Quote:
Originally Posted by Profiler
Thanks Don
With the benefit of a wife who speaks French the reviews are very interesting.
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Let me throw a cat amongst the pigeons and make that magazine review worthless
Here is an extract from a post I made on Cloudy Nights regarding that very same review a couple of months ago.
The laboratory tests were conducted by a French Astronomy magazine with whom Televue is one of their major advertising contributors. Pentax on the other hand does not advertise its astronomy products outside Japan.
I have seen countless product reviews conducted by astronomy magazines over the past 40 years and very few of them have portrayed their major advertisers products as inferior to non advertisers products. That's just business. There are some exceptions to this and there has been a previous exception in this magazine. Would the publisher let Televue run second twice in an eyepiece review? Food for thought.
When I read that the overall scores from those tests were that the 10mm DELOS scored 16/20; and 10mm PENTAX XW scored 12/20; I though hmmmm !!! that's pretty amazing, the 10mm DELOS is a 33% better eyepiece than the 10mm PENTAX XW. That wasn't consistent with my experience based on extensive use of both eyepieces and with my extensive use of the 6mm DELOS and 7mm PENTAX XW.
I decided I needed to delve a bit deeper into the accuracy and basis of those laboratory tests.
Here are some very pertinent facts in regard to those laboratory tests.
1) The tests were conducted at F3.5 and at F7. Coma correction was not used in determining the results at F3.5. In the tests at F3.5 the 10mm TV DELOS outpointed the 10mm PENTAX XW, by quite a margin. Only problem here is I don't know anyone who uses a telescope faster than F4 that it is not a large aperture Newtonian and all of the large aperture Newtonian users that I know always use a paracorr at anything faster than F4; 95% of them use a paracorr in any Newtonian faster than F5. So I rate the testing at F3.5 without a paracorr absolutely pointless. Testing at F7 and maybe F4.5 would have been much more realistic and meaningful. If we remove the test results at F3.5 the overall result of the tests are much different.
2) Lets look at some of the specific optical tests
The one which tests optical quality on axis at F7 in red light is interesting. In this test the 10MM DELOS tested at lambda/109 and rated 5/6; whereas the lowly 10mm PENTAX XW only tested at lambda/53 (what a lemon). The same on axis test in green light showed the 10mm DELOS at lambda/133 with a 6/6 rating and the lowly 10MM PENTAX XW rated 4/6 at lambda/86 (what a lemon). Lambda / 53 was the worst on axis optical performance of the 10MM Pentax XW. Dayyam dud eyepiece !!
Now this poses an interesting situation.
Is there anyone out there who can detect the difference in optical performance between either of these eyepieces, in red light and green light?
Is there anyone out there who owns a refractor with a combined optical quality of objective and diagonal in excess of lambda/53?
Is there anyone out there with a Newtonian whose combined optical quality of primary and secondary mirror is in excess of lambda/53?
Is there anyone out there with a Catadioptic Telescope whose combined optical quality of primary, secondary, corrector plate and star diagonal is in excess of lambda/53?
Most importantly is there anyone out there with an eyeball that is close to lambda/53 and also with the ability to detect optical errors at lambda/53?
Truth is unless you satisfy both the telescope criteria and the eyeball criteria you won't see a difference. I know some very skilled observers with some very high end equipment and I don't know anyone who can satisfy both criteria. Consequently, I rate that review as being worth what it cost me to read it, "ZERO". I let my own eyes and telescopes do the analysis for me.
Cheers,
John B