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By Steely Stan
Now I've got my telescope working and I'm regularly shouting at the sky with cloud-rage, I'm starting to think about eyepieces. My telescope (Celestron Nexstar 8SE) only comes with a single 25mm Plossl, so my thinking was to lay hands on a zoom, say 7-21 or 8-24, and work out what settings I use most and then buy dedicated fixed focal length eyepieces accordingly.
With that strategy in mind, I've been waiting to get lucky on flea-bay for a Baader mk 3 or even mk 4 zoom but its such a waiting game not knowing if you can win an auction. - looks like about 2 a week come up. There seem to be three options...
Get a brand new Baader - £185
Lurk on eBay till you get lucky - £100 to £125
Lose patience and drop a crafty £40 on a SVbony 7-21 and find it good enough to perform my experiment, or perhaps better than the price might indicate.
Anyway, the point of this is to ask, do the better quality, and probably pricier zooms earn their corn becoming "keepers"; or do they inevitably get relegated when one finds one's sweet spot with two or three fixed eyepieces?
as a follow up of the discussion on 12mm planetary eyepieces: [settled] 12 mm planetary eyepiece ortho or zoom I though I share with you my experience with my newly acquired EPs which arrived last Monday from Aunty FLO 😉. Just before placing an order, I had a change of mind and went for the 10 mm BCO instead the Q-turret barlow. So here is the list of EPs in this comparison:
Hyperflex 7E1 Zoom: 7.2 - 21.5 mm (which has already a very good reputation as we all know) Baader Classic Ortho 18 mm Baader Classic Ortho 10 mm Seben Super Plössl Zoom: 8 - 24 mm (same as Skywatcher, Starguider, Zhumell, Agena, ....)
So here are the contenders. I am well aware that all those have been reviewed and compared, but I though I share my experience with them in the hope that somebody finds it useful.
The comparison was done with my 180 SkyMax Mak-Cass, set up with the original VB, an Omegon ADC, a TS-1.25" star diagonal and then the EPs. In this configuration, which works really well to correct for atmospheric dispersion, my scope has an effective focal length of 2940 mm. I had the chance to use the EPs two nights in a row, one with ok seeing and yesterday with good seeing conditions. After cooling the scope for about an hour (where I try to place the scope outside for cooling when the outside air temperature is the same as the storing temperature of the Mak, about 24 deg C) I went to work comparing the EPs. Each comparison was done for about an hour, where I switched EPs back an forth, using the orthos as baseline for quality.
Comparison on Saturn at 10mm, so the BCO 10, the Hyperflex at 10 and the Seben at 10 were compared. That's at 294x magnification:
The BCO 10 is really sharp (as expected) and to me surprisingly comfortable to use. I was initially sceptical about the 8 mm eye relief, however for me it works and thus gives superb views. 52 deg FOV is also very comfortable. The Cassini Division was clear and easily discernible. The Hyperflex, even though with a smaller FOV, was very close to the performance of the BCO 10. Also expected, I read a lot of good reviews on the Hyperflex. Again Cassini Division nice and clear. The Seben zoom also performed, however noticeably less good than the Hyperflex or even the BCO 10. Basically I missed some sharpness, obviously in comparison with the BCO, but also with the Hyperflex. For my eye it was harder to make out the Cassini Division through the Seben. Comparison on Jupiter at 18 mm: BCO 18, Hyperflex and Seben at 18. That's at 163x magnification. Here a picture of how Jupiter should have looked like to describe what I managed to see:
Again the BCO 18 gave superb views, sharp with lot's of contrast (as expected for an ortho). Quite some structure visible in the cloud bands.The two main bands where easy to see, no problem there. I was able to see the short dark band below the lower main band, as well as the eddy structure to the right of it (referring to the picture above). I have to say I was impressed. The Hyperflex zoom was quite up there with the BCO, maybe a bit less contrast, but I still could make out the short dark band. With the Seben zoom I had a hard time discerning the short dark band as well as the eddy structure to the side of it. Would I not have known where to look, I would have missed that. So noticeably less contrast in the Seben. Summary comments:
Using the BCOs as baseline, they both produce very sharp and contrast rich views. The 52 deg FOV is very comfortable to view planets. As said I was surprised how comfortable the BCO 10 is to use even though with its short eye relief (8 mm). Obviously not useful to people who have to wear glasses. The Hyperflex zoom is quite close to the BCOs, even though with a narrower FOV. Sharpness and contrast are comparable. Probably one would not switch too often to the BCOs and happily observe with the Hyperflex. The Seben zoom is a good EP, but not there with the Hyperflex or the BCOs. To my eyes its a workable zoom, but you miss out on details of the planets with respect to sharpness and contrast. I can recommend going for a Hyperflex (as so many have said before) if your are looking for a zoom EP. These three EPs, BCO 10, 18 and the Hyerflex are a very functional base set for a 180 Skymax. BCO 10 very sharp on Saturn (looking forward to see Mars with that). BCO 18 produces contrast rich views of Jupiter. And the Hyperflex for everything between 136x - 408x 😉. Maybe another fixed focal length EP in the 14-15 mm range, just to bridge the gap between the BCO 10 and 18. However the Hyperflex does a great job at that already. A yes, and I really can only recommend an ADC. Without it the cloud band details on Jupiter disappeared even in the BCO 18 and the typical blue/red colour seams were clearly visible. Clear skies,
Does anyone who has one of these zoom eyepieces know if there is a t-thread hidden under the twist-up rubber eye-cups like there are on some other zooms?
I don't have a zoom in my set yet and don't want to break the bank. I just aim to use it mainly for visual e.g. being lazy with one 'no faff' eyepiece or when I'm being more dedicated, scoping out the seeing at different magnifications before changing to a dedicated eyepiece.
I'd only use it for occasional photography but would rather buy one with a T-thread.
For reference here are the different branded versions I can find:
OVL Hyperflex version: https://www.firstlightoptics.com/ovl-eyepieces/hyperflex-72mm-215mm-eyepiece.html
Skywatcher Hyperflex version: https://www.365astronomy.com/SkyWatcher-HyperFlex-7E-7.2-21.5mm-High-Performance-Zoom-Eyepiece.html
I had read in the previous thread that the Lunt version of this zoom is also generic but the only one I can find looks quite different and is twice as expensive and has a different field of view so not sure about that?
Thanks for any feedback (or any other recommendations for circa £100 zoom lens that might have a hidden T-thread)!!!
as well today the sun is shining brightly here. I set up the Lunt to have a look at it, at first just for observing. However, somehow I cannot resist and have to do a sketch This time I've chosen reddish pastels on grey paper to better catch the color of the view in the eyepiece.
Telescope: Lunt LS50THaB600PT
Eyepiece: Celestron X-cel 10mm
Date & Time: May 15th, 2020 / 1400-1430 CEST
Location: home terrace, Dusseldorf region, Germany
Technique: red and orange Koh-i-Noor pastels and pastel pens on grey Canson Mi-Teintes pastel paper
Size: 24 x 32 cm
Clear (and sunny) skies!
I finished observations of the Mizar A spectroscopic binary.
Calibration for the Hα line made on water lines contained in the Earth's atmosphere.
I used LowSpec spectrograph with 1800 grooves/mm reflective holographic grating, APM APO 107/700, QHY163M camera and HEQ5 mount with guiding.
It turned out that the Earth's movement practically compensated for the radial velocity of the Mizar A system.
Based on the analysis, I received the result:
vr = -8.8 km/s
in fact the system is approaching at a radial velocity of -6.3 km/s.
I also determined the phase plot of radial velocities based on my measurements for the Na (together for both lines) and separately for Hα line:
Error is based on half my spectral resolution (0.2 Å/pix corresponds to rv = 10 km/s). Each measurement corresponds to the stack a few images.
The most important purpose of observing this binary system was to record the historical Ca II line (often called as CaK, 3933.66 Å).
The distances in the violet part of the spectrum are almost 2x smaller than the corresponding shifts for the Hα line. This line initiated the discovery of spectroscopically binary systems, and Mizar A was the first discovered system of this type.
These were the spectroscopic observations in the 19th century:
I've made several observations of this line in the last two weeks:
Animation showing the changes in the CaK line based on my observations:
Not only the Ca II is split, but the surrounding lines also, shown below in a wider environment:
Balmer hydrogen lines are becoming more dense as Balmer's gap approaches (3646 Å).
Observation result of the Hα line:
And animation showing the changes in this line:
The Na I doublet was much more difficult to observe, because stars with A spectral type contain very faint lines of this metal:
Animation showing the changes in the sodium doublet:
We received the sodium quartet