5 replies to this topic

[dhferguson]

Cheers,

 

Does anyone know what the RGB transmissions are for Astro-Tech XWA eyepieces or their clones?

 

Thanks in advance,

 

Don

 

[Starman1]

I do not know figures for every focal length, and it is reasonable to expect up to a 3% variation from unit to unit, but here are some tested figures:

The figures, in order, are RGB, red/green/blue.

20mm  96/94/85

13mm  94/94/89

9mm  96/97/91

7mm  96/94/92

 

The red and green figures indicate they are close to what is theoretically possible with conventional 99.5% transmission BBAR coatings.

Blue transmission likely represents absorption by the glass.

Edited by Starman1, 20 June 2025 - 01:20 PM.

[havasman]

Without personal need for measured data here but having owned XWA models from William Optics, Myriad, and APM over 10 or so years as well as 100^o​ AFOV models from ES and TV I would apply Rolls Royce's description of horsepower and speed of their cars and say XWA transmission is adequate. Fully so.

Edited by havasman, 20 June 2025 - 01:24 PM.

[dhferguson]

Cheers,

 

... and thank you Don.

[Procyon]

I do not know figures for every focal length, and it is reasonable to expect up to a 3% variation from unit to unit, but here are some tested figures:

The figures, in order, are RGB, red/green/blue.

20mm  96/94/85

13mm  94/94/89

9mm  96/97/91

7mm  96/94/92

 

The red and green figures indicate they are close to what is theoretically possible with conventional 99.5% transmission BBAR coatings.

Blue transmission likely represents absorption by the glass.

That's pretty interesting compared to some other 100º samples:

 

Explore Scientific 5.5mm 100° 89.9/89.0/87.9
Explore Scientific 9mm 100° 90.9/86.8/83.9
Explore Scientific 14mm 100° 93.5/90.8/86.9

21mm TV Ethos 100º 91/90/85

 

I found the 7mm, can't find the rest, so thanks.

Would you happen to know the % of ES 25 100 and ES 92's also?

 

I wonder if I'll see black beans if I try a 7mm, like I did with 20mm non twist top types. 

Or add a different eyeguard to it.

Edited by Procyon, 20 June 2025 - 10:17 PM.

[Starman1]

That's pretty interesting compared to some other 100º samples:

 

Explore Scientific 5.5mm 100° 89.9/89.0/87.9
Explore Scientific 9mm 100° 90.9/86.8/83.9
Explore Scientific 14mm 100° 93.5/90.8/86.9

21mm TV Ethos 100º 91/90/85

 

I found the 7mm, can't find the rest, so thanks.

Would you happen to know the % of ES 25 100 and ES 92's also?

 

I wonder if I'll see black beans if I try a 7mm, like I did with 20mm non twist top types. 

Or add a different eyeguard to it.

I got the data by checking Ernest Maratovich's data.

Here is a link.  Click on the name of an eyepiece (underlined) to go to the test report for that eyepiece.

It helps to have an automatic page translator like Edge does, though similar add-ons can be found for most browsers.

https://astro-talks....2&t=1483#p41976

Alas, he didn't do an RGB transmission test for the ES 25mm 100° or the two 92° eyepieces.

I can tell you personally, the 92s are much better eyepieces than the 25x100, which I regard the weakest focal length in the 100° series.

[all 3 tested in a 12.5" f/5.75 (includes Paracorr) under dark skies].

It's too bad ES hasn't released shorter versions of the 92s.  Many years ago, they told me they had designed a 22mm, 8.8mm, and 6.5mm, but I guess we're never going to see them.

Many eyepieces get designed and then never made.

 

As for the 7mm, though its eye relief is tight--12mm--it is easy to use and has zero issues with the exit pupil.

It would be very difficult to get inside the exit pupil and see blackouts.

It is a permanent eyepiece in my kit as long as my astigmatism isn't obvious when using it.

It is the best of the entire series.

It is not usable with glasses, of course.

 

The 20mm has 15.5mm of eye relief.  Perhaps those extra few mm makes positioning the eye a bit sensitive.

I converted from Nagler T6s (12mm eye relief) to Ethos eyepieces (15mm eye relief) many years ago and at first found the Ethos tough to use because of the extra 3mm or eye relief.

The exception was the two Ethos SX, which had a bit less eye relief and I found easy to use.

Several years later, I had zero problems with the Ethos and found the T6s a bit tight.  So part of eyepiece pupil sensitivity is getting used to a particular eye relief.

Edited by Starman1, 20 June 2025 - 11:14 PM.