SR4 v TMB, lol

[Ags]

I gave my grandson his Celestron Firstscope today and he pronounced it 'awesome'. Out of curiosity tonight, I tried the SR4 EP that comes with the firstscope in my Mak. I compared the view with my 6mm TMB clone.

I was a bit surprised that the view was more or less comparable, the SR4 actually gave an acceptable view of Saturn, which is the last thing I was expecting.

I had the same result when I compared the FirstScope's Huygens 20mm to an Omni plossl 15mm I was thinking of giving away with the scope. To my surprise the Huygens gave a sharper view in the FirstScope. But I do suspect there is something wrong with my Omni plossl.

[david o]

You'll find that long fL 'scopes (like your Mak at 1325mm) are very forgiving on EPs.

Someone correct me if I'm wrong, but I think that it's something to do with the shallower light cone of long fL optics being less demanding on the lenses within any given EP.

[cs1cjc]

I am not surprised by this. I find the TMB eyepieces (and clones) are easy to use with acceptable eye relief (for glasses) and a nice field of view, but they give less contrast in details on jupiter and saturn than with barlowed Antares (similar to Baader) orthoscopic eyepieces.

[Ags]

I think it may also have something to do with the narrow (maybe 25deg) AFOV of the SR4 - I read somewhere that wider fields tend to introduce more scatter. And of course the SR4 only has two elements... A true high performance miracle EP! Lol

I suppose the moral of the story is I need to buy some orthos.

[david o]

I'd heartily recommend Orthos for anything where their narrow AFoV (~ 40-45º) and generally short fL isn't an issue - lunar, planetary, double stars and small, bright DSOs.

I've built up a set of the volcano tops and they work really well in both my big Mak and the small 'frac. The 25mm seems to "fit" particularly well with the Skymax 180.

[Ags]

I had another go with the SR4 and the TMB 6mm in the early evening, with my grandson assisting in the comparison. The seeing was very stable.

When we changed from the 6mm to the SR4, my grandson announced he could see a gap in Saturn's ring, which was not apparent to him with the TMB. He was not looking for or expecting the Cassini Division, so that seems a true observation. Regardless of eyepiece, I have not managed more than doubtful glimpses of the cassini division myself.

We tried switching between the EPs a few times, and the general impression remained we were seeing more and clearer through the SR4. That despite the fact that 300x magnification should be far too much for my scope.

Obviously seeing and differences of scale play a part, but I must say I am dissapointed - I had expected my TMB clone to outclass the little SR4.

Eye relief by the way did not seem to be much of an issue for us in practice, even though SR4s are commonly derided for their poor eye relief.