724 replies to this topic

[Scott in NC]

I got my LEDs from CN member peleuba, and never asked him where he bought them from.  Maybe he’ll see us and let us know.  Another CN member recently told me that he bought some from Digi-Key.

 

I can’t vouch for the quality of these, but here’s a link to an Amazon seller that will show you what the LEDs that you need look like:  https://www.amazon.c...9941417757&th=1

Here’s a link to show what the Digi-Key lights look like: https://www.digikey....roaAq8rEALw_wcB.  I like that Digi-Key provides a spec sheet showing you the exact wavelength of their lights.

[Scott in NC]

A Stellarvue SV85S LOMO f/6.9 doublet just fell into my lap.  I'm off work today, and it's not dark yet, so what shall I do with it?  Hmm...

 

 

 

[CreatorsHand]

Here’s a link to show what the Digi-Key lights look like: https://www.digikey....roaAq8rEALw_wcB.  I like that Digi-Key provides a spec sheet showing you the exact wavelength of their lights.

I recently purchased mine from Digi-Key, after they were recommended by Moshen. This is a screenshot of my order form, which have the part numbers he had ordered and recommended to me. I found their site confusing if you don't have part numbers to enter. I have not used them yet, as I just received them yesterday, and have some other parts still coming needed to build my DPAC rig. They are not far off from the Amazon price, although these don't have wires, and some on Amazon do, but in addition to the specific wavelength of light they put out, the data sheets also specify the voltage range they are designed for.

 

 

[Scott in NC]

SV85S LOMO in green:

 

Inside focus:

 

 

 

At focus:

 

 

 

Outside focus:

 

[Scott in NC]

SV85S LOMO in red:

 

Inside focus:

 

 

At focus:

 

 

 

Outside focus:

 

[Scott in NC]

SV85S LOMO in blue:

 

Inside focus:

 

 

At focus:

 

 

Outside focus:

 

[Scott in NC]

SV85S LOMO in white:

 

Inside focus:

 

 

At focus:

 

 

Outside focus:

 

[Scott in NC]

This scope tests pretty similarly to my FS-102, another doublet apo.  Both of these scopes have some overcorrection in green and blue, and seem to have the best spherical correction in red.  The white light images show mild CA, as one would expect from a relatively fast doublet at f/6.9.  Not a bad lens, but still not as close to perfection as my SV80 f/6 and f/7.5 LOMO triplets.  But then if LOMO could have gotten perfection out of a doublet, then why would they ever have taken the trouble to make their world-class triplets?

[Scott in NC]

Now for the estimated Strehl calculations for the SV85S LOMO f/6.9 doublet.

 

SV85S LOMO in green: estimated Strehl = 0.973

 

 

[Scott in NC]

SV85S LOMO in red: estimated Strehl = 0.989

 

 

[Scott in NC]

SV85S LOMO in blue: estimated Strehl = 0.925 (I actually got 0.938 for the intrafocal measurement and 0.925 for the extrafocal measurement, but chose to take the lower of the two readings.)
 

 

Edited by Scott in NC, 24 March 2023 - 03:50 PM.

[Scott in NC]

Even blue is still much better than "diffraction limited," but as has been previously demonstrated, if you're best corrected in red, then green will be a little below that, and blue will be even farther off.  Remember the old "ROYGBIV" mnemonic, and for best correction all across the visual spectrum, it's best to null in the middle (G).

[Scott in NC]

So in summary, this nice 85mm LOMO doublet isn't quite up to the same "over the top" level of perfection of the 80mm LOMO triplets that I've tested, but I suspect it will still give very nice views of the heavens. Hopefully I'll be able to test it out under the stars this weekend, if the weather will cooperate.

[Kitfox]

Scott, you’ve got to get a Quark…You need to stay out of the basement on days like this!

[Scott in NC]

I've been in the dining room and living room doing DPAC testing and analyzing, but same thing I guess.  And I do have both white-light and H-alpha solar gear, it just that we're having landscaping done in our yard and it's really windy, so there's lots of dust, dirt, and pollen blowing everywhere.  Not stuff that I really want to get on my optics or in my eyes.

 

Plus I had a day off work and got a new scope that I wanted to check out!

[Alan S]

I've been in the dining room and living room doing DPAC testing and analyzing, but same thing I guess.  And I do have both white-light and H-alpha solar gear, it just that we're having landscaping done in our yard and it's really windy, so there's lots of dust, dirt, and pollen blowing everywhere.  Not stuff that I really want to get on my optics or in my eyes.

 

Plus I had a day off work and got a new scope that I wanted to check out!

I’ll remind you again; as long as you are in the dining room, don’t forget to eat

[Scott in NC]

It is hard to remember to eat when you're having fun, but fortunately my wife is here to remind me!  And I really should be working on my taxes, but this is my way of procrastinating.

[Alan S]

Yes, taxes…that is my day tomorrow and Sunday…no patience to finish in one sitting…

[Kitfox]

Get an extension…test more scopes!

[Joe G]

Scott,

 

I sort of got it to work.  But it is finicky.  How far above the Ronchi screen is your LED?

 

Thanks again.

[Scott in NC]

I’ve not measured it, but it’s only a few mm at most.  Keep working with it.  When I first started I couldn’t see anything so gave up and tried it again the following morning.  Don’t even worry about taking pictures at first, but just keep practicing getting it set up right so you can see the Ronchi pattern easily with your eyes.  And if you can’t see anything, the most likely issue is that your flat isn’t perfectly lined up with the objective and the longitudinal axis of your scope.

[CrazyPanda]

I recently purchased mine from Digi-Key, after they were recommended by Moshen. This is a screenshot of my order form, which have the part numbers he had ordered and recommended to me. I found their site confusing if you don't have part numbers to enter. I have not used them yet, as I just received them yesterday, and have some other parts still coming needed to build my DPAC rig. They are not far off from the Amazon price, although these don't have wires, and some on Amazon do, but in addition to the specific wavelength of light they put out, the data sheets also specify the voltage range they are designed for.

 

 

LED Order.JPG

DigiKey is indeed confusing. I like ordering from https://www.ledsupply.com/ for any components that they do have. They don't have Digi Key's selection, but if you need some basic stuff, their prices are good and their shipping is free.

[RichA]

I really don’t want to risk dropping any of my prized Taks into a pan of oil.  And in case you’re thinking that there’s no way that this would happen, believe me, I’d find a way!

Use mercury.  Not wetting.  Plus, you can use a dimmer LED.

[Kitfox]

The only thing that kills more brain cells than debating with oneself the pros and cons of one more refractor is…

 

…mercury vapor 

[Joe G]

So I have tested two scopes in green:  a Orion EON 120ED FPL 53 doublet and a WO FLT 132 triplet.

 

Visually everything looks good.  I don't see a turned edge.  Lines are pretty straight.

 

But I am struggling taking a picture of them.

 

I jimmied together my own Ronchi eyepiece using a 2"-1.25 adapter.  I think part of my issue is I bought an Edmund Optics grating.  It is kind of small so maybe harder to see things?

 

I went to a Fedex store and had them print a 100l/in transparency.  That doesn't seem to work very well.  Not sure if it is user error or the resolution of the printout isn't good enough.

 

This thread is so long.  Is there someone making these Ronchi eyepieces and gratings?  I'd be more than happy to pay a good price to ease the Ronchi pain.