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Great skies tonight, very clear, dark and cold - perfect for the easy to wheel 15" f4.8 dob.

Back to the Pleiades for a different perspective on the object compared to the shorter fl scopes with the Merope neb the specific target. This set up- 1828mm fl, f4.8 with the 20mm Lunt HDC gives a super view of the fan shaped Merope neb. The other features of the Pleiades are enhanced with the shorter scopes and are my preferred choice on the object as a whole. However, the Merope neb itself is well matched to the 15" dob FOV wise and object size in the EP. It is very easy to see this nebula in this scope, direct vision and I don't believe much experience or skill is involved. A bit of the inner lanes show but the FOV is restrictive compared to the SW120ED/TSA120 and the Heritage 130. The H130 shows the Pleiades quite a bit better than the 90mm SV Raptor, which was the first scope to show me the Merope neb.

Another comparison was on M1, the Crab nebula. The 20mm Lunt hinted at structure and the excellent 17.3mm Delos brought more out-but- it is obvious that M1 needs more illumination than I was using, problem is there are no 25mm-28mm eyepieces in the same class as the 2 mentioned.  The 24" f4.1 gives VG illumination with the 20mm Lunt and at a bigger size- this pulls out much more detail, in part due to the eyepiece class used.

The 24" falls short on the Merope though- a bit too big image scale for my liking here.

My feeling is an 18" f4 would be a super scope on most everything and still not too big.

One last thing- the HH was easily visible in both the 20mm and 17.3mm/UHC but on the Flame neb the 17.3 Delos really brought out some bright structure in the pillars and with a VG FOV to keep Alnitak at bay. This 17.3mm Delos is proving itself more and more. Well its time for Colbert now lol!

Edited by jetstream
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Great comparison between focal lengths, a lot of times it's a toss up between FOV and brightness/detail on larger targets. I think of Mel Bartels and some of his faster/shorter focal length scopes (his DIY 6" f2.8 and 10.5" f2.7 in particular). Sounds like you had great conditions, hope the snow isn't too deep! Been quite a mild winter here, temp wise. 

Cheers!

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Interesting account Gerry, the characteristics of the Merope nebula certainly respond to various focal lengths at low power, with a medium aperture dob. The Flame does seem to respond at varied mid power eyepieces. I used my 13E and 10D each conjuring a good balance between contrast and brightness, probably the Delos worked best for a narrower field of view, in my case more pronounced without a UHC filter. Would be interesting to use a 17.3mm Delos. 

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