constraining the saturation channel by the luminance channel, so the saturation is only pushed in bright areas, not in the background.

Last night, with @MartinB's advice on going for Ha-RGB rather than SHO or the like on the Flaming Star Nebula in mind, I grabbed 2 h 40 minutes worth of RGB subs using the ASI183MC rather than the ASI183MM-Pro behind the Sigma 50-100 mm F/1.8 zoom. I would have liked more, but clouds cut the session short. The result after stacking wasn't too impressive: There is just a little nebulosity visible, and the stars tend to bloat a bit. Nonetheless, some of the blue reflection components are visible, so I decided to combine this with this image: Which is 2 hours (and 2 minutes) of H-alpha data obtained on February 27 and March 2 with the ASI183MM-Pro. After combining them in Gimp, denoising them in Affinity Photo and another stretch and crop in Gimp, I am quite pleased with the first result There are still some colour gradients I want to tackle, and I would like to see whether mixing in O-III and S-II data might help, but I am rather chuffed with this first result. More data to get rid of noise is of course also need.

Managed 4 hours and 48 minutes on the Spaghetti Nebula, using my Sigma 50-100 mm F/1.8 zoom at full aperture and 100 mm, with the ASI183MM-Pro, and Baader F/2 H-alpha filter. Stacked, gradients removed and automatic stretch in APP, and some tweaks in Gimp I should perhaps use a bigger aperture for this, and create a mosaic, but I am quite pleased with this first effort on a difficult target

Had to stop after 4 hours and 48 minutes of data. Not bad for a predicted 98% cloud. Single subs definitely show hints of filamentous structure.

2.5 hours in the bag. Things still working smoothly

Will try to get RGB later, perhaps with the ASI183MC

Really transparent skies here, despite Clear Outside suggesting 96% clouds. I set up the ASI183MM-Pro with Sigma 50-100 mm F/1.8 zoom at 100 mm and full aperture with a Baader F/2 H-alpha filter. Will keep shooting until the skies cloud over. I am certainly in the right place, just one or two very faint hints of nebula showing. I will need a lot of data to make this work, I suppose