82 replies to this topic

[DAVIDG]

 Merry Christmas too All ! I hope Santa left you all some amazing optics !

 

 "  It would take a 3mm turned edge (which is really pretty severe) to affect 10% of the optical surface. "

Just to put that in perspective, a 3mm turned edge is just under 1/8" in width. In DPAC that would look pretty small and from what I see on many DPAC images  that is the size I see. 

 

   Also you have to remember the size of the  slope of the error is what is doing the harm. A turned edge has  a large slope  so  it throws  the light way out of focus.   You can have what looks like an ugly zone in the middle of the lens and  it does less harm because the slope is smaller then errors at the edge.

 

  " David, how would I repeat the double pass Ronchi test using an incandescent bulb in place of my white LED? I didn’t think they made incandescent bulbs small enough to fit into my Ronchi grating holder. Or am I misunderstanding what you meant?"

 

    Yes that is what I'm saying. I use a light bulb that is used in the mini Maglite flashing lights. They are very small and also bright. In  a well color corrected lens you will see very little color on the edges of Ronchi screen or when you do a knife edge test at the best null. The more color the worse the chromatic aberration.  As I said  you have  to combine both spherical correction and also the color corrections to determine how well the lens is made. 

 

 Like these https://www.amazon.c...WoaAtX_EALw_wcB

 

    In general what I see  with the DPAC images posted are well corrected lens that will  give great images especially at the prices they are being sold at. It is a great time to be amateur astronomer ! 

 

           Merry Christmas and Happy New Year !

                         - Dave 

  

[Scott in NC]

Thanks, Dave—your advice is greatly appreciated. And Merry Christmas to you too!!!

[JohnB1989]

Just took delivery of mine two days ago. Love to see this since I haven't been able to use mine yet! 

[Scott in NC]

Congrats, John—I think you’re going to love it!

[syxbach]

Looks like my 3545 has somewhere to use

[Scott in NC]

Looks like my 3545 has somewhere to use

I bought another used FTF3545 with plans to put it on this scope, but I like the stock focuser so much that I’ve decided to just save the FT focuser for another future scope. The one I bought from you is currently on my FS-128.

[Scott in NC]

I redid the testing this evening using my certified Zygo 6" flat.  When I use the 8" flat I can rest that against the end of the dew shield, but when I use the 6" flat I need to remove the dew shield and rest the flat directly against the end of the lens cell, since the dew shield is 7" in diameter.  I think that performing the test this way may lead to more accurate results, since the objective is closer to the flat and is less likely to suffer from misalignment due to non-orthogonality of the dew shield.

 

First, the obligatory picture of the set up.  Note how I've replaced the Tak clamshell with More Blue rings and D-plates and replaced the stock Tak visual back with a Baader Click-Lock.  I do think the Tak clamshell looks better, but the rings and D-plates make it easier for me to carry and mount this heavy scope (I weighed it at 28.8 pounds!).

 

[Scott in NC]

Green inside/outside focus:

 

 

Red inside/outside focus:

 

 

Blue inside/outside focus:

 

 

White inside/at/outside focus:

 

[Scott in NC]

I think the edges look much cleaner in these images, leading me to believe that much of what I saw in the first testing procedure was artifact related to either diffraction (most likely) or imperfections in my 8" flat (less likely, but I can't rule this out at this point).  I suspect that the biggest issue the first time around was merely the fact that there was a few inches of distance between the flat and the objective lens, and I was operating under the assumption that the dew shield (against which the flat was resting) was perfectly orthogonal to the rest of the OTA.

 

Not only do the edges of the Ronchi bands look smoother this time around, but there is less chromatic aberration, and the "at focus" white light image looks smoother.  The increased smoothness this time around is attributable to the fact that my 6" flat is pristine, and my 8" flat has a few scratches that have accumulated over years of use.

 

So the bottom line is that this scope has a very nice lens, and also I've learned that I really need to use my best 6" flat (and remove the dew shield when possible) when testing scopes with objectives 5" or less in diameter.

[RedzoneMN]

Nice to see this report. The TOA design is a sure winner.

[Erik Bakker]

With all that wonderful, meticulous and now even more accurate testing out of the way, it is time to enjoy this formidable scope under the stars. It is likely one of the best 150mm of aperture to observe the universe with.

 

And a big thank you for doing all those telling independent unbiased tests and making them available here for all to see 

[DAVIDG]

 Errors  in the surface of the flat is not going to cause a false turned edge.  If the flat isn't optically smooth, the zones in it will show in the test.

   The zone in the middle is real since it showed with both flats and while the turned edge looks better, the reason could be the lens was at a different temperature. Like I said if the retainer is too tight it can warp the edge with a  change in temperature and change the pressure on the edge.

  All the outside images show  the lines bowing inward toward  the middle of the lines so not dead straight. The lens has a broad hill in the middle as well. The hill is affecting both the spherical correction and the color correction. 

 

              - Dave 

[Scott in NC]

The lens was at the same temperature for both tests, indoors on my dining room table, at 70°F.

[HYQID]

When I coupled my TOA130 with a 30mm prism diagonal,the already small spherochromatism was almost cleaned,producing white outer rings in or out of focus when doing star test with bright white stars.I also did a mono-color star test to it with a 656nm artifitial star and it showed identical images in or out of focus to me just using my short-time memory.

With the prism diagonal it has the most perfect star test I have ever seen  but I rarely use it because a 4 incher is much easy to use with acceptable details sacrificed and the most important reason is that I am afraid that TOA would go out of collimation as it seems to be a not-so-rare problem for such wide-divided triplet.

So it probably will be a decoration on wall in my house .I really appreciate the radical design.

Edited by HYQID, 28 December 2023 - 02:51 AM.

[Scott in NC]

That’s a shame, to have such a fine telescope and to be afraid to use it. If I were in that situation then I’d sell it without hesitation to someone who would plan to put it to the use for which it was intended on a regular basis.

[25585]

When I coupled my TOA130 with a 30mm prism diagonal,the already small spherochromatism was almost cleaned,producing white outer rings in or out of focus when doing star test with bright white stars.I also did a mono-color star test to it with a 656nm artifitial star and it showed identical images in or out of focus to me just using my short-time memory.

With the prism diagonal it has the most perfect star test I have ever seen  but I rarely use it because a 4 incher is much easy to use with acceptable details sacrificed and the most important reason is that I am afraid of TOA goes out of collimation as it seems to be a not-so-rare problem for such wide-divided triplet.

So it probably will be a decoration on wall in my house .I really appreciate the radical design.

I know how you feel. Perfection needs protection. 

[CHASLX200]

That’s a shame, to have such a fine telescope and to be afraid to use it. If I were in that situation then I’d sell it without hesitation to someone who would plan to put it to the use for which it was intended on a regular basis.

Same here. I am gonna use it at least once unless it is tooooo heavy to deal with. And i have bought big Newts for the mounts and never used the OTA's due to weight.

[HYQID]

That’s a shame, to have such a fine telescope and to be afraid to use it. If I were in that situation then I’d sell it without hesitation to someone who would plan to put it to the use for which it was intended on a regular basis.

I did try to sell it to someone in the same city,but a 5 inch apo is not very competitive in my area with good seeing and slow temperature changing.A c8 with good adjusting would show pretty planet pictures not much behind a 5 inch apo.A 10-inch newt properly set up will overwhelm it in my experience.The perfect stars it gives can be given by good 4 inchers.That's embarrassing.

[Lagrange]

When I coupled my TOA130 with a 30mm prism diagonal,the already small spherochromatism was almost cleaned,producing white outer rings in or out of focus when doing star test with bright white stars.I also did a mono-color star test to it with a 656nm artifitial star and it showed identical images in or out of focus to me just using my short-time memory.

With the prism diagonal it has the most perfect star test I have ever seen  but I rarely use it because a 4 incher is much easy to use with acceptable details sacrificed and the most important reason is that I am afraid of TOA goes out of collimation as it seems to be a not-so-rare problem for such wide-divided triplet.

So it probably will be a decoration on wall in my house .I really appreciate the radical design.

I wouldn't worry about your TOA going out of collimation. The lens cell is incredibly well engineered by all accounts and is very heavy duty, so each element is kept perfectly positioned and aligned over years of use. It makes for a heavy instrument, but that massive cell clearly does the job because you don't hear of people having issues with TOAs very often, even with older scopes.

 

No point owning something like that and not using it - might as well enjoy the benefits of its sunk cost!

[Lagrange]

It would be very interesting to see the effect of a small prism diagonal if that's something you're able to do. When Wolfgang Rohr tested a TOA-130 he found that adding some glass in the form of a prism with a 26mm optical path resulted in even better colour correction.

 

A 2" prism is too much glass, but Takahashi's 1.25" prism diagonal or something similar like the Baader T-2 32mm prism (BAK4 with a 32mm optical path) could be ideal.

[HYQID]

It would be very interesting to see the effect of a small prism diagonal if that's something you're able to do. When Wolfgang Rohr tested a TOA-130 he found that adding some glass in the form of a prism with a 26mm optical path resulted in even better colour correction.

 

A 2" prism is too much glass, but Takahashi's 1.25" prism diagonal or something similar like the Baader T-2 32mm prism (BAK4 with a 32mm optical path) could be ideal.

Yes,I use prism to TOA130 after reading Rohr's test.

Edited by HYQID, 28 December 2023 - 02:40 AM.

[Lagrange]

Yes,I use prism to TOA130 after reading Rohr's test.

When I saw those reports on the TOA-130/TOA-150 showing how the correction improved with a small prism, I wondered if it would be noticeable so it's interesting to have your real-world experience with your TOA-130 which backs up Rohr's tests.

[Scott in NC]

I’ve got a Tak 1.25” prism diagonal and a Baader BBHS 2” prism diagonal, but I don’t really like using the 1.25” diagonal with anything other than lightweight eyepieces no heavier than a 24mm Panoptic. I’ll give this a try one day with my 2” diagonal to see if I notice a difference between that and my AP Maxbright 2” mirror diagonal (which is what I use most often with my refractors).

[HYQID]

When I saw those reports on the TOA-130/TOA-150 showing how the correction improved with a small prism, I wondered if it would be noticeable so it's interesting to have your real-world experience with your TOA-130 which backs up Rohr's tests.

As for real stars,sirius in high magnification can make some difference.I found that even an excellent air-spaced SD triplet can barely control the color from leaking when doing that.Besides TOA130 with small prism,my 102 f/11 SD doublet can do a good job too.

[25585]

I wouldn't worry about your TOA going out of collimation. The lens cell is incredibly well engineered by all accounts and is very heavy duty, so each element is kept perfectly positioned and aligned over years of use. It makes for a heavy instrument, but that massive cell clearly does the job because you don't hear of people having issues with TOAs very often, even with older scopes.

 

No point owning something like that and not using it - might as well enjoy the benefits of its sunk cost!

That was a deal maker for me (& applies to my TSA also). My LZOS is supposed to have a super cell for its optics too.