Adam J

As a scientist and statistician I would say that maybe its not possible and that you just got lucky in your guessing. Unless you can see a clear pattern over multiple observation sessions in which you average more than 2/4 correctly identified then it is just too easy to fluke 2 out of 4 (incidentally the rate of correct ID that you would expect on average through random chance alone is 2/4 correct).

Yes but its not as pretty to look at.

Very impressive in terms of signal from such a short exposure. The thing that has put me off a RASA though is the spot diagrams which show spots of 8um or more at the centre of the FOV, hence not too sharp for such a large aperture. Can you or Olly or Gorann maybe comment on sharpness in comparison to some of the optically slower alternatives? I do note that this is 2xbin though. Adam

I would kill it with UV before removing it with the alcohol.

Yes, I think that you are lucky really as with the modular design of the Borg you should be able to easily get to the rear lens surface with a isopropol on a pure cotton bud.

Specifically a UVC bulb, lower energy UV will not sterilise the surface.

Vale should be obvious as to which one you have.

Any chance the filter itself is incorrectly labelled? I have heard it before shine a light through it. Does it look green?

Just a little test image to get the bugs out of the new ASKAR FMA180 mounting system.

I always thought that the 115mm fpl51 triplet from TS optics was a great price to performance.

Yes good test. I would say you need to remove some backfocus maybe 1-2mm to get a flatter field. I think this is the issue as opposed to just focus as other have suggested.

Not everyone else, I would go mono LRGB too and fast cycle the filters to ensure I get a full set. Requires and autofocuser though. Mono is just faster if slightly more work.

The 100 without question. Aperture rules and you will not notice the additional CA. I assume they are both doublets.

Personally I would go with the spacers as I have tried the varilock an it's too fiddly for me.

Yes will work.

Do you have it set in bin 1?

I will not be swapping my AD 5nm set out for the baader 3-4nm any time soon. But I would say that something is actually wrong with that OIII if baader replace it we will know. That's a very bright star though.

The reflection from the sensor is the strongest. But you also get a grid of reflections from the micro lens array. So its more complex than that. But still the primary sensor reflection is brightest by some margin.

Yet the reflection is blue so its not the red light that's causing it. Perhaps UV, so would be interesting to place a UV/IR cut in line with the filter.

Maybe but why only that stat and not the others?

You cant do much about it its because one of the two spider vane pairs is partially blocked by the focus tube and hence less diffraction will take place. Also the secondary is offset so wider in one plane than the other again blocking a portion of the spider. Have you cut your focus tube down??

I have done exactly this technique myself on a modified DSLR and the answer is yes there is a danger if you use a too higher power laser, a low power 1mw red pointer is fine, shine a 500mw blue laser and at it and you are going to burn a hole in the sensor. Adam

not sure its that to be honest. I would expect that the ring from a filter reflection would be much larger than that. If it reminded me of anything its gravitational lensing but this is something that you would normally only see on large galaxies. It is very odd, I would be interested if you can see it in all your subs of just the stacked image. It would also be interesting to look at more recent images of the heart and see if its something new. Excluding these possibilities its probably a processing artefact. Adam

That doesn't appear on my 2019 image of the heart nebula. Is this narrow band? It's possible it's something that only shows up in lrgb.

1.25 are fine for that scope and I would not use unmounted unless I needed to as they are quite fiddly.