Replacent Secondary Mirror?

I'm thinking about replacing the 2.6" minor axis secondary mirror in my 12.5" f/5 Discovery newt. A quick search reveals at least 3 probable sources:

AstroSystems 1/10th wave (p-v or rms?) pyrex $150.00

Protostar .101 lambda (which might mean ~1/10th wave) pyrex $135.00

Antares Optics 1/15th wave (p-v) pyrex $169.00 (Better wave numbers available for extra $$ from Antares)

Since the supplied secondary from Discovery is supposed to be a 1/10th wave mirror I imagine it would be a waste of time/money to get another 1/10th wave mirror so I lean towards the 1/15th wave (or better) Antares product and I know Floyd B. likes the Antares product.

Any thoughts, opinions or experiences with any of these products would be appreciated!

TIA,

Ed Moran

Hi Ed,
First off, the Discovery secondary may be fine or it may be not too good. When they state 1/10 wave on Discovery, read the print.
[COLOR="Blue"]We guarantee our primary mirrors to be 1/15-1/20 wave RMS or better.[/COLOR]
This is RMS and not PV which is what we normally talk about in 1/10 wave.
To give some perspective a 1/15 wave PV mirror will be some where near 1/66 wave RMS or better. So a 1/15 wave RMS would be no better than 1/4 wave PV most likely.
So, which is better of the other mirrors? Not sure that there would be any difference as long as they are all 1/10 wave or 1/15 wave PV. But, there is a difference in the figure of many flats. Some will be potato chipped and some have wide turned edges and low or high spots all over. Most any flat will have a low edge to some degree.
Take a look at this one that I bought, the edge is slightly lower than the center. But it is a very narrow and slight difference. The majority of the flat is very flat. The edge is covered by the secondary holder, but it would not have effected the view anyway because it is so little difference in actual height. 1/21 wave PV and 1/111 wave Surface/Wavefront. I bought this one for a Discovery 12.5" scope and it worked very well.
I have interferograms of some that were badly potato chipped or other surface problems, so I alway look the the test before I buy. Frederick at Antares will send them to you if you ask. Tell him I sent you and say hi for me.

Attached Image:

I'm thinking about replacing the 2.6" minor axis secondary mirror in my 12.5" f/5 Discovery newt. A quick search reveals at least 3 probable sources:
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Do you have some reason to think that it is not up to snuff??

You can have it tested to see...

jon

Ed,
You may also try Nova Optical, an astromart sponsor. I suspect Nova gets them from Discovery which is the same maker for Astrosystems(at least they were several years ago when I bought mine). Nova has the best price on them and they state they test each one. There's another optical company, (American Optical?), that also makes OEM flats and other optics and might be a supplier to some of these vendors.
If I recall correctly, the main aberration introduced by a poor quality flat is astigmastism, so if it's not present, your present flat is probably ok...