DPAC venture

[Rusted]

Optical flats can be tested under water with a monochromatic light source.
I used a mercury monochromatic yellow light when making 3 x 8.75" Monax flats.
Unfortunately I used a [freely donated] matching blank with a chip on the back.
That was enough to twist the whole blank into being worthless for cold pressing polishing laps.

[John]

5 hours ago, 900SL said:

It will certainly lead to higher prices, and people returning perfectly useable scopes because their test results were less than ideal.

 

I wonder if it might also lead to the situation where used scopes that have not been DPAC tested will be harder to sell or will need to be priced at a lower level ?

 

[jetstream]

2 hours ago, John said:

You ED120 is clearly at one end of the performance scale for the model and mine must be closer to the other end !

DPAC will tell us both how good our scopes are

[Deadlake]

7 minutes ago, jetstream said:

DPAC will tell us both how good our scopes are

Also just as good as the tester... 

I wonder what it will do now scopes from premium manufactures will be DPAC tested, do you send them back?

[jetstream]

11 minutes ago, Deadlake said:

Also just as good as the tester... 

The beauty of DPAC is that it doesnt care about the tester- no fringes will be seen if the flat isnt square to the objective, so as long as the flat is reasonably flat the results say it all...

You want to get your LZOS DPAC'd?

[PeterW]

7 hours ago, Captain Scarlet said:

@PeterW?

Happy to ask, not sure what’s currently used, think Dave has retired.  They measured some ultra flat ceramic disks I had some years back on a zygo. You can use a liquid surface if it’s big enough. Met a chap from PTB once who had an autocollimator that could measure the earths diameter from the curvature on a cup of water…..

Peter

 

[jetstream]

6 hours ago, nicoscy said:

The product as tested should consistently be of a high standard.

Yuris response to the recently tested TEC 140 on CN was very professional and validated the tester and his DPAC results. An excellent response which is noted- as I might be looking at a large (ish) refractor and TEC is top on my list.

[John]

54 minutes ago, jetstream said:

DPAC will tell us both how good our scopes are

Well that is the interesting thing isn't it. I've been very happy with my ED120 for the near decade that I have owned it. Let's say that someone (it won't be me) DPAC tests it and the results show that it is a mediocre scope.

This could have 2 effects:

- my enthusiasm / enjoyment for the scope is dampened, which would be sad.

- my confidence in my observing ability would be dented, which would also be sad and might even lead to me pulling out of the hobby.

But I guess that "knowing the truth" is more important than anything else 🙄

 

 

 

 

[jetstream]

2 minutes ago, John said:

. Let's say that someone (it won't be me) DPAC tests it and the results show that it is a mediocre scope.

Why would you even consider that it could be a mediocre scope given the views?

My 120ED might have hope as I believe collimation is off a bit and also wonder if the lens assy is decentered a squeak. I dont know but I hope DPAC illustrates the issue which can hopefully be rectified.

I bought the TSA120 as a scope to which others are compared to and to my eyes its vg in its role. I can see what @mikeDnight is talking about I think- and I believe it to be resolution with respect to contrast ie MTF resolution. The TSA 120 showed this on a set of crater features the other night-  while both the apertures should have shown the distinct features because of their size only one did...

I believe that what we are going for here is contrast- actually contrast is everything to me- and having a balanced colour correction of high spec in a smooth set of lenses greatly adds to this.IMHO.

 

[Highburymark]

Three things:

I second Jeremy’s comment earlier - I think Nicos has done a great job moderating the CN thread. Rather you than me mate……

I’ll follow your DPAC progress with interest Gerry. I don’t think you need a justification for investing in this gear besides an interest in optics. But whether I’d submit a telescope I am entirely happy with for testing is another matter. Perhaps it would show up my own shortcomings as an observer more than anything else……

With the quality of premium refractors so high and consistent these days, the CN thread has made me wonder the ramifications of amateurs having access to kit measuring how solar Ha etalons perform. Compared with expensive apos, the variation in etalons is dramatic - and yet a few solar experts are now able to test Ha filters with hydrogen spectrum tubes. That really could shake up the market. 

[Deadlake]

1 hour ago, jetstream said:

You want to get your LZOS DPAC'd?

Both where tested in the green, thr interest would be the drop off in the red.

The only scopes with a high poly Strehl I can think of would be an AP110GTX and Zeiss APQ’s but I stand to be corrected…

[900SL]

I have no idea about the nuances of optical testing or theory, but I'm becoming a smatterer from this convolution, as are many I suppose. I kind of accept that a fool and his money are easily parted, being an imager with no idea about optics

I'm pretty happy with my feeble 90mm though. Should I be concerned about this zygo certificate, or any disingenuity therein?

 

 

 

[jetstream]

8 minutes ago, 900SL said:

Should I be concerned about this zygo certificate, or any disingenuity therein?

I dont see an aperture on the test? How come the fringes are all hooked in one direction? A testing mis alignment maybe?

 

[jetstream]

1 hour ago, Deadlake said:

Both where tested in the green, thr interest would be the drop off in the red.

The only scopes with a high poly Strehl I can think of would be an AP110GTX and Zeiss APQ’s but I stand to be corrected…

Lets throw 'er on the DPAC and see what she says I am very interested in how LZOS handled a 130mm f6 spherochromatism wise... seriously- you in?

[jetstream]

1 hour ago, Highburymark said:

Compared with expensive apos, the variation in etalons is dramatic - and yet a few solar experts are now able to test Ha filters with hydrogen spectrum tubes.

We are on the same page Mark- this same thought crossed my mind ie how to test etalons. The variation in them is why I'm waiting for a while before plunging in- I need more education on them, before blowing a wad of cash one one.

[900SL]

19 minutes ago, jetstream said:

I dont see an aperture on the test? How come the fringes are all hooked in one direction? A testing mis alignment maybe?

 

90mm f6 and I have no idea

[jetstream]

48 minutes ago, 900SL said:

90mm f6 and I have no idea

Thats the thing- is this a batch test of one scope of your type or is it your actual test report. I think but dont know many of these tests are marketing tools... all this doesnt matter if your happy with it.

[Rusted]

Should we now automatically demand a photographic DPAC test?
With witness signatures on every lens cell?
What about adding AI image handling?
Let's throw in "typical seeing conditions."

Why stop there? Simulation of aging eyesight?
A smidgen of "visual acuity" or none at all? 
Decades of visual observing experience on similar objects?
Or none of the above? 
DPAC RAW? Or DPAC Lite?

Isn't this optical snobbery a sign of serious self doubt? Buyer's guilt?
That the huge sums being asked for "premium optics" might just be a fancy sales pitch.
But we have no real idea if it is a scam because we have no valid test to prove it.. yet?
Can we trust our own eyes to measure to £kx tolerances?

Has optics become Hifi? Where only subjective nuances of "golden eared reviewers" are the accepted measuring stick?
Who here has the "golden eyes" worthy of testing our kit to be validated as "pukka?"

 

[Deadlake]

Well Vic has responded

https://www.stellarvue.com/dvx-optics/

For AP null in red and for visual null in green.

Is it as simple as that?

Edited March 18, 2023 by Deadlake

[900SL]

8 hours ago, jetstream said:

Thats the thing- is this a batch test of one scope of your type or is it your actual test report. I think but dont know many of these tests are marketing tools... all this doesnt matter if your happy with it.

It's specific to the serial number of my scope, so the actual test report. I have to confess I have no idea what most of it means, or whether it is accurate.

I use the scope for imaging and I'm  happy with the results. No significant issues with abberations AFAICT 

 

[900SL]

26 minutes ago, Deadlake said:

Well Vic has responded

https://www.stellarvue.com/svx-optics/

For AP null in red and for visual null in green.

Is it as simple as that?

I would say no. The initial post on CN started a bush fire which may seriously damage or bring down the business of SV... which is why I cautioned about locking the thread earlier.

The most recent post there raise the potential commercial and legal consequences succinctly...

 

[JeremyS]

1 hour ago, Deadlake said:

Well Vic has responded

https://www.stellarvue.com/svx-optics/

For AP null in red and for visual null in green.

Is it as simple as that?

Seems odd. Those that have bought SV until now seem therefore to have ended up with scopes optimised for imaging, even though they might be visual observers. What a mess!

Edited March 18, 2023 by JeremyS

[CraigT82]

19 minutes ago, JeremyS said:

Seems odd. Those that have bought SV until now seem therefore to have ended up with scopes optimised for imaging, even though they might be imagers. What a mess!

It also contains this wording, copied verbatim, which is just plain wrong:

CCD and CMOS cameras are most sensitive to red light

…and this section just screams ‘damage limitation’

We are making a large investment this year in a customized phase shifting laser interferometer that will allow us to figure our objectives in green light creating high strehl optics optimized solely for visual users. These telescopes will be made with a slightly different part number using the prefix: SVX-G. This will differentiate if the telescope optic is nulled in green light or red light. SVX-G optics will be made for discriminating visual observers.

Edited March 18, 2023 by CraigT82

[JeremyS]

3 minutes ago, CraigT82 said:

It also contains this wording, copied verbatim, which is just plain wrong:

CCD and CMOS cameras are most sensitive to red light

 

Hadn’t spotted that, but you are right. My mono CCDs are red sensitive, but not good for those doing imaging with tri-colour detectors 

[Deadlake]

Here are some LZOS Strehl data points across the spectrum:



An AP110GTX as well:



Not sure why SV has gone after red, when the above do well in the red and the green...
SV is aiming to be high end so I've pulled these in.

Edited March 18, 2023 by Deadlake