DPAC venture

[Space Hopper]

I think Paul Leuba has tested plenty more scopes. I find it a fascinating subject.

I also remember he tested a TEC140FL 2 or 3 years ago. 

It tested well, although i don't think it was exceptional, but pretty decent.

More than happy with the performance of my own scope and I doubt 55 year old eyes would notice much amiss anyway.

More of an issue is the grotty UK sky's and weather i subject my scope to......

 

EDIT : it was Jeff B not Peleuba over on CN who did that test. My mistake.

Edited March 16, 2023 by Space Hopper

[jetstream]

2 minutes ago, John said:

I can recall Herr Rohr testing quite a few ED120's (or clones) and the results were really rather better than many expected. My own example seems a cracker 👍

Rohr seems to be a resource many quote eventhough some question his results as is bound to happen espc the interferometer results. Apparently interferometer results are hard to duplicate between units and the conditions they test in ie horizontal vs vertical, atmospheric concerns and type of interferometer used.

DPAC appears to be an easy and accurate test to use and can be easily repeatable. Good opticians use many tests to evaluate optics as they are being made including testing in multiple wavelengths of light.

I think the future will bring many many test results for us to view and this will tell the tale.IMHO.

[jetstream]

10 minutes ago, Space Hopper said:

I think Paul Leuba has tested plenty more scopes. I find it a fascinating subject.

Yes, I read the results and I too find this fascinating. I can say this- DPAC catching on will force scope makers and vendors into providing more consistent optics.

[nicoscy]

I am a moderator on Cloudy Nights and the thread is a challenge to keep running. However, the value in learning more about what we are purchasing outweighs any burden on the moderators. Yes, a sample of one as noted, but only a run of 50, costing $18K in the least expensive configuration, with a waiting period of about two years. I think expectations were set high, and rightfully so.

I am but a humble egg myself in this and trying hard to learn as much as I can on the subject. I "think" that my scopes are quite good - this after using them extensively, but a certain qualitative measure (images via DPAC) and a certain quantitative measure (AOS software) would be welcome (yes, thinking of setting up my own rig at some point), just because. 

DPAC appears to be a relatively simple methodology to use, with parts easy and relatively inexpensive to procure - meaning that this may kick amateur astronomers into a testing frenzy and separate manufacturers in terms of men vs boys. There have been plenty of tests in the past three years, about 20 or so added to a pinned topic and it makes for good reading, plus it allows comparisons.

I hope scope fabricators are taking notice - customers want more and are now learning to check whether they are getting their money's worth...

[900SL]

Personally I think you should have closed the thread after the summary. Discussion about DPAC should be in a separate thread

[nicoscy]

I guess different rules in each forum. Over there, if there is more to discuss in relation to a topic (in relation, not directly), it remains open.

But, that's on CN. I prefer to focus on this thread which I will be viewing for updates as I want to learn more on the subject

[900SL]

I guess drama is good for ratings, right?

[nicoscy]

I prefer less drama and more substance. But, I am one of many and since we are not Borg, no collective consciousness and no assimilations!

[John]

9 hours ago, jetstream said:

Rohr seems to be a resource many quote eventhough some question his results as is bound to happen espc the interferometer results. Apparently interferometer results are hard to duplicate between units and the conditions they test in ie horizontal vs vertical, atmospheric concerns and type of interferometer used.

DPAC appears to be an easy and accurate test to use and can be easily repeatable. Good opticians use many tests to evaluate optics as they are being made including testing in multiple wavelengths of light.

I think the future will bring many many test results for us to view and this will tell the tale.IMHO.

Judging by the DPAC threads on CN, I think that technique will get a fair share of results scrutiny as well and some of it quite "lively". Only to be expected I guess - people can get very sensitive when the soundness of their prized possessions are questioned, even if it is not their particular example 🙄

[nicoscy]

Many test optics. Ed Reis in the UK, Wolfgang Rohr in Germany, a gentleman in a Dutch forum but his name escapes me, and many others.

See here re Wolfgang Rohr's website. Pass through Google Translate and feast your eyes on tests galore!

But, it is slowly spreading I guess...

[jetstream]

2 hours ago, nicoscy said:

I prefer less drama and more substance. But, I am one of many and since we are not Borg, no collective consciousness and no assimilations!

Me too- the test results do the talking so to speak and its hard to refute the DPAC method of testing. Ive talked to opticians and they confirmed the validity of the test. What Im still not sure about is the specs of the flat and possibly testing vertical vs horizontal ie edge distortion in the flat.

My feeling is a flat of 1/10 on the wave front would be great for tworeasons- one for the obvious optical quality and two to add validity to the test ie one less thing for naysayers to pick apart.

The edge distortion is most likely not an issue either but I was just thinking out loud really.

Btw, you are doing a great job under difficult circumstances, my hats off to you.👍

[jetstream]

3 hours ago, 900SL said:

Personally I think you should have closed the thread after the summary. Discussion about DPAC should be in a separate thread

I normally dont care if my threads wander but I dont want it to wander in the direction of criticizing a moderator on another forum and I also dont want this thread to be the focus of the 180mm SV tested, or SV in general.

What I hope to get here is interest in DPAC and some banter about its methodolgy so that I (we) can get on board and do some proper testing, should anyone choose to do so.

Thanks, Gerry

[CraigT82]

3 hours ago, nicoscy said:

customers want more and are now learning to check whether they are getting their money's worth

Whilst I agree that it’s good to have a method whereby you can hold the manufacturer to account… I can’t help but think that if you can’t tell you’ve got a good or bad one by looking through it or imaging with it, then what’s the point of testing?! 

[jetstream]

6 minutes ago, CraigT82 said:

Whilst I agree that it’s good to have a method whereby you can hold the manufacturer to account… I can’t help but think that if you can’t tell you’ve got a good or bad one by looking through it or imaging with it, then what’s the point of testing?! 

One point for me is to compare what I see through the eyepiece as "sharpness" for example to what the fringes indicate.

Another point is to compare manufacturer supplied test reports ie Zygo, whatever to the DPAC fringes.

Many people using low to mid mag might think they have a good optic...  and may have paid a hefty price for those optics. Sure be nice to know we are getting our moneys worth and base purchasing decisions on things other than word of mouth or manufacturer supplied tests, IMHO

Any reason to DPAC test is up to the individual.

[nicoscy]

13 minutes ago, CraigT82 said:

Whilst I agree that it’s good to have a method whereby you can hold the manufacturer to account… I can’t help but think that if you can’t tell you’ve got a good or bad one by looking through it or imaging with it, then what’s the point of testing?! 

I agree. Something that you cannot evaluate, simply does not exist for you. But what about the honesty of vendors, who may rely on 99% gullible customers and simply refunding the other 1%, making a killing in the process by skinning said 99%?

[davidc135]

If an expensive telescope came with a, say, 30 day grace period and there happened to be clouds or poor seeing during that time you would be glad to be able to test it indoors.

Or generally you would like to be able to distinguish between the quallity of the optics and all the other possible causes of disappointing performance.

And besides, it's fun.

David

[Deadlake]

On 13/03/2023 at 16:16, John said:

DPAC can deliver some surprises. Here is one that I don't think many saw coming:

Bench Test of a StellarVue SVX180 Apochromat - Refractors - Cloudy Nights

 

Well if you knew SV was testing red you might. The colour band was not on SV’s site until this blew up and you would of only got a hint if you looked at SV’s Facebook page.

[Deadlake]

10 hours ago, nicoscy said:

I prefer less drama and more substance. But, I am one of many and since we are not Borg, no collective consciousness and no assimilations!

In some ways the CN thread has run it’s course. I do not see any thing more to add once the scope got taken back, unless Vic decide’s to use green wavelength to null the lens too. It’s not the end of the discussion,  it they could be on other threads and maybe less pruning for you. I see you have your work cut out with the NVD forum as well. 😃

[John]

1 hour ago, Deadlake said:

Well if you knew SV was testing red you might. The colour band was not on SV’s site until this blew up and you would of only got a hint if you looked at SV’s Facebook page.

What wavelength of light is hindsight best tested with ? 😁

I think it's been accepted for a while that the most exacting light to test scope optics in is green. 

[nicoscy]

6 hours ago, Deadlake said:

In some ways the CN thread has run it’s course. I do not see any thing more to add once the scope got taken back, unless Vic decide’s to use green wavelength to null the lens too. It’s not the end of the discussion,  it they could be on other threads and maybe less pruning for you. I see you have your work cut out with the NVD forum as well. 😃

We are all chatty people, so as long as people are on point, why stop the flow of conversation? But, there are 220 emails in my inbox now - that’s the “not fun” part of it! As for the NVD forum, it is still going though growing pains I would say. But, I am excited about the technology and what it offers. I think less expensive NVDs will come in the future and make this aspect of our hobby more accessible!

[nicoscy]

6 hours ago, John said:

What wavelength of light is hindsight best tested with ? 😁

I think it's been accepted for a while that the most exacting light to test scope optics in is green. 

Not hindsight as much as being consistent and fair with your marketing and not peddle snake oil off the back of a wagon. If one cares to go to sci.astro group and search for “Stellarvue” and go all the way back to 2000, you will catch Vic and Valery slinging mud at each other. The issue with Stellarvue marketing is a recurring theme unfortunately.

I do hope this becomes a learning experience for all and that SV decides to accommodate the - now a lot more informed - potential buyers. I do think they have the makings of becoming one of the great scope makers of our era, in the same league as AP and TEC for example. But, it is up to them…

Edited March 17, 2023 by nicoscy

[JeremyS]

Well I’ve just read all 37 pages (36 when I started!). Quite a story! And congratulations to @nicoscy for his work as a CN moderator- in real time at some points! His summary on post 637 is very helpful.

Edited March 17, 2023 by JeremyS

[nicoscy]

Thanks Jeremy - we aim to please 😁

[Deadlake]

8 hours ago, John said:

What wavelength of light is hindsight best tested with ? 😁

I think it's been accepted for a while that the most exacting light to test scope optics in is green. 

The point is SV are the only manufacturer I can think of that tests in red, green is as far as I can see an industry standard. No hindsight then, a red flag. Ho ho ho.

Edited March 17, 2023 by Deadlake

[CraigT82]

10 hours ago, davidc135 said:

And besides, it's fun

Well… if you’re the one who’s just discovered your prized $18k scope is a lemon I imagine it’s not that fun! 
 

But I do agree, this testing method and being able to do it at home indoors is a very good thing for the hobby and will hopefully make manufacturers think twice about employing any marketing tricks.

16 minutes ago, Deadlake said:

The point is SV are the only manufacturer I can think of that tests in red, green is as far as I can see an industry standard. No hindsight then, a red flag. Ho ho ho.

I’ve seen plenty of test certificates posted up on here with no mention of the testing wavelength on them, not just SV.