Lunt H-alpha Zoom 7.2-21.5mm first impressions

[michael.h.f.wilkinson]

Yesterday a secondhand Lunt H-alpha Zoom 7.2-21.5mm arrived. The build quality looks decent, if not quite as solid as the MaxVisions or Pentax XW and XF I had been using for solar so far. On the plus side, that means it is lighter, so ideal for travel.

I made a few first observations, comparing it to a 7mm Pentax XW, and a 12mm Nagler at the appropriate settings. Conditions were too hazy to make definite judgements, but the first impressions were good. The FOV is of course rather small, and the eye relief less than I am used to but still OK. At the long end there seems to be a slight reflection from the field stop, but not too disturbing.

I am now dodging clouds and having peeks at the sun, and I like the rapid way I can adjust the magnification to rapidly varying conditions. Well pleased so far.

[Pig]

Excellent news then Michael considering the eyepieces used for comparison   Is the field of view an issue with the sun ?

[michael.h.f.wilkinson]

FOV is not a huge problem, the whole disk fits

[Pig]

That's good then, that's all one needs.  

The full Moon is approximately the same size, by degrees, as the sun from earth thus the zoom should be useful for both.

[AndyWB]

Any further impressions on this yet? I could be tempted by one, and FoV doesn't bother me that much.

[michael.h.f.wilkinson]

Alas, no. grey skies abound. It might clear later today, and tomorrow is reportedly going to be very sunny. I'll post more as soon as I get a chance.

[michael.h.f.wilkinson]

Just gave it another little spin, only against the XF8.5 and MaxVision 20mm at the appropriate settings of the zoom. I did have to contend with some cloud, but the seeing was not bad, as it supported the XF8.5 magnification without difficulties. My main comparison was between the XF and Lunt Zoom, and I must say the XF won by a very narrow margin in terms of optical performance. In the centre of the FOV, the view was more or less the same, but at the edges, the XF clearly has the edge. That does not mean the Lunt is mushy, it is just not quite as sharp as the XF. Comfort-wise there is no contest: the XF wins easily. The 15mm rated eye relief of the Lunt, combined with its much smaller eye lens make eye placement much less easy for me (with glasses!), compared to the very comfortable 20mm eye relief of the XF. This does not mean the Lunt is not a reasonably comfortable EP once you get your eye right, it just is not as good as the Pentax. Compared to the 20mm MaxVision, the difference is smaller, but 16mm vs 15mm eye relief is noticeable, as is the larger eye lens of the MaxVision. The Lunt also displays a reflection off some aperture or edge of lens element at the long end. Not dreadful, but I could have done without it. What is nice about the Lunt is the ease of switching magnification to match conditions. This would work even better if the EP were not used in a helical focuser, as shifting zoom position often knocks the scope out of focus in this case.

Tomorrow conditions should be better, and I hope to give a more full report. I also hope to do some night-time testing.

[Pig]

Nice snappy report Michael, mine has been delivered today so I will also write a review it tomorrow