Opticstar AR90s & Baader Herschel Wedge

[johninderby]

Opticstar AR90s & Baader Planetarium 2" Herschel Safety Wedge Solar Prism

I had been using an older AR90s I picked up fairly cheap second hand for a dedicated white light solar scope with a Baader film filter. Worked very well and it was nice and compact. I had been intending to get a Baader Herschel wedge and found that Astroshop.de had it on sale at Euro 399.00 or about £320.00 (best UK price £409.00). I actually ended up getting it from Telescope Service as they had it in stock and will price match. I also got a Baader 2" polarising filter which comes in handy for adjusting the brightness.

I've also fitted a WO type finder mounting foot to the focuser. Just had to drill and tap a mounting hole and it looks as if it came that way. I already had the solar finder. The finder screen on the back of the wedge is very good but it's often pointing at the ground so the regular finder on the top is convenient. Dug out an old solar shield I had sitting around and fitted that and it does help a lot. Rather than buy a set of rings I simply fitted a SkyWatcher mounting block to the bottom of the OTA and fitted a short dovetail. Works fine, and as I already had the bits the price was right

Now the only problem with the Baader wedge is that it requires a lot of infocus and so won't work on some scopes. Unfortunately on the AR90s I found it needed a bit more infocus travel, and yes I tried a number of eyepieces. But being a bit stubborn I wasn't going to let that stop me. So I unscrewed the focuser, shortened the tube by 20mm, disassembled the focuser and put the focuser body in the lathe and skimmed of the screw thread on the flange so that it was now a tight pushfit in the OTA tube. Then I drilled and tapped mounting holes in the flange and fastened it in place with three screws as typically used on SkyWatcher refractors.

Now to the first test. Compared to the Baader film sunspots were more distinct with better contrast and faculae were also clearer and surface granulation was easier to observe. Another advantage of the wedge is that it will take more magnification. Very pleased with the results. I also tried the wedge with my ZS80FD and it wasn't any better than the AR90s, so for this specific task the cheap AR90s will do just fine. BTW I did have a Lunt wedge for a while, and while it was a bit better than the Baader film, the Baader wedge is noticeably sharper.

Very pleased with the result as it gives me a nice lightweight and portable dedicated white light scope for not a lot more than just the wedge on it's own.

John

[johninderby]

While pleased with the way the set-up is working it's still a single speed crayford. I suppose I've been spoiled by having dual speed focusers on my other scopes and it does make it easier to get the focus spot on.

I could have bought a dual speed crayford and modified the flange to fit but didn't want to spend that amount right now and got hold of a Baader 1.25" to T-thread micro focuser instead. A small fraction of the price and it does the job very well. Just attaches to a T-thread to 2" adaptor and drops into the wedge in place of the 1.25" to 2" eyepiece adaptor. Very smooth and precise focusing.

BTW the manual that comes with the Baader wedge has a lot of solar observing info in it and it's well worth a read even if you're not using a Baader wedge.

John

HERSCHEL_PRISM_MANUAL.pdf