Megrez problems

[mch62 (Mark)]

Star test images from Megrez .
These 5 are with out a barlow using a ToUcam.
Going from no2 outside focus focused to no6 inside focus.
Frames extracted and the best ones picked.

The conditions were quite good as seen from Andrews Newtonian and his 100mm f5 Achromate at 4/5, and there was a first 1/4 moon .
We allowed the scope to cool down inverted and no obstruction in the focuser for 1hr and Dan had the scope case open all afternoon so that the scope was not insulated.

It was initially obvious that there was some improvement from before visually .

Visually we used a Radian and orthoscopics eyepieces with and with out an Orion 3 element 2x APO barlow and a 4x Powermate

Imaging we used the 2x Barlow as well as just the imager.

Overall the central part of the star tests was steadier than before but still showed the same heat like distortions and haze masking the inner rings.
At first you would say that this is heat distortion except that on both nights it showed no improvement over the whole night. 4hours plus.

You would assume there to be some improvement over 4 hours if it was heat.
The temperate drop on both nights was not extreme and the nights were fairly mild for winter.
So the objective should have been able to come to temperature .

You can see the centre is a wash with a blue and green haze and the focused star has a blue halo surrounding it .
The focused star a tad worse than my Celestron 80Ed or Tony's Orion Ed.
My star test pics can be seen at the review section for comparison and show a very well defined ring system.

Even Andrews old F5 Achromate showed a better star test.

No mater how far in or out of focus we racked the Megrez it just would not show a well defined diffraction rings or show the central star and you can see the outer was better than the inner focus.

The last thing we did was cranked up the power on the moon to 90x per inch ---280x , and was surprised to see a fairly well defined view with little atmospheric heat distortion.
This was quite a good result .
Jupiter would not take this magnification and 112x was it's limit .
This had me thinking that may be the star test was acceptable ????

This had me thinking all the way home , so when I got home that night I pulled out the Celestron with the same power and no cool down and it was still a better image.
90x per inch is pretty dam good for a refractor thou and as Dan points out low power views are very good..
This is what i bought my ED for low power imaging and not high power planetary use.

As I have said before , mechanically the Megrez is first class but optically there is some thing amiss.
If this is a heat issue life is to short to wait for the triplet to come to temperate.

Williams did offer Dan the choice of spending even more money and buying the Florite APO.
From what I have read on the forums this appears to bve the model of choice for imaging but comes at a much higher price.

I am just hopping that some one at the Queensland Astrofest will have another Megrez triplet or another brand of triplet APO there that I can have a looky through just for a comparison as this has got me baffled.

Mark

[mch62 (Mark)]

This lot with the APO barlow.
Notice the distortions at 180degs to each other????????????

The powermate was the same and is obvious that the Megrez did not like the higher powerfor the star tests.

[ausastronomer (John Bambury)]

Mark,

I have to say those star test images are not good. But as you rightly allude to, the important issue is not how it star tests out of focus, but the quality of the in focus images, we don't do a lot of observing out of focus However, for a supposedly premium triplet it should star test a lot better than that IMO.

CS-John B

[grandpanancy]

Thanks for posting the star test images Mark!!!

Cheers
Dan

[mch62 (Mark)]

I have never had such a difficult time star testing an optical system before , but then i have never had a APO triplet to test before.
No mater how much we racked the focuser or waited for cool down it just didn't want to play ball.
A real mixed bag.

I had my cheapy 20x80mm triplet binoculars(not an APO) apart a week ago re blackening the interior of the barrels and fixing a few little annoyances and did a star test image from one of the individual barrels with the original eyepiece and prisms removed and an old 3x barlow and a12.5mm orthoscopic held in place , like a telescope system.
Any way it was easy to produce a very nice star test pattern inside and out side focus and colour was obvious but not what you would expect from an f4ish triplet lens assemble at that magnification. 80x approximately
Worse colour than the Megrez but not as bad as an f5 Acromatic refractor.


I will attempt to get a TouCam image from them after Astrofest and compare to the other refractor tests done to date.
I also will be doing a Bino review before I destroy them between them and a pair of Celestron(Vixen) 11x 80's .

I love pulling things like this apart and there only fairly new.
Putting them back together was not as much fun due to the very simplistic prism mounts.
I tried different wide field eyepieces to see how they work and have toyed with the idea of using the objectives and making a neck friendly 45deg binocular , with interchangable eyepieces.
By my avaitar you see why.